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The connection of a great number of distributed generation (DG) plants may cause a critical voltage regulation problem in actual medium voltage (MV) radial distribution networks. After a synthetic survey of different strategies reported in literature to solve this problem, a proposal for an active management of the distribution system which makes use of an innovative controller that coordinates the on load tap changer (OLTC) action with the regulation of reactive exchanges between DG plants and feeders, is presented.In order to test the effectiveness of the proposed regulation, the distribution management system coordinated controller (DMSCC) is applied to a realistic radial structure distribution network and its behaviour simulated in managing the MV system during its worst foreseeable working conditions.

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... In the other centralized control study, the reactive power absorption is adjusted and, if this reactive power absorption is not sufficient, the APC is realized by inverter-based PV for voltage regulation, based on V-P (voltage-active power) and V-Q sensitivity coefficients technique [17]. The coordination of OLTC and DGs are proposed for voltage regulation in [18], the reactive power of DGs along the feeders and OLTC tap position are set by the central control strategy. Similar to [18], DG reactive power set points, the amount of APC and OLTC tap positions are determined for voltage regulation by the central SCADA unit in [19]. ...

... The coordination of OLTC and DGs are proposed for voltage regulation in [18], the reactive power of DGs along the feeders and OLTC tap position are set by the central control strategy. Similar to [18], DG reactive power set points, the amount of APC and OLTC tap positions are determined for voltage regulation by the central SCADA unit in [19]. ...

... The studies touched upon above mainly use and focus on existing methods (such as: droop control, MPC and MADRL), but this paper totally presents new algorithm-based method for voltage regulation. Additionally, the studies in [16,18] implement APC for voltage regulation, whereas this new method does not require APC by using reactive power capacity of inverter-based DG. The methods in [33], [30] and [38] use optimization problem solver which need more power flow analysis to find optimum settings of reactive power support components which are included in voltage regulation and the number of power flow analysis changes according to the cases. ...

The voltage violation in distribution networks may occur frequently due to the rising integration of flexible demands and supplies. In this paper, the reactive power of the inverter-based distributed generator (DG) and OLTC tap position are adjusted for voltage regulation in coordinated manner. Firstly, the reactive power adjustment for the voltage regulation has been carried out by use of the DG reactive power capacity. Afterwards, the tap position of the OLTC has been changed to regulate the bus voltage that has a voltage violation problem in the case of insufficient reactive power capacity of the DG inverter. The value of the distributed generator reactive power output that regulates the voltage on the bus that has a voltage violation is found with proposed curve-fitting method and tested with the Grid Search, Artificial Bee Colony methods. The proposed method derives mathematical expressions between DG reactive power output and bus voltages as quadratic equations by curve-fitting technique. Moreover, addition to inherent upper and lower reactive power limits of the DG inverter, they are determined by the proposed curve-fitting based technique while considering voltage constraints on all buses. Proposed method is much faster than other two methods because of its plain structure and gives adequate accurate results.

... Note that it is ineffective to use V/V function in Low Voltage (LV) networks. Conventionally, DGs have acted passively in the grids [6][7][8] and hence their hosting capacity has been limited [9][10][11]. To increase the hosting capacity of passively operating DGs and to enhance the voltage stability, an On-Load Tap Changer (OLTC) and shunt capacitors have been used to regulate the voltage [10,12]. ...

... Energies 2016, 9,929 3 of 14 Figure 1 shows the interface of DGs under IEC 61850-90-7 and describes three levels of hierarchy in data exchange, where PCC stands for Point of Common Coupling. The lower section describes autonomous DGs which respond to local conditions. ...

... This means that SV/V has to have a positive value, while it is conventionally a negative value. The positive value of SV/V is needed to reduce line loss by increasing the voltage level and it is effective only for constant power loads as shown in Equation (9). However, in practical ...

International Electronical Committee (IEC) 61850-90-7 is a part of the IEC 61850 series which specifies the advanced functions and object models for power converter based Distributed Energy Resources (DERs). One of its functions, the Voltage/VAR (V/V) control function, is used to enhance the stability and the reliability of the voltage in the distribution system. The conventional V/V function acts mainly for flattening the voltage profile as for a basic grid support function. Currently, other objectives such as the minimization of line loss and the operational costs reduction are coming into the spotlight. In order to attain these objectives, the V/V function and hence the DER units shall actively respond to the change of distribution system conditions. In this paper, the modification of V/V function and new requirements are proposed. To derive new requirements of V/V function, loss minimization is applied to a particle swarm optimization (PSO) algorithm where the condition of voltage constraint is considered not to deteriorate the voltage stability of the distribution system.

... The voltage value at the sending bus is defined to guarantee voltage compliance at the furthest node of the feeder [2,20]. HV/MV transformers are generally equipped with an AVR, which drives the on-load tap changer (OLTC), whereas MV/ LV transformers typically exploit an off-load tap changer [21]. Transformers with tap changers can provide voltage regulation following two different schemes. ...

... In consequence, the most critical node could not coincide with the furthest node of the feeder and be different at each time. In the distribution system, bidirectional flows constrain the effectiveness of voltage regulation strategies since voltage profiles are no longer decreasing monotonic [21,27]. Moreover, the decentralized energy production may determine voltage imbalance issues in low voltage networks [28]. ...

Purpose of Review
Decarbonizing the power system entails the need to update voltage control strategies, traditionally based on synchronous generators, and energy flows from transmission to distribution grid level. We analyze the voltage control strategies implemented up to now, considering both the technical and economic views.
Recent Findings
We study how the transmission and distribution grid operators in Spain, Croatia, and Thailand improved their voltage control strategies to exploit potentials from power electronics from wind and photovoltaic generation. Moreover, we analyze economic fundamentals and market design issues related with the implementation of these new strategies, essential to set efficient economic incentives for their successful implementation.
Summary
We discuss recent innovative projects and solutions implemented in some countries that show promising and relevant potential from the implemented renewable-based voltage control strategies. However, we highlight that there are very few empirical analyses in real conditions, which are essential to implement improved and efficient voltage control strategies.

... Renewable and alternative energy sources (RES), as the photovoltaic (PV), have been increasingly used in distribution systems (DS) as distributed generation resources (DG) close to consumer units. The DG penetration is leveraged by the evolution of equipment, by reduced investment paybacks and by meeting contemporary environmental sustainability requirements, reducing dependence on fossil fuels [1]. However, the intermittent feature of RES is a challenge for the planning and operation of the DS. ...

... The power of this system (kW) in period u, P k pv,u , is formulated in (1), where N k pv is the number of type k PV modules, Au k pv is the area of a module ( m 2 ), Rad u is the instantaneous radiation ( kW/m 2 ) and k pv,u is the module efficiency, calculated in (2) [33]. In Eq. (2), k mod and inv are the reference efficiencies of the module and inverter, respectively. ...

The continuous proliferation of distributed generation is leading end users to look for new tools that help to design hybrid electrical energy systems (HEES). Thus, this work proposes a novel approach for optimal planning of HEES, which comprises the optimization of the type and capacity of distributed generation connected to the end user. The main objective is to minimize the project’s total cost, considering the net metering scheme. To this end, the bioinspired meta-heuristic artificial immune system is proposed to optimally determine the number and type of photovoltaic panels. In addition, a nonlinear programming model is proposed to optimize the diesel generator and BESS capacity, considering the energy supply to the consumer by the HEES and the main distribution grid. Case studies involving commercial and residential customers in Brazil are introduced considering the normative resolutions from ANEEL, the Brazilian Regulatory Agency. Comparative analyses are made concerning an exhaustive search procedure and the commercial software Homer Pro, designed to optimize the operation of HEES systems. An important conclusion is that the proposed approach is as effective as the cutting-edge tools, with reasonable computational effort.

... However, in networks with a high saturation of distributed generation, the efficiency of such a method of voltage regulation is increasingly often insufficient. High generation variability (wind, photovoltaic generation) deteriorates the voltage profiles on the grid [2][3][4][5][6][7][8][9]. An equally important problem is periodically too low or too high voltage in the network [10,11]. ...

... Too high voltage occurs as a result of a change in the typical direction of power flow (flow-from HV/MV substations to consumers) caused by a large generation volume, e.g., as a result of favorable weather conditions. The possibilities of improving the quality of regulation, which can be found in the literature, e.g., [2][3][4][5][6]10,12], most often include various methods of coordination of the operation of the transformer regulator with various devices operating in the MV network. This coordination can be decentralized or centralized. ...

The development of renewable energy, including wind farms, photovoltaic farms as well as prosumer installations, and the development of electromobility pose new challenges for network operators. The results of these changes are, among others, the change of network load profiles and load flows determining greater volatility of voltages. Most of the proposed solutions do not assume a change of the transformer regulator algorithm. The possibilities of improving the quality of regulation, which can be found in the literature, most often include various methods of coordination of the operation of the transformer regulator with various devices operating in the Medium-Voltage (MV) network. This coordination can be decentralized or centralized. Unfortunately, the proposed solutions often require costly technical resources and/or large amounts of real-time data monitoring. The goal of the authors was to create an algorithm that extends the functionality of typical transformer control algorithms. The proposed solution allows for reducing the risk of voltage collapse. The performance of the proposed algorithm was validated using multivariate computer simulations and tests with the use of a physical model of the distribution network. The DIgSILENT PowerFactory environment was used to develop the simulation model of the proposed algorithm. Then, tests were conducted on real devices installed in the LINTEˆ2 Laboratory at the Gdańsk University of Technology, Poland. Selected test results are included in this paper. All results have shown that the proposed algorithm makes it possible to increase the reserve of the voltage stability of the node, in which it is applied, thus mitigating the risk of a voltage collapse occurring. The proposed algorithm does not require complex and costly technical solutions. Owing to its simplicity, it has a high potential for practical application, as confirmed by the real-time control experiment in the laboratory.

... However, the intermittent nature of these resources has also started to obscure the optimal operation of Distribution Networks (DNs), which demands the implementation of new management schemes as a consequence. In view of this, several Active Distribution Network (ADN) management schemes have been proposed [1], which can be broadly classified under the topics of coordinated voltage control [2,3], DER control [4][5][6], DN reconfiguration [7,8], distributed energy storage control [9,10] and optimal allocation of DERs [11,12]. In addition to these strategies, Losses Allocation (LA) methods have also been developed for DNs as LA schemes proposed for transmission networks cannot be applied to DNs due to their peculiar nature and characteristics such as topology, nonuniform distribution of end-users etc. ...

... Due to unfeasibility of assigning neutral losses to phases, the MPLAP proposed in this paper provides an explicit mathematical formulation of neutral losses allocation by treating neutral conductor(s) like any other phase conductor. For the multi-conductor branch shown in Fig. 3, active power losses can be determined, as mentioned in (3), by extending (2) to include neutral branch current in its formulation ...

... However, the intermittent nature of these resources has also started to obscure the optimal operation of Distribution Networks (DNs), which demands the implementation of new management schemes as a consequence. In view of this, several Active Distribution Network (ADN) management schemes have been proposed [1], which can be broadly classified under the topics of coordinated voltage control [2,3], DER control [4][5][6], DN reconfiguration [7,8], distributed energy storage control [9,10] and optimal allocation of DERs [11,12]. In addition to these strategies, Losses Allocation (LA) methods have also been developed for DNs as LA schemes proposed for transmission networks cannot be applied to DNs due to their peculiar nature and characteristics such as topology, nonuniform distribution of end-users etc. ...

... Due to unfeasibility of assigning neutral losses to phases, the MPLAP proposed in this paper provides an explicit mathematical formulation of neutral losses allocation by treating neutral conductor(s) like any other phase conductor. For the multi-conductor branch shown in Fig. 3, active power losses can be determined, as mentioned in (3), by extending (2) to include neutral branch current in its formulation ...

... • assignment of location-dependent voltage control methods for voltage support The proposed voltage control solution combines the advantages of local droop [183] and remote control [184] and may contribute to the development of active network management solutions. Local droop control reacts within seconds and is defined as a decentralized and automatic control that can use remote sensors and concentrators at MV/LV sub-stations as well data from the low voltage network. ...

... The coordination is assumed to be automated with control systems, e.g. supervisory control and data acquisition, energy management systems, or distribution management sytems [174,184,185]. Alternatively, the local controller at the primary sub-station level can perform real-time analysis and send set-points to the contracted Virtual Power Plant units and unit clusters depending on local measurements and power system conditions. ...

The paradigm shift towards a more sustainable energy supply with a less detrimental environmental impact successively changes the energy sector from a polycentric towards a more distributed energy system. The presence of distributed and renewable energy sources combined with the anticipated electrification of the transport sector results in changes along the entire value chain. This so-called transformation process is accompanied by energy market deregulation and restructuring of the power system. However, in order to increase energy efficiency and improve environmental protection, investigations are needed to establish reliable and secure infrastructures. This will be accompanied by the development of suitable computer aided software solutions for energy market participants and system operators. With further advances in information and communication technology and system automation, there are significant opportunities for realizing such a sustainable energy future. In this context, the thesis provides a comprehensive discussion of the potential application and deployment of Virtual Power Plants. Here, the aggregation concept serves as a vehicle for the implementation of coordinated and optimized control decisions by means of interconnected and interoperable solutions. The developed methodologies and functionalities are implemented through the service-oriented design and control scheme of the Virtual Power Plant for the determination of economic and technical feasible solutions in energy market and power system operations. Following the framework conditions of liberalized energy markets, an energy management algorithm for joint market operations is established which aims to integrate various distributed, renewable and mobile energy sources. A mixed integer linear programming formulation is proposed for solving the unit commitment and dispatch problem of the Virtual Power Plant operator in multi-period optimization processes. The presented methodology allows trading of various market products with variable time increments capable of solving real-time market transactions. By providing a uniform model architecture for scalable power plant portfolios, deterministic planning methods and comprehensive investigations are performed. In particular, electric vehicles are considered as additional sources of energy in joint market operations for the provision of service-oriented operations. Furthermore, multilateral transactions are reflected in the hierarchically structured optimization problem formulation for enhancing the allocation of power system services. The simulation results of the market-related interactions serve to identify the temporal and spatial effects in power system operations. Within this framework, a coordinated voltage control is proposed which combines both local droop controls with remote control algorithms. This allows the additional flexibilities provided by a comprehensive set of distributed, renewable and mobile energy sources to be exploited to mitigate time-varying voltage variations. In addition, the modeling of an active network management is carried out for the purpose of conducting control algorithms for electric vehicles charging in distribution systems. Appropriate evaluation functions and programming indicators are presented to determine the simulation results.

... The proposed coordination reactive power control approaches were implemented on a realistic MV network which can be found in [22]. The network is presented in Fig. 5. ...

... Referring to the Italian regulation, the allowable change in voltage limits is ± 5% around the rated value. Fig. 5Distribution network under study [22] ...

Due to increasing penetration level of renewable energy based Distributed Generation (DG), voltage/reactive power control in distribution networks is currently an important topic. This paper proposes two coordinated voltage/reactive power control approaches in active distribution grids. The proposed coordination control is achieved based on predefined procedures to increase speed response and to reduce complexity of computations. Simulations were carried out on a realistic Medium Voltage (MV) network using measured data of DG output power. The results were taken for different three weeks in the year representing different seasons. The results of the proposed approach were compared with previously published centralized control approach. The results indicate that the proposed approaches reduce the number of OLTC operations, reduce system losses, minimize the voltage fluctuation in the distribution system, and increase the hosting capacity of DG power.

... The strategy first measures local data and then calculates the required voltage at the overrun node using a controller. In order to achieve voltage control within the sub-district, Fabio et al. (2008) used the particle swarm optimization algorithm, which is based on the ability of the PV inverter to compensate for a certain amount of reactive power. The goal is to absorb reactive power or active shear amount, depending on the degree of over-voltage and the degree of demand for voltage regulation and control. ...

The use of distributed photovoltaics (PVs) on a large scale often causes voltage over-limit problems in distribution networks. This paper proposes a distributed photovoltaic cluster collaborative optimization voltage control strategy based on an improved community algorithm to address the issue of centralized control being unable to respond quickly to the randomness of distributed photovoltaics and the difficulty of achieving overall coordination with local control. First, by improving the community algorithm, the division of reactive and active clusters, considering the power balance and node coupling degree, is realized. Then, the cluster-coordinated voltage control strategy is proposed by making full use of the power control ability of a photovoltaic inverter. Finally, a voltage regulation ability evaluation index is proposed to assess the node regulation ability within the cluster and select key nodes. This effectively reduces the number of control nodes. The simulation analysis of the improved IEEE 69 distribution network shows that the proposed voltage control strategy can mitigate the issue of voltage over-limit in high-permeability distributed photovoltaic access distribution and enhance the photovoltaic consumption capacity.

... An ESS is considered a multifunctional device, and includes the following components [21,22]: a semiconductor converter that can work in the rectification mode (when the battery is being charged) or in the inverting mode, converting a constant voltage from AB alternating voltage 50 Hz; a long-term (electrochemical) storage system (otherwise known as a battery); and an automated control system, the functionality of which depends on the tasks to be solved. The choice of ESS is mainly based on the determination of two parameters: power and storage capacity [6,23]. To select these parameters, it is advisable to use the actual daily load schedules. ...

The paper considers the issues of maintaining an equality of flow in generated and consumed electric energy in an electric network incorporating an electric power storage system. An analysis of ways to equalize the energy and power balance was carried out, and the advantages of using electricity storage systems in electrical networks was assessed. Upon simulation using the Power Factory program, we noted that, after switching on the load, a transient process occurs, characterized by a jump in active power, which was caused by the need for time to initiate the electric energy storage system. However, immediately after this, the process of issuing the accumulated energy to the electrical network and compensating for energy consumption began. Moreover, when the load was disconnected, there is a certain dip in the active power curve and a further increase in consumption. This was found to be due to the transition of the electricity storage system to the modes of energy storage and battery charging. As a result of this simulation, data on the charging and discharging time of the electricity storage system were obtained. The studies show that the use of electricity storage systems in electrical networks allows for the stable operation of all main generators, and thus increases the safety and reliability of the entire system.

... The positive or negative voltage regulation in distribution or transmission networks investigating loading impression is noticeable in power system operation studies. Through the typical definition of voltage regulation formulated based on active and reactive power flow, recognition of worst-case scenarios is achievable [41]. Concerning Figure 1, drop voltage for the whole feeder is equal to the collection of drop voltage of each branch. ...

Abstract The Volt/Var optimization (VVO) problem is used for scheduling the voltage regulation and reactive power compensation equipment in distribution networks to minimize power loss and voltage violation. In order to solve the VVO problem for a forthcoming time horizon, it is necessary to predict some parameters such as load demand and renewable energy production. The prediction of these parameters is always accompanied by uncertainty that robust optimization can be used to solve this concern. This paper presents a scenario‐based robust Volt/Var optimization (RVO) method that significantly reduces the number of scenarios required for the worst‐case approach. Solving the VVO problem with the worst‐case scenarios reduces the computational burden and maintains the voltage security of the distribution network against the severe events. The proposed RVO is formulated based on a mixed‐integer second‐order cone programming (MISOCP) model in which Volt/Var control (VVC) equipment is scheduled over a two‐stage strategy. The proposed method is validated using modified 33‐bus and 69‐bus IEEE test systems. The results demonstrate that the proposed RVO method maintains the network's voltage profile within the acceptable range against uncertainties.

... In this paper, a power distribution system with a voltage level of 20kV and 45 nodes is taken as an example, and the network reference is (Bignucolo et al., 2008). In the distribution network, there are 4 wind power grid-connected nodes, namely node 2, node 7, node 11, node 15 and 5 photovoltaic grid-connected nodes, namely node 19, node 22, node 30 and node 40. ...

With the increasing penetration of renewable energy in the distribution network, however, due to the randomness and volatility of renewable energy output, the large-scale grid connection of renewable energy will bring challenges to the safe and stable operation of the distribution network. The calculation of renewable energy hosting capacity of distribution network is not only beneficial to the construction of renewable clean and low-carbon power system, but also of great significance for the planners of power grid to carry out renewable energy planning. Renewable energy hosting capacity calculation involves many constraints, including a large number of nonlinear constraints, and the hosting capacity calculation model is very complex, lacking efficient solution algorithm. Aiming at the existing problems, the calculation model of renewable energy hosting capacity of distribution network is established based on full consideration of power quality, relay protection and thermal stability test. A multi strategy improved adaptive manta ray foraging optimization algorithm (MSAMRFO) is proposed to solve the hosting capacity model. MSAMRFO algorithm adopts half uniform initialization strategy, adaptive variable step size strategy and local convergence mutation strategy to improve manta ray foraging optimization algorithm (MRFO) algorithm. Finally, the effectiveness of the proposed model and method is verified by an example. The example shows that the MRFO algorithm after multi strategy improvement has outstanding effect both in convergence speed and algorithm stability.

... Fontes renováveis e alternativas de energia, como a solar, têm sido cada vez mais utilizadas em sistemas de distribuição (SD) como geração distribuída (GD) localizada próximaàs unidades consumidoras. A penetração de GDé impulsionada pela evolução dos equipamentos, redução do tempo de retorno do investimento e requisitos contemporâneos por sustentabilidade ambiental (Bignucolo et al., 2008). No entanto, a característica intermitente dessas fontesé um desafio para o planejamento e operação do SD. ...

... DN's expected adjustment requires a lot of time, investment, and innovation, which is difficult to justify financially and ensure acceptance of the management. For example, it has been practically confirmed that the best voltage control results are obtained when the voltage management logic is integrated into the distribution management system (DMS) [13][14][15]. Despite that, DPUs are not yet ready to replace the classic local control via AVR with a centralized real-time control directly from the DMS, and AVR is still the only regulatory resource in most DNs. ...

The basic prerequisites for the correct operation of the classic on-load tap-changing voltage control (CVC) are that the distribution network (DN) is passive. However, by installing distributed generators (DGs), today's DNs become increasingly active. Consequently, by measuring only the current and voltage magnitudes at the on-load tap-changing transformer secondary side, its automatic voltage regulator receives a false image of the DN load. In such a case, it is impossible to determine the optimal voltage value at the transformer secondary side in all possible states. Therefore, the CVC must be adapted to the new situation. This paper presents a simple, efficient, and inexpensive adaptive on-load tap-changing voltage control (AVC) for active DN with DGs and customers placed on different feeders. The adaptation refers only to the false image of DN load correction, based on the DN load assessment without the influence of DG. Practically, this correction is realized by minimal investment into the existing equipment and infrastructure. Thus, complicated methods requiring an expensive upgrade of DN in terms of communication infrastructure expansion, installation of new sensors and control devices, their coordination, and integration with modern IT/OT systems are avoided. The verification of the AVC is performed in real-life in the real-world active DN.

... The latter has a voltage level of 230kV. The remaining 109 buses comprise the distribution systems [32,33].The DS voltages are 20kV, so it is unnecessary to use specific techniques to convergence the power flow. ...

Encouraged by the increasing electric energy consumption, the distributed generation has been widely included in the electrical power system. However, renewable energy resources have intermittent characteristics. When the distributed generation is high at certain times of the day, the energy generation at distribution systems can become higher than the required power. The surplus energy is returned to the transmission system, giving rise to active distribution networks. This paper proposes an approach to optimally managing the existing distributed generation and voltage control devices. The management is performed by solving an optimal power flow problem, aiming to find an operating condition for the system in which the losses are minimized, and the voltage profiles are improved. A combined transmission and distribution system is proposed. Some scenarios are considered to assess the impact of distributed generation insertion and the contribution of these sources in support of reactive power. The results indicate the need for adequate active distribution networks management, which depends on the distribution generation insertion level and the generation sources’ power factor.

... Some researchers were carried out on DG technology and its impacts on the energy system. These impacts may concern network planning, losses, voltage, energy quality and reliability [3][4][5][6][7][8]. The large number of DG ...

p>Day by day, the integration of decentralized generation in medium voltage networks becomes more important during the last years and even in the near future. This increase causes, at the same time, several negative effects and rarely positive impacts on the stability of the network. Therefore, this work aims at analyzing the impact of ambient temperature on radial distribution network parameters’ e.g.: voltage drop and stability voltage level (index). Based on MATLAB program, different analyses of distributed generation (DG) insertion influence’s on voltage drop in the radial distribution feeder, as well as the influence of climatic conditions such as ambient temperature on network parameters. The Integration of Photovoltaic DGs in MV networks can play an important role in reducing the global warming effect (in voltage drop, and voltage stability index) especially in radial distribution feeder. Furthermore, it protects network’s parameters if its location and power are well selected.</p

... The biggest voltage drops happen at the end of each feeder branch. Three traditional voltage devices are used: automatic voltage control relays applied to the onload HV/MV transformer tap changer [2], off-load calibration of MV/LV transformer tap position, and capacitor banks [3]. ...

In this paper, an alternative strategy for real-time control of active distribution network voltage is developed, not by controlling the bus voltage as in the various centralized, decentralized, and local approaches presented in literature but rather by only eliminating the impact produced by active and reactive power of distributed generation (DG) units on the voltage of all network nodes and keeping the traditional voltage control systems dealing with the same constraints of passive systems. In literature, voltage deterioration introduced by DGs has been reported as one of the main obstacles for the interconnection of large amounts of DG units to the existing networks. In this paper, the novel control strategy is based on a sensitivity formula developed to calculate the compensation needed for additional distributed flexible AC transmission system (D-FACTS) devices to push and pull the exact reactive power and to eliminate the impact produced by DGs on the network voltage profile. The criteria of the allocation of the var devices and the required network reinforcement are developed in this paper, considering all possible topology structures, and an innovative codification method is introduced to reduce the needed computation time and communication data to actualize the sensitivity coefficients and get the proposed control approach flexible with network topology reconfiguration. The risk of the conflict of the proposed control system with the traditional voltage equipment is reduced due to the fast capability of D-FACTS devices to regulate their reactive power in finer granularity. A case study of two meshed IEEE 15-bus feeders is introduced to compare the voltage behavior with and without the presence of DG units and to evaluate the total system losses. The proposed method could be used for the interconnection of the first generation units in emerging networks, which does not yet have an active voltage control strategy, as it could be used for DG units not able to be connected to existing centralized control systems and it could also be used as the principal voltage control strategy, with the extension for several neighboring units and the preservation of the traditional voltage control systems.
1. Introduction
Without the presence of a distributed generation unit in low and medium voltage distribution systems, the network voltage magnitudes fall along the feeders, depending only on cable characteristics and the demanded load at each node [1]. The biggest voltage drops happen at the end of each feeder branch. Three traditional voltage devices are used: automatic voltage control relays applied to the onload HV/MV transformer tap changer [2], off-load calibration of MV/LV transformer tap position, and capacitor banks [3].
However, those three pieces of equipment are not responsible for keeping the network voltage within the tolerance limit. This has been wrongly reported in several papers in literature [4, 5]. The way traditional distribution networks are designed and developed guarantees that the voltage magnitudes do not deviate outside the permitted range. Before the introduction, the modification, or the elimination of any load, a feasibility study on cables, lines, or electric devices and distribution utilities was conducted, by evaluating the voltage drop levels considering the worst scenarios of power demands and topology structure. Onload and off-load tap changers of HV/MV and MV/LV transformers are only used to set transformers’ secondary voltages close to the maximum.
However, with the integration of DGs, traditional methods and devices are no longer able to control the network voltage profile [6], and the steady-state voltage rise has been reported in literature as one of the main obstacles for the interconnection of large amount of generation units to the existing distribution systems [7, 8].
In literature, several centralized [9], decentralized [10], local [11], and distributed control [12] approaches are developed to get the violated voltages return inside the permitted range. Both decentralized and local approaches have been advanced for practical application for voltage rise in active distribution networks. Also, various efforts have been developed to avoid the heavy extension of sensing; communication and control infrastructure is required for the implementation of the centralized approaches, as in the method presented in [13], based on the use of solar and demand forecasts, and also in [14], where the authors present a short-time scheduler to define DG setpoints and to minimize the voltage deviations with respect to the rated values.
The efforts presented in literature focus on adapting, improving, or even totally changing the traditional devices and systems. However, those modifications lead not only to wasting conventional voltage control equipment and methods but also to abandoning all the practical experiments and good practices collected over generations by the utility personnel, in terms of network control operation and development.
In this paper, we propose an alternative solution to mitigate the voltage profile in active distribution systems: the suppression of the impact of the active and reactive power produced or consumed by distributed generation units on the network voltage, in a fast way to avoid the risk of any conflict of the proposed tool with the conventional voltage control devices. The purpose of the proposed approach is not to control the bus voltage, but rather to only eliminate the impacts of DG units on the voltage of all network nodes and keep the traditional systems and devices dealing with the same constraints, as in a passive system.
A decentralized voltage control approach, which is flexible with network topology reconfiguration and based on a sensitivity analysis, is developed in this paper, with the main aim of eliminating the impact of a DG unit. The computation of the sensitivity coefficients presented in [15] and used in [16, 17] is adopted in this paper, which is based on the topological structure of the network and independent of the network operation point.
A criterion for the implementation of the participated D-FACTS devices in the voltage control is developed in Section 2, considering network topology reconfiguration. And a powerful codification method is developed in Section 3 to alleviate the communication between SCADA and the proposed decentralized system and to get the decentralized control aware of any topology reconfiguration with a minimum effort.
The proposed voltage control strategy in this paper could be implemented for the first DG units in emerging networks, as in the case of Morocco and several African countries, which are not yet ready to receive a generation unit or do not yet have a voltage control strategy for active systems. The proposed method could also be applicable for generation units not able to be connected to an existing centralized voltage control system, as it could be intended as the principal voltage control strategy with a possible extension of the approach to eliminate the impact of several neighboring generation units.
The principal advantages of the proposed approach are as follows: (i)An efficient control strategy able to avoid as much as possible both disconnection and curtailment of distributed generation(ii)A control strategy that saves the traditional voltage regulation equipment and keeps the utility personnel dealing with the same constraints(iii)Ease of implementation, with no need for load demand data or powerful electric meter infrastructure(iv)With the proposed codification method and with no requirement of any load flow analysis, the proposed approach is able to get implemented for real-time application
The main contributions of this paper are as follows: (i)The introduction of a novel approach to mitigate the voltage control of active distribution systems(ii)The development of an analytical method for an optimal allocation of voltage control devices with the consideration of the network topology reconfiguration(iii)The presentation of a codification method able to reduce the needed communication data to actualize the sensitivity coefficients and get the decentralized control flexible with network topology reconfiguration
2. Impacts of Distributed Generation on the Voltage Profile of Distribution Networks
Let us consider a distribution network with nodes. Without the presence of any distributed generation, the voltage of a node depends on the powers injected by or absorbed from all network nodes and the network line and cable characteristics:
The distribution networks are always developed in meshed topology but operate in a radial structure. For a defined topology fixed structure, will be constant and the voltage will be impacted by the variation of the active and reactive power at each node.
The linearized form of the voltage with the Taylor series expansion at each node is shown as follows:
With the introduction of a DG unit, connected to a node, which will be named DG, the active and reactive power produced or consumed will impact the voltage of all the network nodes:
The changes in voltage at each node will depend on the variation of the two new variables of introduced DG: and , as demonstrated in equation (5):
3. The Proposed Approach
The purpose of the proposed approach in this paper is to add “” devices “”, able to regulate their reactive power, in such a way that the impact of the DG at the nodes “” is equal to zero. Several advanced devices with the ability to act on their reactive power have been presented in literature as D-FACTS and supercapacitors [18].
The size and site and also the number of those pieces of equipment should be optimized.
Now, we will prove that the impact of the DG unit has been eliminated for the voltage of all network points. To do so, we consider that the additional D-FACTS devices have eliminated the impacts of the DG unit on the voltage of the nodes . So for node from the nodes ,
For node “” different from the nodes , the impact of the DG unit and the additional devices is
By the application of the Chasles relation,
And becomes
So
So equation (7) becomes
So
And equation (10) becomes
So by the elimination of the impact of a DG unit on the voltage of some certain nodes, the voltage of all network points will become independent of the small variation of the active and reactive power introduced by the DG unit; in the next section, an analytical approach based on the work presented in [17] is discussed, with an improvement by considering all the possible network topology structures.
4. Allocation of Voltage Regulation Devices
The proposed method in this section for the identification of the site and size of voltage regulation devices that needed to eliminate the impact of a DG unit on the network voltage profile is built on the progress of the optimal approach developed in [19], where such a method is used to identify the optimal allocation of capacitor banks to reduce voltage deviation without the consideration of network topology reconfiguration.
To calculate the sensitivity coefficients, we consider the formula presented in [15] and used in [16, 17]: where are (i)for the sum of the branch lengths forming the path from the origin (node 0) to node (ii)for the sum of the branch lengths forming the path from the origin to the common node of the paths formed by the origin and nodes and
From this formula, we can observe that with network topology reconfiguration, the highest values of and will correspond to the nodes presenting the longest common path from the substation to the DG node, which means that the voltage magnitudes of the nearest nodes to the DG are the most impacted parts due to the active and reactive power variations, which will be confirmed through following the numerical application of equation (14), for two meshed IEEE 15-bus feeders, driven from two separate HV/MV substations A and B, as shown in Figure 1, and three topology structures obtained by changing the open point: structure no. 1 (open point) at the node “15A-5B,” structure no. 2 at the node “3B,” and topology no. 3 at the node “2A.”

... A new CVC method with a reactive power management scheme has been studied in [30]. A method that combines reactive power injection by SVC with tap control, using information from sensors across the distribution line, is proposed in [31]. Finally, in [32], real power control is preferred in order to control the voltage. ...

Renewable Energy Sources are becoming widely spread, as they are sustainable and low-carbon emission. They are mostly penetrating the MV Distribution Networks as Distributed Generators, which has determined the evolution of the networks’ control and supervision systems, from almost a complete lack to becoming fully centralized. This paper proposes innovative voltage control architectures for the distribution networks, tailored for different development levels of the control and supervision systems encountered in real life: a Coordinated Control for networks with basic development, and an optimization-based Centralized Control for networks with fully articulated systems. The Centralized Control fits the requirements of the network: the challenging harmonization of the generator’s capability curves with the regulatory framework, and modelling of the discrete control of the On-Load Tap Changer transformer. A realistic network is used for tests and comparisons with the Local Strategy currently specified by regulations. The proposed Coordinated Control gives much better results with respect to the Local Strategy, in terms of loss minimization and voltage violations mitigation, and can be used for networks with poorly developed supervision and control systems, while Centralized Control proves the best solution, but can be applied only in fully supervised and controlled networks.

... Likewise, stochastic methods are used for the optimal allocation of these storage devices [13]. In other proposals the bat algorithm is used to size the batteries [14], and in [15] they propose a type of stochastic optimization to determine the optimal sizing of energy storage devices in a hybrid wind system -diesel. Because the main proposal is not a battery location problem, this paper uses an energy dispatch procedure to determine the location of the BESSs and the capabilities required in the weak nodes. ...

This paper analyzes the impact of battery energy storage system (BESS) dynamics in micro grids subject to active power variations. The micro grid is connected to the utility through a high impedance feeder to consider poor contribution. Thus, the dynamic of the sources and loads connected will be greater to obtain a more complex operating scenario allowing the interaction between different types of non-regulated sources and energy storage systems. The microgrid can operate on island due to some contingency, by a normal operating condition or with a weak link; any of these conditions the energy required to supply the loads will depend meanly on the renewable and non-renewable sources. The interconnection of the BESS in strategic points will allow to improve the regulation of energy. The latency times of battery charging and discharging and the limit of daily operations are shown as a real consideration in the control of the energy of the micro grid systems. The sizing and location of the batteries is made in the weakest nodes. The results show that the dynamic of BESS have an important impact in the energy availability for the microgrid operation. Keywords-battery energy storage system, distribution management system, weak microgrid.

... The existing distribution networks and the corresponding voltage control equipment have been designed to operate in the conditions of planned centralized generation. It implies the radial topology with a unidirectional power flow from the high voltage (HV) substation to the MV system, and then to LV customers [36]. A one-line diagram that is applied to analyze the voltage drop in the distribution network is demonstrated in Figure 3.6. ...

Renewable distributed generation (RDG) has become more accessible, affordable, and widespread than it was just a few years ago, leading to increasing number of connections to distribution networks. One of the technical challenges of such tendency is to maintain an acceptable voltage level that becomes inconsistent because of the inherent variability in the power output of RDG units. Therefore, it necessitates the development and implementation of effective voltage control strategies to reliably supply energy to the equipment of end users. To solve this problem, a modified automatic voltage control (AVC) algorithm that can operate utilizing a model of a controlling network and/or real-time measurements was proposed to keep the voltage within the acceptable limits. Also, the effectiveness of demand response (DR) algorithm for stand-alone voltage control was investigated to evaluate its perspectives. The cooperation of the modified real-time AVC algorithm with both reactive power control (RPC) of photovoltaic (PV) systems and DR was investigated to decrease the number of on-load tap changer's (OLTC's) operations. The effectiveness of the developed dispersed voltage control algorithms was tested in different simulation conditions on a verified model of a power grid that has been created in MATLAB ®. The results of the research have proven the reliability of both versions of the modified AVC algorithm in distribution networks with RDG. Furthermore, the results also allowed evaluating the amount of controllable load for stand-alone voltage control based on DR algorithm. The cooperation of AVC algorithm with DR algorithm reduced the use of OLTC, while the combined actions with RPC of PV systems were less effective and resulted in the same number of OLTC's operations in comparison to the stand-alone performance of AVC algorithm in the same conditions.

... Likewise, stochastic methods are used for the optimal allocation of these storage devices [13]. In other proposals the bat algorithm is used to size the batteries [14], and in [15] they propose a type of stochastic optimization to determine the optimal sizing of energy storage devices in a hybrid wind system -diesel. Because the main proposal is not a battery location problem, this paper uses an energy dispatch procedure to determine the location of the BESSs and the capabilities required in the weak nodes. ...

... A centralized control applied to MV networks is proposed in [15], which coordinates OLTC with DERs connected on each feeder. This optimizes the reactive power exchange in each feeder and reduces power losses while maintaining the voltage within steady state limits. ...

Passive distribution networks are rapidly transforming to active networks due to ever growing penetration of
mainly renewable distributed energy resources. The integration of these resources has positive impact from
environmental perspective but their penetration has raised serious issues on secure and reliable operation of a
network, owing to their intermittent and not dispatchable output. To maintain an optimal operation of a network,
extensive research studies have been carried out under the theme of network management. This paper
discusses the concept of losses management, which falls under the same theme, in active distribution networks.
The methods related to modelling of such systems and end-users, numerical tools required for system analysis,
active network management schemes for losses minimization and fair losses allocation to passive and active
consumers are reported and investigated. Therefore, the aim of this paper is to provide a concise yet comprehensive
comparison of the most recently proposed losses management approaches and strategies.

... Though effective, this method does not address the voltage drop issue in the upstream MV network, which may directly affect voltage regulation in the tested LV network. Some examples of volt/var control method in MV networks are presented in [12] and [13], however, since LV networks are not considered, the proposed methods may not be adequate to improve network wide voltage profiles. ...

... In this section, the effectiveness of the proposed day-ahead power scheduling framework is verified in two cases. Figure 1 shows the line diagram of Case 1, which is a 20 kV AC/DC hybrid distribution network modified from [22]. The resistance data of the DC feeder is obtained by ignoring the reactance of the AC feeder. ...

With the great increase of renewable generation as well as the DC loads in the distribution network; DC distribution technology is receiving more attention; since the DC distribution network can improve operating efficiency and power quality by reducing the energy conversion stages. This paper presents a new architecture for the medium voltage AC/DC hybrid distribution network; where the AC and DC subgrids are looped by normally closed AC soft open point (ACSOP) and DC soft open point (DCSOP); respectively. The proposed AC/DC hybrid distribution systems contain renewable generation (i.e., wind power and photovoltaic (PV) generation); energy storage systems (ESSs); soft open points (SOPs); and both AC and DC flexible demands. An energy management strategy for the hybrid system is presented based on the dynamic optimal power flow (DOPF) method. The main objective of the proposed power scheduling strategy is to minimize the operating cost and reduce the curtailment of renewable generation while meeting operational and technical constraints. The proposed approach is verified in five scenarios. The five scenarios are classified as pure AC system; hybrid AC/DC system; hybrid system with interlinking converter; hybrid system with DC flexible demand; and hybrid system with SOPs. Results show that the proposed scheduling method can successfully dispatch the controllable elements; and that the presented architecture for the AC/DC hybrid distribution system is beneficial for reducing operating cost and renewable generation curtailment.

... A centralized control is proposed in [13] which coordinates with OLTC and DERs connected on each feeder. This optimizes the reactive power exchange in each feeder, reduces power losses, and maintains the voltage within steady state limits. ...

The proliferation of Distributed Energy Resources
(DERs) in the distribution network has hindered the optimal
operation of the grid due to multiple technical issues such as
voltage rise, reverse power flow, voltage unbalance, islanding
etc. Therefore, optimal management of DERs is becoming a
key research area to improve the system power quality. In this
context, several Active Network Management schemes have been
proposed to mitigate the issues associated with DERs integration
to the grid and ultimately reduce the network power losses. This
paper provides a comprehensive review of these schemes along
with a discussion on the distribution network modelling and load
profiling. Further, it also reports the possible future research
areas in the field of losses management.

... Based on the case in [17], one feeder with partial expansion is used to verify the strategy proposed in this paper. The topological connection is shown in Figure 6. ...

... Active network management (ANM) approaches are used to mitigate adverse impacts brought by large DG penetrations. Studies on ANM for DG integration have been conducted extensively, including the use of on-load tap changer (OLTC) [2], the automatic voltage control (AVC) [3] and DG generation curtailment [4]. ...

High penetration levels of distributed generation (DG) become new challenges for traditional electrical distribution networks. The increase of DG penetration can be facilitated by means of Network Reconfiguration (NR) and Soft Open Point (SOP). SOP is a power electronic device installed between adjacent feeders of a distribution network, with the capability to control real and reactive power flows through its connecting points. This paper explores the maximum DG penetration level that distribution network can accommodate before violating any operational constraints using three approaches: NR, SOP, and a combined method using NR to coordinate with SOP operation. The impacts of DG concentrations and SOP locations on achievable DG penetration levels are analysed. The effectiveness of the proposed approaches and the significant benefits obtained by using the combination of NR and SOP are demonstrated on a 33-bus distribution network.

... In Closed-Loop System Command Governor fact, because control actions are made on the basis of a partial knowledge of the network, only suboptimal performance can be achieved. The introduction of advanced power electronic and ICT systems into modern smart grids opened to new communication facilities involving DGs and OLTC and gave rise to several more effective control strategies mainly based on the presence of central control center ([21][28]) capable of monitoring and managing the entire MV/LV grid. However, centralized control approaches present two major disadvantages: (1) a lot of, even too long, time to determine the control action; (2) a big amount of information to be conveyed to the control center, processed and sent to local control devices. ...

High penetration of distributed generation (DG) in medium voltage (MV) power grids may easily lead to abrupt voltage raises in the presence of either low demand conditions or high power production from renewable sources. In order to cope with the possibly occurring voltage limit violation, the active power injected by the distributed generators is typically curtailed, being, however, such an approach suboptimal from an economical point of view and presenting several other disadvantages. To address this issue, the online management and coordination of the reactive power injected/absorbed by the distributed generators acting on the grid are proposed here. The approach is based on command governor ideas that are used here to optimally solve constrained voltage control problems in both centralized and distributed ways. The approach foresees an active coordination between some controllable devices of the grid, e.g., distributed generators and MV/high voltage transformers, in order to maintain relevant system variables within prescribed operative constraints in response to unexpected adverse conditions. Simulation results show that the proposed approach is more effective than approaches suggested by the current Italian norms on DGs connection.

... Some loads may still out of service during repairing fault period (RFP) depending on fault location. When a fault occurs at the first branch of a radial feeder, all loads will remain out of service during RFP [4]. ...

The rapid increase of distributed generations (DGs) has many benefits for distribution systems and could result in some negative effects. Identifying the optimum locations and sizes for these units increases the benefits and limits the negative effects. Many researches tried to define the optimal DG siting and sizing. Either normal operation or faulty conditions have been considered in this process. In this paper, repairing fault periods (RFP) in loop distribution systems is considered in the optimization process. Comprehensive comparisons between results of considering only normal operating periods (NOP) and those considering both NOP and RFP are introduced. The main aim of the proposed methodology is to minimize the energy loss. An actual 15-bus loop distribution system is implemented to represent the case study. Genetic Algorithm (GA) technique is used for solving the objective function. The results show significant effect for RFP on the optimization results. Thus, considering both NOP and RFP is essential for optimal sizing and siting of DG in loop distribution systems.

... Energies 2017, 10, 156 2 of 16 systems (ESSs). Both of them could be involved by the distribution system operator (DSO) in regulating the network operating conditions, e.g., as illustrated in [6][7][8][9]. ...

The recent growing diffusion of dispersed generation in low voltage (LV) distribution networks is entailing new rules to make local generators participate in network stability. Consequently, national and international grid codes, which define the connection rules for stability and safety of electrical power systems, have been updated requiring distributed generators and electrical storage systems to supply stabilizing contributions. In this scenario, specific attention to the uncontrolled islanding issue has to be addressed since currently required anti-islanding protection systems, based on relays locally measuring voltage and frequency, could no longer be suitable. In this paper, the effects on the interface protection performance of different LV generators’ stabilizing functions are analysed. The study takes into account existing requirements, such as the generators’ active power regulation (according to the measured frequency) and reactive power regulation (depending on the local measured voltage). In addition, the paper focuses on other stabilizing features under discussion, derived from the medium voltage (MV) distribution network grid codes or proposed in the literature, such as fast voltage support (FVS) and inertia emulation. Stabilizing functions have been reproduced in the DIgSILENT PowerFactory 2016 software environment, making use of its native programming language. Later, they are tested both alone and together, aiming to obtain a comprehensive analysis on their impact on the anti-islanding protection effectiveness. Through dynamic simulations in several network scenarios the paper demonstrates the detrimental impact that such stabilizing regulations may have on loss-of-main protection effectiveness, leading to an increased risk of unintentional islanding.

... Furthermore, the above mentioned methods increase their effectiveness when integrated with advanced power electronic and ICT systems of modern smart grids that open to new communication facilities and make reliable the coordination among the DGs and OLTC. Control strategies in this respect can be found in Tedesco and Casavola [2013], Bignucolo et al. [2008]. This paper focuses on the development of a constrained supervision strategy, based on Command Governor (CG) ideas, for the coordination of an OLTC device and DGs in order to maintain the voltage at each connection node within prescribed bounds in spite of consistent load variations. ...

High penetration of Distributed Generation (DG) in Medium Voltage (MV) power grids is usually a reason of abrupt voltage raises. In this respect critical scenarios are represented by both low demand conditions and high power production from renewable sources. In order to cope with the possibly resulting voltage limits violation, a typical adopted approach is the disconnection of the distributed generators or the curtailment of the generated power leading to several disadvantages. To address this issue an online management of the reactive power of distributed generators is presented. The approach is based on Command Governor (CG) ideas and is aimed at solving a constrained voltage regulation problem in both centralized and distributed ways. The approach foresees an active coordination between some controllable devices of the grid, e.g. distributed generators, MV/HV transformers, in order to maintain relevant system variables within prescribed operative constraints in response to unexpected adverse conditions. Simulation results show that the proposed approach is more effective than approaches suggested by the current Italian norms on reactive power compensation.

... Each solution is currently investigated by different stakeholders and their feasibility is overviewed in [6]. In addition, coordinated voltage control strategies, such as using the OLTC at the substation level and using the active/reactive power at the distributed generation level, are studied in the literature [13], [14]. ...

This article investigates the control logics of an on-load tap-changer transformer by means of experimental system validation. The experimental low-voltage unbalanced system consists of a decoupled single-phase on-load tap-changer transformer, a 75-m 16-mm² cable, a controllable single-phase resistive load, and an electric vehicle that has the vehicle-to-grid function. Three control logics of the on-load tap-changer transformer are described in the study. The three control logics are classified based on their control objectives and control inputs, which include network currents and voltages, and can be measured either locally or remotely. To evaluate and compare the control performances of the three control logics, all of the tests use the same loading profiles. The experimental results indicate the modified line compensation control can regulate voltage in a safe band in the case of various load and generation conditions.

... From a review of similar energy storage behaviour algorithms [16] [17][18] [19] Simulink was chosen as a viable candidate to accurately measure system interactions. This allowed for fixed time step simulation of input data with varied resolutions, and further allowed for optimization and multiple-run execution within the MATLAB environment. ...

As the economic feasibility of rooftop photovoltaic (PV) electricity generation becomes increasingly accessible to the average consumer, electrical utilities face unprecedented demand disruption. Renewable energy generation has the potential to create a sustainable electricity future, but the problem of intermittent generation becomes an increasingly pressing issue. Recent developments in energy storage technology, particularly in the development and recent residential sizing of lithium-ion batteries means that electrical demand and resource can be handled by the utility so as to minimize grid strain and costs to the consumer. This work develops an energy storage system (ESS) to accurately model the interaction between solar panels, batteries and the electrical grid. A sample electrical grid in Vermont was examined for potential demand arbitrage, and the load profile served as input for the ESS. A variable-period mean approach to demand leveling was implemented, which allowed for optimization of ESS capacity sizing. Through variance and kurtosis analysis, the ESS is able to establish an empirically beneficial battery usage profile given a unique load characteristic. Results suggest that the most successful approach to promote grid health is an initially quadratic relationship between capacity and averaging period that converges on a period of 24 hours for values of installed capacity greater than approximately 10% of average daily grid electricity usage.

Energy consumption with recovery of surplus production and availability at peak times is desirable for sustainable environments. The objective of the present paper is to plan storage systems based on battery banks in electrical distribution systems having distributed resources. In particular, wind-based power is considered, and the goal is to determine the quantity, location and capacity of batteries, as well as their operation conditions considering investment and operating costs. In this sense, a three-stage method is proposed. The first one determines candidate buses for battery allocation by applying a proposed sensitivity index that seeks to improve the quality and computational efficiency, obtained from an optimal power flow model. The second stage comprises a metaheuristic algorithm to optimize quantity and location of batteries and an optimal power flow to determine the batteries’ capacity, where the power injected or absorbed by batteries is modeled as an optimization variable. Finally, the optimal power flow of the third stage seeks to optimize the batteries and system operation. Four case studies are presented with different test systems. The proposed approach proved to be applicable for these systems, since it provides a reduction in the total planning and operating cost considering grid reliability and gives results that have good cost reduction from comparison with other solutions of literature. The main motivation is to show the applicability of a novel approach based on optimization procedure and sensitivity index to investigate issues that are relevant for planning storage systems in distribution networks.

This article proposes a voltage regulation scheme for distributed energy resource-connected distribution networks based on static synchronous compensator to compensate for both short-term and long-term voltage sags. The proposed voltage regulation scheme provides a fast and precise control on the nodal voltage, with no need to load shedding, capacitor switching, transformers, or power management schemes. The principles supporting the proposed voltage regulation scheme are discussed and the effectiveness of the proposed control is demonstrated through time-domain simulation of a two-unit test distribution network in the PSCAD/EMTDC software environment.

Dual CPU redundant operation of PLC is of great significance to the reliability of industrial automation control system. In view of the problems existing in the traditional dual CPU PLC redundancy control mode based on hardware strategy, this paper proposes a dual CPU redundancy control idea based on software strategy, and describes in detail the specific scheme of Dual CPU redundancy software design using A-B ControlLogix series PLC.

The proliferation of distributed generators (DGs) and electric vehicle charging stations (EVCSs) has brought voltage regulation challenges to distribution networks. This article proposes a distributed control algorithm to dispatch surplus reactive power from EVCSs and DGs for proper voltage regulation without violating their converters’ capacities or stressing conventional voltage control devices, such as on-load tap changers (OLTCs). Further, an active power curtailment strategy is proposed for DGs to properly integrate OLTCs in voltage regulation when the reactive power support is deficient. The proposed control algorithms rely on the average consensus theory and sensitivity analysis to provide optimized voltage support while satisfying the agents’ self-objectives. Simulation results of a typical distribution network confirm the effectiveness of the proposed distributed control algorithms in maintaining proper voltage regulation with minimum voltage support from EVCSs and DGs, and reduced daily tap operation for OLTC.

With increasing connection of distributed generations (DGs), the power flow in electric distribution network is no longer unidirectional and the network has become active distribution network. Thus, the connection of DGs in electric distribution networks has created a challenge for distribution network operators due to bidirectional power flow. One of the main technical challenges of an active distribution network is to maintain an acceptable voltage level in the system. This has initiated efforts in using various voltage control strategies to regulate the network voltage profile so that the voltage is maintained at its allowable voltage limits. A number of voltage control methods have been applied to solve voltage control problems associated with the connection of DGs in a distribution system. These voltage control strategies may be classified as decentralized or distributed and centralized or coordinated voltage control. From the literature, a number of coordinated voltage control strategies have been implemented to provide better and faster control to the system. This chapter presents an improved coordinated voltage control method in active electric distribution network by coordinating the three voltage control methods, namely, power factor control, on load tap changer control and generation curtailment control. These voltage control methods are coordinated using fuzzy logic by considering the load bus voltages and DG power as inputs and the voltage control actions as the outputs. The fuzzy logic if-then control rules which are generated to build the fuzzy logic control system are based on the simulations results as well as from the previous works. Results obtained using the fuzzy logic based coordinated voltage control has shown that the voltages are able to be kept within its permissible limits.

In terms of the improvement of reliability and efficiency, integration of distributed generation (DG) into distribution network has gained significant interest in recent years. However, existing distribution systems were not designed considering large-scale penetration of DG. Due to the increasing penetration of DG, several technical challenges may arise which include voltage control, power quality and protection issues, etc. Therefore, additional components need to be modelled together with conventional distribution system components in order to study the impact of DG on the distribution system. The first objective of this paper is to review the required models of system components, the impacts of DG on system operation, mitigation of challenges, associated standards and regulations for the successful operation of distribution systems. A number of commercial and open source tools are available for modelling and analysis of distribution systems. An ideal computational tool should include necessary functionalities to study the impacts of increased DG penetration as well as various options to overcome possible operational problems. Based on the first objective, the second objective is to make a summary of characteristics and features that an ideal computational tool should have to study increased DG penetration. A comparison study of two commonly used computational tools is also carried out in this paper.

When a malfunction occurs in a smart-grid electricity-provisioning system, it is vitally important to quickly diagnose the problem and to take corrective action. The self-healing problem refers to the need to take action in near real time in order to reallocate power to minimize the disruption. To address this need, we present a collection of integer linear programming (ILP) models that are designed to identify the optimal combinations of supply sources, the demand sites for generators to serve, and the pathways along which the reallocated power should flow. The models explicitly support multiple time periods and the uncertainty associated with alternative sources such as wind power. Model solutions are evaluated using a simulator configured with multiple, intelligent, distributed software agents.

With the increasing permeability of wind farms, the reactive power regulation capability of wind farms based on the fully-rated converted wind turbine can be reasonably considered for the reactive power dispatch of distribution system. Actually, the power grid needs the distributed reactive power source to support the voltage control flexibly and fast, which makes it possible for the wind farms to participate in the automatic voltage control (AVC). This paper proposes an AVC method based on the adaptive zone-division for the distribution system with wind farms. This method has an objective to aptly dispatch the reactive power from wind farms to maintain the voltage stability of the power network. The efficiency of proposed method is validated via a case study on a real power grid of China.

This paper proposes optimal voltage control strategies for distribution systems that have multiple voltage regulator devices. The system must operate reaching desirable voltage profiles for scenarios that consider extreme loading (heavy and light), unbalanced loads and distributed generation connection. The problem is modeled as an optimization problem that ensures the attendance of the constraints related to voltage limits, power balance and control devices' capacity. The decision variables are the taps of the voltage control devices, which play an important role on Volt/Var control. A genetic algorithm implemented through a computer interface between Matlab and OpenDSS packages determines the number of control operations. It is assumed that the distribution system has a centralized control with all necessary communication infrastructure. To confirm the validity of the proposed method, simulations were performed by using the IEEE 34 node test feeder. The results showed that the strategies contributed to reduce the voltage deviation along the feeder, the voltage unbalance and the total feeder losses.

Voltage regulation by means of coordinated voltage control is one of the challenging aspects of distribution system operation. Integration of distributed generation (DG), which can also be operated in voltage control mode, in distribution systems may introduce adverse effects including control interactions, operational conflicts and long term oscillations. The seamless operation of distribution systems embedded with DG for effective voltage control is one of the challenging tasks, mainly because (a) DG may interact with the conventional voltage control devices and (b) prioritised operation of different voltage control devices depends on the network topology and real-time characteristics of the system. Coordinated operation involving multiple voltage control devices (i.e., on-load tap changers and voltage regulators in addition to local capacitor banks) and DG units is one of the feasible technical solutions at medium voltage distribution system level. In most of the methods proposed in the literature, the voltage control devices and DG units are tuned and coordinated online using Volt/VAR optimization strategies in accordance with the time-graded operation. However, there is no mechanism to operationally minimize the interactions between DG units and the voltage control devices in real-time between any two consecutive control states. In such case, more generic approach needs to be developed for examining interactions between the DG units and the voltage control devices. In this paper, interactions among multiple DG units and the voltage control devices are identified using their simultaneous and non-simultaneous responses.

The paper investigates the effects and potential of distributed generation (DG) on the operation of weak distribution networks. It focuses on the development of a new method to increase the integration capacity of DG in an existing network. The paper considers voltage issues and the load transfer capability of distribution network including windmills. The proposed method is based on ring operation of the distribution network and control of windmill active and reactive power. The applicability of the proposed method is tested with load-flow simulations on a real life distribution network and planned windmills. The studies have proved the capability of the proposed method to increase the integration capacity of DG units without major network investments.

Until recent years, the connection of dispersed Independent Power Producers to electrical networks has not been a problem for utilities, due to the fact that installed power represented a small amount of the total power connected to the system. But nowadays, with the types of generators used in wind farms, it is reasonable to think that wind generators should take part in the control of electrical variables of the network they are connected to. This paper reports an investigation to determine the impact of reactive power control in voltage regulation of electric networks and theefects of islanding operation. The studies have been carried out on a real wind farm located in Navarra, North of Spain.

INTRODUCTION This paper presents an overall summary of the impact of distributed generation on the control and stability of distribution networks. The paper is intended as a discussion paper.

Distributed generators are normally operated in automatic power factor control, although this can be more difficult in weak areas of the distribution network as they are frequently connected to long open-ended radial feeders, which have low X/R ratios and high resistance. The un-constrained bi-directional power flow may cause unacceptable voltage fluctuations that would cause generator or other system protection to operate. Operating the generator in constant voltage mode is only occasionally acceptable to distribution network operators, since an unconstrained machine may attempt to define voltages that conflict with setting of their automatic voltage control equipment. Line-Rise Compensation (LRC) is a network control technique that may lower steady-state overvoltages. This paper will discuss the implications, consequences and benefits of network LRC control compared to flexible control of power factor and voltage of the distributed generator.

The increased presence of distributed generation sources into the distribution systems calls for revisiting the current practices concerning distribution systems operation. This paper presents a comprehensive approach to voltage control in the presence of distributed generation, which takes into account the time and spatial variation of generation and loads and the possible contribution of voltage-controllable local generators to distribution system voltage control. The paper recalls the characteristics and modelling of the voltage controllers, including the standard voltage controller (modelled as a PV node with reactive power limits) and the combined voltage/reactive power regulator, which operates either in the voltage-support or in the voltage-following mode for controlling voltage or reactive power, respectively. The voltage control problem is then formulated as an optimisation, by using an objective function based on the voltage deviations with respect to given voltage references. The solution is provided through a mixed heuristic approach, with the use of genetic and Ant Colony Search-based operators. Numerical results are provided on a real MV rural distribution system.

Passive electricity distribution networks will have to evolve, both technically and economically, into actively managed networks. Such networks, with a new range of paid-for system services, should prove to be the best tool to facilitate embedded generation in a deregulated electricity market. In this paper, EA Technology describe their research on active networks conducted within the Strategic Technology Programme, a co-operative research programme for electricity distribution companies funded by European distribution network operators.

The increasing amount of wind power generation in European power systems requires stability analysis considering in-teraction between wind-farms and transmission systems. Dynamics introduced by dispersed wind generators at the dis-tribution level can usually be neglected. However, large on-and off-shore wind farms have a considerable influence to power sys-tem dynamics and must definitely be considered for analyzing power system dynamics. Compared to conventional power stations, wind power plants consist of a large number of generators of small size. There-fore, representing every wind generator individually increases the calculation time of dynamic simulations considerably. Therefore, model aggregation techniques should be applied for reducing cal-culation times. This paper presents aggregated models for wind parks consist-ing of fixed or variable speed wind generators.

Voltage control is a major factor in the design of distribution system, so much so that it is a statutory requirement [1] in many countries that customers receive a voltage that remains within stated parameters. In addition to its magnitude, other factors such as continuity and freedom from harmonics are also important. Each of these parameters has cost implications for the utility. This paper concentrates primarily on the impact of distributed generation on voltage control. Traditionally, voltage control in distribution systems consisted principally of onload tap changers in bulk supply point stations. When necessary, these were augmented by booster transformers and possibly capacitors to increase the voltage where it dropped to too low a level. Distributed generation has a tendency to increase the voltage at its terminals. Where possible, this effect should be harnessed to contribute to voltage control. Where the generator cannot assist with voltage control, its impact has to be managed to ensure an acceptable voltage appears at the busbars of all customers.

In this paper a procedure that allows distributed generation plants (DGs) to be operated as a virtual power plant (VPP), maintaining meanwhile the voltage profiles on medium voltage (MV) feeders within the permissible interval, is presented. To this aim a co-ordinated controller is proposed. It acts both on the on line tap changer (OLTC) and on the reactive power production of specific plants so that voltage regulation is performed whatever the working condition (generation units disconnected or partially loaded or working at maximum power). In particular this controller can influence a VPP economic criteria dispatch by bounding, for example, the maximum active power generated by each unit in order to obtain the DG reactive generations required by the management of the distribution system. Thus, as a consequence some lower variable cost productions might have to limit their active outputs which represent a possible cost increase in VPP management. These automatic limitations, imposed by the controller, allow the distribution system operator (DSO) to control voltage on the whole distribution system and the DG plants to guarantee their connection to the network. Simulations on a realistic network case study are carried out to compare the VPP management impact on voltage profiles with a traditional voltage regulation (only OLTC action) and with a coordinated control system. Results demonstrate that the proposed procedure is able to preserve distribution network from dangerous under and over voltages with limited interferences with the VPP optimisation algorithm.

This paper presents a novel method of allocating new generation capacity within existing grid using optimal power flow (OPF). New generation capacity and connections to external networks are modelled as generators with quadratic cost functions. This allows preferences to be expressed regarding the location of new capacity and a focus on a specific part of the network whilst, at the same time, considering the technical and economic impact of exports and imports of power on the broader network. Sequential quadratic programming (SQP) is used to solve the OPF as it produces signals that can be used in planning mechanisms for the efficient development of the network.

Voltage regulation in Medium Voltage networks is approached in two main different ways: load-dependent (compounding) and load-independent regulation. In order to adopt a unified method for the utility Nuon, both have been compared. Because of its sensitivity to load patterns, cogeneration is a distortion factor for compounding. This is why there are different visions on whether or not compounding should be applied. The research covers the question whether compounding is effective with the current degree of cogeneration in the Dutch MV-grid. A couple of 50/10 kV transformers were modeled, as well as the outgoing MV-feeders. The behavior of each transformer was simulated both with load-independent regulation and compounding. Within the utility Nuon measurements of the load patterns (P and Q) from the transformers and the current of each feeder are available, as well as the maximum load of all low-voltage substations. Using this data and varying the compounding degree, load flow simulations on these networks were performed to determine the optimal tuning of the voltage regulation on the transformers. A statistical analysis of the results shows that by a moderate degree of cogeneration a small amount of compounding does not give any problems, whereas by a large degree of compounding the problems are considerable. Conclusion of this study is that on the greater part of the network the voltage profile at the low-voltage substations as a result of compounding is notably better than the one gotten by independent-load voltage regulation. This means less investment on voltage improvement in the net. On this moment the implementation phase within the utility Nuon is been carried out.

Preface INTRODUCTION Operating States of a Power System Power System Security Analysis State Estimation Summary WEIGHTED LEAST SQUARES STATE ESTIMATION Introduction Component Modeling and Assumptions Building the Network Model Maximum Likelihood Estimation Measurement Model and Assumptions WLS State Estimation Algorithm Decoupled Formulation of the WLS State Estimation DC State Estimation Model Problems References ALTERNATIVE FORMULATIONS OF THE WLS STATE ESTIMATION Weaknesses of the Normal Equations Formulation Orthogonal Factorization Hybrid Method Method of Peters and Wilkinson Equality-Constrained WLS State Estimation Augmented Matrix Approach Blocked Formulation Comparison of Techniques Problems References NETWORK OBSERVABILITY ANALYSIS Networks and Graphs NetworkMatrices LoopEquations Methods of Observability Analysis Numerical Method Based on the Branch Variable Formulation Numerical Method Based on the Nodal Variable Formulation Topological Observability Analysis Method Determination of Critical Measurements Measurement Design Summary Problems References BAD DATA DETECTION AND IDENTIFICATION Properties of Measurement Residuals Classification of Measurements Bad Data Detection and IdentiRability Bad Data Detection Properties of Normalized Residuals Bad Data Identification Largest Normalized Residual Test Hypothesis Testing Identification (HTI) Summary Problems References ROBUST STATE ESTIMATION Introduction Robustness and Breakdown Points Outliers and Leverage Points M-Estimators Least Absolute Value (LAV) Estimation Discussion Problems References NETWORK PARAMETER ESTIMATION Introduction Influence of Parameter Errors on State Estimation Results Identification of Suspicious Parameters Classification of Parameter Estimation Methods Parameter Estimation Based on Residua! Sensitivity Analysis Parameter Estimation Based on State Vector Augmentation Parameter Estimation Based on Historical Series of Data Transformer Tap Estimation Observability of Network Parameters Discussion Problems References TOPOLOGY ERROR PROCESSING Introduction Types of Topology Errors Detection of Topology Errors Classification of Methods for Topology Error Analysis Preliminary Topology Validation Branch Status Errors Substation Configuration Errors Substation Graph and Reduced Model Implicit Substation Model: State and Status Estimation Observability Analysis Revisited Problems References STATE ESTIMATION USING AMPERE MEASUREMENTS Introduction Modeling of Ampere Measurements Difficulties in Using Ampere Measurements Inequality-Constrained State Estimation Heuristic Determination of F-# Solution Uniqueness Algorithmic Determination of Solution Uniqueness Identification of Nonuniquely Observable Branches Measurement Classification and Bad Data Identification Problems References Appendix A Review of Basic Statistics Appendix B Review of Sparse Linear Equation Solution References Index

Voltage control in distribution networks becomes increasingly important with an increasing penetration of distributed generation (DG). As distribution networks are much more resistive than transmission networks, the conventional technique of reactive power compensation in order to control the voltage cannot be applied very well. For that reason other voltage control techniques have to be applied. In this contribution several options for voltage control in distribution networks are analyzed and related to important grid parameters such as the short-circuit ratio and the X/R ratio of the grid. For networks with a high X/R ratio reactive power can be used for voltage control. For networks with a low X/R ratio several new voltage control techniques are proposed. These techniques are voltage control with active power, inserting a controllable inductance in the grid and series compensation by DG unit converters.

The increase of dispersed generation (DG) has a strong impact on power system operation. A distribution network, where most of dispersed generators are connected, cannot be considered as passive anymore. Active character of the distribution networks brings problems and uncertainties, but at the same time offers more possibilities for control. Control of distribution networks with DG can be performed by means of primary controllers of dispersed generators, compensating devices and tap changers of transformers. Most of the control normally is using only local measurements. At the same time, it is obvious that the problems, which will arise with the increase of the DG in the future, must be solved by partially decentralized control (control, centralized inside defined area). In this paper, possible structure for such control is presented.

High penetration of distributed generation is currently limited by passive operating methods of distribution networks. At distribution level, insufficient measurements are available to allow satisfactory control, so measurement is extended through the use of state estimation. Aspects that are described in this paper include optimal measurement location, the problems occurring with few measurements, and load models used for “pseudo-measurements”. Two control philosophies are described. The first, applicable to smaller network segments, is a local control, working with existing control devices such as transformer automatic voltage control (AVC) relays. The second philosophy is optimal control with constraints.

The hosting capacity for distributed energy resources (DER) identifies the acceptable degree of DER penetration under given circumstances. It depends on various parameters such as the characteristics of the generation units, the configuration and operation of the network, the requirements of the loads as well as national and regional requirements. To determine the hosting capacity and to find ways to expand it by overcoming existing barriers is one subject of the ongoing European research project EU-DEEP. This paper describes the impacts of non-controlled DER units on the resulting voltage profiles as these impacts showed to be a main limitation for the hosting capacity for DER in existing distribution networks. The methodology for the analysis is introduced and basic results of the case studies performed are demonstrated. Generally the hosting capacity for DER can be extended applying different technical measures all leading to additional investments into the network. In future active distributions networks will provide a cost-effective solution to increase DER penetration.

The reactive power service is one of the control area ancillary services that must be in place to make the electric energy delivery possible. It may be of interest to examine the advantage of providing the necessary reactive power support by local devices, namely shunt capacitors or Dispersed Generators (DG) where available. To this purpose the paper first defines costs for the service performed by these devices, then it proposes an optimal co-ordination method which allows distributors to select, for every operating condition, the more profitable combination of reactive sources in order to maintain the network voltage levels within a desired range and to minimise the regulation action global cost.

This paper proposes the advanced online control method of the Under-Load Tap Changer (ULTC) transformer for distribution voltage regulation which considers the unbalanced load diversity on multiple feeders and the hysterical tap changing mechanism of the ULTC transformer. The proposed method determines the optimal tap position of the ULTC transformer to maintain the customers' voltages within the permissible limits as much as possible. The numerical formulations of the proposed method are presented. The results from a case study show that the proposed method can be practically applied to voltage regulation methods on power distribution systems that have unbalanced load diversity on multiple feeders and large voltage drops on feeders.

In this paper, an efficient expansion planning method for distribution networks based on reactive tabu search is proposed. This method consists of two-step procedures to determine the location of SVR and SVC to be installed. In the first procedure, the allocation of SVR is determined and the optimal tap positions of SVRs are selected by a static optimization. In the second procedure, output changes of distributed generators are considered and the allocation of SVC is determined and optimal tap positions of SVRs are determined against voltage deviations caused by connections of distributed generators by a dynamic optimization. This proposed method can take the installation cost of both SVR and SVC into account as an economic criterion, and is able to incorporate the upper and lower limit of voltage at each node and also the upper limit of line currents as constraints.

Voltage regulation of long weak distribution lines is a challenging problem, particularly when it is not economic to upgrade the entire feeder system. Power electronic converter systems offer an attractive alternative, with their potential to provide both steady state and transient voltage compensation for a limited capital investment. However, operation of these systems with weak networks and/or with multiple distributed installations needs careful attention to avoid unexpected interactions and to achieve optimum regulation performance. This paper explores the use of distributed D-STATCOM compensators to achieve stable steady state and dynamic compensation of the voltage profile along a radial distribution network under widely varying load conditions. Both simulation and experimental results are presented.

A new approach to optimal reactive power and voltage control
problem in a radial distribution system is proposed in this paper. The
optimal control problem is to find a proper dispatch schedule for shunt
capacitor banks and on-load tap changer at substation and shunt
capacitor banks on feeders such that the power loss is minimized and the
voltage profile is improved. To reduce computation burden, the whole
problem is decomposed into two sub-problems, namely sub-problem on
substation level and sub-problem on feeder level. A simplified dynamic
programming and a fuzzy logic control algorithm are used to deal with
the two sub-problems respectively. Coordination of the two algorithms
provides an appropriate solution to the whole control problem. The
numerical results demonstrate that the proposed approach is effective
and feasible

State estimation is important for the automatic management and control of complex distribution networks with significant distributed generation. State estimation has been used extensively on transmission systems where, generally, measurements of busbar voltages and line power flows exist. However, distribution systems normally have only a limited number of measurements. In such systems additional measurements are expensive and careful selection of location becomes important. The paper presents a heuristic approach to identify potential points for location of voltage measurements for state estimation as part of a proposed distribution management system controller. The developed technique identifies measurement locations to reduce the voltage standard deviation of the busbars which do not have a measurement. It addresses the problems of classical transmission meter placement methods, which are not directly applicable to distribution systems due to limited measurements, and unobservability of the network.

The penetration of wind power into electricity networks is increasing and many large wind farms use doubly-fed induction generator (DFIG) based wind turbines. A voltage control strategy for a DFIG-based wind farm is essential for compliance with some wind farm connection requirements. Such a control strategy may also have commercial benefits. This paper presents a voltage control strategy and illustrates the advantages of this methodology when applied to a DFIG implemented wind farm connected either to a transmission system or embedded within a distribution system. Dynamic linear time invariant models of the DFIG including its associated voltage source convertor and controllers are derived in the synchronous d-q reference frame. In addition, the local on-load tap changer is modelled as a finite state machine and the co-ordinated controllers for both systems are described. Simulation results are presented to illustrate the effectiveness of the controllers within both a transmission system and a distribution system.

Connections of embedded wind generation (EWG) in the rural
distribution system are susceptible to voltage rise. Current operating
policy, based on the passive operation of the distribution network,
limits the capacity of connected generation based on extreme conditions
of minimum load and maximum generation. It is demonstrated that an
active distribution network will allow considerably greater penetration
of EWG. Three alternative control strategies are evaluated to increase
the penetration level of EWG: EWG generation curtailment during low
demand; reactive power management using a reactive compensator; and
area-based OLTC co-ordinated voltage control. The application of these
schemes is illustrated on a rurally connected 11 kV wind farm in a
realistic 265-node generic distribution system model. Advanced optimal
power flow is used to quantify the benefits of alternative control
schemes for various EWG penetration levels. The impact of these schemes
on network losses is also assessed

This paper presents fuzzy-based reactive power and voltage control in a distribution system. The main purpose is to find the combination of main transformer load tap changer (LTC) positions and capacitors on/off switching operations in a day, such that the voltage deviations at the secondary bus of main transformer become as small as possible, while the reactive power flows through the main transformer and the real power losses at feeders become as little as possible. To minimize system repair cost, the total number of switching operations of LTC and capacitors in a day must be kept as few as possible. From the descriptions above, the linguistic expressions such as "as small as possible," "as little as possible," and "as few as possible" are not clear. So in this paper, the reactive power and voltage control problem is first formulated with fuzzy sets then an annealing searching technique is used to find a proper combination of LTC positions and capacitors on/off switching operations in a day. To demonstrate the effectiveness of the proposed method, reactive power and voltage control in a distribution system within the service area of Yunlin District Office of Taiwan Power Company (TPC) are analyzed. It is found that a proper dispatching schedule for LTC positions and capacitors switching operations can be reached by the proposed method.

This paper presents a dynamic programming method for solving
reactive power/voltage control problem in a distribution system. The
objective of this paper is to properly dispatch main transformer under
load tap changer, substation capacitor and feeder capacitors based
forecast hourly loads of each feeder section and primary bus voltage
such that the total feeder loss can be minimized, voltage profile can be
improved, and the reactive power flow into main transformer can be
restrained. The constraints that must be considered include maximum
allowable number of switching operations in a day for under load tap
changer and each capacitor, the voltage limit on the feeder, and limited
secondary bus voltage. To demonstrate the usefulness of the proposed
approach, reactive power/voltage control in a distribution system within
the service area of Yunlin District Office of Taiwan Power Company is
performed. It is found that a proper dispatching schedule for each
capacitor and under load tap changer can be reached by the presented
method

In the restructured electricity industry, the engineering aspects of planning need to be reformulated even though the goal to attain remains substantially the same, requiring various objectives to be simultaneously accomplished to achieve the optimality of the power system development and operation. In many cases, these objectives contradict each other and cannot be handled by conventional single optimization techniques. In this paper, a multiobjective formulation for the siting and sizing of DG resources into existing distribution networks is proposed. The methodology adopted permits the planner to decide the best compromise between cost of network upgrading, cost of power losses, cost of energy not supplied, and cost of energy required by the served customers. The implemented technique is based on a genetic algorithm and an ε-constrained method that allows obtaining a set of noninferior solutions. Application examples are presented to demonstrate the effectiveness of the proposed procedure.

This paper presents fuzzy-based reactive power and voltage control in a distribution system. The main purpose is to find the combination of main transformer load tap changer (LTC) positions and capacitor on/off switching operations in a day, such that the voltage deviations at the secondary bus of main transformer become as small as possible, while the reactive power flows through the main transformer and the real power losses at feeders become as little as possible. To minimize system repair cost, the total number of switching operations of LTC and capacitors in a day must be kept as few as possible. The linguistic expressions such as "as small as possible," "as little as possible," and "as few possible" are not close. In this paper, the reactive power and voltage control problem is first formulated with fuzzy sets, and then an annealing search technique is used to find a proper combination of LTC positions and capacitors on/off switching operations in a day. To demonstrate the effectiveness of the proposed method, reactive power and voltage control in a distribution system within the service arm of Yumlin District Office of Taiwan Power Company (TPC) is analyzed. It is found that a proper dispatching schedule for LTC positions and capacitors switching operations can be reached by the proposed method.

This paper presents a dynamic programming method for solving reactive power / voltage control problems in a distribution system. The objective of this paper is to properly dispatch main transformers under load tap changers, substation capacitors, and feeder capacitors based on hourly forecast loads of each feeder section and primary bus voltage such that the total feeder loss can be minimized, voltage profile can be improved, and the reactive power flow into the main transformer can be restrained. The constraints that must be considered include the maximum allowable number of switching operations in a day for under load tap changer and each capacitor, and the voltage limit on the feeder and secondary bus voltage is limited. To demonstrate the usefulness of the proposed approach, reactive power /voltage control in a distribution system within the service area of the Yunlin District Office of Taiwan Power Company is performed. It is found that a proper dispatching schedule for each capacitor and under load tap changer can be reached by the presented method.

This paper presents an overview of the state of the art in reactive power compensation technologies. The principles of operation, design characteristics and application examples of Var compensators implemented with thyristors and self-commutated converters are presented. Static Var generators are used to improve voltage regulation, stability, and power factor in ac transmission and distribution systems. Examples obtained from relevant applications describing the use of reactive power compensators implemented with new static Var technologies are also described.

Voltage Control-lability of Distribution Systems with Local Generation Sources, IREP, Bulk Power System Dynamics and Control, Cortina d

- E Carpaneto
- G Chicco
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- R Donno
- Napoli

E. Carpaneto, G. Chicco, M. De Donno, R. Napoli, Voltage Control-lability of Distribution Systems with Local Generation Sources, IREP, Bulk Power System Dynamics and Control, Cortina d'Ampezzo, Italy, 2004.

Benefits of active voltage controls in distribution networks, UPEC meeting

- D Cao
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D. Cao, D. Pudjianto, S. Grenard G. Strbac, Benefits of active voltage
controls in distribution networks, UPEC meeting, Cork, UK, September
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Active Local Distribution Network Management for Embedded Generation

- S White

S. White, Active Local Distribution Network Management for Embedded Generation, DTI Publication, 2005.

Real-time voltage regulation of distribution networks with distributed generation

- H Leite
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- P F Gale

H. Leite, H.Y. Li, N. Jenkins, P.F. Gale, Real-time voltage regulation of
distribution networks with distributed generation, CIRED meeting,
Barcelona, Spain, May 2003

Distributed controllers for distribution networks, UPEC meeting

- J B O'donnel
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J.B. O'Donnel, A.R. Wallace, Distributed controllers for distribution
networks, UPEC meeting, Cork, UK, September 2005

Improvement of automatic voltage control of on load tap changer transformer in a distribution system with embedded generators

- F Jiang
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F. Jiang, S.K. Salman, V. Elaveeti, R. Gupta, Improvement of automatic voltage control of on load tap changer transformer in a distribution system with embedded generators, in: UPEC Meeting, Swansea, UK, September, 2001.

Improvement of automatic voltage control of on load tap changer transformer in a distribution system with embedded generators, UPEC meeting

- F Jiang
- S K Salman
- V Elaveeti
- R Gupta

F. Jiang, S.K. Salman, V. Elaveeti, R. Gupta, Improvement of automatic
voltage control of on load tap changer transformer in a distribution system
with embedded generators, UPEC meeting, Swansea, UK, September 2001

Optimal reactive power and voltage control for radial distribution system

- Y Liu
- P Zhard
- X Qiu

Y. Liu, P. Zhard, X. Qiu, Optimal reactive power and voltage control for
radial distribution system, IEEE Power Engineering Society Summer
Meeting, Seattle, USA, July 2000

Contribution of DG units to voltage control: active and reactive power limitations

- J Morren
- S W H De Haan
- J A Ferreira

J. Morren, S.W.H. de Haan, J.A. Ferreira, Contribution of DG units to
voltage control: active and reactive power limitations, IEEE PowerTech
Conference, St. Petersburg, Russia, June 2005

Voltage control in distribution systems as a limitation of the hosting capacity for distributed energy resources, CIRED meeting

- C Schwaegerl
- M H J Bollet
- K Karoui
- A Yagmur

C. Schwaegerl, M.H.J. Bollet, K. Karoui, A. Yagmur, Voltage control in
distribution systems as a limitation of the hosting capacity for distributed
energy resources, CIRED meeting, Torino, Italy, June 2005

A multiobjective evolutionary algorithm for the sizing and siting of distributed generation

- G Celli
- E Giani
- S Mocci
- F Pilo

G. Celli, E. Giani, S. Mocci, F. Pilo, A multiobjective evolutionary
algorithm for the sizing and siting of distributed generation, IEEE Trans.
Power Systems, vol. 20, No. 2 (may 2005), 750-757

Control aspects of distribution networks with dispersed generation

- A Ishchenko
- J M A Myrzik
- W L Kling

A. Ishchenko, J.M.A. Myrzik, W.L. Kling, Control aspects of distribution
networks with dispersed generation, IEEE PowerTech Conference, St.
Petersburg, Russia, June 2005

Active local distribution network management for embedded generation, DTI publication

- S White

S. White, Active local distribution network management for embedded
generation, DTI publication, 2005

Improvement of automatic voltage control of on load tap changer transformer in a distribution system with embedded generators

- Jiang