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Reactive Power Management for Voltage Rise Mitigation in Distribution Networks with Distributed Generation: a Command Governor Approach
Abstract
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.
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A distributed multi-agent supervision strategy (S-CG) based on Command Governor ideas is proposed to solve constrained voltage regulation problems in electrical Medium Voltage (MV) power grids in the presence of Distributed Generation (DG). The idea is that an active management of the set-points of some controllable variables of the grid, e.g. the power either provided by the distributed generators or consumed by the loads, can be an effective tool not only for maintaining relevant system variables within prescribed operative constraints in response to unexpected adverse conditions, but also for implementing some smart-grid functionalities. The supervision problem is formulated as a distributed constrained optimization problem by imposing that the voltages at certain nodes have, compatibly with all prescribed constraints and changed conditions, minimal deviations from their nominal values. Simulation results show that the proposed approach ensures, under certain conditions, feasible evolutions to the overall power grid under critical events.
n this paper a novel distributed FeedBack Command Governor (FB-CG) supervision strategy is presented for multi-agent networked systems subject to pointwise-in-time coordination constraints on the overall network evolutions. Specifically, a sequential distributed strategy where only one agent at a time is allowed to manipulate its own reference signal is fully detailed and its stability, feasibility and viability (liveness) properties rigorously proved. It is shown that, unlike the centralized case, liveness (the absence of deadlock situations) can be ensured only if the constraints satisfy a Constraints Qualification (CQ) condition. Several results and open problems in the liveness analysis are discussed and a counterexample is also provided for showing that for multi-input agents case the issue requires further investigations.
In this paper a novel distributed FeedBack Command Governor (FB-CG) supervision strategy is presented for multi-agent networked systems subject to pointwise-in-time coordination constraints on the overall network evolutions. Specifically, a sequential distributed strategy where only one agent at a time is allowed to manipulate its own reference signal is fully detailed and its stability, feasibility and viability (liveness) properties rigorously proved. It is shown that, unlike the centralized case, liveness (the absence of deadlock situations) can be ensured only if the constraints satisfy a Constraints Qualification (CQ) condition. Several results and open problems in the liveness analysis are discussed and a counterexample is also provided for showing that for multi-input agents case the issue requires further investigations.
In this paper a control strategy based on predictive control ideas is proposed for reconfiguring on-line the on-load tap changer (OLTC) voltage set-point in electrical medium voltage (MV) power grids in the presence of distributed generation (DG). The idea is that an active management of the set-point can be effective for maintaining relevant system variables within prescribed operative constraints in response to unexpected adverse conditions, e.g. changing loads or generation failures. The voltage set-point reconfiguration problem is formulated as a constrained optimization problem by imposing that the voltages at certain nodes have, compatibly with all prescribed constraints and changed conditions, minimal deviations from their nominal values. Simulation results show that the proposed approach ensures, under certain conditions, feasible evolutions to the overall network whenever critical events occur.
The aim of this paper is to present a methodology based on interval mathematics to deal with load uncertainty in power electric systems. The approach is suitable to model two types of uncertainty in power flow analysis, namely: (i) the influence of the load measurement errors at all system buses on the voltage profile; (ii) the voltage profile behavior under a load variation during a specific period of time. This methodology entails an interval power flow model and the resulting interval nonlinear system is solved using Krawczyk's method. We implemented the algorithm in the Matlab environment using the IntLab toolbox. Results for IEEE test-systems and a comparison with related work are presented.
A novel distributed Parallel Feedback Command Governor (FB-CG) supervision strategy is presented for multi-agent interconnected networked systems subject to pointwise-in-time constraints which need to be enforced during the overall system operations for subsystems coordination purposes. The paper extends some recent results related to this coordination-by-constraint approach by resorting to and extending Sequential Distributed Command Governor ideas. This novel Parallel distributed strategy is fully described and analyzed and it is compared with earlier Parallel Feed-Forward Command Governor (FF-CG) strategies in the final example.
The voltage rise caused by photovoltaic (PV) power feed-in is one of the main network constraints limiting the PV penetration in distribution networks. In this paper, a local voltage control approach for PV inverters based on reactive power management is proposed and investigated into detail. Through a parametric study, various inverter settings are considered and compared for a real medium voltage network with a high PV penetration level and for which a demonstration is planned within the project MetaPV. The purpose of this work is to investigate the suitability of such control concepts to compensate the voltage rise caused by the PV power feed-in and to provide some guidance on the adjustment of the settings of such control mechanisms. For the assessment of the performance of the control concept with different settings, extensive load flow simulations have been performed for a voltage-dependent reactive power control (Q(V) characteristics) on the basis of 15-minute profiles. As a result, voltage time-series over a period of 1 year are obtained for each case and analysed into details. Apart from the voltage profiles, other features such as network losses and reactive energy import have been quantified because they are also of noticeable importance for network operators. The simulation results show that suitable settings are necessary to maintain the voltage within the prescribed limits. A comparison between the considered cases shows that reactive power control Q(V) with a power factor down to 0.9 is necessary to achieve satisfying results. The use of a dead-band is recommended for the voltage-dependent reactive power control in order to limit the losses and reactive energy import. Copyright © 2011 John Wiley & Sons, Ltd.
As non-controllable power sources, photovoltaics (PV) can create overvoltage in low voltage (LV) distribution feeders during periods of high generation and low load. This is usually prevented passively by limiting the penetration level of PV to very conservative values, even if the critical periods rarely occur. Alternatively, one can use active power curtailment (APC) techniques, reducing the amount of active power injected by the PV inverters, as the voltage at their buses increase above a certain value. In this way, it is possible to increase the installed PV capacity and energy yield while preventing overvoltage. This paper investigates a number of approaches for sizing and controlling the PV power generated by 12 net-zero energy houses equipped with large rooftop PV systems in a typical 240 V/75 kVA Canadian suburban radial distribution feeder. Simulations of a one year period with typical solar irradiance and load profiles are conducted with PSCAD to assess the performance of the different approaches in terms of overvoltage occurrence, sharing of the burden for overvoltage prevention per house and total energy yield of the residential PV feeder.
Discrete-time, linear control systems with specified pointwise-in-time constraints, such as those imposed by actuator saturation, are considered. The constraints are enforced by the addition of a nonlinear ‘reference governor’ that attenuates, when necessary, the input commands. Because the constraints are satisfied, the control system remains linear and undesirable response effects such as instability due to saturation are avoided. The nonlinear action of the reference governor is defined in terms of a finitely determined maximal output admissible set and can be implemented on-line for systems of moderately high order. The main result is global in nature: if the input command converges to a statically admissible input and the initial state of the system belongs to the maximal output admissible set, the eventual action of the reference governor is a unit delay.
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.
Reference technical rules for the connection of active and passive consumers to the HV and MV electrical networks of distribution Company (2015)
- Comitato Elettrotecnico
- Italiano Norm
Comitato Elettrotecnico Italiano Norm CEI-016
" Reference technical rules for the connection of
active and passive consumers to the HV and MV
electrical networks of distribution Company (2015) ",
url:http://www.ceiweb.it/it/comunicati/news/569-
norma-cei-0-16.html.