Jacob Østergaard

Technical University of Denmark | DTU · Department of Electrical Engineering

The growing penetration of stochastic renewable energy sources increases the need for operational flexibility to cope with imbalances. Existing proposals for flexibility procurement are envisioning markets where the transmission system operator (TSO) can access flexible resources located at the distribution system operator (DSO)-level and vice vers...

The Danish government has set very ambitious binding targets regarding decarbonization. By 2030, carbon dioxide emissions must be reduced by 70% compared to the 1990 level. This can be achieved primarily through a predominantly renewables-based electricity system and the electrification of energy demand...

In current practice, the day-ahead market-clearing outcomes are not necessarily feasible for distribution networks, i.e, the network constraints might not be satisfied. Hence, the distribution system operator may consider an ex-post re-dispatch mechanism, exploiting potential flexibility of local distributed energy resources (DERs) including demand...

This paper proposes a distributed coordinated active and reactive power control scheme for wind farms based on the model predictive control (MPC) along with the consensus-based distributed information synchronization and estimation, which can optimally dispatch the active power of wind turbines (WTs) and regulate the voltages within the wind farm....

This paper presents a Model Predictive Control (MPC)-based coordinated voltage control scheme for distribution networks with high penetration of distributed generation (DG) and energy storage. In this scheme, the DG units, energy storage devices and on-load tap changer (OLTC) are optimally coordinated to maintain all bus voltages in the network wit...

This paper proposes an enhanced voltage control strategy (EVCS) based on model predictive control (MPC) for voltage source converter based high voltage direct current (VSC-HVDC) connected offshore wind farms (OWFs). In the proposed MPC based EVCS, all wind turbine generators (WTGs) as well as the wind farm side VSC are optimally coordinated to keep...

It is expected that bad data and missing topology information will become an issue of growing concern when power system state estimators are to exploit the high measurement reporting rates from phasor measurement units. This paper suggests to design state estimators with enhanced resilience against those issues. The work presented here include a re...

This paper presents a contingency screening method and a framework for its on-line implementation. The proposed method carries out contingency screening and on-line stability assessment with respect to first-swing transient stability. For that purpose, it utilizes the single machine equivalent method and aims at improving the prior developed contin...

A method for superimposing voltage sources is sought optimized by using a sparse triangular solver and multi-processing. A revision to the method is suggested which exploits Schur’s complement of the network admittance matrix and optimal re-use of computations. The algorithm is implemented and parallelized for shared memory multiprocessing. The pro...

Coordinated control strategies to provide system inertia support for main grid from offshore wind farm that is integrated through HVDC transmission is the subject matter of this paper. The strategy that seeks to provide inertia support to the main grid through simultaneous utilization of HVDC capacitors energy, and wind turbines (WTs) inertia witho...

A method for superimposing voltage sources is sought optimized by using a sparse triangular solver and multiprocessing. A revision to the method is suggested which exploits Schur's complement of the network admittance matrix and optimal re-use of computations. The algorithm is implemented and parallelized for shared memory multiprocessing. The prop...

The rapid development of photovoltaic (PV) systems in electrical grids brings new challenges in the control and operation of power systems. A considerable share of already installed PV units is small-scale units, usually connected to low-voltage (LV) distribution systems that were not designed to handle a high share of PV power. This study provides...

Photovoltaic (PV) systems are among the renewable sources that electrical energy systems are adopting with increasing frequency. The majority of already-installed PV systems are decentralized units that are usually connected to lowvoltage (LV) distribution grids. The PV hosting capacity of an LV grid is usually limited by overvoltage, and the effic...

This paper proposes a methodology to address the trading strategies of a proactive distribution company (PDISCO) engaged in the transmission-level (TL) markets. A one-leader multi-follower bilevel model is presented to formulate the gaming framework between the PDISCO and markets. The lower-level (LL) problems include the TL day-ahead market and sc...

This paper presents a methodology to obtain the optimal trading strategies between the proactive distribution company (PDISCO), heterogeneous distributed generation owners (DGOs) and wholesale market in a real-time trading framework. In this framework, the PDISCO’s decisions cover the power procurements from DGOs and the transactions within the rea...

In this paper, we present a real-time trading framework for distribution networks where a rational aggregator is identified as a broker by contracting with individual demands and dealing with the distribution company. Demand response capability is characterized by the coexistence of elastic and inelastic demand components. A one-leader multi-follow...

An improved Thevenin equivalent method for real-time voltage stability assessment that uses wide-area information from synchrophasors is proposed. The improvements are a better modeling of the limited synchronous generators, and a processing that anticipates the effect of field current limiters, before the latter are activated. Several study cases...

Management measures for peak-load shifting are employed to alleviate power shortages during the peak hours in some countries with power-supply shortages, such as China. One of the most popular measures is to rank the electricity users with respect to their relative importance in the society. In ranking the sequence, the decision maker may encounter...

The increased penetration of grid-connected photovoltaic (PV) systems in low-voltage (LV) grids creates concerns about overvoltage in these grids. The proposed methods to prevent overvoltage, such as reactive power absorption by PV inverters and active power management of customers, focus on decreasing the voltage rise along LV feeders, and the pot...

In this article we investigate the impact of residential solar PV plants on energy losses in distribution networks and their impact on distribution transformers lifetime. Current guidelines in Denmark states that distribution transformers should not be loaded with more than 67% solar PV power to avoid accelerated loss of life. If a solar PV plant c...

The paper introduces a new method to early identify the critical machine cluster (CMC) after a transient disturbance. For transient stability assessment with methods based on the equal area criterion it is necessary to split the generators into a group of critical and non-critical machines. The generators in the CMC are those likely to lose synchro...

Solar energy from photovoltaic (PV) is among the fastest developing renewable energy systems worldwide. Driven by governmental subsidies and technological development, Europe has seen a fast expansion of solar PV in the last few years. Among the installed PV plants, most of them are situated at the distribution systems and bring various operational...

The distributed economic dispatch for distributed generation is formulated as an optimization problem with equality and inequality constraints. An effective distributed approach based on multi-agent system is proposed for solving the economic dispatch problem in this paper. The proposed approach consists of two stages. In the first stage, an adjace...

An approach to evaluate the HVDC interconnections models to be used in real-time voltage stability assessment is proposed. The existing models for the HVDC interconnections, that are based on voltage source converter, were studied selecting the ones that are suitable for its application in Thevenin equivalent methods for voltage stability assessmen...

In this paper a new method is proposed to mitigate voltage unbalance caused by single-phase solar inverters in low voltage (LV) networks. The method is based on uneven reactive power absorption and injection by three-phase solar inverters. Independent control of each phase is performed to achieve this uneven injection. The average values of phase v...

This paper proposes a method to consider the impact of the wind farms maximum current limits on real-time voltage stability assessment. The approach is based in a multi-port equivalent of the system which makes possible to assess the effect of each wind farm limit on the stability boundary, the approach indicates the distance to the limit activatio...

This article characterizes experimentally the relation between phase and magnitude error from Phasor Measurement Units (PMU) in steady state and study its effect on real-time stability assessment methods. This is achieved by a set of laboratory tests applied to four different devices, where a bivariate Gaussian mixture distribution was used to repr...

Power generators contain control systems that are able to regulate system frequency, but the frequency setpoint values are rarely modified from nominal values. This paper describes design considerations for a communication system from generators to frequency-sensitive distributed energy resources (FS-DER) using changes to frequency setpoint values...

This paper presents a method that in real-time determines remedial actions, which restore stable operation with respect to aperiodic small signal rotor angle stability (ASSRAS) when insecure or unstable operation has been detected. An ASSRAS assessment method is used to monitor the stability boundary for each generator in real-time. The ASSRAS boun...

The concern of the environment and energy sustainability requests a crucial target of CO2 abatement and results in a relatively high penetration of renewable energy generation in the transmission system. For maintaining system reliability and security, the transmission company (TRANSCO) has to make strategic planning to handle the uncertainty chall...

The paper introduces an approach to investigate voltage sags, which are caused by large generator rotor swings following a transient disturbance. Therefore, the method exploits sensitivities derived from the algebraic network equations. These provide information on the impact of a generator on the voltage magnitude at a load bus and the effect of l...

A method that exploits Thevenin equivalent representation for obtaining post-contingency steady-state nodal voltages is integrated with a method of detecting post-contingency aperiodic small-signal instability. The task of integrating stability assessment with contingency assessment is challenged by the cases of unstable post-contingency conditions...

The significant growth of distributed energy resources (DERs) associated with smart grid technologies has prompted excessive uncertainties in the transmission system. The most representative is the novel notation of commercial aggregator who has lighted a bright way for DERs to participate power trading and regulating in transmission level. In this...

To achieve active control of the AC voltage magnitude of wind power plant (WPP) collector network and improve the fault ride-through (FRT) capability, an FRT scheme based on feed forward DC voltage control is presented for voltage source converter-high voltage direct current (VSC-HVDC) connected offshore WPPs. During steady state operation, an open...

Electric vehicles (EVs) are widely regarded as valuable assets in the smart grid as distributed energy resources in addition to their primary transportation function. However, connecting EVs to the distribution network and recharging the EV batteries without any control may overload the transformers and cables during peak hours when the penetration...

The concerns of sustainability and climate change have posed a significant growth of renewable energy associated with smart grid technologies. Various uncertainties are the major problems need to be handled by transmission system operator (TSO) planning. This paper mainly focuses on three uncertain factors, i.e. load growth, generation capacity and...

The possibilities offered by the use of Phasor Measurement Units (PMU) in real-time monitoring provide interesting ways to ensure secure operation of power systems. This paper studies the specific case of voltage stability and the possible improvements to the Thevenin equivalent methods, which is applied generally with local measurements. This pape...

This article studies the influence of PMU's accuracy in voltage stability assessment, considering the specific case of Thévenin equivalent based methods that include wide-area information in its calculations. The objective was achieved by producing a set of synthesized PMU measurements from a time domain simulation and using the Monte Carlo method...

This paper presents the hardware-in-the-loop (HIL) test of the demand as frequency controlled reserve (DFR). The HIL test refers to a test in which parts of a pure simulation have been replaced by actual physical components. It is used to understand the behavior of a new device or controller. The DFR has been tested by offline simulations to illust...

With the development of smart grid technologies, some of the electric demands which are traditionally considered fixed and inflexible will become promising distributed energy resources in future power systems. However, the participation of small scale or household energy sources into balancing power might challenge the operation of electric distrib...

New challenges are arising in managing power systems as these systems become more complex due to the use of high levels of distributed generation, mainly based on renewable energy sources, and due to the competitive environment within the power sector. At the same time, the use of Phasor Measurement Units (PMUs) provides more information and enable...

This paper presents a novel controller design for controlling appliances based on local measurements of voltage. The controller finds the normalized voltage deviation accounting for the sensitivity of voltage measurements to appliance state. The controller produces a signal indicating desired power consumption which can be mapped to temperature set...

The paper introduces an approach to investigate voltage sags, which are caused by large generator rotor swings following a transient disturbance. Therefore, the method exploits sensitivities derived from the algebraic network equations. These provide information on the impact of a generator on the voltage magnitude at a load bus and the effect of l...

Renewable energy plays an important role in the future energy framework of the European Union. The European Union will reach a 20 % share of renewable energy in total energy consumption and increase energy efficiency by 20 % by 2020. Smart grids will be the backbone for facilitating the integration of renewable energy resources into future energy s...

In the future energy framework of European Union and other countries, renewable energy plays an important role tackling the problems of the climate change and security of energy supply. The share of fluctuating and less predictable renewable power production will increase significantly the needs of securing proper balancing between generation and d...

In [1], the lower upper bounds estimation (LUBE) method is proposed to construct combined nonparametric prediction intervals (PIs) of wind power generation, which is also used in [2]. We would like to commend the authors for their efforts in exploring probabilistic wind power forecasting, which is an important research area toward a renewable-energ...

The expanding share of the fluctuating and less predictable wind power generation can introduce complexities in power system reliability evaluation and management. This entails a need for the system operator to assess the system status more accurately for securing real-time balancing. The existing reliability evaluation techniques for power systems...

A practical parameter estimation procedure for a real excitation system is reported in this paper. The core algorithm is based on genetic algorithm (GA) which estimates the parameters of a real AC brushless excitation system with limited information about the system. Practical considerations are integrated in the estimation procedure to reduce the...

Future electric power systems will face new operational challenges due to the high penetration of distributed energy resources (DERs). In Denmark distribution system operator (DSO) expects a significant congestion increased in distribution grids. In order to manage these congestions and mobilize the DERs as economically efficient as possible in the...

Development of a method for real-time assessment of post-contingency nodal voltages is introduced. Linear network theory is applied in an algorithm that utilizes Thevenin equivalent representation of power systems as seen from every voltage-controlled node in a network. The method is evaluated by comparing with results from time domain simulations...

In this paper a new method is proposed to determine the minimum energy storage required to be installed at different locations of a low voltage (LV) grid in order to prevent the overvoltage due to high residential photovoltaic (PV) penetration. The method is based on the voltage sensitivity analysis of feasible scenarios associated with the net inj...

In order to provide a vehicle fleet that realistically represents the predicted Electric Vehicle (EV) penetration for the future, a model is required that mimics people driving behaviour rather than simply playing back collected data. When the focus is broadened from on a traditional user-centric smart charging approach to be more grid-centric, it...

Distributed energy resources (DERs), like electric vehicles (EVs), can offer valuable services to power systems, such as enabling renewable energy to the electricity producer and providing ancillary services to the system operator. However, these new DERs may challenge the distribution grid due to insufficient capacity in peak hours. This paper aim...

This paper presents the power hardware in the loop (PHIL) validation of a feed forward DC voltage control scheme for the fault ride through (FTR) of voltage source converter (VSC) high voltage DC (HVDC) connected offshore wind power plants (WPPs). In the proposed FRT scheme, the WPP collector network AC voltage is actively controlled by considering...

As wind power plants (WPPs) gradually replace the power production of the conventional generators, many aspects of the power system may be affected, in which the small signal stability is included. Additional control may be needed for wind turbine generators (WTGs) to participate in the power oscillation damping. The feasibility of implementing thi...

Industrialized countries are increasingly committed to move towards a low carbon generating mix by increasing the penetration of renewable generation. Additionally, the development in communication technologies will allow small end-consumers and small-scale distributed energy resources (DER) to participate in electricity markets. Current electricit...

This paper presents the analysis of the impact of electric vehicle (EV) integration on medium voltage (MV) distribution networks and the cost evaluation of replacing the overloaded grid components. A number of EV charging scenarios have been studied. A 10 kV grid from the Bornholm Island in the city area has been used to carry out case studies. The...

This paper presents a view of the Danish FlexPower project to reform the existing electricity market by coordinating vast Distributed Energy Resources (DERs) for integration in future scenarios. Aiming to maximize the preservation of the existing market structure, Aggregator, the key player in mobilizing small-scale DERs to participate in the exist...

Generation expansion planning (GEP) is the problem of finding the optimal strategy to plan the construction of new generation while satisfying technical and economical constraints. In the deregulated and competitive environment, large-scale integration of wind generation (WG) in power system has necessitated the inclusion of more innovative and sop...

Rapid deployment of renewable energy sources (RES) and concerns regarding their impacts on power systems provide new opportunities for utilizing more electrical energy storage system (EESS) in power systems. Peak-shaving in high Photovoltaic (PV) penetration conditions and providing ancillary service in high load conditions are among the applicatio...

The paper introduces an algorithm for control of autonomous loads without digital communication interfaces to provide both frequency regulation and voltage regulation services. This hybrid controller can be used to enhance frequency sensitive loads to mitigate line overload arising from reduced load diversity. Numerical simulations of the hybrid co...

The high penetration of distributed energy resources (DERs) will significantly challenge the power system operation due to their intermittent characteristic. In order to utilize the DERs as economically efficient as possible in the distribution grid, an Aggregator-based Flex-market is proposed in this paper. With the brand new notion of Flexibility...

This paper analyzes the suitability of existing methods for long-term voltage stability assessment for real-time operation. An overview of the relevant methods is followed with a comparison that takes into account the accuracy, computational efficiency and characteristics when used for security assessment. The results enable an evaluation of the ru...

Fault-tolerance in electrical distribution relies on the ability to diagnose possible faults and determine which components or units cause a problem or are close to doing so. Faults include defects in instrumentation, power generation, transformation and transmission. The focus of this paper is the design of efficient diagnostic algorithms, which i...

Low-voltage (LV) grid feeders with high penetration of photovoltaics (PVs) are often affected by voltage magnitude problems. To solve such issues, previous research has shown that reactive power methods, active power curtailment and grid reinforcement can be used for voltage support, yet showing several limits. We introduce the use of electric vehi...

As renewable energy sources increase their penetration, the traditional providers of frequency regulation service, i.e., fossil fueled thermal power plants, will be displaced, motivating the search for novel providers such as demand-side resources. This paper presents the results of field experiments using demand as a frequency controlled reserve (...

Wind power plants (WPP) are for power system stability studies often represented with aggregated models where several wind turbines (WT) are aggregated into a single up-scaled model. The advantage is a reduction in the model complexity and the computational time, and for a number of study types the accuracy of the results has been found acceptable....

This paper presents the details of a new real-time stability assessment method. The method assesses a particular mechanism of stability: each generator's capability to generate sufficient steady state electromechanical torque. The lack of sufficient steady state torque causes aperiodic increase in rotor angle and a loss of synchronism, referred to...

The paper presents a new control strategy to enhance the ability of reactive power support of a doubly fed induction generator (DFIG) based wind turbine during serious voltage dips. The proposed strategy is an advanced low voltage ride through (LVRT) control scheme, with which a part of the captured wind energy during grid faults is stored temporar...

In this paper, it is investigated how detailed the model of a synchronous machine needs to be in order to assess transient stability using a Single Machine Equivalent (SIME). The results will show how the stability mechanism and the stability assessment are affected by the model detail. In order to identify the transient stability mechanism, a simu...

The grid impact study of electric vehicle (EV) integration on distribution networks has been carried out in order to analyze the effects of EV demands on the electric component loading and voltage drop along electric distribution network feeders with different EV penetration levels, EV charging power options, and EV charging scenarios. The Bornholm...

The potential of regulating power from electric vehicles (EVs) in Denmark is analysed in order to quantify the available regulating power capacity from EVs and the economic return to the EV users. The driving pattern in Denmark has been analysed in order to obtain the energy needs of EVs for driving purposes and the EV availability for providing re...

A day-ahead grid tariff scheme has been developed in order to alleviate the congestion which might be caused by EV charging demands. The distribution system operator (DSO) determines the day-ahead varying grid tariffs according to the expected EV demands within its grid. The locational marginal prices have been used in order to determine the day-ah...

Renewable energy will play an important role in the energy framework of the future. The European Union will reach a 20% share of renewable energy in total energy consumption and increase energy efficiency by 20% by 2020. High renewable energy penetration results in significant impact on power system security and reliability, which will increase the...

Grid connected Photovoltaic (PV) systems are among the increasingly growing electric power generation units worldwide. The majority of new installations are expected to be residential PVs that are connected into distribution systems. However, the PV hosting capacity of low voltage (LV) grids is limited due to the voltage rise at the point of connec...

In recent years, a large number of Distributed Generation units (DG units) such as Wind Turbines (WTs) and Combined Heat and Power plants (CHPs) have been penetrating the distribution systems. Meanwhile, an intentional island operation of distribution systems is proposed as a potential measure against power supply outages by continuously running DG...

This paper develops a co-ordinated electricity and heat dispatching model for a Microgrid under a day-ahead environment. In addition to operational constraints, network loss and physical limits are addressed in this model, which were always ignored in previous work. As an important component of the Microgrid, a detailed combined heat and power (CHP...

This paper proposes a decentralized storage strategy to support voltage control in low-voltage (LV) residential feeders with high photovoltaic (PV) capacity installed. The proposed strategy is capable of preventing overvoltage situations during high PV generation periods, by the use of locally controlled battery energy storage systems (ESS) at the...

This paper presents the heat pump (HP) demand profile with high HP penetration in the Nordic area in order to achieve the carbon neutrality power system. The calculation method in the European Standard EN14825 was used to estimate the HP electricity demand profile. The study results show there will be high power demand from HPs and the selection of...