Reactive Power Ancillary Service Research Articles

DER-Inverter Based Reactive Power Ancillary Service for Supporting Peer-to-Peer Transactive Energy Trading in Distribution Networks

DER-Inverter Based Reactive Power Ancillary Service for Supporting Peer-to-Peer Transactive Energy Trading in Distribution Networks

Design of Robust Var Reserve Contract for Enhancing Reactive Power Ancillary Service Market Efficiency

Design of Robust Var Reserve Contract for Enhancing Reactive Power Ancillary Service Market Efficiency

Synchrophasor Data Based Q-V Droop Control of Wind Farm Integrated Power Systems

With increasing scalability of grid-integrated wind farms (WFs), reactive power ancillary service through Q-V droop control of doubly-fed inducton generators (DFIGs) is one of the prime interests of power system operators. However, variable and uncertain availability of wind-resource at the wind turbines creates challenge against allocating reactive power reserve at the WFs for maintaining voltage stability of the grid. This issue can be resolved through online coordination among the WFs. This paper proposes a synchrophasor data based Q-V droop (SQVD) control technique for the WFs integrated to the grid through different point of common couplings (PCCs) in the power system transmission network. The data from the phasor measurement units (PMUs) at the WF-connected PCCs are used to obtain synchronized Q-V droop gain for each WF. Further, distributed coordination among DFIGs within each WF is performed to allocate optimum reactive power share at the converters. The total reserve of each WF is employed by their synchronized droop, in improving voltage stability at both the local PCC and neighboring PCCs. Performance of SQVD is verified at 418-bus practical Indian power system, in different dynamic situations of the grid, and found to be more effective as compared to the constant Q-V droop and variable Q-V droop control methods.

Leverage Reactive Power Ancillary Service Under High Penetration of Renewable Energies: An Incentive-Compatible Obligation-Based Market Mechanism

Power systems are undergoing fundamental changes with increasing penetration of renewable energies. A reactive power ancillary service market is of significance to incentivize private providers, such as thermal power units and renewable power plants (RPPs), to participate in maintaining voltage security. Because of the local nature of reactive power, one of the recognized issues is that monopolistic participants may have great market power and strategically manipulate their costs. To pursue economic efficiency, this paper proposes an incentive-compatible mechanism based on Vickery-Clarke-Groves (VCG) auctions for the day-ahead reactive power ancillary service market. The obligations of reactive power ancillary service are quantified in the VCG-based market mechanism. Depending on the expected performance of participants compared with the corresponding obligations, payments are obtained for thermal power units, RPPs, and loads. Hence, providers have the incentive to declare their true costs and undertake obligations. Furthermore, a scarcity price is employed to reward the provision of scarce reactive power resources and ensure reliable market clearing. The proposed mechanism is illustrated using the IEEE 24-bus and 118-bus systems. The results verify the effectiveness of the proposed mechanism. Moreover, high rewards or penalties are observed for voltage weak areas, thereby inducing appropriate investments in reactive power capacities.

Multi-mode optimal operation of advanced adiabatic compressed air energy storage: Explore its value with condenser operation

The weather-dependent renewable energy sources(RESs) and voltage stability performance associated with reactive power balance pose immense challenges to power systems' operation. Salt cavern advanced adiabatic compressed air energy storage(S-CAES) is one of the most promising options to cope with the emerging issues. Though S-CAES has been extensively studied, limited attention focuses on the value of its reactive power ancillary service. This paper presents a novel S-CAES condenser operation mode that consumes little compressed air and less heat for synchronization and warm-keeping while releasing reactive power by the turbine-generator unit's excitation system for voltage regulation. The merits of condenser mode are highlighted, and the accurate thermodynamic model of S-CAES with multi-parameter coupled charging/discharging power functions is developed. Then, an optimal dispatch model linking the part-load characteristics and multiple service requirements is proposed and further formulated as a mixed-integer linear programming(MILP) problem. Numerical simulation results indicate that S-CAES operating in condenser mode contributes its application in ancillary services markets, and neglecting the part-load characteristics will lead to overly optimistic or even infeasible dispatch results. The breakeven point of the peak-valley ratio is 1.725, below which S-CAES will not participate in the energy market. Besides, sensitivity analysis provides a primary reference for S-CAES's heat supplement optimization and the design of condenser compensation mechanisms in the power system with a high proportion of RESs.

An integrated market solution to enable active distribution network to provide reactive power ancillary service using transmission–distribution coordination

The active distribution network (ADN) can provide the reactive power ancillary service (RPAS) to improve the operations of the transmission network operations (such as voltage control and network loss reduction) as distribution generation grows. In this context, an RPAS market is required to motivate the ADN to provide the RPAS to the transmission network since the transmission system operator (TSO) and the distribution system operator (DSO) are different entities. Hence, to obtain the TSO–DSO coordination in the RPAS market, this study proposes a two-stage market framework on the basis of the successive clearing of the energy and RPAS markets. Additionally, a distributed market-clearing mechanism based on an alternating direction method of multipliers (ADMM) is adopted to guarantee TSO's and DSO's information privacy. Furthermore, a binary expansion (BE) method is used to linearise the non-convex bilinear terms in the market-clearing model. The effectiveness of the proposed RPAS market framework and distributed market-clearing mechanism is validated using two different test systems with different system scales.

Day-ahead optimal reactive power ancillary service procurement under dynamic multi-objective framework in wind integrated deregulated power system

This paper deals with the investigation of a day-ahead reactive power ancillary service procurement problem to minimize cost and voltage deviation under wind power generation uncertainties in a pool-based deregulated system. This reactive power procurement problem is formulated as a dynamic bi-objective optimization problem and is solved using a developed Pareto-based multi-objective artificial electric field algorithm (MO-AEFA). The developed MO-AEFA utilizes nondominated sorting principle and an external archive to store Pareto optimal solutions. Sign and reorder mutation operators are used to avoid trapping in local optima and enhance population diversity. The numerical results obtained from MO-AEFA are compared with other algorithms to validate the efficacy of proposed approach. The optimization algorithm utilizes a fast Newton power flow employing sparse matrix techniques to diminish computational burden. The capacitor switching is decided with consideration of marginal prices. The proposed methodology has been tested on modified IEEE 30-bus and IEEE 118-bus test systems. The performance of both test systems is analyzed for two studies namely, VAr dispatch without wind integration, and VAr dispatch under wind integration. The analysis with wind integration is further investigated for different wind penetration levels. The convergence characteristic of Pareto solutions is measured through statistical distance and diversity metrics.

Game Theoretical Approach to Novel Reactive Power Ancillary Service Market Mechanism

In deregulated power systems, reactive power ancillary service through electricity market is becoming relevant where private generation companies participate in maintaining system wide bus voltage within the permissible limits. Marginal cost price (MCP) based real time reactive power ancillary service market faces several challenges due to the localized nature of reactive power. In this paper, a market mechanism for real time reactive power ancillary service market based on Stackelberg game model is proposed considering voltage-apparent power coupled subsystems. In the proposed Stackelberg game model, Independent System Operator (ISO) is considered as the leader, and GENCOs as followers. In the formulation, each GENCO is associated with a relevance factor in the partitioned subsystem so as to consider the real time voltage support requirement in the system. The market is then formulated as Mathematical Program with Equilibrium Constraints problem (MPEC). Existence of equilibrium, incentive compatibility, and individual rationality of the proposed market mechanism is then analysed in this work. The numerical examples are illustrated in PJM 5-bus system, and tested on IEEE 30- bus system, and Nordic 32 Bus-system. The mechanism induces truth-telling behavior of GENCOs, yields a non-negative profit, and the system wide bus voltage is improved.

Voltage Variation Mitigation Using Reactive Power Management of Distributed Energy Resources in a Smart Distribution System

Inverters (dc/ac converters) are commonly used to connect distributed energy resources (DERs) to the grid. Hence, the penetration rate of inverters is growing in distribution systems along with DERs. Depending on their development and penetration level, grid requirement standards for DERs are revised. New grid codes allow DERs to control their output reactive power to provide reactive power ancillary service. In this paper, the main contribution is reactive power management of inverter-based DERs (IBDER) through a practical procedure, which controls the available volt-ampere (headroom) of inverters to improve voltage profile and distribution system operation when confronting with short-term voltage magnitude variations. In this regard, a two-level control strategy (namely, central and local control levels) is proposed. In the central controller, reactive power management of IBDERs is optimized in short time intervals for mitigating voltage variations. The optimized data is sent to the local controllers of IBDERs to increase the speed of reaction to voltage variations in each time interval. The improvement of distribution systems operation with a high penetration rate of IBDERs is illustrated by performing the simulation of the proposed control strategy on a smart distribution test system.

Grid connected converters as reactive power ancillary service providers: Technical analysis for minimum required DC-link voltage

Providing solutions for reactive power compensation next to reactive loads is beneficial for the efficiency of the overall grid system. The main reactive power compensation solutions are based on passive VAR generators (like capacitor banks) or active VAR generators (like static VAR generators). Extra use of VAR generators can be avoided by providing reactive power through renewable energy systems or loads, which are connected to the grid through Grid connected Converters (GcCs). In fact, GcCs can be controlled so that, in addition to their main control task, they realize an additional reactive power ancillary service. In this context, this paper investigates the achievement of reactive power ancillary service using three-phase GcCs and presents a detailed analysis regarding the determination of the minimal required DC-link voltage level for proper operation of GcCs as reactive power ancillary service providers. This analysis is done under both steady-state and transient conditions. Several simulation and experimental results are presented to confirm the validity of the obtained analytical results.

Plug-in electric vehicles as a harmonic compensator into microgrids

Plug-in Electric Vehicles (PEVs) can be used as harmonic compensator by injecting/absorbing harmonic current to/from the grid. Considering harmonic power compensation as an ancillary service, similar to reactive power ancillary service market (RPASM) or reserve market, PEVs can participate in harmonic power ancillary service market and thereby PEVs should offer their prices in the harmonic power market. For this approach, Harmonic Expected Payment Function (HEPF) of PEV is constructed based on the capability curve of PEVs. The HEPF includes the cost of losses as well as lost opportunity cost (LOC) incurred by reduction of active power for harmonic power compensation. The harmonic power market (HPM) is cleared by minimizing Harmonic Total Payment Function (HTPF), which in fact, is the amount of dollars paid to the accepted PEVs in the market. The effectiveness of the proposed HPM is studied on a 14-node microgrid. The results indicate that, with the proposed framework, PEVs can incorporate in the harmonic market with enough economic incentives. The distribution system operator (DSO) concern about the harmonic disturbance can be remarkably relieved as well.

Active and Reactive Power Optimal Dispatch Associated with Load and DG Uncertainties in Active Distribution Network

In order to reduce the adverse effects of uncertainty on optimal dispatch in active distribution network, an optimal dispatch model based on chance-constrained programming is proposed in this paper. In this model, the active and reactive power of DG can be dispatched at the aim of reducing the operating cost. The effect of operation strategy on the cost can be reflected in the objective which contains the cost of network loss, DG curtailment, DG reactive power ancillary service, and power quality compensation. At the same time, the probabilistic constraints can reflect the operation risk degree. Then the optimal dispatch model is simplified as a series of single stage model which can avoid large variable dimension and improve the convergence speed. And the single stage model is solved using a combination of particle swarm optimization (PSO) and point estimate method (PEM). Finally, the proposed optimal dispatch model and method is verified by the IEEE33 test system.

Models of reactive power‐related wind park losses for application in power system load flow studies

AbstractIn power system load flow studies, it is common to ignore wind park (WP) losses completely, since WPs are obliged to provide reactive power as a free‐of‐charge ancillary service. Strongly simplified WP loss estimations are also widespread. Prevailing loss modelling approaches may result in substantial and so far usually ignored reactive power allocation inefficiencies. The innovation of this paper lies in demonstrating this and in presenting an alternative modelling approach that combines speed, ease‐of‐use and accuracy.Calculations are based on a generic WP connected to 110 kV. It is simulated once using gearless permanent magnet synchronous generators and once using doubly fed induction generators. In this way, for the first time, the consequences of neglecting differences between wind generator types when calculating reactive power‐related losses are systematically quantified. Loss‐minimal dispatch is assessed using heuristic optimal power flow. Relevance of findings is demonstrated for the application of reducing system losses based on reactive power control of WPs in closed‐loop optimal power flow schemes. It is shown that non‐consideration of WP losses may lead to dispatch decisions where the increase in WP losses outweighs the achieved loss reduction in the 110 kV system by 400%. The study facilitates comparing reactive power ancillary services from WPs to that of other technologies from an economic perspective. It concludes by a benchmarking overview of pros and cons of modelling alternatives. Copyright © 2017 John Wiley & Sons, Ltd.

A New Approach to Optimal Allocation of Reactive Power Ancillary Service in Distribution Systems in the Presence of Distributed Energy Resources

One of the most important Distribution System Operators (DSO) schemes addresses the Volt/Var control (VVC) problem. Developing a cost-based reactive power dispatch model for distribution systems, in which the reactive powers are appropriately priced, can motivate Distributed Energy Resources (DERs) to participate actively in VVC. In this paper, new reactive power cost models for DERs, including synchronous machine-based DGs and wind turbines (WTs), are formulated based on their capability curves. To address VVC in the context of competitive electricity markets in distribution systems, first, in a day-ahead active power market, the initial active power dispatch of generation units is estimated considering environmental and economic aspects. Based on the results of the initial active power dispatch, the proposed VVC model is executed to optimally allocate reactive power support among all providers. Another novelty of this paper lies in the pricing scheme that rewards transformers and capacitors for tap and step changing, respectively, while incorporating the reactive power dispatch model. A Benders decomposition algorithm is employed as a solution method to solve the proposed reactive power dispatch, which is a mixed integer non-linear programming (MINLP) problem. Finally, a typical 22-bus distribution network is used to verify the efficiency of the proposed method.

Multi-stage Model for Voltage Control and Reactive Power Ancillary Services Allocation Costs in Electricity Markets

This paper presents a three-stage model for voltage control and reactive power ancillary services allocation costs in re-structured electric sectors. At the first stage, the system operator (SO) determines the technical requirements of the service considering different scenarios for the next year's period, including contingency analysis; furthermore, at this stage, the SO calculates cap prices differentiated by type of generator. At the second stage, within a day in advance, and once that energy and frequency control service prices are known, the SO estimates the variable costs associated to the service by evaluating the contingencies required to apply a set of preventive reactive power and voltage control actions. The third stage consists of evaluating real variable costs, once these have been incurred, and added to the fixed costs to conform the total costs of the service. Total costs are allocated to consumers by two methodologies. The first methodology prorates costs in terms of sensitivities and load values for each consumer and for every evaluated scenario. The second methodology is based on sensitivities to determine reactive areas, such that total costs are divided by each scenario and reactive area, and prorated among the consumers of those reactive areas in terms of their load presented at each scenario.

Reactive Power Ancillary Service of Synchronous DGs in Coordination With Voltage Control Devices

This paper presents an optimal way to control steady-state voltage in distribution feeders using reactive power ancillary service that is provided by synchronous distributed generators (DGs). Based on load forecasts provided one day in advance, DG reactive power is dispatched on the hour in coordination with the switching operations of an on-load tap changer (OLTC) and shunt capacitors (SCs). This aims to reduce not only distribution line power losses but also the number of switching operations of the OLTC and the SCs, which affect the feeder voltage quality and switching device lifetime. For the reactive power dispatch, a mixed-integer nonlinear optimization problem is formulated using a multiobjective function and solved using a particle swarm optimization (PSO) algorithm. Modules using evolutionary and dynamic programming are incorporated into the PSO algorithm to be less susceptible to becoming trapped in local optima and have a better chance of reaching global optimum. Simulation case studies using small- and large-scale distribution networks were performed using MATLAB to demonstrate that the coordinated reactive power support of the DGs, OLTC, and SCs can achieve the objective effectively, resulting in improved voltage quality.

Power Flow Tracing Based Reactive Power Ancillary Service (AS) in Restructured Power Market

Power Flow Tracing Based Reactive Power Ancillary Service (AS) in Restructured Power Market

Reactive Power Ancillary Service by Constant Power Loads in Distributed AC Systems

Reactive power is one of the power system ancillary services and can be supplied from either static or dynamic VAR sources. Provision of reactive power in the proximity of load is clearly beneficial for the efficiency of the overall system. Reactive power provision as an ancillary service by the load itself could greatly increase the margin to voltage collapse and, therefore, influence the stability of the power system. Constant power loads (CPLs), interfaced by active rectifiers, have the potential for providing reactive power to the ac distributed system they are connected to. These types of loads with negative resistance characteristic are, at the same time, the most susceptible to voltage stability problems under abnormal operating conditions. This paper first investigates the effect that a large share of CPLs will have on the voltage stability of distributed ac systems during voltage dips. It then investigates the influence of introducing reactive current control by the active rectifiers on the overall voltage stability of the system. The critical clearing time of the system is selected as a measure of the transient stability limit for investigating and comparing the cases of CPLs with and without reactive current control. Centralized reactive compensation by a STATCOM is used as reference to compare with distributed compensation by the CPLs. Results show that the total required distributed injection of reactive current is lower compared to the rating of a centralized STATCOM. The influence of reactive compensation on the total attainable CPL current is investigated analytically as well as through simulations. It is observed that an optimal reactive current injection by CPL reduces the total current to a minimum value.

Evaluation of contribution for voltage control ancillary services based on social surplus

AbstractReactive power supply plays an important role in active power supply with adequate system voltages. Various pricing mechanisms for reactive power supply have been developed and some of them have been adopted in some power systems, but they are in a trial stage. The authors also focus on development of a pricing method for reactive power ancillary services. This problem involves two technical issues: rational estimation of the cost associated with reactive power supply, and fair and transparent allocation of the estimated cost among the market participants. This paper proposes methods for evaluating the contribution of generators and demands. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 36–45, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21016

Can PV plants provide a reactive power ancillary service? A treat offered by an on-line controller

This paper proposes an auto-adaptive controller that enables to suitably manage the reactive power supplied by the inverters of PV units whishing to provide the reactive power ancillary service on the base of standard needs or on a voluntary basis. The derived controller is based on an optimization procedure involving the sensitivity theory in conjunction with the Lyapunov function and provides control laws feeding the inverters of the PV units. The controller promptly minimizes system losses preserving the active power produced by the PV plants against the reactive one. In fact, when the PV modules do not get enough sunlight to generate active power, the proposed procedure forces the PV inverters to provide a reactive power equal to the rated power. On the contrary, in order to preserve the major economic benefits for the investor deriving from the produced active power during the sunlight hours, the method automatically reduces the injection of reactive power. The computer simulations, performed on a distribution system, demonstrate that the controller is capable to control the network in the real-time, mainly due to its ability to be auto-adaptive at any changes in the system operating conditions.