Reactive Power Control Strategy Research Articles

The Evolution for Voltage and Reactive Power Control in Smart Distribution Systems

This paper has been arisen to show the necessity of the evolution for voltage and reactive power control in distribution systems from conventional to active control techniques. The paper addresses the drawbacks and conflicts that the conventional voltage and reactive power control schemes will face in future distribution systems, especially with high penetration of Distributed Generation (DG). Some of these drawbacks have been verified by carrying out various simulation studies for different IEEE unbalanced radial distribution test systems. The results show that applying the conventional utility voltage regulation control practices in smart grid configuration is intolerable. Therefore, the issue of voltage and reactive power control in smart distribution systems is significant and an evolution of the current control schemes from passive to active is necessary. Using the smart grid technologies, a distributed single layer cooperative control scheme between substation regulators, line regulators and DG units has been proposed. The proposed cooperative scheme is based on the concept of multi-agent systems. Simulation results have been carried out to show the effectiveness of the proposed control scheme.

RTDS hardware implementation and simulation of SHAF for mitigation of harmonics using p-q control strategy with PI and fuzzy logic controllers

The main objective of this paper is to develop PI and fuzzy controllers to analyze the performance of instantaneous real active and reactive power (p-q) control strategy for extracting reference currents of shunt active filters (SHAFs) under balanced, unbalanced, and balanced non-sinusoidal conditions. When the supply voltages are balanced and sinusoidal, both controllers converge to the same compensation characteristics. However, if the supply voltages are distorted and/or unbalanced sinusoidal, these controllers result in different degrees of compensation in harmonics. The p-q control strategy with PI controller is unable to yield an adequate solution when source voltages are not ideal. Extensive simulations were carried out with balance, unbalanced, and non-sinusoidal conditions. Simulation results validate the superiority of fuzzy logic controller over PI controller. The three-phase four-wire SHAF system is also implemented on a real-time digital simulator (RTDS hardware) to further verify its effectiveness. The detailed simulation and RTDS hardware results are included.

Improved Grid Voltage Control Strategy for Wind Farms with DFIGs Connected to Distribution Networks

This paper presents an improved grid voltage control strategy for wind farms with doubly-fed induction generators (DFIGs) connected to distribution networks based on an analysis of the operation limits of DFIG systems. A modified reactive power limit calculation method in different operation states is proposed and a reactive power control strategy during grid voltage dips/rises is further discussed. A control strategy for compensating unbalanced grid voltage, based on DFIG systems, by injecting negative sequence current into the grid through the grid side converter (GSC) is proposed. In addition, the negative current limit of the GSC is discussed. The distribution principle of the negative sequence current among the different DFIG systems in a wind farm is also introduced. The validity of the proposed voltage control strategy is demonstrated by Matlab/Simulink simulations. It is shown that the stability of a wind farm and the power grid can be improved with the proposed strategy.

Power quality enhancement in autonomous microgrid operation using Particle Swarm Optimization

This paper presents an optimal power control strategy for an autonomous microgrid operation based on a real-time self-tuning method. The purpose of this work is to improve the quality of power supply of the microgrid where some Distributed Generation (DG) units are connected to the grid. Voltage and frequency regulation, and power sharing are the main performance parameters which are considered in this work, particularly during the transition from grid-connected to islanding operation mode and also during load change. In this work, two typical DG units are connected in parallel to configure the microgrid. The controller scheme is composed of an inner current control loop and an outer power control loop based on a synchronous reference frame and the conventional PI regulators. The power controller employs two typical strategies: active–reactive power (PQ) control strategy and voltage–frequency (Vf) control strategy. Particle Swarm Optimization (PSO) is an intelligent searching algorithm that is applied for real-time self-tuning of the power control parameters. The proposed strategy in this paper is that both DG units adopt the Vf control mode once the microgrid is islanded in order to regulate the microgrid voltage and frequency, whereas during the load change, only the second DG unit invokes the PQ control mode to ensure maximum power exportation. The results show that the proposed controller offers an excellent response to satisfy the power quality requirements and proves the validity of the proposed strategy.

Research of SVC Control System Based on Real-Time Operation System for Wind Farm

Wind power generation was developed rapidly in China. And many wind farms are configured Dynamic Static Var Compensators (SVCs) as reactive power compensator, which can meet the dynamic demands of the reactive power compensation for the wind farm. The paper put forward a coordination control strategy of reactive power for wind farm based on embedded real-time operation system in DSP, and by using LabVIEW to realize PC management and network communication management, and provides the research foundation for coordination and the optimal control of reactive power in large wind farm.

Reactive Power Dynamic Assessment of a PV System in a Distribution Grid

Accommodating more and more PV systems in grids has raised new challenges that formerly had not been considered and addressed in standards. According to recently under-discussed standards, each PV unit is allowed to participate in reactive power contributions to the grid to assist voltage control. There are some PV models in the literature however those models mostly assumed unity power factor operation for PV systems owing to the contemporary standards. Therefore, there is a need to develop a PV model considering the reactive power contribution and its dynamic influence on power system. This paper describes non-proprietary modeling of a three-phase, single stage PV system consisting of controller scheme design procedure and coping with the important aspects of three different reactive power regulation strategies and their impact assessment studies. The model is implemented in PSCAD to examine the behavior of the proposed model for recently codified reactive power strategies. Furthermore, this model is integrated in a distribution grid with two PV systems in order to effectively investigate consequences of the different reactive power control strategies on the distribution network.

Performance evaluation of a DG voltage controller for smart grids

Abstract In a previous paper a DG reactive power control scheme aimed at improving the voltage profile in a smart grid has been proposed. In this paper the control scheme is recalled and validated by detailed numerical simulations. In particular, the performance is tested in presence of uncertainties of the load variations, interactions of the proposed control scheme with the control system in the primary substation and large random variability of the DG primary source. The analysis of the results and a comparison with classical DG reactive power regulation give evidence of the obtained improvements of the voltage profile.

SmartPark as a Virtual STATCOM

Power electronic-based FACTS devices such as STATCOMs are sometimes essential for voltage support in transmission networks. They can also be used for continuous operation of doubly-fed induction generator-based wind turbines during faults. However, these devices are quite expensive and therefore cannot be used extensively. This paper explores the potential of a low-cost solution that utilizes the reactive power and voltage support capabilities of plug-in vehicles parked in charging stations (SmartParks) so that they can behave as virtual STATCOMs. For this solution, a 12-bus multimachine power system is considered wherein one of the conventional units is replaced by a 400 MW wind farm. Twelve SmartParks are developed and integrated into the test system. First, they are connected to a weak bus in the system and used in voltage control mode. Their performance is compared with a STATCOM of a similar rating. Next, the SmartParks are connected to the wind farm bus, and a coordinated reactive power control strategy is proposed to improve the fault-ride-through capability of the wind farm without exceeding the current limits of rotor and grid-side converters. The entire study is carried out in real time on a real-time digital simulator platform.

Modeling and Control of IGBT Converter-Based High-Voltage Direct Current System

This paper presents modeling and control for the emerging IGBT converter-based high-voltage direct-current system (IGBT-HVDC). This paper adds to the representation of the IGBT-HVDC system in the dq-synchronous reference frame and its decoupled control scheme. Additionally, since the IGBT-HVDC is able to actively support the grid due to its capacity to control independently active and reactive power production, a reactive power control scheme is presented in order to regulate/contribute to the voltage at a remote location by taking into account its operational state and limits. The ability of the control scheme is assessed and discussed by means of simulations using ahybrid power system, which consists of a permanent magnetic synchronous-generator (PMSG) based wind turbine, an IGBT-HVDC, and a local load.

Modeling and Simulation of Voltage Source Converter–Medium-voltage DC System for Stability Analysis

This article presents the modeling and simulation of a simple two-terminal and a multi-terminal voltage source converter based medium-voltage DC system, representing a simplified shipboard distribution network, for angular stability analysis. The control modes considered for the voltage source converter include the voltage control mode and the active and reactive power control schemes. The impact of these control modes on maintaining the DC voltage and, subsequently, on the transient as well as small-signal stability of the medium-voltage DC systems has been examined with the help of simulation in MATLAB/Simulink® (The MathWorks, Natick, Massachusetts, USA), and the results have been compared with an alternative medium-voltage AC distribution scheme. The impact of adding a power system stabilizer to enhance the small-signal stability has also been examined in the case of the medium-voltage AC architecture. Results indicate that that generators with the type 0 exciter are unstable with the medium-voltage AC architecture and stable with the medium-voltage DC architecture; using a type 1 exciter in the medium-voltage DC system improved the damping of the system. Use of a power system stabilizer for a medium-voltage AC system improved the damping, but the improvement was more significant with the placement of an static var compensator, in agreement with the results of participation analysis.

Coordination Control Strategy for Active and Reactive Power of DFIG Based on Exact Feedback Linearization under Grid Fault Condition

In this paper, a control strategy for operation of rotor side converter (RSC) of Doubly Fed Induction Generators (DFIG) is developed by injecting reactive power into the grid in order to support the grid voltage during and after grid fault events. The novel nonlinear control method is based on differential geometry theory, and exact feedback linearization is applied for control system design of DFIG. Then the optimal control for the linearized system is obtained through introducing the linear quadratic regulator (LQR) design method. Simulation results on a single machine infinite bus power system show that the proposed nonlinear control method can inject reactive power to fault grid rapidly, reduce the oscillation of active power and improve the transient stability of power system.

Fuzzy Controller Based 3Phase 4Wire Shunt Active Filter for Mitigation of Current Harmonics with Combined p-q and Id-Iq Control Strategies

As more and more variable frequency drives (VFDs), electronic ballasts, battery chargers, and static Var compensators are installed in facilities, the problems related to harmonics are expected to get worse. As a result Active power filter (APF) gains much more attention due to excellent harmonic compensation. But still the performance of the active filter seems to be in contradictions with different control strategies. This paper presents detailed analysis to compare and elevate the performance of two control strategies for ex-tracting reference currents of shunt active filters under balanced, un-balanced and non-sinusoidal conditions by using Fuzzy controller. The well known methods, instantaneous real active and reactive power method (p-q) and active and reactive current method (id-iq) are two control methods which are extensively used in active filters. Extensive Simulations are carried out with fuzzy controller for both p-q and Id-Iq methods for different voltage conditions and adequate results were presented. Simulation results validate the superior per-formance of active and reactive current control strategy (id-iq) with fuzzy controller over active and reactive power control strategy (p-q) with fuzzy controller.

Control of a hybrid high-voltage DC connection for large doubly fed induction generator-based wind farms

This study presents the control method for a new hybrid high-voltage dc (HVDC) connection for large wind farms with doubly fed induction generators (DFIGs). The hybrid HVDC system consists of a line-commutated converter plus a static synchronous compensator (STATCOM) on the rectifier side and a pulse-width modulation (PWM) current source inverter (CSI) on the inverter side. The overall control strategy is divided into three parts, where the STATCOM subsystem supports the island bus voltage; the rectifier subsystem delivers the active power generated by the wind farm; and the CSI subsystem injects the active power - as well as reactive power, if necessary - to the grid. Taking into account the non-linear and coupling characteristics of each subsystem, a series of control schemes is proposed: for the STATCOM subsystem, a state feedback linearisation and decoupling method is employed; for the rectifier subsystem, a double-loop controller is designed and its inner loop is based on the inverse-system control techniques; for the CSI subsystem, independent active and reactive power control scheme is proposed. Through Simulink/SimPowerSystems simulations on a representative hybrid HVDC system, the startup process is demonstrated and system performances under both normal and fault conditions are investigated.

Research of Control Strategy of STATCOM in AC/DC Hybrid Power System

This paper analyzed the control strategy of dynamical reactive power in AC/DC hybrid power grid, and presented the limitation of the control strategy based on location bus voltage, which can improve the transient stability under AC line faults but not DC block faults. Thus, control strategy of STATCOM based on real-time wide-area signal was presented by introducing the tie-line power flow of power grid. To consider the transient stability, the dynamical stability and the voltage stability at the same time, a nonlinear control mode in sections is also proposed. Simulation results showed that the control strategy would increase the transient stability and improve the dynamical stability of the AC/DC hybrid system under AC line faults either DC block faults

Fuzzy and PI Controller Based SHAF for Mitigation of Current Harmonics with P-Q Method Using Matlab and RTDS Hardware

The main objective of this paper is to develop PI and Fuzzy logic controllers to analyse the performance of instantaneous real active and reactive power (p-q) control strategy for extracting reference currents of shunt active filters under balanced, un-balanced and balanced non-sinusoidal conditions. When the supply voltages are balanced and sinusoidal, then all controllers converge to the same compensation characteristics. However, when the supply voltages are distorted and/or un-balanced sinusoidal, these control strategies result in different degrees of compensation in harmonics. The p-q control strategy with PI controller is unable to yield an adequate solution when source voltages are not ideal. Extensive simulations were carried out; simulations were performed with balance, unbalanced and non sinusoidal conditions. Simulation results validate the dynamic behaviour of Fuzzy logic controller over PI controller. The 3-ph 4-wire SHAF system is also implemented on a Real Time Digital Simulator (RTDS Hardware) to further verify its effectiveness. The detailed simulation and RTDS Hardware results are included.

Modeling and control of PMSG-based variable-speed wind turbine

This paper presents a control scheme of a variable-speed wind turbine with a permanent-magnetic synchronous generator (PMSG) and full-scale back-to-back voltage source converter. A comprehensive dynamical model of the PMSG wind turbine and its control scheme is presented. The control scheme comprises both the wind-turbine control itself and the power-converter control. In addition, since the PMSG wind turbine is able to support actively the grid due to its capability to control independently active and reactive power production to the imposed set-values with taking into account its operating state and limits, this paper presents the supervisory reactive power control scheme in order to regulate/contribute the voltage at a remote location. The ability of the control scheme is assessed and discussed by means of simulations, based on a candidate site of the offshore wind farm in Jeju, Korea.

Active Use of DFIG-Based Variable-Speed Wind-Turbine for Voltage Control in Power System Operation

This paper presents an active use of doubly-fed induction-generator(DFIG)-based variable-speed wind-turbine for voltage control in power system operation. For reasonable simulation studies, a detail dynamic model of a DFIG-based wind-turbine grid-connected system is presented. For the research objective, an innovative reactive power control scheme is proposed that manipulates dynamically the reactive power from the voltage source converter(VSC) with taking into account its operating state and limits.

Active Use of DFIG-Based Variable-Speed Wind-Turbine for Voltage Regulation at a Remote Location

Renewable energy sources are presently exempted from control functions. This, in turn, simplifies the requirements for the renewable energy source interconnection as well as the project developer, allowing connection to the system without having to take part in the overall stabilization effort. Thus, in order to maintain the power generation and consumption balance, necessary for stable functioning of the power system, the traditional power plants always exert necessary control actions. However, the present practice requires the independent power producers and/or generators who want to connect to the grid to meet the so-called connection requirements of the local electric utility (the grid company). Therefore, this paper proposes an innovative reactive power control scheme for voltage regulation at a remote location that manipulates dynamically the reactive power from the voltage source converter (VSC) with taking into account its operating state and limits.

Reactive Power Adequacy in Distribution Networks with Embedded Distributed Energy Resources

This paper addresses reactive power adequacy problems in distribution networks that include a significant number of distributed energy resources. The voltage profile of the distribution network is analyzed under increasing amounts of generation provided by the distributed energy resources. Both static and dynamic voltage disruption phenomena resulting from increasing distributed generation are described and the need for remedial actions identified. Different reactive power control schemes are then proposed to keep both an appropriate voltage profile and an appropriate voltage stability margin. Finally, an economic appraisal of remedial actions is carried out and the responsible parties identified. Results from a realistic case study are presented and discussed. Conclusions are duly drawn.

Stabilization of Tie-Line Power Flow by Robust SMES Controller for Interconnected Power System With Wind Farms

This paper presents the use of superconducting magnetic energy storage (SMES) with robust controllers for stabilization of tie-line power flow in a longitudinally interconnected power system with wind farms. The high penetration of wind power with abrupt changes causes fluctuations of tie-line power flow and significantly affects the effective use of transmission lines. A simultaneous active and reactive power control scheme of SMES including a characteristic of SMES coil current is employed for realizing a permissible range of SMES operation. Moreover, a multiplicative uncertainty model is considered in the parameter optimization of robust SMES controllers by using a heuristic method. Finally, simulation results are carried out to show the effectiveness and robustness under various situations.