Reactive Power Control Strategy Research Articles

Reactive Power Optimization for Distribution Network Based on Distributed Random Gradient-Free Algorithm

The increasing penetration of distributed energy resources in distribution systems has brought a number of network management and operational challenges; reactive power variation has been identified as one of the dominant effects. Enormous growth in a variety of controllable devices that have complex control requirements are integrated in distribution networks. The operation modes of traditional centralized control are difficult to tackle these problems with central controller. When considering the non-linear multi-objective functions with discrete and continuous optimization variables, the proposed random gradient-free algorithm is employed to the optimal operation of controllable devices for reactive power optimization. This paper presents a distributed reactive power optimization algorithm that can obtain the global optimum solution based on random gradient-free algorithm for distribution network without requiring a central coordinator. By utilizing local measurements and local communications among capacitor banks and distributed generators (DGs), the proposed reactive power control strategy can realize the overall network voltage optimization and power loss minimization simultaneously. Simulation studies on the modified IEEE-69 bus distribution systems demonstrate the effectiveness and superiority of the proposed reactive power optimization strategy.

A grid-side reactive power control strategy for highly offshore wind power penetrated systems

A grid-side reactive power control strategy is proposed in this paper, which aims to enhance the voltage stability of highly offshore wind power penetrated systems. The basic idea of the strategy is to establish an evaluating system including the voltage stability index (VSI), VSI sensitivity index, and reactive power residual adjustment capability index (RPRACI). The indexes can be applied to identify the voltage dangerous nodes, locate the compensation nodes, and determine each node's amount of compensation. The strategy is particularly suitable for large-scale offshore wind power integrated systems because it is designed to deal with large disturbances such as offshore wind power fluctuations. This strategy can be specified in three steps. First, voltage dangerous nodes are identified by the nodal VSI. Next, adjustable nodes are chosen according to the sensitivities of each node to the dangerous nodes and RPRACI of each node. Finally, reactive power compensation of each adjustable node is allocated depending on the magnitudes of the sensitivity indexes. The simulation results in the IEEE 14-bus system indicate that the proposed strategy can effectively improve the local grid voltage stability when large-scale offshore wind power is injected into the system.

Research on Active Management Strategy of Distributed Power Supply Access to Distribution Network

With the wide access of distributed power supply, the planning and operation mode of distribution network becomes more and more complex, and the economy and the mode of supervision of distribution network have also been greatly affected. Based on the active management of distribution network fault management level, voltage control and power flow management (Active Management AM) technology, from the current, voltage and power loss are analyzed in terms of DG electrical characteristics, proposed to cut active, reactive power control and active management strategy of load transformer regulation. It has positive significance for model analysis and Strategy Research of distributed power supply access to distribution network, and has certain reference and application value.

Integrated optimal active and reactive power control scheme for grid connected permanent magnet synchronous generator wind turbines

This research presents a novel approach for optimal active and reactive power control using permanent magnet synchronous generator with fully rated converter (PMSG-FRC). The power output variations and wind energy intermittent performance create significant challenges for power system integration, operation, and control. A fast and reliable sensorless optimal wind speed (WS) control system-based extreme learning machines and complete ensemble empirical mode decomposition with adaptive noise is developed. Also, an approximate entropy-based complexity measure is used for online WS estimation. The fuzzy controller system is used for calculating the optimal wind turbine (WT) speed, power, and torque, and then adjusts WT by the optimal speed value. Moreover, the wind farm (WF) active and reactive power controller is utilised for obtaining the active and reactive power reference values for every region/feeder. The system is applied and integrated to power system grid by using IEEE standard models, and the speed of WT is adjusted by the required active power level and the estimated WS value to increase the maximum power capture from WF. The simulations results using different cases studies and power system voltage levels have confirmed the validity and accuracy of the proposed control algorithms for practical applications and demonstrated excellent performance for power system integration.

Reactive Power Management in Renewable Rich Power Grids: A Review of Grid-Codes, Renewable Generators, Support Devices, Control Strategies and Optimization Algorithms

Power electronic converter (PEC)-interfaced renewable energy generators (REGs) are increasingly being integrated to the power grid. With the high renewable power penetration levels, one of the key power system parameters, namely reactive power, is affected, provoking steady-state voltage and dynamic/transient stability issues. Therefore, it is imperative to maintain and manage adequate reactive power reserve to ensure a stable and reliable power grid. This paper presents a comprehensive literature review on the reactive power management in renewable rich power grids. Reactive power requirements stipulated in different grid codes for REGs are summarized to assess their adequacy for future network requirements. The PEC-interfaced REGs are discussed with a special emphasis on their reactive power compensation capability and control schemes. Along with REGs, conventional reactive power support devices (e.g., capacitor banks) and PEC-interfaced reactive power support devices (e.g., static synchronous compensators) play an indispensable role in the reactive power management of renewable rich power grids, and thus their reactive power control capabilities and limitations are thoroughly reviewed in this paper. Then, various reactive power control strategies are reviewed with a special emphasis on their advantages/disadvantages. Reactive power coordination between support devices and their optimal capacity are vital for an efficient and stable management of the power grid. Accordingly, the prominent reactive power coordination and optimization algorithms are critically examined and discussed in this paper. Finally, the key issues pertinent to the reactive power management in renewable rich power grids are enlisted with some important technical recommendations for the power industry, policymakers, and academic researchers.

Coordinated Control Strategy of Distributed Energy Resources based Hybrid System for Rural Electrification

This paper proposes coordinated active and reactive power control strategy of wind-biogas based hybrid system for rural electrification (HSRE) in order to provide continuous and reliable source of electricity to a cluster of villages. In the control strategy used for HSRE, a predefined part of load is being supplied by the grid and the remaining part, under steady state as well as small signal disturbances, is taken care by a hybrid system of controllable and intermittent sources of energy. Induction generator (IG) based wind energy conversion system (WECS) has been considered as a source for HSRE. Since reactive power is needed by both IG and load, an additional source of reactive power, static synchronous compensator (STATCOM) is used to fulfill the reactive power requirement. The synchronous generator has been used for power generation from biogas-genset which is fitted with electronic speed governor and automatic voltage regulator (AVR). The concept of defined grid operation is achieved by considering dynamics of system voltage angle as well which cannot be achieved by the usual control techniques for frequency and voltage magnitude. The developed hybrid system is given a small signal disturbance in load as well as input wind power. The robustness of proposed control strategy has been showed from the dynamic performance results by maintaining power balance between system components while regulating the system voltage and frequency.

An accurate reactive power control study in virtual flux droop control

Abstract This paper investigates the problem of reactive power sharing based on virtual flux droop method. Firstly, flux droop control method is derived, where complicated multiple feedback loops and parameter regulation are avoided. Then, the reasons for inaccurate reactive power sharing are theoretically analyzed. Further, a novel reactive power control scheme is proposed which consists of three parts: compensation control, voltage recovery control and flux droop control. Finally, the proposed reactive power control strategy is verified in a simplified microgrid model with two parallel DGs. The simulation results show that the proposed control scheme can achieve accurate reactive power sharing and zero deviation of voltage. Meanwhile, it has some advantages of simple control and excellent dynamic and static performance.

DVR based reactive power control strategy of DFIG for wind energy generation during unbalanced grid voltages

This document offers a whole new one on direct power control (DPC) technique for a doubly fed induction generator (DFIG)-based the wind vitality era program. This tactic relies on the one on one supervision regarding system productive and reactive strength by simply deciding on applicable voltage vectors on the rotor feature. This strategy works by using the mechanical system flux that take away the complications linked to rotor flux. This guidelines with this strategy rectangular calculate delineated intimately with this document. The one unit parameter needed by the projected DPC technique is usually which the mechanical system resistance as their effect on the system effectiveness is located to get minimal. Simulation final results on the 1.5 MW DFIG program exhibits the effectiveness and robustness in the projected supervision tactic in the course of versions regarding unit details. DVR is usually given to management the facility excellent issues and thereby management the active and reactive power.

Control strategy for reactive power and harmonic compensation of three-phase grid-connected photovoltaic system

This study investigates a grid-tied photovoltaic (PV) system with active power injection, reactive power compensation and harmonic current elimination capability. The equivalent electric model presented in the literature is used to implement the PV system. In non-linear loads, low-frequency synchronous reference frame (SRF) methods cannot eliminate second- and third-order harmonics which appear in the grid current. In this study, a mathematical analytical SRF approach is proposed to compensate reactive power and eliminate current harmonic of a non-linear load with active power injection. Simulation results are presented in order to verify the suggested control approach and the system feasibility.

Two-Tier Reactive Power and Voltage Control Strategy Based on ARMA Renewable Power Forecasting Models

To address the static voltage stability issue and suppress the voltage fluctuation caused by the increasing integration of wind farms and solar photovoltaic (PV) power plants, a two-tier reactive power and voltage control strategy based on ARMA power forecasting models for wind and solar plants is proposed in this paper. Firstly, ARMA models are established to forecast the output of wind farms and solar PV plants. Secondly, the discrete equipment is pre-regulated based on the single-step prediction information from ARMA forecasting models according to the optimization result. Thirdly, a multi-objective optimization model is presented and solved by particle swarm optimization (PSO) according to the measured data and the proposed static voltage stability index. Finally, the IEEE14 bus system including a wind farm and solar PV plant is utilized to test the effectiveness of the proposed strategy. The results show that the proposed strategy can suppress voltage fluctuation and improve the static voltage stability under the condition of high penetration of renewables including wind and solar power.

Direct power control of grid connected voltage source inverters using port-controlled Hamiltonian system

This paper presents a new direct active and reactive power control (DPC) scheme for a three-phase grid connected voltage source inverter (VSI) based on the passivity viewpoint using the port-controlled Hamiltonian (PCH) system. The proposed controller consists of feedforward and feedback parts. The feedforward part (the reference inputs) is generated through the flatness of the dynamics of the VSI model, which makes the error dynamics in the form of PCH system. The nonlinear feedback part is designed to enhance the damping of the error dynamics by using its Lyapunov function. The proposed control method has an ability of the finite time reaching condition similar to sliding mode control (SMC). Moreover, the exponential stability and uniform performance are guaranteed over all operating points without need for reaching a certain manifold. The proposed method is validated by using an experiment through hardware-in-the-loop system with a digital signal processor. The experimental results for the proposed method are compared with those using SMC-DPC method. The proposed method significantly reduces the total harmonic distortion in the output current without deteriorating the transient response of the active and reactive powers. In addition, it provides robust performance against the line impedance variations and the grid voltage sag.

A Dynamic Operational Scheme for Residential PV Smart Inverters

This paper presents an operational scheme for photovoltaic (PV) inverter reactive power control to accommodate higher levels and leverage efficient use of rooftop PV penetration in distribution systems. The scheme proposes three states of operation with specific operational goals for the PV inverter based on weather conditions and voltage at the interconnection point, and adapts the reactive power control strategy accordingly. In normal state with slowly changing solar irradiance, the control modulates reactive power to reduce power losses. In fluctuating state with rapidly varying solar irradiance due to intermittent passing clouds, the control dynamically changes the reactive power in order to mitigate voltage fluctuations. In contingency state in which the PV terminal voltage violates the nominal operating range, the control adjusts the PV inverter as reactive power sink or source in order to push the voltage back within the range. This paper also proposes a coordination strategy in order to switch control between the states and manage interaction between the fast PV inverter controllers, and the slow on-load tap-changer for voltage regulation. A large-scale distribution network based on the IEEE 37-node test feeder was developed in order to investigate performance of the proposed algorithm.

Analysis of reactive power strategies in HVDC‐connected wind power plant clusters

AbstractOffshore wind power plants (WPPs) built near each other but far from shore usually connect to the main grid by a common high‐voltage DC (HVDC) transmission system. In the resulting decoupled offshore grid, the wind turbine converters and the high‐voltage DC voltage‐source converter share the ability to inject or absorb reactive power. The overall reactive power control dispatch influences the power flows in the grid and hence the associated power losses. This paper evaluates the respective power losses in HVDC‐connected WPP clusters when applying 5 different reactive power control strategies. The case study is made for a 1.2‐GW–rated cluster comprising 3 WPP and is implemented in a combined load flow and converter loss model. A large set of feasible operating points for the system is analyzed for each strategy. The results show that a selection of simulations with equal wind speeds is sufficient for the annual energy production comparison. It is found that the continuous operation of the WPPs with unity power factor has a superior performance with low communication requirements compared with the other conventional strategies. The optimization‐based strategy, which is developed in this article, allows a further reduction of losses mainly because of the higher offshore grid voltage level imposed by the high‐voltage DC voltage‐source converter. Reactive power control in HVDC‐connected WPP clusters change significantly the overall power losses of the system, which depend rather on the total sum of the injected active power than on the variance of wind speeds inside the cluster.

A Large Scale Grid Data Analysis Platform for DSOs

The number of fluctuating distributed energy resources (DER) in electricity grids is continuously rising. Due to the lack of operational information on low-voltage (LV) networks, conservative assumptions are necessary to assess the connection of generators to the grid. This paper introduces the hosting capability (HC) as a measure to assess the amount of DER that can be integrated in LV-feeders. The HC of a feeder is the minimum amount of DER that can be hosted in a feeder without reinforcement needs for a given DER-scenario and for a given admissible voltage rise. The hosting capability assessment was performed on the entire LV-grid data of two Austrian Distribution System Operators (DSOs) with more than 36,000 LV-feeders. In total, 40 HC-scenarios were calculated with varying admissible voltage rise levels, DER-scenarios and reactive power control strategies. It turned out that only few feeder parameters such as the resistance at the end node and the lowest ampacity value of feeders show a high correlation with the calculated HC. Further, the impact of the DER-scenario on the share of voltage and loading constrained feeders is rather limited. The gathered results are suitable to validate equivalent LV-feeders models to perform integrated power flow studies on the transmission and distribution grids. Besides the results obtained for the network data of the two DSOs, a performant, modular and parallelizable tool has been developed to automatically analyze large LV network sets.

Research on Inverter Integrated Reactive Power Control Strategy in the Grid-Connected PV Systems

In order to solve the problems caused by the susceptibility to changing weather conditions and the complex load conditions of photovoltaic (PV) systems, and the fact a single target inverter control strategy cannot effectively mitigate large voltage fluctuations at point of common coupling (PCC), an integrated reactive power control strategy for PV inverters is proposed. According to the weather and load conditions, this strategy is divided into four control modes: normal operation control mode, reverse power control mode, cloudy control mode and night control mode. The four control modes switch between each other under the specific switching rules to ensure an appropriate quantity of reactive power injection or consumption in the PV inverter. The effects of the four control modes in isolated operation were significant. The deviation rate of PCC voltage from its standard value was mitigated at about 2% under the integrated control strategy. Therefore, the proposed control strategy has a high application value in improving power quality and maximizing utilization of PV inverters.

Review of Reactive Power Dispatch Strategies for Loss Minimization in a DFIG-based Wind Farm

This paper reviews and compares the performance of reactive power dispatch strategies for the loss minimization of Doubly Fed Induction Generator (DFIG)-based Wind Farms (WFs). Twelve possible combinations of three WF level reactive power dispatch strategies and four Wind Turbine (WT) level reactive power control strategies are investigated. All of the combined strategies are formulated based on the comprehensive loss models of WFs, including the loss models of DFIGs, converters, filters, transformers, and cables of the collection system. Optimization problems are solved by a Modified Particle Swarm Optimization (MPSO) algorithm. The effectiveness of these strategies is evaluated by simulations on a carefully designed WF under a series of cases with different wind speeds and reactive power requirements of the WF. The wind speed at each WT inside the WF is calculated using the Jensen wake model. The results show that the best reactive power dispatch strategy for loss minimization comes when the WF level strategy and WT level control are coordinated and the losses from each device in the WF are considered in the objective.

Strategy to enhance the low-voltage ride-through in photovoltaic system during multi-mode transition

With the increasing capacity of distributed generation (DG) connected to the power grid, the future generation of photovoltaic (PV) systems are expected to provide a full range of voltage regulation during grid faults in order to enhance the low-voltage ride-through (LVRT) capability of a PV system. In such a condition, the DG should remain connected to the grid for reactive power support, thereby improving voltage profile. This paper aims to propose a control strategy of active and reactive power for a single-stage three-phase grid-connected PV system to enhance the LVRT. The dynamic behaviours of the system were investigated by considering various scenarios such as varying irradiance, local load disconnection, and short circuits, at different locations during the multi-DG operation. Results confirm that the grid-connected PV system is able to remain connected to the power grid during steady-state and transient-state conditions without violating the grid code requirements. The established dynamic behaviour analysis model of the proposed control for grid-connected PV systems can be used in planning an operational strategy for a practical system.

Mitigating techniques for the operational challenges of a standalone hybrid system integrating renewable energy sources

Renewable energy sources (RESs) combined with energy storage can significantly increase the resilience of standalone systems. However, the intermittent nature of renewable energy resources creates a number of operational challenges for standalone systems. In this paper, the potential challenges facing the operation of a standalone hybrid system with solar photovoltaic (PV) and wind turbine energy generation and battery energy storage are addressed. Control strategies for the system sources are developed to mitigate the potential challenges. A droop-based voltage and frequency control strategy is proposed for the battery energy storage to balance the mismatch between the renewable generation and the load and to maintain the system stability. An active and reactive power control strategy with maximum power point tracking (MPPT) is proposed for the PV and wind sources to maximize the generation when there is a lack of energy resources and to supply quality power from the sources. A simulation was completed to determine the viability of the proposed control strategies. Results show that the proposed control strategies are able to regulate the system voltage and frequency within the acceptable ranges irrespective of variations in the sources and the load-demand.

Reactive Power Strategy of Cascaded Delta-Connected STATCOM Under Asymmetrical Voltage Conditions

Cascaded static synchronous compensator (STATCOM) is an effective solution for reactive power support in middle/high voltage conditions, and it has been widely employed to control reactive power in photovoltaic (PV) plants, wind farms, and industrial occasions. In this paper, reactive power control strategy of cascaded delta-connected STATCOM under asymmetrical voltage conditions is investigated. A new phase current reference calculation method is proposed to support reactive power continually under abnormal voltage conditions considering cluster voltage balancing control and phase current limitation. Constrains between voltage and current phasors of STATCOM are deduced. Then, the analytical expressions of phase currents and circulating current references are solved. Therefore, reactive power support and the safe operation of STATCOM can be obtained simultaneously by limiting the peak value of the phase current references. Furthermore, the reactive power support capability of cascaded STATCOM under asymmetrical voltage conditions is explored and compared by combining the proposed references calculation method with the three generalized current references calculation strategies. Finally, simulation and experimental results have been given to verify the theoretical studies.

Reactive Power and Voltage Optimization Control Strategy in Active Distribution Network Based on the Determination of the Key Nodes

The distributed generation which is integrated in the active distribution network changes power flow, bringing new challenges to the voltage control. When voltage limit violation happens, in order to make the voltage return to normal range and improve the voltage quality, a novel voltage control strategy is proposed. Considering the voltage quality and node importance, the electrical closeness centrality and key node contribution degree are defined, and the key nodes are determined by the orders of the key node contribution degree. This paper uses the reactive power compensation devices which are installed at the key nodes coordinated with the reactive power output of the distributed generation to realize the voltage optimization control. The voltage optimization control model is established by taking the minimum power loss as an objective function. Using the particle swarm optimization algorithm solves the model. The simulation results of the improved IEEE-33 bus system verify the effectiveness of the proposed method.