Reactive Power Sharing Research Articles

Stability and Reactive Power Sharing Enhancement in Islanded Microgrid via Small-Signal Modeling and Optimal Virtual Impedance Control

In the context of integrating Renewable Energy Sources, Microgrid (MG) development is pivotal, particularly as a foundational technology for Smart-Grid evolution. Despite advancements in control techniques, challenges persist in ensuring system stability and accurate power sharing across diverse operational conditions and load types. The objective of this research is to control numerous paralleled inverters-based distributed generators (DGs) that contribute to power sharing in an island MG. The proposed methodology involves developing an innovative small-signal model for islanding MGs that incorporate virtual impedances. Subsequently, optimization algorithms based on Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) are proposed and compared for designing the virtual impedances. These algorithms analyze all potential operating points, aiming to minimize reactive power mismatches while maximizing MG stability. The suggested objective function facilitates the simultaneous achievement of these objectives. The proposed approaches were tested using MATLAB-Simulink software, and the comparison of the results between conventional approach and the proposed optimal approaches shows significant improvement in terms of the dynamic response during load changes, such as a decrease in response time by up to 20%, a reduction in overshoot percentage by approximately 15%, and a settling time improvement of nearly 25%. These quantified improvements highlight the effectiveness of the GA and PSO methods in minimizing the reactive power-sharing error while optimizing MG performance and stability.

Reactive Power Sharing in Parallel Inverters and Stability Improvement of Parallel Inverters in AC Microgrid Comprising Active Loads

Reactive Power Sharing in Parallel Inverters and Stability Improvement of Parallel Inverters in AC Microgrid Comprising Active Loads

Distributed Optimization for Reactive Power Sharing and Stability of Inverter-Based Resources Under Voltage Limits

Distributed Optimization for Reactive Power Sharing and Stability of Inverter-Based Resources Under Voltage Limits

A Practical Method for Optimized Reactive Power Sharing Among Passive Filters

This paper presents a practical method for reactive power sharing among harmonics filters. The proposed method minimizes the total harmonic distortion of the current. The current is measured at the incoming bus to which harmonics filters are connected. The total harmonics distortion and individual harmonics of the voltage at the bus to which the harmonic filters are connected and the individual harmonics of the current measured at the mentioned measurement point are used as constraints of optimization. The Optimization Toolbox of MATLAB software is used in this paper. The simulation results show the efficiency and robustness of the proposed method.

A Small-AC-Signal Injection Based Decentralized Secondary Voltage Control for Parallel Inverters With Accurate Reactive Power Sharing in Islanded Microgrids

A Small-AC-Signal Injection Based Decentralized Secondary Voltage Control for Parallel Inverters With Accurate Reactive Power Sharing in Islanded Microgrids

A consensus-based control for precise reactive power-sharing in AC microgrids

The objective of this work is to propose a control structure for managing the energy of distributed generators connected through a meshed AC network, which supplies a set of distributed loads. To avoid the need for algorithm switching in the event of faults (such as line losses or generator disconnections), all converters operate in grid forming mode. A control strategy based on nonlinear droop control ensures optimal network operation (equal sharing of active and reactive power) even in the presence of uncertainties. Only local voltage measurements are exchanged between neighboring nodes and used by a consensus algorithm to achieve the control objectives. The design of control parameters and hardware-in-the-loop (HIL) validations are presented in the article. The findings demonstrate that a low communication rate network is sufficient to achieve the desired objectives.

Reactive Power Sharing Among Distributed Generation Sources in Islanded Microgrids to Improve Voltage Stability

Reactive Power Sharing Among Distributed Generation Sources in Islanded Microgrids to Improve Voltage Stability

Robust Volt-VAr Control Strategy for Improvement in Reactive Power Sharing in a Droop Based Islanded Microgrid

Robust Volt-VAr Control Strategy for Improvement in Reactive Power Sharing in a Droop Based Islanded Microgrid

Accurate Active and Reactive Power Sharing Based on a Modified Droop Control Method for Islanded Microgrids.

When multiple paralleled distributed generation (DG) units operate in an islanded microgrid, accurate power sharing of each DG unit cannot be achieved with a conventional droop control strategy due to mismatched feeder impedance. In this paper, a small AC signal (SACS)-injection-based modified droop control method is presented for accurate active and reactive power sharing among DG units. The proposed control method adjusts the voltage amplitude of each DG unit by injecting small AC signals to form a reactive power control loop. This strategy does not need communication links or to specifically obtain the physical parameter of the feeder impedance and only requires the local information. Moreover, the parameter design procedure and stability analysis are given full consideration. Finally, simulation and experimental results verify the effectiveness of the proposed control scheme, and accurate active and reactive power sharing can be achieved.

An Improved Reactive Power Sharing in an Isolated Microgrid with a Local Load Detection

An Improved Reactive Power Sharing in an Isolated Microgrid with a Local Load Detection

A Virtual Parallel Inductor Approach for Mitigating Reactive Power Sharing Error in a VSG Controlled Microgrid

Virtual synchronous generators (VSGs) deployed into an islanded microgrid emulates the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q-V</i> droop nature of a synchronous generator. Although the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q-V</i> droop control of VSGs enhances the voltage stability, the installed distant VSGs have unequal line impedances due to their random location and rated capacity. The unequal line impedance hinders the proportional reactive power-sharing between VSGs. The proposed study is focused on minimizing the reactive power sharing error by introducing a virtual parallel inductor (VPI) concept. A mathematical model is proposed to create and exploit the analogous relation between the exponential behavior of the VPI and the controllable voltage source to mitigate the reactive power sharing error and simultaneously strengthen the voltage control accuracy. In addition, a droop within a droop strategy is introduced to enhance the reactive power sharing capability of the VSGs. Furthermore, a detailed eigenvalue analysis is conducted to evaluate the limitations of the proposed model. Finally, to test the superiority of the proposed model over the state-of-the-art methods, simulation and hardware experimental results are presented.

Reactive Power Matching Through Virtual Variable Impedance for Parallel Virtual Synchronous Generator Control Scheme

Virtual synchronous generator (VSG) control has received much attention for interfacing renewable energy sources, thus creating a low-inertia microgrid. However, proportional reactive power-sharing and voltage accuracy is still a serious concern due to unequal feeder impedances between VSG controlled DGs and the point of power coupling. This article proposes a virtual variable impedance (VVI) based VSG control technique to mitigate the reactive power sharing error by improving the line-impedance ratio among multiple DGs. The proposed VVI control is designed to estimate the value of variable virtual impedance by establishing an exponential relationship with the inverter's output reactive power. The reactive power communication method is also introduced to identify the proportion of reactive power share being injected by the DG. The effectiveness of the proposed VVI control is further analyzed through the small-signal stability analysis and Lyapunov stability analysis of a multi-VSG system. Finally, the proposed controller is tested in MATLAB/Simulink software and on an experimental setup that includes inverter hardware and dSPACE simulator. Results have shown that the proposed method allow only 0.026% of reactive power sharing error as compared to the conventional droop control and state-of-the-art virtual capacitor-based droop control that experiences 2.86% and 2.8% error, respectively.

Accurate Reactive Power Sharing Strategy for Droop-Based Islanded AC Microgrids

In islanded ac microgrids, the mismatched impedances of the interfacing feeders between the inverters and the load bus cause poor reactive power sharing when the conventional frequency and voltage droop control technique is employed. Such operation endangers the whole microgrid reliability as it may lead to overloading certain inverters and, consequently, triggering protection relays and causing cascaded failure. Thus, this article proposes an accurate reactive power sharing strategy that considers the mismatched feeder impedances in islanded ac microgrids. It is based on the optimal tuning of the virtual complex impedance for each inverter. The proposed strategy has several advantages. First, it has a physical meaning as it establishes an explicit relationship between the mismatched values of the actual resistive–inductive feeders and the assigned values for the proposed virtual complex impedance to each inverter. Hence, further degradations in the microgrid voltages are prevented. Second, there is no need for prior knowledge about the actual feeder impedances in the design stage as they are estimated online from the available measurements. Finally, the proposed control is reliable and fault-tolerant as it copes with unexpected failures such as failure of (or sudden switching <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> ) some inverters and communication disruptions/delays. It ensures accurate power sharing even under the primary controllers after losing communication links with the secondary controller. The simulation and experimental verification results are presented to validate the performance of the proposed technique.

Impact of Secondary Control Design on the Microgrid Domain of Stability Considering Reactive Power Sharing

Impact of Secondary Control Design on the Microgrid Domain of Stability Considering Reactive Power Sharing

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.

Seamless plug-in plug-out enabled fully distributed peer-to-peer control of prosumer-based islanded AC microgrid

Recent innovations in microgrids consumers converted into Prosumers (local generator + local load). This paper proposes a fully distributed peer-to-peer (P2P) control strategy for the prosumer-based islanded alternating current (AC) microgrid (MG). Prosumers would be independent to operate as producers or consumers. The proposed scheme uses droop control with each distributed generator (DG) to balance local generation and demand, while gossip communication-based distributed P2P control is employed with each Prosumer to restore voltage and frequency deviations across the MG. The prosumers are synchronised concerning their nearest point of common coupling (PCC) instead of a single PCC to avoid the effective line impedance mismatch among the DGs that causes circulating current flow among the DGs and results in poor reactive power-sharing. A prosumer-based islanded AC MG consisting of three differently rated Prosumers and a common load has been modelled in the MATLAB/Simulink environment and simulated with the Opal-RT 4510 real-time simulator to validate the effectiveness of the proposed study. The captured results and the frequency response analysis shows accurate power-sharing by the prosumer-DGs, seamless strategic or individual plug-in plug-out, and consumer operation of prosumers maintaining the MG's power quality and stability.

Distributed control strategy for voltage and frequency restoration and accurate reactive power-sharing for islanded microgrid

For a conventional droop-controlled islanded microgrid, the poor reactive power-sharing and drop of bus voltage and frequency caused by line impedance mismatch and droop characteristics are inevitable. So far, consensus-based distributed control algorithms, in which a secondary control layer with the integration of voltage and frequency restoration and reactive power-sharing compensation mechanisms, has been treated as a promising solution. However, for most of the currently available distributed algorithms, it is the active power-sharing rather than the reactive power-sharing that was made the control goal, which is opposite to the fact that accurate power-sharing could always hold considering the integration effect in the active power control loop. Although a few recently published distributed algorithms added the reactive power-sharing goal in the second control layer, the system efficiency and reliability may deteriorate because a large circulating current could be induced at the malfunction of the communication network since there is no virtual impedance injected at the bottom control layer to limit that. This paper proposes a voltage and frequency restoration method based on the dynamic average consensus algorithm and an accurate reactive power-sharing method based on a first-order consensus algorithm and virtual impedance method. A simple pseudo-unidirectional communication network with a narrow communication band is adopted for the proposed distributed control to lower the communication burden and system complexity. The operational principle is first analyzed in detail. The proposed strategy is easily implementable and features not breaking droop characteristics. Then simulations and hardware-in-the-loop (HIL) real-time experiments verify the proposed approach.

A Novel Droop Control Strategy of Reactive Power Sharing Based on Adaptive Virtual Impedance in Microgrids

Droop control strategy is widely used to control parallel inverters in a microgrid. However, due to the mismatched line impedance, the traditional droop control strategy is difficult to evenly share the reactive power and restrain the circulating current among multiple parallel inverters. In this article, an adaptive virtual impedance-based droop control strategy without communications is proposed to solve the reactive power sharing problem caused by the difference of line impedance. The reactive power output and voltage of each distribution generator are introduced into the adaptive virtual impedance controller to achieve a tradeoff between reactive power sharing accuracy and voltage drop. Small-signal stability analysis of the inverters equipped with the proposed controller is conducted to determine the optimal control parameters. Simulation and experimental results demonstrate the effectiveness of the proposed droop control strategy.

Distributed secondary controller to ensure proportional sharing of reactive power in AC microgrid

In an ac microgrid, reactive power sharing accuracy is affected due to unequal values of interconnecting cable impedances. To resolve this issue, secondary controllers are used to compensate the effect of cable impedances. Various types of secondary controllers are suggested in the literature which includes linear proportional plus integral (PI) controllers to minimize the difference in reactive power sharing created by conventional E−Q droop law. The reference value of the PI controller is the average value of reactive powers supplied by the sources. When the PI controller is used to minimize the difference between the actual and reference value of reactive power, the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads has a nonzero value. Therefore, the performance of these controllers becomes poor in the case of ac microgrid having sources of unequal ratings. To resolve this issue, a proportional reactive power-sharing (PRPS) controller-based distributed secondary controller is proposed in this paper. The PRPS controller modifies the droop gain of the E−Q droop control loop of each source in such a way that each source supplies reactive power equal to its proportional value of reactive power. The proportional value of reactive power supplied by each source is the power when the equivalent output impedance of all sources as seen by the loads are identical. The key advantage offered by the proposed controller is the accurate reactive power-sharing in the case of ac microgrid having sources of unequal ratings. The proposed controller ensures zero value of the difference between the algebraic sum of reactive powers supplied by the sources and the reactive powers demanded by the loads. This ensures accurate sharing of reactive power among the sources. The validation of the proposed controller is carried out for islanded mode of operation of ac microgrid. Further, the proposed controller requires of low bandwidth communication for its implementation. The effect of the proposed controller on the stability of the system is demonstrated using reduced order small-signal model. The effect of communication delay on the performance of the system is analyzed with the help of roots locus plots. To validate the efficacy of the proposed controller, detailed simulation studies are carried out in Matlab/Simulink.

Enhanced Reactive Power Sharing and Voltage Restoration Based on Adaptive Virtual Impedance and Consensus Algorithm

In this paper, power-sharing management control on an AC islanded microgrid is investigated to achieve accurate reactive power sharing. The droop control method is primarily used to manage the active and reactive power sharing among the DGs in the microgrid. However, the line impedance mismatch causes unbalanced reactive power sharing. As a solution a consensus-based adaptive virtual impedance controller is proposed, where the consensus algorithm is used to set the reactive power mismatch; then a virtual impedance correction term is generated through a proportional-integral controller to eliminate the line impedance mismatch. Thus, reactive power sharing is achieved without knowledge of the line impedances or using a central controller. Moreover, the consensus algorithm is used to restore the AC bus voltage to the nominal value by estimating the DGs average voltage using neighbor communication to compensate for the decreased magnitude of the voltage reference. Matlab/Simulink is used to validate the accuracy of reactive power sharing and voltage restauration achievement of the proposed solution through simulation of different scenarios. In addition, a dSPACE DS1104 is used within a developed experimental testbench based on two parallel DGs to validate the effectiveness of the proposed solution in the real world.