Reactive Power Control Strategy Research Articles

Research on Double-Circuit Direct Current Control System Based on PSCA

This article introduces the double-circuit Direct Current system on the same tower, and then analyses the hierarchical structure of the double-Circuit Direct Current Control System Based on PSCA. For the power control, the double-circuit power coordinated control strategy and the low-load reactive power control strategy are made in-depth research and analysis, and then made a simulation model of the double-circuit coordination of the double-circuit DC system on the same tower based on PSCA. Finally, based on the existing dual-circuit power control function of the system, it can reduce the ground electrode current and maintain the reactive power balance of the converter station to optimize the distribution coefficient of the two-circuit DC power, and effectively increase the reactive power in the conversion process.

Artificial Intelligence-Aided Minimum Reactive Power Control for the DAB Converter Based on Harmonic Analysis Method

With the aim of reducing the reactive power for the dual-active-bridge (DAB) converter, this letter proposes an artificial intelligence (AI) aided minimum reactive power control scheme based on the harmonic analysis method. Specifically, as an advanced algorithm of the deep reinforcement learning (DRL), the deep deterministic policy gradient (DDPG) is used to train an agent off-line. During the training of DDPG algorithm, the three-phase-shift (TPS) modulation is adopted and the zero-voltage-switching (ZVS) constraints are considered. Thus, the trained agent of the DDPG which likes an implicit function, can provide optimal control strategies for the DAB converter in real-time with the minimum reactive power and soft switching performance in the continuous operation range. Finally, experimental results validate the feasibility and correctness of the proposed AI based optimized method.

Distributed optimal active and reactive power control for wind farms based on ADMM

In this paper, a distributed optimal active and reactive power control (DARPC) strategy based on the alternating direction method of multipliers (ADMM) is proposed for wind farms (WFs). The WFs operate in a distributed manner to minimize the network power loss, voltage deviations of buses from the rated voltage, and active power output deviations of WTs from their proportional distribution (PD)-based power reference. An optimization problem is formulated as a quadratic programming (QP) problem by using the linearized DistFlow model. The ADMM-based solution is used to decompose the centralized optimization problem to several subproblems which are solved in individual local controllers with exchanged information from their practical neighbor controllers. Compared with existing distributed/hierarchical optimal control, the impacts of the active power injection from the WTs are taken into consideration and optimized while meeting the dispatch command from the transmission system operator (TSO). The ADMM-based distributed solution eliminates the requirement of a central unit. Compared with conventional centralized optimal control, the scalability of the WFs is improved. A WF consisting of 20 WTs is simulated in MATLAB/Simulink to test the control effectiveness of the proposed DARPC strategy.

Reactive PowerControl of Grid-Connected Photovoltaic Power Generation

In order to solve the problem of grid-connected point voltage exceeding the limit caused by large-scale photovoltaic power stations connected to the grid, and to increase the penetration rate of photovoltaics in the grid, photovoltaic power stations should have more flexible reactive voltage regulation capabilities to provide reactive power support to the grid. To this end, this paper establishes an equivalent aggregation model for large-scale photovoltaic power plants. Under the premise that the photovoltaic power station is not equipped with reactive power compensation devices and the inverter reactive power output is zero, it is analyzed that due to the existence of line and transformer impedance, photovoltaic access reduces the grid the problem of voltage stability. Based on the above reasons, this paper proposes a three-layer reactive power control strategy for photovoltaic power plants from the perspective of the cooperation between the reactive power compensation device and the grid-connected inverter. This strategy coordinates the reactive power output between the reactive power compensation device and the photovoltaic power generation unit and between the inverters of a single photovoltaic power generation unit. Under this control strategy, the photovoltaic power plant can regulate the grid voltage more effectively, and the active and reactive power losses of the grid are minimized on the premise that the grid voltage is maintained within the required range. Combined with the photovoltaic array power reduction operation strategy, the stable operation of the power grid is ensured under the premise of a certain reactive power output capacity of the photovoltaic power station. Finally, an example is used to verify the correctness and effectiveness of the strategy.

Techno-Economic Assessment of Flexibility Options Versus Grid Expansion in Distribution Grids

In this paper five different flexibility options are analysed from a techno-economic perspective as alternatives to traditional grid expansion for a specific distribution grid in Germany. The options are: two reactive power control strategies with photovoltaic inverters (as a function of the power feed-in, or of the voltage at the connection point), one residential and two large scale battery storage applications (primary control reserve with autonomous reactive power control or self consumption maximisation strategy with autonomous reactive power control). For the pilot grid located in Southern Germany a photovoltaic expansion pathway is determined. The main goal of this work is to quantify the grid expansion actions that can be avoided by applying these five flexibility options for the assumed expansion pathway, focusing on large scale battery storages. It is shown that the five flexibility options increase the hosting capacity for PV systems, compared to a scenario without, by up to 45%. Furthermore, the results of the economic assessment indicate that the analysed flexibility options might be a viable alternative to traditional grid expansion as all of them show a cost reduction potential for the pilot region. These results could encourage DSOs to consider the integration of additional PV and battery storage systems not as a problem which triggers grid expansion, but as part of the solution reducing future grid expansion costs.

Voltage stability augmentation of hybrid power system using robust reactive power control strategy of PV plant

The involvement of large-scale grid-tied photovoltaic (PV) systems is growing speedily, and enormous effort is given to design the robust control mechanism of PV systems to augment the performance of the PV system in both transient and steady-state states. The terminal voltage may fluctuate at steady-state conditions due to the alternating nature of solar irradiance and affect the LVRT aptitude at the transient period. Therefore, in this paper, a cascaded grid-side AC-DC inverter control strategy is developed by modifying the inverter input signal to control the terminal voltage. The proposed dead-band-based inverter controller maintains the terminal voltage at rated value during steady-state and augments LVRT aptitude at transient conditions by injecting an efficient quantity of reactive power. The overall scenario, including PV system, conventional power plant, and load, has been designed and examined using the “PSCAD/EMTDC” platform. The traditional control system is taken into comparison with the proposed control system to verify the effectiveness of this innovative control technique.

Distributed Reactive Power Control Scheme for the Voltage Regulation of Unbalanced LV Grids

This article proposes a new control strategy for the voltage regulation of unbalanced low-voltage (LV) distribution grids with high penetration of distributed renewable energy sources (DRESs). The proposed method uses the available reactive power of DRESs as the primary means for voltage regulation. Furthermore, its distinct feature is the use of a distributed control architecture prioritizing the response of DRESs to maintain the network voltages within permissible limits and minimize the network losses. The prioritization process is locally implemented by each DRES combining two types of information: (a) the sensitivity matrix that quantifies the impact of reactive power variations on the network voltages and (b) voltage measurements along the network. Time-domain and time-series simulations on the IEEE European LV test feeder are performed to evaluate the performance of the proposed method against existing decentralized, distributed and centralized, optimization-based methods.

Reactive Power Control Strategy of Demand Side Back-to-Back Converter Based on VSM

Background: The Demand Side Management (DSM) technology is playing an increasingly important role in the power system, in order to promote the real-time supply and demand balance of the power grid and improve the economy and safety of the power grid. Objective: To realize the flexible and continuous reactive power control of demand side load, a reactive power control strategy for the demand side back-to-back converter (DS-B2BC) is proposed. Methods: First, DS-B2BC is proposed. Then, the reactive power control model of DS-B2BC and its control loop are designed, and the reactive power control model, based on the Virtual Synchronous Motor (VSM), is established. Results: The simulation results verify that the reactive power control strategy proposed in this paper is effective, which can control the demand side load reactive power flexibly and continuously. Conclusion: Moreover, the strategy can counteract the disturbance from the power grid simultaneously.

Evaluation of sensitivity based coordinated volt-var control and local reactive power for voltage regulation and power exchange across system boundaries in smart distribution networks

This paper presents a hierarchical coordinated volt-var controller (VVC) at medium voltage level for the containment of voltages at the critical nodes in a smart distribution network. VVC finds the optimal set-points for distributed generators and tap position of the transformers in order to contain the voltage at the critical nodes with-in limits and to minimize the total reactive power dispatched. In addition to the voltage regulation, VVC can track reactive power as a reference signal to control the power exchange across system boundaries. The proposed approach is compared with the optimal power flow that requires load flow calculation for each control update. In comparison, VVC is based on a sensitivity matrix based approach that reduces the complexity of the problem. The paper presents separate and combined evaluation of the proposed VVC with reactive power support from inverters at low voltage in order to quantify the combined impacts. The comparison is performed based on the voltage deviation and performance indices, line loading and reactive power exchange at the system boundary. The simulations spanning one year are performed on a synthetic network. The study leads to comprehensive insights into factors influencing the effectiveness of the reactive power control strategies.

A Consensus-Based Adaptive Virtual Output Impedance Control Scheme for Reactive Power Sharing in Radial Microgrids

This article presents a distributed secondary control scheme for accurate reactive power sharing in an islanded multibus radial microgrid. The scheme employs consensus control to adaptively tune the virtual output impedance (VOI) into achieving reactive power correction. The adaptive VOI-based control structure is essentially nonlinear. However, this work shows that the approximate range of stable coupling gain can be established by linearizing the problem about every probable operating point of the distributed energy resources (DERs). On the basis of islanding mode, it is also shown that only the dynamic VOI component is needed while the static component, which has been used extensively to date, can be nullified. It will also be shown that under the established gain tuning guideline, the virtual reactance typically results in quicker correction dynamics as compared to the virtual resistance. The proposed control scheme can realize an accurate power sharing among the DERs regardless of the microgrid topology, load condition, and communication delay (within the allowable limits defined by the consensus theorem). This study is carried out in conjunction with an islanded microgrid model modified from the IEEE 34 Node Test Feeder.

Co-ordinated and real time voltage control of DSTS-biomass based isolated hybrid power system using Grey Wolf optimization

This paper proposes a co-ordinated reactive power control strategy analysis in Line Side Converter (LSC) of Doubly Fed induction generator (DFIG) and in the Automatic voltage regulator (AVR) of synchronous generator (SG) in isolated Dish Stirling solar Thermal(DSTS) – Biomass hybrid power system. This co-ordinated control strategy greatly maintains the autonomous hybrid power system voltage deviation by adjusting the reactive power imbalance caused due to the impulsive reactive power nature of DFIG coupled with the DSTS and load. Gain values of Integral Order Proportional Integral (IO-PI) controller in LSC and AVR are optimized to maintain the system voltage stability. Modern and simple Grey wolf optimization algorithm has been used to extract the superior PI gain values to maintain system stability with less reaction time. The proposed co-ordinated control strategy has been tested with various load disturbance and with dynamic input power feed from DSTS to validate the system robustness. Also, the optimized gain value based voltage deviation values are validated in real time with dSPACE.

Coordinated virtual resistance and capacitance control scheme for accurate reactive power sharing and selective harmonic compensation in islanded microgrid

Line impedance mismatch and unregulated harmonic currents cause serious problems for an islanded microgrid, such as inaccurate reactive power sharing and voltage distortion at the point of common coupling (PCC). To overcome these issues, a coordinated virtual resistance and capacitance are introduced together with its control scheme for parallel distributed generation (DG) in an islanded microgrid. The proposed coordinated virtual impedance control scheme directly modifies the DG output impedance at the fundamental frequency to realise accurate current sharing among DG units. In addition, a variable harmonic impedance control loop is proposed for each DG to absorb the non-linear load harmonic current. Thanks to the proposed control scheme, the PCC harmonic voltage distortion is successfully compensated and power-sharing among DG units is accurately achieved. The stability of the microgrid system was analysed in detail to verify the feasibility of the coordinated virtual impedance control scheme. Experiments on a laboratory prototype microgrid are performed to validate the performance of the proposed control scheme.

A robust adaptive control method for reactive power of doubly-fed induction wind generator

Some of the existing control strategies for reactive power of doubly-fed wind generators are only based on the simplified transfer function model without considering the existence of disturbance and some require real-time adjustment of the algorithm to meet different operating conditions. In order to overcome the above problems, a robust adaptive control method is introduced into the field of reactive power control of doubly-fed induction wind generator in this paper. An adaptive reactive power control strategy for the grid-side converter of doubly-fed wind generator is proposed, and the effectiveness of the algorithm is verified through simulation verification.

Design and implementation of fuzzy logic based modified real-reactive power control of inverter for low voltage ride through enhancement in grid connected solar PV system

In a grid connected solar PV system, during grid faults, increase in grid current, dip in voltage at point of common coupling and overshoot in dc link voltage in the inverter side are observed. The solar PV system gets disconnected from the grid whenever the grid voltage goes below a certain nominal value in order to safeguard the cascaded power converter systems from high currents and over voltages. This paper proposes an intelligent fuzzy based real and reactive power control of inverter for effective Low Voltage Ride Through (LVRT) capability during grid faults. The proposed fuzzy logic based modified inverter real and reactive power control strategy, stabilizes the grid voltage by injecting reactive current and limits the grid over current by reducing active power flow into the grid. To regulate the overshoot in dc link voltage during grid faults, a braking chopper and dynamic braking resistor strategies are included in the proposed LVRT scheme. The performance of the proposed inverter control strategy is studied through simulation of 100 kW grid connected solar PV system in MATLAB/SIMULINK 2018a platform. The algorithm is validated in real time hardware of 1 kW grid connected solar PV system. The simulation and hardware results validate the superior performance of the proposed inverter LVRT control strategy in comparison with other conventional schemes during grid faults.

Two‐tier combined active and reactive power controls for VSC–HVDC‐connected large‐scale wind farm cluster based on ADMM

To reduce the voltage fluctuations inside the wind farm cluster (WFC), a combined active and reactive power control schemes based on model predictive control is proposed. The aims of the proposed control scheme are to maintain the collector bus and wind turbine (WT) terminal voltages within the feasible range. With the size of WFC increasing, conventional centralised optimal control may no longer be suitable for a large-scale WFC due to the high computation burden of the WFC central controller. To improve the calculation efficiency and protect information privacy, a two-tier control structure with alternating direction method of multipliers (ADMMs) algorithm is used to solve the large-scale optimisation problem in distributed/hierarchical manner. In the upper-tier distributed control, the active and reactive power outputs of the WFs are coordinated to enhance the voltage control performance. In the lower-tier control, an ADMM-based hierarchical control is developed to minimise the voltage deviation of the WT terminals. Case studies demonstrate the efficacy of the proposed two-tier combined active and reactive power controls.

The Influence of VSC–HVDC Reactive Power Control Mode on AC Power System Stability

Voltage source converter-based high-voltage direct current (VSC-HVDC) has the advantage of fast and independent controllability on active and reactive power. This paper focuses on effects of commonly proposed reactive power control modes, constant reactive power control and AC voltage margin control. Based on the mathematical model of single machine infinity equivalent system with embedded VSC-HVDC, the influence of VSC-HVDC with different reactive power control strategies on transient stability and dynamic stability of the AC system is studied. Then case studies were conducted with a realistic model of grid. The dynamic responses of AC/DC systems for different VSC-HVDC reactive power control modes were compared in detail. It is shown that compared to constant reactive power control, AC voltage margin control can provide voltage support to enhance the transient angle stability of an AC system. However, the fluctuant reactive power injected into a weak AC system may adversely affect power system oscillation damping for VSC-HVDC with AC voltage margin control, if the parameters of the controller have not been optimized to suppress the low-frequency oscillation. The results of this paper can provide certain reference for the decision of an appropriate VSC-HVDC reactive power control mode in practice.

Research on Hierarchical Coordination and Coordinated Realization of DC System

DC converter station needs to consume a large amount of reactive power when transmitting active power. Insufficient or excessive reactive power will cause fluctuations in the AC voltage, which will affect the safety and stability of the entire system in severe cases. Simulation results verify the correctness, robustness, and superiority of the proposed active power allocation principle. This paper proposes a reactive power control strategy by fixing the position of the converter transformer tap and increasing the trigger angle/cut-off angle during the low-load operation of the DC transmission system.

배전계통에서 전압상승 완화를 위한 재생 발전기의 새로운 무효전력제어 전략

배전계통에서 전압상승 완화를 위한 재생 발전기의 새로운 무효전력제어 전략

Distributed control scheme for accurate reactive power sharing with enhanced voltage quality for islanded microgrids

This study presents a distributed control scheme for islanded microgrids to eliminate power sharing errors as well as frequency and voltage deviations based on distributed cooperative control. A consensus algorithm is developed through adaptive regulation of the virtual impedances for accurate power sharing regardless of load variations. The proposed power sharing controller is quite easy to implement with only one simple integral gain. It is achieved without using information about the feeder impedances, load powers or detailed microgrid structure. To remove the deviations in the frequency and voltage magnitude, conventional droop equations are enhanced by adding compensating signals, which are simply determined from the neighbors’ droop information without a PI controller. Therefore, the control complexity is significantly reduced. The control performance is theoretically analyzed using a small-signal state-space model to evaluate the system dynamics and stability. A digital simulation is done using PSIM, and experiments are carried out with a scaled-down microgrid prototype to verify the proposed scheme.

ADMM-based distributed optimal reactive power control for loss minimization of DFIG-based wind farms

In this paper, a distributed optimal reactive power control (DORPC) scheme is proposed for minimizing the total losses of doubly fed induction generator (DFIG)-based wind farms (WFs), including the losses of generators, converters, filters, and networks. The DORPC minimizes total WF losses by optimally coordinating reactive power outputs of the DFIG stator and the grid-side converter. The optimal control problem is solved in a distributed manner by using the consensus alternating direction method of multipliers (ADMM). With the consensus ADMM, the total WF loss optimization problem is transformed into a distributed optimal power flow problem considered with DFIGs’ optimal operation. The optimization problem with local constraints considers the reactive power limit of DFIG-based wind turbines (WTs) and the voltage limits at all WT terminal buses inside the WF. In the DORPC, the optimal control problem is solved by the collector bus station controller and WT controllers in parallel, only with the information exchange between immediate neighbors. It eliminates the need of a central controller and centralized communication, implying better robustness and plug-and-play capability. A WF with 20 DFIG-based WTs was used to validate the proposed DORPC scheme.