Reactive Power Control Strategy Research Articles

Coordinated reactive power control for hybrid cascaded high‐voltage direct‐current links in weak AC grids

AbstractThe hybrid cascaded high‐voltage direct‐current (HC‐HVDC) links are recently introduced for ultra‐high voltage bulky power transmissions. However, as wind power becomes more prevalent, the grid is gradually weakened and will face voltage stability issues. This paper proposes a coordinated reactive power control strategy for HC‐HVDC links to enhance the voltage stability of AC bus. Firstly, the impact of HC‐HVDC on the static voltage stability of the AC bus is studied by the voltage sensitivity coefficient. Then, the limitation of reactive power capability of modular multilevel converter in the HC structure is identified. Based on the analysis results, a coordinated reactive power control strategy based on adaptive voltage droop is proposed. In the strategy, the DC voltage ratio is regulated according to the fluctuation degree of the AC bus voltage to adjust the reactive power of HC‐HVDC, which realized the dynamic voltage support for the AC bus. Finally, electromagnetic simulations in power systems computer aided design (PSCAD)/electromagnetic transients including DC (EMTDC) are performed, and the results validate the theoretical findings and the effectiveness of the control strategy.

Inverter PQ Control With Trajectory Tracking Capability for Microgrids Based on Physics-Informed Reinforcement Learning

The increasing penetration of inverter-based resources (IBRs) calls for an advanced active and reactive power (PQ) control strategy in microgrids. To enhance the controllability and flexibility of the IBRs, this paper proposed an adaptive PQ control method with trajectory tracking capability, combining model-based analysis, physics-informed reinforcement learning (RL), and power hardware-in-the-loop (HIL) experiments. First, model-based analysis proves that there exists an adaptive proportional-integral controller with time-varying gains that can ensure any exponential PQ output trajectory of IBRs. These gains consist of a constant factor and an exponentially decaying factor, which are then obtained using a model-free deep reinforcement learning approach known as the twin delayed deeper deterministic policy gradient. With the model-based derivation, the learning space of the RL agent is narrowed down from a function space to a real space, which reduces the training complexity significantly. Finally, the proposed method is verified through numerical simulation in MATLAB-Simulink and power HIL experiments in the CURENT center.With the physics-informed learning method, exponential response time constants can be freely assigned to IBRs, and they can follow any predefined trajectory without complicated gain tuning.

Generalized Predictive Control of the Active and Reactive Stator Powers of the DFIG for Wind Energy Generation

This paper proposes a Generalized Predictive Control (GPC) strategy for Wind Power Generation (WPG) based on a doubly fed induction generator (DFIG). The objective is to study and apply a robust active and reactive power control strategy based on GPC of the DFIG, this is likely to optimize the energy production and improve the quality of the energy produced. In order to maximize the amount of WPG taken even when the turbine is uncertain or the wind speed varies abruptly, the design is built utilizing the Maximum Power Point Tracking (MPPT) theory. Through numerical modeling with the aid of the Matlab/Simulink software, the predictive control (GPC) of the active and reactive stator powers of the DFIG was validated. A comparison between the GPC of the GADA and the indirect method based on a typical PI controller is developed in order to illustrate the viability of the suggested method. According to the simulation results of this comparison, the suggested method is viable and has promising results.

Adaptive active and reactive power control strategy for virtual synchronous generator

SummaryWith the increase in the penetration level of renewables into the grid, the virtual synchronous generator (VSG) concept has emerged as an attractive solution for controlling grid‐tied inverters. The variation in reactive power also affects the real power of the system as well. To address the voltage variations and phase angle variations occurring because of the energy storage elements, the control of the reactive power loop (RPL) is important. Also, it is used to maintain voltage regulation and improve the power factor of the VSG system. This paper focuses on the damping of oscillations occurring because of load variation by proper adjustment of the rotational inertia, damping coefficient, droop coefficient, and regulatory coefficient of reactive power with a proposed adaptive control strategy. Small‐signal analysis of the active and reactive power and point of common coupling (PCC) have been derived, and the detailed dynamic performances are analyzed. The influences of parameters perturbation on PCC voltage and reactive power were investigated. Furthermore, adaptive control includes optimizing dynamic indexes such as rise time, delay time, and response settling time. Finally, the performance and improvement in the results of VSG with and without adaptive control are compared.

Ultra-Low Reactive Power Operation and Control Strategy of Hybrid Line Commutated Converter Based on IGCT for HVdc Application

Existing line commutated converter (LCC) based high voltage DC (HVDC) systems require large reactive power during operation and reactive power compensation equipment under construction. However, the equipment is expensive and occupies a huge area. In this letter, a novel operation of hybrid line commutated converter based on integrated gate commutated thyristor (IGCT) is proposed to achieve ultra-low reactive power (LR-LCC), and the corresponding control strategy is developed by utilizing IGCT's active blocking and bidirectional voltage withstanding capability. It can almost eliminate the system's extinguishing angle (γ), and the power factor is close to 1. This novel LR-LCC can result in advantages including a much lower manufacturing cost and volume of reactive power compensation equipment for HVDC application.

A consensus based adaptive virtual capacitor control strategy for reactive power sharing and voltage restoration in microgrids

A consensus based adaptive virtual capacitor control strategy for reactive power sharing and voltage restoration in microgrids

Transient stability analysis of a grid-connected type-4 wind turbine with grid-forming control during the fault

Thanks to the ability of the inertia provision and the voltage support, the virtual synchronous generator with reactive power control (RPC) is a promising solution among various grid-forming control schemes. This paper analyzes the transient angle stability of the grid-connected type-4 wind turbine with virtual synchronous generator and reactive power control strategy during the fault. By deriving the analytical criterion with the transient energy function, various key factors on the transient stability of the system can be revealed comprehensively and jointly. Additionally, the impacts of the integral coefficient of the RPC and the power reference switching delay on the transient stability are also analyzed by plotting the phase portraits of the derived third-order large-signal model of the grid-connected wind turbine system. The analytical result can be helpful for the determination of the parameters of the grid-connected wind turbine in order to keep transient stable and keep connected with the grid during the fault. Finally, the robustness and the effectiveness of the theoretical analysis results are validated by the electromagnetic transient simulation in MATLAB/Simulink under various conditions.

Fault Ride-Through for PMVG-Based Wind Turbine System Using Coordinated Active and Reactive Power Control Strategy

This study investigates a fault ride-through capability for grid-connected permanent magnet vernier generator (PMVG)-based wind turbine system (WTS) using coordinated active and reactive power control strategy. To do this, the generator peak current and speed limitation schemes are proposed for the machine-side converter to satisfy grid code requirements during grid fault conditions. At the same time, the reactive power control is implemented on the grid-side converter to meet the reactive current requirement of the grid code. And then, to suppress the DC-link power unbalance during grid fault conditions, an efficient variable exponential reaching law-based sliding mode control is designed. Further, the coordinated control schemes are employed to ensure the stable DC-link voltage and maintain the converter's maximum peak current during grid faults. Finally, the proposed control methods demonstrate their superiority through simulations on 5-kW PMVG, 1.5 MW PMSG-based WTS, and its application potential is shown through the experimental prototype of a 5-kW PMVG-based WTS.

Analysis of single-phase cascaded H-bridge multilevel inverters under variable power conditions

Easy modular I action is one of the benefits of a cascaded H-bridge (CHB) inverter. This study proposes an only one multilevel inverter comes with a unique H-bridge unit. The structure of the proposed topology is then enhanced in order to make use of switching devices and DC-link voltage inputs while creating a massive number of voltage steps. A cooperative active and reactive power control strategy is offered to earn a better real and reactive power management for every DC voltage source of a photovoltaic (PV) module, as well as boost systems power quality and reliability. A unique control approach and proportional pulse width modulation (PWM) modulation are described for the cascaded H-bridge multilevel inverters for grid-connected systems. Each Hbridge module can give different power levels thanks to this control. To supply the DC source, use the system's proportional, integral and derivative (PID) controller. The functionality and achievements of the proposed scheme with its associated algorithms in production of all operating voltage have been proven using experimental data from a nine-level single-phase inverter. Finally, to construct a cascaded H-bridge nine-level inverter, the proposed control strategy is developed and implemented in MATLAB software.

Coordinated active and reactive power management for enhancing PV hosting capacity in distribution networks

AbstractThis paper proposes an operational planning model based on optimal active and reactive power control strategies to enhance solar photovoltaics (PV)’ hosting capacity in distribution networks. Reactive power control is carried out through optimum static VAr compensators (SVCs) placement, while active power control is performed through flexible loads, particularly shiftable and interruptible loads. The first stage of the proposed two‐stage stochastic model assigns decision‐making regarding calculating PV hosting capacity at different nodes, in addition to the allocation and capacity of SVCs. In the second stage, the first stage decisions are assessed to ensure the power flow constraints under various uncertainties such as daily load and stochastic PV generation. The presented model is investigated through numerical analyses on modified IEEE 15‐bus and IEEE 33‐bus distribution systems considering different active‐reactive strategy cases. While most previous works only rely on one type of active or reactive power control strategy, this study investigates the challenges of the respective application of active and reactive power control in various modes of fundamental practices. The obtained results prove the superiority of the proposed hybrid active‐reactive control strategy for enhancing PV hosting capacity compared to respective active or reactive power controls.

Series APF based on Five and Seven-Level NPC Inverters using modified PQ Method

This paper presents the performance analysis of Series Active Power Filter (Series APF) based on five and seven-level neutral point clamped (npc) using modified instantaneous reactive power control strategy to use for harmonic and all voltage disturbances compensation. The conventional configuration based on standard voltage source inverter (VSI) with hysteresis controller presents several drawbacks such us uneven switching frequency and limited power applications. Multi-level inverters such us Five and seven-level are currently being investigated and used in various industrial applications; their advantages include the capability to reduce the harmonic content and decrease the voltage or current ratings of the semiconductors with low switching losses, low electromagnetic interference, and low acoustic noise. Fuzzy controllers are successfully employed in various industrial applications and are found more robust than conventional controllers; they represent a good alternative to classic control systems. To benefit of all these advantages two configuration of Series APF are presented in this paper adopting the same control scheme based on Phase Disposition-Sinusoidal Pulse Width Modulation (PD-SPWM) and fuzzy logic control (FLC). The proposed two series APF are evaluated using MATLAB-Simulink software and SimPowerSystem Toolbox for harmonic compensation and in case of all voltage disturbances compensation. The simulation results show the performance and the efficiency of the proposed Series APF based on seven-lever (npc) inverter in the improvement of the power quality.

Optimal Control of a Single-Stage Modular PV-Grid-Driven System Using a Gradient Optimization Algorithm

There are many studies that focus on extracting harmonics from both DC and AC sides of grid-interfaced photovoltaic (PV) systems. Based on these studies, the paper introduces an efficient method depending on hybrid DC voltage, and an active and reactive power (DC-V PQ) control scheme in a single-stage three-phase grid-interfaced PV system. The proposed scheme is designed to regulate DC voltage to minimize power loss and energy share between the network reconfiguration and the utility grid. Moreover, the technique is more effective at dealing with uncertainty and has higher reliability under various operating scenarios. These operations are the insertion of linear load 1, nonlinear load, and linear load 2. Moreover, a novel objective function (OF) is developed to improve the dynamic response of the system. OF is coupled with a particle swarm optimization (PSO) algorithm and a gradient optimization (GBO) algorithm. The analysis and the comparative study prove the superiority of GBO with counterfeits algorithm.

Analysis method for the design of long submarine cables

The recent push for renewable electrical energy sources has resulted in a significant increase in the installation of the offshore wind farms. These farms become much bigger than their earlier counterparts and the generated power is much larger. This puts additional performance requirements on the export cables. Long submarine export cables are not only subjected to changing laying conditions along the route, including depth and seabed material variations, but also the loading patterns vary significantly over time. Additionally, applied reactive power compensation measures and the time-dependent grid situation change the distribution of the current along the route. These unique features of long submarine power cables necessitate a new type of approach to their design and construction optimization. This paper introduces a new approach for ampacity calculations of long submarine power cables. As the ampacity calculations form a basis for the design of a cable route, it is of paramount importance that they are performed as accurately as possible. The approach can be applied to general-purpose circuit solvers, and this paper describes how to implement it using the ATP-EMTP software, which is extended to the consideration of concurrent electrical and thermal effects. The approach permits considering all the important local and time-dependent parameters of the analysis simultaneously. In particular, the approach allows simultaneous analysis of the varying laying conditions along the route including changes in the depth of burial and thermal resistivity of the soil together with the temporal variations of the cable loading. Additionally, current characteristics in long AC cable conductors are strongly affected by the reactive power flow, which in turn depends on the location of the reactive power compensation, the reactive power demand for grid operation, and the wind farm voltage reactive power control strategy. Such analysis cannot be performed with any existing analytical tool. Also, numerical tools cannot handle such problems because a 3-dimensional time-dependent analysis of a cable route which is 100 km long would encounter convergence problems as the size of such model would be prohibitive. Hence, at present, the proposed approach is the only one available to solve this complex electro-thermal problem. Several numerical examples illustrate an application of the proposed methodology.

Research on Integrated Control Strategy of Reactive Power and Voltage for Distributed Generation

The access of distributed photovoltaic power sources will change the power flow distribution in the distribution network. When the line load is light and the photovoltaic access capacity is large, the distribution network will become a multi-source network, which will cause the reverse flow of the line, increase the line voltage, and affect the power quality of the distribution network. Aiming at this problem, this paper studies the voltage control strategy after photovoltaic grid-connected, and proposes a four-level reactive voltage control strategy to solve the voltage problem when photovoltaic large-scale grid-connected. Finally, the method is verified by an example.

Distributed reactive power control strategy based on adaptive virtual reactance

In high-voltage microgrid, the line impedance is mainly inductive and the reactive power of the load cannot be shared equally and reasonably due to the transmission line impedance mismatches. This paper proposes a distributed reactive power control strategy combined with an adaptive virtual reactance method. The proposed control strategy does not require line impedances estimation or a central controller; each DG only needs information from its neighbours to achieve control of the reactive power, which can reduce communication costs and improve system reliability. An adaptive compensator is employed to reduce voltage deviations. Finally, MATLAB/Simulink simulation and hardware-in-the-loop experiment are conducted to verify the effectiveness of the proposed control strategy.

An improved reactive power control strategy for LCC-HVDC to mitigate sending end transient voltage disturbance caused by commutation failures

The sending end transient voltage disturbance (TVD) caused by commutation failure of line commutated converter-based high voltage direct current (LCC-HVDC) systems, which is characterized by “first reduce then rise”, has received increasing attention due to its threat to the stable operation of renewable energy integrated modern power systems. To mitigate the TVD, this paper devises an improved reactive power control strategy that takes into account the signal delay between converter stations. Firstly, the mechanism of the TVD is investigated. It is found that the voltage dependent current order limiter (VDCOL) and signal delay between the rectifier and the inverter stations are two vital factors that impact the TVD, while the VDCOL cannot well cope with commutation failure suppression and TVD mitigation at the same time. On this basis, an improved closed-loop reactive power control (CLRPC) strategy is proposed for the LCC-HVDC to mitigate the TVD. The CLRPC can regulate the reactive power demand of the rectifier station by adjusting the DC current order, which replaces the conventional VDCOL during the disturbance. Furtherly, a delay compensation unit is augmented in the proposed scheme to suppress the adverse effect of signal delay. Simulation results conducted in PSCAD/EMTDC verify that the CLRPC can not only alleviate the TVD effectively but also suppress the occurrence of successive commutation failures, thus, enhancing the overall performance of the sending end power system.

Reactive power control strategy for integrated photovoltaic inverter

Rising penetration of photovoltaic (PV) power also poses several threats to electrical system which demands proper inverter control schemes to be designed. One major issue is that as PV systems are inherently non-inertial in nature, they do not participate in regulating voltage or reactive power and hence become highly sensitive to external disturbances. Any perturbation in voltage or frequency may cause some serious consequences in terms of loss of transient stability and reliability. Thus controlling the PV inverter for smooth operation of system while interfacing with grid brings a challenging task of maintaining both voltage and frequency well within the acceptable limits. Another important aspect is intermittency in PV output which demands application of some advance tracking algorithms. Therefore, novel control strategies for PV interfacing have been presented in this paper. The proposed synchroconverter based inverter controller enables the system to inject both active and reactive powers and facilitates the integrated PV system to withstand voltage or frequency perturbation. Whereas an enhanced control algorithm is applied here that can estimate panel parameters precisely offering effective tracking for any conditional variance. Proposed synchroconverter based controllers have been analyzed through simulations for different spans of time according to voltage and frequency variations.

Enhanced Harmonics Reactive Power Control Strategy Based on Multilevel Inverter Using ML-FFNN for Dynamic Power Load Management in Microgrid.

The shift of the world in the past two decades towards renewable energy (RES), due to the continuously decreasing fossil fuel reserves and their bad impact on the environment, has attracted researchers all around the world to improve the efficiency of RES and eliminate problems that arise at the point of common coupling (PCC). Harmonics and un-balance in 3-phase voltages because of dynamic and nonlinear loads cause a lagging power factor due to inductive load, active power losses, and instability at the point of common coupling. This also happens due to a lack of system inertia in micro-grids. Passive filters are used to eliminate harmonics at both the electrical converter’s input and output sides and improve the system’s power factor. A Synchronous Reference Frame (SRF) control method is used to overcome the problem related to grid synchronization. The sine pulse width modulation (SPWM) technique provides gating signals to the switches of the multilevel inverter. A multi-layer feed forward neural network (ML-FFNN) is employed at the output of a system to minimize mean square error (MSE) by removing the errors between target voltages and reference voltages produced at the output of a trained model. Simulations were performed using MATLAB Simulink to highlight the significance of the proposed research study. The simulation results show that our proposed intelligent control scheme used for the suppression of harmonics compensated for reactive power more effectively than the SRF-based control methods. The simulation-based results confirm that the proposed ML-FFNN-based harmonic and reactive power control technique performs better in terms of MAE, for the case of MSE, and when evaluating based on the RMSE.

Intelligent reactive power control of a renewable integrated hybrid energy system model using static synchronous compensators and soft computing techniques

Modern power system faces a severe problem of instability, largely due to inconsistent reactive power. It causes damage to the power grid within a few milliseconds. Therefore, proper management of reactive power under disturbing situations plays a key role in its safe operation. Devices such as flexible alternating current transmission systems (FACTS) accurately manage the system’s reactive power in accordance with the load demand. In this study, a new reactive power control strategy is employed for optimization of the reactive power along with the stability improvement of the system under different small perturbed conditions. Therefore, this study focuses on controlling the reactive power for an isolated wind-diesel hybrid power system model (WDHPSM) with the aid of a static synchronous compensator (STATCOM) together with the use of an integral minus proportional derivative (IPD) controller keeping a derivative-based filter (IPDF) as a secondary controller for better utilization of its purpose. The obtained results are compared when the no-control strategy is applied in the model. Another comparison has been done between the multiple applied soft computing techniques (oppositional harmonic search, ant lion optimization, binary-coded genetic algorithm, and symbiosis organisms search) that optimize the parameters of the controller of WDHPSM.

Optimized Reactive Power Control of Module Power Imbalance of Cascaded Converter

In the medium voltage cascaded converter, the power imbalance problem among the converter modules will result in certain converter modules over-modulated. Reactive power control (RPC) scheme is an effective way to balance the cascaded converters. Many efforts, such as reactive power sharing control and apparent power sharing control have been used to solve the overmodulation issue. This paper investigates an optimization RPC scheme to solve the overmodulation problem by minimizing the total required reactive power. An improved minimum reactive power (IMRP) RPC scheme is presented, the feasible area for the active power imbalance is evaluated and compared with the reactive power sharing control scheme and the apparent power sharing control scheme. Finally, the control scheme is verified on a three-module scaled-down cascaded inverter.