Minimum Reactive Power Research Articles

РЕГУЛЮВАННЯ НАПРУГИ ТА РЕАКТИВНОЇ ПОТУЖНОСТІ В РОЗПОДІЛЬНИХ ЕЛЕКТРИЧНИХ МЕРЕЖАХ ШЛЯХОМ ВИКОРИСТАННЯ РОЗОСЕРЕДЖЕНИХ ВІДНОВЛЮВАНИХ ДЖЕРЕЛ ЕНЕРГІЇ

The problems of mode regulation of distribution networks in Ukraine are investigated in this paper. Authors propose to regulate the modes of distribution networks by the means of convertors of renewable energy sources (solar power plants etc.) connected to this networks according to the Smart Grid concept. The analysis of multicriteria mode optimization results of the distribution network was performed and the most perspective criterion were selected according to the features of structure and functioning of distribution networks in Ukraine. The target function of multicriteria optimization by the criteria of minimization of reactive power on the main section of the line and minimization of standard voltage deviations from the nominal value is formalized by the authors. To calculate the optimal value for the target function, the Multivariable extremum seeking control method was chosen, this method was improved by adding additional filters of individual frequency channels. An example of calculations is given in the paper; it illustrates the efficiency of the proposed method of modes regulating of the distribution networks. References 24, figures 3, tables 2.

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.

Variable Frequency Phase-Shift Modulation Symmetrical Series-Resonant Bidirectional DC-DC Converter—Analysis and Verification of ZVS Performance and Reactive Power Minimization—

Variable Frequency Phase-Shift Modulation Symmetrical Series-Resonant Bidirectional DC-DC Converter—Analysis and Verification of ZVS Performance and Reactive Power Minimization—

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.

Minimum reactive power loss optimization of power grid systems based on improved differential evolution algorithm

With the expansion of power system scale, the operation of the power grid system has been greatly challenged. Reactive power optimization can make the power system operate safely and economically. In this paper, an improved differential evolutionary algorithm is applied to reactive power optimization of power system. We take the minimum power system loss as the objective function, the power balance condition as the equality constraint, the control variables and state variables as the inequality constraint conditions to establish the system model. Finally, IEEE30 bus and IEEE33 bus power system are selected to verify the effectiveness of the proposed algorithm.

Impact of integrating large-scale DFIG-based wind energy conversion system on the voltage stability of weak national grids: A case study of the Nigerian power grid

This paper investigates the impact of integrating large-scale Doubly-Fed Induction Generator (DFIG)-based wind energy conversion system (WECS) on the voltage stability of the 52-bus, 330 kV Nigerian power grid. Indices derived from Active Power–Voltage (PV) and Reactive Power–Voltage (QV) analyses have been utilized to determine the voltage stability limits in terms of the maximum active power margin (APM) and minimum reactive power margin (RPM) of the system with the associated critical voltage-reactive power ratio (CVQR) of the system buses. Simulations have been done in DIgSILENT PowerFactory and the results analysed using MATLAB. This work also demonstrates the effectiveness of DFIG-based WECS in mitigating the overvoltage issues in the Northern region by ensuring that all bus voltages are within the acceptable limits of 1.0 ± 0.05 p.u. The results show that the optimal DFIG-based WECS penetration level (PL) that satisfies a bus voltage criterion of 1.0 ± 0.05p.u with the APM and CVQR not falling below their respective base case values and the loading of all critical power system equipment not exceeding 80% is 35%. Therefore, this work has demonstrated the possibilities of large-scale DFIG-based WECS as a viable solution for voltage stability improvement of a weak National grid while meeting the increasing energy demand.

PMSG-Based Dual-Port Wind-Energy Conversion System With Reduced Converter Size

In this study, a dual-port wind-energy conversion system has been proposed. A double-fed permanent-magnet synchronous generator (DFPMSG) forms the central part of the system, where the concentrated single-layer winding configuration of the generator enables electric and magnetic isolation between the ports. DFPMSG has two three-phase terminals out of the stator; one is connected directly to the grid, whereas the other is tied to the grid through a back-to-back converter. This study investigates design issues caused by the DFPMSG port with a direct grid connection. The unique design issues of the proposed system include determining the slot/pole combination using wind data and determining the minimum reactive power requirement for the port with a direct grid connection. Next, the load-sharing capability among the ports of the proposed system is presented through a detailed investigation of three schemes. Experimental work is presented for a 5-kW prototype DFPMSG system to illustrate the isolation among the ports, minimized reactive power demand on the port with direct grid connection, and load-sharing ability among the ports for different control schemes.

A Single-Stage Dynamically Compensated IPT Converter With Unity Power Factor and Constant Output Voltage Under Varying Coupling Condition

Leakage and magnetizing inductances of a loosely coupled transformer are constantly changing due to the relative positions of the primary and secondary transformer windings in inductive power transfer systems. In order to counteract the nonnegligible inductances and extract desirable characteristics from the system, various compensation networks have been proposed to obtain unity input power factor and constant output voltage for minimum reactive power and ease of control for battery charging or other power electronic applications. However, most of the existing control methods with fixed compensation networks, which are usually designed for a specific coupling coefficient, have failed to fulfill both requirements simultaneously due to the mismatch between the resonant frequencies of the networks after the deviation of the designed coupling condition. In this article, a dynamic series/series–parallel compensation network based on a switch-controlled capacitor is proposed to rematch the series- and parallel-resonant frequencies of the network such that the magnetizing inductance can be adaptively compensated for different sizes of air gap/misalignment. By doing so, the requirements of load-independent output voltage and unity input power factor can be simultaneously fulfilled, while zero-voltage switching on the primary bridge is still maintained under different coupling conditions by a single-stage converter. An experimental prototype with the air gap ranging from 10–16 cm is built to verify the idea.

Analysis and Design of a New Current-Source Output Load Resonant Converter With High Capability in Line and Load Regulation

In this paper a fourth-order Passive Resonant Tank (PRT) is introduced using a topological modification in LLC tank for current-source output applications of Load Resonant Converters (LRCs). The design procedure is based on the output current/input voltage ratio decoupling from the load coefficient. Therefore, output current can be independent of load variation topologically. In this condition, new criterions are applied on the operational frequency and PRT components ratio. Moreover, kVA/kW ratio of the LRC is considered as a comparing index, to optimize the converter size as well as reduction of voltage/current stresses on the PRT components. To reduce the discrete components number, transformer parasitic inductances and bridge capacitors are used as the PRT components. Also, a simple and accurate PWM-based Quasi-Proportional Controller (QPC) is designed to maintain the output current constant against input voltage variations. Minimum reactive power, low circulating and turn-off current, and ZVS of the inverter switches in a wide loads range are obtained as the advantages of the designed LLCC-LRC. Moreover, sinusoidal shape of the PRT input current and minimum switching losses on the rectifier are maintained. Finally, an experimental prototype with 3.5A output current and 93.9% efficiency is presented for results verification.

Analysis and Demonstration of a Dynamic ZVS Angle Control Using a Tuning Capacitor in a Wireless Power Transfer System

In this article, a dynamic zero-voltage switching (ZVS) angle control scheme on the wireless power transfer (WPT) system inverter is proposed by implementing a tuning capacitor. High-frequency (HF) and high-power WPT systems are desired in battery charging applications to reduce the battery charging time. Consequently, the power semiconductor devices are subjected to increased voltage, current, and thermal stresses. In this article, the switching losses in the primary-side inverter of a WPT system are suppressed by realizing the ZVS operation during the battery charging process. A dual-loop control strategy is proposed, which involves traditional phase shift control between the inverter phase legs to maintain constant-current (CC)/constant-voltage (CV) at the output and a tuning capacitor to dynamically tune the ZVS angle. The dynamic tuning of the ZVS angle ensures a minimum reactive power requirement from the input source and, therefore, helps to improve the overall efficiency of the system. Closed-loop simulations of the proposed control strategy are carried out using the piecewise linear electrical circuit simulation (PLECS) simulation software. The proposed control strategy is verified on a 10-W WPT prototype by performing the open-loop experimental validations. The maximum efficiency of the proposed control strategy is found to be ~ 87 % during the CC/CV charging modes. The improvement of ~ 10 % in the dc-dc efficiency is achieved with the proposed ZVS control strategy.

Reactive Power Optimization Control for Bidirectional Dual-Tank Resonant DC–DC Converters for Fuel Cells Systems

Compared to the traditional LC-type dual active bridge (DAB) series resonant converter, the DAB series resonant converter with dual tanks has a larger power transmission range, wider voltage gain, and broader soft switching range. However, this new proposed converter has a larger reactive power than the traditional one, so its efficiency is affected. Therefore, the model of the reactive power is first derived, the control object is defined as the minimum reactive power, and then, a new control scheme for reactive power optimization based on function monotonicity is proposed in this article. At the same time, all switches operate with the zero voltage switching, so the efficiency of the converter is improved. At last, a 500-W prototype is built, and the simulation results and experimental results verify the feasibility of the optimal control scheme.

Determination of Minimum Reactive Power Compensation for the Stable Operation of Type-1 WTG in Grid-Connected mode

The current energy demand scenario leads to tremendous increase in the renewable energy sector, but the integration of these renewable causes various stability issues of the system. Increasing share Wind energy has several shortages due to its energy harnessed from the wind. These shortages can be improved by compensating reactive power into the wind plant. The wind farm consist of fixed speed squirrel cage Induction generator absorbs reactive power from the grid for stable operation and it can be injected using reactive power compensator. In this context, the main aim of the research is to find the minimum reactive power compensation required for stable operation for different rating of Type-1 WTG in grid connected mode. In this paper, a detailed model of constant speed Squirrel Cage Induction Generator is carried out in MATLAB/SIMULINK-2017a to analyze the need of reactive power compensation to maintain voltage and frequency stability of the system during normal condition. The work also focuses on to investigate the impact of induction generator inertia level on compensation level. The modified IEEE 5-bus radial distribution system is used to conduct these investigations and the simulation results clearly show that: (1) The necessity and minimum additional reactive power support to the wind farm to improve and maintain stability of the system; (2) the inertia level of wind farm and reactive power compensator level both are independent each other.

Optimal Phase-Shift Control to Minimize Reactive Power for a Dual Active Bridge DC–DC Converter

In a dual active bridge (DAB) dc–dc converter, modulating the phase-shift ratios can suppress reactive power and increase the efficiency under non-unity voltage gain conditions. Derivation of the optimal phase-shift ratios to achieve the minimum reactive power is challenging because a DAB can operate in four different scenarios (forward/backward, buck/boost) and each scenario has five operating modes. This paper first introduces a transformation in which different DAB operating scenarios (forward/backward, buck/boost) can be equivalent to one another; then optimization of only one scenario (forward/buck) is required. Next, for the five modes in forward/buck scenario, based on a graphical method, this paper proves that each operating point of Modes 1, 2, and 5 can be mapped into that of Mode 3 with lower conduction losses, and only two modes require detailed analysis. The optimization process of these two modes are derived step-by-step. Global optimal phase-shift signals that minimize the reactive power under four different DAB operating scenarios (forward/backward, buck/boost) are presented. A simple table and control block diagram are presented for practical implementation of global reactive-power minimization control. Experimental comparison with other modulation schemes verifies the efficiency improvement of the proposed control method.

Improving the Performance of Long Distance Tuned AC Transmission Systems

The line series reactance and shunt susceptance can be tuned by adopting series and shunt compensation. Practical, size and economic constraints will lead to limitations in location of the compensating elements at optimal points along the line. While planning long-distance transmission, it is necessary to determine not only the average degrees of compensation required, but also ensure the stable and uniform voltage profile with minimal reactive power flow.

Energy Management and Control of Single-Stage Grid-Connected Solar PV and BES System

In general, Solar Photovoltaic (SPV) is integrated to grid through a DC-DC converter and Voltage Source Converter (VSC) for real power injection (called two-stage conversion). In view of efficiency point, the single-stage conversion becomes popular and in which Maximum Power Point Tracking (MPPT) of SPV and real power injection are achieved with VSC alone. But, if Battery Energy Storage (BES) supported by bidirectional DC-DC converter is presented in the single-stage conversion system, then co-ordination between DC-DC converter and VSC is required to achieve simultaneous operation of MPPT and real power injection. In this paper, a co-ordinated control of single-stage grid connected SPV and BES system is proposed along with energy management. In which, the algorithm coordinates VSC and bidirectional DC-DC converter based on the State of Charge (SoC) of the battery such that MPPT and power injection is achieved simultaneously. The proposed method not only injecting real power, but also works to compensate load reactive power and unbalanced neutral current minimization. Further, an active rectification operation during non-SPV hours is discussed for better utilization of VSC capacity. The multi-functional features of the proposed method are explained using simulation studies and are also validated through experimental studies.

Particle Swarm Optimization Algorithm Based Reactive Power Optimization in Distribution Network

Minimization of power loss is the first priority of the power companies. Generally power loss is directly proportional to the reactive power demand and minimization of this is known as reactive power optimization (RPO). In this paper we are trying to minimize the reactive power loss with help of distributed generation. Distributed generation provides active as well as reactive power locally so, there is no need of taking the reactive power from the generator consequently reactive power loss minimizes. Now problem arises that where to place the distributed generation to have minimum power loss. To find the optimal location of the distributed generation, we have used particle swarm optimization algorithm (PSO). For that we have defined the fitness function as well as constraints. Constraints limits the value of variable within the defined range. Fitness function is sum of real power loss index, reactive power loss index and voltage deviation index. We have also used genetic algorithm just to compare the results and to find which one is better out of genetic algorithm and PSO. RPO increases the power transfer capability, reduces the line loss and boost the system stability therefore it can be applied in the distribution network.

Multi-layer spectral clustering approach to intentional islanding in bulk power systems

Intentional controlled islanding (ICI) is a final resort for preventing a cascading failure and catastrophic power system blackouts. This paper proposes a controlled islanding algorithm that uses spectral clustering over multi-layer graphs to find a suitable islanding solution. The multi-criteria objective function used in this controlled islanding algorithm involves the correlation coefficients between bus frequency components and minimum active and reactive power flow disruptions. Similar to the previous studies, the algorithm is applied in two stages. In the first stage, groups of coherent buses are identified with the help of modularity clustering using correlation coefficients between bus frequency components. In the second stage, the ICI solution satisfying bus coherency with minimum active and reactive power flow disruptions is determined by grouping all nodes using spectral clustering on the multi-layer graph. Simulation studies on the IEEE 39-bus test system demonstrate the effectiveness of the method in determining an islanding solution in real time while addressing the generator coherency problem.

Energy storage system control algorithm for voltage regulation with active and reactive power injection in low-voltage distribution network

The voltage drop affecting consumers at the end of distribution lines is one of the problems regarding power quality. The solutions applied to transmission lines are not fully effective in distribution lines, where line parameters are significantly high. In low-voltage distribution network, the reactive power compensation method is not as effective as active and reactive power compensation. This effect occurs on lines where the significant series resistance becomes remarkable in relation to the total line impedance. This paper presents the design and implementation of a four-wire, three-phase voltage source converter (VSC) with output current control for voltage regulation at the point of common coupling (PCC), using active and reactive power injection. A reactive power prioritization and minimization of active power strategy is proposed to overcome the problem of distribution line parameters. Digital design methodology is used to design the management controllers and loops, and a digital signal controller (DSC) is used for the entire implementation. The mathematical analysis results are validated using numerical simulation and proven with the construction of a 3.8kVA prototype. The results showed that the converter accomplished an effective voltage regulation at the PCC with reduced active power.

Genetic algorithm approach for efficiency maximization and power factor enhancement of a grid connected doubly fed induction generator

Ensuring maximum efficiency of a DFIG automatically translates into the need for minimizing generator losses and maximizing active power extraction from the turbine. The goal of loss and reactive power minimization as well as maximum power tracking can be achieved by exercising proper control over DFIG rotor current. This means that the rotor current must be controlled with variation in wind speed. In this work, GA method is applied to determine rotor current references which yield maximum active power, minimum loss and minimum reactive power for a range of generator speed. The novelty of this work is the development of a simple method of DFIG efficiency and power factor control, using GA. Objective functions of output power, generator loss and reactive power have been created. GA toolbox of MATLAB has been used to maximize output power objective function while the other two functions have been minimized. Efficiency and power factor of the system has been computed after optimization to validate the effectiveness of the proposed technique.

Direct Power Control Method With Minimum Reactive Power Reference for Three-Phase AC-to-DC Matrix Rectifiers Using Space Vector Modulation

This paper proposes a direct power control (DPC) method with a minimum reactive power reference for ac-to-dc matrix rectifiers using space vector modulation. Based on the calculated active and reactive power reference values, the developed DPC algorithm directly controls both the active and reactive power components of the source by operating the three-phase matrix rectifiers, thereby obtaining the sinusoidal input currents and output dc voltage/current of the rectifier. The proposed DPC method instantaneously determines a source reactive power reference command to achieve a unity input power factor or maximum achievable power factor on given input and output conditions, because ac-to-dc matrix rectifiers cannot always attain a unity power factor due to the existence of the input capacitors. In addition, the developed algorithm calculates the minimum reactive power reference without using any circuit parameters. Thus, the proposed algorithm is free from any inevitable parameter uncertainty, resulting in a more robust and accurate power factor control for the rectifier. Based on the minimum reactive power reference, the proposed algorithm enables matrix rectifiers to operate at an input power factor that can be maximally obtained at all times. The effectiveness of the proposed method was verified by the simulations and experiments.