Amount Of Reactive Power Research Articles

Voltage Support Experimental Analysis of a Low-Voltage Ride-Through Strategy Applied to Grid-Connected Distributed Inverters

In recent decades, different control strategies have been designed for the increasing integration of distributed generation systems. These systems, most of them based on renewable energies, use electronic converters to exchange power with the grid. Capabilities such as low-voltage ride-through and reactive current injection have been experimentally explored and reported in many research papers with a single inverter; however, these capabilities have not been examined in depth in a scenario with multiple inverters connected to the grid. Only few simulation works that include certain methods of reactive power control to solve overvoltage issues in low voltage grids can be found in the literature. Therefore, the overall objective of the work presented in this paper is to provide an experimental analysis of a low-voltage ride-through strategy applied to distributed power generation systems to help support the grid during voltage sags. The amount of reactive power will depend on the capability of each inverter and the amount of generated active power. The obtained experimental results demonstrate that, depending on the configuration of distributed generation, diverse inverters could have different control strategies. In the same way, the discussion of these results shows that the present object of study is of great interest for future research.

An optimization method of UFLS/UVLS considering the interaction of system state information

Because of the differences of grid network architecture, generator parameters, and load characteristics, frequency and voltage at grid nodes show certain spatial distribution characteristics when faults happen. Therefore, the same stability control measures may result in different control effects if applied at different nodes. Meanwhile, in order to improve the control effect and reduce stable control cost, the impacts of the interactions between strongly coupled factors, such as frequency, voltage, active power, reactive power and other quantities, on the effects of stability control measures need to be considered. A new optimization control strategy of under‐frequency load shedding/under‐voltage load shedding is proposed in this paper based on the load control sensitivity index. The method takes into consideration the spatial distribution characteristics of frequency and voltage, as well as the real‐time interaction characteristics of the coupled electrical quantities. Compared with the traditional load‐shedding scheme, the proposed scheme can achieve better control results. The effectiveness of the proposed method is verified through a time‐domain simulation of two actual provincial power grids. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Power management and second-order sliding mode control for standalone hybrid wind energy with battery energy storage system

The purpose of this article is to provide a high performance control of a renewable distributed generator to guarantee an electric power quality and jointly reduce the mechanical stress despite any possible uncertainties such as the random nature of wind speed, the presence of parameters uncertainties, and external perturbations acting on the system (sudden load variation). The renewable distributed generator integrating a wind generator associated with a batteries module is considered as an energy storage device and a variable load. The proposed method is designed by a power management supervisor and a sliding mode control technique. First, the power management supervisor is used to monitor the power flows transferred between the different system devices depending on the load variation and on the intermittency of wind production. In fact, it enables to ensure the balance at the continuous, Direct Current (DC) bus between the powers supplied by the renewable distributed generator and those demanded by the load. In addition, it prevents batteries from exceeding its maximum or minimum state of charge ( SOCbat) by keeping it at an acceptable level [30%, 90%]. Second, a second-order sliding mode control based on the super-twisting algorithm is suggested to control the two subsystems (generator side and load side converters). The main target of the first one is to extract the maximum wind power taking into account the parameter variations and the fluctuating nature of wind. The second one is to investigate a second-order sliding mode control of active and reactive load power quantities, which provides better results in terms of attenuation of the harmonics present in the load voltage and current while considering the sudden load variations. In addition, a proportional–integral controller is also designed and simulated to establish a comparison framework. According to the simulation results, the second-order sliding mode control successfully deals with the nonlinearity of the renewable distributed generator compared with the proportional–integral performance.

The Application of One-Cycle Control Technology in Electric Spring System

This paper first introduced the function, application and the control algorithm of the electric spring (ES), then the working principle of ES are explained. Aiming at the problems that the existing control algorithms have complex structures and are not conducive to accurate tracking of AC voltage signals on sensitive loads, this paper proposes the ES control strategy based on one-cycle control (OCC) technology. In Matlab/SimulinK, the ES system based on the OCC strategy is modeled and simulated. Through the waveform analysis, it is known that when the power of the photovoltaic system injected into the power grid fluctuates, the ES based on the OCC strategy system can operate in a capacitive, inductive or resistive mode automatically, which can achieve a direct and accurate tracking of a given AC voltage signal under the condition that a small amount of reactive power is injected into the grid, thus the voltage of the sensitive load is stabilized, and at the same time the voltage fluctuations on the grid side voltage can be transferred to non-sensitive loads in series with the ES.

A Centrality Index Based Approach for Selection of Optimal Location of Static Reactive Power Compensator

Reactive power management and voltage control are the two key facets of any electrical power system due to their support for reliability of the system. While managing reactive power and voltage during system operation, minimization of real power loss is also achieved. As reactive power doesn’t travel far, the point of reactive power compensation must be carefully chosen to achieve the best effect of injected reactive power. This paper focuses on placement of reactive power compensator using “Centrality” measure, which is an index for identifying most important vertex within a graph. Earlier “Electrical centrality measures” were used for vulnerability analysis of electrical networks as well as analysis of blackouts and brownouts. The contributions of this paper are threefold. First, in this paper, a generalized methodology has been introduced for calculating “electrical centrality measures” based on graph theory. Next, the proposed centrality index has been used for identifying the location for reactive power compensation. Finally, the amount of reactive power required to maintain voltage profile throughout the system has been optimized. The proposed method is tested for multiple test systems of different sizes to demonstrate the applicability and usefulness of the proposed method.

Power factor correction using capacitors & filters

Power factor is the ratio of the real current or voltage received by a load to the root mean square (rms) value of the current or voltage that was supposed to be acquired by the same load. The fact that the two become different is due to the presence of reactive power in the circuit which gets dissipated.Improving the power factor means reducing the phase difference between voltage and current. Since majority of the loads are of inductive nature, they require some amount of reactive power for them to function. Therefore, for the better use of electrical appliances with minimum amount of electrical consumption, the power factor should necessarily be increased and should be brought near to 1. This can be easily done by the help of Automatic Power Factor Correction Capacitors and Active filters.

Local and Distributed Voltage Control Algorithms in Distribution Networks

In this paper, we consider a voltage control problem in power distribution grids. The specific goal is that of keeping the voltages within preassigned operating limits by commanding the reactive power output of the microgenerators connected to the grid. We propose three strategies. The first two strategies are purely local, meaning that each microgenerator updates the amount of reactive power to be injected based only on local measurements of the voltages’ magnitude. Instead the third one is distributed, namely, the microgenerators, to perform the updating steps, require some additional information coming from the neighboring agents. The local strategies are simpler to be implemented, but they might fail in solving the voltage control problem. Instead, the distributed one requires the microgenerators to be endowed with communication capabilities, but it is effective in driving the voltages within the admissible intervals and, additionally, it exploits the cooperation among the agents to reach also a power losses minimization objective. Theoretical analysis and extensive numerical simulations are provided to confirm the arguments aforementioned.

Voltage Stability Improvement of Transmission Systems Using a Novel Shunt Capacitor Control

AbstractThis paper proposes a novel shunt capacitor (SC) based voltage stability method for a power system operation. The integration of distributed generators e.g. wind and PV powers to the grid, and fluctuations nature of load power cause the attention of voltage stability management for a power system operation and planning. The SC based proposed method improves the voltage stability by using the flow of active and reactive powers in the transmission line. The Voltagestability index (VSI) is utilized for the voltage stability analysis. The SC is installed at the load bus so that it can inject a proper amount of reactive power for ensuring the voltage stability of power system. The proposed method is investigated in the IEEE-14 bus test system. Simulation results are compared with the non-SC based method. Extensive simulation analyses have been done by the MATLAB/Simulink software.

Compensation of Reactive Power of Squirrel-Cage Asynchronous Generators, Used in Wind Power Plants and Small Hydroelectric Power Stations

Abstract Reactive power compensation of asynchronous generators of wind power plants and small hydroelectric power stations increases a reliability of their operation when they are connected to the so-called “weak” electrical networks of power systems. The methods of reactive power compensation for asynchronous generators of various performances are shown. Attention is paid to compensation of reactive power in the start-up conditions, because just in the start-up conditions a considerable amount of reactive power is required. This reactive power will help to prevent a voltage drop in the renewable power sources’ connection places, which have the rotating electromechanical converters, consisting of squirrel-cage asynchronous generators and frequency converters in their stator’s circuits. It was revealed, that carrying out of start by underfrequency relay allows reducing significantly a value of required reactive power of static capacitor banks.

Stabilization of Wind Farm by Using PMSG Based Wind Generator Taking Grid Codes into Consideration

This paper presents a new operational strategy for a large-scale wind farm (WF) which is composed of both fixed speed wind turbines with squirrel cage induction generators (FSWT-SCIGs) and variable speed wind turbines with permanent magnet synchronous generators (VSWT-PMSGs). FSWT-SCIGs suffer greatly from meeting the requirements of fault ride through (FRT), because they are largely dependent on reactive power. Integration of flexible ac transmission system (FACTS) devices is a solution to overcome that problem, though it definitely increases the overall cost. Therefore, in this paper, a new method is proposed to stabilize FSWT-SCIGs by using VSWT-PMSGs in a WF. This is achieved by injecting the reactive power to the grid during fault condition by controlling the grid side converter (GSC) of PMSG. The conventional proportional-integral (PI)-based cascaded controller is usually used for GSC which can inject small amount of reactive power during fault period. Thus, it cannot stabilize larger rating of SCIG. In this paper, a suitable fuzzy logic controller (FLC) is proposed in the cascaded controller of GSC of PMSG in order to increase reactive power injection and thus improve the FRT capability of WF during voltage dip situation due to severe network fault. To evaluate the proposed controller performance, simulation analyses are performed on a modified IEEE nine-bus system. Simulation results clearly show that the proposed method can be a cost-effective solution which can effectively stabilize the larger rating of SCIG compared to conventional PI based control strategy.

Stability Augmentation of a Grid-Connected Wind Farm by Fuzzy-Logic-Controlled DFIG-Based Wind Turbines

Wind farm (WF) grid codes require wind generators to have low voltage ride through (LVRT) capability, which means that normal power production should be resumed quickly once the nominal grid voltage has been recovered. However, WFs with fixed-speed wind turbines with squirrel cage induction generators (FSWT-SCIGs) have failed to fulfill the LVRT requirement, which has a significant impact on power system stability. On the other hand, variable-speed wind turbines with doubly fed induction generators (VSWT-DFIGs) have sufficient LVRT augmentation capability and can control the active and reactive power delivered to the grid. However, the DFIG is more expensive than the SCIG due to its AC/DC/AC converter. Therefore, the combined use of SCIGs and DFIGs in a WF could be an effective solution. The design of the rotor-side converter (RSC) controller is crucial because the RSC controller contributes to the system stability. The cascaded control strategy based on four conventional PI controllers is widely used to control the RSC of the DFIG, which can inject only a small amount of reactive power during fault conditions. Therefore, the conventional strategy can stabilize the lower rating of the SCIG. In the present paper, a new control strategy based on fuzzy logic is proposed in the RSC controller of the DFIG in order to enhance the LVRT capability of the SCIG in a WF. The proposed fuzzy logic controller (FLC) is used to control the reactive power delivered to the grid during fault conditions. Moreover, reactive power injection can be increased in the proposed control strategy. Extensive simulations executed in the PSCAD/EMTDC environment for both the proposed and conventional PI controllers of the RSC of the DFIG reveal that the proposed control strategy can stabilize the higher rating of the SCIG.

Improving Transient Stability in Power Systems by Using Fuzzy Logic Controlled SVC

<span>This paper presents the capability of a fuzzy logic based stabilizer used for generating the supplementary control signal to voltage regulator of static VAR compensator (SVC) for improving damping oscillations in power systems. Generator speed deviation and line active power were chosen as input signals for the fuzzy logic controller (FLC). The quantity of reactive power supplied/absorbed by SVC is determined based on the two input signal and deviation of terminal voltage at each sampling time. The effectiveness and feasibility of the proposed control is demonstrated with Single Machine Infinite Bus (SMIB) system and multi machine system which show improvement over the use of a fixed parameter controller. It has been observed that a robust controller is obtained with fuzzy logic controller.</span>

Advanced Reactive Power Reserve Management Scheme to Enhance LVRT Capability

Abstract: To increase the utilization of wind power in the power system, grid integration standards have been proposed for the stable integration of large-scale wind power plants. In particular, fault-ride-through capability, especially Low-Voltage-Ride-Through (LVRT), has been emphasized, as it is related to tripping in wind farms. Therefore, this paper proposes the Wind power plant applicable-Effective Reactive power Reserve (Wa-ERPR), which combines both wind power plants and conventional generators at the Point of Interconnection (POI). The reactive power capability of the doubly-fed induction generator wind farm was considered to compute the total Wa-ERPR at the POI with reactive power capability of existing generators. By using the Wa-ERPR management algorithm, in case of a violation of the LVRT standards, the amount of reactive power compensation is computed using the Wa-ERPR management scheme. The proposed scheme calculates the Wa-ERPR and computes the required reactive power, reflecting the change of the system topology pre- and post-contingency, to satisfy the LVRT criterion when LVRT regulation is not satisfied at the POI. The static synchronous compensator (STATCOM) with the capacity corresponding to calculated amount of reactive power through the Wa-ERPR management scheme is applied to the POI. Therefore, it is confirmed that the wind power plant satisfies the LVRT criteria by securing the appropriate reactive power at the POI, by applying of the proposed algorithm.

Guidelines for distribution system operators on reactive power provision by electric vehicles in low-voltage grids

The increasing success of electric vehicles is bringing new technical challenges to power system operators. This work intends to provide guidelines for distribution system operators in terms of reactive power requirements when evaluating and authorising electric vehicles supply equipment with fast charging capability in existing low-voltage distribution feeders. The aim is to prevent the voltage to exceed the permitted values when charging at high power, by exploiting the effect of the reactive power. The proposed guidelines for distribution system operators are reported in a matrix, which indicates the amount of reactive power that an individual electric vehicle is expected to provide when connected to a low-voltage feeder to benefit of the desired voltage rise effect in comparison to the case of unitary power factor.

Single phase transformerless inverter topology with reduced leakage current for grid connected photovoltaic system

Leakage current is the main concern of the grid connected transformerless photovoltaic (PV) inverters. Many single phase transformerless inverter topologies with reduced leakage current have been introduced in the past few years. These are mainly classified on the basis of leakage current reduction methods Galvanic isolation without- common mode voltage (CMV) clamping and with-CMV clamping. It has been shown that leakage current generation is highly dependent on CMV. CMV of the topologies without- CMV clamping oscillates and oscillation amplitude depends on switches’ junction capacitances and parasitic parameters of the topology. In order to eliminate the leakage current completely, CMV must be constant throughout the inverter operation. Moreover, inverter should also be capable to inject definite amount of reactive power into the grid, as demanded by the international regulations. In this study, reduced leakage current CMV clamped topology is proposed which can eliminate leakage current and capable of injecting reactive power into the grid. Total harmonic distortions (THD) of injected grid current at various solar irradiance levels are also analyzed. In order to verify the theoretical explanations, the proposed topologies are simulated in Matlab/Simulink environment. Finally, the simulated results are validated experimentally.

Sequence Control Verification of a Central Solenoid Converter for Nuclear Fusion Reactors by Using a Hardware-in-the-Loop

In this paper, verification of a four-series connected central solenoid (CS) converter sequence control of a nuclear fusion reactor to reduce reactive power by using a real-time digital simulator is described. The unit CS converter supplies voltage (±975 V) and current (±45 kA) to the CS superconducting magnets to induce current in plasma. The output voltage of the unit CS converter is limited because of the rated voltage of thyristor switches. However, the CS superconducting coil needs more operating output voltage. Thus, the CS converter must be connected in four series to provide the required operating output voltage. Adequate reactive power support is important to improve the electrical grid stability, because four-series connected CS converter generate large amounts of reactive power. However, other reactive compensators require high costs and a large area. Hence, sequence control is applied to the voltage control of the four-series connected CS converter in order to reduce the reactive power. The sequence controller calculates and transmits the individual voltage command to each unit CS converter according to the total voltage command via safe ring-type communication channel. To verify the feasibility of the proposed sequence control of four-series connected CS converter, five real Zynq-based controllers are assembled and a power system, including the four unit CS converters, is implemented in a real-time digital simulator for hardware-in-the-loop verification. Maximum reactive power is reduced by 16%, from 225 to 190 Mvar.

An improved single phase transformerless inverter topology for grid connected PV system with reduce leakage current and reactive power capability

Abstract Single phase transformerless inverters are widely being adopted for small scale grid connected PV systems due to their high efficiency, lower cost and high power density. However, leakage current is the main concern in these inverters which needs to be addressed carefully. Moreover, PV inverters should also be capable of injecting a definite amount of reactive power into the grid as prescribed by the international regulations. In this paper, an improved H6 common mode voltage (CMV) clamped topology with modified modulation strategy is proposed. The proposed topology offers low loss ac side decoupling, complete elimination of leakage current via CMV clamping and reactive power generation capability. The proposed modulation technique facilitates the flow of current in order to generate zero voltage state during negative power flow. Total harmonic distortion (THD) of injected grid current at various solar irradiance levels is also analyzed. Moreover, implementation of inverter control algorithm in real time digital simulator (OP-5600) has been discussed in detail. In order to justify the suitability of the proposed topology for grid-tied PV system, simulations have been carried out in Matlab/Simulink environment and validated through an experimental setup.

Reactive Power Billing Under Nonsinusoidal Conditions for Low-Voltage Systems

This paper analyzes reactive power definitions for billing purposes in low-voltage installations with high harmonic distortion levels. First, the theoretical definitions of power under nonsinusoidal conditions and their outcomes are presented and two of them are chosen as the focus to determine which one is the most appropriate for billing: nonactive power and fundamental reactive power. The regulatory framework of different countries is then analyzed and compared with the theoretical definitions. Subsequently, different reactive power measurement methods are analyzed and their outputs are again compared with the definitions. Simulations performed with typical nonsinusoidal voltage and current signals show that several measurement techniques can easily be used for fundamental reactive power measurement, whereas the measurement of nonactive power requires more effort. Finally, a regulatory comparison of the pros and cons of each reactive power quantity is conducted. It is concluded that the surplus of reactive power in electricity grids should be controlled via fundamental reactive power (or displacement power factor), since it is independent of the harmonic distortion, the responsibility for it can be easily assigned, and it is easy to be measured with the use of several simple electronic measurement techniques.

Decentralized Reactive Power Compensation Using Nash Bargaining Solution

We consider a distributed reactive power compensation problem in a distribution network in which users locally generate reactive power using distributed generation units to contribute to the local voltage control. We model and analyze the interaction between one electric utility company and multiple users by using the Nash bargaining theory. On one hand, users determine the amount of active and reactive power generation for their distributed generation units. On the other hand, the electric utility company offers reimbursement for each user based on the amount of reactive power dispatched by that user. We first quantify the benefit for the electric utility company and users in the reactive power compensation problem. Then we derive the optimal solution for the active and reactive power generation, as well as reimbursement for each user under two different bargaining protocols, namely sequential bargaining and concurrent bargaining. Numerical results show that both the electric utility company and users benefit from the proposed decentralized reactive power compensation mechanism, and the overall system efficiency is improved.

Аналіз енергоефективності активного випрямляча з покращеною гістерезисною системою керування

The article describes the active three-phase boost rectifier with power factor correction, as known as active front-end rectifiers, with hysteretic control system in conditions of the ideal voltage and distorted voltage. In many industrial applications active front-end rectifiers (AFEs) have emerged as an attractive topology. When compared to traditional diode-based rectifiers, AFEs allow one to obtain sinusoidal input currents with low harmonic distortion, whilst at the same time providing an accurate rectifier voltage. Moreover, the amount of reactive power drawn from the source can be manipulated in order to reach a unity power factor in the input, or also to compensate a lack of reactive power in the source grid. Another area where AFEs play an important role is when a reduction of harmonic distortion is sought. In fact, this converter is widely used as an active filter in which case the AFE is connected in parallel to the nonlinear load thereby generating the harmonic currents necessary to reduce the pollution in the source. The research of the active rectifier was made in the Matlab R2011. Presented an improved hysteresis control system that allows improve the harmonic content generated by the phase currents and thus improve power factor in implementing the conditions of distortion of mains voltages.