Reactive Power Compensation Devices Research Articles

A Novel High-Impedance Fault Detection Technique in Smart Active Distribution Systems

Identification of high impedance fault (HIF) is important in smart active distribution systems (SADSs). The existing protection methods fail to detect HIF, as HIFs have peculiar fault current characteristics. However, if HIFs are left undetected, they result in severe fire hazards and arcing. The paper proposes a novel fault detection indicator that utilizes the differential energy associated with the positive sequence current components during faults. IEEE-13 bus and IEEE-34 bus system is used for simulation in Real Time Digital Simulator (RTDS). The results show that proposed technique accurately identify HIFs and perfectly discriminates the transients due to HIFs, non-linear loads and voltage and reactive power compensation devices. Furthermore, it differentiates HIFs from other switching transients like capacitor or load switching events. Other factors, like transformer inrush currents, effect of noise and sampling rate are also considered to ensure the accuracy and reliability of the proposed method. Moreover, the practical feasibility of the proposed method is also experimentally validated.

Research on Building Power Quality Assessment and Control Technology Based on Online Monitoring

This study is to improve the assessment accuracy and control efficiency of building power quality by adopting online monitoring and integrating multiple technical indicators and control methods. A whole set of power quality technical index system is developed in the study, involving voltage deviation, harmonic voltage/current limit, and so on. The power quality indicators are quantitatively evaluated through standardization and weight determination. The assessment results show that the measured power quality indicators vary within the interval of 0 to 9, which verifies the effectiveness of the assessment system. In terms of control technology, this paper discusses in depth the static reactive power compensation (SVC) device and its role in improving building power quality, and confirms its efficacy in optimizing power quality through simulation experiments. This work not only successfully evaluates the building power quality, but also proposes practical control strategies, which provide theoretical and practical guidance for the stable operation of power systems and the further improvement of power quality.

Design and Verification of Cascaded Multilevel STATCOM Active Filter Function

STATCOM can be used as both dynamic reactive power compensation device and active power filter to improve the power quality of a power grid. This paper describes the active filter function implemented into an existing STATCOM control. The paper explains firstly the filtering control system of the STATCOM, starting from the introduction of active power filter principle, harmonic current detection and tracking control. After that, the parameter design, open-loop characterization and simulation verification of the proposed filtering control scheme are carried out. The PSCAD simulation results show that the active filtering control scheme proposed in this paper can effectively reduce the harmonic content in the system and has good stability.

Investigation of power quality issues in 14-bus electrical network with high penetration of renewable generation

Power quality issues arise in electrical networks when variable renewable energy (VRE) is integrated into them due to their random and intermittent nature which depends on weather conditions and other factors. The variation of solar irradiance throughout the day affects the energy produced by solar panels and the integration of solar power into electrical networks will result in changes and fluctuations in the voltage profile of buses. Reactive power compensation is required to improve the bus voltage levels of the electrical network to be within the required limits and the optimal allocation of reactive power compensation devices in the network is a complex problem to be investigated for the optimum injection of reactive power to obtain better voltage profiles for the entire network. This research investigated the penetration of variable solar energy into an electrical network in terms of voltage and reactive power flow. A variety of literature was reviewed in the scope of reactive power management in power systems and a gap in addressing the optimal allocation of compensation devices in the IEEE-14 bus was addressed based on the proposed methods followed by discussions of the results in terms of voltage profiles and reactive power flow in the buses. The objective is to produce an output power of higher quality and reliability for the loads so that intermittent sources of renewable energy can be more competent with energy sources such as fossil fuels that do not depend on weather conditions. Integration of methods using compensation optimisation (optimal allocation of capacitors) and volt-var regulation (smart inverter) to improve the voltage profile that was dropped and the fluctuations after penetration of solar power were carried out. A solar bus with variable energy generation was connected to the IEEE-14 bus to study the voltage variations. This was executed by the power flow calculation module to determine the voltages and reactive power in the buses of the network. With the optimum allocation of the capacitors, the voltage levels in all weak buses of the IEEE-14 bus were increased to be between 0.95 p.u. and 1.05 p.u. which was the voltage specifications of the Malaysian Grid Code Requirements. The voltage for every weak bus in the IEEE-14 bus showed a rise of 5.7% from 7 a.m. to 12 p.m. With that, the volt-var function was used for reactive power regulation at the point of common coupling (PCC) and a reduction of voltage deviation of 2.828 to 1.3% in the IEEE-14 bus was observed. The average voltage profile of all buses managed to attain a value of 98.99% from 95.673% (with solar power) with the optimal allocation of capacitors and volt-var regulation. The beneficiaries of this project will be the Sustainable Energy Development Authority (SEDA) which administers the Net Energy Metering (NEM) scheme and Tenaga Nasional Berhad (TNB) which is the Malaysian multinational electrical company focused primarily on the generation, transmission, and distribution of electricity in Peninsular Malaysia. The Energy Commission and Ministry of Energy and Natural Resources are also beneficiaries as they carried out a competitive bidding programme for large-scale solar (LSS) known as the LSS@MEnTARI or LSSPV4 to attain bids for the development of around 1000 MW AC of LSS power plants to be operational in Malaysia by 2022. This work will also be beneficial in future research in planning reactive power compensation devices in networks of multiple VRE sources, communication, and coordinated control of smart inverters, and incorporation of these devices for smart grid applications.

Collaborative Disturbance Rejection Voltage Control Technology for Distribution Stations under Distributed Resource Coordination

In order to improve the stability of the voltage in the distribution system, a distributed resource coordination-based coordinated anti-interference voltage control technology for distribution stations is proposed. The study analyzes the anti-interference capabilities of different types of renewable energy, energy storage, electric vehicles, and control distributed photovoltaic grid-connected inverters based on the analysis results. The objective function and constraints of voltage control are set. Voltage control is performed by adjusting the photovoltaic inverter and reactive power compensation device. The experimental results show that the proposed method can achieve stable control of system voltage under both photovoltaic output fluctuations and load fluctuations, indicating that its control effect is good.

Research on Reactive Power Coordination Control Strategies of Multi-Infeed Line-Commutated Converter–High-Voltage Direct Current Systems

For a receiving-end power grid with multi-infeed LCC-HVDC systems, simultaneous commutation failures may seriously threaten the safe and stable operation of the system. To evaluate the impact of commutation failure and improve the voltage stability of the commutation buses in multi-infeed HVDC systems, this paper proposes a method for evaluating the voltage stability of commutation buses and a reactive power coordination control (RPCC) method for commutation failure of multiple HVDC systems. Firstly, three indicators and the entropy weight method are adopted to comprehensively evaluate the voltage stability of commutation buses. Then, an RPCC method is proposed to resist commutation failure. The proposed RPCC method uses the voltage interaction factor (VIF) to screen out DC systems that are strongly related to dynamic reactive power compensation devices and activates the devices to provide RPCC to the DC systems through an auxiliary controller. Finally, the effectiveness of the proposed method is verified through a practical example of the Jiangsu power grid.

A New Control Strategy of Hybrid Reactive Power Compensation System in Distribution Network

Reactive power compensation is an important measure to improve the power quality of distribution networks, especially with the increasing connection of distribution transformers, heavy industrial electrical equipment, and asynchronous motors, which generate a large amount of reactive power demand. Traditional reactive power compensation devices, such as fixed capacitors (FC) and thyristor switched capacitors (TSC), have some drawbacks, such as low response speed, harmonic generation, and switching shock. A static synchronous compensator (STATCOM) is a flexible AC transmission system (FACTS) device that can provide fast and continuous reactive power compensation, but it also has some limitations, such as high cost, large capacity requirement, and low utilization rate. Therefore, hybrid reactive power compensation systems that combine FC or TSC with STATCOM have attracted much attention in recent years. Many researchers have proposed and studied different topologies and control methods of hybrid systems to overcome the disadvantages of single devices and achieve better performance. However, most of the existing hybrid systems are designed for low or medium-voltage distribution networks, and their performance under high-voltage distribution networks is still unclear. Moreover, the coordination control strategy of the hybrid system and its subsystems is also a key issue that affects the effectiveness and efficiency of reactive power compensation. In view of this, this paper aims to propose a TSC+STATCOM hybrid reactive power compensation system for high-voltage distribution networks, which optimizes the shortcomings of traditional reactive power compensation devices. The system uses the synergistic effect of TSC and STATCOM to achieve large-scale static reactive power and small-scale dynamic reactive power compensation and adopts a switching strategy based on an expert decision system. This paper introduces the working principle of each subsystem of the hybrid reactive power compensation system in detail and builds a simulation model of the hybrid reactive power compensation system under a high voltage distribution network on Matlab/Simulink platform. The simulation results verify the feasibility and excellent performance of the system control method in reactive power compensation and improving power quality.

Volt-Var Control for Utility-Scale Solar PV Plants to Downsize SVCs and Curtailment Effects

One way to increase solar photovoltaic penetration in the grid is the management of voltage fluctuations. This is because a photovoltaic plant cannot be interconnected to the grid if it causes voltage violations. Voltage violation is where voltage exceeds the acceptable range. Often, grid operators request photovoltaic plant owners to regulate voltage sufficiently with expensive and space-consuming static Var compensators. Unfortunately, this sometimes makes the project less feasible. This paper argues that there are better ways to regulate voltage. It also asserts that these ways must be sought before blindly procuring a static Var compensator or seeking battery storage. We simulated with a 70-MW photovoltaic plant as an addition to the grid. Without voltage regulation, voltage violations in Spring were found to be particularly significant. However, the proposed reactive power compensation removed all voltage violations smartly. Furthermore, the study results demonstrated that the operator-induced curtailment effectively reduced the necessary amount of reactive power compensation, leading to a smaller size of SVC, as it occurred specifically at certain overvoltage points. This paper argues that the economic and spatial efficiency of reactive power compensation devices is key to increasing photovoltaic penetration. It argues that one-sided bearing of the cost of reactive compensation devices is inefficient.

Optimal Configuration of Reactive Power in Distribution Network with Power Electronic Transformer

Traditional means of reactive power regulation are limited to adjusting the ratio of the On-Load Tap Changer or changing the access position of the reactive power compensation device and its access capacity. In order to save the cost of putting in reactive power compensation devices, this paper proposes to use the characteristics of the reactive power output function on both sides of the power electronic transformer to regulate the system reactive power distribution. For this purpose, a reactive power optimization model including distributed power supplies and power electronic transformers is constructed with the objectives of minimizing voltage excursions, maximizing voltage stability margins and minimizing active losses in the network. At the same time, based on the characteristics of decision variables, cross-feedback hybrid optimization algorithm is used to solve different types of variables, and an improved wolf pack algorithm using Tent chaotic map and Levy flight strategy is proposed to improve the solution efficiency of the algorithm. The experimental results conclude that the proposed model and algorithm are valid, and the algorithm has significant advantages in terms of model solution time and global search capability when compared with the traditional Wolf Pack algorithms and Particle Swarm Optimization algorithms.

Research on Reactive Power Optimization Control Method for Distribution Network with DGs Based on Improved Second-Order Oscillating PSO Algorithm

With the increasing penetration of distributed generation (DG) in the distribution network, the original network structure of the distribution network has been changed. In addition, the randomness and intermittency of renewable power generation will also have an impact on the voltage and power flow of the distribution network. To solve this problem, this paper proposes a reactive power optimization control method for distribution network with DGs based on second-order oscillating particle swarm optimization (PSO) algorithm with a constriction factor. Considering the economic operation of the distribution network, the proposed control method realizes the coordinated operation of the DGs and battery group with the conventional static reactive power compensation device, so as to improve the voltage quality of the distribution network and reduce the system network loss. At the same time, an improved second-order oscillating PSO algorithm is proposed to improve the speed and convergence of the multiobjective algorithm. Finally, the effectiveness of the proposed control method is verified by using MATLAB/Simulink on IEEE 33 bus distribution network with DGs in both static and dynamic situations.

Selection of the Parameters of Reactive Power Compensation and Harmonic Filtering Devices for an HVDC Transmission System Based on Voltage Source Converters

This article describes a method for selecting the parameters of AC and DC filters for a multi-terminal HVDC transmission system based on voltage source converters (VSC-HVDC). The equivalent circuit model of a multi-terminal VSC-HVDC system with the parameters ±500 kV and 500 MW was developed in the Matlab Simulink software package and presented in d-q coordinate axes. The system voltage source converters in the model were controlled using a three-level pulse-width modulation (PWM) to reduce the level of current and voltage higher harmonic components and decrease the capacity of AC and DC filters. To select the most efficient filter for use as part of a multi-terminal VSC-HVDC system, high-pass filters (HPF) and low-pass filters (LPF) were considered.

A Consideration of the Single-Phase Photovoltaic and Energy Storage Joint Regulation of a Three-Phase Unbalanced Control Strategy in a Power Distribution System

With a large amount of distributed power and energy storage access, the traditional three-phase unbalanced treatment of a power distribution system is mainly aimed at the three-phase unbalance of a load, which cannot effectively address the three-phase unbalance problem of a power distribution network after a large number of single-phase photovoltaic access. Therefore, this paper proposes a three-phase unbalanced treatment strategy for the distribution network, which considers the joint regulation ability of single-phase photovoltaic and energy storage and the regulation ability of a reactive power compensation device. Firstly, the joint regulation ability of single-phase photovoltaic and energy storage under different photovoltaic permeability is analyzed. Secondly, according to the joint regulation ability of single-phase photovoltaic and energy storage and the regulation ability of reactive power compensation device, the three-phase power optimization model is constructed to minimize the three-phase unbalance degree and regulation cost, and the JAYA optimization algorithm is used to solve the model. Finally, the 33-node distribution system is used to verify the effectiveness of the proposed strategy.

RESEARCH OF VALVE MOTOR CONVERTER CONTROL METHODS

A technique for selecting the electrical equipment of a valve motor with machine commutation has been developed, which takes into account the ways of controlling the inverter. The installed capacity of the electrical equipment of the valve motor (VD) is determined by technological requirements and depends on the structure of the converter, the method of commutation of the converter keys and the methods of controlling the inverter. The use of autonomous inverters with artificial switching, the keys of which are switched due to the reactive energy accumulated in additional switching devices, increases the utilization factor of the synchronous machine. However, in this case, the circuit becomes more complicated and the installed power of the converter increases. The use of IGBT transistors and IGCT thyristors leads to a significant increase in the cost of the equipment.
 To reduce the influence of the rectifier VD on the network and match the drive voltage with the supply voltage, a matching transformer and reactive power compensation device may be needed. The amount of power of this equipment is affected by the method of controlling the rectifier, the nature of the engine load and the range of speed changes.
 Voltage regulation of the rectifier can be symmetrical or asymmetrical. Several methods of asymmetric regulation are known, among which one of the most expedient is alternating. In the case of alternating control in the three-phase bridge circuit, an artificial zero circuit is created, as a result of which the duration of the current flowing through the secondary windings of the transformer becomes less than 2/3 of the half-cycle of the supply voltage. In addition, the energy indicators also increase, in particular, the reactive power consumption decreases and the shift and power coefficients increase.

Reliability enhancement of radial distribution system by placing the reactive power compensators and distribution systems

Distribution systems (DSs) are highly stressed with addition of newer loads like electric vehicle charging stations and lower scope for expansion due to urbanization. Any line outage could cause interruption to major loads. Reliability studies have gained importance for lowering the frequency and lowering the duration of interruption for supply systems. In this paper a bi-stage method for optimum placement of reactive power compensation devices and distributed generations (DGs) for enhancing voltage stability and system reliability. A new method named delta analysis method is used to optimally locate the reactive power compensation devices and DGs. IEEE-33 radial DS, which is taken as experimental system. Based on the study, the fixing of reactive power compensation devices and DGs are to increase voltage outline of buses and decrease power fatalities. After the placement of DGs, the enhancement in reliability indices following line contingency is studied using MATLAB simulation.

A two-stage coordinated line loss reduction model based on elephant herding optimization and second-order cone programming

Aiming at the problem of high line loss caused by the access station of distributed generation (DG), a two-stage coordinated line loss reduction model based on elephant herding optimization (EHO) and second-order cone programming (SOCP) was put forward by using static var generators (SVG) and energy storage system (ESS) to reduce the line loss from reactive and active power aspects, respectively. Firstly, based on the elephant herding optimization, the location model of distributed generation, SVG and ESS was constructed and determined. On this basis, a cooperative line loss reduction model is proposed, which takes into account multiple line loss reduction methods, such as SVG reactive power compensation device and energy storage. By properly dealing with power flow constraints of distributed generation, the influence of operation control mode of distributed generation on optimal distribution and line loss reduction is precisely explained. The constraint is transformed into a second-order cone programming problem by using second-order cone relaxation. In this way, the coordinated reduction of line loss is realized, and the goal of line loss minimization and voltage stability maximization is achieved. Finally, a practical station is taken as an example to verify the correctness of the proposed model and algorithm and the effectiveness of the proposed method.

Improvement of Grid-connected Reactive Power Compensation for Wind Farms Based on STATCOM

Due to the recent rapid development of wind power generation, people have higher requirements for the stability of wind power systems. The randomness and intermittency of wind farms are strong. When the system is disturbed, or the line fails, it is easy to cause voltage instability. In order to ensure the stable operation of the power system, it is necessary to set up a static reactive power compensation device (STATCOM) to provide reactive power in the power system. This paper simulates and analyzes the wind power generation system with a STATCOM device. The results show that the operation process of the wind power system with STATCOM is more stable.

Research on temperature rise test of low voltage reactive power compensation device

Research on temperature rise test of low voltage reactive power compensation device

Nonlinear Transient Mathematical Model of Large-Capacity Synchronous Condenser Based on Time-Varying Reactance Parameters

Large-capacity synchronous condenser (SC) is an essential dynamic reactive power compensation device in an Ultra-high voltage direct current (UHVDC) transmission system. The particular transient operating state and structural characteristic of SC lead to a severe magnetic saturation effect during transient operation. To accurately describe the dynamic characteristics of SC, it is urgent to establish a transient mathematical model considering the magnetic saturation effect. Therefore, this paper proposes a nonlinear transient mathematical model for SC based on time-varying reactance parameters and gives a calculation method for time-varying reactance parameters. The mathematical model proposed in this paper is verified by taking a 300MVar SC as the research object. This condenser is connected to the power grid at the sending end of the UHVDC transmission system. The proposed mathematical model, the traditional fixed-parameter transient mathematical model, and the saturated standard SG model used in the power system were used to simulate the voltage generated by dynamic reactive power compensation characteristics of SC during a drop failure. Compared with the fault test results, the accuracy of the proposed mathematical model is verified. The effect of magnetic saturation on the dynamic reactive power compensation characteristics was analyzed, respectively. In addition, the accuracy of the proposed mathematical model is closer to the actual motor state, which is helpful for further research on the operation analysis and state monitoring of SC.

A meta-heuristic optimization-based method for parameter estimation of an electric arc furnace model

Throughout distribution systems, it is usual to find non-linear time-varying loads, such as electric arc furnaces (EAFs), which are widely used in the steel-making industrial sector. Due to the process of melting and refining metals, the EAFs consume large blocks of power (active and reactive power) causing significant power quality disturbances, such as harmonics and voltage fluctuations on distribution networks. Different EAF parametric models have been proposed with the purpose to predict the voltage and current waveforms and then evaluate the performance of the reactive power compensation devices. This paper proposes a novel methodology for the optimal estimation of parameters of an electric arc furnace model, which can achieve lower execution times and error rates compared to some state-of-the-art methods. The methodology was evaluated using three meta-heuristic optimization algorithms such as the particle swarm optimization (PSO) algorithm, the vortex search algorithm (VSA) and the crow search algorithm (CSA); using real and simulated data. From the results, the proposed methodology based on meta-heuristic optimization approaches worked efficiently, allowed estimating the parameters of the electric arc furnace model using a single optimization step, capture the non-sinusoidal, non-linearity and time-varying random behavior that exhibit the real electric arc furnace samples and obtained relative errors of the total harmonic distortion between the measured and estimated voltage and arc current signals around 1.23% and 0.62%, respectively.

Improved transient stability of virtual synchronous generators for grid voltage cascading faults

• The basis of the investigation is a cascading fault of a grid-connected inverter in both low and high voltage power grids. • Pay attention to the fault with equilibrium point and the fault without equilibrium point while dealing with low-voltage faults, and utilize the phase portrait to assess stability. Finally, a control technique is given to ensure that the two defects are well controlled. • The equal area method is utilized to assess the fault in high voltage faults, and it is inferred that there must be an equilibrium point in high voltage faults. Finally, a control technique for active power transient overshoot mitigation and PCC voltage support during faults is provided. The topic of VSG grid voltage fault ride through has drawn increasing attention as virtual synchronous generator (VSG) technology has been widely applied in the field of renewable energy power generation. Due to the delay of the reactive power compensation device after the low-voltage fault recovery, the high-voltage fault will happen immediately after the grid's low-voltage fault is resolved. This phenomenon is known as low and high voltage cascading faults. There is not enough research on this specific voltage fault right now. For specific investigation, the low and high voltage cascading faults in this paper are separated into low-voltage fault stages and high-voltage fault stages. The equal area criterion (EAC) is used to analyze the specific process at the low-voltage fault stage. In addition, the dynamic damping control (DDC) is utilized to resolve the problem of low-voltage fault stability. Under low voltage fault, the phase portrait studies the single-period stability with an equilibrium point in a single-period and the multi-period stability without an equilibrium point in a single-period, respectively. Using a phase portrait to analyze system performance during a high voltage fault, and a virtual capacitor feedback control (VCFC) is offered to effectively reduce active power overshoot due to high voltage fault. The EAC is used to analyze the specific process of the high voltage stage, it is concluded that there is always an equilibrium point in the high-voltage fault where IGBT limitations are ignored. Finally, the correctness and feasibility of the theory are verified by simulation, and the specific analysis results are given.