Hybrid Reactive Power Compensation Research Articles

Influence of Ultra-High-Voltage hybrid reactive power compensation on interruption performance of circuit breakers under different faults

For extremely large ultra-high-voltage (UHV) power transmission and distribution lines with typical project using hybrid reactive power compensation (HRPC), single-phase earth fault (1LG), three-phase ground fault (3LG), phase-to-phase fault (2LS), and two-phase grounding fault (2LG) often occurs. Circuit breaker is one of the most critical equipment of UHV transmission system. And the interruption performance is crucial to circuit breakers’ breaking capability. In this study, formal expressions of the indicators for the interruption performance of the circuit breaker are deduced in case of different faults based on the equivalent-valued parameter circuit based on the structure a UHV demonstration project. The simulations are used to validate the accuracy of formal expressions. Then, the influence of such factors as the location of the fault and the degree of HRPC on the interruption performance of the 1LG, 2LG, 3LG, and 2LS is analyzed. Finally, the interruption performance of circuit breakers under different faults are compared. A quantitative evaluation of the influence of changes in the relevant indicators on the interruption performance of circuit breakers can provide a technical basis for choosing the appropriate design of the circuit breaker in light of the application as well as equipment development and assessment.© 2017 Elsevier Inc. All rights reserved.

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.

Research on Control Strategy of Hybrid Reactive Power Compensation System for Wind Farms

With the increasing scale of wind farms and the increasing proportion of wind power generation in the energy system, the grid has higher and higher requirements for the voltage stability of wind farms. In this paper, we propose a hybrid reactive power compensation system and its control strategy for weakly connected asynchronous wind farms, which can effectively control the compensation cost while improving the continuity of reactive power regulation. It also verifies the correctness and feasibility of the proposed hybrid reactive power compensation system and its control strategy through simulation.

The ping-pang variable amplitude limiter used in the coordinated controller of a hybrid reactive power compensation system

The hybrid reactive power compensation system, which connects different reactive power compensation devices to the same bus, will be essential equipment for future power systems. In a power grid with a high proportion of photovoltaic, wind turbines, and power electronic devices, it is significant to design a coordinated control strategy for the hybrid reactive power compensation system. In this paper, a kind of ping-pang variable amplitude limiter is used in the linear optimal controller. The ping-pang variable amplitude limiter can improve the transient stability of a hybrid reactive power compensation system. The effects of the coordinated controller are verified in simulation. Compared with the conventional linear optimal controller, the coordinated controller with the ping-pang variable amplitude limiter has a better optimization effect in large disturbance conditions.

Study on Very Fast Transient Overvoltage Characteristics of Gas-Insulated Switchgear Substation Based on Hybrid Reactive Power Compensation

In recent years, gas-insulated switchgear (GIS) substations have become widely used in power systems. Due to their compact structure, extremely high oscillation frequencies are prone to extremely high oscillation transient overvoltages or very fast transient overvoltages (VFTOs) when the isolating switch or circuit breaker is operated. The characteristics of these special fast transient processes in GIS and the effect of hybrid reactive power compensation (HRPC) on these fast transient processes were studied. A simulation of the GIS model was established, and based on the transient model of HRPC and the theory of the transmission line, the effects of VFTO produced by HRPC switching operation and the parameters of HRPC on VFTO were studied and the differences in the characteristics of VFTOs in substations with or without HRPC. Based on the conclusions of our study on the influence of HRPC on VFTO, the inhibitory effects of a ferrite magnet ring and an inhibitor busbar on VFTO were verified.

Improved Hybrid Reactive Power Compensation System Based on FC and STATCOM and Its Control Method

The purpose of this study is to solve the main problems in distribution networks, including increased line loss and reduced power supply quality caused by insufficient capacitive reactive power. To reduce the capacity, voltage, and current stress of an active module of a compensation device and improve the cost performance of the device, an improved hybrid reactive power compensation system based on a fixed capacitor (FC) and a static synchronous compensator (STATCOM) is proposed. The topological structure and basic operating principle of the proposed reactive power compensation system are introduced. In addition, from the perspectives of output voltage, current, power, loss of the active part, and system compensation cost, the performances of the proposed reactive compensator and the inductively coupled STATCOM (L-STATCOM) are compared and analyzed. Furthermore, the key parameters of the proposed system are designed, and the joint optimization control strategy of the FC and STATCOM is studied. The correctness and effectiveness of the proposed topology structure and control method are verified by simulations.

Investigation of GIS enclosure circulating current in UHV substation with hybrid reactive power compensation

There are typically large circulating current losses when such a current is produced in a gas-insulated switchgear (GIS). An excessive circulating current also causes a heating phenomenon and insulation aging, as well as hidden dangers and adverse effects on the normal operations of power systems. In addition, the installation of hybrid reactive power compensation (HRPC) may increase the complexity of the circulating current. Thus, a detailed investigation of GIS enclosure circulating current on an ultra-high-voltage (UHV) substation with HRPC is imperative. Here, the mechanism of the enclosure circulating current is thoroughly discussed, and models of the GIS busbar, and enclosure are established based on the partial element equivalent circuit (PEEC) method. Combined with HRPC equivalent circuit model, the equivalent calculation model for the GIS enclosure circulating current with HRPC equipment is established. The influence of the structural parameters on the circulating current, such as the inlet capacitance of the stepped controlled shunt reactor (SCSR), enclosure radius, enclosure height from the earth, and distance between earthing points, are considered in terms of the simulation model as built using transient simulation software. The factors that influence the enclosure circulating current and their associated rules are used to develop suppression measures.

Simplified Modelling of Transient Ground Potential Rise of GIS in Ultra-high-voltage Substations with Hybrid Reactive Power Compensation

The application of hybrid reactive power compensation (HRPC) in ultra-high-voltage substations has a nonnegligible impact on the characteristics of transient ground potential rise (TGPR) in the gas-insulated switchgear (GIS) enclosure. In this paper, according to the principle of series compensation and stepped controlled shunt reactors under a very fast transient overvoltage, a simplified model of an HRPC device is established. Based on the generation mechanism of TGPR and the theory of transmission lines, the equivalent simulation circuit of GIS in a substation is designed under the occurrence of TGPR. Simulation experiments comparing the characteristics of TGPR with and without HRPC are conducted to explore the factors that influence TGPR. This paper proposes specific methods of reducing TGPR, and provides a theoretical basis for the construction of GIS protection devices for ultra-high-voltage substations.

Impact of the hybrid reactive power compensator on the power grid used a fuzzy PI regulator

The work presented in this article is a contribution to the problem of controlling reactive powers and voltages in an electrical network. Among these control tools, the static reactive power compensator (SVC) was chosen because of its simplicity of control. SVC is one of the Alternative Flexible Current Transmission Systems (FACTS) devices which help to solve the problems encountered in the operation of electrical networks, either on the distribution side or on the transport side. To increase its compensation efficiency in the face of harmonic currents which cause voltage distortion, we have introduced a three-phase harmonic filter. This new hybrid SVC is used to control the reactive power, the voltage and in addition to reduce the voltage distortion and the correction of the power factor in the electrical energy transport network. In order to improve its efficiency, two voltage regulation systems have been chosen in the control system for this compensator, the fuzzy PI regulator and the PIP regulator.

New energy grid-connected power quality management system based on internet of things

As a clean and renewable energy source, solar energy has the advantages of inexhaustible, pure and pollution-free. Photovoltaic power generation is different from traditional thermal power generation in that it is more susceptible to external environmental factors. In addition, there are a large number of power electronic devices in the entire system. These various factors will bring a significant shock to the grid power quality after grid connection. The research of grid-connected power quality system is becoming more and more important. A series of researches are carried out around a complete three-phase photovoltaic grid-connected system, which are modeled separately, connected to the distribution network for simulation analysis, and analyzed the power quality impact on the distribution network. Based on the traditional disturbance observation method, this paper proposes a new MPPT algorithm that combines the constant-voltage tracking method with the three-point comparison method (an algorithm derived from the traditional disturbance observation method). This complete three-phase photovoltaic grid-connected system was connected to an IEEE 14-node distribution network, and the impact of grid-connected capacity and grid location on the power quality of different nodes in the distribution network was analyzed. An improved power management scheme is proposed. Finally, the paper analyzes the improvement of power quality by connecting a group of hybrid reactive power compensation device which is composed of static reactive power compensator and shunt capacitor. The results show that the voltage deviation is reduced and the harmonic content is reduced. It can be considered that this measure has achieved the purpose of power quality control to a certain extent.

Influence of UHV hybrid reactive power compensation on interrupting characteristics of circuit breakers in the event of phase-to-phase faults

This paper presents a theoretical study of the interrupting characteristics of circuit breakers in the event of phase-to-phase faults in UHV transmission lines with hybrid reactive power compensation (HRPC). The study uses the transmission line parameters of the Jindongnan–Nanyang–Jingmen UHV AC pilot demonstration project in China and establishes a simplified model for the distribution parameters of transmission lines. Mathematical expressions describing the relationships between circuit breaker interrupting parameters and compensation degrees of HRPC are derived. Based on these mathematical expressions and their comparisons with simulation results, the effects of HRPC on circuit breaker interrupting characteristics and on the parameters of the phase-to-phase fault circuit are determined, in which case the validity of the analytical method is verified. The results of this study will provide a theoretical foundation for practical implementation of HRPC in UHV transmission.

Research on Dynamic Hybrid Compensation Technology and Device in Low Voltage Distribution area of Transformer

In order to solve the problem of three-phase unbalance and low power factor caused by distributed power supply to low-voltage distribution network, a hybrid reactive power compensation system based on “intelligent capacitor +SVG” is designed. The system is composed of a small capacity Static Var Generator (SVG) with high precision compensation and several smart capacitors. Firstly, the structure of three-level SVG in the hybrid compensation system is analyzed, and the two-level SVPWM vector synthesis method is applied to three-level compensation. The control mode of intelligent capacitor is analyzed. Then the principle of reactive power distribution in hybrid compensation system is analyzed. Finally, a hybrid reactive power compensation system is designed with TMS320F28335 as the core controller of the hybrid system. The experimental results show that the hybrid reactive compensation system can effectively compensate the reactive current dynamically.

A Practical Structure and Control for Reactive Power Sharing in Microgrid

Due to the uncertainty of feeder impedance, conventional droop control-based power sharing scheme presents poor reactive power sharing accuracy in microgrid. As microgrid configuration becomes more and more complicated, reactive power sharing between various distributed generation (DG) equipment is very challenging. To achieve proper power sharing with a simple control method in microgrid, a new structure and power sharing method is proposed in this paper. Instead of using complicated reactive power sharing scheme, this paper proposes separated energy server (ES) units to provide reactive power. Then, active power supplying and reactive power supplying can be achieved separately by energy routers (ERs) and ESs, respectively. With the introduction of ES, the power sharing between DG units can be easily achieved without any supplementary communications or control algorithms. In addition, to reduce costs,a hybrid reactive power compensation configuration with capacitor banks and ESs is provided. Operation principle and power control strategy for DG units and ESs are explained and analyzed in this paper. In order to properly select the coefficients of the power controllers, sensitivity and stability of the system are investigated. Simulation and experimental results are presented to prove the validity of the proposed power sharing method, showing that ERs can effectively share the active power and ESs can effectively share the reactive power according to their capacity.

Multi-variable dependent forecast algorithm for predicting secondary arc characteristics in UHV systems with HRPC

Hybrid reactive power compensation (HRPC) combines step-controlled shunt reactors and series compensation, and will be employed in ultra-high-voltage (UHV) power systems. The single-phase auto-reclosure characteristics of secondary arcs in systems with HRPC require further investigation. In this paper, both the arc-recalling voltage and subsidiary variations in arc current are investigated with and without HRPC. The frequency components of the secondary arc current and variations in arcing time are analyzed for various influential factors, such as the neutral reactor, arc resistance, fault location, degrees of compensation of HRPC, and the length of the transmission line. The non-dominated sorting genetic algorithm II (NSGA-II) and support vector machine regression are combined to create a multi-variable dependent forecasting algorithm to predict the characteristics of the secondary arc in UHV systems with HRPC. This paper provides a theoretical reference for optimizing the parameters of HRPC, and for developing adaptive auto-reclosure schemes and protection equipment.

Characteristics of very fast transient currents in ultra high-voltage power system with Hybrid reactive power compensation

Hybrid reactive power compensation (HRPC) consists of a stepped controlled shunt reactor (SCSR) and a series compensation (SC), which will find applications in future ultra high-voltage (UHV) power grids to resolve the problems due to the frequent change of reactive power and bulk power transmission. However, very fast transient currents (VFTCs) are inevitably generated during switching, which would lead to insulation breakdown. In the present work, we first develop the equivalent model for HRPC, following which we deduce the expression of VFTCs in the time domain by using an inverse Laplace transform. The analysis indicates that the amplitude and frequency of VFTCs are both affected by the capacitance of the SCSR and of the SC, as well as the line length, stray capacitance, etc. The oscillating frequency, peak, and amplitude of the main frequency of the VFTCs in the substation can be modified by adjusting the silicon-controlled rectifiers in the SCSR when the disconnecting switch in gas-insulated switchgear is switched on. When the disconnecting switch in the SC is switched on, the VFTC oscillation frequency in SCSR decreases with increasing stray capacitance of SC, but the frequency and peak of the VFTC remains quite large. Increasing the line length between the SC and the SCSR suppresses the VFTC in UHV power systems. These results lay the foundation for developing HRPC methods to suppress VFTCs in UHV substations.

Circuit Breaker Rate-of-Rise Recovery Voltage in Ultra-High Voltage Lines with Hybrid Reactive Power Compensation

With the development of ultra-high voltage (UHV) technology, hybrid reactive power compensation (HRPC) will be widely applied in the future. To study the mechanism by which HRPC influences the characteristics of circuit breakers in UHV transmission lines, this paper establishes an improved electromagnetic coupling transmission line model for out-of-phase and short-line faults. Based on the HRPC equivalent model, a simulation analysis was performed on the characteristics of the circuit breaker when a fault occurs. Using an equivalent lumped parameter circuit, the rate-of-rise of recovery voltage (RRRV) computational formula was deduced and computed. The RRRV variation in the circuit breakers in the system, with and without HRPC, was obtained. Given the circuit breaker interruption characteristics, the research results provide an analysis foundation and a theoretical basis for optimizing the HRPC parameters and selecting the arrangements of circuit breakers in an UHV transmission line.

Influence of Hybrid Reactive Power Compensation on the Secondary Arc of Ultra-High-Voltage Transmission Lines (May 2018)

Hybrid reactive power compensation (HRPC) which consists of series compensation and a stepped-controlled shunt reactor will see use in China's future ultra-high-voltage (UHV) transmission system. As a result, some new characteristics of the secondary arc during a single-phase-to-ground fault on UHV transmission lines with HRPC may be raised. In this paper, the secondary arc characteristics during the single-phase auto-reclosure (SPAR) operation have been simulated with regard to the UHV AC system installed with HRPC. Based on the UHV system model with HRPC and its secondary arc model, the influence mechanism of HRPC on secondary arc current is theoretically derived with the simulated waveforms and the Fourier analysis. Besides, the relationship among the secondary arc current, the arcing time with different HRPC compensation degrees, neutral reactance, as well as the grounding fault locations have been investigated in detail. Finally, an improved time sequential control strategy of bypass breaker and SPAR has been put forward. The research presented in this paper will provide necessary theoretical basis and technical support for the future application of HRPC in UHV transmission lines.

Influence of ultra‐high‐voltage hybrid reactive power compensation on the interrupting characteristics of CB at out‐of‐phase faults

The influence of hybrid reactive power compensation on the interrupting characteristics of circuit breakers (CBs) after out-of-phase interruptions has been analysed in this study. Comprehensive and accurate computations to compute the interrupting current, the transient recovery voltage (TRV) and the rate of rise of recovery voltage (RRRV) are provided. The computation results match the simulation results well and can provide valuable theoretical reference to evaluate the TRV of CBs at out-of-phase fault conditions. It can be concluded from the test results that the overvoltages can be effectively suppressed by installing opening resistor, but cannot be restrained when metal–oxide arresters are used or the compensation degrees of controlled shunt reactors are rapidly increased.

Three‐layer coordinated control of the hybrid operation of static var compensator and static synchronous compensator

Aiming at the problems that static var compensator cannot suppress the voltage flicker and the cost of static synchronous compensator is expensive, a three-layer hybrid reactive power compensation scheme was proposed in this study based on the expert-decision, differential-slope voltage regulation, and the expert-decision subsystem combining with fuzzy self-tuning proportional–integral (PI) control. By switching in a dynamic load which can always change the bus voltage, the whole system was simulated under the much reactive power shortage and the less shortage. The simulation results verify the effectiveness of the proposed coordinated control method in the reactive compensation and the suppression of the voltage flicker.

A Novel 3-Phase Hybrid Harmonic and Reactive Power Compensator

The application of shunt active filters for the harmonic and reactive power compensation in the high power range is mainly restricted because of their low efficiency and the high cost of inverters with high switching frequency. Moreover; the compensation effect is completely lost in case of internal fault in active filter. Hybrid active filters as the combination of a low power PWM inverter and passive filters have been researched and developed to overcome the limitations of shunt active filter. However, they do not have control over fundamental reactive power. This paper proposes a new hybrid active compensator for harmonic and fundamental reactive current compensation, which consists of two small-rated active filters and one bank of passive filters. Simulation and experimental results are presented to show the advantages of the proposed compensator topology.