Reactive Power Compensation Capacity Research Articles

Study on fast transient overvoltage characteristics of substation under UHV disconnector operation

Abstract Due to the short duration of fast transient overvoltage in the substation, the suppression effect under the control strategy of traditional optimization equipment and switches is not good. Therefore, the characteristics of fast transient overvoltage in substation under the operation of a UHV disconnector are proposed. The fast transient condition of the substation is analyzed, the corresponding simulation method is set, and it is simulated. The elimination operation is carried out by using the reverse sequence backtracking formula, and the relevant parameters of the fast transient condition simulation of the substation are obtained. The inductance of the substation is calculated in the fast transient process, the potential in the equivalent circuit is obtained by using the capacitance and inductance, and the reactive power compensation capacity on the electromagnetic transient model of the fast transient process is comprehensively considered, so as to calculate the rapid transient overvoltage of the substation and realize the research on overvoltage characteristics. The method in this paper can ensure the rapid transient overvoltage level decline, successfully realize the automatic voltage regulation, effectively maintain the stability of voltage, and effectively restrain overvoltage to keep it within an acceptable range.

Collaborative Control of Reactive Power and Voltage in a Coupled System Considering the Available Reactive Power Margin

This article proposes a hierarchical collaborative reactive power and voltage control method aimed at meeting the internal voltage requirements of a coupled system composed of centralized new energy stations such as wind and solar power and traditional thermal power units, with particular attention paid to the reactive power regulation ability of power units in new energy stations. This method is implemented in two layers: At the transmission layer, the overall reactive power compensation capacity of thermal power units and stations on the transmission lines within the system is determined according to the engineering requirements of different node voltages in the coupled system, the regulation voltages of the high-voltage grid-connected points and the point of common coupling (PCC) of the stations are found, and the actual regulation voltages of the PCCs of the stations are given as commands. At the station layer, based on determining reactive power distribution between power units and continuous reactive power compensation devices within each station, voltage optimization is carried out using the voltage command issued by the transmission layer as a reference. At the same time, consistency coordination between the transmission layer and the station layer is achieved based on the Analytical Target Cascading (ATC) method at different layers. Finally, simulation analysis was conducted on a regional coupled system in Dalian. The results showed that the method proposed in this paper can effectively control the voltage safety requirements of each region and PCC in the coupled system and, to some extent, improve the economic efficiency of system operation.

Grid‐side flexibility assessment based on security distance of dispatchable region for AC/DC hybrid system using approximate second‐order cone relaxation

AbstractThe rapid growth of offshore wind power has resulted in a mismatch between generation and demand because of its variability. To quantify the maximum wind power penetration of the transmission network, the dispatchable region is defined as the largest region in the uncertainty space. The security distance is defined as the minimum distance from the operating point to the boundaries of the dispatchable region. System operators can use security distance as a metric to assess the flexibility of the power system. This paper proposes a method to construct the dispatchable region for the AC/DC hybrid system with VSC‐HVDC by outer convex relaxation firstly. The second‐order cone relaxation is employed to reformulate non‐convex and non‐linear power flow equations. Next, a polyhedral approximation is adopted to obtain the convex hull of the dispatchable region. Subsequently, an efficient algorithm known as adaptive constraint generation (Ad‐CG) is introduced to calculate the boundaries of the dispatchable region. Furthermore, solving the Chebyshev centre problem determines the minimal security distance. The modified IEEE 5‐bus and 39‐bus system is used for validating effectiveness of the proposed method and evaluating the impact of the converter reactive power compensation capacity and generation dispatch on the dispatchable region.

Coordinated control strategy of reactive power compensation based on a flexible distribution network transformer

In order to solve the problem of the power quality caused by distributed power access to the distribution network, this paper proposes a coordinated control strategy of reactive power compensation based on a flexible distribution transformer. First, the working principle of the flexible distribution transformer is analyzed, and the mathematical model of energy acquisition and the regulation converter of the flexible distribution transformer are studied as well. The device-level control strategies of energy acquisition and regulation converters are proposed, respectively. Then, in order to maintain the stability of the bus voltage and quickly respond to the reactive power changes of the system, a coordinated control strategy for the reactive power compensation of flexible distribution transformers is proposed. The priority herein is to maximize the reactive power compensation capacity of the energy harvesting converter. When the energy harvesting converter reaches the compensation upper limit, the control converter is used for reactive power compensation to further suppress the grid voltage fluctuation. Finally, it is verified through simulations that the flexible distribution transformer can realize the reactive power compensation of the distribution network and effectively improve the power quality of the distribution network.

Integrated Reactive Power Optimisation for Power Grids Containing Large-Scale Wind Power Based on Improved HHO Algorithm

Large-scale wind power grid integration will greatly change the system current distribution, making it difficult for the reactive power regulator to adjust to the optimal state. In this paper, an integrated reactive power optimisation method based on the improved Harris Hawk (HHO) algorithm is proposed. Firstly, a reactive power regulation model is constructed to solve the reactive power regulation interval of wind turbines, and the reactive power margin of wind turbines is used to participate in the system’s reactive power optimisation. Finally, a reactive power compensation capacity allocation optimisation model considering nodal voltage deviation, line loss and equipment investment cost, is established, and a reactive power optimisation scheme is obtained using the Harris Hawk optimisation algorithm on the basis of considering the constraints of the wind turbine reactive power output interval. The improved HHO algorithm is used to solve the reactive power optimisation scheme considering the constraints of tidal power, machine end voltage, a conventional generator and wind farm reactive power. In the simulation, the effects of the improved Harris Hawk optimisation algorithm and the particle swarm optimisation algorithm are compared, and the experimental results prove that compared to the particle swarm algorithm, the optimisation result of the improved Harris Hawk optimisation algorithm reduces the average loss of the system by 42.6% and reduces the average voltage deviation by 30.3%, which confirms that the improved Harris Hawk intelligent optimisation algorithm is effective in proving its superiority and solving the multi-objective model for reactive power optimisation.

English

Induction machines play an important role in popular electrical loads, leading to many relevant control methods. One of the most crucial control strategies is to design an efficient method to minimize power losses against continuous and random voltage variation. This paper proposes a novel optimal scheme to minimize power losses of loads containing 3-phase induction motors, considered critical loads of an electric power grid. The study evaluates the effects of the voltage fluctuation on the 3-phase induction AC motors, presenting an effective method to design a newly reactive power compensator. This compensated system includes decentralized compensators at each load together with a central compensator unit using only one common controller to optimize the operation and efficiency of the whole network. The paper introduces a step-by-step procedure to control reactive power compensation capacity for each induction motor, improving voltage quality at loads, reducing active power losses, and prolonging the devices' lifespan. Simulation results and experiments are also provided to demonstrate the effectiveness and applicability of the proposed method.

Research and Application of Combined Reactive Power Compensation Device Based on SVG+SC in Wind Power Gathering Area

With the increasing proportion of wind power access year by year, it brings many challenges to the voltage stability of power systems. In order to maintain the stability of the voltage in the power grid, it is impossible to take into account the regulation ability and economy when a single reactive power compensation device is installed. In this paper, a combined reactive power compensation device was installed, which is composed of a static var generator (SVG) and a parallel capacitor bank. The SVG has the characteristics of fast and smooth adjustment, and the application of the capacitor bank reduces the overall investment cost and has a great economy. The modal analysis method was used to find the optimal installation position for the reactive power compensation device. The improved particle swarm algorithm was used to optimize the capacity of the optimal reactive power compensation device to ensure the best performance of the compensation device. Finally, by formulating the control strategy of the combined reactive power compensation system, the reliable switching of the compensation device is controlled. The PSCAD simulation software was used to model the power grid in the Hami area, and six different configuration programs were set for static voltage stability simulation verification and three different configurations. The program was simulated and verified for transient voltage stability, and comparative analysis showed that the proposed method was correct, which strongly supports the voltage stability of the region and meets the demand of reactive power compensation of the power grid. This provides a good reference program for other wind power gathering areas.

Research on improving transient voltagestability of energy storage system

The transient overvoltage and voltage sags caused by DC blocking in HVDC transmission systems cause great harm to the stable operation of transmission equipment and power system. This paper analyzes the AC/DC equivalent circuit model of battery energy storage system, and deduces the calculation method of the transient voltage of the converter bus at the rectifier side when the remaining reactive power compensation capacity of the converter station is known. According to the results of regulating the transient voltage of the bus at the dc latched rear end of the energy storage station, the calculation method of reactive power of charge and discharge of the energy storage station is further derived. On this basis, the reactive power control method of regulating the transient voltage of the bus at rectifier side of the energy storage station is given. The power system comprehensive simulation program based on IEEE-39 node system is used to conduct simulation analysis to verify the correctness and effectiveness of the theoretical analysis, and the conclusion is drawn that the energy storage power station has a good regulating effect on the voltage fluctuation caused by DC blocking after being connected to the grid.

Analysis of reactive power compensation of railway 20kV primary through line

With the increase of power load along the railway and stations and the popularization and use of 20kV distribution network, it has a great impact on the selection of voltage level of railway power supply. To solve this problem, the capacity rise effect of power through line, reactive power compensation capacity configuration of 10kV and 20kV Voltage levels are calculated and analyzed, and the MATLAB simulation model is established for simulation verification.

Distributed Reactive Power Compensation Method in DC Traction Power Systems With Reversible Substations

This paper proposes a potential distributed reactive power compensation method in dc traction power systems with reversible substations. It utilizes the entire capacity of reversible substations during night hours and the reminding capacity except for regenerative braking energy feedback during day hours. A unified dispatch scheme is developed to allocate reactive power compensation capacity for each reversible substation. During night hours the entire capacity is used to accomplish the optimal power flow objective. During day hours the excess capacity after active power production is used to improve the system reactive power factor dynamically. The different objectives throughout the day are implemented in a unified formula which avoids manually change. In addition the outage of reversible substations and the low dc voltage conditions are considered and an over-modulation suppression strategy is included in the unified dispatch scheme to adjust the reactive power allocation among reversible substations. This novel utilization method of reversible substations is able to provide significant improvements in the power factor of dc traction power systems which would otherwise require expensive additional equipment such as static synchronous compensator. Finally the effectiveness of the proposed method is verified with MATLAB/SIMULINK.

Active and Reactive Power Collaborative Optimization for Active Distribution Networks Considering Bi-Directional V2G Behavior

Due to their great potential for energy conservation and emission reduction, electric vehicles (EVs) have attracted the attention of governments around the world and become more popular. However, the high penetration rate of EVs has brought great challenges to the operation of the Active Distribution Network (ADN). On the other hand, EVs will be equipped with more intelligent chargers in the future, which supports the EVs’ high flexibility in both active and reactive power control. In this paper, a distributed optimization model of ADN is proposed by employing the collaborative active and reactive power control capability of EVs. Firstly, the preference of EV users is taken into account and the charging mode of EVs is divided into three categories: rated power charging, non-discharging, and flexible charging–discharging. Then, the reactive power compensation capacity of the plugged-in EV is deduced based on the circuit topology of the intelligent charger and the active–reactive power control model of the EV is established subsequently. Secondly, considering the operation constraints of ADN and the charging–discharging constraints of EVs over the operation planning horizon, the optimization objective of the model is proposed, which consists of two parts: “minimizing energy cost” and “improving voltage profile”. Finally, a distributed solution method is proposed based on the Alternating Direction Method of Multipliers (ADMM). The proposed model is implemented on a 33-bus ADN. The obtained results demonstrate that it is beneficial to achieve lower energy cost and increase the voltage profile of the ADN. In addition, the energy demand of EV batteries in their plugin intervals is met, and the demand preference of EV users is guaranteed.

Study on Reactive Power Compensation Strategies for Long Distance Submarine Cables Considering Electrothermal Coordination

Long-distance high voltage alternating current (AC) submarine cables are widely used to connect offshore wind farms and land power grids. However, the transmission capacity of the submarine cable is limited by the capacitive charging current. This paper analyzes the impacts of reactive power compensation in different positions on the current distribution on long-distance submarine cable transmission lines, and tests the rationality of the existing reactive power compensation schemes based on electrothermal coordination (ETC). Research shows that compensation at the sending end has obvious impacts on current distribution along the cable, and the maximum current occurs at the sending or receiving end. Moreover, the reactive power compensation at sending end will reduce the current at receiving end of the line. On the contrary, it will increase the current at sending end. Compared with the directly buried laying method of the submarine cable in the landing section, the cable trench laying method can increase the cable ampacity of the landing section and reduce the reactive power compensation capacity at the sending end. The ampacity is the current representation of the thermal limits of the cable. ETC exploits the cable ampacity to coordinate current distribution on transmission lines under existing reactive power compensation schemes, thus optimizing the reactive power compensation schemes and avoiding the bottleneck point of cable ampacity.

Optimal Allocation of Comprehensive Resources for Large-Scale Access of Electric Kiln to the Distribution Network

With the significant progress of the “coal to electricity” project, the electric kiln equipment began to be connected to the distribution network on a large scale, which caused power quality problems such as low voltage, high harmonic distortion rate, and high reactive power loss. This paper proposes a two-stage power grid comprehensive resource optimization configuration model. A multi-objective optimization solution based on the joint simulation platform of Matlab and OpenDSS is developed. The solution aims to control harmonics and optimize reactive power. In the first stage, a multi-objective optimization model is established to minimize the active network loss, voltage deviation, and equipment cost under the constraint conditions of voltage margin, power factor, and reactive power compensation capacity. Furthermore, the first stage uses a particle swarm optimization (PSO) algorithm to optimize the location and capacity of both series and parallel compensation devices in the distribution network. In the second stage, the optimal configuration model of the active power filter assumes the cost of the APF as the objective function and takes the harmonic voltage content rate, the total voltage distortion rate, and the allowable harmonic current as the constraint conditions. The proposed solution eliminates the harmonics by uniformly configuring active filters in the distribution network and centrally control harmonics at the system level. Finally, taking the IEEE33 distribution network as the object and considering the change of electric furnace permeability in the range of 20%–50%, the simulation results show that the proposed algorithm effectively reduces the distribution network’s loss, its harmonic content and significantly improve its voltage.

Improved Coordinated Control Approach for Evolved CCC-HVDC System to Enhance Mitigation Effect of Commutation Failure

The evolved capacitor commutated converter (ECCC), embedded with anti-parallel thyristors based dual-di-rectional full-bridge modules (APT-DFBMs), can effectively reduce commutation failure (CF) risks of line-commutated con-verter-based high voltage direct current (HVDC) and improve the dynamic responses of capacitor-commutated converter-based HVDC. This paper proposes an improved coordinated control strategy for ECCC with the following improvements: 1 under normal operation state, series-connected capacitors can accelerate the commutation process, thereby reducing the overlap angle and increasing the successful commutation margin; 2 under AC fault conditions, the ability of ECCC to mitigate the CF issue no longer relies on the fast fault detection, since the capacitors inside the APT-DFBMs can consistently contribute to the commutation process and further reduce the CF probability; 3 the inserted capacitors can output certain amount of reactive power, increase the power factor, and reduce the required reactive power compensation capacity. Firstly, the proposed coordinated control approach is presented in detail, and the extra commutation voltage to mitigate the CFs provided by the proposed control approach and an existing approach is compared. Secondly, the mechanism of the improved control approach to accelerate commutation process and improve the power factor is analyzed theoretically. Finally, the detailed electromagnetic transient (EMT) simulation in PSCAD/EMTDC is conducted to validate the effectiveness of the proposed coordinated control. The results show that the proposed approach can present a further substantial improvement for ECCC, especially enhancing the CF mitigation effect.

Dynamic Surface Backstepping Control for Voltage Source Converter-High Voltage Direct Current Transmission Grid Side Converter Systems

This paper studies the coordination control of active and reactive power of the voltage source converter-high voltage direct current transmission (VSC-HVDC) grid side converter. Firstly, the high-order VSC-HVDC converter system is decomposed into three subsystems by using the backstepping control method, and the control laws are designed for each subsystem to realize the control of VSC-HVDC converter systems. Secondly, the dynamic surface control method is used to deal with the problem of “explosion of complexity” in the traditional backstepping control method. Finally, the simulation results demonstrate that the VSC-HVDC converter systems can provide a certain capacity of reactive power compensation under the proposed method in this paper. In addition, the control method proposed in this paper does not require the information of the second derivative of active power and reactive power.

A New Quantitative Analysis Method for Overvoltage in Sending End Electric Power System With UHVDC

With the development of renewable electric power generation and ultra-high voltage direct current (UHVDC) transmission, the transient overvoltage in the sending end electric power system with UHVDC occurs, but it is lack of quantitative transient voltage assessment index (TVAI) to assess the overvoltage. To deal with the above problems, this paper proposes a new quantitative transient voltage assessment index considering overvoltage and voltage dip in the sending end electric power system with UHVDC, and applies it to analyze different influencing factors of overvoltage and determine the dynamic reactive power compensation capacity. In detail, first, according to the principle of the transient voltage assessment index considering voltage dip and the overvoltage assessment index for the distribution network, a new transient voltage assessment index considering transient overvoltage in the sending end electric power system with UHVDC is proposed with the approximated step function. Then, based on the requirements of the system with UHVDC, the parameters of the proposed transient voltage assessment index are determined. Furthermore, with the absolute and relative sensitivity, the impact of the parameters of voltage dependent current order limiter and current control amplifier on the transient overvoltage is analyzed and compared quantitatively. Finally, the impact of reactive power compensation equipment, such as synchronous condenser, static var compensator, and static var generator, on the transient overvoltage of the system with UHVDC is compared quantitatively, and the reactive compensation capacity needed to maintain transient voltage security and stability is estimated. The two applications show the effectiveness and advantages of the proposed index in the sending end electric power system with UHVDC.

A Modified One-Cycle Control for Vienna Rectifiers with Functionality of Input Power Factor Regulation and Input Current Distortion Mitigation

In this paper, aiming at incorporating reactive power compensation functionality into the Vienna rectifiers, a modified one-cycle-control (MOCC) strategy is proposed by which the three-phase Vienna rectifier can be regulated in leading, lagging or unity power factors with near-sinusoidal input current waveform. First, a brief review of the working principle of the conventional OCC (COCC) strategy is conducted. Then, the MOCC strategy with the functionality of input current phase-shift control is discussed in detail. To mitigate input current distortion caused by the current phase-shift, a method whereby the signal of one phase current which is flowing in an uncontrollable region is injected into the other two phases’ current command signals is further presented. The constraints to the implementation of the MOCC scheme and the reactive power compensation capacity of the rectifier under MOCC control are analyzed as well. The proposed MOCC strategy is as easy to implement as the COCC strategy. Moreover, the MOCC strategy also preserves all other advantages of the COCC strategy, such as no phase-locked loop, no frame transformation and constant switching frequency. Finally, the theoretical analysis of the proposed MOCC strategy is fully verified by simulation and experimental results from a 1 kV·A three-phase Vienna rectifier prototype.

Start-Up Control of a Synchronous Condenser Integrated HVDC System With Power Electronics Based Static Frequency Converter

The operation of thyristor-based high-voltage direct current (HVDC) system requires abundant reactive power support. Synchronous condensers, as rotating devices with large capacity of reactive power compensation, are generally utilized in HVDC systems. In this paper, the start-up control of a synchronous condenser integrated HVDC system with power electronics based static frequency converter (SFC) is investigated with the following 3 contributions: (1) Three different variable frequency starting methods are proposed regarding the main start-up control component, SFC. (2) Dynamic behaviors of AC voltages, reactive power of the system are studied when the synchronous condenser is integrated into the HVDC with different start-up control methods. An evaluation index, including successive rates of integration, reactive power surges, and lengths of start-up period, are established using different start-up control methods. (3) Synthesizing the characteristics of three different start-up control methods, an optimized variable frequency starting control is proposed and the control strategy is further developed. A simulation model of a synchronous condenser integrated HVDC system with an SFC is established in PSCAD/EMTDC. Simulation results justify the effectiveness and superiority of the optimized start-up control strategy proposed.

Security region-based small signal stability analysis of power systems with FSIG based wind farm

Based on the Security Region approach, the impact of fixed-speed induction generator based wind farm on the small signal stability of power systems is analyzed. Firstly, the key factors of wind farm on the small signal stability of power systems are analyzed and the parameter space for small signal stability region is formed. Secondly, the small signal stability region of power systems with wind power is established. Thirdly, the corresponding relation between the boundary of SSSR and the dominant oscillation mode is further studied. Results show that the integration of fixed-speed induction generator based wind farm will cause the low frequency oscillation stability of the power system deteriorate. When the output of wind power is high, the oscillation stability of the power system is mainly concerned with the inter-area oscillation mode caused by the integration of the wind farm. Both the active power output and the capacity of reactive power compensation of the wind farm have a significant influence on the SSSR. To improve the oscillation stability of power systems with wind power, it is suggested to reasonably set the reactive power compensation capacity for the wind farm through SSSR.

An approach to the ultimate goal of power grid development—constant voltage operation

The concept of constant voltage operation is proposed in this paper and it is demonstrated that the ultimate goal of power grid development is constant voltage operation. The topic is expanded into three aspects: the benefits of constant voltage operation, the technology and equipment to realize constant voltage operation, and the reactive power compensation capacity needed for constant voltage operation. The benefits of constant voltage operation have four aspects: 1) Constant voltage operation is the ultimate presentation of the strong smart grid; 2) Constant voltage operation can resist grid disturbances in the most powerful manner and greatly improve the power system stability; 3) Constant voltage operation can effectively eliminate the voltage fluctuation problem involved with the integration of large scale renewable energy; 4) Constant voltage operation can minimize the grid power loss. The means to realize constant voltage operation is primarily the modular multilevel converter based STATCOM (MMC-STATCOM), which has encountered great acceptance during recent years. Simulation verifications are run in a modified IEEE 300-bus system and the Pearl River Delta grid in PSS/E. The results indicate that constant voltage operation can greatly improve the stability of power systems and the capacity of installed MMC-STATCOMs is within an acceptable range.