直流电压控制是多端柔性直流输电(voltage sourced converter based multi-terminal high voltage direct current transmission,VSC-MTDC)系统稳定运行的重要因素之一。下垂控制策略无需通讯、可靠性较高,但存在直流电压质量较差、功...直流电压控制是多端柔性直流输电(voltage sourced converter based multi-terminal high voltage direct current transmission,VSC-MTDC)系统稳定运行的重要因素之一。下垂控制策略无需通讯、可靠性较高,但存在直流电压质量较差、功率分配不独立、参数设计困难等问题。首先,研究MTDC系统中下垂控制参数对直流电压与电流(功率)的影响机理。接着,分析应用于MTDC系统的下垂控制策略的约束条件,研究满足MTDC系统功率平衡和直流电压稳定的V-I(V-P)下垂特性曲线。在此基础上,提出一种改进的自适应下垂控制策略,通过引入功率影响因子实现下垂系数的闭环控制,优化不同工况下的系统运行特性。该控制策略能够减小MTDC系统的直流电压偏差,简化控制器参数设计,同时不依赖于上层控制系统与换流站之间的高速通讯,有利于提高系统可靠性和稳定性。算例分析和仿真结果验证了所提出方法的正确性和有效性。展开更多
Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stability by compensating the power for a disturbed AC ...Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stability by compensating the power for a disturbed AC system.However,it is difficult to reasonably allocate frequency-regulation resources due to a lack of coordination mechanisms between wind farms and the MTDC system.Moreover,it is difficult for the frequency control of the wind farms to manage changes in wind speed;and the risk of wind-turbine stalls is high.Thus,based on the kinetic energy of wind turbines and the power margin of the converters,the frequency-regulation capability of wind turbines is evaluated,and a dynamic frequency-support scheme considering the real-time frequency-support capability of the wind turbines and system frequency evolution is proposed to improve the frequency-support performance.A power adaptation technique at variable wind speeds is developed;the active power in the frequency-support stage and restoration stage is switched according to the wind speed.A hierarchical zoning frequency-regulation scheme is designed to use the frequency-regulation resources of different links in the MTDC system with wind farms.The simulation results show that the novel frequency-regulation strategy maintains frequency stability with wind-speed changes and avoids multiple frequency dips.展开更多
Static synchronous compensators(STATCOM)can be used as a reactive power compensation for induction motor(IM)loads due to its effective control and good compensation.Terminal voltage control(TVC)in a STATCOM has a grea...Static synchronous compensators(STATCOM)can be used as a reactive power compensation for induction motor(IM)loads due to its effective control and good compensation.Terminal voltage control(TVC)in a STATCOM has a great influence on voltage dynamics which is a significant concern in a system with many IM loads.This paper investigates the interaction between IM loads and TVC in a STATCOM under weak grid conditions from the viewpoint of active and reactive power flow.A corresponding induction machine model is proposed,based on which the interaction mechanism between IM loads and TVC in a STATCOM can be intuitively understood.It is shown that the negative damping component provided by TVC in a STATCOM can lead to system oscillation instability.Grid strength and the inertia constant of the induction machine affect the extent of such interaction.Time-domain simulation results of IM loads connected to an infinite system through a long transmission line,with STATCOM compensation implemented in MATLAB/Simulink,validate the correctness of the analyses.展开更多
Transients in load and consequently in stack current have a significant impact on the performance and durability of fuel cells.The delays in auxiliary equipments in fuel cell systems (such as pumps and heaters) and ba...Transients in load and consequently in stack current have a significant impact on the performance and durability of fuel cells.The delays in auxiliary equipments in fuel cell systems (such as pumps and heaters) and back pressures degrade system performance and lead to problems in controlling tuning parameters including temperature,pressure,and flow rate.To overcome this problem,fast and delay-free systems are necessary for predicting control signals.In this paper,we propose a neural network model to control the stack terminal voltage as a proper constant and improve system performance.This is done through an input air pressure control signal.The proposed artificial neural network was constructed based on a back propagation network.A fuel cell nonlinear model,with and without feed forward control,was investigated and compared under random current variations.Simulation results showed that applying neural network feed forward control can successfully improve system performance in tracking output voltage.Also,less energy consumption and simpler control systems are the other advantages of the proposed control algorithm.展开更多
文摘直流电压控制是多端柔性直流输电(voltage sourced converter based multi-terminal high voltage direct current transmission,VSC-MTDC)系统稳定运行的重要因素之一。下垂控制策略无需通讯、可靠性较高,但存在直流电压质量较差、功率分配不独立、参数设计困难等问题。首先,研究MTDC系统中下垂控制参数对直流电压与电流(功率)的影响机理。接着,分析应用于MTDC系统的下垂控制策略的约束条件,研究满足MTDC系统功率平衡和直流电压稳定的V-I(V-P)下垂特性曲线。在此基础上,提出一种改进的自适应下垂控制策略,通过引入功率影响因子实现下垂系数的闭环控制,优化不同工况下的系统运行特性。该控制策略能够减小MTDC系统的直流电压偏差,简化控制器参数设计,同时不依赖于上层控制系统与换流站之间的高速通讯,有利于提高系统可靠性和稳定性。算例分析和仿真结果验证了所提出方法的正确性和有效性。
基金supported by the National Key R&D Program of China(No.2022YFB2402700).
文摘Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stability by compensating the power for a disturbed AC system.However,it is difficult to reasonably allocate frequency-regulation resources due to a lack of coordination mechanisms between wind farms and the MTDC system.Moreover,it is difficult for the frequency control of the wind farms to manage changes in wind speed;and the risk of wind-turbine stalls is high.Thus,based on the kinetic energy of wind turbines and the power margin of the converters,the frequency-regulation capability of wind turbines is evaluated,and a dynamic frequency-support scheme considering the real-time frequency-support capability of the wind turbines and system frequency evolution is proposed to improve the frequency-support performance.A power adaptation technique at variable wind speeds is developed;the active power in the frequency-support stage and restoration stage is switched according to the wind speed.A hierarchical zoning frequency-regulation scheme is designed to use the frequency-regulation resources of different links in the MTDC system with wind farms.The simulation results show that the novel frequency-regulation strategy maintains frequency stability with wind-speed changes and avoids multiple frequency dips.
基金supported in part by National Basic Research Program of China (973 Program) (No.2012CB215100)Major Program of National Natural Science Foundation of China (No.51190104)National Natural Science Fund for Excellent Young Scholars (No.51322704)
文摘Static synchronous compensators(STATCOM)can be used as a reactive power compensation for induction motor(IM)loads due to its effective control and good compensation.Terminal voltage control(TVC)in a STATCOM has a great influence on voltage dynamics which is a significant concern in a system with many IM loads.This paper investigates the interaction between IM loads and TVC in a STATCOM under weak grid conditions from the viewpoint of active and reactive power flow.A corresponding induction machine model is proposed,based on which the interaction mechanism between IM loads and TVC in a STATCOM can be intuitively understood.It is shown that the negative damping component provided by TVC in a STATCOM can lead to system oscillation instability.Grid strength and the inertia constant of the induction machine affect the extent of such interaction.Time-domain simulation results of IM loads connected to an infinite system through a long transmission line,with STATCOM compensation implemented in MATLAB/Simulink,validate the correctness of the analyses.
文摘Transients in load and consequently in stack current have a significant impact on the performance and durability of fuel cells.The delays in auxiliary equipments in fuel cell systems (such as pumps and heaters) and back pressures degrade system performance and lead to problems in controlling tuning parameters including temperature,pressure,and flow rate.To overcome this problem,fast and delay-free systems are necessary for predicting control signals.In this paper,we propose a neural network model to control the stack terminal voltage as a proper constant and improve system performance.This is done through an input air pressure control signal.The proposed artificial neural network was constructed based on a back propagation network.A fuel cell nonlinear model,with and without feed forward control,was investigated and compared under random current variations.Simulation results showed that applying neural network feed forward control can successfully improve system performance in tracking output voltage.Also,less energy consumption and simpler control systems are the other advantages of the proposed control algorithm.
