With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV sy...With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV system is controlled to keep grid connected, as well as inject reactive current to grid when fault occurs. The mathematical model of PV system is established and the fault characteristic is studied with respect to the control strategy. By analyzing the effect of reactive power supplied by the PV system to the point of common coupling (PCC) voltage, this paper proposes an adaptive voltage support control strategy to enhance the fault ride-through capability of PV system. The control strategy fully utilizes the PV system’s capability of voltage support and takes the safety of equipment into account as well. At last, the proposed control strategy is verified by simulation.展开更多
针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统...针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统输电线路故障发生后的故障特征,以及大时间尺度下,直流系统对交流故障的响应。研究结果表明:基于实时数字仿真(Real Time Digital Simulation,RTDS)搭建的交直流混联系统模型在有效控制故障发展的前提下,不同故障条件、控制策略下具有相对应的故障特征,如:交流并网线路故障时,负序电流将被抑制,换流站仅向故障点提供有限的正序电流,且优先输出无功功率,直流线路累积不平衡功率出现直流过电压现象,计及直流电压波动引起受端换流站的dq轴电流发生变化,造成交流线路故障电流短时间内增大约20%。直流线路发生单极接地故障时,故障极电压以最大700 kV/ms的速率迅速下降到0,非故障极电压上升为原来的两倍,且故障电流会随着接地电阻的增大而减小;当发生双极故障时,故障电流能够在数毫秒内达到额定电流的几十倍,最大速率可达8.25 kA/ms,严重威胁电力电子器件的安全,并且电压迅速降至0,此时通过混合直流断路器快速动作,在故障电流上升至额定电流2倍前切除故障线路,使系统满足N-1运行原则。仿真结果与理论分析结论相符。展开更多
直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除...直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除直流侧故障,是实现直流故障穿越的理想拓扑。该文首先分析现有换流阀闭锁保护策略下电容放电阶段和换流阀闭锁阶段的等效电路,推导电容电压和电流的解析式。针对实际工程中功率模块具有恒功率负载特性,换流站闭锁期间功率模块电容电压逐渐发散并最终导致交流断路器跳闸的问题,提出一种FBMMC-HVDC的故障穿越控制保护策略。在故障穿越期间,换流器处于可控状态,能够避免电容电压发散,无需切断交直流系统连接;在故障清除后能够立即恢复正常运行,具备暂时性和永久性直流故障穿越能力。在PSCAD/EMTDC软件中构建了FBMMC-HVDC仿真模型,对比上述两种保护策略,分析两种策略各自的优缺点。展开更多
文摘With continuously increasing of photovoltaic (PV) plant’s penetration, it has become a critical issue to improve the fault ride-through capability of PV plant. This paper refers to the German grid code, and the PV system is controlled to keep grid connected, as well as inject reactive current to grid when fault occurs. The mathematical model of PV system is established and the fault characteristic is studied with respect to the control strategy. By analyzing the effect of reactive power supplied by the PV system to the point of common coupling (PCC) voltage, this paper proposes an adaptive voltage support control strategy to enhance the fault ride-through capability of PV system. The control strategy fully utilizes the PV system’s capability of voltage support and takes the safety of equipment into account as well. At last, the proposed control strategy is verified by simulation.
文摘针对具有故障穿越策略的永磁风电场经多端柔性直流(Voltage Source Converter Based Multi-terminal Direct Current,VSC⁃MTDC)输电系统外送的交直流混联系统,分析故障穿越控制目标下受端交流电网故障和考虑输电线路频变特性的直流系统输电线路故障发生后的故障特征,以及大时间尺度下,直流系统对交流故障的响应。研究结果表明:基于实时数字仿真(Real Time Digital Simulation,RTDS)搭建的交直流混联系统模型在有效控制故障发展的前提下,不同故障条件、控制策略下具有相对应的故障特征,如:交流并网线路故障时,负序电流将被抑制,换流站仅向故障点提供有限的正序电流,且优先输出无功功率,直流线路累积不平衡功率出现直流过电压现象,计及直流电压波动引起受端换流站的dq轴电流发生变化,造成交流线路故障电流短时间内增大约20%。直流线路发生单极接地故障时,故障极电压以最大700 kV/ms的速率迅速下降到0,非故障极电压上升为原来的两倍,且故障电流会随着接地电阻的增大而减小;当发生双极故障时,故障电流能够在数毫秒内达到额定电流的几十倍,最大速率可达8.25 kA/ms,严重威胁电力电子器件的安全,并且电压迅速降至0,此时通过混合直流断路器快速动作,在故障电流上升至额定电流2倍前切除故障线路,使系统满足N-1运行原则。仿真结果与理论分析结论相符。
文摘直流故障穿越是柔性直流输电(voltage sourced converter based high voltage direct current transmission,VSCHVDC)技术面临的重要问题之一。全桥型模块化多电平换流器(full bridge modular multilevel converter,FBMMC)能够快速清除直流侧故障,是实现直流故障穿越的理想拓扑。该文首先分析现有换流阀闭锁保护策略下电容放电阶段和换流阀闭锁阶段的等效电路,推导电容电压和电流的解析式。针对实际工程中功率模块具有恒功率负载特性,换流站闭锁期间功率模块电容电压逐渐发散并最终导致交流断路器跳闸的问题,提出一种FBMMC-HVDC的故障穿越控制保护策略。在故障穿越期间,换流器处于可控状态,能够避免电容电压发散,无需切断交直流系统连接;在故障清除后能够立即恢复正常运行,具备暂时性和永久性直流故障穿越能力。在PSCAD/EMTDC软件中构建了FBMMC-HVDC仿真模型,对比上述两种保护策略,分析两种策略各自的优缺点。
