风电经柔性直流组网系统受端交流故障过电压分析及穿越策略

Overvoltage Analysis and Ride-Through Strategy of AC Fault at Receiving-End of the Flexible HVDC System Integrated with Wind Farms

为降低风电经柔性直流组网系统受端换流站发生近区交流短路故障(以下简称“受端交流故障”)的穿越成本,提出了一种自适应最近电平逼近策略(adaptive nearest level modulation,ANLM)与风电机组内部斩波电阻协同配合的故障穿越策略。故障发生后,送端换流站配合风电机组内部斩波电阻实现风电场快速降载。在风电场大幅度降载前,ANLM策略通过减少子模块投入数量的方式增大换流站等效电容,吸纳柔性直流电网累积的不平衡能量,限制直流过电压,为风电场降载争取充裕的时间。风电场减载完成后,换流站存储的不平衡能量逐渐释放。所提策略仅利用系统自身的调控潜力,能够降低穿越成本。最后,基于PSCAD软件仿真模型,以最严重的受端交流故障情景为例,对所提策略的有效性进行了验证。

To cut down the ride-through cost when the near-area AC short-circuit fault occurs at the receiving-end converter(hereinafter called receiving-end AC fault)of the flexible high voltage direct current(HVDC)system integrated with wind farms,this paper proposes a fault ride-through strategy where the adaptive nearest level modulation(ANLM)strategy and the chopper resistances in wind turbines work together.After the fault occurs,the sending-end converter cooperates with the chopper resistances within wind turbines to quickly realize the aim of wind farm load reduction.Before a significant load reduction in the wind farm,the ANLM strategy increases the equivalent capacitance of the converter station by reducing the number of sub-module inputs,absorbs the ac⁃cumulated unbalanced energy of the flexible HVDC power grid,limits DC overvoltage,and strives for sufficient time for wind farm load reduction.The unbalanced energy stored in the converter is gradually released after the wind farm completes load reduction.The proposed strategy can reduce the ride-through cost only by using the regulation potential of the system.Finally,based on the simulation model of PSCAD software,the effectiveness of the proposed strategy is verified by taking the most serious receiving-end AC fault scenario as an example.