弱电网直驱风机低电压穿越特性及其对机端暂态电压的影响

Effect of the Low Voltage Ride Through Characteristics on PMSG Terminal Transient Voltage in Weakly-synchronized Gird

新能源常通过特高压交/直流输电系统送出,新能源汇集送端电网配套火电机组少,电网强度弱,直流闭锁或交流严重短路故障后的暂态过电压易引发风电脱网。该文基于典型电压穿越策略建立永磁直驱风机(permanent magnet synchronous generato rbased wind generator,PMSG)并网模型,研究弱电网中送出线路远端短路故障时的PMSG功率特性,揭示故障发生与清除时刻PMSG控制产生误差的原因,分析PMSG控制策略与参数对机组功率特性以及机端暂态过电压特性的影响。研究结果表明,远端短路故障清除时刻PMSG网侧电压相位一般向后跳变,由于锁相环存在时延,使暂态过程中锁相结果超前于实际相位,导致PMSG有功/无功控制不解耦,电流控制产生误差,由于锁相结果超前实际相位产生的控制误差会抑制网侧电压的快速抬升。

Renewable generators are often connected to the UHVAC/DC power transmission system.The power grid with plenty renewable generators usually has fewer thermal power plants,which makes the strength of the power grid is weak.Transient voltage instability problems often occur after DC blocking or severe AC short circuit faults,which may lead the wind turbines with off-gird problem.Based on the typical voltage ride-through strategy,this paper established a mutil-pole permanent magnet synchronous generator(PMSG)-based wind generator grid-connected model.The PMSG transient characteristics were studied when short fault appears on the remote transmission line in a weak power grid.The PMSG active/reactive control coupling and control error at the time of fault occurrence were revealed.The influences from PMSG control strategy and parameters on the unit power characteristics and terminal transient voltage were analyzed.The results show that the voltage phase of the PMSG terminal generally jumps backwards at the time of the remote short-circuit fault clearing,which makes the phase-locked loop result bigger than the actual phase.As a result,the PMSG active/reactive power control is not decoupled,and the current control produces errors.The control error caused by the phase-locking result will inhibit the rapid rise of the PMSG terminal voltage.