抑制换相失败期间送端电网过电压的控制策略研究

The control strategy for suppressing overvoltage of sending grid during commutation failure

在受端交流系统发生故障时,基于电网换相换流器的直流输电系统存在换相失败的问题,这会导致直流输送功率中断,送端无功功率过剩将造成送端交流电网过电压,可能会造成风机等新能源设备脱网。因此,提出了一种抑制换相失败期间送端过电压的控制策略,在发生换相失败时快速投入逆变侧旁通对,并根据交流滤波器总输出无功功率计算出故障期间低压限流控制特性(VDCOL)的直流电流指令值。该策略可使直流系统在有功功率中断的运行模式下,保证送端换流阀能够正常换相并维持一定的直流电流,从而避免发生送端交流电网过电压的问题。仿真结果验证了该控制策略的有效性,在不同短路比的强、弱交流系统中均可适用。

When the AC system of the receiving end fails,the DC transmission system based on the grid commutator has a problem of commutation failure,which will cause the DC transmission power to be interrupted.The excess reactive power at the sending end will cause the AC system to overvoltage.In turn,it is possible to cause new energy equipment such as wind turbines to be disconnected from the network.Therefore,a control strategy is proposed to suppress over-voltage at the transmitting end during commutation failure.The specific strategy is to quickly input bypass switch of the inverter side when the commutation failure occurs and calculate the DC current command value during the fault according to the reactive power consumption before the fault.The strategy can maintain a certain DC current in the mode of the active power interruption,thereby ensuring the converter valve can normally commutate and have a certain reactive power consumption to avoid the overvoltage problem of AC grid.The simulation results verify the effectiveness of the control strategy which can be applied to both strong and weak AC systems with different short-circuit ratios.