直流电网暂态过电压机理与抑制策略

Study on the Mechanism and Suppressed Strategy of Transient Over-voltage in DC Power Grid

在柔性直流输电系统受扰后,当直流电网存在盈余不平衡功率时,将导致直流过电压问题,进而对IGBT、电容器等器件造成不可逆的损坏。针对直流电网故障下的直流过电压问题,首先分析了不平衡功率导致直流过电压的机理,得到了直流电压与直流电网内不平衡功率的定量关系;然后提出一种抑制直流电压上升的虚拟调制控制策略,并针对单极和双极2种故障类型采取2种不同控制策略;最后,基于PSCAD/EMTDC搭建了四端柔性直流电网仿真模型,验证发生受端短路故障、受端单站闭锁故障和受端单极闭锁故障3种典型故障时所提控制策略的有效性。仿真结果表明,虚拟调制控制策略能有效地延缓直流电压上升速度,与耗能装置配合可以显著降低耗能装置的投入容量。

In the VSC-HVDC system,the unbalanced power in DC power grid can lead to DC over-voltage,which may damage IGBT,capacitor and other devices.For the problem of DC over-voltage under the fault of DC power grid,this paper proposes a control strategy to suppress the rise of DC voltage.Firstly,the mechanism of the DC overvoltage is studied,and the relationship between the rise of DC voltage and the unbalanced power in DC power grid is quantitatively obtained.Then a virtual modulation control strategy to suppress the rising of DC voltage is proposed,and different control strategies are adopted for different faults.Finally,a simulation model of a four-terminal VSC-HVDC is built on PSCAD/EMTDC,and the effectiveness of the proposed control strategy is verified by simulation of three typical faults:short-circuit fault,single station blocking fault and monopolar blocking fault at the receiving end.