交流系统不对称故障时VSC-HVDC控制策略研究

Research on VSC-HVDC Control Strategy in Asymmetric Fault of AC System

在电网系统发生不对称故障时,交流侧电压和电流中将出现大量的负序分量,对整个VSC-HVDC直流输电系统的运行产生巨大的威胁。首先,根据瞬时对称分量的概念将不对称的三相电压进行正、负序分量的分解,并推导出在两相坐标系下的模型。然后,设计了一种能同时检测对称分量和同步相位的一体化检测电路,可不受负序分量的影响。并针对内、外环的PI调制,提出2种新的算法。最后,在PSCAD上建立了VSC-HVDC系统的不对称模型并对其进行仿真。仿真结论验证了控制策略和PI调制算法的有效性。

During the actual operation of the grid system,when an asymmetric fault occurs in the system,a large number of negative sequence components are present in the AC voltage and current,which will threaten the security operation of the whole VSC-HVDC system.In this paper,the asymmetric three-phase voltages were decomposed to positive and negative sequence components according to the concept of instantaneous symmetric components,and then their models in two-phase coordinate system were deduced.An integrated detection circuit that can simultaneously detect the symmetric components and synchronous phases was designed,which is not affected by the negative sequence components.Two new algorithms were proposed for PI modulation of inner and outer loops.Finally,the asymmetric model of VSC-HVDC system was established on PSCAD and its simulation was carried out.The simulation results verify the effectiveness of the control strategy and the PI modulation algorithms.