改进型串联电压换相换流器及其控制策略

Improved Series Voltage Commutation Converter and Its Control Strategy

串联电压换相换流器(series voltage commutation converter,SVCC)是一种可以有效抑制高压直流输电换相失败的新型换流拓扑,但当交流系统故障程度超过SVCC抑制范围时,直流电流将急剧上升,对SVCC子模块中的绝缘栅双极型晶体管(insulated gate bipolar transistor,IGBT)造成较大电流冲击,亟需研究应对措施减轻换相失败后IGBT所承受的电流应力。为此,提出了一种改进型串联电压换相换流器(improved-series voltage commutation converter,I-SVCC)拓扑,通过控制子模块6种工作状态的灵活切换,可实现对阀组的辅助换相;并在换相失败发生后,能够迅速将子模块电容从换相回路中切除,避免了子模块电容的故障过压问题,同时还降低了换相失败后故障电流对子模块中各IGBT的冲击,提升了其工程实用性。此外,还针对I-SVCC设计了系统换相失败后子模块的重新投入策略,使得I-SVCC具备了后续换相失败抑制能力。最后,在PSCAD/EMTDC环境下搭建了模型进行验证,结果证明了I-SVCC在降低IGBT峰值电流和抑制后续换相失败方面的有效性。

Series voltage commutation converter(SVCC)is a new converter topology which can effectively suppress the commutation failure of the HVDC transmission.However,when the fault degree of the AC system exceeds the range of SVCC suppression,the DC current will rise sharply,which will cause great current impact on the IGBT in the SVCC sub module.It is urgent to study countermeasures to reduce the current stress of the insulated gate bipolar transistor(IGBT)after a commutation failure and improve the engineering practicability of the SVCC.Therefore,this paper proposes an improved series voltage commutation converter(I-SVCC)topology,which can realize the auxiliary commutation of the valve groups through the flexible switching among the six working states of the control sub module.After a commutation failure,the sub module capacitor can be quickly removed from the commutation circuit to avoid the fault overvoltage of the sub module capacitor.At the same time,the impact of the fault current on each IGBT in the sub module after the commutation failure is reduced,improving the engineering practicability of the IGBTs.In addition,a strategy is designed for the I-SVCC to put the sub modules back into operation after the commutation failure,so that the I-SVCC has the ability to suppress any subsequent commutation failures.Finally,a model is built in the PSCAD/EMTDC environment to verify the effectiveness of the I-SVCC in reducing the peak current of the IGBT and suppressing the subsequent commutation failures.