中文摘要：

相比于两电平VSC-HVDC输电系统,模块化多电平HVDC输电系统功率运行区间的确定还需考虑子模块电容电压波动这一因素。分析子模块电容电压与功率运行点之间的关系,并确定以子模块电容电压波动范围、最大调制比以及换流阀通流能力为约束条件的系统功率运行区间。在此基础上,提出三倍频调制电压注入和子模块电容电压基值调整两种功率区间优化方法,并设计用于抑制二倍频负序、四倍频正序相间环流的环流控制器和子模块直流电压基值控制器。非线性优化计算结果表明,通过配置合理的优化参数,系统功率运行区间显著扩大。基于PSCAD/EMTDC,针对典型功率运行点进行仿真分析,验证了理论分析及控制策略的正确性。

英文摘要：

Comparing to the two-level converter based VSC-HVDC,the voltage fluctuations of the sub-module capacitor of modular multilevel converter is another factor that needs to be considered while determining the system operation region.The relationship between the sub-module capacitor voltage and power operating point was analyzed,and the system operation region was determined considering the constraints of the fluctuation of sub-module capacitor voltage,maximum modulation index and the current passage capability of the valve.On this basis,the triple fundamental frequency zero sequence modulation voltage and the base value control of sub-module voltage were introduced to optimize the system operation region.The circulating current controller was improved which could both suppress the double fundamental frequency negative sequence component and the quadruple fundamental frequency positive sequence component,and a base value controller of sub-module voltage was proposed.Nonlinear optimization calculation results show that,by setting the optimization parameters reasonably,the system power operation region could be expanded significantly.Based on PSCAD/EMTDC software environment,the simulation results at the typical operation points were conducted which verify the correctness of the theoretical analysis and control strategy mentioned.