适用于MMC-HVDC的优化均压策略

模块化多电平换流器(modular multilevel converter,MMC)的子模块均压效果和绝缘栅双极型晶体管(insulated gate bipolar transistor,IGBT)开关频率是两个相互制衡的重要指标。提出了一种在保证子模块均压效果的基础上求取最优开关频率的均压策略。通过分析子模块电压均衡的基本原理,提出将同一桥臂上的子模块按照投入/切除状态分组排序,然后基于投入/切除组对应的子模块电压差、桥臂电流方向以及预设的均压效果阈值生成投入/切除组对应的最优交换值。最优交换值是在满足均压效果阈值条件下,投入组和切除组需要交换的最少模块数。基于最优交换值优化调整生成的触发脉冲可有效降低开关频率,能以最小的投切变位即最优开关频率来保证均压效果。最后通过仿真分析,构建基于RTDS实时仿真系统的MMC-HVDC硬件在环半实物仿真平台和背靠背柔性直流输电实验平台,验证了所提策略的有效性。

Optimized Voltage Balancing Strategy for MMC-HVDC

Voltage balancing effect of sub-modules(SMs)and switching frequency of insulated gate bipolar transistor(IGBT)are two important indicators of mutual checks and balances in modular multilevel converter(MMC).This paper presents a voltage balancing strategy to obtain the optimal switching frequency on the basis of guaranteeing the effect of voltage balancing.By analyzing the basic principle of voltage equalization of SMs,it is proposed that SMs on the same bridge arm are sorted within the grouping according to the switch on/off state,and then the optimal exchange value is generated corresponding to the switch on/off group,based on the voltage difference of SMs corresponding to the switch on/off group,the current direction of the bridge arm,and the preset threshold of voltage balancing effect.The optimal exchange value is the minimum number of modules that need to be exchanged between the switch on group and the switch off group under the condition that the preset threshold of voltage balancing effect is satisfied.The firing pulses generated by optimal adjustment based on the optimal exchange value can effectively reduce the switching frequency,and ensure the voltage balancing effect with the minimum switching change which is the optimal switching frequency.Finally,through simulation analysis,an MMC-HVDC hardware-in-the-loop simulation platform based on RTDS real-time simulation system and an experimental platform of back-to-back voltage source converter based HVDC are constructed,and the effectiveness of the proposed strategy is verified.