采用载波移相调制的模块化多电平换流器电容电压平衡控制

Capacitor Voltage Balancing Control by Using Carrier Phase-shift Modulation of Modular Multilevel Converters

针对模块化多电平换流器(modular multilevel converter,MMC)的底层控制策略,研究载波移相调制(carrier phase-shift modulation,CPSM)方法及相应的直流电容电压平衡控制策略。首先,以桥臂为单位设计CPSM策略,推导出保证桥臂输出特性不变的约束条件;其次,从理论上分析控制子模块直流电容电压的原理,揭示出桥臂的能量自然平衡状态,进一步提出电容电压的附加平衡控制。在10 kVA实验室样机上进行的稳态和动态实验,验证了所提控制策略的有效性。CPSM结合电容电压附加平衡控制方法,可以使各子模块的开关频率确定,不引起额外的开关损耗,并能够避免计算量过大的问题。

The aim of this paper was to investigate the application of carrier phase-shift modulation （CPSM） to the apparatus-level controller of modular multilevel converters （MMC）, and to propose a relevant capacitor voltage balancing control strategy. Firstly, the paper designed CPSM strategy of an arm and deduced constraints of maintaining the output voltage of an arm. Secondly, the capacitor voltage control principle was theoretically analyzed and the natural energy balancing state of an ann was revealed. Furthermore, additional balancing control strategy was proposed. Experimental results on a 10 kVA laboratory prototype verify the validity of the proposed control method under both steady and dynamic states. The additional balancing control strategy combined with CPSM can guarantee definite switching frequency without costing extra switching loss, and can avoid large calculation efforts.