新型多电平VSC子模块电容参数与均压策略

Submodule Capacitance Parameter and Voltage Balancing Scheme of a New Multilevel VSC Modular

通过深入分析一种新型电压源换流器(voltage source converter,VSC),即模块化多电平VSC的本质工作机制,从换流器桥臂功率脉动与能量脉动角度,结合子模块电压纹波系数,对其子模块电容参数进行合理设计;并针对其关键的各子模块电容电压均衡问题,提出一种切实、可行的均压策略,有效确保了各子模块电容电压处在相同的等级范围,各功率半导体器件承受相同的应力;同时也给出一种简单且有效的子模块电容预充电策略,与传统通过交流系统为电容充电方式所不同的是,此预充电策略控制灵活,无需采用抑制冲击电流的限流电阻,并且可以使VSC具有一定的"黑启动"能力。通过仿真较好地验证了上述各种策略。

The capacitance parameter of the submodule in a new voltage source converter （VSC）, i.e. modular multilevel VSC, is designed ideally from the viewpoint of pulsation of power and energy of its phase leg, based on the detailed analysis of its essential working mechanism, with the voltage ripple factor of submodule being considered. Aiming at the critical problem about capacitor voltage balancing of each submodule, a feasible voltage-balancing scheme is presented. This scheme could effectively ensure each submodule at the same capacitance and voltage level and each power semiconductor device enduring equal stress. In addition, a simple and effective capacitor precharge scheme on the submodule is presented. Different from the traditional capacitor precharge method through AC system, this precharge scheme can be controlled flexibly, don＇t need the current limiting resistance for damping the surge current and can make the VSC have certain ＂black start＂ capability. The abovementioned various schemes were verified well by simulations.