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

Abstract

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.