An Improved PDPWM for a Modular Multilevel Inverter used for Micro Grid

This modulation method is based on selective virtual loop mapping, to achieve dynamic capacitor voltage balance without the help of an extra compensation signal. The concept of virtual sub module (VSM) is first established, and by changing the loop mapping relationships between the VSMs and the real submodules, the voltages of the upper/lower arm’s capacitors can be well balanced. This method does not requiring sorting voltages from highest to lowest, and just identify the MIN and MAX capacitor voltage’s index which makes it suitable for a modular multilevel converter with a large number of submodules in one arm. Compared to carrier phase-shifted PWM (CPSPWM), this method is more easily to be realized in field-programmable gate array and is conducive to the control of circulating current. Its feasibility and validity have been verified by simulations. KeywordDynamic Voltage Balance (DVB), Modular Multilevel Converter (MMC), Phase disposition Pulse Width Modulation (PDPWM), Photovoltaic (PV), Selective Virtual Loop Mapping (SVLM) __________________________________________________________________________________________________