Abstract: A novel multiple-loop control system in 400 Hz inverter of power supply based on unipolar sine pulse midth modulation（SPWM） was proposed.The reasons of imbalance in three-phase combined inverter power system were analyzed,and a new control strategy was presented.In order to reduce the THD of high power inverter system output voltage,unipolar SPWM modulation was added with this new control strategy.Above-mentioned inverter power system controller was realized with DSP.The inverter system has a lot of merit characteristics such as phase self regulation and low output harmonic contents.The simulation and experimental results indicate the advantages and the correctness of this novel inverter power system were proved.