An improved PWM control method to reduce surge current through capacitors in hybrid-clamped multilevel inverter

An improved pulse width modulation (PWM) control method for three-phase hybrid-clamped multilevel inverters (HCMLI) is proposed in this paper. It can significantly reduce the surge currents through the DC link capacitors by changing the relative phase of the three-phase PWM carriers. The surge currents increase the capacitor losses and decrease the capacitor life, thus increasing the cost and reducing the reliability of inverters. The operating principle of the hybrid-clamped multilevel inverter, the generation mechanism of the surge currents, and the principle of the improved PWM method are given. The simulated and experimental results show that compared with the general PWM method, the improved PWM method can effectively reduce the voltage ripples on the DC link capacitors, consequently decreasing the surge currents through them.