Pulse Width Modulation Method for Reliability Improvement of DC-link Capacitors and Power Devices of NPC Inverter

Power devices and DC-link capacitors are considered reliability-critical components in power converters. Thermal stress caused by power loss leads to wear-out failures of DC-link capacitors and power devices. Previous studies have proposed various PWM methods to reduce the thermal stress of DC-link capacitors and power devices, respectively. However, the existing methods did not consider the reduction of thermal stress of DC-link capacitors and power devices simultaneously. This paper proposes the PWM method for improving the reliability of the NPC inverter by decreasing the thermal stress of DC-link capacitors and power devices concurrently. Through the simulations and experiments, the feasibility and effectiveness of the proposed PWM method are verified.

I. Introduction

The three-level neutral-pointed-clamped (NPC) inverter has been widely used in various power electronic applications because of its advantages, such as lower total harmonic distortion (THD) of the outputs and higher efficiency compared with the two-level inverter. Furthermore, as shown in Fig. 1, the three-level inverter allows using power devices with lower rated voltage because the DC-link voltage is divided across two power devices connected in series [1]–[3].