Study of PWM frequency and its impact to adjustable speed drive reliability

Pulse Width Modulation (PWM) control method has been widely studied and applied in the industrial area. For majority of the conditions, the PWM frequency is fixed to guarantee easier control implementation. However, the time constant of the IGBT thermal system is much lower than that of the inverter fundamental frequency at low speed. The lifetime of the inverter are severely reduced under low speed and high output conditions. To improve the lifetime of the inverter at lower speed without reduce the output current, a natural way is to reduce the PWM frequency under this condition. This paper evaluated the inverter performance under different PWM frequencies. After that, it studies the impact of PWM frequency to inverter losses, inverter reliability and system performance. It is concluded that operating the inverter at low switching frequencies may not sacrifice the output current waveform quality. Moreover, the inverter lifetime can be significantly increased. Analytical, simulation and experimental results will be presented to show its effectiveness.