Analysis of PWM frequency control to improve the lifetime of PWM inverter

Studies have shown that the power cycling Mean Time to Failure (MTTF) of the IGBT bond wire in an adjustable speed drive (ASD) may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on junction temperature variation (DeltaTj) of the inverter IGBT. It has the following advantages. Firstly, it only reduces the PWM frequency under low speed higher torque condition; secondly, the inverter can be started more smoothly and safely under higher command switching frequency and high torque condition. Thirdly, the overall MTTF of the inverter IGBT can be improved dramatically. Theory analysis, simulation and experimental result will be provided to show these advantages.