Double-Time-Scale Active Thermal Control for Single Inverter with Variable Frequency SPWM

Excessive fluctuation of junction temperature and high mean junction temperature are the main reasons of IGBT thermal fatigue failure. Traditional active thermal control (ATC) changes the PWM frequency on a long-time-scale to compensate for device losses and reduce amplitude of junction temperature fluctuations. Combining the variable frequency SPWM (VFSPWM), which can change PWM frequency on a short-time-scale, a double-time-scale active thermal control (DTS-ATC) method is proposed. It combines advantages of both by using long-time-scale frequency regulation to reduce temperature fluctuation amplitude and short-time-scale frequency variation to reduce mean temperature. DTS-ATC IGBT loss calculation equation is derived and verified. Then basic frequency and intercept of envelop of DTS-ATC are obtained by solving the nonlinear loss equation using the Newton's method to track the mean loss. Simulation results show that compared with long-time-scale ATC method, the proposed DTS-ATC method can further suppress the mean junction temperature, reduce the IGBT junction temperature fluctuation amplitude and its damage to device, and extend the device's estimated lifetime. Experiments are also carried out to verify the proposed method.