Active Thermal Control of Power Semiconductor for High Power Electric Drive Applications

Abstract

Abstract Electric vehicle applications, driven by the need for space and mass savings, increasingly demand high-power density inverters. However, this reduction in mass has led to a decrease in thermal capacity, badly exposing power emiconductors to larger temperature swings and thermal cyclic stress. The vulnerability of wire bonds and chip solder in the power semiconductor to failure due to thermal cycling necessitates a solution. This solution, actively controlling the junction temperature during operation, is the focus of this research and is referred to as active thermal control techniques (ATC). Different active thermal control strategies are explored in the literature via manipulation of losses or heat dissipation and they are discussed in this work. Some of the methods require specific hardware, such as specialized gate drivers. The control of junction temperature without any extra hardware can be achieved by controlling the PWM frequency, load current, and modulation methods. However, controlling load current requires implementing an online current reference estimation. Additionally, changing the modulation method would increase control complexity. Therefore, this work investigates active junction temperature control by varying the PWM frequency. The junction temperature is controlled using a hysteresis band-type controller with some modifications. The influence of the control band and average junction temperature calculation on the inverter’s control effectiveness, prolonged lifetime, and improved efficiency is investigated. The inverter’s losses are calculated analytically, and the inverter is implemented together with a heavy-duty truck and machine model in simulations. Drive cycle-based analysis is combined together with rain flow counting and a lifetime model to estimate the influence of the controller on the devices’ lifetime. Simulation results show that the active control of the junction temperature can result in more than 246% increase in lifetime and simultaneously increase efficiency by 0.30%.