Design of High Power Density Inverters for Traction Applications

Abstract

Abstract The shift towards electrification in the automobile industry aims to achieve net-zero emissions by 2050, with electric car sales reaching 10 million in the past decade. Based on the recent trend in automotive, the focus has shifted towards high power density than efficiency to reduce volume, weight, and cost, which may create additional space for batteries as well. A key technology, enhancing power density is the use of wide band gap (WBG) devices, which offer high efficiency, lower switching loss, and faster switching speeds in traction inverters. However, these devices also present thermal challenges and over voltage spikes causing EMI, switching losses and device breakdown due to high di/dt during high-frequency operations. This thesis work addresses these challenges by first estimating the semiconductor losses and junction temperature using an analytical loss function-based model. Experimental verification of the same is performed with the prototype inverter built with Infineon HybridPack SiC power modules and the challenges are discussed. To mitigate the over voltage spikes, the impact of DC bus bar stray inductance is studied with two different designs, exhibiting a 26% difference in stray inductance. The influence of bus bar stray inductance on switching losses was analysed through switch-level Double Pulse Test (DPT) simulations, inverter-level drive cycle simulations, and experimental voltage overshoot measurements with the prototype inverter. Key findings reveal that a 26% difference in bus bar stray inductance results in a 3.2% increase in losses for design-1, reduced to 2% with the improved overlap design- 2 in DPT simulations. Drive cycle simulations showed similar trends, with a 2.53% increase for design-1 and a 1.14% increase for design-2. Voltage overshoot analysis indicated a 12% reduction in voltage stress on the switch due to reduced stray inductance, consistent across both simulations and experiments. These insights are crucial for designing high power density inverters, allowing for optimized thermal and bus bar designs that minimize voltage stress without compromising efficiency. voltage stress without compromising efficiency.