Variable Switching Frequency Control for Efficiency and Power Density Improvement of a GaN-based Traction Inverter for EV Applications

Wide–band gap (WBG) semiconductor devices have gained significant interest over conventional silicon (Si) insulated gate bipolar transistor (IGBT) devices for traction inverters in electric vehicle (EV) propulsion applications due to their improved energy efficiency and power density. This paper investigates the utilization of Gallium Nitride’s (GaN) fast switching capability towards further efficiency and power density increase in a traction inverter application. An electrothermal model of the GaN inverter is developed and the model’s efficiency map is compared to experimental measurements to validate the accuracy to within 0.3% efficiency or 100 W loss difference in most operating regions. A novel variable switching frequency strategy is proposed that considers the DC link voltage ripple limitations to increase inverter efficiency up to 5% in comparison to a fixed switching frequency approach. The variable switching frequency technique is combined with the fast switching capability of GaN to achieve a 35.7% reduction in capacitor size while achieving improved drive cycle efficiency with increased inverter power density.