Impact of Dynamic Gate Drive on System Level Efficiency of SiC-Based ElectricDrive Units

Abstract

Abstract The Electric Drive Unit (EDU) is a critical subsystem in Battery Electric Vehicles (BEVs), responsible for converting electrical energy from the battery into mechanical power for propulsion. A central element of the EDU is the inverter, which converts DC power into AC to drive the electric motor. Silicon Carbide (SiC) inverters are increasingly employed in BEVs due to their high efficiency and thermal performance. However, their fast switching characteristics introduce challenges such as voltage overshoots, current spikes, and Electromagnetic Interference (EMI), potentially affecting system reliability and efficiency. This thesis investigates a Dynamic Gate Drive (DGD) strategy, in which the external gate resistance is adjusted for the turn-off transition of SiC MOSFETs to balance switching losses and voltage overshoot. Circuit-level simulations were performed using a Double Pulse Test (DPT) setup in LTspice to evaluate switching behaviour, while conduction losses were estimated based on the relationship between device voltage rating and on-state resistance RDS. Motor performance under different operating conditions was assessed in Motor-CAD, and system-level losses was analysed under a Worldwide Harmonized Light Vehicle Test Procedure (WLTP) drive cycle. The results indicate that the DGD approach can reduce inverter losses, particularly under low initial state-of-charge (SOC) conditions, and provide marginal improvements in overall EDU efficiency. However, the impact of DGD on the efficiency of the electric machine was not straightforward, and no clear trend could be established. Nevertheless, reduced voltage overshoot allows for a modest increase in DC link voltage utilization, contributing to higher base speed, increased torque output, and improved peak power performance in the constant power region. While the improvements at the system level are limited, the findings highlight that, in principle, DGD is a method to enhance inverter performance and enable more effective utilization of existing powertrain components in electric vehicle applications.