An active discharge scheme for DC-bus capacitors in EV powertrain

During the emergency situations, key-OFFs, or maintenance, discharging the inverter dc-bus capacitor voltage within seconds is imperative due to safety concerns (inverter not used to control motor). Conventional discharge methods rely on external resistors, additional switches, or motor windings, increasing cost, space requirements, and control complexity. This article presents a cost-effective and space-efficient solution that enables fast capacitor discharge by operating the inverter's SiC mosfets-either discrete devices or power modules-in linear mode. The proposed method utilizes a constant power tracking approach with pulse frequency modulation to safely discharge the high-voltage bus capacitor without external components. When the car is off, the proposed scheme discharges a 1000-V dc bus within 1 s using a single low-side SiC switch to test a worst-case scenario. In practice, all six devices can be used to share thermal stress, and the discharge time can be extended to 5 s as suggested by safety standards. Optimal operating conditions, including gate-source voltage (V{GS}) and pulse width (t{ON}}), are identified for different mosfets from various vendors. To assess long-term reliability, devices undergo more than 200 000 discharge cycles, with intrinsic parameter monitoring and failure analysis conducted to determine degradation mechanisms. The findings help establish safe operating conditions, ensuring robust and reliable integration of the proposed discharge method within the main powertrain inverter.