Silicon Carbide (SiC)-Based Soft-Switched Power Converters with Autonomous Gate Drivers for Electric Vehicles
Time: Fri 2025-10-24 13.00
Location: Room no: 132, Code: F3 (Flodis), Floor: 02, Lindstedtsvägen 26 & 28
Video link: https://kth-se.zoom.us/j/63418851724
Language: English
Subject area: Electrical Engineering
Doctoral student: Khizra Abbas , Elkraftteknik, Power Electronics
Opponent: Professor Jacek Rabkowski, Warsaw University of Technology, Warsaw, Poland
Supervisor: Professor Hans-Peter Nee, Elkraftteknik
QC 20250926
Abstract
The electrification of transportation demands power conversion systems that are highly efficient, compact, reliable, and exhibit low electromagnetic interference (EMI). In electric vehicle (EV) drive applications, the two-level three-phase traction inverter is a key component that should exhibit high efficiency across varying loads and reliable operation at elevated switching frequencies.
This thesis presents a scalable, high-performance inverter design that combines autonomous gate drivers (AGDs) with optimized magnetic components. It incorporates snubber capacitors across each SiC MOSFET and a compact LC low-pass filter between the inverter output and motor terminals to enable effective soft switching and reduce EMI. This approach addresses key challenges in EV power conversion, offering a path toward compact, efficient, and EMI-compliant traction inverters for next-generation electric mobility.
The novel AGD design achieves zero-voltage switching (ZVS) under triangular current mode (TCM) control by continuously monitoring the switch voltage and current to determine optimal switching instants in real time. Direct sensing of switch conditions removes communication delays and ensures efficient ZVS at both turn-on and turn-off. The turn-off timing is set by an externally defined reference current transmitted through a galvanically isolated amplifier.
Simulation of a 10 kW two-level, three-phase inverter employing the proposed AGDs demonstrates over 99 % efficiency, sinusoidal current waveforms, and fast torque response with minimal overshoot and EMI. The integrated LC filter improves the output waveform quality while supporting soft-switching operation.
Experimental validation of the AGD concept was performed using a buck converter prototype. The AGDs operated independently of a central controller, initiating turn-on based on negative voltage detection and enabling lossless turn-off through a snubber capacitor. The system achieved ZVS at both transitions, confirming the practicality and scalability of the proposed gate-driving approach. For current sensing, the AGD employs the on-state resistance (Rds(on)) of SiC MOSFETs, eliminating the need for external shunt resistors. This reduces component count, avoids parasitic effects, and potentially increases reliability.
The thesis also investigates the design of filter inductors suitable for TCM-based ZVS inverters. Three prototypes were constructed using ferrite pot cores with Litz wire, copper foil, and solid round copper wire windings. Inductance was measured experimentally, and power losses were evaluated through Ansys Maxwell simulations under high ripple current and variable frequency conditions. Litz wire demonstrated superior performance in minimizing both copper and core losses. A dual-inductor configuration per phase—six inductors in total—is recommended for effective current handling and thermal management.