Refining Electric Powertrain Efficiency: SiC vs. Si Semiconductor, Thermal Solutions, and Optimal Power Conversion Strategies

Doktorsavhandling, 2025

This work first establishes a concrete numerical system simulation model to
quantify the impact of junction temperature feedback on power and energy
losses in three-phase silicon carbide (SiC)-based propulsion inverters com-
pared to traditional silicon-insulated-gate bipolar transistors (Si-IGBTs). It
then proposes and demonstrates improved heat spreading within a SiC power
module using graphene-assembled films in both the packaging and a pin-fin-
based heatsink through comprehensive thermal simulations.
Using a loss minimization approach, this work further determines the opti-
mal DC-link voltage across the full drive range. It includes a detailed power
loss analysis of a propulsion inverter, incorporating temperature variations,
alongside finite element method (FEM)-based loss modeling of an interior
permanent magnet (IPM) synchronous machine under variable DC-link volt-
ages.
Finally, this study focuses on identifying the optimal switching frequency for
SiC-based motor drives vs. IGBT counterparts across a wide range of operat-
ing conditions. The approach involves conducting a comprehensive real-time
FEM analysis of losses induced by pulse width modulation (PWM) voltages
in an IPM synchronous machine, compared to conventional sinusoidal current
excitation feeding.
Utilizing a graphene layer in the SiC module reduced the MOSFET junction
temperature by 10◦C, corresponding to an applied power loss per SiC chip in
steady-state simulations. Additionally, graphene integration in the heatsink
lowered the SiC chip temperature rise by 11.5% compared to aluminum.
The optimized DC-link profile over WLTC reduced energy losses by 58%
in the SiC system and 54% in the IGBT system compared to operating at a
fixed 300 V DC-bus, with significant reductions also observed against a 450 V
boosted DC-link. Furthermore, applying the optimal PWM frequency profile
over WLTC lowered accumulated energy losses by up to 11% for SiC inverters
and 4.2% for IGBT inverters compared to a fixed 10 kHz switching frequency.