Design issues in silicon carbide power converters
Date of Issue2016
School of Electrical and Electronic Engineering
Rolls-Royce@NTU Corporate Laboratory
The trend towards more electric aircraft (MEA) requires replacement of the existing non-propulsive powers including hydraulic, pneumatic and mechanical systems by the electric power. Due to the strict demands on space and weight for lower fuel consumption in aircraft, a high power density converter (HPDC) is needed. The conventional Si power converter has difficulty meeting all these requirements due to the switching frequency limitation. In addition, the trend to directly mount the electric generator/starter with power converter on the shaft of gas turbine engine will subject the power converter to high ambient temperatures above 200 °C, which makes Si totally unacceptable for this application. The wide bandgap (WBG) material silicon carbide (SiC) is regarded as the next- generation semiconductor for the high power density and hash environment applications. In this thesis, the key technologies related to the development of SiC-based HPDC for MEA application are investigated. Basically, there are two strategies to push the power density envelope. From the electrical point of view, the power converter needs to operate at high switching frequency to reduce the size of passive components, like the DC-link capacitor and output filter. From the thermal point of view, the heat sink size needs to be minimized by use of advanced cooling method. Hence, the issues encountered when applying these two strategies are addressed in this work. By maximizing the switching frequency of SiC power converter, this tends to deteriorate the electromagnetic interference (EMI) issue and dv/dt, di/dt effects. Hence, the circuit simulation models for the SiC power devices are developed to assist the gate driver and converter design firstly. Then the gate driver is optimized and a novel gate assisted circuit is proposed to resolve the shoot-through issue in the classical half bridge configuration. In addition, a novel high-speed short-circuit protection scheme based on gate charge detection is proposed. The stray inductances for both gate driver and converter are minimized during layout design. To reach the optimized converter design, the switching characterizations for various SiC power devices are conducted based on the universal double pulse testing setup. Furthermore, an integrated micro-channel heat sink is proposed for the SiC power module. Hence, the size of heat sink can be minimized while the cooling efficiency is maximized. Finally, the 1st generation prototype of liquidcooled SiC-based HPDC based on three-phase two-level voltage source inverter is developed and tested with 50 kW output power, ±375 Vdc input voltage, 230 Vac out voltage, 60 kHz switching frequency, 98% efficiency, and 32 kW/L power density.
DRNTU::Engineering::Electrical and electronic engineering::Power electronics