All-SiC Three-Phase Converters for High Efficiency Applications

The dissertation aims to improve the efficiency of three-phase converters using SiC power devices.The methodology to design a high efficiency all-SiC three-phase converter is presented. Four aspects are included: SiC power device evaluation, power loop parasitics analysis, high efficiency current source rectifier, and paralleled current source rectifier system.

The SiC JFET and MOSFET are tested based on voltage source and current source structures respectively. The dissertation proposes a device switching test circuit based on current source topology to simulate current commutation processes. The circuit can evaluate the switching performance and calculate switching loss of a power device used in a three-phase current source converter.

The impacts of power loop parasitics on SiC devices’ switching performance and switching loss are studied. The power loop parasitic inductance in a voltage source converter may cause phase-leg shoot-through during a fast switching transient. The key inductances include power device gate loop inductance and converter DC bus inductance. The influence of different parasitic capacitances on device switching loss in three-phase current source converters is analyzed. An inductive snubber circuit is proposed to reduce the impact of parasitic capacitance and reduce power device switching loss in a three-phase current source rectifier.

The design method and procedure of high efficiency three-phase converters are proposed through the development of a 7.5 kW all-SiC three-phase current source rectifier for data center power supplies as the front-end rectifier. The rectifier full load efficiency of 98.54% is obtained.

Master-slave control is proposed for paralleled three-phase current source rectifiers. The balanced output currents, rectifier module hot-swap, and paralleled rectifier system redundancy can be achieved with this master-slave control. A 19 kW front-end rectifier system using three paralleled all-SiC current source rectifiers is developed for data center power supplies with 98.3% peak efficiency and 98.1% full load efficiency.