Silicon Carbide Inverter for EV/HEV Application featuring a Low Thermal Resistance Module and a Noise Reduction Structure

This paper presents the technologies incorporated in an electric vehicle (EV)/hybrid electric vehicle (HEV) inverter built with power semiconductors of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) instead of conventional silicon (Si) insulated gate bipolar transistors (IGBTs). A SiC inverter prototype of 2.9 L in size for driving an 80-kW motor was fabricated and evaluated on a motor test bench. The SiC inverter prototype attained average efficiency of 98.5% in the Worldwide harmonized Light-duty Test Cycle (WLTC) driving mode. The two main technologies achieved with this SiC inverter prototype are described. The first one is a new direct-cooled power module with a thick copper (Cu) heat spreader located under the semiconductors that improves thermal resistance by 34% compared with a conventional direct-cooled power module. The SiC chip size is smaller than that of Si IGBTs, so this technology solves the problem that cooling characteristics typically worsen with a smaller chip cooling area. The second technology is an inverter structure that reduces transmission of generated noise to the inverter case. This structure makes it possible to take advantage of the inherent characteristic of SiC MOSFETs that their switching speed is faster than that of Si IGBTs. As a result, switching loss is reduced and efficiency is improved. The fabrication and evaluation of this SiC inverter prototype have confirmed that these key technologies elicit the advantages of SiC MOSFETs and compensate their drawbacks, thereby reducing the size and improving the efficiency of the SiC inverter.