Mitsubishi Electric has developed a prototype forced-air-cooled three-phase inverter with power modules that use only silicon carbide (SiC) power semiconductors. The 156kVA output inverter, with a power density of 50kVA per litre, is expected to lead to smaller, lighter power electronic equipment for industrial and automotive applications, among others.
The power module, which is rated at 1.2kV/300A, incorporates SiC Mosfets (metal oxide semiconductor field effect transistors) and SBDs (Schottky barrier diodes). To achieve the high power density, Mitsubishi had to increase electric current densities by lowering electric resistance. It has developed a low-resistance wiring technique that bonds the power semiconductor chips directly to the main terminals, eliminating the need for conventional high-resistance aluminium wires.
To achieve the high current densities, low-loss (low-resistance) power chips have been used. This required high-speed protection circuits to prevent large destructive currents from flowing during short circuits. Mitsubishi has used a SiC Mosfet with a built-in current-sensing function and a high-speed short-circuit-protection circuit, making it possible to use a low-resistance SiC Mosfet, even at high current densities.
SiC is widely regarded as a promising next-generation power semiconductor material, with advantages over the silicon (Si) traditionally used in power semiconductor devices. Compared to silicon, SiC has a critical electric field for breakdown that is about 10 times higher. This reduces power losses, in turn reducing the need for cooling equipment, and leading to smaller, lighter electronic components for industrial and automotive uses.
Mitsubishi plans to further downsize its SiC inverters further to make them commercially viable.