INVERTER: Hitachi has developed a silicon carbide hybrid inverter for electric multiple-units using a 1·5 kV overhead power supply. The inverter uses hybrid modules rated at 3·3 kV, which are approximately two-thirds the size of standard silicon modules.
The updated design has a simpler circuit configuration and smaller dimensions. By combining silicon carbide diodes and silicon insulated gate bipolar transistors, the hybrid module minimises both diode and IGBT power losses. The use of lightweight oil-free capacitors also reduces overall weight by around 40% compared to current products. Hitachi has also developed proprietary soft-gate control technology to counter electromagnetic noise generated during AC/DC switching.
As EMU inverters are generally cooled by airflow as the vehicle moves, the temperature of coolers is lower upwind when air is taken in and higher downwind. Fluid analysis technology has been used to revise the pipe configuration to limit this differential, resulting in size and weight savings.