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Silicon carbide electric vehicle motor-drive is half the size

08 March, 2012

Mitsubishi Electric has developed a prototype electric vehicle (EV) drive system based on a permanent magnet motor with an integrated silicon carbide inverter which, it claims, is the smallest of its kind and is half the size of systems with external inverters. Losses are said to be less than half those of silicon-based systems.

The new motor-drive (shown above, with the inverter on the left and the motor on the right) could allow EV manufacturers to develop vehicles with more passenger space and higher efficiencies. Mitsubishi plans to commercialise the system after finalising technologies for cooling, downsizing and efficiency.

Because EVs and hybrid EVs require relatively large spaces for their battery systems, there is pressure to reduce the size and weight of their drive systems and other equipment to maximise the space available in the passenger compartment.

Mitsubishi`s existing EV drive systems consist of separate motors and inverters driving the motors, requiring more space for these components and their cabling. The new cylindrical inverter matches the diameter of the motor, enabling the two components to be connected coaxially, and resulting in a substantial downsizing of the drive system.

Although silicon-based power devices still dominate the inverter switching market, silicon carbide has attractive characteristics, including high-temperature operation and a breakdown electric field that is 10 times higher than those of silicon devices. This allows the production of thinner chips, reducing their electrical resistance and lowering their losses.

All of the power devices in the new inverter are based on silicon carbide, resulting in a reduction of losses of more than 50% compared to silicon-based inverters.

The new drive system uses a permanent magnet motor incorporating neodymium rare-earth magnets. A proprietary high-density winding structure has allowed Mitsubishi to use its “poki-poki” motor production technology, which wraps the coils around an extended core, to reduce the size of the motor.

The size and configuration of the stator and rotator poles have been optimised using a sophisticated magnetic design technology, resulting in an improved magnetic efficiency and a 5% increase in power output compared to Mitsubishi’s previous motors.




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