SiC-Based Power Unit and High Power Density Electric Machine for HEVs

Mitsubishi Electric Corporation has developed what is believed to be the world's smallest power unit for a two-motor hybrid electric vehicle (two inverters and one converter), measuring just 2.7 liters in volume, offering a world-leading 150 kVA/L power density. The motor also boasts top-class output-power density of 23 kW/L.

Featuring an all SiC power semiconductor module, high-density packaging technology and an asymmetric rotor structure, Mitsubishi Electric's new power unit and motor will help to improve fuel efficiency while enabling flexible installations and more space for vehicle cabins.

Key Features:

• World's smallest volume (2.7 L) and world's top power density (150 kVA/L) power unit for HEVs

The power unit consists of three main components: power module, reactor and capacitors. Mitsubishi Electric improved both the circuit structure and the high-density mounting of the control circuit board to which the insulating coating is applied, thereby reducing the volume of the power module, including the control circuit board, to 1/3 the size of the company's existing power unit.

By driving the converter with an SiC power device that achieves small switching loss at high frequency, the total volume of the reactor and capacitors (passive components) was reduced to 1/2 that of the company's existing power unit. Also, it features an excellent heat-dissipation structure that efficiently transfers heat loss to the cooling system.

• Top-class 23kW/L output power density achieved in high-torque concentrated-winding motor

A newly-developed asymmetric rotor structure and concentrated-winding enable Mitsubishi Electric's new motor to offer top-class output-power density. Considering that most of the motor's energy is used for driving the vehicle forward, not backward, an asymmetric rotor was developed to preferentially increase forward-direction rotational torque.

Also, output-power density was greatly enhanced by installing a novel magnetic slit in the iron core of the concentrated-winding motor, which is basically weaker than a distributed-winding motor. In addition, a high-efficiency oil cooling structure with an oil-water heat exchanger enables the use of extra-strong magnets, which conventionally are not suited to high temperatures.