Mitsubishi Integrates Inverter With EV Motor System

Mar 9, 2012
Tsunenori Tomioka, Nikkei Monozukuri
Mitsubishi Electric's EV motor system whose inverter and motor are integrated
Mitsubishi Electric's EV motor system whose inverter and motor are integrated
[Click to enlarge image]
The back side of the new EV motor system. The printed-circuit board of the inverter can be seen.
The back side of the new EV motor system. The printed-circuit board of the inverter can be seen.
[Click to enlarge image]

Mitsubishi Electric Corp developed a motor system whose output power is more than 70kW for electric vehicles (EVs) by integrating an inverter and a motor on the same axis.

The volume of the new system is only half that of the company's motor system whose inverter and motor are separated, which was exhibited at the 42nd Tokyo Motor Show 2011. The integration enabled to shorten electric lines between the inverter and motor as well as to integrate pipes for water cooling that are required for each of the inverter and motor in the old system.

The mass of the new system is about 10% less than that of the old one. And the total efficiency of the new system is 3-5 points higher than that of the old system under the JC08 test mode.

"(To integrate the inverter and motor,) the most difficult challenge was to prevent heat generation," Mitsubishi Electric said.

Because the motor and inverter generate a large amount of heat, the company not only increased cooling capability but also made improvements to each of the motor and inverter to reduce heat generation. Specifically, it changed the magnetic design of the motor and employed a silicon carbide (SiC)-based power device for the inverter. With the SiC-based power device, the loss of the inverter was reduced by half, compared with the inverter of the old system that uses a silicon (Si)-based power device.

This time, Mitsubishi Electric used a motor containing a permanent magnet. Also, it improved output power per unit volume by 5% by employing a concentrated winding method to increase coil space factor and using magnetic design technologies to optimize the shape of the motor.

Currently, the motor system can be used for rotating tires and for simulated driving based on actual driving patterns in a laboratory. To commercialize the system, it is necessary to improve its structure for volume production, fine-tune it and further reduce its weight by 10 to 20%, Mitsubishi Electric said.

The company aims to commercialize the system in 2017. And it plans to commercialize an EV motor system whose inverter using a Si-based power device and motor are separated in 2014.