|New EV motor system with built-in silicon carbide inverter. Click to enlarge.|
Mitsubishi Electric Corporation has developed a prototype electric vehicle (EV) motor system with a built-in silicon carbide inverter. The EV motor system is the smallest of its kind, measuring just half the dimensions of Mitsubishi Electric’s existing motor system that uses an external inverter, and loss is below half that of silicon-based systems.
The new motor system is expected to enable manufacturers to develop EVs offering more passenger space and greater energy efficiency. The company plans to commercialize the motor system after finalizing other technologies for motor/inverter cooling, downsizing and efficiency.
The global demand for EVs and hybrid EVs (HEVs) has been growing in recent years, reflecting increasingly strict regulation of fuel efficiency and growing public interest in saving energy resources and reducing carbon dioxide emissions. As EVs and HEVs require relatively large spaces to accommodate their battery systems, there is a strong need to reduce the size and weight of motor systems and other equipment to ensure sufficient room in passenger compartments, Mitsubishi reasons.
Mitsubishi Electric’s existing system—comprising separate motors and inverters driving the motors—requires more space for these components and their wiring. The newly developed cylinder-shaped inverter matches the diameter of the motor, enabling them to be connected coaxially within a chassis, resulting in a substantial downsizing of the motor system.
Silicon chips have been widely used in power devices for inverter switching. Silicon carbide, however, is now recognized as a more suitable material for chips owing to its electrical characteristics, including a breakdown electric field that is 10 times greater compared to silicon chips. This greater breakdown electric field enables thinner chips, which reduces electrical resistance and lowers loss.
All power chips in the inverter are silicon carbide-based, resulting in a more than 50% reduction of loss compared to the company’s silicon-based inverter system.
The motor is a permanent magnet motor that uses a neodymium magnet. Mitsubishi Electric’s proprietary dense-winding structure enabled the company to utilize its Poki-Poki motor production technologies that essentially entail wrapping coils around an extended core to enable higher density and using a joint lapping technique (earlier post) to reduce the size of the motor.
(Mitsubishi has developed the Poki-Poki motor manufacturing technology since 1993 and has applied it to various motors used in such products as information devices, industrial equipments, electrical household appliances, motor vehicles and elevators.)
The size and configuration of the stator and rotator poles were optimized using Mitsubishi Electric’s high-level magnetic-design technology. As a result, magnetic efficiency was increased and power output was improved by 5% over previous motors.