The rapidly growing electric and hybrid segment of the automotive industry is driving considerable changes. While these vehicles still lag far behind the sales of their fossil fuel counterparts, carmakers have learned quite a bit from their efforts. As a result, automobile designers no longer can settle for motion control components developed for industrial applications.
Carmakers are exercising their combined purchasing power to get new products more in line with their needs. Concurrently, changes for electric propulsion are occurring in power electronics, microcontrollers, system design and development tools, and more.
Motoring Along
Electric motors provide propulsion, and those with dual functions (motor-generators) recover energy from a variety of new vehicle classifications. In addition to the well-known Prius hybrid pioneered by Toyota, several carmakers are now developing or offering plug-in hybrid, mild hybrid, and even micro hybrid (no propulsion) as well as electric vehicles (see the table). While the terminology each manufacturer uses may vary slightly, the permanent magnet synchronous motor (PMSM) is the machine of choice for most carmakers.
The motor or motors are the central item of a motion control system in vehicle propulsion, so carmakers and suppliers are continuously improving existing designs and exploring new alternatives. There are at least two departures from current vehicle trends. One involves a new motor design, and the other uses more familiar approaches.
On the familiar side, the rising cost of neodymium magnets, the key enabler of the high performance in permanent magnet motors, is instigating carmakers and their Tier 1 suppliers to reevaluate alternate motor designs, specifically induction motors.
At the 2011 SAE Congress in Detroit, Jon Lutz, vice president of engineering at UQM Technologies, developer and manufacturer of high-efficiency electric motors, generators, and power electronic controllers, discussed alternatives to permanent magnet motors.
Based on the cost almost quadrupling and availability concerns for the neodymium magnets used in permanent magnet motors whose main supply comes from China, induction and wound field designs that had previously been viewed as less desirable are getting more attention, Lutz said.
Lutz also identified ongoing material research that could minimize the amount of neodymium required for a particular motor rating and alternate magnet materials. Improvements from power semiconductor technologies including silicon carbide (SiC) and gallium nitride (GaN) were among his reasons for expecting improved performance from the alternate motor technologies.
On the more radical side, in-wheel motors (IWMs) will provide a significant improvement to electric and hybrid vehicles according to Andy Watts, chief technology officer for Protean Electric. The company’s Protean Drive is a fully integrated, three-phase, permanent magnet direct-drive solution for vehicle propulsion. Each motor has a built-in inverter, control electronics, and software (Fig. 1).
The company has installed four IWMs in a Ford F-150 battery electric vehicle (BEV). Operating at 400 V dc, a Protean Drive PD18 with integrated inverter technology, an 18-in. IWH, achieves more than 300 Nm of torque at 1300 rpm with a peak power of 84 kW and 54-kW continuous power.