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Higher-efficiency, cooling-free motor will extend EV ranges

27 July, 2012

Engineers at GE Global Research have developed a prototype permanent magnet (PM) motor for electric vehicles (EVs) that, they say, is 3–5% more efficient than similar existing traction motors, as well as achieving almost twice the power density. The 55kW (peak) motor can also operate continuously at high temperatures (105ºC) without needing dedicated cooling,

The motor (above), developed as part of a $5.6m US Department of Energy (DoE) project, could help to extend the range that EVs can travel before needing recharging, as well as delaying the point at which hybrid EVs need to switch to conventional fuels.

According to GE, the motor will cost less to make than comparable motors on the market today, as well as being more powerful and efficient. The technology is scalable and could lead to more efficient industrial motors and generators.

“This is a significant accomplishment,” says Ayman El-Refaie, an electrical engineer in GE Global Research’s Electrical Machines Lab. “We are pushing the boundaries to build more robust, yet more efficient, motors for hybrid and fully electric platforms. We have built a motor that is substantially more powerful than what’s commercially available now, while improving efficiency by up to 5%.”

Unlike conventional traction motors, which typically run at 65ºC and need their own dedicated cooling loops, GE’s motor can operate continuously at 105ºC over a wide speed range – from 2,800–14,000 rpm at 30kW – and can be cooled using engine coolant. Avoiding the need for additional cooling lines could make hybrid EVs lighter and cheaper.

The interior permanent magnet motor also delivers the required torque using a much lower DC bus voltage than usual – as low as 200V, compared to the 650V typical of other systems.

As part of the project, GE developed high-resistivity (3X) permanent magnets with lower losses, which could reduce or eliminate the need to segment the magnets. This will help keep costs down even more.

The company has built and tested several prototypes of the new motor, but says that more reliability testing is needed before it is ready to consider commercial production.

“This technology is scalable and flexible enough that it can be leveraged in a number of capacities,” says El-Refaie. “What we learned through this project will help us build higher efficiency industrial motors, high-speed oil and gas compressor motors, and generators for aerospace applications.”

GE engineers have embarked on a four-year follow-up project to develop a comparably performing motor which does not need rare-earth magnets.

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