High-speed motor offers improved power density for EVs

The new high-speed motor designed and built by the team at UNSW is an improvement on existing IPMSMs (Interior Permanent Magnet Synchronous Machine Motor), which are predominantly used in traction drive of electric vehicles
The new motor designed and built by the team at UNSW is an improvement on existing IPMSMs (Interior Permanent Magnet Synchronous Machine Motor), which are predominantly used in traction drive of electric vehicles (Image: Dr Guoyo Chu)

UNSW engineers have built a new high-speed motor which has the potential to increase the range of EVs.

The design of the prototype IPMSM type motor was inspired by the shape of the longest railroad bridge in South Korea and has achieved speeds of 100,000 revolutions per minute. 

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The maximum power and speed achieved by this novel motor have successfully exceeded and doubled the existing high-speed record of laminated IPMSMs (Interior Permanent Magnet Synchronous Motor), making it the world’s fastest IPMSM ever built with commercialised lamination materials.

Most importantly, the motor is able to produce a very high power density, which is beneficial for EVs in reducing overall weight and therefore increased range for any given charge.

The new technology, developed by a team headed by Associate Professor Rukmi Dutta and Dr Guoyu Chu from the UNSW School of Electrical Engineering and Telecommunications, is an improvement on existing IPMSMs, which are predominantly used in traction drive of electric vehicles.

An IPMSM type motor has magnets embedded within its rotors to create strong torque for an extended speed range.

However, existing IPMSMs suffer from low mechanical strength due to thin iron bridges in their rotors, which limits their maximum speed.

But the UNSW team have patented a new rotor topology which significantly improves robustness, while also reducing the amount of rare-earth materials per unit power production.

The new design is based on the engineering properties of the Gyopo rail bridge, a double-tied arch structure in South Korea, as well as a compound-curve-based mechanical stress distribution technique.

And the motor’s impressive power density potentially offers improved performance for electric vehicles where weight is extremely important.

“One of the trends for EVs is for them to have motors which rotate at higher speeds,” Dr Chu said.

“Every EV manufacturer is trying to develop high-speed motors and the reason is that the nature of the law of physics then allows you to shrink the size of that machine. And with a smaller machine, it weighs less and consumes less energy and therefore that gives the vehicle a longer range.

“With this research project we have tried to achieve the absolute maximum speed, and we have recorded over 100,000 revolutions per minute and the peak power density is around 7kW per kilogram.

“For an EV motor we would actually reduce the speed somewhat, but that also increases its power. We can scale and optimise to provide power and speed in a given range—for example, a 200kW motor with a maximum speed of around 18,000rpm that perfectly suits EV applications.

“If an electric vehicle manufacturer, like Tesla, wanted to use this motor then I believe it would only take around six to 12 months to modify it based on their specifications. 

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“We have our own machine design software package where we can input the requirements of speed, or power density and run the system for a couple of weeks and it gives us the optimum design that satisfies those needs.”

Apart from electric vehicles, the motor has many other potential applications. One of them is large heating, ventilation, and air conditioning (HVAC) systems which require high-speed compressors to use a new form of refrigerant which significantly reduces the impact on global warming.

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