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Aussie motor ‘doubles speed record’ and cuts rare-earths

15 September, 2022

Australian researchers have built a high-speed electric motor that, they claim, is much more robust that other IPMSMs (interior permanent magnet synchronous motors), while using far fewer rare-earth materials and being cheaper. The prototype motor has achieved speeds of 100,000 rpm, more than doubling the previous speed record for laminated IPMSMs, according to the developers.

IPMSM motors have magnets embedded in their rotors to create powerful torque for extended speed ranges. However, most existing IPMSMs suffer from low mechanical strength because of thin iron bridges in their rotors, limiting their top speeds.

The researchers from the University of New South Wales School of Electrical Engineering and Telecommunications have patented a new rotor topology which improves robustness “significantly”, while also reducing the amount of rare-earth materials needed. The design was inspired by South Korea’s longest rail bridge, which has a double-tied arch structure.

The team, headed by associate professor Rukmi Dutta and Dr Guoyu Chu, developed the motor using their own AI-assisted optimisation program which evaluated a series of designs for different physical aspects – electrical, magnetic, mechanical and thermal. It assessed 90 potential designs, then selected the best options to generate a new range of designs, until the optimum design was achieved. The final motor was the 120th generation analysed by the program.

“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,” explains Dr Chu.

“Most high-speed motors use a sleeve to strengthen the rotors and that sleeve is usually made of high-cost material such as titanium or carbon fibre,” he adds. “The sleeve itself is very expensive and also needs to be precisely fitted and that increases the manufacturing cost of the motor.”

“Our rotors have very good mechanical robustness, so we don’t need that sleeve, which reduces the manufacturing cost. And we only use around 30% of the rare-earth materials of other motors, resulting in a big reduction in material costs – making our high-performance motors more environmentally friendly and affordable.”

The researchers believe that their motor has many potential applications, including in large HVAC (heating, ventilation and air-conditioning) systems that need high-speed compressors for use with new refrigerants with reduced global warming effects.

The high-speed motors could also be used to allow precision CNC machines to mill or drill with small diameters. Another potential application is to provide electrical power on aircraft.

A prototype of the new Australian motor being tested
Photo: Dr Guoyo Chu

Perhaps the most promising use for the high power density motors is in electric vehicles, where they could save weight and extend ranges.

“One of the trends for EVs is for them to have motors which rotate at higher speeds,” says Dr Chu. “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 rpm 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,” he continues. “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 18,000 rpm 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 6-12 months to modify it based on their specifications.”

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