UNSW team develops new very-high-speed IPMSM motor with improved power density for EVs; new rotor topology
Engineers at the University of New South Wales (UNSW), Australia, have built a new high-speed motor which has the potential to increase the range of electric vehicles. The maximum power and speed (100,000 rpm) 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 commercialized lamination materials.
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.
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.
One of the trends for electric vehicles is for them to have motors which rotate at higher speeds. 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 electric vehicle motor we would actually reduce the speed somewhat, but that also increases its power. We can scale and optimize 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.
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.—Dr Chu
The design of the new IPMSM motor took its ispiration from the double-tied arch rail bridge in Gyopo, South Korea. Image from Dr Guoyo Chu
The new IPMSM prototype motor was developed using the UNSW team’s AI-assisted optimization program which evaluated a series of designs for a range of different physical aspects: electrical, magnetic, mechanical and thermal. The program evaluates 90 potential designs, then selects the best 50% of options to generate a new range of designs and so on, until the optimum is achieved. The final motor is the 120th generation analyzed by the program.
The UNSW team’s new motor also offers a significant cost advantage over existing technology and uses less rare earth materials such as neodymium.
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. 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 rare earth materials, which includes a big reduction in the material cost—thus making our high-performance motors more environmentally friendly and affordable.—Dr Chu