Design and Control of Novel High-speed Bearingless Motors

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Bearingless motors are a type of electric machine where the rotor is magnetically levitated and rotated by a single stator. These motors can eliminate the issues of mechanical bearings, such as friction, wear, lubrication, and heat dissipation, and therefore are favorable for high-speed industrial applications. However, bearingless motors have been so far applied only to niche applications, e.g. blood pumps, where the required speed and power are moderate. High-speed bearingless motor technology is still at a laboratory level, mainly because it involves multidisciplinary design and control challenges. The long-term goal of this research program is to establish high-speed (?>100 krpm) and high-power (P>10 kW) bearingless motor technology for industrial applications. During my doctoral study at MIT, I developed bearingless motors with magnet-free rotors for low-cost disposable blood pump impellers. Compared to conventional motors with permanent-magnet rotors, our design has potential for extremely high-speed operations due to the improved rotor strength. Also, the magnet-free rotors are favourable for high-temperature industrial machinery, such as steam and gas turbines. Within this 5-year Discovery Grant period, my group will push the speed limit of medium power (P~1 kW) bearingless motors by leveraging the magnet-free rotor topologies. Our key approaches include: 1) design and optimize bearingless motors with magnet-free rotors; 2) develop power electronics systems for high-speed current control of multiphase winding; and 3) establish multivariable estimation and control methods for high-speed rotor stabilization. The research program will train five HQP, including two PhD and three MASc students. Our mechatronics research activities will accompany innovations across various disciplines in science and engineering, such as electromechanics modeling and simulation, rotordynamics, measurement and instrumentation, power electronics, and control. Electric motors are used as the primary electromechanical energy conversion devices in industry. They form a basis for blowers, compressors, and pumps, which are indispensable to the energy and environment sectors. Therefore, even a slight performance improvement on electric motors can have a large impact in energy saving. For example, the efficiency of conventional chiller pumps in HVAC systems drops by more than 10 % due to the contact-type bearings' lubricants leaching into the refrigerant. Bearingless motors can save such a loss by eliminating the need for mechanical bearings and lubricants. Beyond the socioeconomic impacts, the proposed research program will also make an intellectual impact by enriching our knowledge on the design and control of precision mechatronic systems.