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Szoke, Simon

University of British Columbia

Bearingless motors are an emerging technology with applications in various niche markets. In this context, bearingless refers to “mechanical bearingless”, and these motors use magnetic bearings to constrain the rotor. The current prior art of bearingless motors are still quite limited in their performance, and they tend to have some weaknesses that limit their usefulness. However, these machines are advantageous for use in high speed machinery, such as centrifuges and turbo-molecular pumps. The magnet-free rotor of this machine also makes it suitable for high-temperature applications, such as steam turbines and turbochargers in engines. This project aims to take a step towards establishing a high performance bearingless motor design. The proposed design is of the homopolar slice motor variety, and a novel quadruple three-phase winding scheme is presented as one of the main performance enhancing features. This motor falls within a sub-category of synchronous permanent magnet machines. In this case, the permanent magnets are located on the stator, and they magnetize the rotor through the air gap, creating a bias flux. The bias flux passively stabilizes the rotor’s axial translation and tilt, which reduces the sensing and controller complexity. The rotor’s radial suspension is actively stabilized with a controller and the use of eddy current position sensors. The motor uses a 2-pole suspension and 8-pole rotation excitation pattern, which physically decouples the rotation and suspension controls. The winding scheme uses four three-phase amplifiers to power the 12 windings of the motor. Each group of three windings are connected in a wye configuration. This allows for higher speeds compared to a regular 3-phase arrangement because each winding is allowed approximately 4 times the maximum phase voltage. So, the speed and thus power density is increased for a given DC link voltage. We built a prototype motor for testing. The motor achieved 9200 RPM using a 48V DC link. This is below the design capability, although higher than the previous three-phase counterpart. The limiting factor is the suspension current draw at high speeds. Future work should focus on improving upon this area by implementing controller improvements and better power electronics.

Text

2022-07-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82216

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/