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Ibrahim, Hosam

University of British Columbia

Bearingless motors are an emerging class of electric machines that combines the functionality of an active magnetic bearing (AMB) and an electric motor into the same stator structure. This integration benefits from the advantages of AMBs while addressing their shortcomings, resulting in more compact magnetically levitated systems with reduced system complexity and cost. However, despite these advantages, the relatively low power density of bearingless motors has primarily limited their use to research settings and niche applications with low power demands. The operation of a bearingless motor necessitates the generation of two distinct field components in the airgap for torque and radial force generation. Traditionally, this was achieved using separate suspension and torque windings. However, this results in an inefficient winding volume utilization and reduced power density. Consequently, a shift has emerged towards combined windings, utilizing the same windings for both suspension and rotation. This is achievable through the use of multiphase windings, offering additional degrees of freedom to simultaneously generate torque and suspension forces. To support research on multiphase bearingless motors and exploit the advantages of combined windings, we develop a custom multiphase motor control platform that integrates the controller, sensor interface, and power electronics into a reconfigurable system. The design consists of a two-level twelve-leg inverter with isolated inline shunt-based phase current sensing and isolated DC bus voltage sensing. A 12-phase inverter is realized using GaNFET-based half-bridge power stages. The DC bus voltage and the phase currents are measured using isolated delta-sigma modulators. An FPGA is used to implement a sophisticated motor control algorithm with high temporal determinism. The performance of the motor drive is evaluated with a homopolar bearingless motor prototype. Development of the drive enables the use of custom control strategies, such as sensorless control, which allows the prototype motor to operate up to its rated speed (36000 r/min) as limited by the available DC link voltage (30 V). This represents an almost fourfold increase in the maximum no-load speed of 9500 r/min reached when using off-the-shelf power electronics and a DC link voltage of 48 V.

Text

2023-08-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85733

Mechanical Engineering

University of British Columbia

UBCV

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