DESIGN AND CONTROL OF A HIGH-PRECISION PERMANENT-MAGNET AC MOTOR USING A HALBACH MAGNET ARRAY

Abstract

This work presents, designs, models, and tests a two-phase permanent-magnet (PM) external-rotor AC motor utilizing a Halbach array for the purpose of precision positioning. The motor is made up of twelve coils and nine pitches of the Halbach array and controlled through the use of a National Instruments data acquisition (DAQ) board paired with MATLAB’s DAQ toolbox. The motor makes uses of the Halbach array and the lack of any ferromagnetic materials in the system to ensure the internal magnetic field is sinusoidal. The motor takes advantage of this fact to generate a torque that is independent of both the rotor position and current distribution. Whereas most PM motors rely on the requirement that the coil windings are sinusoidally distributed, this motor is able to compensate for not having sinusoidally distributed coil windings by instead adjusting the current phase vector based on rotor positioning.

After characterizing the motor and through the utilization of data collected during the normal operation of the motor, and several procedures designed to account for discrepancies in the timing of the DAQ board’s clocks, the response of the three embedded Halleffect sensors were mapped to the position of the rotor. Linear sections of this mapping were then used to control the position of the rotor down to an accuracy of just a few hundred thousandths of a degree. Additionally, due to the inherent nature and stability of the system, the only controller required to achieve these results is a PID controller.