Control of axial force and motor torque of an axial gap self-bearing motor using two fourconcentrated-coil stators

Abstract

This paper proposes a novel structure of an axial gap self-bearing motor. The axial gap self-bearing motor controls both axial force and motor torque by using a similar structure to a disc motor, thus simplifying its structure and control system. In this paper, for further simplifying the structure, the number of stator coils is reduced to four for the side stators in a 4-pole disc rotor. Because one of the side stators produces only a 4-pole magnetic flux, all of the stator coils can be connected in series and driven by the single amplifier. Two stators are required to produce continuous motor torque and the bidirectional axial force; therefore, the drive system is composed of eight concentrated coils and two power amplifiers. To obtain continuous motor torque, the permanent magnets are attached to the rotor with a phase difference of 45 degrees between the two sides of the disc. In this study, the axial force and motor torque of the proposed structure are analyzed theoretically, and a control method for the axial force and motor torque is derived. Experimental results show that the proposed motor can control the axial position and the rotation speed simultaneously.

Keywords

• magnetic levitation
• magnetic bearing
• axial gap self-bearing motor
• permanent magnet disc motor