A PWM Amplifier for Self-Sensing Active Magnetic Bearings with Low-Sensitivity to Cable Length

Abstract

A magnetic bearing system usually contains position sensors that detect the gap length between the electromagnet and the rotor. Employing the position sensor is obstructions of downsizing and cost reductions of the system. To solve the problem, self-sensing techniques are developed.
This paper proposes a new PWM (Pulse Width Modulation) amplifier for self-sensing magnetic bearings. A self-sensing magnetic bearing reported in this paper solves the problem that sensing characteristics are affected by the length of the cable between the PWM amplifiers and electromagnets.
This methodology is verified by supporting the rotor of a high-speed motor with the proposed self-sensing magnetic bearings in two axes and conventional magnetic bearings with sensors in the other three axes. In the verification, the rotor revolving at 47, 000 r.p.m. has stably been suspended in the various cases of the cable length.