Rotor Displacement Self-Sensing Approach for Permanent Magnet Biased Magnetic Bearings Using Double-Axis PWM Demodulation

The self-sensing magnetic bearing technology offers significant cost savings and the potential for dynamics advantages due to its fundamental sensor-Actuator collocation. This paper proposes a rotor displacement self-sensing scheme for the permanent magnet bias magnetic bearings (PMB) using double-channel PWM demodulation with a 90-degree phase shift. Based on the proposed structure of PMB, the self-sensing principle is presented by the magnetic circuit analysis. Then, the linear relationships between the rotor displacement and neutral voltage of the coil coupled in the x-and y-Axis are derived. The two triangle carrier waves with a 90-degree phase shift are used to obtain two uncorrelated linear equations. For the hardware implementations, the rotor displacements in the x-and y-Axis can be solved within a PWM cycle by the logic gate demodulation circuit. To validate the proposed self-sensing method, experiments are carried on a 10 kW magnetic levitated motor; the experiment results show that the self-sensing magnetic bearing has a characteristic of high sensitivity, large linear range, and wide dynamic range.