Rotor displacement self-sensing of permanent magnet bias magnetic bearings using three-level switching amplifier power 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 three-level amplifier demodulation. Based on the proposed structure of radial PMB, the self-sensing principle is presented by the magnetic circuit analysis. Then a mathematical expression which includes voltage of the coil, neutral point voltage of the coil and coil current is derived. Based on the derived formula, a practical self-sensing algorithm adapting for three-level switching power amplifier (PA) is proposed. In three-level switching PA, voltage of the coil is non-ideal at high level or low level because of inductive load. If signals are sampled at these non-ideal times, the detection precision becomes worse. The problem is solved through sampling at zero level and singular point will not appear. The experiment on a magnetically suspended motor show that this method can satisfy the performance demand of magnetic bearings system and the rotor speed can reach 3342 RPM.