A Novel Power Failure Compensation Control Method for Active Magnetic Bearings Used in High-Speed Permanent Magnet Motor

Active magnetic bearings (AMBs) have been proved superior to conventional bearings in many ways. However, the AMB system will lose magnetic force if the power fails which may cause fatal damage to the rotor and the backup bearings. In order to improve the reliability of the AMB system, a power failure compensation control (PFCC) method is proposed in this paper. A novel hardware composition of PFCC is designed to cooperate with the motor drives using either pulse-width modulation (PWM) or pulse-amplitude modulation techniques. Once the power fails, the motor works as a generator and the back electromotive force (back EMF) is rectified by the antiparallel diodes of the inverter. Meanwhile, a buck converter is utilized to convert the voltage from dc-link of the inverter to the supply voltage for the AMB system. When the motor speed is too low to supply high back EMF for the buck converter, the switches of the inverter are used to boost the dc-link voltage with the motor windings. Furthermore, a hybrid controller combining sliding mode control with PID algorithm is introduced to improve the transient response of the buck converter. Several experimental results confirm the feasibility and effectiveness of the proposed method.