An Improved Transient Control Strategy for Active Magnetic Bearing Open-Circuit Fault-Tolerant

Active magnetic bearing plays an essential role in high-speed rotational machines. Due to the need for multiple coils, the active magnetic bearing (AMB) system requires a significant amount of power electronics switches which increases the risk of switch failure. In previous studies, facing switch open-circuit, proper designing of redundant devices, and implementing current reversal to reconstruct electromagnetic force are necessary. However, fault-tolerant is not only the reconfiguration of circuit but also the prevention of the rotor colliding with the protective bearing. Hence, this article analyzes the rotor dynamic characteristics during the transient of fault-tolerant. By the analysis, rotor displacement fluctuation is closely related to the transient time necessary for current reversal. Thus, this article employs discontinuous pulsewidth modulation (DPWM), suitable for multiaxis AMB systems, to enhance dynamic response. In the multiaxis system, DPWM can nearly double the rate of current change and markedly reduce transient displacement fluctuations by means of the three-step switch algorithm. A series of fault-tolerant experiments verify the feasibility of the proposed method.