A feedback signal of the rotor radial displacement is essential for realizing the stable suspension for bearingless flux-switching permanent magnet machines (BFSPMMs). Although the recent smart sensors technology is developing rapidly, the mechanical sensors will increase the complexity of the system while reduce its reliability. Thus, an alternative is urgently needed to achieve the compact and practical motor structure. Herein, a novel rotor radial displacement observer is presented, and a radial displacement sensorless control system based on the observer for a BFSPMM is built. First, the mathematical model of the motor concerning rotor eccentricity is established. The theoretical expressions of flux linkages are derived, which are closely related to the eccentric distance and angle. Second, the rotor displacement signal is estimated by the difference of the symmetric-winding flux linkages. And a closed-loop compensation method is designed to reduce the phase lag of the signal in the observer due to the filter. Besides, the convergence regarding the proposed observer is analyzed. Ultimately, the observed result is used as a feedback signal to control the suspension force of the system. The simulation and experimental results verified the validity of the proposed scheme.

It is a key to realizing stable suspension operation of bearingless motor that the rotor radial displacement information is acquired accurately. Sensor applications are sensitive to environments, limiting to scenarios, and increasing costs. Herein, a radial displacement sensorless control method in the full speed range for single-winding bearingless flux-switching permanent magnet motor is proposed. First, an eccentric modulation function is presented, and the flux linkage equation of each winding with rotor eccentricity is derived based on the air-gap magnetic field modulation theory. Therein, the phase inductance and flux are functions of the rotor displacement. Second, the bias-flux equations of the symmetric windings are deduced, and the rotor displacement observer of the medium-high speed is established based on the bias-flux amplitude. Due to flux information being difficult to extract at low speed, the high-frequency current signal is injected into the d_T -axis of the torque plane. The rotor displacement observer of the zero-low speed is established based on the high-frequency bias-induced EMF amplitude. Besides, a novel smooth switching process is designed. Finally, the observers are analyzed, and the radial displacement sensorless control strategy is built. The experimental results verified the validity of the proposed method.

The failure of the inverter bridge arm or the open circuit of the phase winding may occur during the operation of a combined winding bearingless flux-switching motor, causing both rotor rotation and suspension to malfunction, hence fault-tolerant control is vital for the motor's reliability and stability. In this paper, a fault-tolerant operation control strategy for combined winding bearingless flux-switching permanent magnet motors under open-circuit fault condition is proposed. Firstly, how to control the electromagnetic torque and suspension force acting on the rotor with the combined winding structure is explained, and then the mathematical models of the torque and suspension force which can be controlled individually by different current components are deduced in detail. Afterward, the relation of the phase current without and with winding fault is discussed, and the operation conditions of maintaining constant torque and suspension force after fault are demonstrated. Whereupon, the fault-tolerant control block diagram is constructed. Finally, the experimental results are presented to demonstrate the performance of the proposed strategy.

A suspension flux internal model control method is proposed to address the problem of the strong coupling of a single-winding bearingless flux-switching permanent magnet motor leading to a significant ripple of the rotor radial displacement. Firstly, based on air-gap magnetic field modulation theory, the stator flux equation considering rotor dynamic eccentricity is established to reveal the relationship between the eccentric rotor and the magnetic field. Secondly, according to the dynamic characteristics of the motor and the variation law of the air-gap magnetic field, the suspension-plane flux is substituted into the rotor dynamic model, and the suspension flux-dynamics internal model and corresponding output are constructed, respectively. Finally, a complete control strategy is established, and the rotor is stably suspended by PWM control. The simulation and experimental results show that the proposed method has better steady-state and dynamic performance than traditional PID control, and the maximum radial displacement ripples of the rotor are reduced by 53% and 50% in steady-state and dynamic operation.