Accurate and fast fault-diagnosis is the foundation of fault-tolerance. To develop the faulttolerance of magnetic-levitated bearing system, this paper presents an online fault-diagnosis approach of electromagnetic actuator based on variation characteristics of sampled load current in the modulation to identify the time constant of the electromagnetic coil, and then to diagnose the broken circuit or partial short-circuit faults. After analysing the variation characteristics of the load current theoretically, the simulation is constructed to verify the effectiveness of the proposed approach. Considering the real-time requirement of fault-diagnosis, we develop a fast sampling and calculating method for the equivalent slope of the load current in the modulation, which represents the variation characteristics of the load current. The experimental results demonstrate that the proposed approach is effective for diagnosing broken circuit and partial short-circuit faults, and the execution time for the fault-diagnosis is about 2 ms, proving its excellent real-time performance.
At present, magnetic bearings are a better energy-saving choice than mechanical bearings in industrial applications. However, there are strongly coupled characteristics in magnetic bearing–rotor systems with redundant structures, and uncertain disturbances in the electrical system as well as external disturbances, and these unfavorable factors degrade the performance of the system. To improve the anti-interference performance of magnetic bearing systems, this paper proposes the inverse of the current distribution matrix W−1 meaning that the active disturbance rejection control simulation model can be carried out without neglecting the current of each coil. Firstly, based on the working mechanism of magnetic bearings with redundant structures and the nonlinear electromagnetic force model, the current and displacement stiffness models of magnetic bearings are established, and a dynamic model of the rotor is constructed. Then, according to the dynamic model of the rotor and the mapping relationship between the current of each coil and the electromagnetic force of the magnetic bearing, we established the equivalent control loop of the magnetic bearing–rotor system with redundant structures. Finally, on the basis of the active disturbance rejection control (ADRC) strategy, we designed a linear active disturbance rejection controller (LADRC) for magnetic bearings with redundant structures under the condition of no coil failure, and a corresponding simulation was carried out. The results demonstrate that compared to PID+current distribution control strategy, the LADRC+current distribution control strategy proposed in this paper is able to effectively improve the anti-interference performance of the rotors supported by magnetic bearings with redundant structures.
Fault-tolerance is one of the practical and effective approaches to improve the reliability of magnetic-levitated bearings. Linearization of the EMF (electromagnetic force) from the redundant structures is the crucial basis of the design of fault-tolerant controller. This paper proposes an accurate linearization approach for the heteropolar magnetic-levitated bearings with redundant structures, by solving the Taylor series expansion equation of the current distribution matrix (W) in the non-equilibrium position and introducing a set of displacement compensation matrices to establish a unified accurate EMF model including the controlled current and rotor position. The approach proposed can effectively decrease the EMF error between actual physical and linearized model compared with the existing methods for the consideration of rotor position. Also, the solutions of the current distribution matrix and relevant optimization approach have been presented based on the proposed approach to help to design the high-performance fault-tolerant controller at the whole rotor displacement range. The numerical results demonstrate the noticeable accuracy advantages of the proposed EMF model.
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