Study On Control And Monitoring Technology Of Magnetic Bearing For High-Speed Machine

The high speed permanent magnet (PM) machine has been widely investigated in the field of electrical engineering since it has small volume, high power density and high efficiency. Compared with the convertional low-speed machine, the rotor speed can reach up to or even above 100000r/min, so that the mechanical bearing is difficult to meet the requirements of the high-speed operation. The active magnetic bearing(AMB), which levitates a rotor by magnetic forces, has many merits, such as no contact, frictionless and so on, particularly suitable for high speed motors. However, it also is a nonlinear and open-loop unstable complicated. control system. Therefore, how to improve the stability and reliability of magnetic bearing is the key of high-speed motor for safe operation.The research work of this thesis is a part of the project-"The distributed high speed generator system driven by micro-turbines and its energy conversion system", which is supported by the National Natural Science Foundation of China (No. 50437010). The study of the thesis is concentrated to the suspension force analysis of AMB, linear active disturbance rejection control, PID control, and online monitoring of AMB fault. The main contents are as follows:(1) Due to the strong nonlinearity of magnetic bearing, a levitation force analysis of magnetic bearing based on field-circuit combined method was used. The linear operation range of AMB was determined. The factor of linear expressions for magnetic levitation force was revised, and the nonlinear expressions of magnetic levitation force was deduced by polynomial approximation. Moreover, the dynamical model of rotor-bearing system, model of control system and model of rotor displacement measuring system were established.(2) The linear active disturbance rejection control and PID of AMB control were studied. Because the tranditional PID control method for radial AMB cannot achieve good results, the linear active disturbance rejection controller was designed, which can enhanced the anti-disturbance capability for radial AMB. For axial AMB, the incomplete differential type PID controller was desingn, the PID parameters were optimized based on genetic algorithms.(3) Base on three-level power amplifier with carrier triangular wave reversed-phase method, the AMB control system was designed by using DSP as its micro-controller. Then, the AMB control platform was established, the static suspension experiment and high speed running experiment were carried out, and the stable levitation of AMB in 5 degrees of freedom was realized.(4) The monitoring system of AMB was designed based on LabVIEW, a method of failure judgement was proposed by using the wavelet energy distribution vectors, and the correctness and effectiveness of the failure judgement approach are verified by the experiments.