Parameter Design And Operation Control Of5-DOF Single-Winding Bearingless Switched Reluctance Motor For Flywheel Batteries

With the rapid development in the fields of new energy generation, distributed generation, hybrid electric vehicle and aerospace, the energy storage technology has becoming a world-wide research topic. In frequently-encountered energy storage technologies, the flywheel battery has been paid high attention all over the world since it has some remarkable advantages such as high-power, high-efficiency, long-life, non-pollution, high energy density, etc. As a novel energy storage device combing the electronic technology, mechanical technology and control technology, many vital issues, such as the performance and control of bearing systems and integrated high-speed motors or ultra-high-speed motors, still exist in the flywheel battery, which limit its engineering application. In order to reduce bearing losses, the flywheel battery is usually supported by some magnetic bearings, which increases flywheel axial length, reduces critical speed and makes the system bigger and more complicated in the meantime. To resolve this problem, a novel five-degree-of-freedom (5-DOF) compound supporting system is presented based on the single-winding bearingless switched reluctance motor. In this supporting system, the radial bearing and motor in the flywheel battery are integrated, which reduces flywheel axial length and bearing losses, increases critical speed, power density and system integration. Thus, it has vital application and research value in high-speed, low-loss flywheel batteries.Supported by the National Natural Science Foundation of China under grant61074019and60774044, and the Innovation Project of Jiangsu Province, some key theoretical and technological problems are studied to realize the high-speed, low-loss operation of5-DOF bearingless motors, such as the main structure of the proposed compound supporting system, the optimal design of the low-loss permanent magnet-biased axial radial magnetic bearing, the optimal design method and the high-speed operation control strategy of the single-winding beaingless switched reluctance motor, the digital control system design and so on. The main contents and the corresponding results are as follows:(1) A novel5-DOF supporting and driving system in flywheel battery was presented based on a bearingless motor, which is supported by an axial permanent magnet bearing a permanent magnet-biased axial radial magnetic bearing and a single-winding bearingless switched reluctance motor. Based on the analysis of dynamic toad and static load, the structure of5-DOF bearing system was determined aiming to reduce loss and improve controllability of suspension forces. The suspension force, torque, efficiency and power density of the single-winding bearingless switched reluctance motor and the dual-winding bearingless switched reluctance motor with the same power were analyzed, and then the selection of the motor in the flywheel battery was present.(2) The optimal design of the permanent magnet-biased axial radial magnetic bearing was put forward. Based on the rotating electro-magnetic field theory, the iron loss can be reduced by lessening flux fluctuation frequency in rotor core, and then the structure of low-loss permanent magnet biased axial radial magnetic bearing was designed. The distribution characteristics of magnetic flux lines at the axial and radial air gap were analyzed. The mathematical models of the axial and radial suspension forces were constructed, and then the position stiffness and current stiffness were obtained. The parameters, such as pole area, coil number, structural size, were design by using magnetic circuit method. The calculation model of the rotor iron loss was built and the results verify the low-loss characteristic of this proposed magnetic bearing at high speed.(3) The optimal design of the single-winding bearingless switched reluctance motor was put forward based on the relevance vector machine and particle swarm optimization algorithm. The calculation model of main dimension was built and then the winding structure was optimized with the objective of maximum motor output and minimal coupling between different phases. According to the flywheel battery’s requirements to motor performance parameters, such as suspension force, torque, efficiency and power density, the sensitivity of the structure parameters to performance parameters was simulated, and then the key parameters were obtained. The multi-objective optimization function with the motor’s performance was constructed. The unified-objective function with weight factors and base values was built and then the non-parametric model for key parameters and the unified-objective function was built by relevance vector machine. The key parameters were optimized by particle swarm optimization algorithm. Finally, the simulation results verify the correctness of this proposed method.(4) The two-phase-excitation high-speed decoupling control strategy of the single-winding bearingless switched reluctance motor was put forward, by which the suspension force and torque are produced by different phases. The effective producing areas of the suspension force and torque were analyzed. An excitation method of the suspension phase and the torque phase was presented. An optimal control method of chopped current amplitude and turn-off angle were proposed to reduce torque ripple and increase response speed of the suspension force subsystem. The proposed control strategy was verified to be effective by simulation and experiment on the test motor.(5) The radial displacement self-sensing method of the single-winding bearingless switched reluctance motor was put forward. The relevance vector machine algorithm with adaptive Gaussian kernel function was presented by considering the high saturation and wide frequency band of the motor data at high speed. The prediction models of radial displacement were built with flux linkage, current and rotor angle as the input and with radial displacement as the output. This proposed control strategy was verified to be real-time and precise by the simulation results, which well meet the requirements of suspension operation at high speed.(6) The high-speed digital control system of5-DOF single-winding bearingless switched reluctance motor for flywheel batteries with DSP and FPGA was designed. The flywheel battery’s requirements to digital control system were analyzed. The allocation and implementation methods of control algorithms were presented. The hardware modules, such as power converters, detection circuits of rotor angle and radial displacement, control circuits of current lagging loop and PWM drive circuits and so on, were also designed. As a conclusion, the summarization of the whole contents is given. The content and emphasis of the further research is also given.