Study Of A Novel Double-Winding Bearingless Switched Reluctance Generator And Its Control System

A bearingless switched reluctance motor(BSRM) not only has the merits of magnetic bearing motors, but also can work high axial utilization ratio, small capacity, and low power consumption. By synchronously utilizing bearingless technology and generation technology, it runs as a generator. Mechanical wear and friction loss can be eliminated, and it can output direct current(DC) current, which can be widely applicated in electromobile and power engineering fields, and is especially fit for momentum compensation, peak adjustment, and load balance in regenerative energy synchronizing, and has wide engineering applicaton foreground and reaserch significance. However, in traditional bearingless switched reluctance motors, there exists complex electromagnetic coupling between radial force windings and torque windings. Furthermore, traditional BSRMs usually generate in periodically time-sharing generation mode, in which the torque winding can only output electric egergy in negative-torque period and the generation power density is low. All the shortcomings mentioned above for traditional BSRMs and periodically time-sharing generation mode have formed the bottleneck restriction for their development. So, it is necessary to design a novel bearingless switched reluctance generator(BSRG) which can conquer these problems, and study its drive control methods.A novel double-winding bearingless switched reluctance generator is proposed in this thesis, then the study is carried out aiming at a series of key theories and technique problems such as magnetic characteristic analysis, magnetism parameter design, basic mathematic model deduction, control system design and so on. This s work is supported by the National Natural Science Foundation of China(60774044,61074019) and2011Jiangsu Regular High School Postgraduate Students’Scientific Research Innovation Program (CXZZ11_D571). In this generator, the technique of both BSRM and double-winding generation are combined together. Its hybrid stator consists of suspension poles and generation poles.The radial force windings can provide radial force to suspend the rotor. Within the generation poles, the excitation windings provide magnetic excitation, and the generation windings output electric power. The decoupling between suspension subsystem and generation subsystem can be weakened significantly. And the generation windings can output power even when the excitation windings are conducted, that is to say, during the whole period, there is electric power to be generated. And the generation power density can be increased.The main contents of this paper are as follows:(1) Build the Ansoft model of this novel double winding bearingless switched reluctance generator to analyze its magnetic characteristics. Then with the finite element analysis results, the running principle is described and magnetism parameter is designed and optimized.(2) The mathematical models of radial force and generation voltage are calculated considering the nonlinear magnetizing characteristic. Then matlab and ansoft are utilized to confirm the mathematical model.(3) The control algorithms for suspension winding current and generation winding current are studied. And robust PID controllers for radial suspension system are designed to conquer the problems of external force disturbance, parameter perturbation, and the interference of excition current for stability and robustness increment for rotor suspension.(4) Utilize FPGA to realize complex combinational logic of control signal, then combines with DSP main control unit, signal detection circuit, and surrounding interface circuit to constitute the high-speed digital control system. And the power inverters for radial force winding, excitation winding, and generation winding are designed as well.(5) The radial displacement sensorless technique is studied based on high-frequency injection method, and the radial displacement self-testing system is also erected.The achievements are as follows:(1) The salient poles of stator are set as suspension poles and generation poles in turn. The radial force windings are solely coiled in suspension poles. While the excitation windings and generation windings are synchronously coiled in generation poles. This novel double-winding bearingless generator has clear struct and explicit functions, and is easy to maintain and control.(2) The mutual inductance between suspension winding and generation winding is effectively decreased, and the coupling between suspension poles and generation poles is correspondingly weakened. So the serious coupling between suspension system and generation system in traditional bearingless switched reluctance generators can be conquered.(3) Radial force does not vary with rotor position angle. So when rotor is totally unaligned to rotor, the problem of insufficient radial force production in traditional BSRMs can be conquered. Radial load ability can be increased, and the radial suspension can be improved.(4) Generation winding flux linkage changes with rotor position angle, and no smooth region exsits, that is to say, there will be rectified generation voltage to be output during the full working period. So, the generation power density can be increased, and output voltage is easy to be adjusted.(5) Modeling by mechanism, finite element analysis, and simulation are bonded to buid the mathematical models fit for not only linear magnetic circuit but also saturated nonlinear magnetic circuit. So it can remedy the shortcomings of those existing models based on non-saturation hypothesis, which are not suitable for magnetic-saturated condition. And can also provide more reliable theoretical rules for running characteristics analysis, motor optimum design, and control strategy study.(6) A kind of practical radial displacement self-test method is put forward in this paper. With this method, no special radial displacement sensor is required anymore, and the temperature and electronic sensity of traditional displacement sensors can be conquered. Even the geometry size, cost, and complexity can be reduced, and the reliability of whole system can also be improved.(7) The control algorithms for suspension winding current and generation winding current are studied. And robust PID controllers for radial suspension system are designed to conquer the problems of external force disturbance, parameter perturbation, and the interference of excition current for stability and robustness increment for rotor suspension.