The Investigation On The Design And Control Of Bearingless Motor

In the research domain of the electrical drive with high and ultra high speed, bearingless motor is a new type of magnetic suspension motor combining the driving and self-suspension, which can not only produce the torque for load driving, but also produce the magnetic levitation force for realizing no mechanical friction rotation.This dissertation focuses mainly on the theory and realization of induction-type and permanent magnet-type bearingless motor, including analytical expression of the magnetic levitation force, flux field oriented vector controllers, the feedback control of the levitation force, the design principle and consideration of the permanent magnet-type bearingless motor, digital control system design, and the sensorless operation of the permanent magnet-type bearingless motor.Firstly, a relatively accurate analytical expressions of the magnetic levitation force for the induction-type and permanent magnet-type bearingless motor is proposed in the dissertation with the eccentricity in the location of stator and rotor taking into consideration, and their computation accuracy was verified by ANSOFT, an electro-magnetic field analysis software of electrical machines.Secondly, the air-gap-flux oriented control model of the induction-type bearingless motor was put forward applying the proposed analytical levitation force model, and the stable suspension operation in the dynamic process of starting-up were simulated in this dissertation. Furthermore, a kind of optimized air-gap-flux orientated control strategy and its implemental system were suggested to realize whole dynamic decoupling. According to the shortcoming of the traditional modeling of permanent magnet-type bearingless motor, a complete mathematic model is established with the all coupling factors of torque winding, suspension winding and rotor movement considered, of which the computation accuracy was verified by the simulation model based on the rotor flux oriented control system. Furthermore, due to the load disturbance and detecting error of radial displacement, the centers of stator and rotor of a bearingless motor do not coincide with each other in practical operation, which will deteriorate the control performance of stable suspension. With a real-time observation of magnetic levitation force , the closed-loop control scheme of levitation force can be then implemented, and simulation and experiment study verified the effectiveness of the approach in improving the static and dynamic performance of bearingless motor.Thirdly, the design of the permanent magnet-type bearingless motor was studiedbased on the theory analysis, electro-magnetic calculation and finite element computation, the permanent magnet type rotor structure and the parameter design of the torque winding and suspension winding were analyzed, and the permanent magnet thickness of the motor was optimized to avail the levitation control. Moreover, a digital control system based on DSP(TMS320LF2407A) for real-time control was developed to provide a reliable experiment environment for suspension operation studing of the prototype motor.At the last, a novel rotor position estimation scheme using saliency-tracking self-sensing method was suggested in this dissertation, which will meet the need of sensorless operation for a permanent magnet-type bearingless motor, and then, the sensorless vector control system of permanent magnet type bearingless motor was set up based on this position estimation approach. Simulation study demonstrates that the proposed space-saliency tracking method is capable of precisely estimating the rotor space position in the full speed regions for an interior permanent magnet-type bearingless motor and is able to achieve stable sensorless suspension operation under the condition of low or high speeds with heavy load disturbance. An initial experiment result was shown in this dissertation.