The Investigation On The Operation Control Of Permanent Magnet-type Bearingless Motor (PMBLM)

Bearingless motors that combine magnetic bearings with motors electro-magnetically can not only produce the torque for load driving, but also produce the magnetic levitation force for implementing no mechanical friction rotation, which have been proposed for the requirement of high speed, high power and maintenance-free electric drives in many fields. There are mainly three types of bearingless motor, i.e. induction-type, reluctance-type and permanent magnet type. Compared to the other two types, the Permanent Magnet type Bearingless Motor (PMBLM), with the air-gap flux produced by the high energy PM materials, is increasingly suitable for industrial application.The dissertation focuses on the operation control of PMBLM, including the integrated mathematical model, the characters of the hardware and software for the whole digital control system of PMBLM, the control methods for the suspension sub-system, and the suspension operation experimentation on the proto type motor. The main work from this dissertation is presented as follows:Firstly, based on the principle of PMBLM operation, the relatively accurate analytical expressions of the magnetic levitation force is proposed with the eccentricity in the location of stator and rotor taking into consideration, and the computation accuracy was verified by the Finite Element Field Analysis (FEA).Secondly, the control system of PMBLM based on the rotor field oriented control strategy was built. From the two aspects of the hardware and software, the digital system was introduced in details, including the important circuit units, the hardcore of DSP2407 and the software flowchart, and the arithmetic of the main program modules was expatiated. On the experiment equipments, the stable suspension operation was implemented from low speed to high speed.Thirdly, According to the shortcoming of the traditional mathematical model of PMBLM, an integrated mathematic model was purposed with all coupling factors among the torque winding, suspending winding and rotor movement considered. And the main parameters associated with this new model were precisely determined. Through the simulation based on this integrated model, the stable suspension operation is achieved. Compared with the results simulated by using the traditional model, the integrality and accuracy of the integrated model had been thoroughly verified. 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 the implemented, and simulation and experiment study verified the effectiveness of the approach in improving the static and dynamic performance of bearingless motor.At last, aiming at the precise control of radial placement of suspension sub-system,three different control strategies were thoroughly researched: the traditional Proportional-Integral-Differential (PID) control, Fuzzy-PID control and H,,, robust control. Through the analysis of principle, the design of controller, the simulation and experiment research, a better control strategy was found, which can effectively weaken the negative influences of the complex motor model and the real-time changing parameters, and guarantee the robust of the operation control. Finally, some useful conclusions are obtained for improving the operational performances of PMBLM system.