The Investigation On The Sensorless Operation Of Permanent Magnet Type Bearingless Motor System

The sensorless operation of the permanent magnet-type bearingless motor(PMBLM) to realize the highly integration of the motor and sensor is a new research topic, which will meet the requirement of low cost and practical application of the bearingless motors.This dissertation focuses mainly on the sensoless operation of the PMBLM, including the motor design of the PMBLM, the development of the mathematical model of the levitation force, the robust control of the levitation system. The design and control of a three degree-of-freedom permanent magnet biased radial-axial magnetic bearing was also introduced to form a five degree-of-freedom levitation system. The position/speed sensorless operation and the displacement sensorless operation of the PMBLM were studied theoretically and experimentally.In this dissertation the design of PMBLM was introduced based on the principle of PMBLM operation. An inset-type permanent magnet rotor which has the concept of integration of the motor and self-sensing was proposed to enhance radial suspension force generation and to generate the saliency needed during the signal injection method for sensorless operation. A relatively accurate analytical expression of the magnetic levitation force for the PMBLM was proposed with the eccentricity of stator and rotor taken into consideration. As the parameter of the levitation force model is the key to control the suspension force and realize the stable suspension operation, the extraction principle of the key parameter was studied in detail, and realized by using the finite element method.Based on the extended magnetic circuit theory, the mathematical model of the permanent magnet biased radial-axial magnetic bearing was deduced and a prototype magnetic bearing was designed according to this model. The coefficients of current stiffness and displacement stiffness were also deduced. A three level PWM amplifier was proposed in this paper to reduce the current ripple and to achieve the successful suspension of the magnetic bearing.The dynamical model of the five degree-of-freedom rotor supported by the PMBLM and the radial-axial magnetic bearing was then deduced. An H∞robust controller was proposed to improve the suspension characteristic of the PMBLM. Result show that the performances of the proposed controller were superior to those of the traditional PID controller in the aspect of being robust to model uncertainties and disturbances.A novel rotor position and speed estimation scheme using the combined rotor position self-sensing method was suggested, which will meet the need of sensorless operation of the PMBLM. In this scheme, the adaptive sliding-mode observer was used at high speed and the saliency-tracking technology with the injection of high-frequency carrier signal was used at low speed. The principle of smooth switching of these two detecting technology was also proposed. Simulation and experiment studies show that the proposed combined self-sensing method was capable of precisely estimating the rotor space position in full speed range with stable suspension.Based on the rotor space-saliency effect and mutual inductance between the torque winding and suspension winding of PMBLM, a novel rotor position and displacement estimation scheme using the fluctuating high frequency voltage signal injection method was proposed to solve the detecting problem of the rotor space position and radial displacement. Analysis results show that this method can realize decoupling between horizontal and perpendicular directions of detected rotor radial displacement signals. The rotor radial displacement and rotor space position were also decoupled in this method.A digital control system for real-time control was designed based on TMS320F2812 digital signal processor(DSP). This system provides a reliable experimental platform for suspension operation and sensorless operation of the PMBLM and the permanent magnet biased radial-axial magnetic bearing.