Sensorless Control Of Surface Permanent Magnet Synchronous Motor At Low Speed

Permanent magnet synchronous motors (PMSM) are widely used in servo control fields. The traditional servo system needs high precision position and velocity sensors. However, these position sensors or rotational transducers not only increase complexity and cost, but also impair reliability of the system. With this background, the research on sensorless control has become an attractive prospect. At present, there have been numerous achievements on sensorless operation, but most of the techniques only rely on machine fundamental equations which limit the operation at zero and low speeds of the machine and are sensitive to machine parameters. Therefore, this thesis focuses on the sensorless control at low speeds.In this thesis, the work concentrates on the study of surface permanent magnet synchronous motor (SPMSM) drive system without mechanical sensors. Firstly, mathematical model of SPMSM is set up based on motor electromagnetism. The principle of i_d = 0 control method is analyzed systematically based on vector control technique of PMSM. Vector control system is set up. Space vector PWM technology (SVPWM) is introduced.Based on the saliency tracking idea, the fluctuating high frequency voltage signal injection method is discussed. For the nonsalient magnetic structure of SPMSM, principle of developing saliency is introduced. The basic principle of rotor position self-sensing using fluctuating high frequency signal injection method are presented and the simulation model for sensorless vector control systems of a permanent magnet synchronous motor was established and analyzed. Simulation results indicate that the salient pole tracking system that using fluctuating high frequency voltage signal injection method has more advantages, which has simple structure, good static and dynamic performances and easy realization. This method can effectively detect rotor's position and velocity at low speeds .The sensorless vector control system has good static and dynamic performances, and is insensitivity to motor parameter variation. At last, the hardware and software were designed for the sensorless vector control systems of PMSM. Elementary experimentation was studied. DSP was used to confirm the accuracy of high frequency voltage signal method.