Research On AC Servo System Of Vector-Controlled Permanent Magnet Synchronous Motor

AC servo system plays an important role in electric drive field, and becomes an indispensable portion of industrial automation, permanent magnet synchronous motor(PMSM) is applied in small-medium power servo field for its excellent performance. Torque ripple, speed and position control, initial rotor position detection and start of motor have been studied deeply in the paper in order to enhance the performance of PMSM drive system.The theory and realization of vector control with rotor field oriented have been analyzed from the mathematics model of PMSM. Sinusoidal PWM(SPWM) and space vector PWM(SVPWM) have been analyzed deeply, which lay the foundation for the next research.Electromagnetic torque generated by electricity and magnetic field is essential in variable speed control of motor, and is influenced by nonlinear factors. The torque ripple of PMSM has been analyzed from the point of view of inverter, the concept of error voltage vector is introduced to describe dead time effects, the methods of vector transformation, graph synthesis and cycle transformation are adopted to deduce amplitude of the error vector, and the relationship between vector phase and three phase current polarities is obtained also. On the basis, dead time effects of PMSM are analyzed, time and voltage compensation methods of SPWM and SVPWM inverter are presented, brief formula of the time compensation is obtained by the characteristic of SVPWM. The methods of predictive current and current vector are presented to improve accuracy of current polarity detection. The torque ripple caused by SVPWM is analyzed, the torque formulas are deduced respectively taking dead time effects and modulation effect into account, magnitude and ratio of the torque ripple are obtained. The characteristics of the two torque ripples are analyzed, then weakening methods are presented respectively, there is contradiction between the two methods in carrier frequency, several factors in integrative weakening torque ripple are presented.Speed and position control are the two main modes of PMSM servo system. In order to improve speed precision, a mixed speed regulation method is presented, which realizes combination of self-control and other-control, the cut-in condition of self-control to other-control, interior given frequency of other-control and the quick switch of other-control to self-control are analyzed in detail, simulation and experimental results show that the method achieves high speed precision and quick response. In order to improve robustness of PMSM position system to parameter variation, a robust control method based on state transformation of position system is presented, which takes position controller and drive system as one whole, the parameters of feedback controller are synthetically designed by robust quadric stabilization method, then parameter of PI controller and feedback coefficients are obtained, simulation results show that robustness of system is improved to parameter variation.Initial rotor position detection and start of PMSM have been researched, main detection method of initial rotor position is summarized, which has the limitation of depending on motor model and difficult realization at no-load, aiming at the limitation, tiny displacement method of initial rotor position is presented, the methods of tiny displacement and rotating voltage vector are presented respectively in terms of the different displacement characteristics of rotor at no-load and at load, the former is suit for no-load, and the latter is suit for load, experimental results show that detection angle can satisfy the requirement of motor start. A self-start method is presented without initial rotor position in terms of different directions of rotor displacement under different voltage vectors.