Research On Sensorless Vector Control System Of Permanent Magnet Synchronous Motor

The permanent magnet synchronous motor(PMSM) is a superiority performance and widely used motor.The control technology of PMSM has developed rapidly with the fast development of power electronics technology, micro-electronic technology and modern control theory. How to get the rotor angle and speed is very important to the vector control system of PMSM. At present, the common method in most of drive systems is to install the position sensor in the rotor shaft. However, these sensors increase the cost of the system and decrease the reliability and durability.In these backgrounds, there has been an increased interest in developing techniques to obtain the position and speed information for the PMSM without external position sensors. Sensorless control strategy is to get the rotor position and velocity information of PMSM to complete the closed-loop control by measuring the motor current, voltage and other measurable quantities using for specific observer strategy for estimating the rotor position.The speed regulation system of PMSM without sensor not only has a simple structure, high efficiency, excellent performance and easy maintenance, but also has a small volume, low cost, high reliability and some special application. This paper,on the background of application of sinusoidal PMSM, applying the method based on SMO(Sliding Mode Observer), has researched and accomplished the sensorless vector control of drive and control system.The following is main contents of research in this paper:(1) Firstly, mathematic model of permanent magnet synchronous motors is discussed, basic coordinate conversion theory is expounded and module design of coordinate conversion in Matlab/Simulink is made. Then mathematic model of permanent magnet synchronous motors in two-phase stationary coordinate and in two-rotating coordinate are analyzed. Basing on this the theories of the vector control systems are introduced.(2) The space vector pulse width modulation(SVPWM) has clear physical conception, simple arithmetic and high utilization of DC voltage; furthermore, it is easy to realize digization. So it is one of the most common methods in AC motor control. In this paper, SVPWM is deduced and discussed thoroughly and compared with the SPWM. The algorithm of SVPWM, modular design in Matlab/Simulink and the simulation results are given.(3) In the vector control system of PMSM, the changes of the resistance, reactance and other parameters can produce great error in the current of d ,q axes in the wider speed range, which influences the control precision and dynamic response. To overcome these shortcomings, the IMC(internal model control) was proposed for the current regulator of PMSM. Simulation rusults show that the system with IMC current regulation has better tracking performance and higher steady precision than PI current regulation. Moreover, in the case of model mismatch also has a good dynamic and static performance.This improve the robustness of the system.(4) The sliding model control principles and the sliding model controller design method were discussed. The concept of feedback of equivalent control is applied to extend the operating range of sliding mode observer and improve its angle estimation performance. In addition, a flux-based sliding mode observer with adaptive feedback gain is investigated. The constant magnitude of equivalent control makes it easier to design the switching gain of discontinuous control in the sliding mode observer. The problematic chattering phenomenon normally prevailing at low speed due to high switching gains can be mitigated or even eliminated. The simulation results show that its effectiveness and rationality.