Research On Permanent Magnet Synchronous Motor Sensorless Vector Control System

The permanent magnet synchronous motor (PMSM) has the advantages of high power density, simple structure and high efficiency. Thus PMSM is widely applied to household appliances. In order to achieve a high performance control of PMSM, it is necessary to get the accurate position of the motor. However, the installation of mechanical sensor will cause some problems, such as increasing the cost and volume, difficult maintenance and so on. Therefore, this paper studies and designs the sensorless vector control scheme of PMSM. The research has important value on the practicability of sensorless vector control of PMSM.The main work of this paper includes:Firstly, the estimation algorithm of rotor position and speed of PMSM is studied. In order to solve the problem of DC bias in the flux observer algorithm, a low-pass filter is used instead of the pure integrator. The errors of amplitude and phase are compensated in the polar coordinate, which can improve the accuracy of the results. A sliding mode observer is designed based on mathematical model of PMSM. The methods of chattering reduction are researched. To improve results of sliding-mode observer, a phase locked loop is used in the system. The two algorithms are analyzed and compared based on the experimental results. The flux observer algorithm is used to estimate the position and speed in the proposed scheme.Secondly, the sensorless control for wide speed range is studied. The methods of VF control as well as IF control are analyzed. IF control is chosen to open loop start in consideration of the characteristic of the washing machine, which can avoid the problems of overcurrent and miss of synchronization. An appropriate switching scheme is designed, so that the system can be switched from open loop start to the vector control mode smoothly and reliably. Flux-weakening control method is researched. The principle and process of flux-weakening control are analyzed. Direct axis current is given directly to realize flux-weakening control.Thirdly, the design of software and hardware system is completed based on TMS320F28027. The proposed sensorless control system is realized and is applied to washing machine. The experimental results verify that the sensorless control system can work reliably and stably with good control performance and low noise, which has great practical value.