| Permanent magnet synchronous motors(PMSMs),with their small size, light weight, high efficiency and low noise, have been widely used in vector control system and high efficiency and energy saving speed control system, such as robots, new energy vehicles and wind turbine, etc. The key to realize high precision control of permanent magnet synchronous motor is to obtain the information of motor speed and rotor position accurately, which is often acquired by mechanical sensors installed externally or internally. However, the use of sensors will increase the cost and limit the application fields of PMSMs and reduce the system reliability. Therefore, the research of sensorless PMSM control is of great practical significance. Sliding mode observer(SMO) is a hot spot in the research of middle and high speed sensorless PMSM control for its ease of implementation, simple structure, robustness to parameter variations and external disturbance.Contraposed to chattering in sliding mode control, a new design method for SMO in sensorless vector control system of PMSM is studied, which aims to ensure the advantage and precision of sliding mode observation as well as weakens sliding mode chattering to enhance observation accuracy and resistance to interference of SMO. Firstly, variety of problems brought by the use of mechanical sensor is expounded, the importance of sensorless technology is explained, several main sensorless control method of motor and their advantages and disadvantages is discussed respectively, the current several main research directions of the sliding mode observer are illustrated in this paper. Secondly, the mathematical model in terms of voltage, torque and flux linkage is deducted, the reason why coordinate transformation formulas and vector control strategy used are summarized, sliding mode variable structure control theory is described and analyzed, and the causes and suppression methods of chattering is discussed. On the basis of traditional sliding mode control theory, the traditional sign function is replaced by variable saturation function, the use of variable saturation function can effectively reduce the system chattering caused by discontinuous function. Variable lag compensation is used to increase the accuracy of location estimation. A modified two-stage filter combined with a low-pass variable cut-off filtering and Kalman filtering is used to improve filtering effect for the sliding mode observer, which reduces the disturbance of measurement and system errors and enhances the ability of observation and the ability to resist system disturbance. Finally, a PMSM novel SMO servo control system in dSPACE hardware-in-loop simulation platform is designed and implemented, experimental results are analyzed in Control Desk NG.Experimental results show the novel SMO for PMSM proposed in this paper can estimate the motor position and speed information, and the novel SMO has feasibility and reliability for PMSM sensorless vector control system; The variable saturation function set as switching function can significantly weaken the system chattering caused by the using of discontinuous functions; variable lag compensator designed in this paper can compensate the phase lag caused by low-pass filter and improve the accuracy of the observer to estimate the position; by the use of modified two-stage filter combined with a low-pass variable cut-off filtering and Kalman filtering improves the filtering effect significantly, the EMF observation error is reduced, the accuracy of position and velocity estimation calculation is enhanced, and the robustness of the system is greatly improved. |
