Speed Sensorless Control Of The Permanent Magnet Synchronous Motor

As the excitation is provided by permanent magnet, the permanent magnet synchronous motor(PMSM) has relatively simple structure. It is because there is no loss of excitation that its efficiency, power coefficient and power density are greatly improved. Without the structure of collector ring and brush, its failure rate decreases. It is precisely because of these advantages that the low-carbon green motor has been widely used in electric cars, household appliances, robotics, aerospace and many other high performance control field. The precise motion control of motor not only needs the accurate information of rotor position, but also the rotor speed information in the closed loop control. In the speed control system, photoelectric encoder or other mechanical sensor is usually needed to be installed for the sake of measuring exact speed information. However, this increases the motor volume and the cost of the system. In the bad environment, the system’s reliability and robustness are reduced as well. This limits the application of PMSM. With the development of science and technology, many scholars have put forward sensorless control methods of PMSM to avoid the deficiencies of mechanical sensors installation. In these control methods, voltages and currents are measured to estimate rotor position and speed, so as to realize the motor control.In this paper, three different strategies were used to study the speed regulation control for speed sensorless permanent magnet synchronous motor, that were the sliding mode observer based method, the radial basis function(RBF) neural network observer based method, compound control method. In these ways, good performance of speed adjustment has been realized. The main work includes:Firstly, the research purpose and significance of speed sensorless permanent magnet synchronous motor speed control were analyzed, by reading a large number of domestic and overseas literatures and understanding the related theory research status thoroughly. This paper summarized the main existing control methods and the advantages and disadvantages of these control methods, established the mathematical modeling for PMSM and studied the principle of coordinate transformation, the principle of vector control and the vector control system deeply as well.Secondly, the sliding mode observer was applied to implement sensorless speed control of PMSM. The rotor position was estimated by the back electromotive force. In order to improve the estimation accuracy, the speed estimator was proposed, which replaced the direct differential method to calculate the rotor speed. The Lyapunov theory was applied to prove the stability of the designed system. The simulation results indicated that the proposed sensorless speed control system of permanent magnet synchronous motor based on a new sliding mode observer was effective and feasible.Thirdly, a vector control method based on RBF neural network observer for speed sensorless permanent magnet synchronous motor was put forward. The back electromotive force was estimated by two neural network observers, so as to obtain the rotor position and speed. The input variables of each neural network observer were the corresponding current estimate and the current estimation error, respectively. The output of each neural network observer was the back electromotive force. The Lyapunov theory was used to design the neural network adaptive learning rules and prove the stability of the designed RBF neural network observer. The simulation results showed that the proposed control method was effective and feasible. What is more, it had good effect of speed estimate and strong ability to resist external disturbance.Fourthly, due to the existing relevant control methods have respective advantages and disadvantages, some of them are suitable for low-speed and even zero velocity, while some are suitable for high speed. In order to make the speed sensorless permanent magnet synchronous motor has more superior performance and get the full speed range control scheme, the methods have good control performance in different velocity field can be combined and designed reasonably. So we studied the compound control method which was realized by combining the method of sliding mode observer with the signal injection method. By switching the two control methods in different velocity field smoothly, the good full speed compound control of speed sensorless permanent magnet synchronous motor was realized. The simulation results verified the effectiveness of the proposed control strategy.Finally, we summed up the researched speed control methods of the speed sensorless permanent magnet synchronous motor and contrasted the three different control strategies. The existing research deficiencies in this paper were analyzed and the corresponding solving ideas were put forward.