Research On Sensorless Control Algorithms For Permanent Magnet Synchronous Motor

In order to achieve high performance vector control of permanent magnet synchronous machine(PMSM),accurate rotor position information is required.However,the installation and use of mechanical sensors will increase the cost,size.weight and reduce the reliability of the system.Sensorless algorithm obtains position information by detecting electrical signals in the motor,which represents the development trend of high performance control of permanent magnet synchronous motor.In this paper,the research status of sensorless control algorithm for PMSM is introduced comprehensively and deeply.Based on the existing algorithms,some improvements are made.A speed adaptive sliding mode observer is proposed in this paper for high speed operation.Without using low-pass filter,the accuracy of the estimated position is improved and the speed range is extended.An improved magnetic polarity detection method for sensorless control of PMSM is proposed in this paper.A pulsating high-frequency voltage signal is injected into the motor in order to detect the magnetic saliency and estimate the rotor position.Then,a bi-directional low-frequency triangular current is injected into the d-axis.Based on the magnetic saturation effect,the rotor polarity can be identified easily.An asynchronous weighting algorithm of speed and position is proposed in the switching area,which ensures smooth switching of speed from low speed to medium and high speed and Vice versa.The contents of this paper are as follows:The relevant background and theme is introduced in the first chapter.In the second chapter,the equation of PMSM in three-phase static coordinate system is introduced,and the mathematical model in synchronous rotating coordinate system is deduced.Then the principle of vector control is introduced.According to the knowledge of automatic control principle,the expressions of PI parameters of current loop and speed loop are deduced.The second chapter lays a foundation for the following chapter.In the third chapter,the conventional sliding-mode observer is introduced and its shortcomings are analyzed.A speed adaptive sliding-mode observer is proposed.The simulation and experimental results prove the effectiveness of the proposed method.Chapter 4 focuses on two kinds of pulsating high frequency injection methods,sinusoidal pulsating high frequency injection and square pulsating high frequency injection.Square wave frequency can be increased to carrier frequency,which greatly improves the bandwidth of the control system,making the performance of sensorless control algorithm comparable to that of a low-precision position sensor.In Chapter 5,there is no sensorless algorithm can achieve full-speed range sensorless control.The usual approach is to combine the low-speed algorithm with the high-speed algorithm.In this paper,two switching strategies are introduced to realize sensorless control in full speed range.The last chapter summarizes the work of this paper.