Research On Sensorless Control Of Permanent Magnet Synchronous Motor In Low Speed Domain

Permanent magnet synchronous motor has been widely used in industrial fields.Because of its advantages such as high efficiency,small size,etc.Vector control is one of the most commonly used motor control algorithms,because of its superior characteristics.The speed sensor provides the rotor position information for vector control,it not only increases the system cost but also brings maintenance difficulties.Using algorithms to replace the speed sensors has become a hotspot in recent years,but most of the research has focused on high speed domains of the PMSM operation.In this paper,the problems of sensorless control in the zero and low speed domain are studied.In order to solve the control problem of PMSM in the low speed range,this paper has analyzed several different separation strategies of high frequency signal and fundamental frequency signal.Both advantages and disadvantages of these methods are compared.The delay effect of digital filters on the system is greatly reduced,and the observation accuracy of the rotor position can be significantly improved.At the same time,it is combined with the position robust observer,which can improve the system’s response ability.The high frequency square wave injection method used the fixed up frequency voltage signal,the power spectral density of the induced current is concentrated in a very narrow range,which will bring a lot of noise.Therefore,a random frequency square wave injection method is proposed in this paper,which can effectively broaden the frequency distribution of the motor current and obviously weaken the noise caused by the fixed frequency high frequency injection method.Two different random frequency signal generation strategies are proposed.Several different injection methods are analyzed and compared,it verified the superiority of random frequency square waves.At the same time,a filterless strategy which can separate high frequency signals is proposed.It can significantly improve the accuracy of rotor position information.Two methods proposed above are both injecting high frequency voltage signal in a rotating coordinate.Under heavy load,false convergence of the position observer will occur.This paper studied a method of orthogonal square wave injection in a stationary coordinate,which guaranteed a single accuracy of position convergence.The signal processing also used a filterless separation strategy,which completely avoid the use of digital filters and improved observation accuracy of the rotor position of the motor in the low speed domain.Finally,three speed sensorless control methods proposed in this paper are carried out on a 14 k W permanent magnet motor platform.The simulation and experiment verified the principle and the feasibility of the algorithm proposed.