Position Sensorless Control Of Permanent Magnet Synchronous Motor Based On High Frequency Square Wave Signal Injection

Permanent magnet synchronous motor(PMSM)has many advantages,such as small size,high efficiency,high power density and high torque density.It has been widely used in industry,especially in numerical control machine tools,new energy vehicles,robots and other fields.In the motor control system,the vector control system composed of PMSM is the most widely used control mode in recent years.However,in the traditional vector control mode,if PMSM can operate normally,it must obtain accurate rotor position and speed information,which requires the installation of encoder or rotary transformer to obtain rotor position and speed information.However,the installation of position sensor will cause some adverse effects on the motor system.For example,for high-speed motor system,it is difficult to install position sensor because of the limitation of mechanical properties;For some motors with light weight,the installation of position sensor will increase the moment of inertia of the system,then affect the dynamic response speed of motor speed,and increase the system loss;For some motor systems used in harsh environments,the operating conditions are complex and changeable,and the position sensors are vulnerable to environmental impact,Once the position sensor is damaged,in order to ensure the safe operation of the electric vehicle,it is necessary to quickly cut into the control state without position sensor.Therefore,the sensorless control of PMSM has become a hot topic.In recent years,the sensorless control scheme can be roughly divided into three areas according to the speed range: initial position detection,low speed sensorless control and middle high speed sensorless control.In the middle high speed section,the observer method of fundamental wave model is mostly used to calculate the rotor position and speed information.This method needs to use back EMF to estimate the rotor position,and its advantage lies in the simple calculation method.The high frequency signal injection method is suitable for the sensorless control of the low speed and zero speed segments.The method uses the salient polarity of the interior permanent magnet synchronous motor(IPMSM).The high frequency signal is injected,the relationship between the high frequency response current and the rotor position is used to calculate the rotor position information.This method solves the problem of small back EMF,and is widely used in zero speed and low speed.In this thesis by analyzing the estimation error of traditional high frequency square wave signal injection method in rotor position estimation,a sensorless control method based on over sampling high frequency square wave signal injection method is proposed.Because the traditional high frequency square wave signal injection method approximately considers that the quadrature axis current changes linearly when calculating the high frequency response current,which brings errors to the estimation results.Based on this,the improved algorithm can increase the sampling frequency by one cycle at both ends of the effective vector,and increase the angle update frequency by one cycle.Moreover,the sampling frequency at both ends of the effective vector considers the influence of the nonlinear change of the quadrature axis current,so it can make the angle estimation result more accurate.In this thesis,the high frequency square wave signal injection method is used to detect the initial position of the rotor,and the initial position of the rotor is used to start by sensorless control.After starting,it is switched to the position sensor control of the improved algorithm to realize the whole process of zero speed to low speed by sensorless control.Finally,the experiment is completed by the 20 k W IPMSM experiment platform,which verifies the effectiveness of the improved algorithm.