Sensorless Control Of Permanent Magnet Synchronous Motors At Low Speed

Sensorless control technology of permanent magnet synchronous motor eliminates the mechanical position sensor,reduces the system size,reduces the cost,and improves the reliability of system operation.It has become a research hotspot of current permanent magnet synchronous motor control technology.Among many means,the high-frequency signal injection method is the main method to achieve sensorless control in the low-speed range.However,due to the effects of filter phase delay,magnetic field saturation,and other factors,the conventional high-frequency voltage injection method has many disadvantages.In view of the above problems,this paper proposes several square-wave voltage pulse injection position estimation strategies without using a filter.Solving the problem of steady-state position estimation error caused by cross-saturation inductance.At the same time,ADRC is applied to speed loop in the sensorless control system to improve the system's ability to resist external disturbances.The research contents of this paper are as follows:Firstly,the mathematical model of the permanent magnet synchronous motor is established and the vector control technology is illustrated.Next,a systematic overview of the traditional high-frequency signal injection sensorless control methods are introduced,including the basic principle explanation,formula derivation,and simulation verification.Then,the cross-saturation effect is studied detaily with respect to mechanism and influence.The advantages and disadvantages of different methods for compensating the cross-saturation effect based on different coordinates adapting traditional high-frequency signal injection methods are analyzed.This lays the foundation for the subsequent research content of this paper and provides contrast.It is considered that when the load torque is increased,the stator winding current is large,and the motor is in a high-saturation operating state.The magnetic field cross-saturation effect will cause the rotor position estimation error.Aiming at this problem,an arbitrary angle high-frequency square-wave voltage signal injection method(AASWI)is proposed.AASWI introduces the voltage signal injection coordinate fg,injects two pairs of orthogonal square-wave voltage pulses on the two axes of the fg coordinate,calculates the high-frequency current increment,and designs a novel demodulation strategy to eliminate the position estimation error caused by cross-saturation effect,improves the precision of rotor position estimation.At the same time,modified AASWI can also quickly identify the d and q axis inductances in one current loop control cycle.Aiming at the defect that AASWI requires the injection of dual pulses leading longer cycle of current loop control period.This paper proposes another method that variable angle square-wave voltage injection(VASWI)to estimate the rotor position,which continuously adjusts the injection angle according to the magnitude of the q-axis current under different load conditions.VASWI takes the position estimation error angle caused by the cross-saturation effect as the injection angle,injects a square wave voltage on the f-axis,and extracts the g-axis differential current to achieve position estimation to improve the accuracy of position estimation.Aiming at the poor anti-disturbance performance of the traditional PI controller of the speed loop,when sudden change in load torque,it will inevitably lead to large speed fluctuations,and its long recovery time.A speed loop control based on a linear ADRC strategy is designed.The linear extend state observer is used to estimate the comprehensive disturbance,and then the q-axis command current is generated through the combined action of feedforward compensation and linear proportional gain,and a simplified parameter design process is given.Finally,the methods proposed in this paper are experimentally verified.The results show that the arbitrary angle high-frequency square-wave voltage signal injection(AASWI)and variable angle square-wave voltage injection(WASWI)methods both can effectively eliminate the position estimation error caused by the cross-saturation effect.The proposed speed loop liner ADRC can also improve the anti-interference performance and dynamic response speed of the system.The research content of this paper can improve the accuracy of sensorless control,enhance the stability of the system,and ensure the control performance of permanent magnet synchronous motors.