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

Permanent magnet synchronous motors have many advantages such as small size,high efficiency,and high reliability.They are widely used in various AC servo fields such as electric vehicles and CNC machine tools.The key to improve the hub motor's driving control performance is how to get the accurate feedback of rotor position.The traditional mechanical position sensor increases the cost of the system,and the reliability is greatly decreased due to the complicated operating conditions of electric vehicles.In this respect,this paper makes in-depth research on the sensorless control strategy of permanent magnet synchronous motors in the low speed domain.The main contents are as follows:First,a method for detecting the initial angle of a rotor is proposed,and the advantages and disadvantages of detecting the polarity with the method of dual voltage pulse time and amplitude are compared and analyzed.Because a long time is needed for the system to recover to a stable state and it's so difficult to make an accurate judgment.And the pulse amplitude detection method only needs to compare the maximum response current,the algorithm is easy to implement and the reliability is high.So the pulse amplitude polarity detection method is adopted in this paper.Two commonly used position sensorless control algorithms for high-frequency signal injection—high-frequency pulse voltage injection and rotating voltage injection methods—have detailed theoretical derivation and Matlab / Simulink simulation analysis.In respect of the phase delay caused by the use of digital filters in the process of extracting the position,the influence of the position estimation result is analyzed,and a phase delay compensation method based on the offset cancellation of the end point extension sampling points is proposed.And its feasibility is demonstrated through principle derivation.The traditional position sensorless control strategy based on rotating high-frequency voltage injection is studied,and the mechanism of the errors caused by the limited carrier frequency and non-linear high-frequency injection signals is found.A new method for extracting position signals is proposed.The purpose of reducing the amplitude of the error was achieved by advance the phase of actual injecting voltage,and the method of using the adjacent slope to approximate the midpoint tangent slope instead of the midpoint tangent slope was used to extract the rotor position from the differential current response.Theoretical analysis show that this method can improve the tracking accuracy of the rotor position.Finally,an experimental platform for motor towing is established,and the digital filter phase delay compensation method and the new position extraction method proposed in this paper are verified and analyzed.The experimental data proves the accuracy and effectiveness of the compensation method and the new position extraction method.The proposed new method has higher position tracking accuracy,faster dynamic response.