Research On Sensorless Low Speed Control Strategy Of IPMSM Based On Improved Square Wave Injection Method

Permanent magnet synchronous motor(PMSM)have been widely used in electric vehicles,industrial robots,household appliances and other driving applications due to their high power density,large starting torque,small size,and no rotor winding.PMSM can be divided into interior PMSM(IPMSM)and surface PMSM(SPMSM)according to different installation positions of permanent magnets.IPMSM has the advantages of firm structure,high torque,high rotation speed,and more importantly,their intrinsic saliency and polarity.Compared with SPMSM,it is more suitable for position sensorless control.The Field Oriented Control(FOC)is a common high-performance PMSM control technology,in which the rotor position is indispensable.Due to the disadvantages of high cost,poor adaptability to motor size and environmental pollution,traditional mechanical position sensors have been gradually replaced by digital position s ensors.The position sensorless vector control technology has become a research hotspot in the field of PMSM control.Because the back-Electromotive Force(EMF)observation method used in high-speed segments has low signal-to-noise ratio at low speeds,the high-frequency injection method based on the rotor silency becomes the most common method for PMSM operation at low speed(including zero speed).Conventional sinusoidal high-frequency injection methods and square wave injection methods inevitably use various filters in position error extraction and current feedback loops,and the use of filters introduces additional system delays.In order to eliminate the filters,one method is to separate the vector control period from the injection period,but this separation strategy will reduce the dynamic performance of the system.Another method is to calculate the fundamental frequency current and the high frequency current from the average and the difference of the current envelopes of adjacent control cycles in the pulsating square wave injection method,which can replace the role of the filter.However,the assumptions of this method can only be satisfied under the conditions of high injection frequency and light load,and the influence of nonlinear error of the inverter is not considered.To solve the above problems,this paper proposes an improved high-frequency square wave injection method,which eliminates the need for filters to separate the vector control period and the injection period,and at the same time counteracts the influence of the nonlinear error of the inverter in real time.Zero speed is a special condition of the low speed range of the motor.This paper presents an initial position detection scheme based on the improved square wave injection method.In addition,the position observer based on Extended State Observer(ESO)is given to overcome the shortcomings of traditional PI observer such as poor capability of anti-torque disturbance and complex design parameters of Luenberger observer.Finally,a IPMSM sensorless vector control experiment platform was built.The improved high-frequency square wave injection method proposed in this paper was tested under various conditions such as initial position detection,sudden unloading,and other load conditions.Three different square wave injection methods and three different position observer comparison experiments were provided.The experimental results verify the effectiveness of the improved high-frequency square-wave injection method and ESO position observer proposed in this paper and the superiority over other methods.