Research On Sensorless Control Strategy Of Synchronous Reluctance Motor Based On Improved High Frequency Injection In Low Speed Domain

Due to their cost advantages and stable structure,synchronous reluctance motors have become increasingly popular for low-cost AC speed regulation.In order to estimate the rotor angle sensorlessly in the low speed domain,the high-frequency square wave signal injection method is most appropriate due to the synchronous reluctance motor’s distinct saliency.However,the AC and DC axis inductance can experience cross saturation during low-speed operation,which may impact the motor’s dynamic and steady-state performance.Therefore,this article explores the sensorless control of high-frequency square wave injection in the low-speed domain while accounting for cross coupling.To begin with,we establish a mathematical model of a synchronous reluctance motor using coordinate transformation theory.In order to estimate the rotor position,we apply the traditional high-frequency square wave injection speed free control method.Our findings indicate that neglecting the influence of cross saturation leads to significant angle estimation errors,which adversely affect both the dynamic and steady-state performance of the motor.Furthermore,in this article,we adopt a static method to determine the offline parameters of the synchronous reluctance motor and mathematically fit the inductance flux relationship.Based on the fitted model,we calculate the angle estimation error that arises from cross coupling effects.To improve the motor’s dynamic and steady-state performance and eliminate the angle estimation error,we enhance the traditional high-frequency square wave injection control method in two ways.Firstly,we add angle compensation during the signal decoupling process,thereby ensuring better angle estimation accuracy.Secondly,we replace single d-axis injection with dual highfrequency square wave injection to reduce high-frequency amplitude-induced torque ripple.Finally,we establish the feasibility and effectiveness of the improved high-frequency injection speed free control method by building a simulation platform in Matlab and conducting experiments on a 1.5 kW synchronous reluctance motor test rig.Our simulation and experimental results demonstrate that,compared to traditional high-frequency injection methods,the improved method is successful in eliminating angle estimation errors due to cross coupling,reducing the impact of high-frequency signals on torque ripple,and enhancing the motor’s dynamic and steady-state performance.