Research On Current Control Technology For Wide-speed-range Operation Of Doubly Salient Electromagnetic Motor

The doubly salient electromagnetic motor is a reluctance motor which is marked by concentrated stator excitation and salient poles in stator and rotor.It has the advantages of simple structure,high reliability,high speed operation,and low cost.It is competitive in aero starter/generator systems and electric drive systems.However,the phase inductance of a doubly salient electromagnetic motor is highly non-linear and has high harmonic content.It isn’t very easy for the traditional standard square wave current control method to make full use of the torque output capability of the motor.There are problems such as small starting torque,large torque ripple,and narrow speed range.Although the optimal control of the square wave commutation angle can improve the torque performance of the doubly salient electromagnetic motor,due to the high complexity and strong non-linearity of the current commutation model,the optimization of the commutation angle faces the difficulties of accurate modeling,large parameter optimization calculations,and poor versatility,which limit the popularization and application of doubly salient electromagnetic motors.Based on a systematic summary of the current control technology of the doubly salient electromagnetic motor,this paper studies the medium-and-low-speed adaptive commutation angle control,high-speed field weakening control,and low-speed current shaping control technology.At medium and low speed,for solving the problem that the optimal selection of square wave commutation angle depends on the accurate model and much calculation,this paper proposes a synchronous commutation control method: by introducing an additional angle closed-loop to synchronously control the zero-crossing point of phase current and the alignment position of the stator and rotor poles,the adaptive optimization of the commutation angle is realized without the need of accurate model;by shaping the commutation current vector track into a regular hexagon,the commutation torque loss is reduced.This paper also describes in detail the software and hardware implementation of the control algorithm,and designs experiments to verify the adaptive optimization performance of commutation control.In the high-speed operation of the doubly salient electromagnetic motor,there are no effective analysis methods and control strategies for field weakening using the commutation angle and field current cooperatively.On the one hand,this paper studies the field weakening control strategy based on the proposed synchronous commutation control method.On the other hand,by analyzing the inductance characteristics in the rotating coordinate system,the motor is equivalent to a hidden-pole electricexcitation synchronous motor,and the field weakening control strategy is studied based on the rotation vector model and the dual reaction theory.The results show that the field weakening control method based on the vector model can greatly improve torque output in the high-speed region.For low-speed current shaping control,due to the sizable harmonic content of the phase inductance of the doubly salient electromagnetic motor,neither the square-wave current nor the sinusoidal current control can fully utilize the harmonic components of the inductor,and both generate much harmonic torque.In order to obtain the optimal global solution of the desired waveform of the current shaping control,the equivalent model and torque components of the motor are analyzed from the perspective of harmonics.On this basis,the harmonic injection algorithm is solved to optimize the winding loss and suppress the torque ripple.Based on the flux and inductance model of the prototype obtained from the experimental identification,the simulation analysis and verification of the current harmonic injection algorithm are carried out.In summary,this paper studies the current control methods applicable to different speeds: during medium and low-speed operation,a synchronous commutation control method is proposed to improve the commutation control of square wave current;during high-speed operation,the motor model and flux-weakening control strategy are studied from the perspective of the rotation vector;when running at low speed,the motor model is analyzed and current injection methods are studied from the perspective of harmonics.These current control methods improve the torque-current ratio and suppress torque ripple at low and medium speeds and improve torque output at high speed.