Research On Nonlinear Modeling And Control Of Synchronous Reluctance Motor

Synchronous reluctance motor has the advantages of high efficiency,high reliability and high cost performance,which has high application value in aerospace defense,transportation,equipment manufacturing,industrial transmission and other fields.However,the research on its control system by domestic and foreign scholars is in the ascendant.Affected by the unilateral excitation method and the special salient-pole rotor structure,the synchronous reluctance motor exhibits strong coupling nonlinear characteristics,mainly manifested as magnetic circuit saturation,cross-coupling and coupling magnetic field distortion.The resulting accurate modeling of the nonlinear characteristics and related control problems of the synchronous reluctance motor need to be further studied,including:(1)the accurate modeling of the nonlinear behavior of the magnetic circuit of the synchronous reluctance motor;(2)torque oscillation and fluctuation caused by magnetic circuit nonlinearity and coupled magnetic field distortion;(3)the minimum copper loss operating point offset caused by the nonlinearity of the magnetic circuit;(4)rotor position observation and disturbance suppression in full speed domain under the influence of magnetic circuit nonlinearity.In this paper,in-depth research is carried out on the above problems,and new modeling method and improved control strategies for the nonlinear characteristics of synchronous reluctance motors are proposed.The main research contents are as follows:The self-saturation and cross-coupling effects of the magnetic circuit of the synchronous reluctance motor cause the flux linkage and inductance exhibit nonlinear time-varying characteristics.In order to establish an accurate magnetic model of synchronous reluctance motor,the nonlinear mechanism analysis of magnetic circuit based on finite element analysis,electromechanical energy conversion process analysis and offline self-tuning of flux linkage is carried out,and an analytical reciprocal magnetic model is proposed to describe the nonlinear behavior of the magnetic circuit.Then,an adaptive collaborative optimization parameter identification algorithm is proposed to obtain accurate magnetic model parameters.The model parameters are adaptively selected through the parameter identification strategy based on probability quantization,which can improve the stability of the parameter extraction process while ensuring the accuracy of parameter identification.The established reciprocal magnetic model can accurately describe the nonlinear characteristics of the magnetic circuit,and it takes the dq-axis current as the independent variable,which can meet the requirements of online accurate parameter estimation of high-performance control strategies.Torque oscillation and ripple caused by nonlinear behavior of the magnetic circuit of synchronous reluctance motor and coupled magnetic field distortion are the main challenges for current-loop control.Aiming at this problem,based on the established reciprocal magnetic model,the current dynamic coupling mechanism analysis and electromagnetic torque fluctuation mechanism analysis are carried out,and the current dynamic model and torque model are reconstructed.According to the derived dynamic decoupling conditions of the current loop under the influence of system nonlinearity,a method for constructing a hybrid(feedforward + bias)decoupling control network based on adaptive inversion control is proposed.Taking the minimum torque ripple and harmonic additional loss as the control target,a torque ripple suppression method based on optimal harmonic current tracking is proposed.The proposed method realizes the online calculation of the optimal harmonic current based on the multi-specific frequency harmonic adaptive detection,and adopts the multi-resonance controller to improve the tracking accuracy of the optimal harmonic current.The proposed dynamic decoupling method of the current loop and the torque fluctuation suppression strategy could effectively reduce the oscillation and fluctuation of the output torque.Aiming at the problem that the optimal operating point of the motor efficiency changes with the excitation level,a method for online analysis and distribution of optimal reference current based on the reciprocal magnetic model is proposed.Firstly,the relationship equation between electromagnetic torque and optimal current angle under the influence of nonlinear magnetic circuit is constructed,and the sensitivity analysis of optimal current angle on apparent inductance and incremental inductance is carried out by factor analysis method.Through the above work,the analytical expression of the optimal current angle is obtained,and the online optimal distribution of the dq-axis reference current is realized.Then,in order to improve the tracking speed of the speed-loop to the optimal efficiency operating point,an adaptive non-singular terminal synovial speed control scheme considering the nonlinearity of the magnetic circuit is proposed.Finally,a controller combining adaptive fast finite-time arrival law and nonlinear disturbance observer is designed to reduce the optimal operating point tracking deviation caused by load disturbance and parameter disturbance.As for sensorless control of synchronous reluctance motor,the estimation results of rotor position and speed depends heavily on the accuracy of the motor model.Combined with the proposed reciprocal magnetic model,A position sensorless control method in the full-velocity domain is proposed considering the saturation and cross-coupling of the magnetic circuit,which uses the high frequency signal injection method based on constant high frequency current amplitude control and the extended back EMF observation method based on the improved extended state observer to obtain the rotor position estimation error information in the full speed domain.On this basis,combined with the extended state observer,the rotor position-velocity and load disturbance estimation results in the full-speed domain are obtained by means of the phase error weighted average.The feedforward compensation is carried out according to the observed load disturbance,and an improved speed controller is proposed,which can effectively suppress load disturbance and achieve smooth transition between the two rotor position estimation methods.On the basis of the above research,the relevant testing and verification work are carried out by building simulation model using MATLAB/Simulink and prototype experimental platform of the synchronous reluctance motor.The simulation and experimental results show that the reciprocal magnetic model proposed in this paper has higher accuracy and adaptability than the traditional model in characterizing the coupling nonlinear characteristics of the synchronous reluctance motor.Compared with traditional methods,the proposed current-loop dynamic decoupling method,torque ripple suppression method and optimal efficiency operating point tracking method can improve the torque output quality and motor efficiency more effectively,and the proposed full-velocity domain position sensorless control method has higher position observation accuracy and better load disturbance rejection capability.The research work in this paper can provide strong technical support for the promotion and application of synchronous reluctance motor in the industrial fields.