High Frequency Signal Injection Based Synchronous Reluctance Motor Position Sensorless Low Speed Drive Control

Syn RM is regarded as a promising candidate for cost-effective speed regulation drive in the field of motor drives.In many application fields such as household appliances and industrail drives,the low-speed sensorless control is essential.The high frequency signal injection method is a kind of low-speed sensorless control method based on tracking saliency characteristics of motors.Rotor position estimation is the essential part of the field-oriented control system.In order to meet the development and application requirements of industrial drive systems,it is necessary to research in-depth on the key technology issues contained in the sensorless control Syn RM,including:(1)Improvement of parameter variation robustness of sensorless control method based on high frequency signal injection,and the rotor position estimation accuracy;(2)Suppression of high frequency electromagnetic noises and power losses caused by high frequency signal injection,and the improvement of motor drive system efficiency;(3)Limitation of high frequency torque ripples caused by high frequency signal injection,and low frequency torque ripples caused by motor flux harmonics,etc.This dissertation studies the above problems and proposes effective solutions to promote industrial applications of sensorless drive control technology of Syn RM.Detailed contents of the dissertation are as following:The existence of parameter nonlinearity and cross-coupling effect leads to the prominent Syn RM rotor position estimation errors varying along with the change of load.This thesis studies the rotor position estimation method to address the issue.To achieve the precise rotor position estimation under various load,a measured reference frame high frequency voltage injection based low-speed sensorless control method is proposed,where discontinuous square-wave voltage signals are injected in the measured reference frame to induce high frequency current.Based on the current-flux model obtained from parameter identification,the cross-coupling factor is proposed to combine both direct and quadrature axis currents to extract rotor position information based on the analytic rotor position estimation error expression.The rotor position estimation errors caused by cross-coupling effect can be eliminated.A signal processing method is proposed for extracting low and high frequency currents,without low and high pass filters,to improve the robustness against the voltage fluctuation errors,and the accuracy of the rotor position estimation can be improved.To solve the problem that high frequency signal injection could cause audible high frequency noises and power losses,this thesis studies the noise and loss suppression method.When the constant amplitude high frequency signal injection method is adopted to acquire the rotor position information of Syn RM,the amplitude of high frequency current varies greatly with the operation condition.Under heavy load,high frequency noises and power losses increase.For Syn RM drives,an adaptive pseudo-random high frequency square-wave voltage injection based sensorless method is proposed.A signal injection pattern with random frequency and phase is used to suppress the discrete spectrum in the high frequency current power spectral density to reduce high frequency noises.In addition,the adaptive high frequency current control strategy to extract and process high frequency current signals is applied to adjust the amplitude of injected high frequency voltage signals,according to load changes,to keep the high frequency current amplitude constant for reducing the torque ripples and the fluctuation of position observation errors.The proposed method can reduce the high frequency noises and power losses in the low-speed sensorless drive control of Syn RM.High frequency signal injection could cause high frequency torque ripples.In addition,teeth-slot torque and flux harmonics,etc.could cause low frequency torque ripples.This thesis studies torque ripple minimization method.Syn RM high and low frequency output torque ripples could lead to speed fluctuations,mechanical vibrations and noises,which deteriorate the drive performance of Syn RM.To solve this problem,an observed-reference-frame bi-axes same-phase reverse high frequency square wave voltage signal injection method is proposed.The output torque power density spectrum is analyzed,the ratio between the amplitudes of the squarewave voltage signals respectively injected into the direct and quadrature axes are designed based on the motor parameters.Applying the proposed method,the torque power density spectrum can be broadened while the amplitudes of discrete spectrum in the output torque power density spectrum can be effectively suppressed,so as to suppress the high frequency pulsation of the torque.In addition,for low frequency torque ripples,based on the periodic fluctuation of speed tracking errors,the Fourier iterative learning control algorithm,is adopted to limit the low frequency torque ripples.The proposed torque ripple suppression method can effectively reduce the high frequency and low frequency torque ripples of Syn RM sensorless drives.On the basis of the above research,a sensorless drive control platform of Syn RM prototype is built based on a general-purpose inverter.The initial rotor position of the Syn RM is identified,and the specific changes of the self-inductance and mutual inductance of the Syn RM under different load conditions are identified,laying the foundation for the realization of different control algorithms.Based on the motor parameter characteristics under light load,the minimum excitation current for Syn RM sensorless control is proposed.Finally,the researched control algorithm is implemented on this platform,and the steady and dynamic performances of the lowspeed sensorless control of the Syn RM are tested.The performance indicators such as high frequency noises,losses and torque ripples are tested for the proposed method and the conventional high frequency signal injection method.Through comparative analysis,the experimental results verify the effectiveness of the studied Syn RM sensorless control method,as well as its advantages in terms of noises,losses,torque ripples,position estimation accuracy and steady-state performance.