Sensorless Control System Of Single-phase Brushless DC Motor

The single-phase brushless DC motor reduces the winding coils and electronic components by 2/3,and greatly reduces the cost of the motor body and control circuit.Therefore,it has received more and more attention in low-cost and low-power equipment.In order to remove the position sensor in the control system to further reduce the cost,and to optimize the phase current waveform to improve the motor efficiency,this article focuses on the sensorless control of the single-phase brushless DC motor.First of all,a motor model of the body structure of a single-phase brushless DC motor with a tapered air-gap is established.According to the virtual displacement method and partial differentiation method,the discretization expressions of cogging torque and electromagnetic torque are derived and solved.The torque effect of the single-phase brushless DC motor during the positioning and starting process is analyzed.A piecewise linear model of the back-EMF generated by the tapered air gap is established,the phase current expression under open-loop PWM control is solved according to the differential equation,and the causes of phase current distortion are analyzed.Through the comparison of finite element analysis,experimental waveforms and analytical analysis results,the correctness of the proposed mathematical model is verified.Secondly,based on the characteristics of phase current distortion and spikes under open-loop PWM control,a commutation position estimation method through current spike detection is proposed.The change of current distortion and detection parameters in different motor operating states is solved through the established phase current model.The method of judging the initial position of the rotor is proposed.Then,according to the solution of the Fourier series,the sine expression of the back-EMF and the rotor flux linkage is obtained,and the first-order inertial filter is designed to realize the observation of the rotor flux linkage.The AC and DC components are decoupled by the double Park transform,low-pass filter and negative feedback,and the rotor position error component is separated to form a single-phase phase-locked loop,which realizes the observation of the rotor position.Based on the assumption that the amplitude of the rotor flux is fixed,the calculation of the double Park transform and filter is simplified,and a simplified single-phase phase-locked loop is proposed.Based on the phase advance control method,the back-EMF waveform is used as the terminal voltage waveform,and the advance angle is adjusted by detecting the polarity of the phase current at the zero-crossing point of the back-EMF to realize the adaptive phase current shaping controlFinally,the experimental platform of the single-phase brushless DC motor sensorless control system is built,and the sensorless control method and phase current shaping control method proposed in this paper are experimentally verified.