Research On Sensorless Methods Based On Bus Current Detection For Permanent Brushless DC Machines

Brushless DC machines(BLDCMs)are widely used in the fields of household appliances,aeronautics and astronautics,new energy vehicles,because of their high power density,high efficiency and simple control.Admittedly,the position detection is necessary for the speed control system.The position detection with sensors has many problems such as the high installation accuracy,the limited application environment and being easily interfered.Therefore,the sensorless control is a research hot topic of the BLDCM.This paper presents sensorless methods for a surface-mounted BLDCM with small inductance and non-ideal trapezoid but close to sinusoidal back electromotive force(Back-EMF).For the PAM control,this paper proposes a sampling and comparison method based on the bus current.The bus current contains the rotor position signal at low speed when the winding impedance angle can be ignored.Therefore,rotor position signals can be derived from the bus current.The theory proves the convergence of this method.The simulation results show that the method is feasible.For the PWM control,this paper presents sensorless methods based on the average torque control for the BLDCM.The rotor position is detected by sampling and comparison method and slope zero crossing point method based on the bus current envelope.The sensorless control and torque ripple suppression can be realized at the same time under the average torque control.Furthermore,no additional devices are needed.The proposed sensorless methods are simple to be carried out and can expand the application range of the average torque control.Theory and simulation results verify the proposed methods.In order to verify the proposed methods,an experiment platform for the PAM control and the average torque control is built in this paper.An average torque control module based on the hardware circuit is designed in this paper and the position detection is realized based on the software platform.Finally,the experiments under different modulation strategies are completed to verify the algorithm.