Research On Torque Ripple Suppression And Sensorless Control Of Brushless DC Motor

Brushless DC motor(BLDCM)is widely used because of its simple structure,high efficiency and convenient maintenance.BLDCM usually operates in two-phase conduction mode,which has obvious torque ripple in the commutation process.The maximum torque ripple may reach 50% of the average value,and it seriously degrades the operation performance.To reduce the commutation torque ripple,this paper studies the commutation torque ripple suppression method.In the operation of BLDCM,the position sensor is needed for current commutation.However,the position sensor is easy to be interfered by external signals,which reduces the reliability of the system.Therefore,the research on the sensorless control method has important theoretical significance and application value.The back electromotive force(back-EMF)method has become one of the main methods of rotor position detection because of its simple detection and reliable operation.However,the back-EMF method is easily affected by many factors,which makes commutation signals shift and increases the power loss of the motor.To obtain accurate commutation signals,the sensorless control method of BLDCM is studied in this paper.This paper proposes a transformer type auxiliary boost circuit to suppress commutation torque ripple.This paper analyzes the operation principle of the boost circuit.In the noncommutation period,the capacitor is charged according to the load and speed.When the motor begins to commutate,the charging capacitor is connected in series with the voltage source through the switch to increase the bus voltage.By controlling the three-phase inverter,the bus voltage is equal to 4 times of back-EMF,so as to maintain the stability of non-commutation current and reduce torque ripple.The capacitance value and the charging voltage are derived.Simulation and experiment show that the auxiliary boost circuit can effectively suppress the commutation torque ripple and shorten the commutation time.The single ended primary inductor converter(SEPIC)is similar to the operation principle of the auxiliary boost front-end.Experimental comparison with SEPIC,the auxiliary boost circuit has smaller commutation torque ripple and shorter commutation time.This paper presents a new method based on the hall signals delay to suppress commutation torque ripple.The delay influence on the phase current is analyzed,and the current expression during the delay conduction is given.The conclusion is that the delayed hall signals make phase current amplitude increase.Based on the phenomenon,a method of restraining commutation torque ripple is proposed.By delaying the hall signals,the current amplitude increases,and the outgoing phase and the incoming phase current complete commutation at the same time,so that the non-commutation current is stable and the torque ripple is reduced.With the increase of the hall signals delay,the decrease of torque ripple is not obvious.This paper takes the unit duty cycle of power switches as the goal,and the delay time of the hall signals is deduced.The validity and accuracy of the method are verified by simulation under different speed and load conditions.This paper presents a new driving method based on optimal current vector.In this paper,the commutation process of the square wave drive is analyzed in the static coordinate system,and the causes of commutation torque ripple are given from the perspective of vector,and the expression of optimal current vector is derived based on the goal of constant torque and maximum torque current ratio.Through simulation and experiment,it is proved that this method can effectively restrain commutation torque ripple in different speed range.This paper proposes a sensorless control method based on line voltage difference integral to obtain accurate commutation signal.The mathematical expressions of commutation error,phase current and average power are derived,and the influence of commutation error on phase current and average power of motor is analyzed.The function relationship between the line voltage difference integral and the commutation error is established.Besides,the influence of commutation process is considered,and the detection accuracy of commutation error is improved.For non-trapezoidal back-EMF,the PI controller is used to compensate the error and the integral value of back-EMF is used as the feedback to adjust the error,so the compensation accuracy is high.For trapezoidal back-EMF,the analytical solution of the commutation error can be obtained by calculation,which can ensure the accuracy and speed up the error compensation.The validity and dynamic response of the proposed method are verified by experiments,and the error compensation time under different conditions is given.Finally,by testing the power loss under different conditions,it is verified that the power consumption is reduced after the commutation error is compensated.