Control Strategy For Commutation Torque Ripple Reduction Of Brushless DC Motor In Integrated Motor Propulsion

Integrated Motor Propulsion(IMP)is the propulsion plant of Small underwater ocean vehicles.Because Brushless DC(BLDC)motors have 15% more than Permanent Magnet Synchronous motors(PMSM)in efficiency with the same size.BLDC motors are usually used as a propulsion motor in IMP.However,BLDC motor produces much noise when it drives in high speed,which seriously influencing the stealth performance and acoustic communication equipment of underwater ocean vehicles.Thereby,the safety of underwater ocean vehicles is reduced and the scope of work is also restricted.This paper mainly analyzed commutation torque ripple of BLDC motor in IMP,Firstly,based on the mathematical model,this paper analyzed the reason of commutation torque ripple,and simulation model was set up in MATLAB,providing simulation platform for studying control strategies about suppressing the commutation torque ripple.This paper presents control method to suppress commutation torque ripple,which is overlap commutation.Based on overlap commutation method,an approach based on delaying Hall signal for suppressing torque ripple of brushless DC motor was presented.During the delayed conduction period,the back electromotive force(back-EMF)amplitude of outgoing phase declines and the phase current rises due to the terminal voltage keeps constant.The electromagnetic torque can remain steady by regulating the duty ratio.During the commutation interval,the delayed time can be derived for minimizing the commutation torque ripple.On this basis,considering the influence of the resistance,the optimal delayed angle can be obtained by taking the maximum efficiency constraint.The method used in this paper with no need for any additional electrical devices,can obtain the optimal delayed angle under knowing the motor parameters.The results of the simulation in MATLAB verify the correctness of the theories and the effectiveness of the proposed approach,which are based on ideal Hall sensors installation interval is 120° electrical angle.However,the inevitable mechanical installation error may cause Hall signals delay or advance,aggravating seriously electromagnetic torque ripple.Next,this paper presents a novel compensation method for commutation torque ripple reduction of BLDC motor with misaligned Hall sensors.First of all,by comparing phase current stable value with outgoing phase current detected at rising edge of the corresponding Hall signal,Hall sensors delayed or advanced installation is determined.And then,Hall sensors installation error angle can be obtained by deriving the relationship between three phase currents and error angle,which can be compensated by the optimal delayed angle for minimizing commutation torque ripple.At last,the simulation results verify the effectiveness of the theories and the feasibility of the proposed method.At last,the proposed methods are demonstrated effectively by experiment results based on the BLDC motor platform.