Study On Suppression Of Commutation Torque Ripple Of BLDCM Based On Back EMF Compensation

For the trapezoidal back electromotive force(EMF)brushless DC motor(BLDCM)with six sector square wave control,there is a difference in the current change rate between the open phase and the off phase in the commutation phase,which leads to the constant on phase current rise or fall,and then produces torque ripple,which seriously hinders the expansion of its application scenarios.Therefore,two new commutation torque ripple suppression methods based on voltage vector injection and back EMF compensation are proposed by using equivalent method.Because the mathematical model of trapezoidal back EMF BLDCM in three-phase static coordinate system is more complex,it is transformed into two-phase static coordinate system and analyzed in vector form.Then the current condition to avoid torque ripple during commutation is deduced considering resistance.Considering that the expression of electromagnetic torque in vector form contains two influencing factors: current vector and back EMF vector,additional voltage vector is injected and the three-phase voltage of motor is redistributed by using equivalent method.The function of voltage vector is artificially defined as "regulating" back EMF,so as to compensate it to the value just keeping the torque constant.In addition,in order to eliminate the influence of motor parameters on the control effect,an injection voltage vector amplitude adjustment strategy with negative feedback link is designed,which avoids complex duty cycle calculation and is easy to be implemented in engineering.It is difficult to ensure the stable switching between the two current vectors with phase difference of 60 electric angle when the analysis perspective is limited in the short commutation stage.Therefore,the motor is driven by continuously changing current vectors,and only a small electric angle is changed each time to disperse the current regulation pressure in the commutation stage to other moments in a sector.Combined with the vector control of sinusoidal back EMF permanent magnet synchronous motor,the equivalent method is also used.The extra voltage vector is injected to compensate the hexagon back EMF vector trajectory into a circle,and the equivalent current proportional to the electromagnetic torque is introduced.The closed-loop control system constructed by taking it as the control variable can effectively suppress the commutation torque ripple.Finally,based on the simulation,the experimental platform is built with Infineon XE162 FN as the main control chip,and the experimental program is written to verify the two commutation torque ripple suppression methods.The experimental results show that the proposed method is feasible and meets the design objectives.