Torque Ripple Suppression Strategy Of Permanent Magnet Synchronous Motor Based On Harmonic Current Injection

Permanent magnet synchronous motor (PMSM) drivers are widely used inmany high-performance applications such as servo drive, robotics, etc due to its highefficiency and high torque capabilities. The torque smoothness of the PMSM isessential in these applications. However, Sources of divergence from idealconditions in both the motor and associated power converter in PMSM motor drivesmakes PMSM have relatively high torque pulsations which hinder the application ofPMSM in high accuracy systems. Therefore, Research on PMSM pulsating torquesuppression strategy and enhancing torque smoothness have great engineeringsignificance.Instead of conventional optimization design on the machine itself, an approachbased on the control strategy by harmonic current injection to surpress the torqueripples of surface-mounted PMSM is analyzed. Based on analyzing the PMSMsystem structure and working principle, the fundamental mathematical model ofPMSM is established. The harmonic mathematical model of PMSM is established inthe following three aspects. The inverter output error voltage estimation model isdeduced by analyzing the power inverter nonlinearity property. Then, on the basis ofanalyzing rotor flux distortion characteristics, the harmonic mathematical model ofPMSM in the synchronous frame is developed. Moreover, the ralationshipexpressions between the cogging torque and the parameters of PMSM are derivedbased on the mechanism of cogging torque.The torque ripple suppression strategy of PMSM based on harmonic currentinjection method achieve torque ripple reduction by injecting modified current.After a harmonic spectrum analysis on the back electromagnetic force (EMF) andpermmanent magnet flux-linkage, the q-axis current reference is modified based onthe harmonic torque equation in synchronous reference frame. In order to track the,a closed-loop harmonic currents control method is added to achiveing a precisingcontrol of the harmonic current, resulting in producing additional torquecomponents to counteract the torque ripple. After modifying the q-axis currentreference waveform, the harmonic currents injection control strategies are presentedrepectively based on synchronous frame PI regulator and proportional resonantcontroller to suppress the sixth harmonic torque component. In order to improvecurrent control loop bandwidth, the fifth and seventh harmonic currents are trackedby applying synchronous frame PI regulators in synchronous reference frame.Furthermore, in the consideration of the computational load of the implementationof synchronous reference frames, a second method to track the q-axis current referenc by parallel association of conventional PI regulator and proportionalresonant controller is presented.The proposed torque ripple suppresion approachs are first investigated bysimulation based on MATLAB/Simulink model and Simplorer&Maxwell finiteelement (FE) analysis model of PMSM drive system. A FE iterative optimizationstrategy of the q-axis current reference is proposed to minimize the influence of thePMSM nonlinear magnetic feature. The results of simulation verify the validity ofthe proposed compensation method. In the end, the validity and effectiveness of theproposed approach are confirmed by experimental results. The experiments arecarried out on the PMSM hardware platform based on digital signal processor (DSP)whose design methods are presented. The performance of the proposedcompensation scheme is compared with no compensation scheme. The experimentalresults demonstrate that the proposed strategies are effective in suppressing PMSMtorque ripple. The conclusions can be obtained that the effectiveness of the proposedmethods are the experimentally validated from the experimental results.