A harmonic current injection method for electromagnetic torque ripple suppression in permanent-magnet synchronous machines

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Abstract
Electromagnetic torque model is built in this paper for permanent-magnet synchronous machine (PMSM) with non-sinusoidal back electromotive force (back-EMF) and current. Electromagnetic torque is divided into four parts depending on the different combinations of fundamental and harmonic component. Effects of current harmonic order, amplitude and initial angle on average torque and torque ripple are investigated based on the mathematic model. Desired harmonic parameters are obtained from the analysis, in order to suppress the torque ripple as much as possible. Further, a method for reducing the 5th and 7th harmonic components of torque ripple is proposed, according to the characteristics of back-EMF harmonic distribution. The proposed method is greatly simplified and more feasible by only injecting 5th and 7th harmonic currents. The theoretical analysis validity has been proved by finite element (FE) simulation, and the FE results show that torque ripple would be more effectively reduced by injecting proper harmonic current than weakening it merely.

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