Torque ripple minimization in consequent-pole PM machines using harmonic current injection

In this paper, the torque ripple of Consequent-Pole PM Machines (CPPMMs) is reduced by injecting 2nd order harmonic of the armature current. In the proposed method, based on the machine back-EMF spectrum and the current main harmonic, appropriate 2nd order harmonic of the armature current is obtained. An analytical model is developed to obtain back-EMF of CPPMMs. In addition, the obtained analytical model is used to compute the developed electromagnetic torque as a function of the armature currents. Validity of the analytical model is verified using finite-element analysis. To investigate the efficacy of the proposed 2nd order current harmonic in torque ripple minimization, the optimum one is obtained separately by a direct search algorithm and the related electromagnetic torque waveforms for two different obtained 2nd order current harmonics are compared together. The developed analytical model is used in the direct search algorithm for the torque waveform computation. Although the proposed method is not as exact as the direct search method, it is precise enough considering its negligible computation burden over the direct search method.