Harmonic current injection for torque ripple reduction with optimum current trajectory for minimum induced voltage

Electric drives often do not have a smooth torque. In most cases they are coupled with mechanical systems. These tend to have natural frequencies. Therefore, it is advisable to eliminate harmonics from the torque pulsation if they are close to a natural frequency. One possibility to do this is harmonic current injection or HCI for short. However, the question arises, how exactly this harmonic current should be. The fact that a harmonic in the torque can be influenced by the d and q current results in a greater degree of freedom. This paper presents a method to investigate all possible solutions. Furthermore, two optimization possibilities for the current trajectory are presented. The effect of this selection on the maximum torque speed curve is shown. It has been found that the method which minimizes the induced voltage achieves an up to 8% larger range of application in this example.