Torque Ripple Minimization in Exoskeleton Drives with Multiphase Electrical Machines by Current Harmonic Injection

This paper presents a torque ripple minimization technique for multiphase electrical machines in exoskeleton applications. The main focus is the torque ripple generated by the interaction of stator and rotor magnetomotive force. This approach uses current harmonic injection, to suppress the responsible stator mmf components. Therefore, an analytical model, to predict the current amplitude, is presented and the rotor flux oriented control is extended to harmonic subspaces. The coupling of those subspaces, especially for the current harmonics, is analyzed. The approach is applied on a five phase double-sided air cored axial flux machine. For verification, a three dimensional finite element simulation is performed and a prototype was manufactured. The results are very promising and a reduction of the considered torque harmonic of 85% can be measured on the testbench.