Analysis of variable third harmonic injection for five-phase IM

Five-phase induction motor drives have recently drawn attention among multi-phase drives because the third harmonic injection (THI) allows to obtain both a higher output torque/volume relationship and broader stability margins. Previous studies have been focused on constant percentages of THI, requiring high and permanent injection if robustness becomes a main concern. This procedure is not optimal in the whole range of operation, degrading the drive performance. This paper proposes the use of a variable third harmonic injection (VTHI) control scheme that achieves similar robustness of constant third harmonic injection (CTHI) schemes but allows lower percentages of THI at light loads. A bifurcation analysis is presented for both constant and variable THI schemes, fully analyzing the steady state for different parameters conditions. Both the bifurcation analysis and the simulation of the proposed drive confirm the advantage of the proposed VTHI drive over existing CTHI schemes.