Overmodulation Method With Adaptive x-y Current Limitation for Five-Phase Induction Motor Drives

Five-phase induction machines are attractive due to inherent benefits such as lower current rating than three-phase ones. On the other hand, ac motor drives often need to operate in the overmodulation (OVM) region, e.g., to increase the maximum speed or to work with reduced dc-link voltage. Most of the existing OVM strategies for five-phase drives are based on injecting low-order harmonics in the no-torque xy plane while avoiding low-order alpha-beta harmonics (at least up to a modulation index of 1.2311 p.u.), so as to prevent the torque ripple associated with the alpha-beta components. However, in practice the x-y impedance is very small, and hence, this approach can easily lead to overcurrent. This article proposes an OVM method for five-phase induction motors that adaptively modifies the injected components so that at each moment the addition of low-order x-y harmonics is favored over alpha-beta ones but without surpassing the maximum current rms of the drive. In case the total stator copper loss (SCL) tends to exceed its rating during OVM in a given scenario, the proposed scheme automatically reduces the x-y injection to keep the SCL at its rated value. Experimental results verify the theory.

Automated summary

This article proposes an adaptive OVM method for five-phase induction motors that modifies the injected components to favor low-order x-y harmonics, avoiding overcurrent and reducing stator copper losses.