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
$x$
$y$
plane while avoiding low-order
$\alpha$
-
$\beta$
harmonics (at least up to a modulation index of
$\text{1.2311}\,{\;}\text{p.u.}$
), 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.