Switching-Table-Based Direct Torque Control of Six-Phase Drives With $x-y$ Current Regulation

High harmonic contents of the stator currents due to uncontrolled
$x-y$
subspace dramatically overshadow the performance of the switching-table-based direct torque control (ST-DTC) strategy for multiphase drives. The concept of ST-DTC based on virtual voltage vectors (VVs) has been frequently developed to alleviate this problem. However, VVs with fixed duty ratios are incapable of compensating inherent machine/converter asymmetries and dead time harmonics, which are mapped into the
$x-y$
subspace. To solve this problem, this article develops a dynamic duty-ratio-based DTC technique for six-phase induction machine drives, where the duty ratios of the selected VVs are not constant anymore. These duty ratios are updated based on the
$x-y$
voltage commands arising from the closed-loop
$x-y$
current controllers over every sampling period. The attained merits over and above the conventional fixed duty-ratio-based DTC schemes include effective
$x-y$
current cancellation without increase in average switching frequency and decrease in dc-link utilization. Experimental results are presented to validate the effectiveness of the proposed control technique.