Abstract
Classical switching-table-based direct torque control (ST-DTC) of six-phase induction machine (6PIM) drives is seriously penalized by current harmonics as well as torque ripples because of uncontrolled voltage vectors in the low-impedance non-energy subspace and hysteresis torque regulator, respectively. Hence, a virtual subspace-based DTC strategy is proposed to alleviate the impact of low-order current harmonics and torque ripples. The proposed virtual subspace includes 48 virtual voltage vectors (VVs) in the $\alpha -\beta $ subspace with average volt-seconds of zero in the $z_{1}-z_{2}$ subspace, which offers full extent of freedom degrees for 6PIM fed by a two-level voltage source inverter (VSI). The increased number of VVs allows the possibility to design up to nine-level hysteresis torque regulator to minimize the torque ripples. Nevertheless, in this paper, it is found that torque ripple, current harmonics, average switching frequency, and computational burden come to a compromise with a seven-level hysteresis torque regulator. The impact of these VVs on the performance of ST-DTC is experimentally studied and some details of hardware implementation are presented. The performance of the proposed scheme is verified by simulations as well as laboratory experiments, where a complete comparison with recent schemes is made to reveal the superiority of the proposed scheme.
Highlights
PAPER CONTRIBUTION In order to improve the performance of the classical switching-table-based direct torque control (ST-Direct torque control (DTC)) in terms of torque ripples and low-order current harmonics, and at the same time, to retain the fast dynamic and simplicity of ST-DTC, this paper proposes a virtual subspace-based ST-DTC using a seven-level hysteresis torque regulator for a two-level dual three-phase voltage source inverter (VSI)-fed 6PIM
Besides some simulation results which will be presented the performance of the proposed ST-DTC based on virtual subspace is experimentally investigated, and a comparison study is carried out using the following schemes:
This paper is simultaneously aimed at minimizing torque ripple and reducing the harmonic content of stator currents in classical ST-DTC of 6PIM
Summary
S WITCHING-table-based direct torque control (ST-DTC) strategy has much to offer in terms of fast dynamic, simplicity, and low parameter dependency [1], [2]. The reason lies in the fact that the secondary components, i.e., z1 − z2 components, remain uncontrolled when only large voltage vectors are applied These cases highlight the need for an efficient ST-DTC for multi-phase drives. Among possible choices of multi-phase drives, an asymmetrical six-phase induction machine (6PIM) with two three-phase winding sets, which are spatially shifted by π/6, is a promising structure because the three-phase technologies can be conveniently generalized to six-phase ones [11].
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