Effect of DC-Link Voltage Limitation on Postfault Steady-State Performance of Asymmetrical Six-Phase Induction Machines

The asymmetrical six-phase induction machine represents the most common multiphase machine type used in many high-power industrial applications. While a body of research covering control of the machine under fault conditions has been published in the literature, corresponding studies to investigate the dc-link voltage design requirements under postfault operation in a simple and efficient manner have not met the same interest. To this end, this paper first introduces the machine steady-state equivalent circuit under one open-phase fault, which simplifies the estimation of different machine characteristic curves instead of using tedious mathematical techniques. As far as the machine parameters are concerned in this paper, a modified locked-rotor test based on the derived equivalent circuit is also proposed to fully estimate the parameters of different subspaces using a simple technique without the need for additional tests. The proposed steady-state circuit is also used to understand the effect of the secondary subspace impedance, neutral configuration, and the postfault control strategy on the maximum achievable torque for a limited dc-bus voltage. The minimum dc-link voltage magnitude to provide rated output under postfault operation is also given. The proposed concepts have been experimentally verified using a prototype asymmetrical six-phase machine.