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The fault tolerance of electric drives is highly appreciated at industry for security and economic reasons, and the inherent redundancy of six-phase machines provides the desired fault-tolerant capability with no extra hardware. For this reason some recent research efforts have been focused on the fault-tolerant design, modelling and control of six-phase machines. Nevertheless, a unified and conclusive analysis of the post-fault capability of six-phase machine is still missing. This work provides a full picture of the post-fault derating in generic six-phase machines and a specific analysis of the faulttolerant capability of the three mainstream six-phase induction machines (asymmetrical, symmetrical and dual three-phase). Experimental results confirm the theoretical post-fault current limits and allow concluding which is the best six-phase machine for each fault scenario and neutral arrangement.Index Terms Six-phase drives, fault-tolerance, field oriented control.

Abstract-Using the vector space decomposition (VSD) approach, the currents in a multiphase machine with distributed winding can be decoupled into the flux and torque producing α-β components, and the loss-producing x-y and zero-sequence components. While the control of α-β currents is crucial for flux and torque regulation, control of x-y currents is important for machine/converter asymmetry and dead-time effect compensation. In this paper, an attempt is made to provide a physically meaningful insight into current control of a six-phase machine, by showing that the fictitious x-y currents can be physically interpreted as the circulating currents between the two three-phase windings. Using this interpretation, the characteristics of x-y currents due to the machine/converter asymmetry can be analysed. The use of different types of x-y current controllers for asymmetry compensation and suppression of dead time induced harmonics is then discussed. Experimental results are provided throughout the paper, to underpin the theoretical considerations, using tests on a prototype asymmetrical six-phase induction machine.

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