Three-phase current reconstruction technique using dc current information in conventional two-level inverters can be used for the purpose of cost reduction and sensor fault tolerance. A novel phase current reconstruction scheme, with reduced immeasurable area and common mode voltage, is proposed in this paper. A tristate pulse-width modulation technique has been employed, in which three adjacent switching states are used to construct the reference voltage. The active switching states are arranged at the edge and the center of a PWM cycle. Fixed sampling and simultaneous three-phase currents can be easily achieved with very little hardware and software requirements. A detailed analysis of the effects of nonidealities leads to regional modifications of the switching sequence resulting in almost the whole hexagon as the feasible area. The usefulness of the proposed reconstruction algorithm has been verified by experimental results obtained from a 4-kW induction motor drive system. Smooth transitions between the redundant and fault-tolerant modes were observed.

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