Improvement of fault tolerance in AC motor drives using a digital delta-hysteresis modulation scheme

In this paper, a novel digital delta-hysteresis regulation (DDHR) scheme is proposed that allows motor drive systems to maintain relatively accurate control of phase currents in the event of the loss of all phase current sensors. Within the scheme, line currents are reconstructed using knowledge of the DC-link current and switching states. The generation of switching signals is based upon traditional delta-hysteresis regulation (DHR). However, modifications are made to DHR to ensure the DC-link current always contains sufficient information to reconstruct phase currents. Experimental results obtained from a vector-controlled induction machine are used to show that there is a relatively small difference between the performance of the pre- and post- fault systems.