Control of an induction machine fed by a Cascade Multicell converter under fault

Multilevel converters offer good quality load waveforms, which is clearly beneficial to its operation. A significant drawback that affects to all multilevel topologies is the high number of components required, which is related to a high fault probability. Among all the multilevel topologies, cascade multicell converters (CM), characterized by high modularity, allow for power to be easily increased. Moreover, this characteristic also allows any faulty module (cell) to be isolated, so the load can be fed by the remaining operational cells. Modifications to the modulation scheme, based either on the use of redundant states or on modified references have been proposed in literature, avoiding the unbalanced operation. This work presents the transient operation from normal to fault operation when modified references are used and an induction motor is driven by the converter. Modifications to the motor control scheme are proposed based on the use of field weakening to achieve operation and on-line speed reference modifications. In this way, hard torque pulsations are avoided, while the maximum power available from the converter is used.