A Novel Strategy for Minimizing the Variation of Neutral Point Voltage and Switching Frequency in DTC Controlled, NPC Driven Induction Motors

Application of the multi-level converters such as neutral point clamped (NPC) inverter for driving the medium voltage induction motors makes more voltage vectors available for a direct torque control (DTC) method and hence more degrees of freedom in selection of voltage vectors when compared to conventional two-level inverter applications. This can be gained for improving inverter performance indices such as variations of neutral point voltage and/or the switching frequency imposed to NPC inverter. This paper propose a convenient strategy for selecting adequate switching states minimizing both the variation of neutral point voltage and the switching frequency of inverter. This helps the designers to increase the power density of inverter and to reduce the size of DC link capacitors resulting in a considerable reduction of drive costs. Simulation results show the effectiveness of the proposed strategy.