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Direct torque control is a variable-structure control strategy with simplicity, fast response, and tolerance to motor parameter variation, which provides direct control of stator flux and electromagnetic torque by optimally selecting the inverter states in each sampling period. For five-phase drives, the increased number of voltage vectors offers greater flexibility in optimizing the selection of the inverter states, thereby accomplishing more precise control of the stator flux and torque. Nevertheless, the large number of inverter states means that a more elaborate and complex selection criterion is needed. The following two aspects, which are not issues for three-phase drives, are taken into account in designing switching-table-based direct torque control for five-phase drives. First, the low-frequency harmonic currents due to the auxiliary vector plane need to be eliminated. Second, full utilization of the dc-link voltage is desired. A novel switching-table-based direct torque controller fulfilling these objectives is proposed and is combined with a speed-adaptive variable-structure observer. Experimental results substantiate the effectiveness of the proposed sensorless direct torque controller.
Date of Publication: Feb. 2011