Performance evaluation of a direct torque controlled drive in the continuous PWM-square wave transition region

A simplified method of torque and flux control in the transient and field-weakening region based on the direct torque control (DTC) scheme is presented. The simplified method limits the magnitude of the stator voltage reference to the maximum instantaneous value allowable with space vector PWM. The simplified method was compared to an alternative technique which attempts to maintain dead beat control of one of the controlled variables during a transient in the other. The angle of the reference voltage is set equal to that calculated using the previously presented direct torque control method. It is the opinion of the authors that the simplified control scheme yields very satisfactory results, in comparison to the other control, and that the advantages gained by the reduced complexity outweigh the fact that dead-beat control is not available in transient and overmodulation conditions. The direct torque control scheme provides increased bus voltage utilization, and increased dynamic response due to the real-time, predictive nature of the control. This was verified through simulation and experimental results.<
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