Steady-State Performance Degradation of a DTC IM Drive Under Parameter and Transduction Errors

With direct torque control (DTC), the stator flux magnitude and the torque of an induction motor (IM) drive are controlled in a closed-loop way. The actual values of the controlled variables are estimated by processing the inverter dc-link voltage and the stator currents by means of the IM voltage model. Any error in the model parameter (the stator resistance) or in the voltage and current transduction degrades the drive performance. In this paper, a theoretical investigation of the effects of the various errors on a DTC IM drive is carried out. The investigation gives a proof of the drive instability due to some errors and provides, for the other errors, the amount of the deviation produced on the controlled variables in steady state. The theoretical findings are substantiated by experimental and simulation results.