Direct torque control of induction motor using imaginary switching times with 0-1-2-7 & 0-1-2 switching sequences: a comparative study

This paper presents a new strategy of direct torque control of induction motor using imaginary switching times. Determination of effective time from reference voltage vector is eliminated and no requirement of sector and angle identification. Imaginary switching times are derived from flux errors of respective phases. These times are directly responsible for calculating the effective time during which the actual power flows to the motor. Also the stator resistance drop is compensated in terms of imaginary times to improve the performance. In order to further simplify the control strategy, electromagnetic torque is estimated in terms of phase quantities. Simulation results of the proposed method show the effectiveness of the new strategy. Switching sequence 0-1-2-7 (conventional sequence for first sector) is used but in order to reduce switching frequency, 0-1-2 (clamping) sequence is also presented using same program just by changing the offset time. A comparison is made between two switching sequences and concluded that clamping sequence is on leading edge as far as switching losses and performance is concerned. This control strategy guarantees very good dynamic and steady state performance with constant switching frequency.