Increase of Efficiency Induction Motor with Direct Torque Control
The structure of the electric drive with direct control algorithm is given. Features of the classical direct torque control algorithm are presented. It is shown that due to its inability to change smoothly the output flux vector the increased distortion of current and voltage curves are observed and it reduces the level of drives electromagnetic compatibility. The algorithm of space vector (SV-) modulation is described. The mathematical relationships that accompany the separate steps in the transformation of variables in control system are shown. The authors provide timing diagrams of the autonomous inverter. The mathematical modeling of the electric drive with the 75 kW induction motor and direct torque control was done. The graphs of the line voltage and output current of the autonomous inverter are given, as well as their spectral composition for two schemes: with automatic switching and SV-modulation. It is shown that in the case of SV-modulation the electromagnetic torque ripples are decreased, and thanks to the unipolar pulses per half cycle of the fundamental harmonic of line voltage the nonlinear distortion factor of current and voltage at the output of the autonomous inverter are significantly reduced.