Reduction of torque ripple in direct torque control of induction motor drives using space vector modulation based pulse width modulation

A method of deriving the switching instants of different space vectors in the direct torque control of induction motor drives using pulse width modulated voltage source inverters is described in this paper. The switching instants of different space vectors are determined to reduce torque ripple compared to the commonly used space vector concept based on the sinusoidal pulse width modulation technique. The time durations of two adjacent voltage space vectors and the corresponding zero voltage space vectors are determined in this method depending on maximum and average switching frequency, allowable for the switching devices in the three-phase inverter. The sampling rate of the impressed reference voltage vector (in other words the switching frequency of the carrier wave) is varied to keep the torque ripple within the specified limit, determined by maximum allowable switching frequency. This paper also deals with the optimum switching pattern to reduce the average switching frequency of the switching devices. A simulation program is developed in order to verify the validity of the theory.