Unified PWM algorithm based direct torque controlled induction motor drive by using the sampled reference phase voltages

This paper presents a simple and efficient unified pulsewidth modulation (UPWM) algorithm for direct torque controlled induction motor drives. Though the classical direct torque control (DTC) algorithm gives fast dynamic response, it gives large ripples in steady state. To reduce the steady state ripples and to achieve the constant switching frequency operation, space vector pulse width modulation (SVPWM) algorithm is used for DTC drives. But, the SVPWM algorithm requires angle and sector information and hence the complexity involved is more. To reduce the complexity and to generate the all possible PWM algorithms in the entire modulation regions the proposed algorithm is developed by using the instantaneous phase voltages only. By varying the offset time in the proposed UPWM algorithm various continuous PWM (CPWM) algorithms like sinusoidal PWM (SPWM) and space vector PWM (SVPWM) and discontinuous PWM (DPWM) algorithms such as DPWMMIN, DPWMMAX, DPWM0, DPWM1, DPWM2 and DPWM3 can be generated at all modulation indices. To evaluate the performance of the proposed UPWM algorithm based DTC drive, several numerical simulation studies have been carried out and the results are presented. The simulation results show the effectiveness of the proposed algorithm.