This paper presents a new adaptive hysteresis band control approach used in direct torque control (DTC) of the induction motor (IM) drives with the switching tables for the generation of PWM signals. Constant Hysteresis Direct torque control (CHB-DTC) method used the torque and stator flux errors to generate the stator voltage reference and frequency vectors for controlling the three-phase induction motor. The CHB-DTC gives better torque transient performance but it has large steady state ripples. To reduce torque and stator current ripples in CHB-DTC controlled induction motor drives a new adaptive hysteresis band control (AHB) approach is proposed, where the hysteresis band is adapted in real time with the stator flux and torque errors variation, instead of fixed bandwidth. Both classical CHB-DTC method and the proposed adaptive hysteresis band DTC (AHB-DTC) fed three induction motor have been simulated using Matlab/Simulink. The simulation results at different operating conditions over a wide speed range demonstrate the validity, effectiveness, and feasibility of the proposed scheme. The measurements showed that torque ripples were significantly decrease with the new AHB-DTC technique and better speed response in step up or down compared to the CHB-DTC.

In this paper two very efficient pulse width modulation techniques were discussed named Sin pulse width modulation and space vector pulse width modulation. The basic structure of the three-level inverter neutral-point clamped is introduced and the basic idea about space vector pulse width modulation for three-level voltage source inverter has been discussed in detail. Nearest three vectors space vector pulse width modulation control algorithm is adopted as the control strategy for the three phase three level NPC inverter in order to compensate the neutral-point shifting. Mathematical formulation for calculating switching sequence has determined. Comparative analysis proving superiority of the space vector pulse width modulation technique over the conventional pulse width modulation, and the results of the simulations of inverter confirm the feasibility and advantage of the space vector pulse width modulation strategy over sin pulse width modulation in terms of good utilization of dc-bus voltage, low current ripple and reduced switching frequency. Space vector pulse width modulation provides advantages better fundamental output voltage and useful in improving harmonic performance and reducing total harmonic distortion.