With recent advancements in power electronics and digital signal processor (DSP) technology, induction machines driven by static converters are being widely used in variable speed medium power applications. Amongst the techniques being used, direct torque control (DTC) has emerged as a powerful technique for the control of high performance induction machines. This control strategy, through decoupled control of torque and flux provides the same performance as is achieved from a separately excited DC machine. But despite the advantages such as fast dynamic response and simple control structure, DTC suffers from torque and current pulsations. Torque pulsation minimization is an active area of research in the domain of DTC of induction motors.

In this project entitled “Performance Improvement of DTC of Induction Motor” an attempt is made to address this problem of torque ripple minimization and loss minimization. For this purpose, a model for the direct torque controlled induction motor drive has been made in Simulink/Matlab. To minimize the torque pulsations, a fuzzy logic based duty ratio controller has been incorporated. Further, based on insight acquired from the studies and modeling, a simple but novel switching control strategy for minimizing torque pulsation is also proposed and modeled.

Keeping in view the importance of energy conservation, an ANN based controller has been designed and trained to predict the optimal reference flux for achieving maximum efficiency of the motor, given the reference values of speed and torque. Simulations have been carried out for two motors of 2.2 kW and 22 kW rating. 22 kW motors are used in the NTPC plants for variable speed applications such as coal feeder which have scope for improvement of energy efficiency. Simulations have been done at various values of speed and load torque with rated and optimal flux, to demonstrate the energy savings that could be obtained by operating the machine at optimal flux value.