Implementation of a new fast direct torque control algorithm for induction motor drives

Induction motor (IM) drives based on direct torque control (DTC) allow high dynamic performance to be obtained with very simple control schemes. The conventional DTC has two main drawbacks. The first one is the variation of the switching frequency according to the amplitude of the hysteresis bands and the motor operating speed, whereas the second is that the selection of voltage vectors is not optimised inside the flux hysteresis band to give fast torque response, because of the nature of the hysteresis controllers. This study proposes a new DTC method for IM, which enables fast torque response and constant switching frequency. This is achieved by optimising the selection of the voltage vectors to give maximum rate of torque increase. Simulation and hardware implementation results show that both the torque and speed responses are faster than the old method. In addition, the effect of variation of the IM parameters on the system performance is taken into consideration.