| Abstract |
The application of the field oriented control method for variable speed induction motor drives leads to a complex control system structure. Generally, a closed loop field oriented control system consists of the following components: PID controller for motor flux and torque, current and/or voltage decoupling network, complex coordinate transformation, two axis to three axis converter, voltage or current modulator, flux and torque estimator, and PID) (sliding mode) speed controller. In a direct torque control system, as introduced by Takahashi and Depenbrock in the mid 1980's, the first five components are replaced by two hysteresis comparators and a selection table. It has been shown that with this greatly simplified control structure, the drive performance can be significantly improved when compared to field oriented control. In the present paper, the principles and characteristics of a direct torque control system are considered. It is also shown that by means of a more complex selection table, the performance of the direct torque control system may be improved further. |
