Theoretic and experimental study of direct torque control of induction motors

Practitioners in the electric drive community have recently introduced a novel torque control strategy for high power asynchronous machine applications called direct torque control (DTC), which has three distinctive features: it focuses on stator (instead of rotor) flux regulation, it does not aim at an asymptotic system inversion (hence it does not require additional current loops), and it explicitly takes into account the discrete nature of the control actions, which are simply points of a finite set obtained from a switching logic. Besides its simplicity, it is claimed that the achieved performance is (in some instances) superior to classical field oriented strategies because of the digital form of the control structure and the reduced dependence on parameter variations of the stator flux calculations. The objective of the paper is twofold: to carry out a mathematical analysis of the stabilization mechanism of DTC, and second, to propose a modified DTC to improve its dynamical behavior. Experimental results are presented to illustrate the main points of the paper