Direct torque control of induction motors: Stability analysis and performance improvement

Practitioners in the electric drives community have recently introduced a n ovel torque control strategy for high power induction motor applications ca lled direct torque control (DTC), which has three distinctive features: 1) it focuses on stator (instead of rotor) flux regulation; 2) in contrast to classical field-oriented control, it does not aim at an asymptotic system i nversion (hence it does not require additional current loops); and 3) it ex plicitly takes into account the discrete nature of the control actions, whi ch are simply points of a finite set obtained from a switching logic. Besid es its simplicity, it is claimed that the achieved performance is (in some instances) superior to field oriented strategies because of the digital for m of the control structure and the reduced dependence on parameter variatio ns of the stator flux calculations. Our objective in this paper is twofold, first to carry out a mathematical analysis of the stabilization mechanism of DTC, which helps us assess the achievable performance of the current sch eme and provide guidelines for its tuning. Second, to propose a modified DT C to improve its dynamical behavior. Experimental results are presented to illustrate the main points of our paper.