Correction of the Stator Flux Demagnetizing Effect at Low Speeds of the Direct Torque Control of Induction Motor

Abstract

This paper deals with the direct torque control (DTC) of an induction motor. This control allows torque flux to be decoupled without the need for coordinate transformations. It has the advantage of being robust to parametric variations of the machine in tracking mode, and to load disturbances in regulation mode. However, in addition to torque and flux ripples, this control in its conventional version proves insufficient at low speeds due to the demagnetizing effect of the stator flux caused by the ohmic drop across the stator resistor. This demagnetization considerably increases torque and flux ripples and causes current distortions. To alleviate this problem, it is necessary to shift back the flux positions in the (α, β) plane by an appropriate angle. The main objective of this study is to find this offset angle without affecting the entire order in its original version. In speed loop, the parameters of the PI controller are optimized using the Particle Swarm Optimization (PSO) algorithm.