Research On Intellectual Control Method Of Asynchronism Motor Direct Torque Control System

As a new control method ,Direct Torque Control method has its advantages such as robust performance and simple structure compared with Field-orientation control system .But Direct Torque Control system can hardly have as broad as the speeds range which Field-orientation system can have becauseof torque pulses in it .The proposed scheme is based on the conventional Direct Torque Control system .Fuzzy control strategy is adopted to select the state of the switch of the converter to substitute for the Schmitt trigger .Flux and Torque are divided into several sections ,The optional voltage vector is selected according to them which improve control accuracy and dynamic and static performance of the system .To improve the system's performance further, this paper proposed a direct torque control scheme based on Neuro-Fuzzy structure.This scheme uses a controller based on an adaptive NF inference system ( ANFIS)together with a space voltage modulator to replace both the hysteresis comparators and the switching table.The ANFIS controller combines fuzzy logic and artificial neuro networks to evaluate the reference voltage required to drive the flux and torque to the demanded values within a fixed time period.This evaluation is performed using the electromagnetic torque and stator flux magnitude errors together with the stator flux angle.This calculated voltage is then synthesized using Space Vector Modulation.The induction motor drives with the Direct Torque Fuzzy Control and Direct Torque Control ( DTC) have been simulated respectively,and the theory of neuro-fuzzy control has been studied.The results indicate that the starting flux and torque dynamic response and the response to the step changes in command torque with fuzzy controller show a considerable improvement over the conventional control and the steady state reponse in both cases are the same.The new control strategy in the Direct Torque Control based neuro-fuzzy structure guarantees very good dynamic and steady state characteristic with low sampling time and constant switching frequenct.it has certain advantage over fuzzy logic control.