Investigation of direct torque controlled induction motor drive system

Electrical drive systems used to control electric motors in industrial applications adjust the power transferred from electrical network to mecanical load via controlling torque and speed . Researchs about induction motors which are common in industrial systems due to some important advantages are focused on vector based high performans control methods such as field orientation control (FOC) and Direct torque control (DTC).In DTC method, complex current transformations, voltage or current controlled Pulse width modulations are not needed. Optimum switching table depending on flux and torque hysteresis controller outputs is used to control of inverter switches in order to provide rapid flux and torque response.In this study, firstly scalar and vectoral control methods generally investigated. DTC method is explained and compared with FOC method. Adventages and disadvantages of DTC expressed. Mathematical model of induction motor based on d-q reference frame is given and its Matlab/Simulink simulation is done. The simulation model is run under symetrical 3 phase supply, then current, speed and torque responses are presented.Speed control system of induction motor controlled by DTC method is simulated and the results are investigated. A PI controller is used as speed controller. It is observed that the DTC method have rapid torque response. Effects of band widths of flux and torque hystresis controllers on current, flux and torque responses are investigated