Torque Response Improvement of Direct Torque Controlled Three-Phase Inverter Fed Induction Motor Drive

Abstract: Induction motors (IM) play a very important role in both daily life and industry, because of its reduced price, reliability in functioning and less requirement for maintenance. The IM drives controlled with the vector control method is widely used in industry. However, this control technique requires complex coordinate transformation, inner current control loop and accurate system parameters. But in Direct Torque Control (DTC) method, more accurate and speedy torque response is offered without such coordinate transformations, PWM pulse generation and current regulators. The speed controller in DTC-IM drive usually employs the conventional PI controller. But it has characteristic of non-linear saturation, which will make the control performance of the drive much poor. In order to enhance the drive performance, Anti-Windup PI controller is introduced which distinctly control the integral state by feed backing the output of the integrator to the input port of the integrator according to whether the controller output is saturated or not, which allows the system leave saturation soon, resulting in reduced overshoot and settling time of the system. This paper implements the DTC technique for voltage source inverter fed induction motor drive with the speed controller realized both using conventional PI and anti-windup PI controllers and the improved torque response is verified using MATLAB.

Keywords: Induction Motor, Vector Control, Direct Torque Control, PI Controller, Anti Windup PI Controller.