Current Limiting and Torque Pulsation Reduction of the Induction Motors

Abstract

A three-phase induction motor has high initial torque pulsation and high inrush current when it is directly connected to the grid. To mitigate these initial high torque pulsation and peak current, a soft starting method can be used. Starting the motor with a soft starter increases the voltage supplied to the induction motor terminal gradually. A three-phase back-to-back thyristor-based rectifier is usually used to apply a controlled voltage to the induction motor by controlling the firing angle of the thyristors. This paper proposes a new control algorithm to reduce the initial torque pulsation and high inrush current by exponentially decreasing the firing angle. In the proposed algorithm, two different modes of the firing angle control are studied: mode I is the controller without current limit, and mode II is the controller with current limit. To verify the effectiveness of the proposed control algorithms, the simulation case studies are performed in MATLAB/Simulink and control hardware-in-the-loop results are obtained via OPAL-RT.