Simulation of the Impact of Soft Starter Controller on Induction Motor Transients

This research dwelt on the simulation of the impact of soft starter controller on induction motor transients. It was aimed at resolving the various challenges inherent in the dynamic operation of asynchronous motors, which included current and torque surges during motor start up. The method leading to solution include comprehensive mathematical model of asynchronous motor in both steady state and dynamic state conditions, as well as the development of soft starter control scheme and its application for the motor operational control and finally, the simulation of the impact of soft starter controllers on machines performance or behavior during transients from standstill to synchronous speed was carried out using MATLAB/SIMULINK software. The MATLAB/SIMULINK simulation was used to determine the variation of the starting inrush current and starting torque pulsation under different firing angle between = (pi/12) rad. , and = (pi/3) rad. With the applied voltage of 220V, the starting current is between +205A and - 180A and the torque pulsation is between -85Nm and +250Nm when connected directly to the supply. It is seen that the starting inrush current is about 3 to 8 times of the motor no-load current. A control scheme is proposed for reducing the inrush current and torque pulsations. It was observed that the inrush current was about 125A and the torque pulsation is between -150Nm and +130Nm. The inrush current is reduced to about 60.98 %. At no-load condition, it is seen that the rotor accelerates from stall with zero load torque to synchronous speed but the time taken to achieve steady state is increased about 0.7sec. The application of load torque (10Nm) at 1sec results in a sharp drop in the motor speed from 186.3 rad/sec. to 185.2 rad/sec. and an increase in the electromechanical torque up to 10Nm with the applied load torque.