Analysis and Speed Control of Induction Motor during Input Supply Voltage Sag

This paper analyzes the operational behavior of induction motor during input supply voltage sag for speed at and below base speed. The purpose of the analysis is to maintain the torque constant during voltage sag condition. Changes in operating point of the motor is explained by considering the voltage, current and torque equations in voltage plane. Mathematical equations explaining the voltage trajectory to be followed and voltage sag limit are derived. A modified control technique is proposed to ensure that the motor maintains the torque and speed till the voltage sag limit, beyond which the load torque is met with reduced speed. Simulation in MATLAB/Simulink and experimental results conducted on a 3-hp induction motor for a constant load torque are presented.