Closed loop speed control of a three-phase induction motor with load

Closed loop speed control methods are very essential in adjustable industrial speed drive systems. They require a variable voltage and frequency supply from a three-phase voltage source inverter (VSI). This paper presents the speed control of an induction motor fed by a three-phase VSI using the sinusoidal pulse width modulation (SPWM) method and a universal bridge. A PI controller is designed to minimize the steady-state error in speed. The performance analysis of the closed-loop speed control system is conducted in MATLAB-Simulink. As the load torque increases, the motor's speed decreases momentarily but returns to the same level in a very short settling time with minimal undershoot. The simulation results indicate that the speed controller exhibits a superior dynamic response and can effectively control the induction motor's speed and torque. Volts/Hertz (V/f) control of a three-phase induction motor is a popular control method, despite its low dynamic performance, due to its simplicity and cost-effectiveness. A closed-loop system, incorporating an appropriate controller, is employed to achieve effective speed control. The Proportional-Integral (PI) controller is commonly used, and a well-designed controller necessitates an accurate mathematical model of the system. Consequently, achieving a robust controller may compromise the simplicity of the V/f control system.