Design and simulation of closed-loop voltage over frequency speed control for a three-phase induction motor using a PWM inverter in MATLAB

Abstract

This bachelor thesis presents the design and simulation of a closed-loop voltage to frequency (V/f) speed control system for a three-phase induction motor using a pulse width modulation inverter in MATLAB/Simulink. While open-loop voltage by frequency drives are widely used due to their simplicity, they suffer from steady-state speed errors under varying load conditions. To address this limitation, a closed-loop architecture incorporating a proportional integral controller is developed. The system continuously monitors rotor speed via feedback and adjusts the inverter's output frequency and voltage to maintain the desired setpoint. The complete model includes: (1) a three-phase induction motor, (2) a proportional integral based speed controller, (3) a sinusoidal pulse width modulation, and (4) a voltage to frequency calculation block with low-frequency voltage boost. Simulation results demonstrate that the closed-loop system achieves <1% steady-state error and recovers from step load disturbances within 0.5 seconds, significantly outperforming open-loop operation. The findings confirm that closed-loop voltage to frequency control provides robust, load-independent speed regulation while preserving the simplicity of the voltage to frequency principle.