Development of a microcontroller-based AC voltage controller with soft start capability

This paper describes the development of a prototype of a microcontroller-based phase angle controlled single-phase AC voltage controller that can efficiently control AC voltage and also accommodates soft start capability for single-phase induction motors. The output voltage of the controller is regulated to maintain a desired fixed RMS value and provide stabilized output by implementing a feedback control system. One microcontroller generates PWM signals in synchronism with the supply voltage to control the firing angle of thyristors while a second microcontroller remains dedicated for measuring the RMS value of the output voltage and sending that to the main microcontroller for the purpose of feedback control. The provision for soft starting of a load is also incorporated into this prototype.