Paper Title
A Simple Digital Triggering Circuit for Three-Phase Line Commutated SCR Inverter

This paper concerns the design and implementation of a simple microcontroller based triggering circuit for threephase line commutated SCR inverter connected to a three-phase synchronous motor. The control scheme is consisting of motor terminal voltage sensor, comparator, AVR microcontroller, firing angle control system, pulse amplifier and isolating circuit. The gate pulses for the six SCRs of the inverter are generated by the microcontroller using induced emf of the synchronous motor. It is found that the firing angle of the triggering pulses can be controlled satisfactorily from 90o to 180o by changing the reference low dc voltage. The firing angle, once adjusted, remains constant irrespective of the changes in motor terminal ac voltage and frequency. Index terms - Microcontroller; line-commutation; SCR inverter, Constant firing angle, variable voltage and frequency.