single phase ac voltage controller with RL load

AC voltage controllers use pairs of thyristors like SCRs or triacs to control the voltage output without changing frequency. Voltage control is accomplished through either phase control under natural commutation or on/off control under forced commutation using devices like GTOs, transistors, or IGBTs. The document then describes how a single phase AC voltage controller with an RL load uses two thyristors (T1 and T2) to control the output voltage by varying the firing angle (a) of each thyristor during the positive and negative half cycles.