A low distortion 3-phase rectifier using a resonant-mode Y-connected thyristor network

This paper describes the operation of a resonant three-phase Y-connected thyristor network, “3θ SCR Y-switch”, that can be used to lower the line-current harmonic content of a three-phase diode bridge rectifier using AC-line inductors. The current shaping action of the 3θ SCR Y-switch results in close to unity fundamental power factor with an input current harmonic distortion of less than 10% and close to 5%. The resonant-mode action of the 3θ SCR Y-switch has attractive electrical characteristics in terms of a very low per-unit current rating; self-commutation of the thyristors; zero current turn-on and zero voltage turn off; 120 Hz switching frequency. These characteristics make the power converter inexpensive, reliable and useful in medium power applications such as industrial drives for controlling the speed of three-phase induction motors