Regenerative two-quadrant converter

Claim 1

In an AC/DC converter system including an AC bridge having a plurality of static-controlled switches controlled sequentially for conduction across DC-link terminals operative as a DC voltage source and connected to a load, with a capacitor across said DC-link terminals and the load, the system operating in one of a forward and a regenerative mode; the combination of a reactor and a GTO device in series between one terminal of the bridge and a corresponding end of said capacitor; an auxiliary thyristor connected in series with the other end of said capacitor and the other terminal of the bridge; a rectifying device connected between said reactor and said other end of said capacitor; an additional thyristor connected in parallel with said reactor and in opposition to said GTO device, to said rectifying device and to the bridge thyristors of the associated terminal; said GTO device being controlled for conduction together with the bridge thyristors under conduction in the control sequence thereof so as to form a current path via said reactor, said capacitor, the load, and via said auxiliary thyristor; said GTO device being controlled in the regenerative mode for interrupting said current path and said additional thyristor being controlled concurrently for conduction to create a freewheeling current path for said reactor upon commutation of successive bridge thyristors for conduction in the sequence thereof, thereby to allow a zero-current condition under regeneration from the load.