Circuit arrangement for self-commutated inverters

Claim 1

An inverter apparatus for energizing an AC load, said inverter apparatus comprising a plurality of inverter output terminals connected to said AC load and a source of DC current having a first and second DC output terminal, an inverter circuit comprising a first main thyristor circuit comprising a first and second group of main thyristors, the cathodes of said first group of main thyristors being coupled, respectively, to the anodes of said second group of main thyristors, while the anodes of said first group of main thyristors are coupled to said first DC terminal, first connecting means for connecting said cathodes of said first group of main thyristors, respectively, to a first selected one of said plurality of inverter output terminals, and a second main thyristor circuit, the improvement comprising: a first commutation circuit comprising a first commutation thyristor having an anode, connected to said first DC output terminal, a cathode and a gate, an extinguishing circuit connected to said cathode of said first commutation thyristor, a second commutation thyristor having an anode, connected to said extinguishing circuit, a cathode and a gate, a first separating diode connected to said cathode of said second commutating thyristor, and a first block of accumulating diodes having a first DC block terminal, comprising the anodes thereof, connected to said cathode of said first separating diode and a plurality of first accumulating diode output terminals, comprising the cathodes thereof, each being connected to a corresponding one of said inverter output terminals, a second commutation circuit coupled to said second main thyristor circuit and comprising a second block of accumulating diodes having a plurality of anodes, each being connected to a corresponding one of said inverter output terminals, and a plurality of cathodes connected in common to a second DC block terminal, a second separating diode connected to said second DC block terminal, an accumulating capacitor connected to said second separating diode, and a third separating diode interconnected between said accumulating capacitor and said first DC block terminal; wherein said thyristors are energized so that said current passes from said first main thyristor circuit to said first commutation circuit, and from said first commutation circuit to both said second main thyristor circuit and said second commutation circuit; and further comprising means for subsequently blocking said current in said second commutation circuit, whereby said current has transferred from said first main thyristor circuit to said second main thyristor circuit.