Inverter arrangement with two controlled three-phase inverters

Claim 1

An inverter arrangement for use with a DC voltage source comprising: a first inverter having an input adapted to be connected to said DC source, exactly six main valves arranged in a first three-phase bridge arrangement, and first quenching devices for quenching said first main valves, and said first inverter providing a first three-phase system of inverter output voltages which are each of a rectangular waveshape and are phase-shifted by 120° el relative to each other; a second inverter having an input adapted to be connected to said DC source, exactly six main valves arranged in a second three-phase bridge arrangement, and second quenching devices for quenching said second main valves, said second inverter providing a second three-phase system of inverter output voltages which are phase-shifted, in the sense of a time lag, by 30° el and smaller in magnitude by a factor equal to √3 relative to said first system of voltages, said second system of voltages each being of rectangular waveshape and being phase-shifted by 120° el relative to each other; a combining means for combining said first and second systems of voltages to derive a three-phase system of resultant output voltages; a control unit for controlling said main valves and said quenching devices of said first and second inverters so as to fire and extinguish said main valves several times per period of said resultant voltages, and such that each of said inverter output voltages includes per period of said resultant voltages a positive voltage pulse and a negative voltage pulse which are separated from each other by a no-voltage interval of 60° el length, each of said pulses being of a 120° el length and having two no-voltage intervals whose widths are symmetrically adjustable relative to the center of the pulse and are spaced on opposite sides of said center at a distance of 30° el therefrom; said combining means combining one of said inverter voltages of said first system additively with a first inverter voltage of said second system, and subtractively with a second inverter voltage of said second system to generate one of said resultant voltages, said first inverter voltage being displaced 30° el relative to said one inverter voltage and said second inverter voltage being displaced 150° el relative to said one inverter voltage; and said combining means comprising: a first transformer which is connected to said first inverter, said first transformer having three primary windings which are delta connected and three secondary windings, and being connected in a Dy-connection; and a second transformer which is connected to said second inverter, said second transformer having three primary windings which are delta connected and having six secondary windings, and being connected in a Dz-connection and having a transformation ratio which is greater than the transformation ratio of said first transformer by a factor equal to √3; one of said first and second transformers having an open neutral point; the other of said first and second transformers having its neutral point connected as a neutral terminal for said three-phase system of resultant output voltages; and each of said secondary windings of said first transformer being connected in series with a series connection of two of said secondary windings of said second transformer.