Inverter circuit for supplying current to polyphase motors

Claim 1

IN AN INVERTER CIRCUIT FOR SUPPLYING A VARIABLE FREQUENCY POLYPHASE ALTERNATING VOLTAGE OUTPUT FROM A SOURCE OF UNDIRECTIONAL VOLTAGE INPUT, THE COMBINATION COMPRISING AT LEAST ONE PAIR OF INVERTER GROUPS CONNECTED BETWEEN SAID INPUT AND EACH PHASE OF SAID POLYPHASE OUTPUT, EACH SAID INVERTER GROUP INCLUDING A PAIR OF GRIDCONTROLLED VALVES, MEANS PRODUCING A SINUSOIDAL CONTROL VOLTAGE AT A FREQUENCY CORRESPONDING TO THE DESIRED FREQUENCY OF SAID POLYPHASE ALTERNATING VOLTAGE OUTPUT, MEANS PRODUCING FIRST AND SECOND TRIANGULAR CONTROL VOLTAGE AGES HAVING A FREQUENCY HIGHER THAN THE HIGHEST FREQUENCY DESIRED FOR SAID POLYPHASE ALTERNATING VOLTAGE OUTPUT, SAID FIRST AND SECOND TRIANGULAR CONTROL VOLTAGES HAVING THE SAME FREQUENCY AND AMPLITUDE BUT BEING DISPLACED IN PHASE BY 180*, FIRST AND SECOND MIXER MEANS FOR EACH TRIANGULAR AND SINUSOIDAL CONTROL VOLTAGES, SAID FIRST MIXER MEANS HAVING AS AN INPUT THERETO SAID SINUSOIDAL CONTROL VOLTAGE AND SAID FIRST TRIANGULAR CONTROL VOLTAGE, AND SAID SECOND MIXER MEANS HAVING AS AN INPUT THERETO SAID SINUSOIDAL CONTROL AND SAID SECOND TRIANGULAR CONTROL VOLTAGE, SAID FIRST MIXER INCLUDING TWO OUTPUTS CONNECTED RESPECTIVELY TO THE CONTROL GRIDS OF THE VALVES OF ONE INVERTER GROUP AND SAID SECOND MIXER MEANS INCLUDING TWO OUTPUTS CONNECTED RESPECTIVELY TO THE CONTROL GRIDS OF THE VALVES OF THE OTHER INVERTER GROUP, ONE OUTPUT OF EACH SAID MIXER MEANS CARRYING A VOLTAGE WHEN THE INSTANTANEOUS VALVE OF THE APPERTAINING TRIANGULAR VOLTAGE IS HIGHER THAN THE INSTANTANEOUS VALUE OF SAID SINUSOIDAL VOLTAGE, AND THE OTHER OUTPUT OF EACH SAID MIXER MEANS CARRYING A VOLTAGE WHEN THE INSTANTANEOUS VALUE OF THE APPERTAINING TRIANGULAR VOLTAGE IS LOWER THAN THE INSTANTANEOUS VALUE OF SAID SINUSOIDAL VOLTAGE.