Inverter starting circuit

Claim 2

In combination with a DC bus, an electric power rectifier connected between said DC bus and a source of alternating current to apply a direct voltage to said bus, an inverter having an input adapted to be connected to said bus for converting said direct voltage to an alternating output voltage, and at least one capacitor connected in parallel with said inverter input, a circuit for starting said inverter comprising: a. an auxiliary source of direct current at a voltage higher than that of said DC bus; b. a capacitor-charging resistor; c. first means for connecting said resistor in series between said auxiliary source and said inverter input for starting the inverter; and d. second means operative to connect said inverter input to said DC bus and to disconnect it from said auxiliary source when the voltage on said inverter input and parallel capacitor attains a magnitude approximately equal to the magnitude of the voltage on said DC bus.

Claim 3

The combination of claim 1 in which said second means includes means for sensing said capacitor voltage during inverter starting, said sensing means causing operation of the second means when the voltage sensed is at a value slightly exceeding the voltage on said DC bus.

Claim 4

In a frequency changer consisting essentially of a rectifier for converting alternating current to direct current; an inverter for converting direct current to alternating current; a transformer having its primary connected to the AC output of said inverter; at least one capacitor; a first bus interconnecting first terminals of one like polarity of the rectifier DC output, the inverter DC input, and the capacitor; a second bus connected to second terminals of the other like polarity of the rectifier DC output, the inverter DC input, and the capacitor; and a circuit for starting said inverter comprising first normally open circuit interrupter contacts in said second bus between said rectifier and the inverter-capacitor connection to that bus; a capacitor charging resistor; an auxiliary source of direct current including a terminal having the same relative polarity as said second terminal of said rectifier output and having higher voltage than said second rectifier output terminal; a circuit including second normally open interrupter contacts connected in series with said resistor between said auxiliary source terminal and said second terminal of said capacitor; first means energized from said first bus and a portion of said second bus between said first contacts and said second rectifier output terminal for closing said second contacts; voltage responsive means connected to said second capacitor terminal and to said bus portion, said voltage responsive means being operated by a small excess of capacitor voltage over bus voltage; and second means energized from said first bus and said second capacitor terminal by operation of said voltage responsive means, when energized said second means being operative to close said first contacts and to open said second contacts.

Claim 5

In a frequency changer consisting essentially of a rectifier for converting alternating current to direct current; an inverter for converting direct current to alternating current; a transformer having its primary connected to the AC output of said inverter; at least one capacitor; a first bus interconnecting first terminals of one like polarity of the rectifier DC output, the inverter DC input, and the capacitor; a second bus connected to second terminals of the other like polarity of the rectifier DC output, the inverter DC input, and the capacitor; and a circuit for starting said inverter comprising first normally open circuit interrupter contacts in said second bus between said rectifier and the inverter-capacitor connection to that bus; a capacitor charging resistor; an auxiliary source of direct current including a terminal having the same relative polarity as said second terminal of said rectifier output and having higher voltage than said second rectifier output terminal; a circuit including second normally open interrupter contacts connected in series with said resistor between said auxiliary source terminal and said second terminal of said capacitor; first means energized from said first bus and a portion of said second bus between said first contacts and said second rectifier output terminal for closing said second contacts; voltage responsive means connected to said second capacitor terminal and to said bus portion, said voltage responsive means being operated by a small excess of capacitor voltage over bus voltage; and second means energized from said first bus and said second capacitor terminal by operation of said voltage responsive means, when energized said second means being operative to close said first contacts and to open said second contacts.

Claim 6

The starting circuit defined in claim 3 wherein said voltage responsive means is a relay having a low-voltage coil connected in series with a diode for current flow only due to said excess voltage.

Claim 7

The starting circuit defined in claim 3 in which third interrupter contacts are connected in said second bus between said bus portion and said second rectifier output terminal, said bus portion being energized from said rectifier output whenever said third contacts are closed.