Three level inverter device
Aspects of the invention can include capacitors which series-divide the voltage of a DC power source, an inverter circuit formed by bridge-connecting semiconductor switching elements to which diodes are antiparallel-connected, and bidirectional switches connected between a connection point of the capacitors and the AC output terminals of the inverter circuit. When the voltage of the DC power source is lower than a prescribed value, the inverter circuit can be caused to operate as an ordinary three-phase inverter, and when the voltage of the DC power source is higher than a prescribed value the inverter circuit can be caused to operate as a V-connected inverter, and when caused to operate as a V-connected inverter, a halted phase can be switched in sequence according to line voltages or output currents.
1. A three-phase inverter device, comprising:
a DC voltage source series circuit, formed by series connection of a first DC voltage source and a second DC voltage source;
a first terminal connected to a positive-side terminal of the DC voltage source series circuit, a second terminal connected to a negative-side terminal of the DC voltage source series circuit, and a third terminal connected to a connection point of the first DC voltage source and the second DC voltage source; and
three switching element series circuits groups, each formed by series connection of positive-side and negative-side semiconductor switching elements, to each of which a diode is antiparallel-connected,
one end of each of the switching element series circuits is connected to the first terminal and another end being connected to the second terminal, and
each connection point of the positive-side semiconductor switching element and the negative-side semiconductor switching element being a three-phase AC output terminal;
wherein the AC output terminal for each phase of the three-phase inverter device is connected via a bidirectional switch to the third terminal;
wherein, when the voltage across the first and second terminals of the DC voltage source series circuit is higher than a first prescribed value, the positive-side and negative-side semiconductor switching elements of one of the phases are made non-conducting, the bidirectional switch connecting the AC output terminal for the one phase and the third terminal is made conducting, and the positive-side and negative-side semiconductor switching elements of the other two phases and the bidirectional switches connected to the other two phases are caused to perform switching operation;
wherein, when the voltage across the first and second terminals of the DC voltage source series circuit is lower than a second prescribed value, the positive-side and negative-side semiconductor switching elements and bidirectional switches of all phases of the three-phase inverter device are caused to perform a switching operation; and
wherein, when the voltage across the first and second terminals of the DC voltage source series circuit is higher than a third prescribed value, the positive-side and negative-side semiconductor switching elements of two phases for which an absolute value of the voltage across the AC output terminals is highest and the bidirectional switches connected to the two phases are caused to perform a switching operation, the positive-side and negative-side semiconductor switching elements of the remaining one phase are made non-conducting, and the bidirectional switch connected to the remaining phase are made conducting.
2. The three-phase inverter device according to claim 1 , wherein, when the voltage across the first and second terminals of the DC voltage source series circuit is higher than a fourth prescribed value, the positive-side and negative-side semiconductor switching elements of the phase, for which an absolute value of the current output from the AC output terminals is largest, are made non-conducting, the bidirectional switch connected to this phase is made conducting, and the positive-side and negative-side semiconductor switching elements and the bidirectional switches connected to the other two phases are caused to perform a switching operation.