Power conversion apparatus
A power conversion apparatus includes a first single-phase inverter that uses as a DC power source a first DC voltage that is boosted from a solar light voltage by a boosting chopper circuit. The first single-phase inverter is arranged between two single-phase inverters that use second DC power sources that are supplied from the first DC power source. AC sides of the respective single-phase inverters are connected in series. A power conditioner thus configured provides an output voltage using the sum of the generated voltages of the respective single-phase inverters. Chopper circuits are connected between the first DC power source and the second DC power sources, and power is supplied to the second DC power sources from the first DC power source via switching devices in the single-phase inverters.
1. A power conversion apparatus comprising:
a plurality of single-phase inverters, each single-phase inverter including switching devices, receiving DC power from a respective DC power source and producing AC power at an AC-output side, the AC-output sides of the plurality of single-phase inverters being connected in series, wherein the apparatus produces an output voltage that is a sum of respective output voltages generated by the plurality of single-phase inverters; and
a DC-DC converter, wherein
first and second DC power sources of the DC power sources supply DC power to first and second single-phase inverters, the first and second single-phase inverters having their AC-output sides connected to each other, of the plurality of single-phase inverters,
the first and second DC power sources are connected to each other via the DC-DC converter, and
the DC-DC converter supplies power from the first DC power source, having higher DC voltage than the second DC power source, to the second DC power source via the switching devices in the first and second single-phase inverters.
2. The power conversion apparatus according to claim 1 , wherein the DC-DC converter includes a chopper circuit including a reactor, a rectifying device, and a switch.
3. The power conversion apparatus according to claim 2 , wherein, during an operation period when the first single-phase inverter that receives DC power from the first DC power source, turns on the switching devices that connect a positive electrode of the first DC power source to an AC output power line, the switch in the chopper circuit is turned on and off.
4. The power conversion apparatus according to claim 2 , wherein
the first DC power source has the highest DC voltage of the DC power sources and the highest DC voltage is generated from a third DC power source,
the first single-phase inverter, receiving DC power from the first DC power source, includes two AC-ouput terminals, each AC-output terminal connected to the respective second single-phase inverter receiving DC power from the respective second DC power source, and
each second DC power source is connected to the first DC power source via a respective chopper circuit, and is supplied with power from the first DC power source via the switching devices in the first and second single-phase inverters.
5. The power conversion apparatus according to claim 4 , wherein output pulse width of the first single-phase inverter is adjusted, and total power fluctuation calculated by subtracting charging from discharging via the single-phase inverters of the DC power sources, other than the first DC power source, is positive or zero.
6. The power conversion apparatus according to claim 5 , wherein output pulse width of the first single-phase inverter is adjusted so that the total power fluctuation is reduced.
7. The power conversion apparatus according to claim 4 , including a magnetic coupling core of a magnetic material magnetically coupling two reactors in the chopper circuits.
8. The power conversion apparatus according to claim 7 , wherein the two reactors include windings configured so that polarities of electromotive forces induced by the reactors are in the same direction.
9. The power conversion apparatus according to claim 7 , wherein the two reactors include windings configured so that polarities of electromotive forces induced by the reactors are in opposite directions, and including a gap for adjusting the magnetic coupling and located in the magnetic coupling core.
10. The power conversion apparatus according to claim 2 , wherein
the single-phase inverters are connected in ascending or descending order of DC voltages of the DC power sources that supply DC power,
a maximum DC power source of DC power sources has the highest DC voltage of the DC power sources and the highest DC voltage is generated from a third power source,
the plurality of single-phase inverters include a plurality of pairs of the first and second single-phase inverters having their AC-output sides connected to each other and receiving DC power from a respective pair of the first and second DC power sources,
the first and second DC power sources of each pair are connected to each other via a respective chopper circuit, and
each chopper circuit supplies power from the first DC power source, having higher DC voltage than the second DC power source, to the second DC power source via the switching devices in the first and second single-phase inverters, so that each of the DC power sources, other than the maximum DC power source, is supplied with power.
11. The power conversion apparatus according to claim 10 , wherein output pulse width of the single-phase inverter receiving DC power from the maximum DC power source is adjusted, and total power fluctuation calculated by subtracting charging from discharging via the single-phase inverters of the DC power sources, other than the maximum DC powers source, is positive or zero.
12. The power conversion apparatus according to claim 11 , wherein output pulse width of the first single-phase inverter is adjusted so that the total power fluctuation is reduced.
13. The power conversion apparatus according to claim 1 , including a boosting circuit having a switch wherein
a maximum DC power source of the DC power sources has the highest DC voltage of the DC power sources,
the highest DC voltage is generated from a third DC power source via the boosting circuit, and
when the voltage of the third DC power source exceeds a predetermined voltage, on-off operation of the switch in the boosting circuit is stopped to stop boosting.
14. The power conversion apparatus according to claim 13 , including a bypass circuit that bypasses the boosting circuit and, when the voltage of the third DC power source exceeds the predetermined voltage, on-off operation of the switch in the boosting circuit is stopped to stop boosting and the boosting circuit is bypassed by the bypass circuit.
15. The power conversion apparatus according to claim 14 , wherein the bypass circuit includes a relay.
16. The power conversion apparatus according to claim 1 , wherein a predetermined AC voltage and AC current are output and supplied to a load.
17. The power conversion apparatus according to claim 1 , wherein a predetermined AC output is connected in parallel with an AC system and linked to the AC system.