Power Conversion Apparatus

• US 20080192519A1
• Filed: 02/21/2006
• Published: 08/14/2008
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: Yamada, Masaki, Iwata, Akihiko, Kumagai, Takashi, Matsubara, Noriyuki, Harada, Shigeki, Seto, Makoto
• Granted Patent: US 7,719,865 B2
• Time in Patent Office: Days
• US Class Current: 363/71
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 7/483 Converters with outputs that each can have more than two voltages levels
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

In a power conversion apparatus that boosts a solar light voltage, converts it to AC and supplies AC power to a load or system, power loss is reduced and efficiency is improved. An inverter unit, in which AC sides of three single-phase inverters receive DC power from respective sources with a voltage ratio of 1:3:9 as respective inputs are connected in series. Gradational output voltage control of an output voltage is carried out using the sum of the respective generated AC voltages. Also, a solar light voltage is boosted by a chopper circuit to generate the highest voltage DC power source. When the solar light voltage exceeds a predetermined voltage, the boosting of the chopper circuit is stopped, thereby reducing power loss due to the boosting.

Claims

1. A power conversion apparatus comprising:

a plurality of single-phase inverters that convert DC power from a plurality of DC power sources to AC power, the plurality of single-phase inverters being connected in series, wherein

the apparatus provides an output voltage with gradational output voltage control using the sum of generated voltages from a combination of single-phase inverters selected from the plurality of single-phase inverters, and

the plurality of DC power sources that provide inputs of respective single-phase inverters include a first DC power source producing the highest DC output voltage, and second DC power sources; and

a booster circuit including a switch, wherein the highest DC output voltage, produced by the first DC power source, is generated by a third DC power source via the booster circuit, and, when the DC output voltage of the third DC power source exceeds a predetermined voltage, on-off operation of the switch in the booster circuit is stopped to stop boosting.

2. The power conversion apparatus according to claim 1, comprising a bypass circuit that bypasses the booster circuit, wherein, when the voltage of the third DC power source exceeds a predetermined voltage, the on-off operation of the switch in the booster circuit is stopped to stop the boosting, and the booster circuit is bypassed by the bypass circuit.

3. The power conversion apparatus according to claim 2, wherein

the booster circuit includes a reactor and a rectifying device that are connected in series,

the switch has a first end connected to a connection point between the reactor and the rectifying device, and

at least the rectifying device is bypassed by the bypass circuit.

4. The power conversion apparatus according to claim 3, wherein, when a current flowing through the bypass circuit does not exceed a predetermined value, the bypass circuit is open and the current is switched to a current path via the booster circuit with the boosting stopped.

5. The power conversion apparatus according to claim 2, wherein

the booster circuit includes a reactor and a rectifying device that are connected in series,

the switch has a first end connected to a connection point between the reactor and the rectifying device, and

only the reactor is bypassed by the bypass circuit.

6. The power conversion apparatus according to claim 2, wherein the bypass circuit includes a relay.

7. The power conversion apparatus according to claim 1, including a DC-DC converter connecting the first DC power source to respective second DC power sources.

8. The power conversion apparatus according to claim 1, wherein the DC output voltage of the first DC power source is lower than maximum output voltage of the power conversion apparatus.

9. The power conversion apparatus according to claim 1, wherein the second DC power sources include two DC power sources having substantially equal DC output voltages.

10. The power conversion apparatus according to claim 1, wherein the sum of DC output voltages of respective second DC power sources is at least equal to 4/9 of the DC output voltage of the first DC power source.

11. The power conversion apparatus according to claim 1, wherein the output voltage of a predetermined single-phase inverter of the plurality of single-phase inverters is PWM-controlled, and the PWM-controlled output voltage is combined with each output voltage level in the gradational output voltage control.

12. The power conversion apparatus according to claim 1, wherein a predetermined AC voltage and AC current is output and supplied to a load, or the predetermined AC output is connected in parallel with a system, and a third DC power source is linked to the system.

13. A power conversion apparatus comprising:

a plurality of single-phase inverters that convert DC power from a plurality of DC power sources to AC power, the plurality of single-phase inverters being connected in series, wherein

the apparatus provides an output voltage with gradational output voltage control using the sum of generated voltages from a combination of single-phase inverters selected from the plurality of single-phase inverters, and

the plurality of DC power sources that provide inputs of respective single-phase inverters include a first DC power source producing the highest DC output voltage, and second DC power sources; and

a booster circuit including a switch, wherein

the highest DC output voltage, produced by the first DC power source, is generated by a third DC power source via the booster circuit, and

output voltage of the booster circuit is set so that total power fluctuation due to charging and discharging of the respective second DC power sources via respective single-phase inverters does not exceed a predetermined quantity.

14. The power conversion apparatus according to claim 13, including a DC-DC converter connecting the first DC power source to respective second DC power sources.

15. The power conversion apparatus according to claim 13, wherein the output voltage of the booster circuit is set so that the total power fluctuation in respective second DC power sources due to charging and discharging via respective single-phase inverters is substantially zero.

16. The power conversion apparatus according to claim 15, including a DC-DC converter connecting respective second DC power sources to each other.

17. The power conversion apparatus according to claim 13, wherein peak value of the output voltage of the power conversion apparatus divided by the sum of the DC output voltages of the first and second DC power source, is controlled to be within a range from 0.8 to 0.9.

18. The power conversion apparatus according to claim 13, wherein the total power fluctuation in respective second DC power sources via respective single-phase inverters is the sum of respective quantities of power fluctuation in respective second DC power sources or the sum of absolute value of respective quantities of power fluctuation.

19. The power conversion apparatus according to claim 13, wherein, when the voltage of the third DC power source exceeds a predetermined voltage, on-off operation of the switch in the booster circuit is stopped to stop boosting.

20. The power conversion apparatus according to claim 13, wherein the output voltage of the first DC power source is lower than maximum output voltage of the power conversion apparatus.

21. The power conversion apparatus according to claim 13, wherein the second DC power sources include two DC power sources having substantially equal DC output voltages.

22. The power conversion apparatus according to claim 13, wherein the sum of DC output voltages of respective second DC power sources is at least equal to 4/9 of the DC output voltage of the first DC power source.

23. The power conversion apparatus according to claim 13, wherein the output voltage of a predetermined single-phase inverter of the plurality of single-phase inverters is PWM-controlled, and the PWM-controlled output voltage is combined with each output voltage level in the gradational output voltage control.

24. The power conversion apparatus according to claim 13, wherein a predetermined AC voltage and AC current is output and supplied to a load, or the predetermined AC output is connected in parallel with a system, and a third DC power source is linked to the system.

25. A power conversion apparatus comprising:

a plurality of single-phase inverters that convert DC power from a plurality of DC power sources to AC power, the plurality of single-phase inverters being connected in series, wherein

the apparatus provides an output voltage with gradational output voltage control using the sum of generated voltages from a combination of single-phase inverters selected from the plurality of single-phase inverters, and

the plurality of DC power sources that provide inputs of respective single-phase inverters include a first DC power source producing the highest DC output voltage, and second DC power sources;

a booster circuit including a switch, wherein

the highest DC output voltage, produced by the first DC power source, is generated by a third DC power source via the booster circuits; and

a DC-DC converter, wherein

the first DC power source and each of the second DC power sources are connected to each other via the DC-DC converter, and

output pulse width of the single-phase inverter that receives the DC output voltage of the first DC power source is adjusted so that total power fluctuation due to charging and discharging of respective second DC power sources via respective single-phase inverters is reduced.

26. The power conversion apparatus according to claim 25, wherein the total power fluctuation in respective second DC power sources via respective single-phase inverters is the sum of respective power fluctuation in respective second DC power sources or the sum of absolute value of respective quantities of power fluctuation.

27. The power conversion apparatus according to claim 25, wherein, when the voltage of the third DC power source exceeds a predetermined voltage, on-off operation of the switch in the booster circuit is stopped to stop boosting.

28. The power conversion apparatus according to claim 25, wherein the DC output voltage of the first DC power source is lower than maximum output voltage of the power conversion apparatus.

29. The power conversion apparatus according to claim 25, wherein the second DC power sources include two DC power sources having substantially equal DC output voltages.

30. The power conversion apparatus according to claim 25, the sum of DC output voltages of respective second DC power sources is at least equal to 4/9 of the DC output voltage of the first DC power source.

31. The power conversion apparatus according to claim 25, wherein the output voltage of a predetermined single-phase inverter of the plurality of single-phase inverters is PWM-controlled, and the PWM-controlled output voltage is combined with each output voltage level in the gradational output voltage control.

32. The power conversion apparatus according to claim 25, wherein a predetermined AC voltage and AC current is output and supplied to a load, or the predetermined AC output is connected in parallel with a system, and a third DC power source is linked to the system.