Method for converting direct voltage into three-phase alternating voltage

• US 20070179720A1
• Filed: 01/08/2007
• Published: 08/02/2007
• Est. Priority Date: 01/27/2006
• Status: Active Grant

• Current Assignee: SMA Solar Technology AG
• Original Assignee: SMA Technologie AG (SMA Solar Technology AG)
• Inventors: Victor, Matthias, Bremicker, Sven, Greizer, Frank, Becker, Holger, Engel, Bernd, Laschinski, Joachim, Groote, Wilfried, Cramer, Gunther, Westphal, Torben, Dingel, Thorsten
• Granted Patent: US 7,576,449 B2
• Time in Patent Office: Days
• US Class Current: 702/58
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/26 Arrangements for eliminating or reducing asymmetry in polyphase networks
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y02E 40/50 Arrangements for eliminating or reducing asymmetry in polyphase networks

Abstract

A method of converting a direct voltage generated by a decentralized power supply system into three-phase alternating voltage by means of a plurality of single-phase inverters (WR1-WR3), said alternating voltage being provided for supplying an electric mains, is intended to avoid inadmissible load unbalances using single-phase inverters. This is achieved in that, upon failure of one inverter (WR1-WR3), an asymmetrical power supply distribution is reduced by limiting the output of the other inverters. The method makes it possible to simplify three-phase voltage monitoring.

Claims

1. A method of converting direct voltage generated by a mains connected system for decentralized power supply into a three-phase alternating voltage by means of a plurality of single-phase inverters (WR1-WR3), said alternating voltage being provided for supplying an electric mains and for decentralized power supply, whereby upon failure of one inverter (WR1-WR3), an asymmetrical power supply distribution is reduced by limiting the output of the other inverters.

2. The method as set forth in claim 1, wherein that the output of each inverter (WR1-WR3) is durably limited to 2-20 kVA, more specifically to about 4.6 kVA.

3. The method as set forth in claim 1 wherein the output of each inverter (WR1-WR3) is limited temporarily, more specifically for about 10 minutes, to about 5 kVA.

4. The method as set forth in claim 1, wherein the failure of the inverter (WR1-WR3) is registered by a measurement signal of an additional circuit of the inverter, a communication signal resulting from the measurement signal being provided for limiting the output or for disconnecting the inverters from the mains.

5. The method as set forth in claim 4, wherein the communication signal is communicated to the processors of the inverters (WR1-WR3) for limiting the output of the inverters by means of processor control.

6. The method as set forth in claim 4, wherein the measurement signal is generated by a current of a constant current source, said current of said constant current source being in the milliampere range.

7. The method as set forth in claim 1, wherein the communication takes place between the inverters (WR1-WR3), through which each inverter communicates through one or a plurality of external cables that it is ready for supply.

8. The method as set forth in claim 1, wherein the communication takes place between the inverters (WR1-WR3), each inverter communicating by radio that it is ready for supply.

9. A circuit arrangement for implementing the method as set forth in claim 1, with a plurality of single-phase inverters (WR1-WR3) of a decentralized power supply system, wherein each inverter has a failure measuring circuit (1) for reducing the power of the other inverters upon asymmetrical power supply resulting from the failure of the inverter.

10. The circuit arrangement as set forth in claim 9, wherein each measuring circuit includes a direct current source (3), more specifically a constant current source, that may be additionally connected through an electrically conductive bridge (4), so that only one of the current sources (3) delivers the measurement current, each measuring circuit comprising a connection for a measurement and/or output signal in such a manner that a failure or an OK signal can be communicated to the other two inverters.

11. The circuit arrangement as set forth in claim 9, wherein each inverter is implemented with an external communication line (2).

12. The circuit arrangement as set forth in claim 9 wherein a plurality of groups (GR1, GR2) of three single-phase inverters (11-16) is connected to the output side of a three-phase protection switchgear, said switchgear being adapted to be switched off through the manual, external clearing means (18).

13. The circuit arrangement as set forth in claim 12, wherein the switchgear is a contactor (19).

14. The circuit arrangement as set forth in claim 1 being constructed and arranged such that, upon failure of one inverter, all the inverters are disconnected from the mains when the voltage of one phase exceeds, or falls short of, imposed limit values.

15. The circuit arrangement as set forth in claim 14, being constructed and arranged such that the inverters are disconnected from the mains by directly switching them off, a manual, external clearing means (18) being directly connected to all the inverter groups.