Method for activating a multi-string inverter for photovoltaic plants

• US 20090236917A1
• Filed: 02/09/2009
• Published: 09/24/2009
• Est. Priority Date: 03/22/2008
• Status: Active Grant

• Current Assignee: SMA Solar Technology AG
• Original Assignee: SMA Solar Technology AG
• Inventors: Muller, Tobias, Victor, Matthias, Juchem, Ralf, Bettenwort, Gerd
• Granted Patent: US 8,212,409 B2
• Time in Patent Office: Days
• US Class Current: 307/82
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• 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 3/1584 with a plurality of power processing stages connected in parallel
• CPC Class Codes: H02M 7/48 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A method of activating a Multi-String inverter for photovoltaic generators (1a, 1b) of a photovoltaic plant (6), the Multi-String inverter incorporating on the input side a separate DC-DC converter (2a, 2b) for each generator string (photovoltaic generator) (1a, 1b) and each output of the DC-DC converters (2a, 2b) being connected in parallel and to an input of a DC-AC converter (3) and the DC-AC converter (3) being connected with an alternating current mains (4) for feeding into the mains aims at improving efficiency. This is achieved in that one or several electrical variables, namely input current, input voltage and/or input power are measured at each DC-DC converter (2a, 2b) and at least one of the DC-DC converters (2a, 2b) changing its operating condition as a is function of this measurement when a limit value and/or a range is exceeded in such a manner that its power loss is reduced so that the energy yield of the photovoltaic plant (6) is increased.

Claims

1. A method of activating a Multi-String inverter for photovoltaic generators (1a, 1b) of a photovoltaic plant (6),

said Multi-String inverter incorporating one separate DC-DC converter (2a, 2b) for each generator string (photovoltaic generator) (1a, 1b) on its input side

each output of said DC-DC converters (2a, 2b) being connected in parallel and with an input of a DC-AC converter (3)

and said DC-AC converter (3) being connected to an alternating current mains (4) for feeding into the mains,

characterized in that one or several electrical variables, namely input current, input voltage and/or input power are measured at each DC-DC converter (2a, 2b)

and that, when a limit value and/or a window is exceeded, as a function of this measurement, at least one of said DC-DC converters (2a, 2b) changes its operating condition in such a manner that its power loss is reduced,

so that the energy yield of the photovoltaic plant (6) is increased.

2. The method as set forth in claim 1,

characterized in that at least one of the DC-DC converters (2a, 2b) changes its operating condition in that a switch element of the DC-DC converter (2a, 2b) is not activated permanently and is switched off or on in such a manner that its input voltage substantially corresponds to its output voltage.

3. The method as set forth in claim 2,

characterized in that at least one of the DC-DC converters (2a, 2b) at which the highest input voltage applies, is switched off, said input voltage being above a mains peak voltage.

4. The method as set forth in claim 2,

characterized in that at least two DC-DC converters (2a, 2b) are switched off when two input voltages of the DC-DC converters (2a, 2b) lie within a voltage range.

5. The method as set forth in claim 2,

characterized in that at least two DC-DC converters (2a, 2b) are switched off when an input voltage applies at the two DC-DC converters (2a, 2b) at least, which is above the mains peak voltage.

6. The method as set forth in claim 2,

characterized in that at least one of the DC-DC converters (2a, 2b) is activated again when the input voltage of the DC-DC converter (3) is within the range of the mains peak voltage, when a power ratio of the photovoltaic generators (1a, 1b) changes above a limit value and/or when a defined time has past.

7. The method as set forth in claim 1,

characterized in that a Maximum Power Tracking with a shadowing detection for the photovoltaic generators (1a, 1b) is utilized so that the more favourable work point is set for several power maxima.

8. The method as set forth in claim 1,

characterized in that partial shadowing of the photovoltaic generators (1a, 1b) is detected as a function of the operating conditions of the DC-DC converters (2a, 2b).

9. The method as set forth in claim 1,

characterized in that one switches between several Maximum Power Tracking methods.

10. The method as set forth in claim 1,

characterized in that, in an inactive operating condition, an additional switch for bridging a semiconductor switch (SH, ST, Sze, Sse), a diode (DH, DT, Dze, Dse) and/or a choke (LH, LT, Lze2, Lse1) is switched on in at least one of the DC-DC converters (2a, 2b).

11. The method as set forth in claim 1,

characterized in that each DC-DC converter (2a, 2b) is configured to be a boost converter.