Method for matching the power of a photovoltaic system to a working point at which the system produces maximum power

• US 7,564,013 B2
• Filed: 05/07/2008
• Issued: 07/21/2009
• Est. Priority Date: 05/23/2007
• Status: Active Grant

• Current Assignee: SMA Solar Technology AG
• Original Assignee: SMA Solar Technology AG
• Inventors: Arend, Oliver, Reichenbächer, Wolfgang Kurt, Bettenwort, Gerd, Leonhardt, Gerald, Kühnel, Christian, Laschinski, Joachim Ralf, Bremicker, Sven
• Primary Examiner(s): Sohn; Seung C
• Application Number:
  US12/151,492
• Publication Number:
  US 20080290252A1
• Time in Patent Office: 440 Days
• Field of Search: 250/203.4
• US Class Current: 250/203.4
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A method of matching the power of a photovoltaic system producing electric energy by which a working point at which the system produces maximum power is set by changing the working point in an MPP matching process and by comparing the system power, which changes as a result thereof, is intended to be suited both for stationary characteristic curves and for non stationary generator characteristic curves and to be easy to carry out so that the best working point is always set, even when the system is subjected to external interfering factors. This is achieved in that one or several additional control steps or control cycles are performed in order to track during the matching process a power point changing under external impact for a working point of even higher power to be set.

Claims

1. A method of matching the power of a photovoltaic system producing electric energy by which a working point at which the system produces maximum power is set by changing the working point in an MPP matching process and by comparing the system power, which changes as a result thereof, characterized in that at least one additional control step or control cycle is performed for detecting an external meteorological impact on a photovoltaic generator that causes a sudden strong reduction in sun irradiation, whereby the control step or control cycle is performed so that a past working point is set as reference working point to check through one additional control step or control cycle whether an assumed maximum power point indeed corresponds to the actual maximum power point, so that it can be checked if a non stationary characteristic curve exists, and

that said at least one control step or said at least one control cycle is integrated in said MPP matching process,

it being checked in at least one control step or in at least one control cycle whether the generator characteristic curve has changed under the meteorological impact during one MPP matching cycle and a new working point being set in at least one correction step or in at least one correction cycle as a function of the change in position of one reference point so that during the MPP matching process the power point changed under the impact of external meteorological conditions is tracked so as to set a working point at which the system produces more power.

2. The method as set forth in claim 1, characterized in that the one or several additional control portions or control cycles are performed at one or several reference points or reference portions.

3. The method as set forth in claim 1, characterized in that the reference point or the reference points are tracked in cyclical or acyclical intervals to meet the new working point or the new working points or the new working portion.

4. The method as set forth in claim 1, characterized in that the matching process is delayed by one or several search steps, one or several of the control steps or of the control cycles being performed during the delay so that the working point is corrected pursuant to the direction of a change in power induced by an external impact or is maintained if no power change occurs.

5. The method as set forth in claim 1, characterized by an interruption in the matching process in order to set one or several past working points during one or several control steps or control cycles for a past working point to be set as the reference point, saidworking point being set pursuant to the direction of the change in power during a control step or control cycle when the power changes.

6. The method as set forth in claim 1, characterized in that two left-side reference points are set during one control step or control cycle, said reference points being closer to a short-circuit point than a previously left actual working point.

7. The method as set forth in claim 1, characterized in that a control step or a control cycle is respectively performed by electrically loading or unloading the system for a reference point to change.

8. The method as set forth in claim 1, characterized in that, in the matching process, the working point is compulsorily displaced by electrically loading or unloading a current generating generator, matching being dependent on a comparative result of two or several consecutive working points.

9. The method as set forth in claim 1. characterized in that the matching process is performed in a method based on a slope method, the difference quotients between power and voltage being formed from two successive measurements and the sign direction, the search direction and the search width being fixed.

10. The method as set forth in claim 1, characterized in that the system includes a photovoltaic generator.

11. The method as set forth in claim 1, characterized in that it is carried out by means of an inverter.

12. The method as set forth in claim 1, characterized in that the inverter is a photovoltaic inverter.