PHOTOVOLTAIC SYSTEM AND METHOD FOR OPERATING A PHOTOVOLTAIC SYSTEM

• US 20070290636A1
• Filed: 06/01/2007
• Published: 12/20/2007
• Est. Priority Date: 06/03/2006
• Status: Active Grant

• Current Assignee: Adensis Gmbh
• Original Assignee: Adensis Gmbh
• Inventors: Neussner, Thomas, Wenzlik, Constantin, Beck, Bernhard
• Granted Patent: US 7,609,019 B2
• Time in Patent Office: Days
• US Class Current: 318/106
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/40 Synchronising a generator for connection to a network or to another generator
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 7/54 by dynamic converters
• CPC Class Codes: H02P 7/06 for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
• CPC Class Codes: H02P 9/00 Arrangements for controlling electric generators for the purpose of obtaining a desired output Ward-Leonard arrangements H02P7/34; vector control H02P21/00; feeding a network by two or more generators H02J; for charging batteries H02J7/14
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic system includes a plurality of photovoltaic modules and a DC motor connected to a three-phase generator driven by a shaft. The three-phase generator is connected to a power mains. The electric power supplied to the DC motor by the plurality of photovoltaic modules is repeatedly measured and adjusted, by changing an external excitation current of the DC motor, to the peak power attainable at the current ambient temperature and the current incident solar radiation intensity. The peak power is preferably determined by incrementally changing the excitation current in predetermined time intervals, until the supplied electric power produces a power level which can be regarded as the peak power.

Claims

1. A method for operating a photovoltaic system having a DC motor electrically connected to a plurality of photovoltaic modules and a three-phase generator driven by the DC motor and electrically connected to a power mains, the method comprising the steps of:

repeatedly measuring electric power supplied by the plurality of photovoltaic modules to the DC motor; and

changing an excitation field of the DC motor to adjust the supplied electric power to a peak power which the plurality of photovoltaic modules is capable of delivering at a current ambient temperature and a current incident solar radiation intensity.

2. The method of claim 1, wherein the supplied electric power is determined by measuring a DC voltage at the DC motor and a DC current supplied to the DC motor by the plurality of photovoltaic modules.

3. The method of claim 1, wherein the peak power is determined by stepwise changing an excitation current of the DC motor, until the electric power supplied by the plurality of photovoltaic modules produces a power level which can be regarded as the peak power.

4. The method according to claim 3, further comprising the steps of after determining the peak power level, identifying a change in the peak power level by incrementing or decrementing the excitation current in defined time intervals;

and setting the peak power to the changed peak power level.

5. The method according to claim 3, further comprising the step of maintaining the determined peak power for an approximately constant ambient temperature and an approximately constant incident solar radiation intensity and a fixed power mains by causing the excitation current to incrementally oscillate in defined time intervals about an optimum excitation current that produces the peak power.

6. The method according to claim 4, wherein each defined time interval is less than 1 second.

7. The method according to claim 5, wherein each defined time interval is less than 1 second.

8. The method according to claim 4, wherein each defined time interval is less than half a second.

9. The method according to claim 5, wherein each defined time interval is less than half a second.

10. The method of claim 1, wherein to shorten the time required for starting up the photovoltaic system, the excitation current is increased incrementally from a first predetermined experimental value to an optimum excitation current that produces the peak power, or is decreased incrementally from a second predetermined experimental value to the optimum excitation current that produces the peak power.

11. A photovoltaic system comprising:

a plurality of photovoltaic modules;

a DC motor having an input electrically connected to the photovoltaic modules and receiving from the photovoltaic modules a DC voltage and a DC current;

a three-phase generator driven by the DC motor via a shaft and producing an AC output voltage capable of being supplied to a power mains;

a first control unit having two inputs and an output, wherein the first input receives the DC voltage from the DC motor; and

a computing unit having a first input receiving the DC voltage from the DC motor and an output producing an output signal, which is iteratively computed and adjusted by the computing unit in accordance with a maximum permissible peak power for a current incident solar radiation intensity and a current ambient temperature and supplied to the second input of the first control unit,

wherein in response to the signals received at the first and second input, the first control unit produces at the output an output signal which causes an excitation field of the DC motor to change, so that the DC motor generates the maximum permissible peak power.

12. The photovoltaic system of claim 11, wherein the computing unit further comprises a second input receiving an actual value of the DC current produced by the photovoltaic module, with the output signal being iteratively computed and adjusted by also taking into account the actual value of the DC current.

13. The photovoltaic system of claim 11, wherein the first control unit comprises a proportional-integral (PI) controller.

14. The photovoltaic system of claims 11, wherein the DC motor is an externally excited DC motor, and wherein the output signal of the first control unit controls an excitation current of the DC motor.

15. The photovoltaic system of claim 14, further comprising an excitation current measuring unit and a second control unit having two inputs and an output, wherein the output signal of the first control unit is applied to a first input of the second control unit and an excitation current signal measured by the excitation current measuring unit is applied to the second input of the second control unit.

16. The photovoltaic system of claim 15, wherein the second control unit comprises a proportional-integral (PI) controller.

17. The photovoltaic system of claim 14, further comprising a converter receiving electric power from the power mains for supplying the excitation current to the DC motor.

18. The photovoltaic system of claim 15, further comprising a converter receiving electric power from the power mains for supplying the excitation current, wherein the converter is controlled by an output signal produced at the output of the second control unit.

19. The photovoltaic system of claim 11, wherein the system is designed for an output power of more than 800 kW.

20. The photovoltaic system of claim 11, wherein the power mains is a public power grid with a constant internal resistance, as perceived from the AC generator.

21. The photovoltaic system of claim 11, wherein the three-phase generator is a synchronous three-phase generator.

22. The photovoltaic system of claim 21, wherein the three-phase generator supplies an AC voltage of about 400 V.