Photovoltaic system and method employing a number of maximum power point tracking mechanisms

• US 9,219,363 B2
• Filed: 04/08/2013
• Issued: 12/22/2015
• Est. Priority Date: 09/06/2012
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Eaton Corp. (Wisconsin) (Eaton Corporation PLC.)
• Inventors: Liu, Yu, Luebke, Charles J., Thompson, Christopher S.
• Primary Examiner(s): Barnie, Rexford
• Assistant Examiner(s): VU, TOAN T
• Application Number:
  US13/858,420
• Publication Number:
  US 20140062209A1
• Time in Patent Office: 988 Days
• Field of Search: 307/82
• US Class Current: 1/1
• CPC Class Codes: G05F 5/00 Systems for regulating electric variables by detecting deviations in the electric input to the system and thereby controlling a device within the system to obtain a regulated output
• CPC Class Codes: H02J 1/102 being switching converters H02J1/108, H02J1/12 take precedence
• 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: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic system includes a photovoltaic array and a DC/AC inverter. The photovoltaic array includes an output, a plurality of photovoltaic strings each including a plurality of photovoltaic modules electrically connected in series to form an output having a first direct current voltage, and a plurality of DC/DC converters each including a first maximum power point tracking mechanism for a corresponding one of the photovoltaic strings, an input of the output of the corresponding one of the photovoltaic strings, and an output having a second direct current voltage. Each output of the DC/DC converters is electrically connected in parallel or series to form the output of the photovoltaic array having a direct current voltage. The DC/AC inverter includes a second maximum power point tracking mechanism for the photovoltaic array, an input of the output of the photovoltaic array, and an output having an alternating current voltage.

Claims

1. A method of providing maximum power point tracking, said method comprising:

performing by a processor band-based maximum power point tracking in which an upper limit and a lower limit are applied to regulate a direct current voltage for a predetermined time period;

determining that the direct current voltage reached the upper limit or the lower limit during the predetermined time period; and

after the predetermined time period expires, defining by the processor a subsequent predetermined time period having a corresponding subsequent upper limit and a corresponding subsequent lower limit applied to regulate the direct current voltage, wherein the subsequent lower limit applied to regulate the direct current voltage was determined to reach the upper limit during the predetermined time period, and wherein the subsequent lower limit is less than the lower limit if the direct current voltage was determined to reach the lower limit during the predetermined time period.

2. The method of claim 1 further comprising:

defining a voltage range with the upper limit and the lower limit from about 350 volts to about 400 volts; and

defining a time range with the predetermined time period from about 600 milliseconds to about 1200 milliseconds.

3. A photovoltaic system comprising:

a photovoltaic array comprising;

an output,

a plurality of photovoltaic strings, each of the photovoltaic strings comprising a plurality of photovoltaic modules electrically connected in series to form an output having a first direct current voltage, and

a plurality of DC/DC converters, each of the DC/DC converters comprising a first maximum power point tracking mechanism for a corresponding one of the photovoltaic strings, an input of the output of the corresponding one of the photovoltaic strings, and an output having a second direct current voltage, wherein the first maximum power point tracking mechanism performs a band-based maximum power point tracking mechanism in which an upper limit and a lower limit are applied to regulate the output having the first direct current voltage of the corresponding one of the photovoltaic strings for a predetermined time period, wherein after the predetermined time period expires, each of the first maximum power point tracking mechanism of the of the DC/DC converters defines a subsequent predetermined time period having a corresponding upper limit and a corresponding lower limit and wherein the first maximum power point tracking mechanism is further structured to determine if the first direct current voltage of the corresponding one of the photovoltaic strings reached the upper limit or the lower limit during the predetermined time interval, and if so then to increase the corresponding upper limit or decrease the corresponding lower limit, respectively, for the subsequent predetermined time period;

wherein each said output of DC/DC converters is electrically connected in parallel or series to form the output of said photovoltaic array having a direct current voltage, and

a DC/AC inverter comprising a second maximum power point tracking mechanism for said photovoltaic array, an input of the output of said photovoltaic array, and an output having an altering current voltage.

4. The photovoltaic system of claim 3 wherein information is not communicated between the first and second maximum power point tracking mechanisms.

5. The photovoltaic system of claim 3 wherein the first and second maximum power point tracking mechanisms operate at the same time.

6. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism operates faster than the second maximum power point tracking mechanism.

7. The photovoltaic system of claim 3 wherein the second maximum power point tracking mechanism regulates the direct current voltage of the output of said photovoltaic array.

8. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism regulates the first direct current voltage of the output of the corresponding one of the photovoltaic strings.

9. The photovoltaic system of claim 3 wherein the second maximum power point tracking mechanism is a perturbation and observation mechanism.

10. The photovoltaic system of claim 3 wherein each of the first maximum power point tracking mechanism of the DC/DC converters employs the same maximum power point tracking algorithm as the second maximum power point tracking mechanism.

11. The photovoltaic system of claim 3 wherein each of the first maximum power point tracking mechanism of the DC/DC converters employs a different maximum power point tracking algorithm than the second maximum power point tracking mechanism.

12. The photovoltaic system of claim 3 wherein the second maximum power point tracking mechanism regulates the direct current voltage of the output of said photovoltaic array at a frequency of about 0.1 Hz to about 2 Hz.

13. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism regulates the first direct current voltage of the output of the corresponding one of the photovoltaic strings at a frequency of greater than 10 Hz.

14. The photovoltaic system of claim 3 wherein the band-based maximum power point tracking mechanism is structured to function with constant irradiation to the photovoltaic modules.

15. The photovoltaic system of claim 3 wherein the band-based maximum power point tracking mechanism is structured to function with increasing or decreasing irradiation to the photovoltaic modules.

16. The photovoltaic system of claim 6 wherein the first maximum power point tracking mechanism regulates the first direct current voltage of the output of the corresponding one of the photovoltaic strings at a frequency of about 20 Hz.

17. The photovoltaic system of claim 3 wherein the upper limit and the lower limit define a voltage range from about 350 volts to about 400 volts;

and wherein the predetermined time period defines a time range from about 600 milliseconds to about 1200 milliseconds.

18. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism is further structured to change the first direct current voltage of the corresponding one of the photovoltaic strings by a predetermined voltage for a plurality of times during the predetermined time period, and to increase the predetermined voltage after the predetermined time period for the subsequent predetermined time period.

19. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism is further structured to change the first direct current voltage of the corresponding one of the photovoltaic strings by a predetermined voltage for a plurality of times during the predetermined time period, and to decrease the predetermined voltage after the predetermined time period for the subsequent predetermined time period.

22. The photovoltaic system of claim 3 wherein the first maximum power point tracking mechanism is further structured to limit a difference between the corresponding upper limit and the corresponding tower limit to be less than or equal to a predetermined maximum value and to be greater than or equal to a predetermined minimum value.

20. A photovoltaic system comprising:

a photovoltaic array comprising;

an output,

a plurality of photovoltaic strings, each of the photovoltaic strings comprising a plurality of photovoltaic modules electrically connected in series to form an output having a first direct current voltage and

a plurality of DC/DC converters, each of the DC/DC converters comprising a first maximum power point tracking mechanism for a corresponding one of the photovoltaic strings, an input of the output of the corresponding one of the photovoltaic strings, and an output having a second direct current voltage, wherein the first maximum power point tracking mechanism performs a band-based maximum power point tracking mechanism in which an upper limit and a lower limit are applied to regulate the output having the first direct current voltage of the corresponding one of the photovoltaic strings for a predetermined time period, wherein after the predetermined time period expires, each of the first maximum power point tracking mechanism of the DC/DC converters defines a subsequent predetermined time period having a corresponding upper limit and a corresponding lower limit, and wherein the first maximum power point tracking mechanism is further structured to determine if the first direct current voltage stabilized during the predetermined time interval, and if so then to decrease the corresponding upper limit and increase the corresponding lower limit, respectively, of the subsequent predetermined time period;

wherein each said output of the DC/DC converters is electrically connected in parallel or series to form the output of said photovoltaic array having a direct current voltage; and

a DC/AC inverter comprising a second maximum power point tracking mechanism for said photovoltaic array, an input of the output of said photovoltaic array, and an output having an altering current voltage.

21. The photovoltaic system of claim 20 wherein the first maximum power point tracking mechanism is further structured to limit the predetermined voltage to be less than or equal to a predetermined maximum value and to be greater than or equal to a predetermined minimum value.