Method for distributed power harvesting using DC power sources

• US 8,587,151 B2
• Filed: 08/10/2011
• Issued: 11/19/2013
• Est. Priority Date: 12/06/2006
• Status: Active Grant

• Current Assignee: Solaredge Limited
• Original Assignee: Solaredge Limited
• Inventors: Adest, Meir, Handelsman, Lior, Galin, Yoav, Fishelov, Amir, Sella, Guy
• Primary Examiner(s): AMAYA, CARLOS DAVID
• Application Number:
  US13/207,321
• Publication Number:
  US 20110291486A1
• Time in Patent Office: 832 Days
• Field of Search: 307/77, 307/82
• US Class Current: 307/77
• 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 2300/30 The power source being a fuel cell
• CPC Class Codes: H02J 3/18 Arrangements for adjusting, eliminating or compensating reactive power in networks for adjustment of voltage H02J3/16
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• 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 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: Y02B 70/3225 Demand response systems, e.g. load shedding, peak shaving
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y04S 20/222 Demand response systems, e.g. load shedding, peak shaving

Abstract

A system and method for combining power from DC power sources. Each power source is coupled to a converter. Each converter converts input power to output power by monitoring and maintaining the input power at a maximum power point. Substantially all input power is converted to the output power, and the controlling is performed by allowing output voltage of the converter to vary. The converters are coupled in series. An inverter is connected in parallel with the series connection of the converters and inverts a DC input to the inverter from the converters into an AC output. The inverter maintains the voltage at the inverter input at a desirable voltage by varying the amount of the series current drawn from the converters. The series current and the output power of the converters, determine the output voltage at each converter.

Claims

1. A method comprising:

coupling each of a plurality of power sources to a respective one of a plurality of direct current (DC) power converters;

coupling the plurality of DC power converters in series, to thereby form a serial string;

coupling the serial string to an input of a direct-current to alternating-current (DC/AC) inverter; and

fixing a voltage level at the input of said DC/AC inverter to a predetermined fixed constant value, thereby forcing current flowing through the serial string to vary according to power provided by the power sources so as to maintain the voltage level at the fixed constant value.

2. The method of claim 1, wherein said fixing is performed by said DC/AC inverter.

3. The method of claim 2, further comprising:

controlling power output from each power source individually; and

individually varying at least one of an input voltage and an input current to each respective one of the plurality of DC power converters according to a predetermined criterion.

4. The method of claim 3, wherein said controlling power output includes individually tracking a maximum power point of each power source, and said individually varying is performed by setting at least one of the input voltage and the input current to each respective one of the plurality of DC power converters so as to maximize power drawn from each of the plurality of power sources.

5. The method of claim 1, further comprising:

individually converting an input voltage and an input current to each respective one of the plurality of DC power converters to output power at an output current level dictated by the current flowing through the serial string.

6. The method of claim 1, further comprising limiting power output from each respective one of the plurality of DC power converters to a preset safe level until a release signal has been detected.

7. The method of claim 1, further comprising monitoring for a release signal before transferring, with the plurality of DC power converters, power from the plurality of power sources to the DC/AC inverter.

8. The method of claim 1, further comprising monitoring a load on each one of the plurality of DC power converters individually and limiting power output from each one of the plurality of DC power converters to a preset safe level until the load on each one of the plurality of DC power converters reaches a preset value.

9. The method of claim 1, further comprising, for each power source and its respective coupled DC power converter, monitoring power that is output from at least one of the power sources and the respective coupled DC power converter and directing an output current of the power source to a bypass when the monitored power exhibits predetermined characteristics.

10. The method of claim 1, further comprising individually operating each one of the plurality of DC power converters to monitor and report power related data, the power related data monitored and reported from each DC power converter comprising at least one of:

input current to the DC power converter, input voltage to the DC power converter, temperature of the power source coupled to the DC power converter, input power to the DC power converter, and available illumination.

11. A method comprising:

coupling each one of a plurality of DC power sources to a respective one of a plurality of direct current (DC) power converters;

coupling the plurality of DC power converters in series, thereby forming a serial string;

coupling the serial string to an input of a load, wherein the load includes a plurality of components;

maintaining the input of the load at a fixed predetermined constant voltage, the fixed predetermined constant voltage being a safe operating voltage for the plurality of components within the load; and

varying a current output from the serial string to the input of the load according to the power drawn from the plurality of DC power sources.

12. The method of claim 11, wherein the load includes a direct-current to alternating-current (DC/AC) inverter, and the step of maintaining the input of the load at the fixed predetermined constant voltage includes maintaining the fixed predetermined constant voltage at an input of the DC/AC inverter.

13. The method of claim 12, wherein each one of the plurality of DC power sources includes a solar panel, and wherein each one of the plurality of DC power converters includes a direct-current to direct-current DC/DC converter.

14. The method of claim 13, further comprising operating each DC/DC converter to boost a voltage obtained from said solar panel coupled to the DC/DC converter as soon as the solar panel starts to output electrical energy.

15. A method comprising:

coupling each one of a plurality of solar panels to a respective one of a plurality of direct-current to direct-current (DC/DC) converters;

coupling the plurality of DC/DC converters in series to form a serial string;

coupling the serial string to an input of a direct-current to alternating-current (DC/AC) inverter;

operating the DC/AC inverter to maintain a fixed constant voltage at the input of the DC/AC inverter; and

operating each DC/DC converter to individually maximize power drawn from the respective coupled solar panel and to output the drawn maximized power to the string by varying a voltage or a current from the respective coupled solar panel to the DC/DC converter according to a predetermined criterion.

16. The method according to claim 15, wherein operating each DC/DC converter to individually maximize power drawn from the respective coupled solar panel comprises performing maximum power point tracking individually for each DC/DC converter.

17. The method according to claim 16, wherein operating each DC/DC converter individually to maximize power drawn from its respective coupled solar panel comprises individually selecting a power conversion mode by each DC/DC converter such that voltages output to the serial string from the plurality of DC/DC converters result in the fixed constant voltage at the input of the DC/AC inverter.

18. The method according to claim 15, wherein the operating of the DC/AC inverter to maintain the fixed constant voltage at the input of the DC/AC inverter comprises coupling a shunt regulator across the input of the DC/AC inverter.

19. The method according to claim 15, further comprising coupling one or more additional serial strings to the input of the DC/AC inverter, wherein each of the one or more additional serial strings comprises a different respective plurality of DC/DC converters coupled in series, each DC/DC converter of the different respective plurality of DC/DC converters having a different solar panel coupled thereto, and each DC/DC converter of the different respective plurality of DC/DC converters being operated to individually perform maximum power point tracking.

20. The method according to claim 16, wherein operating each DC/DC converter individually to maximize power drawn from its respective coupled solar panel comprises individually selecting a power conversion mode by each DC/DC converter such that the current from all of the coupled solar panels varies so as to maintain the fixed constant voltage at the input of the DC/AC inverter.