System, method, module, and energy exchanger for optimizing output of series-connected photovoltaic and electrochemical devices

• US 9,331,499 B2
• Filed: 08/17/2011
• Issued: 05/03/2016
• Est. Priority Date: 08/18/2010
• Status: Active Grant

• Current Assignee: Volterra Semiconductor Corporation (Analog Devices, Inc.)
• Original Assignee: Volterra Semiconductor LLC (Analog Devices, Inc.)
• Inventors: Ikriannikov, Alexandr, Stratakos, Anthony J.
• Primary Examiner(s): Tso, Edward
• Assistant Examiner(s): Piggush, Aaron
• Application Number:
  US13/211,984
• Publication Number:
  US 20120043923A1
• Time in Patent Office: 1,721 Days
• Field of Search: 320/101, 320/103, 320/140, 320/166
• US Class Current: 1/1
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries

Abstract

An energy transfer device for solar power systems operates to draw power from high-producing photovoltaic devices and apply that power across low-producing photovoltaic devices. An embodiment is a self-regulating energy exchanger using bidirectional DC-DC converters that operates to maintain uniform voltage across each series-connected photovoltaic device. An alternative embodiment is an energy exchanger that is controlled to maintain each of several series-connected photovoltaic devices at a maximum power point by drawing power from high-performing devices and applying that power across low-performing devices to provide uniform current among series-connected photovoltaic devices.

Claims

1. An energy transfer device, comprising:

a first bidirectional DC-DC converter electrically coupled between a first port and a capacitor;

a second bidirectional DC-DC converter electrically coupled between a second port and the capacitor, such that the first bidirectional DC-DC converter, the second bidirectional DC-DC converter, and the capacitor are electrically coupled in parallel with each other;

wherein the bidirectional DC-DC converters are adapted to operate with the first port having a voltage offset from the second port;

wherein the first bidirectional DC-DC converter is adapted to transfer energy between the first port and the capacitor, and the second bidirectional DC-DC converter is adapted to transfer energy between the second port and the capacitor, such that the capacitor acts as a shared energy storage device for each of the first and second bidirectional DC-DC converters; and

wherein the first and second bidirectional DC-DC converters are adapted to transfer energy from the first port to the capacitor and from the capacitor to the second port when energy available at the first port is greater than energy available at the second port, and

wherein a terminal of the capacitor is directly electrically coupled to a common return node.

2. The energy transfer device of claim 1, wherein the first and second bidirectional DC-DC converters are adapted to transfer energy from the second port to the capacitor and from the capacitor to the first port when energy available at the second port is greater than energy available at the first port.

3. The energy transfer device of claim 2, further comprising a third port coupled to a third bidirectional DC-DC converter, the third bidirectional DC-DC converter being coupled to the capacitor;

wherein the third bidirectional DC-DC converter is adapted to operate with the third port having a voltage offset from the first port and from the second port; and

wherein the bidirectional DC-DC converters are adapted to transfer energy from a first selected port having a highest energy provided to the port, the first selected port selected from the group consisting of the first, second, and third ports, the energy being transferred to the capacitor, at least a portion of the energy being transferred from the capacitor to a second selected port having a lowest energy provided to the port.

4. The energy transfer device of claim 1, wherein the energy transfer device further comprises auxiliary circuitry powered by energy drawn from the capacitor.

5. The energy transfer device of claim 1, wherein each of the first and second bidirectional DC-DC converters is a bidirectional charge pump converter.

6. The energy transfer device of claim 1, wherein each of the first and second bidirectional DC-DC converters is a bidirectional Cuk converter.

7. The energy transfer device of claim 1, wherein each of the first and second bidirectional DC-DC converters is a bidirectional SEPIC converter.

8. An energy transfer device, comprising:

a first port coupled to a first interface unit, the first interface unit being coupled to a capacitor;

a second port coupled to a second interface unit, the second interface unit being coupled to the capacitor, such that the first interface unit, the second interface unit, and the capacitor are electrically coupled in parallel with each other; and

a third port coupled to a third interface unit, the third interface unit being coupled to the capacitor;

wherein the interface units are adapted to operate with the first port having a voltage offset from the second port;

wherein the first interface unit is adapted to transfer energy between the first port and the capacitor, and the second interface unit is adapted to transfer energy between the second port and the capacitor;

wherein the first and second interface units are adapted to transfer energy from the first port to the capacitor and from the capacitor to the second port when energy available at the first port is greater than energy available at the second port;

wherein a terminal of the capacitor is directly electrically coupled to a common return node;

wherein the first and second interface units are adapted to transfer energy from the second port to the capacitor and from the capacitor to the first port when energy available at the second port is greater than energy available at the first port;

wherein the third interface unit is adapted to operate with the third port having a voltage offset from the first port and from the second port;

wherein the interface units are adapted to transfer energy from a first selected port having a highest energy provided to the port, the first selected port selected from the group consisting the first, second, and third ports, the energy being transferred to the capacitor, at least a portion of the energy being transferred from the capacitor to a second selected port having a lowest energy provided to the port; and

the third interface unit comprising a bidirectional DC-DC converter including an inductor, the DC-DC converter adapted to operate in a continuous current conduction mode if a magnitude of current transferred by the DC-DC converter is greater than or equal to a threshold value, the DC-DC converter adapted to operate in a discontinuous conduction operating mode if the magnitude of current transferred by the DC-DC converter is less than the threshold value.

9. A system comprising an energy transfer device, the energy transfer device including:

an energy exchange bus;

N ports, N being an integer greater than one; and

N bidirectional DC-DC converters, each of the N bidirectional DC-DC converters electrically coupled between the energy exchange bus and a respective one of the N ports, each of the N bidirectional DC-DC converters being capable of transferring y bidirectionally between its respective one of the N ports and the energy exchange bus;

wherein the N bidirectional DC-DC converters are adapted to operate with each of the N ports having a voltage offset relative to each of at least one other of the N ports; and

wherein the N bidirectional DC-DC converters are adapted to pass energy from a high energy port of the N ports to the energy exchange bus and from the energy exchange bus to a low energy port of the N ports;

wherein the N bidirectional DC-DC converters are either (a) bidirectional Cuk converters, (b) bidirectional SEPIC converters, or (c) bidirectional charge pump converters; and

wherein the N bidirectional DC-DC converters are electrically coupled in parallel with the energy exchange bus.

10. The system of claim 9, wherein N is greater than or equal to three.

11. The system of claim 9, further comprising N energy sources, where each energy source is coupled to a separate port of the N ports of the energy transfer device, and wherein the energy sources are coupled in series.

12. The system of claim 11, wherein switching devices of at least two of the N bidirectional DC-DC converters operate at constant frequency and duty cycle, and wherein energy flow acts to equalize voltages at ports of the energy transfer device.

13. The system of claim 11, wherein the energy sources are battery cells and the energy transfer device operates to equalize voltages across the battery cells while the battery cells are charging.

14. The system of claim 11, wherein the energy transfer device operates to equalize voltages across the energy sources while the energy sources are providing power to an output of the system.

15. The system of claim 14 wherein, the energy sources are battery cells.

16. The system of claim 14 wherein, the energy sources are fuel cells.

17. The system of claim 14, wherein the N energy sources are photovoltaic devices of a solar power system.

18. The system of claim 17, wherein at least one of the energy sources further comprises:

M photovoltaic cells, the M photovoltaic cells being coupled electrically in series; and

a second energy transfer device, including;

a second energy exchange bus;

M ports, M being an integer greater than one, each of the M ports being coupled to an energy port of one of M interface units, where each interface unit is coupled to the second energy exchange bus and is capable of transferring energy bidirectionally between its energy port and the second energy exchange bus;

wherein the M interface units are adapted to pass energy from a high energy port of the M ports to the second energy exchange bus and from the second energy exchange bus to a low energy port of the M ports;

wherein each of the M ports of the second energy transfer device is coupled to a separate photovoltaic cell of the M photovoltaic cells.

19. The system of claim 11, wherein the energy sources are photovoltaic devices, and wherein the energy transfer device further comprises a controller configured and arranged to adjust a voltage gain of each bidirectional DC-DC converter based at least partially on a maximum power point of a respective photovoltaic device coupled to the interface unit.

20. The system of claim 17, further comprising an additional photovoltaic device coupled in parallel with one of the N photovoltaic devices.

21. A solar photovoltaic array, comprising:

a first and a second photovoltaic device each having a positive and a negative terminal, the first photovoltaic device being capable of producing a first electric current at a first voltage when illuminated, and the second photovoltaic device being capable of producing a second electric current at a second voltage when illuminated;

wherein the first and the second photovoltaic devices are coupled electrically together in series with the positive terminal of the first photovoltaic device coupled to the negative terminal of the second photovoltaic device; and

an energy transfer device having a first terminal coupled to the negative terminal of the first photovoltaic device, a second terminal coupled to the positive terminal of the first photovoltaic device and to the negative terminal of the second photovoltaic device, and a third terminal coupled to the positive terminal of the second photovoltaic device, the energy transfer device being capable of receiving energy from its first and second terminals and providing energy to its second and third terminals if a first parameter selected from the group consisting of the first current and the first voltage is greater than a second parameter selected from the group consisting of the second current and the second voltage, and of receiving energy from its second and third terminals and providing energy to its first and second terminals if the second parameter is greater than the first parameter;

wherein the energy transfer device comprises at least a first inductor, and wherein receiving energy from its first and second terminals is performed by alternately closing and opening a first switching device, the first switching device coupling the first inductor across the first and second terminals;

wherein the first photovoltaic device comprises at least a first and second photocell electrically connected in series with the second photovoltaic device, and a second energy transfer device is coupled to transfer energy from terminals of a high producing photocell selected from the group consisting of the first photocell and the second photocell of the first photovoltaic device, and to transfer the energy to terminals of a low producing photocell selected from the group consisting of the first photocell and the second photocell of the first photovoltaic device.

22. The photovoltaic array of claim 21, wherein the energy transfer device comprises a bidirectional Cuk converter.

23. The photovoltaic array of claim 22, wherein the Cuk converter is a transformer isolated Cuk converter.

24. The photovoltaic array of claim 21, wherein the energy transfer device comprises a bidirectional capacitively-isolated Cuk converter.

25. The photovoltaic array of claim 21, further comprising a third photovoltaic device having a negative terminal coupled to the positive terminal of the second photovoltaic device, the third photovoltaic device being capable of producing a third current at a third voltage when illuminated;

wherein the energy transfer device has a fourth terminal coupled to a positive terminal of the third photovoltaic device, and wherein the energy transfer device is capable of receiving energy from its first and second terminal and providing energy to its third and fourth terminals if the first current is greater than the third current.

26. The photovoltaic array of claim 21, wherein the first and second photovoltaic devices are factory-assembled modules comprising multiple photovoltaic cells and adapted for field assembly into a multiple-module photovoltaic array.

27. The photovoltaic array of claim 21, wherein the photovoltaic array is a factory-assembled module adapted for field assembly into a multiple-module photovoltaic array, and wherein the first and second photovoltaic devices are photovoltaic cells within the module.

28. The photovoltaic array of claim 21, wherein the first photovoltaic device is a factory-assembled module incorporating the second energy transfer device and adapted for field assembly into a photovoltaic array.

29. The photovoltaic array of claim 28, further comprising a third photovoltaic device coupled in parallel with the first photovoltaic device.

30. The photovoltaic array of claim 29, further comprising a charge controller and a battery.

31. The photovoltaic array of claim 30, further comprising an energy transfer device coupled to balance charge in the battery by transferring energy from a high voltage cell of the battery to a low voltage cell of the battery.

32. The photovoltaic array of claim 21, further comprising a grid-tie inverter, energy from the photovoltaic devices being coupled to power the grid-tie inverter, the grid-tie inverter capable of synchronously feeding energy into an alternating-current power distribution system.

33. The photovoltaic array of claim 21, wherein the energy transfer device is a transformer-coupled bidirectional converter.

34. The photovoltaic array of claim 21, wherein the photovoltaic array is capable under standard conditions of producing power substantially in excess of a power rating of the energy transfer device.

35. A photovoltaic array, comprising:

a first, a second, and a third photovoltaic device each having a power output port having positive and negative terminals, the first photovoltaic device being capable of producing a first electric current at a first voltage when illuminated, the second photovoltaic device being capable of producing a second electric current at a second voltage when illuminated, and the third photovoltaic device being capable of producing a third electric current at a third voltage when illuminated;

wherein the power output ports of the first, the second, and the third photovoltaic devices are coupled electrically together in series;

an energy transfer device having a first port coupled to the power output port of the first photovoltaic device, a second port coupled to the power output port of the second photovoltaic device, and a third port coupled to the power output port of the third photovoltaic device, the energy transfer device being capable of receiving energy from its first port and providing energy to its second port if a first parameter selected from the group consisting of the first current and the first voltage is greater than a second parameter selected from the group consisting of the second current and the second voltage, and of receiving energy from its second port and providing energy to its first port if the second parameter is greater than the first parameter; and

wherein the energy transfer device is capable of receiving energy from the first port and providing energy to its third port if the first parameter is greater than a third parameter selected from the group consisting of the third current and the third voltage, and of receiving energy from its third port and providing energy to its first port if the third parameter is greater than the first parameter;

wherein the energy transfer device comprises at least a first and a second converter stage, where each converter stage comprises;

a. an inductor having a first terminal coupled to a first terminal of a first port of the converter stage;

b. a switching device for coupling a second terminal of the inductor to a second terminal of the first port of the converter stage;

c. an isolation capacitor having a first terminal coupled to the second terminal of the inductor and a second terminal coupled to transfer power between the first port of the converter stage and a second port of the converter stage;

wherein the first port of the first converter stage is coupled to the first port of the energy transfer device;

the first port of the second converter stage is coupled to the second port of the energy transfer device; and

the second port of the first and second converter stages are coupled together and to a common energy storage device.

36. A system comprising:

a first energy transfer device for transferring energy from a high-producing device to a low-producing device, the first energy transfer device, comprising;

a first port for coupling to a first photovoltaic device;

a second port for coupling to a second photovoltaic device;

a controller for determining a port attached to a low producing device selected from the group consisting of the first port and the second port, and for determining a port attached to a high producing device selected from the group consisting of the first port and the second port;

at least a first inductor, and a first switching device coupled in series with the first inductor, the first inductor being coupled to the first port; and

at least one photovoltaic module coupled to the first port of the first energy transfer device and at least one photovoltaic module coupled to the second port of the first energy transfer device, wherein each photovoltaic module comprises at least a plurality of series-connected photovoltaic cells assembled to a common module substrate;

wherein the energy transfer device is operable with the first and the second ports coupled together in series; and

wherein energy transfer from the first port is performed by a method comprising alternately closing and opening the first switching device at a high frequency, and wherein opening the first switching device disconnects at least one terminal of the inductor from the first port;

wherein at least one photovoltaic module further comprises a second energy transfer device capable of transferring energy from at least one high-producing photovoltaic cell of the module to a lower-producing photovoltaic cell of the module.

37. The system of claim 36, wherein the first energy transfer device is incorporated into a module for assembly into a photovoltaic array, the module further comprising the at least one photovoltaic module coupled to the first port and the at least one photovoltaic module coupled to the second port.

38. The system of claim 36, wherein at least one port of the first energy transfer device is coupled to at least two photovoltaic modules coupled together in parallel.

39. The system of claim 36, wherein the first inductor is part of a CUK converter.

40. A subsystem, comprising:

at least a first photovoltaic device selected from the group consisting of a multiple-junction stacked photovoltaic device having a plurality of photovoltaic junctions coupled electrically in series, and a split-spectrum photovoltaic device having a plurality of photovoltaic junctions coupled electrically in series;

at least a first DC-DC converter coupled to transfer energy between an output of the first photovoltaic device and at least one specific junction of the at least a first photovoltaic device; and

a controller configured to determine switching of at least one switching device of the first DC-DC converter to optimize power output from the first photovoltaic device;

wherein the subsystem provides power through a second DC-DC converter, and further comprising at least a second photovoltaic device selected from the group consisting of a multiple-junction stacked photovoltaic device having a plurality of photovoltaic junctions coupled electrically in series, and a split-spectrum photovoltaic device having a plurality of photovoltaic junctions coupled electrically in series;

at least a third DC-DC converter coupled to transfer energy between an output of the second photovoltaic device and at least one specific junctions of the at least the second photovoltaic device;

a fourth DC-DC converter coupled to receive power from the second photovoltaic device; and

wherein outputs of the second and fourth DC-DC converters are electrically coupled in series.