WO2009146065A2

WO2009146065A2 - Energy interface module and power conversion system

Info

Publication number: WO2009146065A2
Application number: PCT/US2009/039109
Authority: WO
Inventors: Francis P. Harrington
Original assignee: Harrington Francis P
Priority date: 2008-04-04
Filing date: 2009-04-01
Publication date: 2009-12-03
Also published as: WO2009146065A3

Abstract

The system converts the power generated by a solar photovoltaic, (PV), module and efficiently transfers that power to desired loads and/or storage devices. By working directly with an individual PV module, or small group of PV modules, it can operate the module's current and voltage at the ideal operating point for maximum power output. The output of multiple interface modules can then be strung together in a series fashion therefore creating an efficient method of power transfer. Output current of each module is controlled by the interface controller. All modules will output varying voltages to facilitate the maximum transfer of power from the PV module to the desired loads.

Description

ENERGY INTERFACE MODULE AND POWER CONVERSION

SYSTEM

FIELD OF THE INVENTION [0001] The inventions described below relate to systems, methods and devices for interfacing energy sources such as photovoltaic cells to power loads such as electrical utility grids.

BACKGROUND OF THE INVENTION [0002] Solar photovoltaic electric systems convert the sun's energy into useful electrical power that can be used by various electrical loads or stored for later use. Solar PV modules are typically made up of multiple solar PV cells. Most solar PV modules convert the sun's energy into DC electrical power. Solar modules are designed to operate most efficiently at a particular point of voltage and current. This is referred to as the Maximum Power Point, MPP. The MPP will vary based on parameters such as the sun's intensity, the temperature, shading, module age, module variations along with other parameters. When multiple modules are strung together in a series or parallel fashion, current systems will attempt to operate at the MPP. Because no two modules are identical, this new MPP is a compromise of the individual MPP. Therefore the group will operate at a MPP that is less than the sum of the individual module MPPs. Unfortunately, the sum of individual output power will always be higher than the output power of a series or parallel connected string. [0003] In addition, the transfer of power from these series / parallel strings will occur over a wide voltage and current range. Due to I²R losses, transferred power will be reduced when current is high and voltage is low compared to a high voltage and low current transfer method. There is therefore a need for improved systems, methods and devices for coupling energy sources such as photovoltaic modules to a load such as a utility grid. SUMMARY OF THE INVENTION

[0004] The systems, devices and methods described below provide interface modules that result in efficient and effective coupling of energy sources such as photovoltaic cells, to a transmission line; and also provide interface controllers which result in efficient and effective coupling of transmission lines to a load such as a utility grid. The systems, devices and method of the present invention maximize the amount of energy that can be harvested by a particular solar array. Each module is operated at its own MPP, with the output current of the interface module maintained at a minimum, thus minimizing I²R losses. The system maintains the total voltage across a series strings at a maximum by lowering the master current. When this occurs, the series string of voltage increases, and reduces the overall transmission losses by reducing the I²R losses. The system of the present invention effectively and efficiently can be used with dissimilar energy modules (e.g. PV modules). Energy modules may have dissimilar power output, orientation, or other dissimilarities.

[0005] According to a first aspect of the invention, an energy interface module for interfacing at least one energy source to a transmission line is disclosed. The energy interface module includes an input source configured to connect to the energy source or sources, and an output configured to connect to the transmission line. The energy interface module produces an output current at an output voltage. A first controller maintains the output current and a second controller maintains the output voltage. The output voltage may be varied to maintain maximum power transfer from the energy source to the transmission line. Energy sources may include energy derived from wind, liquid motion (e.g. hydroelectric), solar, fuel cell, thermal, and combinations of these.

[0006] In a preferred embodiment, energy is derived from the sun and a photovoltaic (PV) module is used. Multiple interface modules are each attached at their input to one or more PVs, and maintain each PV at its MPP. When multiple PVs are attached, the PVs can be in a series or parallel connection scheme. Interface modules connect to a single conductor transmission line. This conductor may be used to transmit information to or from each interface module and/or a separate wire or wires may be used for information transfer. Additionally or alternatively, wireless communication may be used between any two or more components. [0007] The energy interface module may be powered by the energy source, by the transmission line, and/or by an alternative, independent source of energy. The interface modules include at least one DC-DC converter, and a micro-controller. [0008] According to a second aspect of the invention, an energy interface controller for interfacing a transmission line to a power load is disclosed. The energy interface controller includes an input configured to connect to a transmission line, and an output configured to connect to a power load. A first controller is configured to control the current of the transmission line; a second controller is configured to monitor the voltage of the transmission line; a third controller is configured to control the output current; and a fourth controller is configured to control the output voltage. The power load may be a utility grid, a storage device and/or an independent load. A utility grid may have a power requirement and the interface controller may be configured to synchronize to a utility grid requirement. [0009] In a preferred embodiment, the first controller varies the input current to maximize the power transferred from the transmission line to the power load, such as by varying the current based on the measured voltage from the second controller. In another preferred embodiment, the third controller controls the output current to maximize power output of the energy interface controller. In yet another preferred embodiment, the fourth controller regulates the voltage to a predetermined level, such as a level required by a utility grid (e.g. the utility grid level or a synchronized level). [0010] The interface controller is preferably configured to produce user accessible status information, such as information provided by a local user interface such as a visual display device at the interface controller location; an Internet based access device such as a computer remote from the interface controller location; and/or a cellular signal based device. [0011] According to a third aspect of the invention, a hybrid inverter system is disclosed. The hybrid inverter system interfaces one or more energy sources such as PV modules to one or more power loads. The hybrid inverter system includes at least one energy interface module and an energy interface controller. In an alternative embodiment, multiple energy interface controllers may be used. [0012] In a preferred embodiment, a set of multiple energy interface modules are connected such that the same current passes through each, such as when the voltage across each interface module varies to maximize the power transfer across the set of interface modules. Each interface module may have similar or dissimilar configurations, such as dissimilarities in one or more of: size; power output characteristics and voltage output during use. [0013] In another preferred embodiment, the energy interface controller has a current controller, such as a current controller which determines the energy passing through each interface module.

[0014] In another preferred embodiment, the energy interface module monitors energy source parameters and transmits associated information to the energy interface controller. Energy source parameters include but are not limited to: the input voltage and current, the output voltage and current, the input and output power, and the temperature within the interface module. The information may be transmitted over the transmission line, over a separate wire, and/or using wireless communication. The interface controller receives parameter information and processes the information to provide user accessible information and/or to modify one of the interface controller's parameters. Information may be provided via a local user interface, the Internet, or cellular signal.

[0015] In another preferred embodiment, the hybrid inverter system varies the current input to the interface controller is varied to maintain maximum power produced. [0016] In yet another preferred embodiment, one or more energy interface modules include a switch electrically connected across its output. The switch is configured to operably bypass that module, such as when an energy source fails, or the module fails. [0017] According to a fourth aspect of the invention, a method of transferring energy from a power source to a load is disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 illustrates a typical solar PV module IV curve.

[0019] FIG. 2 illustrates a typical method used to connect PV modules with inverters.

[0020] FIG. 3 illustrates a schematic representation of a hybrid inverter system including multiple interface modules and a single interface controller, configured to connect multiple energy modules to a power load such as a utility grid, consistent with the present invention. [0021] FIG. 4 illustrates a schematic representation of an energy interface module configured to connect one or more PV modules with a transmission line, consistent with the present invention.

[0022] FIG. 5 illustrates a schematic representation of an energy interface controller configured to connect a transmission line to a power load such as a utility grid, consistent with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention describes an energy interface module for interfacing at least one energy source, such as a photovoltaic module, to a transmission line. The input of the energy interface module attaches to the energy source(s), and the output is a transmission line comprising output current and output voltage. The energy interface module includes a controller which maintains the output current, and a controller which maintains the output voltage. The present invention also includes an energy interface controller for interfacing a transmission line (e.g. a transmission line produced by the energy interface module(s) of the present invention) to at least one power load, such as a utility grid. The present invention also includes a system including one or more energy interface modules connected to an energy interface controller. The system configured to connect at its input to one or more energy sources, such as one or more voltaic modules, and to connect at its output to one or more power loads, such as a utility grid. [0024] Referring now to Fig. 1, an IV Curve for a typical photovoltaic (PV) module is illustrated. As depicted by the curve, current and voltage should be controlled to maintain the PV module at the MPP. The MPP is the peak of the power vs. voltage curve. [0025] Referring now to Fig. 2, a typical configuration of attaching PV modules with inverters is illustrated. In this diagram, multiple PV modules are connected in series, and those series strings are connected in parallel before being connected to the inverter. The inverter will control the MPP of the entire system. [0026] Referring now to Fig. 4, an energy interface module of the present invention is illustrated. The Interface module 120 has input 127 configured to be connected to a solar PV module, hi alternative embodiments, other sources of electrical energy could be connected, such as a module which converts energy from heat or cold; moving water (e.g. hydroelectric); and/or wind. Interface module 120 is configured to operate a PV module at its Maximum Power Point, MPP, by maintaining the current and voltage at appropriate levels. Interface module 120 includes DC-DC converter 121, microcontroller 122, current controller 123, voltage controller 124, voltage sensor 125 and current sensor 126, electrically connected as shown. Microcontroller 122, with dashed monitoring lines shown, monitors and/or controls current controller 123, voltage controller 124, voltage sensor 125 and current sensor 126. Microcontroller 122 further controls DC - DC converter 121. The input current and input voltages are represented by (Ip v) and (Vp v). Microcontroller 122 controls these parameters to maintain the PV module at the MPP. hi an alternative embodiment, a second DC-DC converter is used, such as when first DC-DC converter 121 is connected to a first PV module and the second DC-DC converter is connected to a second PV module.

[0027] Interface module 120 further includes output 128 configured to attach to a transmission line. Output current and output voltage are represented by (It) and (Vt) respectively. (It) is controlled by an interface controller, as is described in reference to Fig. 5 herebelow. (Vt) is controlled by maintaining output power at a maximum. [0028] Referring now to Fig. 5, an energy interface controller of the present invention is illustrated. Interface controller 140 includes input 147, configured for attachment to a transmission line, and output 148 configured for attachment to a load, such as a power storage device; a utility grid; an independent load; and combinations of these. Interface controller includes DC-AC controller 141, microcontroller 142, current controller 143, voltage controller 144, voltage controller 145 and current controller 146, electrically connected as shown. Microcontroller 142, with dashed monitoring lines shown, monitors and/or controls current controller 143, voltage controller 144, voltage sensor 145 and current controller 146. Interface controller 140 is preferably connected to one or more interface modules as described in reference to Fig. 4. This connection can be made directly to interface controller 140, or through a series connection of multiple interface modules. Connecting multiple interface modules in series decreases the cost of wiring by allowing multiple energy sources to be connected to a module controller via one set of wires, or a reduced set of wires as compared to existing techniques.

[0029] The input current and input voltages are represented by (It) and (Vt).

(Vt) is a sum of all the series connected PV interface modules in the string. It is controlled to maintain the system at the most efficient point. If the current, (It) is reduced, the PV interface modules will increase their output voltages, therefore increasing (Vt). The output current and voltages are represented by (IL) and (VL). (VL) will be controlled to match the utility grid or the desired voltage if it is connected to a storage device or is not grid connected. (IL) will vary to maintain maximum power output. [0030] In one embodiment, interface controller 140 is integrated into one interface module (e.g. interface module 120 of Fig. 5). In an alternative embodiment, interface controller 140 is a separate device (e.g. in a separate housing independent of an interface module). [0031] Referring now to Fig. 3, a hybrid inverter system of the present invention is illustrated. System 100 includes multiple interface modules 120, such as has been described in reference to Fig. 4, and a single interface controller 140, such as has been described in reference to Fig. 5. Interface modules 120 are installed in between the PV modules and the transmission lines. This configuration allows each PV module to operate at its MPP. hi addition, interface controller 140 minimizes string current to further improve system efficiency and power output. Interface controller 140 further includes monitor output 149 which is configured to transmit information recorded and/or calculated by interface controller and/or interface module 120. Monitor output 149 may provide information to a user via a local user interface, e.g. a monitor such as a touch screen monitor, a wired connection such as the Internet, or a wireless connection such as a cellular service or the Internet. [0032] To maintain maximum power transfer efficiency, the voltage output of each interface module 120 will vary its output voltage. The input power to the interface module 120 is a result of the power generated from the PV module. For example, if the voltage from a PV module is 20 vdc, and the current from the PV module is 5 adc, the power input to the interface module would be 20 * 5 = 100 Watts. If the interface controller 140 is controlling transmission line current to 4 amps, the interface module 130 would control the output voltage to maintain maximum transfer efficiency. Therefore, the output of interface module 120 would also be 100 Watts, or some lesser power because of small efficiency losses in interface module 120. For a 99% transfer efficiency, the output power should be 99 watts. Therefore the output voltage would be 99 / 4 amps = 24.75 vdc.

[0033] In one embodiment, the interface controller 140 operates the current of all module interfaces 120 at a specific current, or it may vary the string current to maximize the voltage of the entire string. In an alternative embodiment, interface controller 140 operates the current to maximize the overall efficiency of the system. Maximizing the voltage and minimizing the current will increase the efficiency of the power transfer by reducing I²R losses.

[0034] Interface module 120 may contain an electrical switch across the output of the interface to allow the module to be bypassed if the interface module 120 or PV module (or other energy source) should fail. This configuration will allow most of the PV module array to continue to produce power when one or more interface modules 120 and/or attached energy sources are not functioning. [0035] In a preferred embodiment, each interface module 120 will transmit

PV module current and voltage information on a routine basis. This data can be accessed by querying interface module 120 or by having interface module 120 transmit the data routinely, such as via wired or wireless communication to a separate device such as interface controller 140, a separate device at the PV location and/or a device remote from the PV location. Interface module 120 may be configured to transmit data representing its output parameters. Wired data transmission can also utilize Power Line Communication, PLC, techniques. Reported data may also include power input, power output, and local temperature, along with other parameters which may be used to control and/or monitor system 100.

[0036] A PV module is connected to input 127 of interface module 120 and the transmission line is connected to the output 128. The PV module is operated at its MPP by maintaining the sum of the voltage and current being pulled from the module at a maximum. In a preferred embodiment, interface module 120 has the ability to store the PV module's operating parameters in order to configure its operation. Interface module 120 has the ability to measure the current, voltage and power of the module and transmit that information to interface controller 140. [0037] Solar PV panels typically have a multiple year warranty. Since most systems do not monitor the production from each PV module, failures of individual modules may go undetected and unnoticed. In the system of the current invention, each module can be individually monitored and non-functioning or sub-optimal functional PV modules can be detected. The detection can result in a modification to maximize power output of the system, and/or notify the user of the issue. [0038] System 100 includes an interface module control algorithm.

(Ipv) and (Vpv) are controlled based on maintaining the PV module at the MPP.

The sum of (Ipv) and (Vpv) equals the input power to the PV interface module. (It) is controlled by interface controller 140. Therefore each interface module 120 will control (Vt) to maintain maximum power output from the module.

(Vt) = (Vpv * Ipv) / (It) In a preferred embodiment, (Vt) will be slightly lower than this equation describes because of losses in the DC-DC converter. [0039] System 100 also includes an interface controller algorithm. (It) is controlled by interface controller 140 to maintain system 100 at its peak efficiency. (Vt) is the sum of all interface modules 120 in series. As (It) is reduced, (Vt) will increase to maintain the maximum power output from the PV interface modules. The output AC voltage (VL) is maintained to match the utility grid or the desired AC output. The output AC current (IL) is controlled to maintain the maximum output power of the PV Interface Controller. [0040] In an alternative embodiment, multiple interface modules are connected in series and the output current of the series string is controlled by interface controller 140. In an alternative embodiment, multiple interface modules are connected in series and the output current of the series string is controlled by one of the interface modules in a master configuration, with the other interface modules in a slave configuration. [0041] While a solar powered photovoltaic source has been described in detail, other energy sources can be connected to the devices and systems of the present invention. Energy sources based on wind; hydroelectric; solar; thermal energy; fuel cell; and combinations of these should be considered within the scope of the invention. [0042] While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. Modification or combinations of the above-described assemblies, other embodiments, configurations, and methods for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the scope of the claims.

Claims

CLAIMS I Claim:

1. An energy interface module for interfacing at least one energy source to a transmission line, said interface module comprising: an input configured to connect to the at least one energy source; an output configured to connect to the transmission line; an output current and an output voltage; a first controller configured to maintain the output current; and a second controller configured to maintain the output voltage.

2. The energy interface module of claim 1 wherein the energy source is selected from the group consisting of: wind; hydroelectric; solar; thermal; fuel cell; and combinations thereof.

3. The energy interface module of claim 1 wherein the energy source is a photovoltaic module.

4. The energy interface module of claim 3 further comprising a third controller configured to operate the photovoltaic module at its Maximum Power Point.

5. The energy interface module of claim 1 wherein said module is configured to attach to a single conductor transmission line.

6. The energy interface module of claim 5 further comprising a port for attaching to a data transmission line.

7. The energy interface module of claim 1 wherein the input is configured to attach to multiple energy sources.

8. The energy interface module of claim 7 wherein the multiple energy sources are connected in series or parallel.

9. The energy interface module of claim 1 wherein the second controller varies the output voltage to maintain maximum amount of power transferred to the transmission line.

10. The energy interface module of claim 1 wherein said module is powered by energy received from the energy source.

11. The energy interface module of claim 1 wherein said module is powered by energy received from the transmission line.

12. The energy interface module of claim 1 wherein said module is powered by energy received from an independent source.

13. The energy interface module of claim 1 further comprising a DC-DC converter and a microcontroller.

14. The energy interface module of claim 13 further comprising at least two DC- DC converters.

15. The energy interface module of claim 14 wherein the first DC-DC converter connects to a first energy source and a second DC-DC converter connects to a second energy source.

16. An energy interface controller for interfacing a transmission line to a power load, said controller comprising: an input configured to connect to a transmission line; an output configured to connect to a power load; a first controller configured to control the current of the transmission line; a second controller configured to monitor the voltage of the transmission line; a third controller configured to control the output current of the energy interface controller; and a fourth controller configured to control the output voltage of the energy interface controller.

17. The energy interface controller of claim 16 wherein the power load is selected from the group consisting of: an independent load; a storage device; a utility grid; and combinations thereof.

18. The energy interface controller of claim 16 wherein the power load is a utility grid.

19. The energy interface controller of claim 18 wherein the output voltage is synchronized to the utility grid.

20. The energy interface controller of claim 16 wherein the first controller varies input current to maximize power transferred from the transmission line to the power load.

21. The energy interface controller of claim 20 wherein the current is varied based on the measured voltage received from the second controller.

22. The energy interface controller of claim 16 wherein the third controller controls the output current to maximize power output of said energy interface controller.

23. The energy interface controller of claim 16 wherein the fourth controller regulates voltage to a predetermined level.

24. The energy interface controller of claim 23 wherein the predetermined level is the operating voltage of a utility grid or a voltage level required to synchronize to a utility grid.

25. The energy interface controller of claim 16 wherein said controller is configured to produce user accessible status information.

26. The energy interface controller of claim 25 wherein said information is accessed through one or more of: a local user interface; web based access; and cellular based access.

27. A hybrid inverter system comprising: an energy interface module selected from any of claims 1 through 15; and an energy interface controller selected from any of claims 16 through 26.

28. The system of claim 27 further comprising a second energy interface module.

29. The system of claim 28 further comprising three or more energy interface modules.

30. The system of claim 28 wherein the same current passes through each energy interface module.

31. The system of claim 30 wherein the voltage across each energy interface module varies to maximize the power transfer of said system.

32. The system of claim 28 wherein the first energy interface module and the second energy interface module have different configurations.

33. The system of claim 32 wherein the configuration difference is selected from the group consisting of: physical size; output power; voltage output; and combinations thereof.

34. The system of claim 28 wherein the first energy interface module and the second energy interface modules are directly connected.

35. The system of claim 28 wherein the energy interface controlled includes a current controller.

36. The system of claim 35 wherein said current controller determines the current passing through each energy interface module.

37. The system of claim 27 wherein the energy interface module monitors one or more energy source parameters and transmits said one or more parameters to the energy interface controller.

38. The system of claim 37 wherein said parameters are selected from the group consisting of: the input voltage or current, the output voltage or current, the input or output power, and the temperature within the interface module.

39. The system of claim 37 wherein said parameters are transmitted wirelessly.

40. The system of claim 37 wherein said parameters are transmitted over a wire.

41. The system of claim 37 wherein the parameters are transmitted over the transmission line.

42. The system of claim 27 wherein the energy interface controller receives one or more parameters of an energy interface module.

43. The system of claim 42 wherein the energy interface controller evaluates the one or more parameters and produces user accessible information.

44. The system of claim 43 wherein the information is accessible via one or more of: local user interface; web based access; cellular based access

45. The system of claim 27 wherein the current input to the interface controller is varied to maintain maximum power produced by said system.

46. The system of claim 27 further comprising a switch connected across the output of a first energy interface module, said switch configured to bypass said module.

47. A hybrid inverter system as described in reference to the above figures.

48. An energy interface module as described in reference to the above figures.

49. An energy interface controller as described in reference to the above figures.

50. An energy transfer method as described in reference to the above figures.