Solar Panel Architecture

Abstract

An apparatus for use in a solar power station (5) including a plurality of photovoltaic panels (10), the apparatus including a plurality of power conditioning units (15) configured to collect DC power at a panel voltage from the plurality of photovoltaic panels (10) and pass the DC power to an intermediate transmission line (20), such as a cable wiring, and a common inverter unit (30) configured to receive DC power from the plurality of power conditioning units (15) via the intermediate transmission line (20) and convert the DC power to AC power for output. A corresponding method of operation is described. The apparatus may be used to provide stable AC power during periods of low DC power collection.

Description

[Technical field]

[0001] The present invention relates to photovoltaic power plants and other solar photovoltaic panel collections. Such solar power plants typically include a large number of solar photovoltaic panels distributed over a large area. [Background technology]

[0002] Utility-scale solar power plants typically contain thousands or hundreds of thousands of individual solar photovoltaic panels distributed over a large area of ​​land, and commercial and industrial-scale solar power plants likewise typically contain at least hundreds of individual solar photovoltaic panels.

[0003] Currently, the area of ​​suitable photovoltaic panels used in such installations is typically around 1.0 to 3.0 m. 2 , each of which contains about 100 independent photovoltaic solar cells capable of generating about 50 volts of electricity in series. A typical maximum output of such a photovoltaic panel under strong sunlight may be around 500 W. Solar-to-electrical conversion efficiencies of around 20% are now routinely achieved, even with single-junction silicon technology.

[0004] Under certain incident light conditions, each solar cell operates according to a current-voltage relationship that exhibits a peak in power output at approximately 70-80% of the open circuit voltage. However, the exact peak power point varies with parameters such as the intensity, spectrum, and polarization characteristics of the incident sunlight, as well as operational factors such as ambient temperature. Therefore, dynamic maximum power point (MPP) control is typically used to collect maximum power from an installed solar panel by controlling the collected current.

[0005] Additionally, solar panels generate DC power, but AC power is typically required for grid injection and for most local industrial and commercial purposes, so DC-AC power conversion circuits are used to convert the DC power collected from solar panels into AC power.

[0006] To collect power from photovoltaic panels in a solar power plant, a small group of panels can be electrically connected in series to a single string inverter unit, which typically implements both maximum power point control and inverter functionality for the panels. Each string inverter unit outputs an optimized level of AC power at a selected voltage, often as three-phase power, suitable for injection into the local grid or for local industrial or commercial use. A typical string inverter unit is designed to connect to around 5-10 photovoltaic panels and outputs several kW at 220-240V (RMS).

[0007] However, while providing a single string inverter for multiple series-connected photovoltaic panels is efficient in that it is relatively easy to manufacture, install, and maintain, the electrical series connection between the panels means that the maximum power point tracking cannot take into account differences in the operating characteristics between the series-connected panels. These characteristics may change over time due to degradation or dirt build-up, electrical faults, or short- or long-term irradiance differences between the multiple panels. As such, the entire string of connected panels tends to be constrained to the output of the worst-performing panel. If the string inverter fails, the entire string of panels is also inoperable until that unit is repaired or replaced.

[0008] As such, solar power plants may use individual microinverter units installed and connected to each solar photovoltaic panel, with the microinverter providing both maximum power point control and inversion of DC to AC power for the associated panel. Such microinverters may be more expensive to manufacture and install than a comparable required string inverter, but by optimizing the power of each panel individually, they can provide superior overall power output, and degradation or failure of one panel or one microinverter unit has less impact on the overall output than if a similar degradation or failure were to occur if a string inverter were used.

[0009] Achieving an optimal balance between the overall efficiency of light conversion to useful power, the cost of the power processing infrastructure, including string or microinverters and associated cabling, and the costs of maintenance and repair, especially on a practical scale, is a complex problem. The present invention seeks to address these and other shortcomings of the relevant prior art. Summary of the Invention

[0010] Embodiments of the present invention seek to combine the advantages of string inverter and microinverter architectures into a single system suitable for use in a solar power plant or similar system that includes photovoltaic panels and minimizes power losses in the cables that transmit power from the photovoltaic panels.

[0011] The present invention thus provides an apparatus for use in a solar power plant or other system including a plurality of photovoltaic panels, the apparatus including a plurality of power conditioning units, each configured to collect DC power at a panel voltage from each of one or more photovoltaic panels associated with the power conditioning unit and pass the DC power to an intermediate transmission line, such as a cabling line, and a common inverter unit configured to receive the DC power from the plurality of power conditioning units via the intermediate transmission line and convert the DC power to AC power for output, e.g. for export, where the AC power can be exported to a power grid, a local power grid, or other AC power grid or distribution system.

[0012] The present invention also provides a solar power plant or other system including the above-described apparatus and one or more solar photovoltaic panels associated with each power conditioning unit, and typically also including an intermediate transmission line.

[0013] All the power conditioning units may be electrically connected in parallel to a common inverter unit via an intermediate transmission line. As will be appreciated, the intermediate transmission line may be configured by intermediate cabling or other suitable connection arrangements for power transfer, such as an intermediate busbar arrangement. As will be appreciated, different transmission line types may be used and combined in an installation.

[0014] Typically, each photovoltaic panel has an active photovoltaic surface area of ​​at least one square meter and / or is rated to produce at least 100 W of power.

[0015] Each power conditioning unit may include a converter, such as a boost converter, flyback converter, push-pull converter, forward converter, or other device arranged to increase the voltage of the collected DC power to a higher level for transmission across the intermediate transmission lines. This higher voltage may be, for example, equal to or greater than the peak voltage of the output AC power and may also be equal to or greater than the panel voltage of any or all of the associated photovoltaic panels. The higher voltage DC power may be the same or substantially the same voltage for all of the intermediate transmission lines and all of the power conditioning units, particularly with attention to parallel electrical connections that may be used between the power conditioning units to a common inverter.

[0016] The high voltage DC power may be at variable voltage levels depending on operating conditions, but typically has a voltage of at least 350 V, or at least 400 V, at least when the common inverter unit is outputting or exporting AC power. In this manner, the inverter functions of multiple panels may be consolidated into a single common inverter unit, while significantly reducing power losses in cabling and / or connector links, etc.

[0017] Further, for example, if a system is arranged such that the voltage of the high-voltage DC power depends on one or both of the simultaneous demand for AC power for output or export and the simultaneous collection of DC power from multiple photovoltaic panels, the voltage level of the high-voltage DC power can be used to signal operating conditions to various parts of the device or system in order to implement appropriate control measures.

[0018] The apparatus may further include an energy storage unit coupled to each power conditioning unit, the power conditioning units arranged to selectively store at least a portion of the collected DC power and selectively release at least a portion of the stored energy from the DC power to the common inverter unit via the intermediate transmission line. Advantageously, the storage of DC power by the energy storage units may be substantially at or within the range of use of the high voltage DC power.

[0019] Advantageously, the selective storage of at least a portion of the collected DC power is controlled in the power conditioning unit at least in part dependent on the voltage of the high voltage DC power.

[0020] Each power conditioning unit may be arranged to regulate the collected DC power using maximum power point tracking to control the panel voltage and / or output current of each of the associated one or more photovoltaic panels.

[0021] The average length of the intermediate transmission lines in the form of cabling between each power conditioning unit and the common inverter unit is at least 5 meters, or at least 10 meters, or at least 20 meters. The average length of the intermediate transmission busbar system may vary depending on the dimensions of the links. The number of power conditioning units passing high voltage DC power to the common inverter unit via the intermediate cabling may be at least 10, and the common inverter unit may be so configured. Each power conditioning unit may be associated with a limited number of photovoltaic panels, for example no more than four photovoltaic panels, or with one photovoltaic panel, and each power conditioning unit may be so configured.

[0022] Each power conditioning unit may be either built into, attached to, located within 3 m of, located within 5 m of, or located on one of the associated photovoltaic panels if there is more than one photovoltaic panel.

[0023] The common inverter unit may include a plurality of separate inverter circuits, each arranged to receive at least a portion of DC power from the intermediate transmission line and convert a portion of the received DC power to AC power for output or export, and the common inverter unit arranged to selectively activate or deactivate one or more of the inverter circuits.

[0024] This allows the common inverter unit to operate at an improved level of power conversion efficiency over a range of levels of output or exported AC power. For example, at least two of the inverter circuits can have different efficiency characteristics from one another with respect to the amount of power converted, and the common inverter unit can be arranged to selectively activate and deactivate different ones of the inverter circuits according to the different efficiency characteristics of the inverter circuits and demand characteristics, such as a detected current demand for AC power output or export by a connected power grid.

[0025] The inverter circuit is often the most failure-prone part of the system. To address this, the common inverter unit may be arranged to detect a faulty or failed inverter circuit and automatically avoid selecting the faulty or failed inverter circuit for converting DC power to AC power for output or export. The common inverter circuit may also generate an alarm or warning signal, which may be communicated, for example, via a data network, to an operator indicating the identity of the faulty or failed inverter circuit.

[0026] To improve reliability of the common inverter unit as a whole or each common inverter unit, the common inverter unit may also be arranged to maintain a reliability measure of one or more of its inverter circuits and selectively limit or reduce the power load of those inverter circuits according to the reliability measure. The reliability measure may be based on a variety of factors, such as manufacturer testing, age, total power conversion to date, contemporaneously measured temperature, etc.

[0027] The common inverter unit may be specifically arranged so that any of the inverter circuits may be removed and replaced without disconnecting the other inverter circuits, e.g., in a hot-swappable arrangement, any of the inverter circuits may be replaced without interrupting operation of the other inverter circuits.

[0028] The invention also provides methods of constructing and operating the above-described apparatus, individual components of the apparatus, or photovoltaic power plants or other systems including the above-described apparatus, such methods including, for example, receiving collected DC power from one or more photovoltaic panels at each of a plurality of power conditioning units arranged to collect DC power at a panel voltage and pass the DC power to an intermediate transmission line, transmitting the DC power from each power conditioning unit via the intermediate transmission line to a common inverter unit, and converting the DC power to AC power having a peak voltage at the common inverter unit for output or export to a power grid.

[0029] The method may further include increasing, at each power conditioning unit, a voltage of the collected DC power to a higher DC voltage above the panel voltage and below a peak voltage for transmission via the intermediate transmission line. For example, the panel voltage is 100V or less and the higher DC voltage is at least 350V, or at least 400V, at least during the time that the common inverter unit is outputting AC power to the power grid. The level of the higher DC voltage may depend at least in part on one or both of a concurrent demand for AC power to output to the power grid and concurrently collected DC power from the one or more solar photovoltaic panels.

[0030] The method may further include selectively storing at least a portion of the collected DC power or selectively discharging at least a portion of the stored collected DC power to the common inverter unit, the storage and discharging being controlled depending on the level of the higher DC voltage.

[0031] In some variations of the described apparatus and methods, the power conditioning unit may receive AC power instead of DC power from the photovoltaic panels. In other variations, the photovoltaic panels may be replaced with different power generating devices, such as wind or hydro turbines, which may provide either DC or AC power that is collected by the power conditioning unit. [Brief description of the drawings]

[0032] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0033] [Figure 1] FIG. 1 illustrates a solar power plant or similar system, showing how multiple photovoltaic panels of the solar power plant, each with one or more associated power conditioning units, are connected to a common inverter unit to provide AC power for output or export. [Diagram 2] 2 illustrates a more detailed aspect of the power conditioning unit and the common inverter unit of FIG. 1; [Diagram 3] 1 and 2 or a similar system operates with respect to the voltage levels of the high voltage DC power carried by the intermediate cabling between the power conditioning units and the common inverter unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Referring to Figure 1, there is shown a solar power station 5 including a number of solar photovoltaic panels 10. These are typically mounted on a frame, optionally movable in some way to track the sun, and are typically installed distributed over a large area of ​​land, but may also be attached to buildings or other structures, bodies of water, etc. A typical solar power station 5 may include hundreds or hundreds of thousands of such solar photovoltaic panels 10. Each solar photovoltaic panel 10 has a width of 1.0 to 3.0 m. 2 The solar power plant has an effective area of ​​about 100 W and is capable of generating at least 100 W or about 500 W under strong sunlight. Each solar power panel is arranged to generate power at a voltage of at least 10 V, more typically 50 V, and the entire solar power plant can generate power from about 50 kW to about 100 MW or more. However, the present invention is also applicable to small-scale solar power plants having, for example, at least 10 solar power panels each rated to generate at least 100 W under strong sunlight.

[0035] The solar power plant also includes a number of power conditioning units 15. Each power conditioning unit 15 is associated with one or more of the solar photovoltaic panels 10. In FIG. 1, each power conditioning unit 15 is associated with only one of the solar photovoltaic panels 10, but it may be associated with up to four of the panels, or potentially more. In FIG. 1, each power conditioning unit 15 is attached to its associated solar photovoltaic panel, but it may instead be incorporated within or disposed proximate to the associated panel.

[0036] Each power conditioning unit 15 is arranged to collect DC power from the associated photovoltaic panel or panels 10 and transfer the DC power to a common inverter unit 30 via an intermediate power cabling 20. The common inverter unit 30 is arranged to convert the DC power to AC power for output or export, e.g. to a main grid or to a more local power supply system in a commercial, industrial or other context. Typically, a common inverter unit 30 may output AC power at 220-240V AC (RMS), or higher voltages as required, and may output, e.g., single-phase or three-phase power. A photovoltaic power station 5 may include many such groups of common inverter units 30 and power conditioning units 15 feeding the common inverter units, e.g., from tens to tens of thousands.

[0037] One common inverter unit 30 can receive DC power from at least several power conditioning units 15, for example five or ten or more such units, and thus from the same or a larger number of photovoltaic panels 10. A typical size of the photovoltaic panels 10 used in a photovoltaic power plant is at least 1.0 m 2Considering the fact that the number of power conditioning units 15 is about 100, and the need to arrange them to avoid mutual solar shadowing, the average length of the intermediate cabling 20 from each power conditioning unit 15 to the common inverter unit 30 may be substantial, e.g., at least 5 meters, at least 10 meters, or at least 20 meters. The intermediate cabling 20 from each power conditioning unit 15 to the common inverter unit 30 may be separate from those from the other power conditioning units, or portions of such cabling may be shared by suitable electrical connections or splices within the intermediate cabling 20. In particular, the intermediate cabling 20 may be arranged such that all power conditioning units are electrically connected in parallel to the common inverter unit 30. Here, the cabling 20 constitutes a form of intermediate power transmission line. In some embodiments, the power transmission line may be provided by or include other means, such as a busbar arrangement or other suitable connections.

[0038] To reduce power losses in the intermediate cabling 20, each power conditioning unit 15 is therefore arranged to step up the voltage of the DC power to a higher, i.e. high voltage DC, for transmission over the intermediate cabling to the common inverter unit. Typically, this high voltage may vary depending on the DC power that can be collected from the photovoltaic panels at any particular time and the simultaneous demand for AC power output by the common inverter units. However, during operation of the power plant, at least when the common inverter units 30 are outputting AC power, this high voltage exceeds the peak voltage of the AC power output by the common inverter units (e.g., about 310-340V for an effective voltage of 220-240V AC) and exceeds the voltage of the DC power collected by the power conditioning units from the photovoltaic panels (sometimes referred to as the panel voltage).

[0039] The voltage of the high voltage DC supplied by all the power conditioning units may be the same, as when all the power conditioning units are commonly connected to the same part of the intermediate cabling, or more specifically when they are electrically connected in parallel to the common inverter unit 30. Such an arrangement also has the advantage of simplifying the intermediate cabling 20 and the common inverter unit 30. Although the panel voltages of each of the separate photovoltaic panels may differ slightly, for example depending on the performance and control of each panel, the high voltage DC may be equal to or greater than the average or highest value of these panel voltages. Typically, the panel voltage may be about 50V. The voltage of the high voltage DC may typically be at least 350V, or at least 400V, and may be set, for example, to about 450V or 900V, or in an operating range of, for example, 420-460V.

[0040] Figure 2 illustrates in more detail and diagrammatically how an embodiment of the photovoltaic power plant 5 of Figure 1 may be implemented. Each power conditioning unit 15 is connected to one or more associated photovoltaic panels 10 (connected to only one in the specific implementation of Figure 2) for collecting DC power from the panels, and is connected to intermediate cabling 20 for transmitting DC power to a common inverter unit 30, such that all power conditioning units are electrically connected in parallel to the common inverter unit 30.

[0041] To extract an improved or maximum amount of DC power from the associated photovoltaic panel 10, each power conditioning unit 15 includes a maximum power point tracker 40. The maximum power point tracker 40 may be implemented in electrical circuits alone or in combination with computer software. Some examples of how such maximum power point tracking may be implemented are given in KH Hussein, I. Muta, T. Hshino, M. Osakada: “Maximum photovoltaic power tracking: an algorithm for rapidly changing atmospheric conditions”, IEE Proceedings - Generation, Transmission and Distribution, Vol.142, Issue 1, January 1995, pp.59-64.

[0042] The sensing and control of the current and / or voltage from the photovoltaic panel 10 by the maximum power point tracker 40 to keep the collected DC power at or very close to the panel's maximum power point can operate on time scales of just a few milliseconds, with perturbations in the panel voltage occurring at fast rates of about 2-5 kHz at high levels of collected DC power, e.g., about 150 W or more, and typically at slower rates up to about 100 Hz at low extracted powers, e.g., 20 W.

[0043] Each power conditioning unit 15 also includes a DC / DC converter 50 to boost the voltage of the collected DC power to a higher voltage DC power that is passed to the intermediate cabling 20. The converter 50 can use an isolated or non-isolated design and can be implemented in various ways, for example using a boost converter, a flyback converter, a push-pull converter, or a forward converter design, see the relevant chapters in Markus Zehendner and Matthias Ulmann, Texas Instruments Incorporated, "Power Topologies Handbook", 2016, at https: / / www.ti.com / seclit / ug / slyu036 / slyu036.pdf. The converter 50 boosts the voltage of the collected DC power from the panel voltage of the collected power output by the maximum power point tracker 40, typically about 50V, to a voltage higher than the panel voltage and higher than the peak voltage output by the common inverter unit 30. This high voltage may be, for example, at least 350 V, or at least 400 V, such as on the order of 450 V or 900 V. Typically, as discussed above, this high voltage level will vary in response to the available DC power from the panels, the demand for AC power output, and the available or available power storage.

[0044] Each power conditioning unit 15 may also include an energy storage switch 60 arranged to selectively direct at least a portion of the collected DC power to a corresponding or associated energy storage unit 70, and to selectively release, at the appropriate time, at least a portion of the stored DC power from the corresponding energy storage unit 70 via the intermediate cabling to the common inverter unit 30. The energy storage switch 60 is preferably connected to the high voltage DC power output by the converter 50 such that the DC power is stored in the energy storage unit 70 at substantially the voltage of the high voltage DC power.

[0045] Whether the energy storage switch 60 operates to store or release collected DC power at any particular time can be controlled in a variety of ways. However, in some embodiments, the energy storage switch 60 operates to store DC power in the energy storage unit 70 when the high-voltage DC power is at a higher voltage level, and to release DC power to the common inverter unit 30 when the high-voltage DC power is at a lower voltage level, e.g., when the high-voltage DC power is above or below a particular voltage threshold, above a first threshold or below a second threshold, or according to some other function. The high-voltage DC power can then be used to indicate to the storage switch the current balance between the demand for AC power for output by the common inverter unit and the availability of DC power for collection from the photovoltaic panels.

[0046] In this manner, the power conditioning unit 15 may operate in conjunction with the energy storage unit 70 to reduce the effects of significant and / or sudden changes in power output by the associated photovoltaic panels, such as when a passing cloud obscures the sun. A drop in panel output may be immediately compensated for by drawing power from the energy storage unit 70, which may allow the power conditioning unit to continue to supply the previous level of power to the common inverter unit for a period of time, or may supply gradually decreasing levels of power to help smooth out fluctuations in the level of power supplied.

[0047] The energy storage unit 70 may be implemented in a variety of ways, such as, for example, using a bank of one or more electrical capacitors or using a bank of one or more chemical battery cells, such as lithium-ion cells. The energy storage unit 70 may be located within or coupled to the power conditioning unit 15, within or coupled to the associated photovoltaic panel 10, or located near the power conditioning unit and / or panel. One or more such energy storage units may be coupled to each power conditioning unit, or one or more such energy storage units may be shared between two or more power conditioning units.

[0048] The common inverter unit 30 receives high voltage DC power via intermediate cabling and converts it to AC power for output to the grid or local power grid. To this end, the common inverter unit may be comprised of a number of separate inverter circuits 80-1, 80-2, 80-3. Six such inverter circuits are shown in FIG. 2, although there may be fewer or more.

[0049] At least two of the inverter circuits may have different efficiency characteristics with respect to each other and to the amount of power converted. Typically, each inverter circuit has an efficiency curve with a peak efficiency at a power level somewhat lower than the maximum power level of that circuit. To this end, a first group of one or more inverter circuits 80-1 is designed to be most efficient at some lower level of power conversion, for example up to about 20 W for each circuit, a second group of one or more inverter circuits 80-2 is designed to be most efficient at an intermediate level of power conversion, for example from about 20 W to about 80 W for each circuit, and a third group of one or more inverter circuits 80-3 is designed to be most efficient at a higher level of power conversion, for example from about 80 W to 300 W for each circuit.

[0050] And, the inverter control unit 85 provided in the common inverter unit 30 is arranged to selectively activate and deactivate and / or control the duty cycle or other activation level of each of the inverter circuits 80-1 to 80-3 to improve or optimize the overall efficiency of the common inverter unit 30 in converting and outputting the high voltage DC power to AC power. As will be appreciated, in this manner, any suitable number of appropriately sized inverter circuits may be selected or deselected to achieve the desired power conversion and output. The ability to deselect inverter circuits may increase the system's tolerance to failed or unavailable inverter circuits.

[0051] The common inverter unit 30 may include a grid detector 90 arranged to detect conditions of the power grid or other power grid into which the AC power is delivered by the common inverter unit 30. The common inverter unit 30 may also or instead receive requests or instructions to control the amount of AC power delivered by the common inverter unit 30 from an operator 105 of the power grid or other power grid, for example via the data network 110, and the common inverter unit 30 may then be configured to implement such requests or instructions. For example, the operator 105 may request that the amount of AC power output be fixed at a certain value, reduced, kept below a certain level, increased, or kept above a certain level.

[0052] If the grid detector 90 detects that the power grid is oversupplied or receives a request from the operator 105 to reduce supply, the inverter control unit 85 can select the most appropriate reduced subset of inverter circuits to supply less output AC power. If the grid detector 90 detects that the power grid is undersupplied or receives a request from the operator 105 to increase supply, the inverter control unit 85 can select the most appropriate increased subset of inverter circuits to supply more output AC power.

[0053] Using these and / or other techniques, the inverter control unit 85 may increase or decrease the amount of AC power provided by the common inverter unit to the AC power output in response to the output of the grid detector, and / or in response to an operator request, and / or in response to available DC power for collection from the photovoltaic panels. Although the inverter control unit 85 in FIG. 2 is depicted as a single element separate from each inverter circuit, the same functionality may instead be provided in all or part of the inverter circuits themselves.

[0054] The state of the power grid can be detected by the grid detector 90, such as by comparing the phase of the AC power on the power grid to an internally created sinusoidal reference signal. Typically, an earlier phase of the power grid can indicate an oversupply, and a later phase of the power grid can indicate an undersupply. The power conditioning unit and the common inverter unit can be arranged such that if the demand for AC power output at the same time exceeds that collected from the photovoltaic panels, the voltage of the high voltage DC is reduced, and if the power collected from the photovoltaic panels at the same time exceeds the demand for AC power, the voltage of the high voltage DC is increased. Thus, the voltage of the high voltage DC can be used as an indicator of any or all of the various power control and storage functions of the power conditioning unit and the common inverter unit.

[0055] For example, in addition to providing an energy storage unit in each power conditioning unit, a further energy storage unit 95 can be provided at, in or adjacent to the common inverter unit 30, and the amount of high voltage DC power shunted to or recovered from the further energy storage unit 95 is controlled by a further energy storage switch 100 in the common inverter unit 30.

[0056] Similar to or instead of selectively activating, stopping, or otherwise controlling each inverter circuit to maximize efficiency of power conversion and / or match concurrent demand for output AC power, inverter control unit 85 may activate, stop, or otherwise control inverter circuits 80-1-80-3 for other purposes or depending on other design features or current performance characteristics of the inverter circuits. For example, inverter control unit 85 may be arranged to detect that one of the inverter circuits is defective and then avoid selection of the defective inverter circuit for converting DC power to output AC power, or to detect a reduced level of efficiency or a level of degradation of one or more inverter circuits and accordingly reduce use of those defective or degraded inverter circuits.

[0057] Similarly, the inverter control unit 85 may maintain a measure of reliability of some or all of the inverter circuits 80-1-80-3 and control the level of power loading or power conversion by each inverter circuit accordingly, for example reducing or limiting the power loading of inverter circuits with lower reliability measures. In this manner, inverter circuits with lower reliability measures may be operated at lower power conversion levels to extend the life of the inverter circuits and improve the reliability of the overall common inverter unit. Such reliability measures may be based on or utilize, for example, the known reliability of the inverter circuits at the time of installation (e.g., based on standard manufacturer testing, known manufacturing quality, etc.), aging (e.g., total hours of operation since installation), total amount of power conversion to date, and / or similar measures.

[0058] The use of multiple separate inverter circuits 80-1 to 80-3 in the common inverter unit 30 also allows for more convenient and cost-effective maintenance since just one faulty inverter circuit can be removed and repaired or replaced without interfering with the remaining inverter circuits. To this end, the common inverter unit 30 may be designed to allow easy or "plug and play" removal of a single inverter circuit, for example by each inverter circuit being provided on a separate circuit board in a separate unplug unit, and this functionality may be provided in a hot-swappable form so that any one of the inverter circuits can be removed and / or replaced without powering down the common inverter unit 30.

[0059] To this end, the inverter control unit 85 and / or other aspects of the common inverter unit 30 can provide data signals over the data network 110 to a remote monitor unit 120, which may be provided by a conventional control panel, personal computer, or other device, to indicate operational aspects of the common inverter unit, e.g., a failure or poor performance of one of the inverter circuits, so that maintenance staff can carry out repairs or replacements.

[0060] 3 illustrates how the power conditioning unit 15 and the common inverter unit 30 operate to manage the collection and conversion of DC power to output AC power in response to changes in the voltage levels of the power available from the photovoltaic panels and the high voltage DC power coupled between these units using intermediate cabling. The vertical axis of the diagram illustrates typical voltage levels of the high voltage DC that may be used to implement the described functions, although of course other specific voltage levels may be used.

[0061] At the bottom of the figure, the peak voltage of AC power for output to the power grid by the common inverter unit is shown as 340V. As the light level of the photovoltaic panels 10 increases and each panel generates a significant level of power, for example at least about 10W, the voltage level of the high voltage DC output by the converter 50 of any of the power conditioning units 15 will reach a base level at which the output of AC power by the common inverter unit 30 will begin. This base level voltage may be, for example, around 420V, and such base level may be detected by the inverter control unit 85 of the common inverter unit 30, which selects the appropriate inverter circuit or circuits 80 for converting such low level collected DC power for AC output.

[0062] If the light level of the panels increases further, each converter 50 operates to increase the voltage level of the high voltage DC power, which is detected by the inverter control unit 85, which may switch in a more efficient inverter circuit at the higher power level and, if appropriate, switch in a more efficient inverter circuit at the lower power level. If the DC power collected from the panels reaches a sufficiently high level such that the voltage level of the high voltage DC power reaches an upper limit level (illustrated as 460V in FIG. 3), each power conditioning unit may operate to fade out, apply an upper limit, or reduce the increase in DC power passed to the common inverter unit, for example, by appropriate control of the maximum power point tracker 40 and / or converters 50, or to stop providing such DC power entirely. Typically, these effects may be achieved by appropriate control of each converter, or by stopping the converter entirely. In general, such converter control may be accomplished using active control means, such as a control circuit measuring the voltage level of the high voltage DC power and providing appropriate control signals to or within converter 50, or using more passive means in which converter 50 is configured to passively or automatically respond to the high voltage DC power as described above.

[0063] Above a base level, shown as 420V in FIG. 3 , where a level of high voltage DC acts to signal the start of AC power output to the common inverter unit 30, a storage level, shown as 440V in FIG. 3 , provides a voltage threshold at which the energy storage switch 60 of the power conditioning unit 15 begins to redirect at least a portion of the DC power to the locally connected energy storage unit 70 and / or the further energy storage switch 100 of the common inverter unit begins to redirect at least a portion of the DC power to the locally connected further energy storage unit 95.

[0064] In some embodiments, the export of AC power by the common inverter unit is stopped when the voltage rises above the storage level, or is gradually reduced above this level as the voltage approaches an upper limit level.

[0065] Although specific embodiments of the present invention have been described with reference to the drawings, those skilled in the art will recognize that variations and modifications can be applied to these embodiments without departing from the scope of the invention as defined in the claims. For example, the present invention has been described with photovoltaic panels in a solar power plant, but it may also be used in other contexts with photovoltaic panels, or other renewable energy sources such as wind turbines, wave or tidal power devices. Aspects of the present invention relate specifically to the described power conditioning units themselves, the common inverter unit itself, and combinations of these aspects, as well as these aspects when implemented in a power system such as a solar power plant.

Claims

1. 1. An apparatus for use in a photovoltaic power station including a plurality of photovoltaic panels, comprising: a plurality of power conditioning units, each configured to collect DC power at a panel voltage from a respective one or more photovoltaic panels associated with the power conditioning unit and pass the DC power to an intermediate transmission line, such as a cabling line; and a common inverter unit configured to receive DC power from the multiple power conditioning units via an intermediate transmission line, convert the DC power into AC power, and output the AC power.

2. 2. The apparatus of claim 1, wherein each power conditioning unit is configured to increase a voltage of collected DC power above a peak voltage of the AC power and above a panel voltage of any associated photovoltaic panel for transmission as high-voltage DC power via an intermediate transmission line to a common inverter unit, and optionally arranged such that when the common inverter unit is outputting the AC power, the high-voltage DC power has a voltage of at least 350V, or at least 400V.

3. 3. The apparatus of claim 2, further comprising an energy storage unit coupled to each power conditioning unit, the power conditioning unit being arranged to selectively store at least a portion of the collected DC power and selectively release at least a portion of the stored DC current to the common inverter unit via the intermediate transmission line, wherein the storage of the DC current by the energy storage unit is substantially at a voltage of the high voltage DC power.

4. 4. Apparatus according to claim 3, characterized in that the selective storage of at least a portion of the collected DC power is arranged to be controlled in dependence on the voltage of the high voltage DC power.

5. 5. The apparatus of claim 2, wherein the voltage of the high voltage DC power is arranged to depend on either or both of a simultaneous demand for AC power for output by a common inverter unit and simultaneously collected DC power from photovoltaic panels associated with the multiple power conditioning units.

6. 6. The apparatus of claim 1, wherein each power conditioning unit is arranged to regulate the collected DC power using maximum power point tracking to control the panel voltage and / or output current of each of the one or more photovoltaic panels associated with the power conditioning unit.

7. 7. The apparatus of claim 1, wherein each power conditioning unit is adapted to collect DC power from no more than four associated photovoltaic panels, or each power conditioning unit is adapted to collect DC power from only one associated photovoltaic panel.

8. 8. Apparatus according to any one of claims 1 to 7, wherein the common inverter unit includes a plurality of separate inverter circuits, each arranged to receive a portion of DC power from the intermediate transmission line and convert the portion of the received DC power to output AC power, and the common inverter unit is arranged to selectively activate and deactivate one or more of the inverter circuits.

9. 10. The apparatus of claim 8, wherein at least two of the inverter circuits have different efficiency characteristics from one another with respect to the amount of power converted, and the common inverter unit is arranged to selectively activate and deactivate the different inverter circuits according to the different efficiency characteristics of the inverter circuits and the detected current demand for the output AC power.

10. 10. The apparatus according to claim 8 or 9, characterized in that the common inverter unit is arranged to detect a faulty inverter circuit and thereafter avoid selecting the faulty inverter circuit for converting DC power to AC power for output.

11. 11. Apparatus according to any one of claims 1 to 10, characterized in that the common inverter unit is arranged to maintain a reliability measure of one or more inverter circuits and to limit the power load of one or more of these inverter circuits in accordance with the reliability measure.

12. The arrangement according to any one of claims 1 to 11, characterized in that all the power conditioning units are electrically connected in parallel to a common inverter unit via an intermediate transmission line.

13. A solar power station comprising the device according to any one of claims 1 to 12, a plurality of solar power generation panels, and an intermediate transmission line.

14. 14. The solar power plant of claim 13, comprising at least ten power conditioning units configured to pass high voltage DC power to a common inverter unit via an intermediate transmission line.

15. 15. The photovoltaic power plant according to claim 13 or 14, characterized in that the average length of the intermediate transmission lines between each power conditioning unit and the common inverter unit is at least 10 meters.

16. 16. The solar power plant of any one of claims 13 to 15, wherein each power conditioning unit is integrated into, mounted to, or located within 5 meters of the plurality of photovoltaic panels or one of the plurality of photovoltaic panels associated with the power conditioning unit.

17. 1. A method of operating a solar power plant, comprising: receiving collected DC power from one or more photovoltaic panels at each of a plurality of power conditioning units arranged to collect DC power at a panel voltage and pass the DC power to an intermediate transmission line, such as a cable wiring; Transmitting DC power from each power conditioning unit to a common inverter unit via an intermediate transmission line; and converting the DC power to AC power having a peak voltage at the common inverter unit and outputting the AC power to the power grid.

18. 18. The method of claim 17, further comprising, in each power conditioning unit, increasing a voltage of the collected DC power to a higher DC voltage above a panel voltage and below a peak voltage for transmission via the intermediate transmission line, optionally, the panel voltage being 100V or less, and the higher DC voltage being at least 350V or at least 400V when the common inverter unit outputs AC power to the power grid.

19. 20. The method of claim 18, further comprising selectively storing at least a portion of the collected DC power and selectively discharging at least a portion of the stored DC power to the common inverter unit, the acts of storing and discharging depending on the level of the higher DC voltage.

20. 20. The method of claim 18 or 19, wherein the level of the higher DC voltage depends at least in part on one or both of a concurrent demand for AC power for output to the power grid and a concurrently collected DC power from the photovoltaic panels.

21. The method according to any one of claims 17 to 20, wherein all the power conditioning units are electrically connected in parallel to a common inverter unit via an intermediate transmission line.

22. 23. The method of any one of claims 17 to 22, wherein the common inverter unit includes a plurality of separate inverter circuits, the method further comprising: controlling each inverter circuit to receive a portion of DC power from the intermediate transmission line and converting the received portion of the DC power to AC power for output; and controlling the common inverter unit to selectively activate or deactivate one or more of the inverter circuits.

23. 23. The method of claim 22, wherein at least two of the inverter circuits have different efficiency characteristics with respect to an amount of power converted, and further comprising: detecting a current demand for the output AC power; and controlling the common inverter unit to selectively activate and deactivate different inverter circuits according to the different efficiency characteristics of the inverter circuits and the current demand for the output AC power.

24. 24. The method of claim 22 or 23, comprising detecting a faulty inverter circuit and avoiding selection of the faulty inverter circuit for converting DC power to AC power for output.

25. 25. A method according to any one of claims 17 to 24, characterized in that a common inverter unit is controlled to maintain a reliability measure of one or more inverter circuits and to limit the power load of these inverter circuits or circuits in accordance with the reliability measure.

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