WO2012083949A1

WO2012083949A1 - Input voltage adaption device

Info

Publication number: WO2012083949A1
Application number: PCT/DK2011/000149
Authority: WO
Inventors: Uffe Borup; Frerk Haase
Original assignee: Danfoss Solar Inverters AS
Current assignee: Danfoss Power Electronics AS
Priority date: 2010-12-21
Filing date: 2011-12-19
Publication date: 2012-06-28
Anticipated expiration: 2013-06-21

Abstract

The invention relates to an electric circuit arrangement (2, 3, 4) for a photovoltaic power plant (1), comprising at least two electric input sections (9), at least one electric output section (12, 14) and at least one regulating device (10, 11, 25), wherein said two electric input sections (9) are at least at times at least in part electrically coupled to each other by said electric circuit arrangement (2, 3, 4). The electric voltage of a regulated one of said electric input sections (9) is regulated by at least one of said regulating devices (10, 11, 25) at least in part and/or at least at times according to the voltage of at least a regulating one of said electric input sections (9).

Description

Input voltage adaption device

The invention relates to an electric circuit arrangement, in particular to an electric circuit arrangement for a photovoltaic power plant, comprising at least two electric input sections, at least one electric output section and at least one regulating device, wherein said two electric input sections are at least at times at least in part electrically coupled to each other by said electric circuit arrangement. Furthermore, the invention relates to a photovoltaic power plant. Even more, the invention relates to a method of controlling a photovoltaic power plant, wherein said photovoltaic power plant comprises at least one electric circuit arrangement, and wherein at least one of said electric circuit

arrangements comprises at least two electric input sections and at least one electric output section, wherein said at least two electric input sections are at least in part and/or at least at times electrically coupled to each other by at least one of said electric circuit arrangements.

Due to an increasing concern about environmental problems and partially even due to public funding, the amount of photovoltaic power plants increases constantly. In photovoltaic power plants, electric current is directly produced from sunlight, using photovoltaic cells. The size of such photovoltaic power plants starts with relatively small arrangements (such as arrangements on a roof of a house for (partially) supplying the house with electrical energy), and goes up to large sized complexes with a power generation of several

megawatts or even more.

Due to the fact that photovoltaic cells can only produce direct current, but presently used electrical consumers are designed to use alternating current (typically 230 V/50 Hz or 110 V/60 Hz), it is necessary to alter the electric current that is produced by the photovoltaic cells into an alternating current. According to the state-of-the-art, circuits known as inverters are usually used for this. Another advantage of alternating currents is that alternating currents can be transformed to high voltages. Using high voltages, the electric current can be transported over long distances without excessive losses. This is particularly useful for large-scale photovoltaic power plants, since normally the electric consumers are located far away from a large-scaled power plant. It has been observed that under certain conditions an unexpectedly early decrease in the efficiency of solar cells, used for photovoltaic power plants, occurs. This degradation of solar cells can even lead to the complete failure of the solar cells. This is particularly the case, if solar cells known as thin-film photovoltaic cells are used. Although the underlying processes are not completely understood so far, experience shows that degradation effects mainly occur, if the photovoltaic cells (or parts thereof) are (partially) operated at an electric potential being lower than ground potential. This causes electric fields that are opposing the desired direction of the electric fields. If thin-film photovoltaic cells are used, the occurring degradation effect is not reversible. Therefore the degradation accumulates with time, leading to a destruction of the photovoltaic cells.

Furthermore, if back-contacted photovoltaic cells are used, similar problems occur. Here, experience shows that the efficiency of back-contacted

photovoltaic cells can decrease comparatively fast. This is known as the so- called "polarisation effect". In certain designs of back-contacted photovoltaic cells, an unfavourable electric potential occurs if the back-contacted

photovoltaic cells (or parts thereof) show a positive potential, relative to ground potential (the opposite condition when compared to thin-film photovoltaic cells). Although the polarisation effect is usually reversible, it is of course preferred if time-consuming regeneration phases can be shortened or even completely avoided. When other designs of back-contacted photovoltaic cells are used, it is found that they benefit from being run (partially) above ground potential. For such back-contacted photovoltaic cells designs, the above given description with respect to thin-film photovoltaic cells is applicable by analogy. To avoid the aforementioned problems, it has been suggested in the state-of- the-art to use voltage sources for setting the sensitive parts of the photovoltaic arrangement at an advantageous potential with respect to ground potential. This is possible because usually transformers are used to increase the voltages, before the generated electric current is introduced into a wide area electric grid. Such transformers, however, are also galvanically isolating. Such systems are described in the German utility model DE 20 2006 008 936 U1 , in the US patent application US 2009/0101191 A1 , in the European patent EP 2 136 449 B1 and in the international publication WO 2010/051812 A1. A simple embodiment, relying on this effect, can be achieved by simply setting an appropriate part of the photovoltaic power plant to ground potential by grounding. However, problems occur if a plurality of power generation units are used (for example solar panels or groups of solar panels, each comprising a plurality of photovoltaic cells), wherein each unit is feeding the direct current produced into a separate inverter. Such a design of the photovoltaic power plant has to be chosen, once a certain size is exceeded, because inverters can only be built (both technically and economically) up to a certain size. Furthermore, it is desired to use so-called transformerless inverters for economic reasons.

However, when using transformerless inverters, it is problematic to simply set one of the power generating units to ground potential in practical applications. This is, because all power generating units are electrically coupled to each other via the transformerless inverters. In particular, the coupling is quite often done at a potential that is different from the ground potential due to the internal design of the inverters used.

If everything would be perfect, all photovoltaic units would generate the same voltage. In reality, however, due to tolerances of the photovoltaic cells (and other parts) and due to shading effects (position of the sun, dirt that is deposited unevenly on the solar modules and so on) the generated voltages of the power generating units will be different. This can lead to the effect that despite of the grounding, some parts of some power generating subunits will be set to an unfavourable potential with regards to ground potential.

A possible way out would be to set one of the units to a sufficiently high electric potential, using a variable voltage source. However, such an approach leads to undesired electrical losses and to an increased complexity of the resulting photovoltaic power plant. Furthermore, the subunit that is generating the largest voltage and/or the voltage differences between the different subunits can vary with time, so that a particularly high offset voltage has to be chosen to be always on the safe side. Such a high offset voltage, however, has adverse effects

It is therefore the object of the invention to suggest an electric circuit

arrangement, in particular an electric circuit arrangement for a photovoltaic power plant that is improved over presently known electric circuit arrangements. Another object of the invention is to provide a photovoltaic power plant that is improved over presently known photovoltaic power plants. Yet another object of the invention is to suggest a method of controlling a photovoltaic power plant that is improved over presently known methods of controlling a photovoltaic power plant.

It is suggested to design an electric circuit arrangement that is comprising at least two electric input sections, at least one electric output section and at least one regulating device, wherein said two electric input sections are at least at times at least in part electrically coupled to each other by said electric circuit arrangement in a way that the electric voltage of a regulated one of said electric input sections is regulated by at least one of said regulating devices at least in part and/or at least at times according to the voltage of at least a regulating one of said electric input sections. In particular, said electric circuit arrangement can be an electric circuit arrangement for a photovoltaic power plant. The electric input sections can be in particular an arrangement of one, two or a plurality of electric conductors. Usually, two electric conductors (for direct current and/or for a mono-phase alternating electric current) or more electric conductors (in particular for poly-phase alternating currents) are provided for this. The electric input sections can comprise connecting devices for the (electric) connection with external devices. In particular, such connecting devices can be plugs, sockets, crimping connections, screwed connections, soldered connections or the like (where a mixture of different connecting methods is possible, even for a single electric connection). In the preferred embodiment of a photovoltaic power plant, the electric input sections can preferably be connected to photovoltaic cells and/or photovoltaic modules. In such a case, the electric input sections are usually connected to a direct current (where it is of course possible that some alternating current "noise" can be present as well). In the case of a photovoltaic power plant, the electric output section is usually an interface comprising a transformer for the handover of the generated electric energy to a long-distance electric grid. The regulation effect by the suggested regulation can be

performed in almost any thinkable way. For example, it is possible that the voltage of the regulated electric input section is always controlled in a way that the voltage is equal to, larger than (preferably by a small "safety margin") and/or smaller than (in particular by a small "safety margin") one, a plurality or even all of the regulating electric input sections/the other electric input sections.

However, it is also possible to provide an interface means for the application of external control signals. For example, a control can be based on external environmental conditions, current electrical output needs, timing signals, solar conditions or the like. These controlling signals cannot only be generated at the time of the regulation process itself, but they can also be provided (in part) by programming or the like. For example, it is possible that an internal timing device is provided and a control sequence that is started at a certain time. Such control sequence can be implemented by programming during the initial setup and/or during maintenance. The decision which electric input section is to be used as a regulated one and/or as a regulating one can also be entered at the time of installation of the arrangement, during maintenance or via an input interface (for example by Internet, intranet, USB or the like). Also, such a decision can be made according to a programmed algorithm that is (at least in part and/or at least at times) based on internal parameters, like the measured voltages, currents and so on. Also, additional sensors can be provided and used for all kinds of control measures. Although it is possible to perform the suggested type of regulation only during certain time intervals, it is preferred to perform said regulation essentially all the time. This does not exclude that such a regulation is temporarily not performed during maintenance, test cycles, regeneration cycles or the like of the installation. Furthermore, said regulation can be switched off as well, if (major) parts of the installation are switched off. A typical example for photovoltaic power plants is that the regulation is switched off during night (when the photovoltaic solar cells do not produce any

electricity). This way, it is possible to avoid unnecessary consumption of electric energy. As a regulating device, essentially all types of regulating devices can be used. In particular, hardware designed and/or software designed regulating devices can be used. In particular, a "mixture" of regulating devices, where some functions are performed by hardware, while some functions are performed by software are possible (and even preferred) as well. In particular, it is possible to perform software based parts of the regulation on an already present electronic computer device (if such a computer device is able to take over the additional numerical tasks). The regulating device can be designed in a way that the regulation answer is performed quickly (for example almost instantaneously). This way, time intervals that are detrimental to the electric circuit arrangement and/or to components, connected with said electric circuit arrangement can be avoided as much as possible. However, it can be sensible as well to provide for some time delay functionality and/or for some dampening means to avoid resonance effects and/or overcontrolling effects that can be problematic as well. Usually, a good compromise can be found for this. In particular, the regulated one (or more) of the electric input sections (or presumably the regulated ones of the electric input sections) is (are) different from the regulating one(s) of said input sections. Also, a regulation is typically not (only) based on a "common" output parameter or all input sections combined, but usually on an "individual" input section that has a typically significant influence on one, a plurality of all of the other input sections.

It is preferred, if at least one of said regulating devices of said electric circuit arrangement comprises at least one electric inverter device, in particular at least one transformerless electric inverter device. Such devices are frequently used for converting direct current to alternating current (and even for changing the frequency of an alternating electric current, in particular to increase the frequency of an alternating electric current). In particular in connection with photovoltaic power plants, such inverters are frequently used for altering the direct electric current, produced by the photovoltaic cells into alternating current, that is the standard for most electric consumers (typically either 230 V/50 Hz or 110 V/60 Hz). Furthermore, alternating current is advantageous if the voltage has to be changed (in particular increased), either for making it compatible with present consumers and/or for transforming it to a high potential, suitable for long-distance transportation of electric energy.

It is further preferred to design the electric circuit arrangement in a way that at least one of said regulating devices, in particular at least one of said electric inverter devices, comprises a plurality of electric input sections and/or if the electric circuit arrangement is designed in a way that it comprises a plurality of said regulating devices, in particular a plurality of said electric converter devices. This way, it is possible to "combine" more electric input parts into a single (or reduced number of) electric output (parts). Of course, a combination of both approaches can be used as well. A typical application for such a design can be found at photovoltaic power plants of a larger size, where the

photovoltaic cells are typically arranged as photovoltaic modules that are grouped together into subunits. These subunits will feed the electricity to a dedicated electric input section and/or to a dedicated regulating device (in particular inverter device). This is because the power output of larger photovoltaic power plants typically exceeds the maximum power limits of power electronics (technically and/or economically). Therefore, the electric power fractions of the subunits will initially be "treated" separately and will be later combined to the overall electric output.

Another possible embodiment can be reached if at least one of said electric input sections is designed and/or used at least in part and/or at least at times as a direct current input section and/or as a two-wired electric input section. Once again, this is the typical case for the use of electric inverter devices and/or when using the electric circuit arrangement as a part of a photovoltaic power plant. Here, separate direct current inputs will have to be "treated" by the electric circuit arrangement.

Yet another possible embodiment of an electric circuit arrangement can be achieved if at least one of said electric output sections is designed at least in part and/or at least at times as an alternating current output section and/or as a mono-phase electric output section and/or as a poly-phase electrical output section. Similar to the previously describes embodiment, this is a typical embodiment when using inverters and/or when using the electric circuit arrangement as a part of a photovoltaic power plant. A mono-phase electric output section will typically comprise two or three wires. Two wires are the standard embodiment if no protective earth is used (i.e. only two active phases and/or one active phase and the neutral phase are present), while three wires are typically used if a protective earth conductor (PE) is present (in addition to the two active phases and/or the active phase and the neutral phase). As a poly-phase electric output section, a three-phase electric output, a four-phase electric output, a five-phase electric output or even an electric output with more phases can be used. If an alternating current with n phases is used, typically either n conductors (n active phases and/or n-1 active phases and one neutral phase) or n+1 electric conductors are used (where the n+1-th electric conductor is used for the protective earth). Preferably, the electric circuit arrangement is arranged in a way that at least one part of at least one of said electric input sections is at least in part and/or at least at times set at a specified potential relative to ground potential, and in particular is at least in part and/or at least at times set to ground potential and/or said electric circuit arrangement is arranged in a way that at least one part of at least one of said electric output sections is at least in part and/or at least at times set at a specified potential relative to ground potential. In particular, setting the potential at a specified potential relative to ground includes to set the potential "exactly" to ground potential. Using such a design, different objects can be solved (while sometimes some of the objects might exclude each other). For example, by using the suggested design, the safety for maintenance personnel or the like can be enhanced. For example, surface parts that can be accidentally touched can be set to a potential that no injuries or even fatalities can occur. Furthermore, it is possible to set certain parts of the arrangement to a potential that reduces electrical losses because of ambient conditions (for example very humid air, rainfall or snow). Furthermore it is possible to avoid an early degradation of photovoltaic cells, in particular of thin- film photovoltaic cells and/or of back-contacted photovoltaic cells due to an adverse electric potential with respect to ground potential. In the simplest design, the respective part can be simply electrically connected to ground potential (by so-called grounding). However, it is also possible to use a voltage source to set the respective part (and therefore the remaining parts of the arrangement as well) to a certain (minimum) potential with respect to ground potential. Although this will typically make the arrangement more complex, such a design can be of use for providing some "safety margin", for example for providing additional safety for maintenance personnel and/or against

degradation effects and/or polarisation effects of the photovoltaic cells. A preferred embodiment can be achieved if the electric circuit arrangement is designed in a way that a negative part of at least one of said electric input sections is at least in part and/or at least at times set to ground potential, in particular if thin-film photovoltaic cells are connected to said electric input section and/or if a positive part of at least one of said electric input sections is at least in part and/or at least at times set to ground potential, in particular if certain designs of back-contacted photovoltaic cells are connected to said electric input section. This way, it is possible to avoid adverse conditions for the respective types of photovoltaic cells. In particular, degradation effects (in particular with respect to a thin-film photovoltaic cell) and/or polarisation effects (in particular with respect to back-contacted photovoltaic cells) can be

achieved. When other designs of back-contacted photovoltaic cells are used, it is found that they benefit from being run (partially) above ground potential, (i.e. a design of the electric circuit arrangement in which a negative part of at least one of said electric input sections is at least in part and/or at least at times set to ground potential can be favourable). Therefore it is preferred if the respective back-contacted photovoltaic cells are held at an appropriate potential with respect to ground potential. Of course, it is also possible to provide a certain "safety margin" by the use of a voltage source or the like (see previous embodiment), instead of setting the respective part "exactly" to ground potential (which is usually not strictly possible due to contact voltages, residual voltages across electronic components and the like). Preferably, at least one of said regulating devices of the electric circuit arrangement is at least in part and/or at least at times designed as a maximum power point tracking device and/or as a DC-DC-converter and/or as a voltage source inclusion and/or exclusion device and/or as a controllable voltage source device. It is a well-known fact that the maximum electric power of a photovoltaic cell is achieved at the so-called maximum power point (which can be dependent on temperature or the like). If deviating from this maximum power set point (for example by varying the voltage and/or the current) the overall electric output of the photovoltaic cell will be reduced. For this reason, usually maximum power point regulators are used in the context of photovoltaic power plants for achieving a maximised electric output. However, in context with the present suggestions, such maximum power point tracking devices can also be used for regulating the voltage of the regulated electric input section in an easy and cost-efficient way. It is to be noted that the efficiency of the respective photovoltaic module subunit will be reduced by this. However, normally only relatively small voltage corrections are needed, so that the resulting power losses are small, in particular when compared to the advantages of the respective setup. In the case that a DC-DC-converter is used, such a converter can be a "step-up"-converter and/or a "step-down"-converter. The "and" can particularly refer to a DC-DC-converter that can both raise and lower the voltage, where the "direction" of the voltage correction can be set depending on the requirements existing at a particular time. Alternatively or additionally it is possible to provide a controllable voltage source device. This can be in particular a controllable DC voltage source. The voltage of the controllable voltage source device can be set by the electric circuit arrangement according to the actual needs. It is possible that the controllable voltage source device forms the input for at least one of the input sections of the electric circuit arrangement. Since the controllable voltage source device has to provide essentially only a specified voltage (with a usually negligible current), this can be a very elegant way to provide the suggested voltage adaption. Of course, the controllable voltage source device can be designed as an integral part of the electric circuit arrangement. Alternatively or (preferably) additionally it is possible to use a voltage source inclusion and/or exclusion devices. This can be realised by electric, electromagnetic or electronic switches. In particular, it is possible to "electrically enlarge" a solar module (or a plurality of solar modules) by setting the switches in a way that the respective voltage source is included into the electric circuit ("electrical removal" is possible as well, of course). The voltage source can be a photovoltaic cell. Also, the voltage source can be of a type, having an controllable output voltage. In particular, one or several voltage sources can be included (or removed) in series and/or in parallel. Furthermore, it is possible to not only "electrically remove" the respective voltage sources from one circuit, but it is also possible to "move it" to another electric circuit, as well.

Another possible embodiment can be achieved if said electric circuit

arrangement is arranged in a way that at least one of said regulating devices is regulating the at least one regulated electric input section at least in part and/or at least at times in a way that the majority, preferably essentially all parts of the electric input sections are above or below ground potential, in particular above or below a certain potential above or below ground potential, respectively. This way, adverse effects for the photovoltaic cells cannot only be avoided for (presumably comparatively small) parts of the electric circuit arrangement and for (parts of) the components, connected thereto, but instead for the majority or (essentially) all parts of the electric circuit arrangement and the components connected thereto. Furthermore, it is possible that at least one of said regulating devices of said electric circuit arrangement is designed as a selecting device, selecting at least one of said electric input sections to be a regulated electric input section and/or to be a regulating electric input section. This way, the functionality of the electric circuit arrangement can usually be enhanced, most of the times even

considerably. In particular with certain applications of the electric circuit arrangement, a change of the "preferred" electric input circuit as a regulating and/or a regulated electric input device can occur during the operation of the respective arrangement. For example, when using the electric circuit

arrangement in connection with photovoltaic power plants, changes can occur due to varying shading and/or different accumulation of dirt on the photovoltaic modules. Such changes are essentially not foreseeable. Using the suggested embodiment, such "non-foreseeable" variations can easily be dealt with. Preferably the electric circuit arrangement comprises a plurality of photovoltaic cells that are preferably arranged as a plurality of photovoltaic modules, wherein said photovoltaic cells are preferably designed at least in part as thin- film photovoltaic cells and/or as back-contacted photovoltaic cells. In particular, the respective photovoltaic modules and/or photovoltaic cells can be connected (usually grouped into subgroups) to the electric input sections of the electric circuit arrangement. Such an arrangement is particularly useful in connection with a photovoltaic power plant. In particular the photovoltaic cells, the photovoltaic modules and/or the subgroups/groups of photovoltaic

cells/photovoltaic modules can be arranged in a way that at least two

subgroups are used in parallel, i.e. that the total current generated is increased. This design can be used in particular in addition to an arrangement of several (in particular two or more) photovoltaic cells/photovoltaic modules in series, so that for each of the subgroups that are arranged in parallel a sensible voltage is generated. The at least two parallelly arranged subgroups of photovoltaic cells/photovoltaic modules typically feed into a single or a plurality of electric inverters that "convert" the usually generated DC-current into an AC-current. In particular, if two, or more than two, subgroups are present (for example three, four, five, six and so on subgroups), it is possible that all subgroups feed into a single inverter, every subgroup has its own inverter and/or that mixtures between those extremes are used (for example, where two subgroups share a common inverter, while every pair of subgroups feeds into a different "double inverter"). Typically, when using photovoltaic cells, a voltage regulating device, in particular a DC-DC-converter, a maximum power point tracking device or another suitable device is/are can be used between the photovoltaic

cells/photovoltaic modules/photovoltaic subgroups and the respective inverter (respective part of the relevant inverter), for changing the "initial" output voltage of the respective photovoltaic cell(s)/photovoltaic module(s)/photovoltaic subgroup to a different voltage (which can be the same, can be higher (in particular slightly higher) and/or lower (in particular slightly lower) than the "initial" input voltage. Therefore, the voltages that are leaving the regulating device (in particular DC-DC-converter and/or maximum power point tracking device) can be adapted to each other. In particular, if DC-DC-converters are used, normally a "step down"-adaption of the voltage (i.e. a presumably slight reduction of the voltage) is performed. The adaption does not necessarily mean that all voltages will be set to the same voltage (spread/level). Instead, it is in particular possible that the voltage (spread/level) and/or the subgroups that is/are grounded (or set at a specified potential with respect to ground potential) is/are selected in a way that (in particular through the partial electric connection by transformerless inverters) essentially all relevant parts of the (such connected parts of a) solar power plant are set at an advantageous level with respect to ground potential (in particular above and/or below ground potential, depending on the type of photovoltaic cells used, on safety considerations etc.). Contrary to previously suggested photovoltaic cell arrangements, the respective subgroups are not regulated solely with a view to maximum electric power production (and presumably, if at all, with respect to a sensible output voltage of a serial connection of individual photovoltaic cells/photovoltaic modules), but different parallel branches (i.e. subgroups) of the photovoltaic cell arrangement are "compared" to each other and influence each other by the use of regulatory means. Furthermore, a photovoltaic power plant is suggested, that comprises at least one electric circuit arrangement according to the previous description. Such a photovoltaic power plant will show the same features and advantages, at least in analogy. Additionally, the photovoltaic power plant can be adapted and modified in the previously described sense. Thus, further functionalities and advantages can be achieved.

Furthermore, a method of controlling a photovoltaic power plant is suggested, wherein said photovoltaic power plant comprises at least one electric circuit arrangement, and wherein at least one of said electric circuit arrangements comprises at least two electric input sections and at least one electric output section, wherein said at least two electric input sections are at least in part and/or at least at times electrically coupled to each other by at least one of said electric circuit arrangements, and wherein the electric voltage of a regulated one of said electric input sections is regulated at least in part and/or at least at times according to the voltage of at least another regulating one of said electric input sections. Preferably, at least one of the electric circuit arrangements used for the method is of a design as previously described. The method will show the already discussed features and advantages as well, at least in analogy.

Furthermore, the method can be adapted and modified in the previously described sense. Thus, further functionalities and advantages can be achieved.

The present invention and its advantages will become more apparent, when looking at the following description of possible embodiments of the invention, which will be described with reference to the accompanying figures, which are showing:

Fig. : a photovoltaic power plant in a schematic view from above;

Fig. 2: potentials of different groups of photovoltaic modules in different circuit arrangements;

Fig. 3: a schematic drawing of a switching device for adapting the voltage of a photovoltaic module. In Fig. 1 , a possible embodiment for a solar power plant 1 (photovoltaic power plant 1 ) is shown in a schematic representation. In the present embodiment, the solar power plant 1 comprises three subunits 2, 3, 4, each comprising a plurality of solar modules 5 (photovoltaic modules). As usual, each solar module 5 is an arrangement of a plurality of solar cells 6 (photovoltaic cells) that are drawn as circles in Fig. 1 for simplicity. Of course, the solar power plant 1 can be designed differently as well. For example, it is possible to use more or less subunits 2, 3, 4 for the solar power plant 1. Furthermore, it is possible that not only one, but a plurality of solar modules 5 can form a logical electrical circuit. Also, the number of solar modules 5 and/or of logical electrical circuits can differ for each subunit 2, 3, 4 and/or for the solar power plant 1. Likewise, the number of solar cells 6 can differ as well.

In the embodiment shown in Fig. 1 , each solar module 5 forms an electric input circuit 7, comprising the solar module 5 and a two wire electric connection 8, leading to an electric input interface 9 of a voltage regulator 10. In the presently show example, each voltage regulator 10 has three electric input interfaces 9, and is consequently supplied by altogether three solar modules 5. Once again, the present numbers are used for illustrative purposes only, and can easily differ, even widely. The voltage regulators 10 will adapt the normally different voltages at the electric input interfaces 9 in a way that is further explained with respect to Fig. 2 in the following. The electric voltages, coming from the solar modules 5 will be handed over to electric inverters 11 by electric cables 12 with a sufficient number of wires. In the present example, one inverter 1 1 is used for each voltage regulator 10. Furthermore, a data bus connection 13 is shown in Fig. 1. Using the data bus connection 13, the respective voltage regulators 10 and/or the inverters 1 1 can exchange information, for example about the current conditions, the respective electric currents and/or voltages. Also, it is possible that the data bus connection 13 is used for sending data out to the "outside world" for monitoring purposes and/or for receiving data from the "outside world" for controlling purposes (for simplicity, this is presently not shown). As usual, the inverters 11 are used for altering the direct current that is produced by the solar cells 6 / the solar modules 5 (and which is usually further altered by the voltage regulators 10) into an alternating current. The alternating currents of the presently three subunits 2, 3, 4 are collected on a common main electric bus 14 and fed into a transformer 15. Here, the electric current is transformed into a high voltage for a handover to a long-distance electric grid 16.

Of course, different layouts of the solar power plant 1 , in particular with respect to the voltage regulators 10, the inverters 1 and the main electric bus 14 are possible, as well. In particular, it is possible that a plurality of voltage regulators 10 feed into a common electric bus (which can be a DC-bus and/or an AC-bus) that is in turn feeding into a single inverter 11. Even more, some kind of "grouping" is possible as well, in a way that a plurality of voltage regulators 10 feed into a (reduced) number of inverters 11. Furthermore, the voltage regulators 10 can be often essentially arbitrary design. For example, the voltage regulators can be (in part) DC/DC-converters, boost converters or buck- converters. In the presently shown example, a grounding contact 17 is used for one of the electric wires (namely of a negative side 21 , wire) of the electric connection 8, connecting the voltage regulator 10 and one of the solar modules 5 of the rightmost subunit 4 (of course, the grounding contact 17 could be placed at a different suitable point as well). Since in the presently shown embodiment, so- called transformerless inverters 11 are used as inverters 11 , this grounding 17 of one subunit 4 will be "transferred" or "coupled" through the voltage regulator 10, the "neighbouring" inverter 11 and the common main electric bus 14 to the other inverters 11 and consequently to the other parts of the remaining subunits 2, 3, as well (i.e. an electric connection between almost all parts of the solar power plant 1 is present). In particular, transformerless inverters 11 are nowadays frequently used because they are cheaper, less space consuming and weigh less. Since the transformer 15 is galvanically isolating the solar power plant 1 and its components from the long-distance electric grid 16, the components of the solar power plant 1 can be set to an essentially arbitrary potential with respect to ground potential. However, if the solar cells 6 in use are of a certain kind, for example of a thin-film solar cell type or of a back-contacted solar cell type, certain electric potentials with respect to ground potential are harmful for the solar cells 6, in particular with regard to their lifetime. In the present example of a solar power plant 1 , back-contacted solar cells 6 are used. If polarisation effects are to be avoided (which will eventually necessitate a regeneration process at certain intervals), no part of any of the solar cells 6 of the complete solar power plant 1 should be above ground potential anywhere.

Of course, if the special conditions would be present, under which it would be preferred to operate the back-contacted solar cells 6 above ground potential, appropriate adaptations of the described "grounding-scheme" can be easily performed.

If all electric and electronic parts in all of the subunits 2, 3, 4 are identical and furthermore the collected radiation (including dirt deposits on the surfaces of the solar modules 5) would be identical, no voltage adaption between the different electric input circuits 7 of the different subunits 2, 3, 4 would be necessary. However, in practical applications this is usually never the case.

In Fig. 2, examples of possibly occurring potentials at one of the subunits 2, 3, 4 are shown (for example subunit 2). In the different sub figures 2a, 2b, 2c, 2d of Fig. 2, different "grounding methods" are shown. In each subfigure of Fig. 2, along the abscissa 18, the potentials of the two electric contacts 8 of each solar module 5 in one of the subunits 2, 3, 4 (for example subunit 2) is shown. Along the ordinate 19, the potential (voltage) with respect to ground potential is drawn for each of the solar modules 5. Hence, the difference between the two electric conductors 8 in each electric input circuit 7 is indicating the voltage, generated by the respective solar module 5. In Fig. 2a, a situation is drawn in which the three solar modules 5 are not galvanically coupled to each other. Such a situation is not possible with the embodiment of a solar power plant 1 , as shown in Fig. 1 , because said solar power plant 1 uses transformerless inverters 11. Nevertheless, subfigure 2a is shown for illustrative purposes. As can be seen from Fig. 2a, the voltages

(length of the lines) of each electric input circuit 7 (i.e. the voltages produced by the solar modules 5) are differing by a certain amount, say by approximately 20%. Furthermore, the potential with respect to ground potential (identical to the ordinate 19 line) will vary between the different electric input circuits 7 as well.

As already stated, because of the transformerless inverters 11 , a part of the electric wires 8 will be electrically coupled to each other. In the presently shown example, this coupling leads to the inputs floating with their positive inputs 20 at the same potential relative to ground. Furthermore, one of the electric input circuits 7 (in Fig. 2b the rightmost electric input circuit 7) is set to ground potential by means of a grounding contact 17. This grounding is performed on the negative side 21 of the respective electric input circuit 7. Furthermore, in Fig. 2b, a situation is shown, where the grounding contact 17 is contacted with an electric input circuit 7 that is not generating the largest voltage (this would be the electric input circuit 7 in the middle of Fig. 2b). This leads to the situation, shown in Fig. 2b, where the negative side 21 of the "middle" electric input circuit 7 is below ground potential. This, however, leads to the situation that at least some of the solar cells 6 in the respective solar module 5 will be below ground potential and will hence be subject to degradation effects and/or polarisation effects.

To avoid such adverse effects, the (initially different) voltages at the electric inputs 9 of the voltage regulators 10 will be measured and adapted to each other. To be able to do this, the measured data can be transmitted to the other voltage regulators 10 and/or to the inverters 11 via the data bus connection 13 provided in the solar power plant 1 , shown in Fig. 1. The voltage regulators 10 have a so-called maximum power point tracker for each of the electric input sections 9. Such maximum power point trackers are already widely used in photovoltaic power plants 1 for generating an optimum power output. Here, the maximum power point trackers are not only used in a way to get an optimum power output, but also to adapt the voltages of the three electric input circuits 7 by (slightly) deviating from the maximum power set point.

By performing such a "complete" voltage adaption between all three electric input circuits 7, the situation shown in Fig. 2c can be reached. As it is clear from Fig. 2c, all parts of every one of the electric input circuits 7 now lie at or above ground potential. Hence, the adverse polarisation effects can be avoided very efficiently. It has to be noted that the avoidance of polarisation effects will overcompensate the comparatively minor loss in power production by far.

Furthermore, it should be noted that a "complete" adaption of the different voltages and/or potentials may not be necessary. Instead, it can prove to be sufficient to adapt the voltage of only one (or several) "adversely affected" electric input circuit 7. This is shown in Fig. 2d. Here, the voltage of the "middle" electric input section 7 has been reduced to be the same as (or presumably even lower than) the voltage of the "right" electric input section 7. Additionally and/or alternatively, this effect could be achieved by increasing the voltage of the "right" electric input circuit 7 to be (at least) as large as the voltage of the "middle" electric input section 7. The voltage of the "left" input section 7, however, remains unchanged. Nevertheless, a situation can be reached in which all parts of every input section 7 lie above the "critical" ground potential. Of course, it is preferred if the necessary voltage adaption is as small as possible. For doing this, the grounding contact 17 should be arranged at the electric input section 7 that is usually expected to have the highest voltage. Additionally or alternatively, switches can be provided, so that the electric input section 7 that is currently producing the largest (uncorrected) output voltage is automatically connected to the grounding contact 17. This way the necessary voltage adaptions can be minimised or even completely avoided. The

determination of the input section 7 to be grounded (or that is to be set at a specified level with respect to ground potential) is preferentially done based on a (comparatively) recent/current measurement. Furthermore, the choosing of the input section 7 is performed (essentially) automatically. This way, user intervention can be minimised and/or a system with a particularly high lifetime can be realised in an easy way.

In Fig. 3, another possible circuit arrangement 22 is shown that is particularly useful for performing comparatively large voltage adaptions. In Fig. 3, two different solar units 23 are shown. Each solar unit 23 comprises a plurality of (fixed) solar cells 6. Furthermore, a "standby" solar cell 24 is provided. This standby solar cell 24 can be added to one of the two solar units 23a, 23b using the electric switches 25. Although the electric switches 25 are presently drawn as electric relays, different embodiments are possible as well.

In the situation, shown in Fig. 3, the "standby" solar cell 24 is included in series with the "left" solar unit 23a. The "right" solar unit 23b is connected to a bypass cable 26. Therefore, the "left" solar unit 23a is "boosted" in voltage, while the "right" solar unit 23b remains unchanged. By an appropriate switching of the electric switches 25, a reverse situation can be achieved. Also, it is possible that both solar units 23a, 23b will bypass the "standby" solar cell 24 (in this situation the "standby" solar cell 25 will be unused).

Instead of a "standby" solar cell 24, it is of course possible as well to use a DC- voltage source. Preferably, the DC-voltage source can be variable as well. The circuit arrangement 22 can be used alternatively or additionally to the maximum power point tracker devices of the voltage regulators 10, used in the embodiment of a solar power plant 1 , as shown in Fig. 1.

Of course, different means for a voltage adaption could be used alternatively or additionally, as well.

Claims

C l a i m s

Electric circuit arrangement (2, 3, 4), in particular electric circuit

arrangement (2, 3, 4) for a photovoltaic power plant (1), comprising at least two electric input sections (9), at least one electric output section (12, 14) and at least one regulating device (10, 11 , 25), wherein said two electric input sections (9) are at least at times at least in part electrically coupled to each other by said electric circuit arrangement (2, 3, 4), characterised in that the electric voltage of a regulated one of said electric input sections (9) is regulated by at least one of said regulating devices (10, 11 , 25) at least in part and/or at least at times according to the voltage of at least a regulating one of said electric input sections (9).

2. Electric circuit arrangement (2, 3, 4) according to claim 1 , characterised in that at least one of said regulating devices (10, 11 , 25) comprises at least one electric inverter device (11), in particular at least one transformerless electric inverter device (11).

Electric circuit arrangement (2, 3, 4) according to claim 1 or 2, in particular according to claim 2, characterised in that at least one of said regulating devices (10, 11 , 25), in particular at least one of said electric inverter devices (11), comprises a plurality of electric input sections (9) and/or characterised by a plurality of said regulating devices (10, 11 , 25), in particular by a plurality of said electric inverter devices (11).

Electric circuit arrangement (2,

3,

4) according to any of the preceding claims, characterised in that at least one of said electric input sections (9) is designed and/or used at least in part and/or at least at times as a direct current input section (9) and/or as a two wired electric input section (9).

5. Electric circuit arrangement (2, 3, 4) according to any of the preceding

claims, characterised in that at least one of said electric output sections (12, 14) is designed at least in part and/or at least at times as an alternating current output section (12, 14) and/or as a mono-phase electric output section (12, 14) and/or as a poly-phase electric output section.

Electric circuit arrangement (2, 3, 4) according to any of the preceding claims, characterised in that at least one part of at least one of said electric input sections (9) is at least in part and/or at least at times set at a specified potential relative to ground potential (17), and in particular is at least in part and/or at least at times set to ground potential (17) and/or characterised in that at least one part of at least one of said electric output sections (12, 14) is at least in part and/or at least at times set at a specified potential relative to ground potential (17).

Electric circuit arrangement (2, 3, 4) according to any of the preceding claims, in particular according to claim 6, characterised in that a negative part of at least one of said electric input sections (9) is at least in part and/or at least at times set to ground potential (17), in particular if thin-film photovoltaic cells are connected to said electric input section (9) and/or characterised in that a positive part of at least one of said electric input sections (9) is at least in part and/or at least at times set to ground potential (17).

Electric circuit arrangement (2, 3, 4) according to any of the preceding claims, characterised in that at least one of said regulating devices (10, 11 , 25) is at least in part and/or at least at times designed as a maximum power point tracking device (10) and/or as a DC-DC-converter and/or as a voltage source inclusion and/or exclusion device (25) and/or as a controllable voltage source device.

Electric circuit arrangement (2, 3, 4) according to any of the preceding claims, characterised in that at least one of said regulating devices (10, 11 , 25) is regulating the at least one regulated electric input section (9) at least in part and/or at least at times in a way that the majority, preferably essentially all parts of the electric input sections (9) are above or below ground potential, in particular above or below a certain potential above or below ground potential, respectively.

10. Electric circuit arrangement (2, 3, 4) according to any of the preceding

claims, characterised in that at least one of said regulating devices (10, 11 , 25) is designed as a selecting device, selecting at least one of said electric input sections to be a regulated electric input section (9) and/or to be a regulating electric input section (9).

11. Electric circuit arrangement (2, 3, 4) according to any of the preceding

claims, characterised by a plurality of photovoltaic cells (6) that are preferably arranged as a plurality of photovoltaic modules (5), wherein said photovoltaic cells (6) are preferably designed at least is in part as thin-film photovoltaic cells and/or as back-contacted photovoltaic cells (6).

12. Photovoltaic power plant (1), characterised by at least one electric circuit arrangement (2, 3, 4) according to any of claims 1 to 11.

13. Method of controlling a photovoltaic power plant (1), wherein said

photovoltaic power plant (1) comprises at least one electric circuit arrangement (2, 3, 4), preferably at least one electric circuit arrangement (2, 3, 4) according to any of claims 1 to 11 , and wherein at least one of said electric circuit arrangements (2, 3, 4) comprises at least two electric input sections (9) and at least one electric output section (12, 14), wherein said at least two electric input sections (9) are at least in part and/or at least at times electrically coupled to each other by at least one of said electric circuit arrangements (2, 3, 4), characterised in that the electric voltage of a regulated one of said electric input sections (9) is regulated at least in part and/or at least at times according to the voltage of at least another regulating one of said electric input sections (9).