Limited Potential Difference Photovoltaic Power Plant in Each Photovoltaic Module

Description

DOMAINE TECHNIQUE ET ART ANTERIEUR

[0001] The invention relates to photovoltaic installations and, in particular, to a novel photovoltaic module structure.

[0002] Installations using photovoltaic (PV) panels are expected to grow.

[0003] There figure 1A represents a photovoltaic (PV) power plant of known type, with a chain (or "string" in Anglo-Saxon terminology) 100 of 3 photovoltaic modules 1, 2, 3 placed in series and one or more converter(s) (or inverter(s)) 10, connected to the electrical network 12 most often via one or more transformer(s), each module input being connected to the output of the previous module in the chain. This representation is simplified because, in an average photovoltaic power plant, a chain comprises many more than 3 modules, the number of modules depending in particular on the electrical power that the power plant must provide. In addition, a photovoltaic installation can comprise several chains 100, 101, ... arranged in parallel, as illustrated in figure 1B .

[0004] The design of rapidly growing photovoltaic farms relies on various technical approaches to optimize production. One such approach is to increase the number of PV modules connected in series per string to increase their power. This improved configuration results in an increase in the electrical voltage across the PV modules and therefore across the cells that make up the module.

[0005] An example of a known structure of a photovoltaic module is shown in figure 2 This module 2 has a front face 4 made of glass or a transparent “PET” type polymer.

[0006] Solar cells 6, 8 are coated between a 1st encapsulation layer 10 and a 2nd encapsulation layer 11, both for example made of a thermoplastic polymer, generally "EVA" (Ethylene-vinyl acetate).

[0007] A rear face 12, also called “Backsheet”, which comprises for example a laminated assembly of polymers, commonly referred to as “TPT” because it is most often composed of Tedlar-Polyester-Tedlar (the term “Tedlar” being the DuPont trade name for PVF (Polyvinyl fluoride)); alternatively, the rear face 12 is a solar glass.

[0008] Reference 15 designates the frame, fixed to a metal chassis (not shown), which is connected to earth.

[0009] The potential difference, which can be significant, between cells 6, 8 and frame 15 (or the periphery of the module), generates an increase in the electric field internal to the module.

[0010] This electric field promotes ionic migration and the accumulation of salts (e.g. sodium, Na + < ) on the cell surface. These cause surface polarization and shunting. As a result, the functionality of the PN junction of the affected cells is disrupted, which reduces the power of the panels. After several years, the panel produces less energy. If the problem is not treated, the encapsulant sometimes turns yellow but, above all, loses its "adhesive" power. The module ends up delaminating and therefore water infiltrates the photovoltaic module. This degradation of photovoltaic panels is known as "Potential Induced Degradation", or "PID" (see for example the standard IEC TS 62804-1: 2015 "Photovoltaic (PV) modules - Test methods for the detection of potential induced degradation (PID)", or the article by S. Koch et al.Entitled “Potential-induced degradation effects on crystalline silicon cells with various anti-reflective coatings”, published in “27th European Photovoltaic Solar Energy Conference and Exhibition”, p.1985-1990” in 2013).

[0011] On the other hand, independently of this phenomenon, the potential difference induced between the cells and the periphery of the module can cause a breakdown of the insulating layers of the module, and consequently the appearance of a sustained electric arc, which could cause a fire to start.

[0012] A photovoltaic power plant structure is known, according to application WO2015 / 015112, in which a transformer connecting the inverter to the high-voltage electrical network is eliminated. However, the possible increase in the voltage of the photovoltaic strings relative to the ground leads to the physical problems mentioned above.

[0013] In figure 3A , we have schematically represented 3 hypothetical high-power modules 17, 18, 19 arranged in series and mounted as indicated above, each module being connected to earth by its frame or its periphery. In the principle example illustrated, the voltage across each module is 1500 V. Each module input (-) being connected to the output (+) of the previous module, the cells of module 18, resp. 19, are subjected to a voltage, relative to earth and therefore relative to their frame or its periphery, of 3000 V, resp. 4500 V. These voltages increase with the number of high-power modules in series, they generate "PID" type problems.

[0014] In practice, such modules with a potential difference of 1500V across their terminals are rare (a typical module has, for example, around 30V-40V across its terminals). However, a photovoltaic installation can be composed of several strings, connected in series, of modules themselves connected in series within the string. Each string can then have this type of high voltage across its terminals. Each cell within a module in a string will then experience the same orders of magnitude of potential differences as in the example of the figure 3A For photovoltaic installations comprising several hundred, or even several thousand, modules, this increase in voltage will be the source of the problems mentioned above.

[0015] There figure 3B illustrates the breakdown problems: Here one pole of the PV generator (consisting of two PV modules) is accidentally brought to the reference (earth or metal ground) (for example by insulation breakdown). The negative terminal of the generator is brought to 0V and the positive terminal of the generator is brought to 2x1500V=3kV. This can cause a new breakdown between the positive pole and the earth (leading to the general short-circuiting of the generator) since the modules are designed to operate at 1500V maximum.

[0016] Document KR102085514B1 describes a photovoltaic power plant.

[0017] The invention aims to solve all or part of these problems. EXPOSE DE L'INVENTION

[0018] The invention firstly relates to a photovoltaic power plant as defined by the subject of claim 1.

[0019] Preferably, all the modules among, respectively, the N modules of the chain or all the modules of the N chains or of the N groups are thus connected, except possibly the first or the last.

[0020] According to examples not necessarily covered by the subject of the claims but useful for understanding the invention, the metallic mass(es) of the module(s) of the chain or group is / are set to a non-zero potential, defined by a module or, respectively, a preceding or following chain or group of modules, for example the preceding chain or group of modules, for example so as to increase the potential of the metallic masses as the voltages of the modules or chains or groups of modules are added together.

[0021] In this way, a reduced potential difference, and therefore a reduced electric field, is applied within each module concerned between the metal frame or chassis and each cell of the module. This minimizes or eliminates the electric field effect on the cells, and limits or avoids the problems mentioned above. The cells are therefore no longer subject to the risks, explained above, of the "PID" type, or of the breakdown type.

[0022] In particular examples the frame or chassis of at least one photovoltaic module may be connected: at a connection point of high or low potential, or of intermediate potential between these two values, of a module or, respectively, of a module of a chain or of a module of a group, which does not immediately precede or follow, in the series, said module or said chain to which said module belongs or said group to which said module belongs; or at a point of high or low potential, or of intermediate potential between these two values: * of said module; * or of a chain or group which includes said module; * or of a module, or of a chain or group which immediately precedes or follows, in the series, said module or said chain to which said module belongs or said group to which said module belongs.

[0023] According to an example useful for understanding the photovoltaic power plant invention, the frame or chassis of at least one photovoltaic module is connected to a connection point of a module or a string or a group of the photovoltaic power plant, which is a potential point which is less than 600 V lower than the low potential of said module or a potential point which is higher than the high potential of said module by a value equal to at most 600 V.

[0024] A photovoltaic power plant according to an example useful for understanding the invention may comprise: N photovoltaic modules forming a string or N strings of photovoltaic modules, in which the frames of all the modules of at least one string are connected to the same potential; and / or N photovoltaic modules forming a string or N strings of photovoltaic modules, the connection point of said at least one module being on the string of K modules comprising said module, for example at an intermediate potential between the high potential and the low potential of the string; this intermediate potential may be the high potential or the low potential of the module of rank K / 2+1 or K / 2-1 if the number K is even and of rank (K+1) / 2 or (K-1) / 2 if the number K is odd.

[0025] A photovoltaic power plant may include: a plurality of photovoltaic modules forming a chain of N modules placed in series, said connection means being able to connect the frame or chassis of one or more modules or of each module to a point of output or input potential, or of intermediate potential between these two values, of the same module or of another module, preceding or following in the chain;or N (N>1) strings of photovoltaic modules, these strings of modules being connected in series, said connection means connecting for example the frame or chassis of one or more modules or of each module of at least one string, to a point of output or input potential, or of intermediate potential between these two values, of a string, each string itself comprising an input (or lower) potential, or an input pad or terminal, intended for example to be connected to such an input potential, and an output (or higher) potential, or an output pad or terminal intended for example to be connected to such an output potential. ;

[0026] According to another embodiment, a photovoltaic power station according to the invention may comprise N (N>1) groups of modules, each group comprising several photovoltaic modules, the modules of each group being connected in parallel to a connection box, the different connection boxes being connected in series; for example, each of these boxes comprises a first terminal block, a second terminal block, and a ground terminal block, the low voltage outputs of each module of the same group being connected to the first terminal block of the associated connection box, the high voltage outputs of each module of the same group being connected to the second terminal block of said connection box; possibly the frames or chassis of each module of the same group may be connected to the ground terminal block of said connection box, which may be for example connected to the first terminal block or to the second terminal block of the group or of the, or of a, previous or following connection box in the series.

[0027] According to a variant of the preceding example, each group of the N (N>1) groups of modules is made up of several parallel-connected strings of modules, each string comprising a set of modules mounted in series. These strings are connected in parallel to said first and second terminal blocks as in the preceding embodiment. Within a given group, the frames or chassis of all the modules constituting each string may optionally be connected to the ground terminal block of the connection box of the group, which may for example be connected to the first terminal block or to the second terminal block of the group or of the, or of a, previous or following connection box in the series.Alternatively, said ground terminal block may possibly be connected to one of the input or output potentials of one of the modules in the group, or of a previous or following group in the series, thus providing access to an intermediate potential between the potential of the first terminal block or the second terminal block of the different groups.

[0028] Each connection box can itself be connected to a DC / DC or DC / AC converter.

[0029] When each converter is of DC / DC type, the set of converters can be connected in series and the low voltage and high voltage terminals of this set of DC / DC converters can be connected to a DC / AC converter.

[0030] For a power station according to the invention comprising several (for example 3) sets, each of several groups of several photovoltaic modules, each converter can be of the DC / AC type, the converters of each set being able to be connected in series and to one of the lines of an electrical network, for example a medium voltage network.

[0031] A photovoltaic power station according to the invention may further comprise means of electrical insulation between two different groups of modules.

[0032] The invention also relates to a method of operating a photovoltaic power plant as defined by the subject matter of claim 9.

[0033] According to examples useful for understanding the invention, the frame or chassis of at least one photovoltaic module is carried: at the high potential or the low potential, or at an intermediate potential between this high potential and this low potential, of a module or, respectively, of a module of a chain or of a module of a group, which does not immediately precede or follow, in the series, said module or, respectively, said chain to which said module belongs or said group to which said module belongs; or at the high potential or the low potential, or at an intermediate potential between this high potential and this low potential, of said module or, respectively, of a chain or a group, comprising said module, or which immediately precedes or follows, in the series, said module or, respectively, said chain to which said module belongs or said group to which said module belongs; or at a potential substantially equal to half the potential of the chain in which said module is located, preferably when all the frames of the modules of the chain are at the same potential.

[0034] In a particular example, the frame or chassis of said at least one photovoltaic module can advantageously be connected to a potential of a module or a string or a group of the photovoltaic power plant, lower than the low potential V b of said module by a value equal to at most 600V (in other words: between V b - 600 V and V b ) or higher than the high potential V h of said module by a value equal to at most 600V (in other words: between V h + 600 V and V h ).

[0035] In a process the photovoltaic power plant can include: N photovoltaic modules forming a chain or N chains of photovoltaic modules, in which the frames of all the modules of at least one same chain can be connected to the same potential; and / or N photovoltaic modules forming a chain or N chains of photovoltaic modules, said at least one module belonging to a chain of K modules and being for example brought to an intermediate potential between the high potential and the low potential of the chain; according to a particular embodiment this intermediate potential can be the high potential or the low potential of the module of rank K / 2+1 or K / 2-1 if the number K is even and of rank (K+1) / 2 or (K-1) / 2 if the number K is odd.

[0036] In the case where the photovoltaic power station comprises N groups of photovoltaic modules, the modules of each group being connected in parallel to a connection box, the different connection boxes being connected in series, the frames or chassis of each module of the same group can be brought to a potential equal to the high potential or the low potential, or to an intermediate potential between this high potential and this low potential, of said group, or of a group of modules connected to the, or to a, previous or following connection box in the series.

[0037] For example, if each connection means comprises a connection box, comprising a first terminal block, a second terminal block, and a ground terminal block, the low voltage outputs of each module of the same group can be connected to the first terminal block of the associated connection box, the high outputs of each module of the same group can be connected to the second terminal block of said connection box; the frames or chassis of each module of the same group can be brought to a potential equal to the high potential or the low potential, or to an intermediate potential between this high potential and this low potential, of said group or of the, or of a, previous or following connection box in the series.

[0038] In such a method, each connection box can itself be connected to a DC / DC or DC / AC converter.

[0039] In case each converter is of DC / DC type, all the converters can be connected in series and the low voltage and high voltage terminals of this set of converters can be connected to a DC / AC converter.

[0040] In the case where the photovoltaic power station comprises several, for example 3, sets of groups of several photovoltaic modules, each converter can be of the DC / AC type, the converters of each set being connected in series and to one of the lines of an electrical network, for example a medium voltage network. BRÈVE DESCRIPTION DES DESSINS

[0041] THE figures 1A-1B schematically represent photovoltaic installations of known type, The figure 2 represents an embodiment of a known photovoltaic module, The figure 3A schematically represents a structure of a known photovoltaic installation, comprising 3 photovoltaic modules or 3 strings of photovoltaic modules and numerical examples of voltages, The figure 3B illustrates a breakdown problem in a known photovoltaic installation; The figure 4A represents an embodiment of several strings of photovoltaic modules connected in series according to the invention, The figure 4B represents another embodiment of several strings of photovoltaic modules connected in series according to the invention; The figure 5 represents an embodiment of a photovoltaic power station according to the invention, comprising several groups of photovoltaic modules, each group comprising several photovoltaic modules, The figure 6 represents another embodiment of a photovoltaic power station according to the invention, comprising several assemblies, each of these assemblies comprising several groups of photovoltaic modules, each group comprising several photovoltaic modules. DESCRIPTION DES MODES DE RÉALISATION

[0042] An example of a first embodiment of the invention is shown in figure 4A In this example, N strings 20, 22, 24 of photovoltaic modules are connected in series by connection means 27, 29.

[0043] Each string consists of several, for example, about 30 to 40, photovoltaic modules, connected in series. In this example: N = 3, but N can be higher than 3. Such a field of photovoltaic modules can, for example, consist of between 30 and 300 modules connected in series for each string, with N between 2 and 10.

[0044] The voltage across each string can be between 600 V and 15 kV (for example 1.5 kV or 3 kV or 10 kV).

[0045] Each chain has an input (or lower) potential, or an input pad or point or terminal, intended to be connected to such an input potential, and an output (or higher) potential, or an output pad or point or terminal intended to be connected to such an output potential.

[0046] Each module of each chain can have the structure described above in relation to the figure 2 . But, here, the frame or chassis of each module is not grounded (except possibly all or part of the modules of the 1st string of the series, whose metallic mass can be grounded), but at a non-zero potential defined by the same string or another string, for example the previous string: thus, in figure 4A , the frames or chassis 24c of all the modules in chain 24 are at the input potential of chain 24 (which is also here the output potential of chain 22), and the frames or chassis 22c of all the modules in chain 22 are at the input potential of chain 22 (which is also here the output potential of chain 20). Thus, the potential of the metal masses (or frames or chassis) can increase as the output voltages of the module chains are added. We also see in the example of the figure 4A the connection 20 1 , 22 1 , 24 1 between the frame or chassis and the input terminal of the corresponding chain.

[0047] In practice, the frame or chassis of at least one module, or of each module, of chain no. i (for 2≤i≤N) is connected to the output potential of the previous chain of modules (no. i-1 in the series).

[0048] In an example not covered by the invention, the frame or chassis of at least one module, or of each module, of chain no. i (1≤i≤N) can for example be connected to the output potential of the chain of modules no. i itself, or to the input potential of this same chain of modules no. i, or to a potential between the output potential and the input potential of this chain no. i.

[0049] Alternatively, the frame or chassis of each module of chain no. i (in particular for 2≤i≤N) may for example be placed or connected to the output potential or the input potential, or to a potential between this output potential and this input potential, of any preceding chain of modules (no. i-1 to no. 2 or to no. 1 in the series); for example, if i is even, this may be the output or input potential, or an intermediate potential, of the chain of rank i / 2 or of rank (i / 2) + 1 or or of rank (i / 2) - 1; or, if i is odd, this may be the output or input potential, or an intermediate potential, of the chain of rank (i-1) / 2 or (i+1) / 2. In other words, it is not necessarily a potential associated with the immediately preceding chain i-1.

[0050] Alternatively, the frame or chassis of a module chain no. i (1≤i <N) peut par exemple être relié au potentiel de sortie ou au potentiel d'entrée, ou encore à un potentiel compris entre ce potentiel de sortie et ce potentiel d'entrée, de la chaîne i+1 de modules suivante ou d'une chaîne de modules suivante (avec un n° ≥ i+1 dans la série). Autrement dit, il ne s'agit pas nécessairement d'un potentiel associé à la chaîne immédiatement suivante i+1.

[0051] Connecting the frame or chassis of a module of a string n°i to a potential of a module or string of rank higher than i in the series makes it possible to generate, in said module of string i, an electric field which will, in this module of this string, reverse the direction of migration of the ionic elements which are the cause of the "shunt" effect on the surface of each cell of the module. This solution can make it possible to regenerate already "sick" modules and / or to clean the surface of the cells without altering the operation of the modules. This solution makes it possible to reverse the PID phenomena, while allowing the production of the panels to be maintained simultaneously.

[0052] In a particular case, all the frames or chassis of the modules of a given chain i which comprises K modules are connected to the output potential or to the input potential of a module of the chain, preferably of rank K / 2 if K even or (K-1) / 2 or (K+1) / 2 if K odd. The effects are those which have been described above.

[0053] If we take the numerical examples of tensions of the figure 4A , and assuming as shown all the frames of the modules of a given chain at the same potential, the frame of a module of the chain 22 is brought to 1500 V (voltage defined by the output voltage of the chain 20) and the frame of a module of the chain 24 is brought to 3000 V (voltage defined by the output voltage of the chain 22). The connection means 27, 29 between two chains of modules may comprise a connecting cable or wire, for example between two connection boxes (or "string combiner boxes") of the chains concerned.

[0054] This allows a reduced potential difference to be established between cells 6, 8 ( figure 2 ) of each module and the frame 15 or the chassis of this same module. The cells 6, 8 are only subjected to a potential difference, with the frame 15, which is reduced compared to that which appears, in the known configuration (connection of the frame to the ground). Thus, the phenomena of ionic migration type and / or accumulation of salts on the surface of the cells, and the “PID” effect, are greatly reduced or eliminated. A possible breakdown of the insulating layers, or the appearance of an electric arc is also avoided. For example, in the configuration of the figure 3A , in which each of the frames or chassis of the modules is grounded (0 V), the potential difference between the cells of the string 18 of modules and the frames of these modules can reach 3000 V, and that between the cells of the string 19 of modules and the frames of these modules can reach 4500 V. In the structure according to the invention ( figure 4A And figure 4B ), the potential difference between the cells of the string 22 of modules and the frame of the modules of this string can only reach 1500 V, and that between the cells of the string 24 of modules and the frame of these modules can also only reach 1500 V.

[0055] What has been explained above can also be applied, with the same effects, to a single chain of N modules connected in series, in which a frame or chassis of at least one module i among these N modules, or the frame or chassis of each module i among these N modules, is connected to a non-zero voltage, input or output, of said module i or of another module of the chain which can be: the module immediately preceding i-1 or a module of rank strictly lower than i-1, in particular for 1 <i≤N ; le module immédiatement suivant i+1 ou un module de rang strictement supérieur à i+1, notamment pour 1≤i<N.

[0056] One or more chain(s) of modules such as that described above, in particular in connection with the figure 4A , may or may be used in a system such as that shown in figure 1A ou 1B .

[0057] Another example of an embodiment of the invention is shown in figure 4B . As in the example of the figure 4A : N strings 20, 22, 24 of photovoltaic modules are connected in series, each string possibly comprising several, for example approximately 30 to 40, photovoltaic modules, connected in series; in this example: N = 3, but N may be higher than 3. Such a field of photovoltaic modules may for example comprise between 30 and 300 modules connected in series for each string, with N between 2 and 10; the voltage across each string may be between 600 V and 15 kV (for example 1.5 kV or 3 kV or 10 kV).

[0058] Each chain has an input (or lower) potential, or an input pad or point or terminal, intended to be connected to such an input potential, and an output (or higher) potential, or an output pad or point or terminal intended to be connected to such an output potential.

[0059] Each module of each chain can have the structure described above in relation to the figure 2 . But, here, the frame or chassis of each module is not grounded (except possibly all or part of the modules of the 1st chain of the series, whose metallic mass can be grounded), but at a non-zero potential defined by the input potential of the same module (which is also here the output potential of the previous module): thus, in figure 4B , the frames or chassis 24c of all the modules of the string 24 are at the input potential of the string 24 which is also the output potential of the string 22, and the frames or chassis 22c of all the modules of the string 22 are at the input potential of the string 22 which is also the output potential of the string 20. Thus, the potential of the metal masses (or of the frames or chassis) increases as the output voltages of the strings of modules are added. In addition, here, the voltage of the cells or of each module relative to the frames or to the carcass does not exceed 1500 V. The references 27 1 and 29 1 designate the connections between 2 neighboring strings. We also see in the example of the figure 4B the connection 20 1 , 22 1 , 24 1 between the frame or chassis 20c, 22c, 24c and the input terminal of the corresponding chain.

[0060] There figure 5 represents an example of another embodiment of the invention, in which a set 100 of N groups 40, 42, 44, 46 of modules; in this example: N = 4, but N can be any, for example up to N = 10, each group of modules comprising a number of modules which can be for example less than or equal to 20000. Here, the modules of the same group are connected in parallel. These groups 40, 42, 44, 46 of modules are connected to DC / DC converters (MPPT functions) 50, 52, 54, 56 without integrated transformers, placed in series so as to obtain the necessary voltage (for example: 45kV DC to be able to inject the desired power into a network 60 at medium voltage (for example: 20kV AC). Thus the groups of modules are also placed in series.

[0061] Each group i (1 <i≤N) de modules [sauf le 1 er< groupe (i=1) de modules de la série de N groupes, dont la masse peut éventuellement être mise à la terre] est connecté à un boîtier de raccordement de chaîne 41, 43, 45, 47, lequel comporte un premier bornier 41 1 , 43 1 , 45 1 , 47 1 pour connecter la polarité (-) de chaque module du groupe, un deuxième bornier 41 2 , 43 2 ,45 2 , 47 2 , pour connecter la polarité (+) de chaque module du groupe, et un troisième bornier, ou barrette de masse, 41 3 , 43 3 , 45 3 , 47 3 pour éventuellement connecter la masse électrique de chaque module du groupe.

[0062] The terminals (+) and (-) of each box can be connected to the input terminals of a DC / DC converter 50, 52, 54, 56. All the DC / DC converters can be connected in series and the 2 polarities (+) and (-) of the series converter chain can be connected to a 62 DC / AC converter, for example of the “Modular Multilevel Converter” or “Stacked Multilevel Converter” or “Flying Capacitor Multilevel Converter” type.

[0063] Each frame of a module can be connected to the input terminal (+) 41 1 , resp. 43 1 , 45 1 , 47 1 of the connection box of the group of modules to which it belongs, by means, for example by a cable, of connection 41 4 ,43 4 ,45 4 , 47 4 . In other words, similarly to what has been explained above, the metal mass of each module of group no. i is not grounded, but at a non-zero potential defined by the input (or low) potential of group no. i of modules to which this module belongs and / or by the input terminal of the corresponding DC / DC converter so as to create a successive voltage rise of the potential of the metal masses. The protective effect of the cells 6, 8 of each module is that already presented above.

[0064] In this example, the upper floor, raised to 45kV, must support a standard insulation level where commercial modules can be used (class 600V, 1000V or 1500V). In variants (not shown) not necessarily covered by the subject of the claims the metal mass of each module of group No. i may be brought to the low potential of the preceding group of modules; or a ground bar of a connection box may be connected to the terminal block (+) (high potential) or to the terminal block (-) (low potential), of a connection box of a preceding group of modules, by means of connection, for example a cable; but this preceding connection box is not necessarily the one which immediately precedes, in the series, the connection box considered; or a ground bar of a connection box may be connected to the terminal block (+)(high potential) or to the terminal block (-) (low potential), of a connection box of a following group of modules by means, for example a cable, of connection 43 4 ,45 4 , 47 4 ; but this preceding connection box is not necessarily the one which immediately follows, in the series, the connection box considered;or a ground bar of a junction box can be connected to the (+) terminal block (high potential) or to the (-) terminal block (low potential) of the module group i itself. ;

[0065] The principles set out above remain applicable if the groups 40, 42, 44, 46 each consist of several strings of modules connected in parallel, each string comprising a set of modules in series. It is then the strings which are connected in parallel on the first terminal blocks and second terminal blocks. All the frames of the modules of a group can then be set to the same potential by a connection to the ground terminal block of the group, itself being able to be set to a non-zero potential according to the principles previously explained.

[0066] In the embodiment illustrated in figure 6 , each of the 3 sets 100 1 , 100 2 , 100 3 of N (in this example: N = 4, but N can be any) groups 40, 42, 44, 46 of modules. For reasons of clarity, only the modules of the 1st set 100 1 and the elements to which they are connected are numbered in the figure. Each of these sets is connected to a line L 1 , L 2 , L 3 of a network, for example a medium voltage network of the HTA type. Each set is identical to that described in connection with the figure 5 , except for the 50', 52', 54', 56' converters which are here of the DC / AC type.

[0067] The N groups 40, 42, 44, 46 of each of the 3 sets 100 1 , 100 2 , 100 3 are connected in series via DC / AC converters 50', 52', 54', 56', which are themselves connected to the lines L 1 , L 2 , L 3 of a network, for example a medium voltage network of the HTA type.

[0068] Within each of the sets 100 1 , 100 2 , or 100 3 , the connection of the frames or chassis of the N groups of modules can be as follows (already described above): each frame or chassis of each group no. i (1 <i≤N) dans la série peut être au potentiel d'entrée de ce groupe i et / ou du convertisseurs DC / AC correspondant 50', 52', 54', 56'. Là encore, l'effet de protection des cellules de chaque module est celui déjà présenté ci-dessus.

[0069] Alternatively (not shown), within each of the sets 100 1 , 100 2 , or 100 3 , the connection of the masses of the N groups of modules is as follows (already described above): the common mass of each group no. i (1 <i≤N) dans la série est au potentiel du groupe (i-1) qui précède (et dont la tension de sortie est inférieure à celle des modules du groupe considéré). Là encore, l'effet de protection des cellules de chaque module est celui déjà présenté ci-dessus.

[0070] The variant explained for the figure 5 , in which the parallel-connected modules within each group are replaced by parallel-connected strings of modules remains applicable here as well.

[0071] As understood from the above description, all of the metal masses of a group (or chain) of modules according to the invention are not connected to the metal masses of another group or chain of modules.

[0072] It is therefore preferable to install insulating means such as: http: / / www.teknomega.com / components-for-panel-boards / low-voltage-insulators / low-voltage-insulators-comprhex.kl or insulating materials such as PVC, Bakelite, Cardboard, Rubber, as well as most plastics, between the supporting structures of two different groups of modules, the sizing of which will be adapted according to the structure and its configuration.

[0073] The structures of the figures 5 And 6 allow to avoid transformers between the network lines and the modules.

[0074] The invention is suitable for the construction of solar power plants with a capacity of up to 10 MW and more, and even beyond 1 GW.

Claims

1. Photovoltaic unit including N photovoltaic modules or N chains (20, 22, 24) of photovoltaic modules or N groups (40, 42, 44, 46) of photovoltaic modules, with N>1, connected in series, each module including a frame (20c, 22c, 24c) or chassis, and connection means (23, 25, 27, 29, 434, 454, 474), characterised in that the connection means connect the frame or chassis of at least one module to a connection point of a module or of a chain or of a group of the photovoltaic unit, which is the high-potential point of the model, or of the chain or of the group that precedes, in the series, said at least one module or the chain to which said at least one module belongs or the group to which said at least one module belongs.

2. Photovoltaic unit according to claim 1, including N photovoltaic modules forming a chain or N chains (20, 22, 24) of photovoltaic modules, wherein the frames of all the modules of one and the same chain are at the same potential.

3. Photovoltaic unit according to claim 1, including N groups (40, 42, 44, 46) of photovoltaic modules, connected in series, the modules of each group being connected in parallel to connection means (41, 43, 45, 47), including a first terminal block (411, 431, 451, 471), a second terminal block (412, 432, 452, 472), and an earth terminal block (413, 433, 453, 473), the low-voltage outputs of each module of one and the same group being connected to the first terminal block of the associated connection box, the high outputs of each module of one and the same group being connected to the second terminal block of said connection box4. Photovoltaic unit according to claim 3, each connection box being itself connected to a DC / DC converter (50, 52, 54, 56) or DC / AC converter (50', 52', 54', 56').

5. Photovoltaic unit according to claim 4, each converter being of the DC / DC type (50, 52, 54, 56), all of these converters being connected in series and the low-voltage and high-voltage terminals of this set of converters being connected to a DC / AC converter (62).

6. Photovoltaic unit according to claim 4, including a plurality of sets (1001, 1002, 1003) of groups (40, 42, 44, 46) of several photovoltaic modules, each converter being of the DC / AC type (50', 52', 54', 56'), the converters of each set being connected in series and to one of the lines (L1, L2, L3) of an electrical network, for example a medium-voltage network.

7. Photovoltaic unit according to claim 6, including three sets (1001, 1002, 1003) of groups (40, 42, 44, 46) of photovoltaic modules.

8. Photovoltaic unit according to one of claims 3 to 7, furthermore including means of electrical isolation between two groups of different modules.

9. Method for operating a photovoltaic unit, including N photovoltaic modules or N chains (20, 22, 24) of photovoltaic modules or N groups (40, 42, 44, 46) of photovoltaic modules, with N>1, connected in series, each module including a frame (20c, 22c, 24c) or chassis, method wherein there is applied, to the frame (20c, 22c, 204c) or chassis of at least one module, a potential equal to the high potential of the module or of the chain or of the group of modules of the unit that immediately precedes, in the series, said at least one module or the chain to which said at least one module belongs or the group to which said at least one module belongs.

10. Method according to claim 9, the photovoltaic unit including N photovoltaic modules forming a chain or N chains (20, 22, 24) of photovoltaic modules, wherein the frames of all the modules of one and the same chain are at the same potential.

11. Method according to one of claims 9 or 10, wherein the photovoltaic unit comprises N groups (40, 42, 44, 46) of photovoltaic modules, connected in series, the modules of each group being connected in parallel to connection means (41, 43, 45, 47), including a first terminal block (411, 431, 451, 471), a second terminal block (412, 432, 452, 472), and an earth terminal block (413, 433, 453, 473), the low-voltage outputs of each module of one and the same group being connected to the first terminal block of the associated connection box, the high-voltage outputs of each module of one and the same group being connected to the second terminal block of said connection box, the frames or chassis of each module of one and the same group being connected to the earth terminal block of said connection box.

12. Method according to claim 11, each connection box being itself connected to a DC / DC converter (50, 52, 54, 56) or DC / AC converter (50', 52', 54', 56').

13. Method according to claim 12, each converter being of the DC / DC type (50, 52, 54, 56), all of these converters being connected in series and the low-voltage and high-voltage terminals of this set of converters being connected to a DC / AC converter (62).

14. Method according to claim 13, the photovoltaic unit including a plurality of sets (1001, 1002, 1003) of groups (40, 42, 44, 46) of several photovoltaic modules, each converter being of the DC / AC type (50', 52', 54', 56'), the converters of each set being connected in series and to one of the lines (L1, L2, L3) of an electrical network, for example a medium-voltage network.

15. Method according to claim 14, the photovoltaic unit including three sets (1001, 1002, 1003) of groups (40, 42, 44, 46) of photovoltaic modules.