DE102020126263A1 - Photovoltaic device and computer program therefor - Google Patents

Abstract

A photovoltaic device with a number of photovoltaic modules (1) is described, each of which has a number of interconnected photovoltaic cells (2). The photovoltaic modules (1) each have a DC step-up converter (3), which is set up to step up the primary voltage (U_in) provided by the interconnected photovoltaic cells (2) to a secondary voltage (U_out) provided at a secondary voltage output of the step-up converter (3). The secondary voltage outputs of the step-up converter (3) of several photovoltaic modules (1) are interconnected on a common voltage supply bus line (S). The voltage supply bus line (S) has a neutral conductor (M), with a first group of photovoltaic modules (1) with the negative pole of the secondary voltage outputs of their step-up converters (3) being connected to the neutral conductor (M) and a second group of photovoltaic modules (1) with the positive pole Pole of the secondary voltage outputs of their step-up converter (3) are connected to the neutral conductor (M).

Description

The invention relates to a photovoltaic device and having a plurality of photovoltaic modules, each of which has a number of interconnected photovoltaic cells. The photovoltaic modules each have a DC voltage step-up converter which is set up to step up the primary voltage provided by the interconnected photovoltaic cells to a secondary voltage provided at a secondary voltage output of the step-up converter. The secondary voltage outputs of the step-up converters of several photovoltaic modules are interconnected on a common voltage supply bus line.

The invention also relates to a computer program with program code means for setting a variable secondary voltage of step-up converters of photovoltaic modules of such a photovoltaic device.

WO 2013/170958 A2 discloses an assembly of a system for generating a direct or alternating current with photovoltaic modules connected together in several strings. Several strings of photovoltaic modules are connected in parallel to a junction box with a step-up converter whose DC output voltage is higher than the DC input voltage of the strings connected in parallel.

This means that junction boxes equipped with step-up converters do not have to be provided for each photovoltaic module.

EP 2 911 284 B1 discloses a circuit arrangement for tapping electrical power from a number of photovoltaic module strings with a matching circuit that has a number of separate inputs to which a respective electrical potential point of each module string is present. The matching circuit controls or regulates an adjusted second output potential point at its output in such a way that an output current of the matching circuit essentially corresponds to the sum of the individual module currents and the output voltage of the matching circuit is between the maximum individual module string voltage and the lowest individual module string voltage. The individual module string voltages are the actual electrical power provided by the individual module strings, which are tapped directly without intermediate step-down or step-up converters. The output voltage provided by the matching circuit can be tapped off by inverters, battery chargers, DC-DC converters and the like.

US 2015/0349533 A1 describes a photovoltaic system in which photovoltaic modules, which contain several photovoltaic cells, are connected to an energy store. The energy storage device has several energy storage elements connected in series and in parallel, as well as controllable coupling elements, which form a step-up or step-down converter.

WO 2008/154918 A1 describes a transformerless inverter unit for thin-film solar panels that is intended to prevent corrosion damage. The transformerless inverter unit has a single-ended boost converter and an inverter, with the positive solar cell terminal connected directly to the positive input of the inverter and the boost converter connected in the connection between the negative solar cell terminal and the negative input of the inverter. The step-up converter is controlled in such a way that the voltage at the negative solar cell connection is positive compared to a specified voltage, so that the maximum occurrence of negative potentials on the solar cells is reduced and the promotion or acceleration of corrosion is correspondingly lower.

DE 10 2017 115 000 A1 describes a photovoltaic unit with a photovoltaic module, a controllable step-up converter and a control unit for controlling the step-up converter so that it is operated resonantly. This means that the efficiency of the photovoltaic unit can be kept very high over almost the entire working range. The photovoltaic modules are connected in parallel to a two-wire bus with the outputs of their step-up converters (ie step-up converters), with inverters being clamped to the two-wire bus between groups of photovoltaic modules.

Proceeding from this, it is the object of the present invention to create an improved photovoltaic device with a plurality of photovoltaic modules.

The object is achieved with the photovoltaic device having the features of claim 1 and by the computer program having the features of claim 11 .

Advantageous embodiments are described in the dependent claims.

For a generic photovoltaic device, it is proposed that the voltage supply bus line has a neutral conductor, with a first group of photovoltaic modules having the negative pole of the secondary voltage outputs of their step-up converter connected to the neutral conductor and a second group of photovoltaic modules connected to the positive pole of the secondary voltage transitions of their step-up converters are connected to the neutral conductor.

This creates a voltage supply bus line which, in relation to the potential on the neutral conductor, has a positive voltage potential on the one hand and a negative voltage potential on the other. In this case, a negative voltage potential does not necessarily have to be present on the photovoltaic modules themselves in relation to the ground potential. This solution improves the current-carrying capacity of the power supply bus line, since only the differential current of the two groups of photovoltaic modules flows via the neutral conductor. This means that a second return conductor can be saved and the wiring work can be considerably simplified.

The use of a DC step-up converter (i.e. a step-up converter) in each photovoltaic module ensures that each photovoltaic module can be operated optimally at its highest efficiency with its individual operating point, which changes over time, among other things, with the service life and depending on the available radiation energy.

The photovoltaic device according to the invention provides a scalable, modular and unstructured energy supply system using photovoltaics, which can be expanded very easily via the voltage supply bus line with a common neutral conductor and can be moved locally without great effort. The use of a common neutral conductor for several groups of photovoltaic modules reduces the amount of wiring and thus also the amount of copper cables. In addition, this makes it possible to double the total voltage potential on the voltage supply bus line for a DC voltage converter, inverter or energy store connected to it.

The same voltage step-up converter can advantageously be operated in resonant mode. This means that the efficiency of the photovoltaic modules can be kept very high over almost their entire working range. In the resonance mode, the step-up converters are operated with a specific switching frequency or switching dead time, which may depend on the operating point, in such a way that the energy drawn from the photovoltaic module assumes the maximum possible value. For this purpose, the current of the photovoltaic module can be set in such a way that the energy yield of the photovoltaic module is as maximum as possible for a given radiation intensity.

The photovoltaic modules can have a control unit for controlling the step-up converter or be connected to one, the control unit for controlling the at least one associated step-up converter by setting the switching frequency, the pulse width and the dead time depending on the primary voltage and the primary current of the interconnected photovoltaic cells of a photovoltaic module is formed at the input of the step-up converter to be regulated, and the secondary output voltage at the output of the step-up converter to be regulated.

The power supply bus line, which carries a base potential on the neutral conductor and a related positive and negative voltage potential on a number of other conductors, can be connected to an electrical energy store. In addition or as an alternative to this, the voltage supply bus line can be connected to a DC voltage converter for converting the DC voltage potentials present on the voltage supply bus line into a DC voltage of a low-voltage DC network that is higher in this regard.

The voltage supply bus line thus provides what is known as a protective extra-low voltage system with regard to the low-voltage direct current network, which allows simple and safe wiring.

The low-voltage direct current network can be connected to a low-voltage inverter for converting the direct voltage of the low-voltage direct current network into an alternating voltage for an alternating current or three-phase network. This can be a standard three-phase system, for example. It is conceivable, for example, that a low-voltage direct current system with a voltage potential of around ±750 V is converted into an alternating current or three-phase low-voltage network with a normal mains voltage of, for example, 230 V (single-phase) or 400 V (three-phase).

It is conceivable that the power supply bus line is connected to a bus voltage inverter for converting the DC voltage on the power supply bus line into an AC voltage of an AC or three-phase network. This can in turn be a standard alternating current system or standard three-phase system of a low-voltage network.

It is conceivable that the AC or three-phase network is supplied with both a low-voltage inverter and a bus-voltage inverter, which are connected in parallel to one another.

The low-voltage inverter and/or the bus voltage inverter can be designed to convert a positive DC voltage and negative DC voltage with respect to the voltage potential of the neutral conductor of the voltage supply bus line to a single-phase AC voltage or polyphase three-phase voltage. By providing both a positive DC voltage and a negative DC voltage, the alternating direction can be simplified and a double voltage potential is provided compared to the simple parallel connection of a group of photovoltaic modules. The voltage potential present on the neutral conductor can be combined with the voltage potential of a neutral conductor of the AC or three-phase network.

It is particularly advantageous if several sections of this voltage supply bus line branch off from the electrical energy store and/or the DC voltage converter and/or the low-voltage inverter and/or the bus voltage inverter on a voltage supply bus line, to which several photovoltaic modules are connected in parallel. This ensures that the current load on the lines of the voltage supply bus line is distributed evenly over the sections and the required line cross-section can thus be kept as small as possible. This saves resources and costs for the line and simplifies the handling of the multi-core power supply bus line.

The photovoltaic device can be used to adjust the variable secondary voltage of the step-up converters of the group of photovoltaic modules connected together on a common voltage supply bus line to a level above the greatest primary voltage at the input of the step-up converter of a photovoltaic module of a group connected together on the common voltage supply bus line, which has the highest voltage value in the group of photovoltaic modules, be trained. This ensures that the photovoltaic modules are each operated with their optimum efficiency. This succeeds in particular when using resonant step-up converters, which convert the photovoltaic voltage of their respective photovoltaic module to a higher level. The step-up converters set the current of their photovoltaic module in such a way that the energy yield is maximum for a given radiation intensity. The secondary voltage of the step-up converter can initially be kept variable, with the secondary voltage advantageously being kept only slightly above the highest output voltage of the photovoltaic module of the photovoltaic device that is most intensively irradiated. The secondary voltage of the step-up converter will be at a value with which it is still possible to set the maximum energy yield of the best photovoltaic module. The step-up converters can be parameterized accordingly so that their output voltage cannot rise above a corresponding maximum.

This can advantageously be achieved using a computer program with program code means for setting a variable secondary voltage of step-up converters of photovoltaic modules of a photovoltaic device if the computer program is executed on a data processing unit, the program code means for determining the greatest primary voltage from the individual available primary voltages of the photovoltaic modules which are connected to a common Voltage supply bus line are interconnected and form a group, and is set up to set the variable secondary voltage of the step-up converter of the photovoltaic modules of this group to a voltage value above the determined largest primary voltage.

• 1 - Skizze einer Photovoltaikeinrichtung mit mehreren Photovoltaikmodulen;
• 2 - schematische Darstellung eines Photovoltaikmoduls mit Photovoltaikzellen und einem Hochsetzsteller.

The invention is explained in more detail below using an exemplary embodiment with the attached drawing. Show it:

• 1 - Sketch of a photovoltaic device with several photovoltaic modules;
• 2 - Schematic representation of a photovoltaic module with photovoltaic cells and a step-up converter.

1 shows a sketch of a photovoltaic device with several photovoltaic modules 1, which are interconnected to form groups on a common voltage supply bus line S.

In a manner known per se, the photovoltaic modules 1 have one or more photovoltaic cells 2 which are connected together in parallel or in series.

It can also be seen that the photovoltaic modules 1 each have a direct voltage step-up converter 3 (DC/DC), which is set up to step up the primary voltage provided by the interconnected photovoltaic cells 2 to a secondary voltage provided at a secondary voltage output of the step-up converter 3.

The DC step-up converters 3 are also known in the art as step-up controllers.

The photovoltaic modules 1 are connected to the outputs of their step-up converters 3 at a common Power supply bus line S connected. It can be seen that all photovoltaic modules 1, which are connected to a common (multi-wire or multiple-conductor) power supply bus line S, are clamped to a common neutral conductor M with an output of their step-up converter 3. A first group of photovoltaic modules 1 with its positive pole (i.e. the connection pole with a positive voltage potential in relation to the other connection pole or ground) of its direct voltage output and a second group of photovoltaic modules 1 with its negative pole (ie the connection pole with a negative voltage potential in relation to the other connection pole or ground) connected to the neutral conductor M. This is in the 1 recognizable by the fact that the two groups of four of photovoltaic modules 1 on the upper side of the voltage supply bus line S are connected to the neutral line M with their right connection (bottom right) of the respective step-up converter 3, while the lower two groups of four of photovoltaic modules 1 with their connection of their step-up converter 3 which is different in comparison thereto (represented by the mirrored arrangement as the connection at the top right, with the same orientation as the upper photovoltaic modules, however, the connection at the bottom left).

It can be seen that the multi-conductor power supply bus line S has two lines for a positive voltage potential (e.g. +48 volts) and two lines for a negative voltage potential (e.g. -48 volts). However, this can also be a common line with a sufficient line cross-section for the positive voltage potential (plus) and a common line for the negative voltage potential (minus). A further division into three or more conductors per voltage potential is also conceivable. This depends on the cable cross-section and the maximum current load to be expected on the respective cable.

By connecting the photovoltaic modules 1 in groups on the one hand with their positive connection pole and on the other hand with their negative connection pole to a common neutral conductor M, the currents cancel out there, so that only a residual current flows on the neutral conductor M. As a result, there is a significantly lower differential current in relation to the total current, so that the cable cross-section can be significantly reduced.

It can also be seen that the voltage supply bus line S is divided into a right and a left section. Between two groups of four of photovoltaic modules 1, for example, there can be a direct voltage converter 4 (DC/DC) for converting the direct voltage present on the voltage supply bus line S of ±48 volts (safety extra-low voltage) into a higher direct voltage, for example of ±750 volts of a low-voltage direct current network B be connected to the power supply bus line S. For this purpose, the neutral conductor M and the conductors for the positive voltage potential +48 volts and for the negative voltage potential -48 volts of the safety extra-low voltage bus system are connected to the primary input of the DC-DC converter 4 on the one hand. The secondary output of the DC voltage converter 4 is connected on the one hand to a base conductor B for a base potential of, for example, zero volts and to potential conductors for the positive and negative DC voltage potentials of, for example, ±750 volts.

It goes without saying that any number of photovoltaic modules 1 can be connected per section of the voltage supply bus S. The number of photovoltaic modules 1 is limited to the available cable cross section.

It is thus conceivable that the voltage supply bus line S is continued to the right and/or left and has further photovoltaic modules 1 . In this case, between further groups of photovoltaic modules 1, further DC-DC converters 4 can be connected in parallel with the DC-DC converter 4, so that several sections of the voltage supply bus line S are connected in series.

However, it is also conceivable for the power supply bus line S to form a star-shaped network with a number of sections, in the middle of which there is a common DC-DC converter 4 .

Alternatively or in addition to the DC-DC converter 4, however, an electrical energy store 6 can also be connected to the voltage supply bus line S.

It can also be seen that a bus voltage inverter 5 for converting the DC voltage on the voltage supply bus line S into an AC voltage of an AC or three-phase network D is connected to the voltage supply bus line S. A bus voltage inverter 5 is provided here by way of example, which is only connected to a line L1 of an AC voltage potential and to the neutral conductor N and earth conductor PE. This bus voltage inverter 5 can have an energy store 6 as a buffer store. But it is also conceivable that the energy store 6 separately for buffering without Bus voltage inverter 5 is used. A storage battery arrangement or a capacitor arrangement, such as supercapacitors or a capacitive cascade, for example, is suitable as the energy store 6 .

If the photovoltaic unit is connected to a low-voltage direct-current network B via the direct-current converter 4, as outlined, a low-voltage inverter 7 can also be provided, which is used to convert the direct voltage of e.g. ±750 volts from the low-voltage direct-current network B into an alternating voltage or is set up in a three-phase voltage of a three-phase network D as shown.

Converters that convert a safety extra-low voltage in the range of approximately 42 volts to 60 volts into a low voltage by means of potential-separated conversion are suitable as DC-DC converters 4 . For example, resonant LL converters, LLC converters or CLLC converters, which can be operated with good efficiency, are suitable for this purpose. These can be designed to convert the protective DC voltage to a level that is just below the maximum permissible DC voltage value for low-voltage networks. In this way, individual systems can be connected to the safety extra-low voltage system over greater distances. Such a DC voltage network can be used, for example, to charge electric vehicles.

The low-voltage direct current network B can be used to supply several of the 1 to connect photovoltaic devices shown together. It is conceivable for the low-voltage direct current network B to be laid permanently to an agricultural farmstead or a transformer station in order to supply agricultural machines with energy from there and, if necessary, to use them as intermediate energy storage and to feed excess energy into a higher-level three-phase current supply network D.

The inverters and DC-DC converters mentioned above are commercially available and therefore do not need to be described in further detail.

Each individual photovoltaic module 1 contains a resonant step-up converter 3, which sets the photovoltaic voltage U_in of the photovoltaic module 1 to a higher level U_out. The step-up converter 3 adjusts the current I_in of the photovoltaic module 1 in such a way that the energy yield is maximum for a given radiation intensity. The secondary voltage U_out of the step-up converter 3 is initially kept variable. It makes sense to keep this secondary voltage U_out only slightly above the highest output voltage of the most intensely irradiated photovoltaic module 1 of the photovoltaic device. The secondary voltage U_out of the step-up converter 3 should therefore be at a value with which it is still possible to set the maximum energy yield of the best photovoltaic module 1. The step-up converter 3 can be parameterized accordingly so that the output voltage U_out cannot rise above a corresponding maximum. In principle, the secondary voltage U_out of the step-up converter 3 is variable.

If the photovoltaic modules 1 of a photovoltaic device have a different orientation (e.g. south, east, west), the photovoltaic device can still be operated with optimum efficiency. All photovoltaic modules 1 are wired in parallel to the common voltage supply bus line S for this purpose. In the morning, the feed-in from the photovoltaic modules 1 oriented to the east predominates. Towards noon, the photovoltaic modules 1 oriented to the east, west and predominantly the south, and towards the evening the photovoltaic modules 1 oriented to the west contribute to the energy yield. All photovoltaic modules 1 are optimally controlled by the integrated step-up converter 3 . If all alignments are now combined, the maximum expected performance can be calculated. The photovoltaic device can now be designed for the combined maximum power. As a result, a significantly higher utilization of the inverters 5, 7 and thus a significantly higher energy yield can be achieved over the day, since the conversion losses are significantly lower at higher utilization.

2 shows a schematic representation of a photovoltaic module 1 with one or more photovoltaic cells 2 and a step-up converter 3. The primary voltage at the input of the step-up converter 3 is designated as U_in and the primary current as I_in. The secondary voltage at the output of the step-up converter 3 is denoted by U_out.

It can be seen that the step-up converter 3 has a switching unit 8 which is designed, for example, as a semiconductor switch. The switching unit 8 can have an internal (parasitic) capacitance 8' and/or an additional capacitance connected in parallel. The switching unit 8, together with an inductance 9, leads to an LC-resonant behavior of the step-up converter 3. The step-up converter 3 also has a diode 10 and a storage capacitance 11.

By controlling the switching unit 8 via the parameters of the switching ratio PWM (pulse width modulation), the switching dead time t_tot and the Switching frequency f_s the step-up converter 3 is controlled in such a way that it is operated with a characteristic switching frequency and thus works resonantly. In this way, the primary current I_in taken from the interconnected photovoltaic cells 2 can be set in such a way that the transferred energy reaches a maximum value at the respective operating point or working point of the interconnected photovoltaic cells 2 . This resonant regulation can ensure that the energy yield of the entire photovoltaic module 1 is optimal and, in particular, is adapted to the working point that varies over time, which depends, among other things, on the radiation intensity, the temperature on the photovoltaic module 1 and the type of photovoltaic module 1 or the used photovoltaic cells 2 depends.

In this way, the control of several photovoltaic modules 1 can also be coordinated with one another in such a way that the photovoltaic modules 1 that work with different levels of efficiency, e.g.

With the photovoltaic device described above, the radiant energy of the sun can be converted into electrical energy in a highly efficient manner by photovoltaic cells 2 . This can be stored and/or converted into usable electrical energy. The photovoltaic modules 1 can be combined in a system with different orientations and shading, whereby even if the orientation of the individual photovoltaic modules 1 is not ideal, each individual photovoltaic module 1 can be operated optimally at its highest efficiency in its individual, time-varying operating point in order to achieve the available Convert radiant energy into electrical energy.

In particular, the photovoltaic device can be scaled with the common voltage supply bus line S, constructed in a modular manner and easily assembled and disassembled.

The photovoltaic device is therefore particularly suitable for use in agriculture. For sustainable cultivation of the fields, the soil must be given time to regenerate. In these regeneration phases, the soil can still contribute to the income of the commercial enterprise, in that the photovoltaic device described is set up during this time on the regenerating field for photovoltaic energy generation. The photovoltaic device can then be moved from year to year according to the crop rotation. The use of the voltage supply bus line with the safety extra-low voltage network system allows a structured coupling of different energy generation units and a modular design, which enable a controlled exchange of energy at their interfaces.

In this case, each individual photovoltaic module 1 can be placed depending on the structural boundary conditions without a special orientation being necessary. Voltages in the photovoltaic system only occur in the range of safety extra-low voltage, so that the photovoltaic system is safer for people. In systems with a combined orientation, the ratio of peak power to average power is significantly lower. Since the inverters 5, 7 always have to be designed for the peak power, the specific investment costs for the inverters 5, 7 in the photovoltaic device according to the invention are significantly lower. At the same time, statistically speaking, the inverters 5, 7 often work in a range that is favorable for their efficiency, as a result of which the conversion losses are minimized and the yield of the photovoltaic device is significantly increased. The photovoltaic device can be easily combined with a battery store without requiring separate power electronics for the battery store.

The photovoltaic device is also intrinsically safe, since the photovoltaic device can only feed into a common intermediate circuit if the voltage of the individual photovoltaic modules 1 is increased, since the secondary voltage of the step-up converter 3 is always kept above the lowest voltage of the photovoltaic modules 1 in a group. The individual photovoltaic modules 1 are decoupled by a diode 10 of the step-up converter 3.

The photovoltaic device can be expanded step by step at any time.

The cellular photovoltaic device shown offers a high level of reliability and can be quickly brought to any location and set up there by scaffolders or trained assistants. As an island system, the system can initially ensure local supply and then also contribute to relieving the stationary infrastructure via the corresponding interface. The photovoltaic device can be used, for example, in civil protection and can also be operated normally in the meantime.

Fast assembly of the photovoltaic device can be achieved by using modular standard components from scaffolding is grabbed. It should be noted that the cross braces are attached in such a way that there is a corresponding headroom. This enables mowers or mobile work machines to be operated under the photovoltaic system. The photovoltaic modules 1 can be pre-assembled on aluminum supports and pushed onto the scaffolding and connected to it by means of a truck with a lifting device.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2013/170958 A2 [0003]
• EP 2911284 B1 [0005]
• US 2015/0349533 A1 [0006]
• WO 2008/154918 A1 [0007]
• DE 102017115000 A1 [0008]

Claims (11)

Photovoltaic device with several photovoltaic modules (1), which each have a number of interconnected photovoltaic cells (2), the photovoltaic modules (1) each having a DC voltage step-up converter (3) which is used to step up the primary voltage (U_in ) is set up for a secondary voltage (U_out) provided at a secondary voltage output of the step-up converter (3), and wherein the secondary voltage outputs of the step-up converter (3) of several photovoltaic modules (1) are interconnected on a common voltage supply bus line (S), characterized in that the voltage supply bus line ( S) has a neutral conductor (M), with a first group of photovoltaic modules (1) with the negative pole of the secondary voltage outputs of their step-up converter (3) to the neutral conductor (M) and a second group of photovoltaic modules (1) with the positive pole of the secondary voltage voltage outputs of their step-up converters (3) are connected to the neutral conductor (M). Photovoltaic device claim 1 , characterized in that the DC step-up converter (3) are operated resonantly. Photovoltaic device claim 1 or 2 , characterized in that the photovoltaic modules (1) have a control unit for controlling the step-up converter (3) by setting the switching frequency (f_s), the pulse width (PWM) and the dead time (t_tot) depending on the primary voltage (U_in) and the primary current ( I_in) of the interconnected photovoltaic cells (2) of a photovoltaic module (3) at the input of the step-up converter (3) to be regulated and the secondary output voltage (U_out) at the output of the step-up converter (3) to be regulated. Photovoltaic unit according to one of Claims 1 until 3 , characterized in that the voltage supply bus line (S) is connected to an electrical energy store (6). Photovoltaic unit according to one of the preceding claims, characterized in that the voltage supply bus line (S) is connected to a DC voltage converter (4) for converting the DC voltage present on the voltage supply bus line (S) into a DC voltage of a low-voltage DC network (N) which is higher in this respect. Photovoltaic unit after claim 5 , characterized in that the low-voltage direct current network (N) is connected to a low-voltage inverter (7) for converting the direct voltage of the low-voltage direct current network (N) into an alternating voltage for an alternating current or three-phase network (D). Photovoltaic unit according to one of the preceding claims, characterized in that the voltage supply bus line (S) is connected to a bus voltage inverter (5) for converting the DC voltage on the voltage supply bus line (S) into an AC voltage of an AC or three-phase network (D). Photovoltaic device claim 6 or 7 , characterized in that the low-voltage inverter (7) and/or bus voltage inverter (5) for converting a direct voltage which is positive in relation to the voltage potential of the neutral conductor (M) of the voltage supply bus line (S) and a negative direct voltage to a single-phase alternating voltage or multi-phase Rotational voltage is formed. Photovoltaic unit according to one of Claims 4 until 8th , characterized in that several sections of the voltage supply bus line (S) branch off from the electrical energy store (6) and/or the DC voltage converter (4) and/or the low-voltage inverter (7) and/or the bus voltage inverter (5). each several photovoltaic modules (1) are connected in parallel to each other. Photovoltaic device according to one of the preceding claims, characterized in that the photovoltaic device for setting the variable secondary voltage (U_out) of the step-up converter (1) of a group of photovoltaic modules (1) connected together on a common voltage supply bus line (S) to a level above the greatest primary voltage (U_in max ) at the input of the step-up converter (3) of a photovoltaic module (1) of a group which is interconnected on the common voltage supply bus line (S) and which has the highest voltage value in the group of photovoltaic modules (1). Computer program with program code means for setting a variable secondary voltage (U_out) of step-up converters (3) of photovoltaic modules (1) of a photovoltaic device claim 10 when the computer program is executed on a data processing unit, the program code means for determining the greatest primary voltage (U_in max) from the primary voltages (U_in) on a common voltage supply bus line (S) together connected group of photovoltaic modules (1) and for setting the variable secondary voltage (U_out) of the step-up converter (3) of the photovoltaic modules (3) of this group to a voltage value above the determined maximum primary voltage (U_in max).

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