Medium-voltage arrangement of solar modules and power converters

Description

[0001] The invention relates to a solar unit comprising a plurality of solar modules and a carrier unit, wherein the solar modules have an insulation strength DC insulation voltage, in particular an insulation DC insulation voltage of up to 1.5 kV DC. The invention further relates to a solar array unit, wherein the solar array unit has at least two such solar units, wherein the solar units are electrically arranged in series with respect to their first connections and second connections. Furthermore, the invention relates to a solar generation unit comprising a power converter and at least one such solar unit and / or at least one such solar array unit. The invention further relates to a solar generation system comprising at least one such solar generation unit, a grid connection point for connecting the solar generation unit to a power grid, and a transformer.Furthermore, the invention relates to a method for feeding electrical energy into an energy supply network by means of such a solar unit, such a solar group unit, such a solar generation unit or such a solar generation system.

[0002] Solar modules, also known as photovoltaic (PV) modules or photovoltaic panels, are connected in series to generate electrical energy from sunlight, so that the voltages of the modules add up. Several solar modules connected in series form a PV string. The voltage of PV strings today is in the range of several hundred volts DC. The housings of the PV panels or their frames / frames are grounded.

[0003] One or more PV strings are connected to one or more power converters, which convert the DC voltage of the solar modules at their respective outputs into an AC

[0004] Generate or generate low voltage and then make it available at the grid connection (typically 0.4-0.69 kV). The point at which the grid connection is made is also called the grid connection point.

[0005] Solar modules exhibit insulation strength. This is the electrical insulation capability between the electrical connections of the solar module, where the electrical energy generated from sunlight is available, and the housing of the solar module or a support unit on or against which the solar modules, in particular the housings of these solar modules, are arranged. The insulation capability is specified by the voltage that can be present between the electrical connections of the solar module and the housing or support unit without causing a current flow, or significant current flow, or damage to the modules. The maximum DC voltage that may be present between one of the electrical connections of the solar module and the housing or support unit is referred to as the insulation DC voltage. Typical insulation DC voltages of today's solar modules are up to 1.5 kV DC.

[0006] EP2386121B1 discloses a photovoltaic device for high-voltage generation, wherein photovoltaic modules are interconnected to form a module block that is insulated from the earth potential by insulation elements.

[0007] The invention is based on the object of improving an arrangement for feeding solar energy into an energy supply network, in particular for high power levels.

[0008] This object is achieved by a solar group unit, wherein the solar group unit has at least two solar units, each with a first connection and a second connection, wherein the solar units each have a plurality of solar modules and a carrier unit, wherein the solar modules have a DC insulation voltage, in particular a DC insulation voltage of up to 1.5 kV DC, with regard to their insulation strength, wherein the solar modules are arranged in a series circuit between the first connection and the second connection, wherein a connection point is arranged on an electrical connection between two of the solar modules arranged in the series circuit,that the magnitude of a first voltage that can be generated by the solar modules arranged between the first terminal and the connection point and the magnitude of a second voltage that can be generated by the solar modules arranged between the second terminal and the connection point are each smaller than the insulation DC voltage, wherein the solar modules are arranged in or on the carrier unit, wherein the carrier unit is at least partially electrically conductive and is electrically conductively connected to the connection point, wherein the solar units are arranged electrically in series with respect to their first terminals and second terminals, wherein the carrier units of the respective solar modules are arranged electrically insulated from one another by means of an insulator. The object is further achieved by a solar generation unit comprising a power converter and at least one such solar array unit,The power converter is designed as a medium-voltage power converter and has a DC side and an AC side, wherein the solar unit and / or the solar array unit is electrically connected to the DC side of the power converter. The object is further achieved by a solar generation system comprising at least one such solar generation unit, a grid connection point for connecting the solar generation unit to a power grid, and a transformer, wherein the transformer is connected to the AC side of the power converter and to the grid connection point. This object is further achieved by a method for feeding electrical energy by means of such a solar array unit, such a solar generation unit, or such a solar generation system.wherein electrical energy generated by the solar modules is fed into a power grid by means of an alternating voltage in the medium voltage range.

[0009] Further advantageous embodiments of the invention are specified in the dependent claims.

[0010] The invention is based, among other things, on the discovery that the arrangement of solar modules can be improved, thus resulting in more efficient arrangements for energy generation with these solar modules. Eliminating the need for grounding solar modules and / or their support units offers advantages, particularly for PV parks, i.e., power generation plants based on PV modules with a capacity of more than 100 MW.

[0011] The solar unit has a series connection of solar modules between the first and second terminals. The solar modules are arranged in series at their solar module terminals, where the electrical power generated from sunlight is available.

[0012] The electrical energy generated from sunlight is made available, for example, to a power grid, electrical consumers, or an energy storage device using a medium-voltage power converter. The medium-voltage inverter converts the voltage from the solar modules into an alternating voltage. In other words, the electrical energy generated by the solar modules is processed by the medium-voltage inverter in such a way that it can be transmitted using an alternating voltage. This alternating voltage has an effective value or amplitude of more than 1000 V. By varying the voltage in amplitude and phase position, the medium-voltage converter can control or regulate the transmission of active power and reactive power independently of one another. The solar modules are arranged on or in support units. These support units each create an electrical potential.This is insulated from ground potential, for example, by means of an insulator on the support unit, which will be referred to below as a support insulator to distinguish it from other insulators. The potential of the respective support unit is determined by the connection point in the series connection of solar modules. In other words, the electrical potential of the respective support units is electrically connected to the connection point. Since this causes the potentials of the respective support units to differ, the support units are arranged in an insulated manner from one another. This is achieved by an insulator, whereby the insulator has an insulation voltage that is greater than or equal to twice the DC insulation voltage of the solar modules. This insulator is arranged between two of the support units.For example, if the insulation voltage of the solar modules is 1.5 kV DC, the insulators arranged between two support units have an insulation voltage of at least 3 kV.

[0013] The insulators between the support units ensure that the two support units connected by an insulator do not exceed a specified voltage between them. This guarantees that the support insulators are not overloaded, i.e., are not subjected to an unacceptably high voltage. The support insulators provide electrical insulation between the solar modules and the accessible parts of the system. A defect in the support insulators therefore poses a risk of endangering people. In the event of a fault, the insulators between the support units would cause the support units to fail first due to their lower insulation voltage compared to the support insulators. This failure can be reliably detected. The solar array unit can then be brought into a safe operating state. This can be done, for example, by reducing the voltages, switching off or bridging individual solar modules, or switching off the solar array unit.

[0014] It has also proven advantageous to install a voltage limiter, such as a varistor, parallel to the insulator between the support units. The varistor's trigger threshold can then be set above the insulation voltage of the insulator, for example, in the range of 1.1 to 1.3 times the insulation voltage. In the event of an insulator failure, the two support units connected via this insulator then have a defined potential relative to each other. This allows continued operation of the solar array unit.

[0015] If the insulation voltage for the insulator between the support units is double the operating voltage between the terminals of the series circuit, and the connection point is located centrally in the series circuit, the solar array unit can continue to operate at full power even if one insulator fails. At the same time, contact protection is reliably ensured because the support insulators are not overloaded. At the same time, it is possible to design the support insulators for the required insulation capacity. Since these not only have to meet the insulation capacity but also meet mechanical static requirements, they are comparatively expensive compared to the insulators between the support units.By using the insulators simultaneously between the support units, the requirements for the insulation strength of the support insulations are significantly reduced without compromising the touch safety of the solar generation system or the solar generation unit.

[0016] The connection point is arranged in the series circuit between two of the solar modules of the respective solar unit in such a way that the maximum voltage that can be present between the connection point and one of the electrical connections, i.e. the first connection or the second connection, of the respective solar unit, is less than or equal to the DC insulation voltage of the solar modules. This makes it possible to create a series connection of solar modules in a solar array unit, whereby the voltage of the series connection of all solar modules in the solar array unit exceeds the DC insulation voltage, twice the DC insulation voltage, and even a multiple of the DC insulation voltage of the individual solar modules. Thus, a voltage is present between each solar module, or each connection of the solar module, and the carrier unit that is less than or at most equal to the DC insulation voltage of the individual solar modules. The solar unit is therefore not grounded.The potential of the carrier unit is determined by the connection point of the solar unit. It usually differs from the ground potential. The potential of the carrier unit is thus insulated from the ground potential, in particular by means of one or more carrier insulators.

[0017] The proposed arrangement allows for a larger number of solar modules to be connected in series, while maintaining the same DC insulation voltage of the solar modules, compared to an arrangement in which a supporting structure of the solar modules is grounded. This higher number of solar modules enables operation with a medium-voltage converter. The voltage on the DC side of the medium-voltage converter can reach a voltage of more than 1.5 kV. Due to the higher voltage of the medium-voltage converter compared to a low-voltage converter used today, the currents are reduced for the same amount of power to be transmitted. In other words, higher power can be transmitted using the medium-voltage converter for the same currents.When lower currents are used, the losses in energy generation are reduced and such a solar generation unit and such a solar generation system has a particularly high efficiency due to the lower currents and the associated lower losses.

[0018] The proposed arrangement is therefore particularly advantageous for large PV parks in the range of more than 100 MW. Very high currents arise there when using low-voltage converters. The lower currents of the proposed solar generation unit also allow the components of the solar generation unit to be arranged at a greater distance from the grid connection point. The alternating voltage of the medium-voltage converter can be selected to be so high that transmission losses can be neglected. This means that transmission distances between the medium-voltage converter and the grid connection point of more than 1 km and even more than 10 km can be easily implemented. In other words, the arrangement is particularly advantageous when the spatial distance between the medium-voltage converter and the grid connection point is greater than 1 km, in particular greater than 10 km.Additional transformers to bridge this distance are unnecessary. For a PV park with a feed-in capacity of more than 100 MW, this results in the elimination of numerous costly transformers.

[0019] At the same time, the requirements for the insulation strength of the individual solar modules are low. A DC insulation voltage of the solar modules used, for example, of 1.5 kV DC, which is already available in large quantities on the market today, is suitable for the proposed arrangement to create a series connection of solar modules that are connected to the medium-voltage converter on the DC side and generate a voltage in the medium-voltage range on the AC side. The fact that the proposed arrangement makes it possible to forgo a higher insulation strength of the solar modules makes the proposed solution not only highly efficient but also particularly cost-effective. In addition, cables can also be used to form the series connection, with the cables connecting the terminals of the solar modules to form the series connection.The cables used only need to be rated for low-voltage DC voltages, particularly DC voltages up to 1.5 kV. The costly use of medium-voltage cables, i.e., cables with an insulation strength of more than 1.5 kV, can be dispensed with.

[0020] The invention is based, among other things, on the finding that it is advantageous to insulate the support unit of the solar module from earth potential. In other words, the solar module is arranged and operated in isolated mode, which can also be referred to as floating mode. The supports, on which the support unit can be mounted and which fix the support unit in its spatial position, can advantageously be realized at least partially by a medium-voltage insulator. In other words, the support insulator is formed by a medium-voltage insulator. Depending on the power range to be covered by the solar unit, the solar array unit, the solar generation unit and / or the solar generation system, it has proven advantageous to use medium-voltage insulators suitable for insulation between 1.5 kV DC and 50 kV DC.The cables used, both to create the series connection within the solar unit and to connect the series connections of different solar units, only require an insulation strength in the low voltage range, such as 1.5 kV DC.

[0021] It is also advantageously possible to arrange several solar array units in a parallel circuit and to connect them to exactly one medium-voltage converter for this parallel circuit. The solar array units are connected on the DC side of the medium-voltage converter. Due to the current intensity and the insulation requirements, busbars, also known as busbars, are particularly suitable for connecting the solar array units in a parallel circuit. These are arranged on other insulators, separated from the earth potential, and optionally also attached to them. To distinguish these other insulators, this insulator is called a busbar insulator. This has the advantage that no medium-voltage cables are required for direct currents, and yet particularly simple and cost-effective installation can be achieved.These busbar insulators are then preferably designed as medium-voltage insulators. These have an insulation voltage of more than 1.5 kV DC.

[0022] Complex conversion of low voltage to medium voltage, for example, for low-loss transmission to the grid connection point, especially to a grid connection point more than 1 km away, can be eliminated because the solar units in the proposed arrangement are already connected to the medium-voltage converter. This makes low-loss transmission to the grid connection point particularly cost-effective, even for connections over 1 km in length, especially over 10 km.

[0023] The solar units are designed in such a way that the solar modules in the series connection of a solar unit can generate a voltage of up to 3 kV, allowing the corresponding insulators to be used particularly advantageously. Only insulators with a DC insulation voltage of up to 3 kV are then required between the support units of different solar units.

[0024] It has proven particularly advantageous for the control and / or regulation of the medium-voltage converter if a transformer in the solar generation system galvanically isolates the terminals of the medium-voltage converter and the terminals of the grid connection point. For this purpose, the transformer is connected to the medium-voltage converter with a first winding and to the grid connection point with a second winding. This achieves galvanic isolation between the solar array unit and the power grid. This prevents potential jumps, or at least only minimal ones, from occurring in the solar generation unit and its components.

[0025] The use of the medium-voltage converter makes the proposed arrangement particularly efficient compared to known solutions using low-voltage converters, as the medium-voltage converter can replace multiple low-voltage converters. Likewise, the use of a transformer, which is used to boost the output voltage of the low-voltage converters to a medium-voltage level, is eliminated. In general, the use of the medium-voltage converter and the associated higher voltage at the same power level reduces the currents or increases the performance of such solar generation units or systems at the same currents. This leads to lower operating costs for such systems. Overall, such a solar generation unit or system has significantly fewer components than known systems, especially systems with a capacity of more than 100 MW.The proposed solar generation units and systems are therefore particularly space-saving, require little maintenance, and are characterized by high availability due to a smaller number of components. Despite the use of a medium-voltage converter, the proposed arrangement allows for the use of a variety of low-voltage components, such as solar modules and cables, which can be designed as low-voltage components.

[0026] In an advantageous embodiment of the invention, the connection point is arranged centrally with respect to the solar modules in the series connection. With the central arrangement of the connection point, the maximum voltage of 3 kV can be generated between the first connection and the second connection of the solar module. This allows the solar modules of the solar unit to be used particularly economically. Even with a lower voltage utilization, for example due to a smaller number of solar modules in the series connection, there is the advantage that a lower voltage is present between the first connection or the second connection of the solar unit and the carrier unit, which voltage must be insulated. This increases, among other things, the service life of the solar unit and makes it less susceptible to contamination that could reduce the insulating capacity of the insulator. Damage caused by faulty insulation is therefore significantly less likely.This applies to both the insulators between the support units and the support insulators to which the support unit is attached and insulated from earth potential.

[0027] A central arrangement of the connection point means that the same number of solar modules is arranged between the connection point and the first connection as between the connection point and the second connection. With an odd number of solar modules in the series connection, a central arrangement is also present if the number of solar modules between the connection point and the first connection and the number of solar modules between the connection point and the second connection differ by one solar module.

[0028] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show: FIG 1 the elements of a solar system, FIG 2 a solar unit, FIG 3 a solar group unit, FIG 4 a solar generation unit, FIG 5 a solar generation system, FIG 6 a fastening of elements of a solar unit and FIG 7 a fastening of the busbar.

[0029] The FIG 1shows the basic structure of a known solar system for generating electrical energy from solar modules 2. The solar modules 2 are arranged in a series circuit 4. The series circuit 4 is connected to the DC side of the power converter 6. The AC voltage generated at the output by the power converter 6 can be transmitted, for example, via a low-voltage cable 50 to a first transformer 91. This can generate a medium voltage, with which the generated energy can then be transported with low loss, even over long distances, using medium-voltage cables 51. At the grid connection point 7, where the electrical energy is fed into a power supply network 8, a second transformer 92 is present, which converts the medium voltage into a voltage of the power supply network 8. In the power supply network 8, energy is usually transmitted via high-voltage lines 52.

[0030] The FIG 2shows a solar unit 1. The solar unit 1 has a series connection 4 of solar modules 2 between a first connection 41 and a second connection 42 of the solar unit 1. The solar modules 2 are arranged in series at their solar module connections, at which the electrical power generated from sunlight is available. A connection point 45 is arranged between two of the solar modules 2 in the series connection 4. The solar modules 2 are arranged in, on or on a carrier unit 3. The carrier unit 3 is at least partially electrically conductive and is electrically connected to the connection point 45. A first voltage U 1 can be generated between the first connection 41 and the connection point 45 and a second voltage U 2 can be generated between the second connection 42 and the connection point 45.

[0031] Two or more solar units 1 can be arranged electrically in series. These solar units 1 arranged in series form a solar group unit 10. Such a solar group unit 10 shows FIG 3 To avoid repetition, please refer to the description of the Figures 1 and 2 and the reference numerals introduced therein. The support units 3 of the individual solar units 1 are insulated from one another by insulators 5. Furthermore, the support units are each insulated from ground potential by a support insulator 61.

[0032] This solar group unit 10 is connected to the terminals of the solar units 1 arranged in series, for example by means of a medium-voltage busbar 54, with a power converter 6, wherein the power converter 6 is designed as a medium-voltage power converter. Such an arrangement is shown in FIG 4 To avoid repetition, please refer to the description of the Figures 1 to 3and to the reference symbols introduced therein. On the DC side of the power converter 6, the latter is connected to the solar modules 2 of the solar array unit 10. Only one solar array unit 10 can be connected to the power converter 6. Alternatively, it is possible for a parallel connection of two or more, i.e. at least two, solar array units 10 to be connected to the DC side of the power converter 6. For reasons of clarity, the insulators 5 between the solar units 1 have been omitted from the illustration; they are arranged in accordance with the FIG 3 are also arranged in this embodiment and electrically insulate the carrier units 3 of the individual solar units 1 from one another.

[0033] The FIG 5shows a solar generation system 200 with a solar generation unit 100, a transformer 9 and a grid connection point 7 as access to an energy supply network 8. To avoid repetition, reference is made to the description of the Figures 1 to 4and to the reference numerals introduced therein. The alternating voltage generated by the power converter 6 can, since it is a voltage in the medium-voltage range, be transported with particularly low losses and thus economically even over longer distances, such as more than 1 km, in particular even more than 10 km, to a transformer 9 located in the vicinity of the grid connection point 7. This transformer 9 adapts the medium voltage generated by the medium-voltage power converter 6 to the voltage level of the energy supply network 8. For this purpose, the transformer 9 is connected with a first winding to the power converter 6 and with a second winding to the grid connection point 7. This achieves galvanic isolation between the solar array unit 100 and the energy supply network 8.With this arrangement, the electrical energy generated in the solar modules 2 can be fed into the energy supply network 8 particularly economically by means of the proposed structure using a medium-voltage power converter 6.

[0034] The FIG 6 shows the mechanical structure of the components solar module 2 and carrier unit 3 of a solar unit 1. To avoid repetition, please refer to the description of the Figures 1 to 5and to the reference numerals introduced therein. The carrier unit 3 serves to attach the housing of the solar module 2. The carrier unit 3 is insulated from earth potential, for example, by means of a carrier insulator 61. This means that the electrical potential of the carrier unit can be specified independently of the earth potential. The insulator can be arranged at a height that cannot be touched by people, in order to ensure touch safety. The lower part of this carrier can then be earthed and meets the touch safety requirements. The carrier insulator 61 is arranged at a specific height, which depends, among other things, on the voltage applied to the carrier unit 3 during operation. The touch safety of the part of this arrangement that is separated from earth potential, which also includes the carrier unit, is then ensured due to a sufficient height of this arrangement.

[0035] In the same way, the contact safety of the medium-voltage busbar 54 can be ensured by arranging it at a sufficient height on a support. An example of this is shown in FIG 7 To avoid repetition, please refer to the description of the Figures 1 to 6 and the reference numerals introduced therein. The lower part of the support can be grounded for reasons of touch safety, and a busbar insulator 62 is arranged only at a no longer accessible part of the support, separating the medium-voltage busbar 54 from ground potential. The electrical connection between the medium-voltage busbar 54 and the solar modules 2 (not shown here) of the solar units 1 or solar array units 10 can be designed for low voltage and, for example, be designed as a low-voltage cable 50.

Claims

1. Solar group unit (10) having at least two solar units (1) each with a first connection (41) and a second connection (42), wherein the solar units (1) each have - a multiplicity of solar modules (2) and - a carrier unit (3), wherein the solar modules (2) have a DC insulation voltage with respect to their insulation resistance, wherein the solar modules (2) are arranged between the first connection (41) and the second connection (42) in a series connection (4), wherein a connection point (45) is arranged at an electrical connection between two of the solar modules (2) arranged in the series connection (4) in such a way that the value of a first voltage (U1) able to be generated by the solar modules (2) arranged between the first connection (41) and the connection point (45) and the absolute value of a second voltage (U2) able to be generated by the solar modules (2) arranged between the second connection (42) and the connection point (45) are each lower than the DC insulation voltage, wherein the solar modules (2) are arranged in or on the carrier unit (3), wherein the carrier unit (3) is designed to be at least partly electrically conductive and is electrically conductively connected to the connection point (45), wherein the solar units (1) are arranged electrically in series with respect to their first connections (41) and second connections (42), characterized in that the carrier units (3) of the respective solar modules (2) are arranged electrically insulated from one another by means of an insulator (5), wherein the insulator (5) is designed as a component.

2. Solar group unit (10) according to Claim 1, wherein the insulator (5) has an insulation voltage which is greater than or equal to twice the DC insulation voltage of the solar modules (3).

3. Solar group unit (10) according to either of Claims 1 and 2, wherein the insulation resistance of the solar modules (2) has a DC insulation voltage of up to 1.5 kV DC.

4. Solar group unit (10) according to one of Claims 1 to 3, wherein the connection point (45) is arranged centrally with respect to the solar modules (2) in the series connection (4).

5. Solar generation unit (100), having - a power converter (6) - at least one solar group unit (10) according to one of Claims 1 to 4, wherein the power converter (6) is designed as a medium-voltage power converter and has a DC-voltage side and an AC-voltage side, wherein the solar unit (1) and / or the solar group unit (10) are / is electrically connected to the DC-voltage side of the power converter (6).

6. Solar generation system (200), having: - at least one solar generation unit (100) according to Claim 5, - a grid connection point (7) for connecting the solar generation unit (100) to an energy supply grid (8), and - a transformer (9), wherein the transformer (9) is connected to the AC-voltage side of the power converter (6) and to the grid connection point (7).

7. Method for feeding in electrical energy by means of a solar group unit (10) according to one of Claims 1 to 4, a solar generation unit (100) according to Claim 5 or a solar generation system (200) according to Claim 6, wherein an electrical energy generated by the solar modules (2) is fed into an energy supply grid (8) by means of an AC voltage in the medium-voltage range.