Photovoltaic system and inverter with a communication interface

Abstract

Photovoltaic system (10, 100) with a photovoltaic generator (11), an inverter (12) and a communication interface (21) configured for connecting an external electrical unit (22), wherein the communication interface (21) is configured for bidirectional power exchange with the external electrical unit (22), characterized in that the communication interface (21) is configured to feed electrical power into the external electrical unit (22), wherein the external electrical unit (22) comprises an energy storage device, in particular a rechargeable battery, and to draw electrical power from the connected external electrical unit (22) in order to supply components of the photovoltaic system (10, 100) with this electrical power.

Description

TECHNICAL AREA OF INVENTION The invention relates to a photovoltaic system comprising a photovoltaic generator, an inverter, and a communication interface for connecting an external electrical unit, in particular an energy storage device. The invention further relates to an inverter for a photovoltaic system and a method for operating a photovoltaic system. STATE OF THE ART A photovoltaic system can generate electrical power and feed it into an alternating current (AC) grid. A conventional photovoltaic system includes an inverter, which is designed to convert direct current (DC) into alternating current (AC). The DC can be generated by a DC generator, particularly a photovoltaic generator, which is connected to the inverter on the DC side. The AC grid can be a public power grid, a local grid for a business or household, or an off-grid grid without connection to a public power grid, and is connected to the inverter on the AC side. Conventional inverters for photovoltaic systems do not have their own power supply, but draw the operating power required for their operation from a connected photovoltaic generator and / or from a connected AC power grid. These inverters typically include a power supply unit, a rectifier, and / or a DC / DC converter to convert the DC or AC voltage applied to the inverter into electrical power suitable for operating its electrical and electronic components. From DE 20 2006 020 751 U1, an inverter is known which includes a communication interface to which an external electrical unit can be connected, wherein the external electrical unit can comprise a data storage device and an electrical storage device, in particular a battery. With the external electrical unit connected, the inverter can be supplied with electrical power from the electrical storage device via the communication interface, so that the inverter can be operated even without any other DC or AC power supply, at least to the extent that data can be transferred from the data storage device to the inverter. This data transfer can be used, in particular, for carrying out software updates in the inverter. From EP 2 463 999 A1, a system of inverters is known in which each inverter has a communication interface through which it is connected to one of the other inverters, whereby electrical power can be transferred to the communication interface of the other inverter via this communication interface. Those skilled in the art are familiar with communication interfaces that include connections according to the so-called USB standard (USB = Universal Serial Bus). Such communication interfaces are designed to exchange data between devices connected via a USB cable, as well as to transmit electrical power via the USB cable from one device to another. US patent 2016 / 0306616A1 discloses a method for updating the firmware of a USB device in which the USB device is connected to a computer via a communication interface. This communication interface, which can be of type "USB-PD", allows for the exchange of electrical power between the computer and the USB device. TASK OF INVENTION The invention is based on the objective of providing a photovoltaic system that can be operated without the input of electrical power from sources connected to an inverter of the photovoltaic system on the DC or AC side, at least in such a way that communication with components of the photovoltaic system, in particular with its inverters, is enabled. SOLUTION The problem is solved by a photovoltaic system with the features of claim 1, an inverter with the features of claim 7, and a method with the features of claim 10. Preferred embodiments are defined in the respective dependent claims. DESCRIPTION OF THE INVENTION A photovoltaic system comprises a photovoltaic generator, an inverter, and a communication interface configured for connecting an external electrical unit. A photovoltaic system according to the invention is characterized in that the communication interface is configured for bidirectional power exchange with the external electrical unit. This allows the photovoltaic system to communicate with the external electrical unit via the communication interface, as well as to feed energy into and draw energy from the external electrical unit. A separate interface for drawing or temporarily storing electrical energy is therefore unnecessary. The communication interface can, in particular, include a USB port. The Universal Serial Bus, or USB for short, is a standardized technology used millions of times worldwide, with many devices having USB ports that can already transfer electrical power. Such devices with USB ports are particularly suitable as external electrical units for a photovoltaic system according to the invention if they can both receive and supply electrical power. The communication interface can preferably be located in the inverter or in a grid connection unit of the photovoltaic system. These components typically already contain electrical and electronic components and are located in the power path of the electrical power generated by the photovoltaic generators and fed into an AC grid by the inverter, possibly via the grid connection unit. The inverter of the photovoltaic system, in particular, can influence the power flow along this power path. Furthermore, data processing and communication equipment is also located, especially in the inverter, for example, processors for controlling the operation of the inverter and thus also the behavior of the photovoltaic system as a whole. In one embodiment, the communication interface is configured to draw electrical power from the connected external electrical unit in order to supply components of the photovoltaic system with this power. This allows an inverter to be directly supplied with the electrical power required for its operation from a connected external electrical unit. Alternatively or additionally, several inverters of a photovoltaic system, connected to the AC grid via a common grid connection unit, can be centrally supplied with electrical power for their operation by an external electrical unit connected to the grid connection unit. In this case, it may be sufficient to provide each inverter with enough electrical power to enable communication with it.This is particularly advantageous when no electrical power is available at the DC or AC side connections of the inverter, for example at night when the photovoltaic generators connected to the inverter on the DC side are not supplying power, or when the AC network connected to the inverter on the AC side has failed or is disconnected from the photovoltaic system, or when the photovoltaic system has been switched off after a fault. Preferably, the external electrical unit can comprise an energy storage device, in particular a rechargeable battery, wherein the communication interface is configured to supply electrical power to the energy storage device. This ensures that the energy storage device contains an electrical charge that can be generated and maintained via the communication interface. In one embodiment, bidirectional power exchange via the communication interface can be achieved by including a bidirectional voltage converter in the communication interface. The bidirectional voltage converter can preferably be a two-quadrant converter, in particular a buck converter, or a four-quadrant converter, in particular a bidirectional inverter. This allows a voltage to be provided at the communication interface that is adjusted according to the desired power flow direction such that electrical power is fed into the external electrical unit via the communication interface from the inverter or the grid connection unit, or drawn from the external electrical unit by the inverter or the grid connection unit. An inverter according to the invention for a photovoltaic system comprises a communication interface configured for connecting an external electrical unit and is characterized in that the communication interface is configured for bidirectional power exchange with the external electrical unit. The communication interface preferably comprises a USB port to which the external electrical unit can be connected. In one embodiment of the inverter according to the invention, the communication interface is configured to draw electrical power from a connected external electrical unit to supply the inverter with this electrical power, and to feed electrical power into the connected external electrical unit, wherein the external electrical unit in particular comprises an energy storage device, for example a rechargeable battery. For this purpose, the communication interface can include a bidirectional voltage converter, wherein the bidirectional voltage converter preferably comprises a two-quadrant converter, which can in particular be configured as a buck-boost converter.This allows the inverter to feed electrical power into the energy storage system via the communication interface and to draw power from the energy storage system, particularly to be put into operation without any other power supply. A method according to the invention for operating a photovoltaic system with a photovoltaic generator, an inverter, and a communication interface configured for connecting an external electrical unit is characterized in that an energy storage device is connected to the communication interface and electrical power is exchanged bidirectionally with the energy storage device via the communication interface. In particular, within the framework of the method according to the invention, components of the photovoltaic system can be operated with electrical power drawn from the energy storage device via the communication interface, especially when the photovoltaic generators are not connected or do not provide sufficient electrical power to operate the components.Furthermore, electrical power can be fed into the energy storage system, particularly if the energy storage system has a charge below its maximum capacity and the photovoltaic generators are providing electrical power that exceeds the power required to operate the components of the photovoltaic system. This ensures that the operation of the photovoltaic system can be guaranteed at all times, at least to the extent that components of the photovoltaic system, especially the inverters and, if applicable, other electrical or electronic devices such as sensors or switching elements, are supplied with electrical power to enable communication with these components or devices, for example, for the purpose of parameterization, commissioning, or software updates. BRIEF DESCRIPTION OF THE FIGURES The invention will now be further explained and described with reference to the exemplary embodiments shown in the figures. Fig. 1 shows a first embodiment of a photovoltaic system according to the invention, and Fig. 2 shows a second embodiment of a photovoltaic system according to the invention. FIGURE DESCRIPTION Fig. 1 shows a photovoltaic system 10 connected to an AC power grid 20. The photovoltaic system 10 comprises a photovoltaic generator 11, which can consist of one PV module or several PV modules connected in parallel and / or in series, and which is connected to an inverter 12. The inverter 12 converts direct current generated by the photovoltaic generator 11 into alternating current and feeds the generated alternating current into the AC power grid 20. A load 30, which may include one or more consumers, can be connected to the AC power grid 20. The load 30 can be connected to the AC power grid 20, in particular in parallel with the inverter 12, so that the load 30 can be supplied with electrical power partially or completely from the AC power grid 20 or from the inverter 12. The inverter 12 includes a communication interface 21. An external electrical unit 22 can be connected to the communication interface 21. The inverter 12 can exchange both data and electrical power bidirectionally with the external electrical unit 22 via the communication interface 21. The inverter 12 typically comprises a generator-side DC voltage section and a grid-side AC voltage section, which are at least spatially and, if necessary, also galvanically separated from each other. The inverter 12 can be designed such that the electrical operating power required for the inverter 12 is drawn exclusively from the DC voltage section, which in turn is supplied with electrical power exclusively from the connected photovoltaic generator 11. In this case, the inverter 12 is only in an operating state when the photovoltaic generator 11 produces sufficient PV power and makes it available to the DC voltage section of the inverter 12. The inverter 12 of the photovoltaic system 10 according to the invention can be supplied with the electrical operating power required for the operation of the inverter 12 by the external electrical unit 22 via the communication interface 21. For this purpose, the external electrical unit 22 can comprise a power supply unit that is fed by the AC power grid 20. Preferably, the external electrical unit 22 comprises an energy storage device from which the operating power of the inverter 12 can be drawn. Particularly preferably, the energy storage device of the external electrical unit 22 can be charged by the inverter via the communication interface, especially if the available PV power (significantly) exceeds the operating power of the inverter 12. The inverter 12 draws its operating power from the photovoltaic generator 11 during normal operation and feeds the excess PV power, less any switching and filter losses, into the AC grid 20. A portion of the PV power can be used to charge or maintain the charge of the energy storage device in the external electrical unit 22. For this purpose, the communication interface 21 can include a bidirectional voltage converter, such as a buck converter or a two-quadrant converter, which controls the power flow between the inverter 12 and the external electrical unit 22, in particular by appropriately adjusting its relative input and output voltages. If the PV output is insufficient to operate the inverter 12, for example at night, in the event of a defect in the photovoltaic generator 11 or individual parts thereof, or after a fault-related shutdown of the inverter 12, the inverter 12 can be put into operation by drawing its operating power from the external electrical unit 22 via the communication interface 21. This allows the inverter 12 to be operated even without or with insufficient PV output. This is particularly useful for enabling communication with the inverter 12, for example, to read data from or write data to the inverter 12. The communication interface 21 can be arranged on the DC voltage section of the inverter 12 and additionally or alternatively on the AC voltage section of the inverter 12; this arrangement is shown with dashed lines in Fig. 1. Arranging the communication interface 21 on the DC voltage section of the inverter 12 allows the inverter 12 to operate with no or insufficient PV power, provided the inverter 12 draws its operating power from the connected photovoltaic generator 11. Arranging the communication interface 21 on the AC voltage section of the inverter 12 allows the inverter 12 to operate in the event of an interruption of the connection to the AC grid 20 or any other fault in the AC grid 20, provided the inverter 12 draws its operating power from the AC grid 20. Fig. 2 shows a further embodiment of a photovoltaic system 100 according to the invention, in which several photovoltaic generators 11 are each individually connected to several inverters 12. The photovoltaic generators 11 can in turn consist of a single PV module or comprise several PV modules connected in parallel and / or in series. The inverters 12 convert the direct current generated by the respective connected photovoltaic generator 11 into alternating current and feed the generated alternating current into the AC grid 20. The inverters 12 are each connected to a grid connection unit 13, the grid connection unit 13 being configured, in particular, to perform various monitoring and protection functions such as grid monitoring, overload or overvoltage protection, and / or potential shifting.Furthermore, the grid connection unit 13 can be configured for communication with and control of the inverters 12, so that, for example, the electrical behavior of the inverters with regard to reactive power, control power, and / or other electrical parameters can be controlled via the grid connection unit 13. For this purpose, the grid connection unit 13 can be configured, in particular, additionally or alternatively for communication with external communication partners, such as metering points, home automation systems, or grid control centers. Various known methods are suitable for communication between the grid connection unit 13 and the inverters 12, for example, via the AC lines between the inverters 12 and the grid connection unit 13 (so-called power line communication), or via separate communication lines or wirelessly. The network connection unit 13 has a communication interface 21 to which an external electrical unit 22 can be connected. The network connection unit 13 can exchange both data and electrical power bidirectionally with a connected external electrical unit 22 via the communication interface 21. In particular, the external electrical unit 22 can comprise an electrical energy storage device that can be charged and discharged by the network connection unit 13 via the communication interface 21. For this purpose, the network connection unit 13 can include a bidirectional voltage converter, in particular a four-quadrant converter, which controls the power flow between the network connection unit 13 and the external electrical unit 22.Such a four-quadrant converter can convert an alternating voltage tapped from the grid connection unit 13 into a direct voltage, which can be used to charge the energy storage device in the external electrical unit 22. Conversely, the four-quadrant converter can convert a direct voltage tapped from an energy storage device in the external electrical unit 22 into an alternating voltage, which can be applied to AC lines within the grid connection unit 21 to generate an alternating current in the AC lines.It is understood that such an inverter operation of the four-quadrant converter in the grid connection unit 12 involves significantly smaller power outputs than the maximum power of the alternating current generated from the photovoltaic generators 11 by the inverters 12 of the photovoltaic system 100, and that the four-quadrant converter can be designed to be correspondingly much smaller than the inverters 12. In the event of a failure of the AC power grid 20, the inverters 12 may shut down automatically. In particular, deliberately disconnecting the photovoltaic system 100 from the AC power grid 20, for example for maintenance or in case of emergency by the fire department, may lead to a standard-required de-energization of the photovoltaic system 100, whereby the entire photovoltaic system 100 must be de-energized. For this purpose, switching elements (not shown here) between the AC power grid 20 and the inverters 12 and / or between the inverters 12 and the respective photovoltaic generators 11 may be activated, so that the inverters 12 can no longer draw their operating power on the DC or AC side. Consequently, the grid connection unit 13 will also typically not have any electrical power available.Furthermore, if the alternating voltage is no longer present at the alternating voltage-side connections of the grid-connected inverters 12, the grid control signal necessary for feed-in is no longer required. In a photovoltaic system 100 according to the invention, under the described circumstances, electrical power can be drawn from the external electrical unit 22 via the communication interface 21 and used to apply a DC voltage and / or an AC voltage to the AC lines between the grid connection unit 13 and the inverters 12 by means of a voltage converter, in particular a four-quadrant converter. Electrical power can be transferred to the inverters 12 by means of a corresponding DC or AC voltage, which can be used to operate the inverters 12. This is particularly useful to enable communication with the inverters 12, for example, to read data from or write data to the inverters 12, and especially to enable or initiate a (re)start process of the photovoltaic system 100.A corresponding alternating voltage can be used as a grid control signal for the grid-connected inverters 12 and / or cause a transfer of operating power from the external electrical unit 21 to the inverters 12. A photovoltaic system 10 or 100 according to the invention can be used particularly advantageously in the following situations. An external power supply can be connected to the communication interface 21, providing electrical power to the inverter 12 according to Fig. 1 or the grid connection unit 21 according to Fig. 2. This electrical power can be used to put the inverter(s) 12 into an operating state that enables at least communication with a control unit in the inverter 12. If the communication interface 21 includes a USB port, a newly installed photovoltaic system 10, 100 can be programmed, configured, initialized, and / or commissioned in this way using a standard charger, a plug-in power supply, or a USB output of a laptop computer, before the photovoltaic system 10, 100 is connected to the AC grid 20 and / or before a photovoltaic generator 11 is connected to one of the inverters 12. The communication interface 21 can be used alternatively or additionally for outputting electrical power. In this case, the inverter 12 in the embodiment shown in Fig. 1, or a bidirectional voltage converter in the grid connection unit 13, provides a maximum electrical power output that ranges from 0.5 watts to 100 watts, depending on the configuration of the communication interface 21. In particular, if the communication interface 21 includes a USB port that conforms to the USB-PD (USB Power Delivery) specification, up to 100 watts can be transmitted via the communication interface 21 to an external electrical unit 22; this is sufficient to power small external devices and to charge a small to medium-sized energy storage device with a capacity of up to approximately 1000 watt-hours.Such an energy storage device can be removed from the photovoltaic system 10, 100 when not in use and used elsewhere, for example to supply portable telephones or similar devices with operating power via their USB ports and, if necessary, to charge energy storage devices included in these devices. If an external electrical unit 22 with an energy storage device is connected to the communication interface 21, switching between the two configurations mentioned above is possible without external intervention. During normal operation of the photovoltaic system 10, 100, the energy storage device is charged or its charge is maintained. At night and / or in the event of a failure of the AC grid 20, the same energy storage device can supply the inverter 12 with electrical operating power in the form of direct or alternating current, and optionally a grid control signal in the form of an alternating voltage, directly via the communication interface 21 or indirectly via the grid connection unit 13. The external electrical unit 22 can alternatively or additionally include a data storage device, the contents of which can be transmitted, at least partially, to the inverter(s) 12 via the communication interface 21. This transmitted content can include, in particular, firmware for operating the inverter(s) 12 and / or other parameters such as nominal characteristics of the AC grid 20, limit values ​​for grid voltage and grid frequency, target values ​​for feeding electrical power into the AC grid 20, communication parameters, and the like. Conversely, data from the inverter(s) 12 can be stored in the data storage device of the external electrical unit 22, for example, power and energy values ​​of the photovoltaic system, error messages, and the like. Reference symbol list 10, 100 Photovoltaic system 11 Photovoltaic generator 12 Inverter 13 Grid connection unit 20 AC grid 21 Communication interface 22 External electrical unit 30 Load

Claims

Photovoltaic system (10, 100) with a photovoltaic generator (11), an inverter (12) and a communication interface (21) configured for connecting an external electrical unit (22), wherein the communication interface (21) is configured for bidirectional power exchange with the external electrical unit (22), characterized in that the communication interface (21) is configured to feed electrical power into the external electrical unit (22), wherein the external electrical unit (22) comprises an energy storage device, in particular a rechargeable battery, and to draw electrical power from the connected external electrical unit (22) in order to supply components of the photovoltaic system (10, 100) with this electrical power. Photovoltaic system (10, 100) according to claim 1, characterized in that the communication interface (21) comprises a USB port. Photovoltaic system (10, 100) according to claim 1 or 2, characterized in that the communication interface (21) is arranged in the inverter (12) or in a grid connection unit (13) of the photovoltaic system (10, 100). Photovoltaic system (10, 100) according to one of the preceding claims, characterized in that the communication interface (21) comprises a bidirectional voltage converter, wherein the bidirectional voltage converter preferably comprises a two-quadrant converter, in particular a buck converter, or a four-quadrant converter, in particular a bidirectional inverter. Inverter (12) for a photovoltaic system (10, 100), wherein the inverter (12) comprises a communication interface (21) configured for connecting an external electrical unit (22), wherein the communication interface (21) is configured for bidirectional power exchange with the external electrical unit (22), wherein the communication interface (21) preferably comprises a USB port, characterized in that the communication interface (21) is configured to extract electrical power from the connected external electrical unit (22) in order to supply the inverter (12) with this electrical power, and to feed electrical power into the external electrical unit (22), wherein the external electrical unit (22) in particular comprises an energy storage device, in particular a rechargeable battery. Inverter (12) according to claim 5, characterized in that the communication interface (21) comprises a bidirectional voltage converter, wherein the bidirectional voltage converter preferably comprises a two-quadrant converter, which is in particular designed as a boost-bubble converter. Method for operating a photovoltaic system (10, 100) with a photovoltaic generator (11), an inverter (12) and a communication interface (21) provided for connecting an external electrical unit (22), wherein the external electrical unit (22) connected to the communication interface (21) comprises an energy storage device, and that electrical power is exchanged bidirectionally with the energy storage device via the communication interface (21), characterized in that electrical power is fed into the energy storage device, in particular when the energy storage device has an energy content below its maximum energy content and the photovoltaic generator (11) provides electrical power that exceeds the electrical power required to operate the components of the photovoltaic system, and that components of the photovoltaic system (10,100) are operated with electrical power drawn from the energy storage system via the communication interface (21), in particular if no photovoltaic generator (11) is connected or the photovoltaic generator (11) does not provide sufficient electrical power to operate the components.

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