BE1024324B1 - Photovoltaic system, DC hybrid switching device, use and method for switching a photovoltaic string on and off - Google Patents

Abstract

The invention relates to a photovoltaic system (1) with a switching device (38) for switching on and off at least one photovoltaic string (10), an electronically controlled DC hybrid switching device for user-controlled switching on and off of at least one photovoltaic string ( 10), the use of a hybrid switch (S1) for switching a photovoltaic string (10), and a method for switching off and on again at least one photovoltaic string (10) of the photovoltaic system (1). The photovoltaic system (1) comprises: at least one photovoltaic string (10), wherein the at least one photovoltaic string is formed by photovoltaic modules (12), which are connected in series with one another by means of a string line and thus generate a string voltage Switching device (38), which is installed in series in the strand line to the at least one photovoltaic string with the switching device (38) on and off, wherein the switching device (38) comprises a hybrid switch (S1) with a relay (54) and a In parallel with the relay (54) connected semiconductor switching device (50) with at least one semiconductor switch.

Description

(30) Priority information:

(73) Owner:

PHOENIX CONTACT GmbH & Co. KG

32825, BLOMBERG

Germany (72) inventor:

HÖFT Wolfgang 32683 BARNTRUP Germany

END Andreas Stefan 31860 EMMERTHAL Germany (54) Photovoltaic system, direct current hybrid switching device, use and method for switching a photovoltaic string on and off (57) The invention relates to a photovoltaic system (1) with a switching device (38 ) for switching on and off at least one photovoltaic string (10), an electronically controlled DC hybrid switching device for user-controlled switching on and off of at least one photovoltaic string (10), the use of a hybrid switch (S1) for switching a photovoltaic string (10) , and a method for switching off and on again at least one photovoltaic string (10) of the photovoltaic system (1). The photovoltaic system (1) comprises: at least one photovoltaic string (10), the at least one photovoltaic string being formed by photovoltaic modules (12) which are connected in series with one another by means of a string line and thus generate a string voltage, one Switching device (38), which is installed in series in the string line in order to switch the at least one photovoltaic string on and off with the switching device (38), the switching device (38) being a hybrid switch (S1) with a relay (54) and one Semiconductor switching device (50) connected in parallel to the relay (54) with at least one semiconductor switch.

BELGIAN INVENTION PATENT

FÖD Wirtschaft, K.M.B., Mittelstand & publication number: 1024324 Energy filing number: BE2017 / 5252

Office of Intellectual Property Boarding. Classification: H02S 50/00

Issued on: 01/25/2018

The Minister for Enterprise

Due to the Paris Treaty of March 20, 1883 for the protection of industrial property;

Introduced under the Act of March 28, 1984 on Inventive Patents, Article 22, for applications prior to September 22, 2014;

Based on Title I “Invention Patents” of Book XI of the Economic Code, Article XI.24, introduced for applications from September 22, 2014;

Based on the royal decree of December 2, 1986 on the registration, granting and maintenance of patents for invention, Article 28;

Based on the protocol, taken on 11/04/2017 at the Intellectual Property Office.

Considering that for patent applications that fall within the scope of Title 1, Book XI, of the Economic Code, in accordance with Article XI.19, Section 4, second paragraph, of the Economic Code, if the patent application is the subject of a search report in which a lack of unity of invention within the meaning of paragraph 1 is mentioned, and if the applicant does not limit his application and does not file a divisional application in accordance with the search report, the granted patent will be limited to the claims for which the search report was created.

DECIDES:

Article 1. - An invention patent is granted to:

PHOENIX CONTACT GmbH & Co. KG, Flachsmarktstrasse 8, 32825 BLOMBERG Germany;

represented by :

for a period of 20 years, subject to the payment of the annual patent fees mentioned in Article XI.48, Section 1 of the Economic Code, for: photovoltaic system, DC hybrid switching device, use and method for switching a photovoltaic string on and off.

INVENTOR:

HÖFT Wolfgang, Breslauer Ring 9, 32683, BARNTRUP;

END Andreas Stefan, Länder 31, 31860, EMMERTHAL;

PRIORITIES) :

SEPARATION:

Partial application of the previous application: Date of filing of the previous application:

Article 2. - This patent is granted without any prior examination of the patentability of the invention, without guaranteeing the merit of the invention or the accuracy of its description, and at the own risk of the patent applicant (s).

Brussels, 25/01/2018, in special representation:

BE2017 / 5252

Photovoltaic system, DC hybrid switching device, use and

Method for switching a photovoltaic string on and off

description

Field of the Invention

The invention relates to a photovoltaic system with a switching device for switching on and off at least one photovoltaic string, an electronically controlled direct-current hybrid switching device for user-controlled switching on and off of at least one photovoltaic string, the use of a hybrid switch for switching a photovoltaic string, and a Method for switching off and on again at least one photovoltaic string of the photovoltaic system.

Background of the Invention

A photovoltaic system typically comprises a large number of photovoltaic modules, which are connected in series to form strings, sometimes also referred to as “strings”, in order to achieve a nominal photovoltaic generator DC voltage of typically currently up to 1000 volts or even 1500 volts. Furthermore, depending on the number of interconnected photovoltaic modules and their individual voltage, if necessary, several of the photovoltaic strings are connected in parallel, of which each photovoltaic string can generate, for example, a nominal current of 10 A. If several lines are connected in parallel, this is also referred to as a multi-line or multi-line connection.

Due to the high voltage and the high currents in the DC voltage part of the photovoltaic system, there is maintenance or malfunctions, e.g. in the event of a fire, the danger that people could be exposed to life-threatening voltages.

For this reason, photovoltaic module protection circuits were developed with which the photovoltaic modules can be switched off individually (cf. WO2013 / 026539 A1 and the product SCK-RSD-100 from the applicant). Furthermore, start boxes were developed with which such "intelligent" photovoltaic modules can be reactivated (cf.

WO2014 / 122325 A1 and the products SCK-RSD-400 and SCK-RSD-600 from the applicant).

DE 10 2016 117 049 (not previously published) also describes a reverse current protection circuit by means of which it is possible to separate a line from the central collection point in order to prevent cross currents. The aim of DE 10 2016 117 049 is to automatically generate a current flow by means of the reverse current protection circuit

BE2017 / 5252 against the direction of flow of the photovoltaically generated electricity from the other photovoltaic strings (cross current or reverse current).

In a German patent application by the same applicant, filed on the same day as the present application, a string shutdown device for single string shutdown in a multistrand photovoltaic system is described.

The present invention is based on this, which is why the disclosure content of DE 10 2016 117 049 and the patent application filed on the same day as the present application (attorney file number 16PH 0346DEP) are hereby incorporated by reference.

To e.g. A suitable DC isolator is required to electrically separate a photovoltaic string from a network of parallel strings in a multi-string photovoltaic system.

Although a photovoltaic system typically has a DC main disconnector in the so-called generator junction box, it can be used to e.g. in the event of damage from fire, water, hail, etc. on the solar panels or on the connecting cables, do not isolate the area in front of the generator junction box. Furthermore, such DC main isolating switches in the generator connection box are typically manually operated, so that a higher-level remote control is typically not possible. In addition, such hand-operated DC main isolating switches are large in size and cost-intensive. Motorized emergency switches are also known, but they are also space and cost intensive. By the way, a selective activation of individual photovoltaic strings is not possible at all.

Nevertheless, a combination of a high DC phase voltage and a high DC phase current is typically to be switched during switching operations within a photovoltaic generator. When switching a high DC voltage and a high DC current, unlike in an application with AC voltage, a non-extinguishing arc can occur due to the lack of zero crossings. With a usual

AC voltage frequency would typically extinguish an arc by itself after 10 ms at the latest.

WO 2016/091281 A1 discloses a device with a switching device for switching an AC voltage or an AC current, which device has a bridging device for bridging the switching device in an operating phase

BE2017 / 5252. However, this device is used exclusively for AC voltage or

AC described.

General description of the invention

The present invention is based, inter alia, on the knowledge that, with the switching device disclosed here, photovoltaic generators in the direct current part (DC part) can be switched on and off, partially or completely, safely and with low power loss, or can be electrically separated and reconnected.

The present invention has for its object to provide a photovoltaic system with a switching device for switching on and off at least one photovoltaic string, the switching device in the typical in photovoltaic systems

DC string voltages and DC string currents is inexpensive, reliable and durable, has low power dissipation and can be accommodated in a small installation space.

Another aspect of the object of the invention is to provide a photovoltaic system with a switching device for switching on and off at least one photovoltaic string, which meets high safety requirements, is easy to maintain and repair and is easy to use for the user.

Another aspect of the object of the invention is to provide a method for switching on and off at least one photovoltaic string of a photovoltaic system, which has a high level of safety and flexibility, e.g. offers maintenance and is easy to use for the user.

Another aspect of the object of the invention is to provide an electronically controlled direct-current hybrid switching device for performing switching operations in the DC part of a photovoltaic system, which is inexpensive, reliable and durable in the case of the string voltages and string currents typical in photovoltaic systems is, and at the same time has a low power loss and can be accommodated in a small space, and with which existing photovoltaic systems can be retrofitted.

The object of the invention is solved by the subject matter of the independent claims. Advantageous developments of the invention are defined in the subclaims.

The invention relates to a photovoltaic system with at least one string or photovoltaic string, which is formed by a plurality of photovoltaic modules which are connected to one another in series by means of a string line in order to achieve the desired

BE2017 / 5252

Generating string voltage and photovoltaically generated electrical power with the desired string voltage and a desired string current to a pantograph, e.g. to supply an inverter (sometimes called a solar inverter). The photovoltaic system can also be used without an inverter, e.g. be connected to a charging unit as a pantograph. According to protection class II, string voltages up to 1000 V DC are possible. A further increase to up to 1500 V DC, the limit value of the low voltage definition according to VDE0100, is being worked on. Within the scope of the invention, DC string voltages are to be switched which are a multiple of the voltage of an individual photovoltaic module.

The photovoltaic system comprises a switching device which is installed serially in the string line in order to switch the at least one photovoltaic string on and off with the switching device, i.e. the at least one photovoltaic string from the pantograph, e.g. from a central collection point or from an inverter.

The switching device comprises a hybrid switch with a, in particular electromechanical, relay and a semiconductor switching device connected in parallel with the relay, which has in particular at least one, preferably two semiconductor switches or transistors. As a result, the switching operations in which the phase voltage has to be switched can be carried out by the semiconductor switching device and the relay relieves the semiconductor switching device of the phase current when the relay is closed in continuous operation. In other words, on the one hand, the relay only switches the remaining voltage across the semiconductor switching device when switching on and off, and on the other hand, due to its low transmission resistance, the relay commutates almost completely the string current generated by the at least one photovoltaic string.

When the photovoltaic string is switched on, the semiconductor switching device, in particular, initially switches the photovoltaic string on by itself, the relay being open and initially remaining open. After a certain time delay, the relay is then additionally closed when the semiconductor switching device is previously closed, so that the semiconductor switching device is relieved of the current flow by the later-connected relay which is connected in parallel. As a result, the relay only needs to switch a low voltage and the semiconductor switching device needs the phase current

BE2017 / 5252 to be worn for a short time and not permanently. This can make cheap

Standard semiconductor switches and standard relays are used and the power loss in continuous operation can still be kept low. Switching off takes place in reverse order; first the relay is opened with the semiconductor switching device still closed and after a certain time delay the semiconductor switching device is opened with the relay already open. In other words, after the relay has been opened, the at least one photovoltaic string is switched off by additionally opening the semiconductor switching device.

The switching device is installed in the direct current part of the photovoltaic generator, preferably in front of the central collecting point, and switches the at least one photovoltaic string on and off here. However, the invention is not restricted to the fact that exactly one switching device switches exactly one photovoltaic string. It is also within the scope of the invention that several photovoltaic strings connected in parallel are switched together by the same switching device and also that the photovoltaic generator has only one photovoltaic string. Accordingly, part or all of the photovoltaic generator is generally switched by the switching device. In particular, however, it is not a circuit at module level with a low module voltage, but rather a circuit of a plurality of photovoltaic modules connected in series in the photovoltaic string, which requires the high switching voltage. So it is

Switching device between the plurality of serially connected photovoltaic modules and the current collector, e.g. the inverter or between the plurality of serially connected photovoltaic modules and a generator junction box. The switching device is electronic and can therefore be triggered externally. Therefore, the switching device, or if there are several switching devices, the switching devices can be triggered remotely by the user, which is advantageous compared to a conventional manually operated DC isolator in the generator junction box.

In spite of the DC string voltages and DC string currents typical in photovoltaic systems, the switching device is advantageously inexpensive, reliable and durable, and has a low power loss. In particular, it can be accommodated in a small installation space.

In an advantageous manner, a photovoltaic system is thus provided, which enables at least one photovoltaic string to be user-controlled and possibly electronic

BE2017 / 5252 triggered on and off, which is comfortable and ensures high safety standards, and is easy to maintain and repair.

The switching device is preferably used in the string cabling. In particular, the switching device is housed by a strand box spanning photovoltaic modules, preferably with a (plastic) housing, and this strand box is used in the strand wiring between the series connection of the photovoltaic modules and the pantograph. The strand box can have connectors at the input and / or output for releasable insertion in the strand line and for retrofitting. This makes it possible to retrofit existing photovoltaic systems.

The switching device can be placed in a string box, e.g. be integrated into a start box according to WO2014 / 122325 A1, which is hereby fully incorporated by reference.

The user can e.g. switch off the associated photovoltaic string at an external switch on the string box spanning the photovoltaic modules or the user selectively sends a switch-off trigger signal from one central control of the multi-string photovoltaic system to one, individual, several or all string boxes, in response to which Associated switching device or devices switches off or switch off the associated photovoltaic strings.

The user can thus advantageously locally on the associated photovoltaic string and / or centrally on the plant side, but in particular controlled across photovoltaic modules, specifically switch off the desired photovoltaic string or the current-carrying connection to the central collection point or inverter .

The switching device preferably switches either the positive pole or the negative pole and thus disconnects the electrical circuit of the at least one photovoltaic string. It can nevertheless be advantageous to insert the string box in both conductors (positive pole and negative pole) of the string line, in front of and behind the first or last photovoltaic module, in the at least one photovoltaic string.

The relay and the semiconductor switching device are connected in parallel to each other and the parallel connection of relay and semiconductor switching device is connected in series in the photovoltaic string. The relay and the semiconductor switching device are accordingly connected in series and parallel to one another in the photovoltaic string.

BE2017 / 5252

The photovoltaic system comprises a photovoltaic generator with one or more photovoltaic strings connected in parallel to one another. If several photovoltaic strings are connected in parallel, either one photovoltaic string or possibly several or all photovoltaic strings can be selectively switched on and off with the switching device, depending on which nominal currents the photovoltaic strings supply and for which current the switching device is designed. I.e. in the case of a plurality of photovoltaic strings, the switching device can be arranged upstream or downstream of the central collection point. The central collection point forms a parallel connection point of several photovoltaic strings. If there are several parallel photovoltaic strings (multi-strand photovoltaic system), however, it is particularly advantageous to arrange the switching device upstream of the central collection point.

This has several advantages: firstly, only the current of one photovoltaic string has to be switched per switching device and secondly, each photovoltaic string can be switched on and off individually. In a multistrand photovoltaic system, two or more photovoltaic strings are connected in parallel and the photovoltaic strings are each formed by series-connected photovoltaic modules.

In other words, in the direct current part of the photovoltaic system, the at least one photovoltaic string is removed from the pantograph, e.g. separated from the inverter by opening the hybrid switch and thereby interrupting the current flow from the at least one photovoltaic string to the pantograph and the at least one photovoltaic string is switched on by closing the hybrid switch and electrically connecting the at least one photovoltaic string to the pantograph that the current flow from the at least one photovoltaic string into the pantograph is made possible.

In particular, the switching device defines a closed and an open state and in the closed state conducts photovoltaically generated current from the at least one photovoltaic string to a current collector and in the open state interrupts the passage of photovoltaically generated current from the at least one photovoltaic string. Preferably, a control device is included, which is designed to open and / or close the switching device or the hybrid switch in response to a user input. Thus the user, e.g. in the event of malfunctions or for maintenance work, selectively switch the at least one photovoltaic string on and off at any time.

BE2017 / 5252

The control device is preferably designed to receive an external user-generated string shutdown trigger signal and to switch off the at least one photovoltaic string in response to the string shutdown trigger signal by the control device opening the switching device and thus separating the at least one photovoltaic string from the pantograph at least on one side. The switching device is therefore in particular an actively switchable and / or electronically controlled switching device.

In a multistrand photovoltaic system, at least one of the parallel photovoltaic strings, preferably all of the parallel photovoltaic strands in their respective associated string line, in particular between the photovoltaic modules of this respective photovoltaic string and the central collection point, has a switching device according to the invention , by means of which the current-carrying connection between this associated photovoltaic string and the central collection point can be user-controlled, i.e. selectively disconnected at the user's request, in order to specifically and individually disconnect the at least one photovoltaic string or any desired photovoltaic string from the parallel connection .

In other words, the switching device according to the invention can also be used for single-strand shutdown in a multi-strand photovoltaic system. I.e. a single or several individual photovoltaic strings can be switched off in a targeted manner and the other photovoltaic strands of the parallel connection remain in operation and can continue to feed in photovoltaically generated electricity via the central collecting point, in particular into the inverter. In this case the user can e.g. For maintenance purposes, repairs or in the event of localized malfunctions, selectively switch off one or more of the photovoltaic strings individually or disconnect the live connection of the photovoltaic strings desired by the user to the central collection point, so that they no longer feed in electricity via the central collection point. Accordingly, entire photovoltaic strings can be switched off (and not just individual photovoltaic modules) or the current-carrying connection of one or more entire photovoltaic strands to the central collection point can be disconnected.

The at least one semiconductor switch or transistor is in particular a field-effect transistor, preferably a MOSFET.

It has proven to be particularly advantageous if the switching device or the hybrid switch is designed to interrupt the current flow not only in one direction, but in both directions in the open state. This means that not only one

BE2017 / 5252

Safety shutdown e.g. in the event of malfunctions or for maintenance, that is to say an interruption in the flow of the current photovoltaically generated by the associated photovoltaic string. Currents in the opposite direction, i.e. cross or reverse currents, e.g. from other photovoltaic strings connected in parallel, in the associated photovoltaic. This is particularly advantageous in multi-strand photovoltaic systems, but is optional for the presently claimed invention.

This can e.g. can be achieved in that the hybrid switch comprises a back-to-back circuit comprising two semiconductor switches or transistors, in particular a back-to-back circuit comprising two field-effect transistors, preferably comprising two MOSFETs, or the semiconductor switching device comprises such a back-to -Back circuit exists. In other words, the hybrid switch is a parallel connection made up of the relay and a back-to-back connection made up of two semiconductor switches, in particular a parallel connection made up of a relay and a back-to-back connection made up of two field-effect transistors, preferably MOSFETs. This parallel connection is connected in series in the string line.

According to a preferred embodiment of the invention, the switching device can additionally comprise a reverse current protection circuit. The switching device can comprise a sensor connected to the control device for measuring an electrical characteristic on the associated photovoltaic string, the control device being designed in response to the electrical characteristic measured with the sensor to connect the associated photovoltaic string to the central collection point to also interrupt automatically in the reverse flow direction. In other words, the switching device is preferably combined with the reverse current protection function according to DE 10 2016 117 049. Thus, the advantages of backflow prevention according to the invention described in DE 10 2016 117 049 and a user-controlled shutdown in the DC part of a photovoltaic system can be combined, but this is optional.

The switching device is preferably designed to first close the semiconductor switching device, in particular the field-effect transistor or transistors, preferably MOSFETs, when the associated photovoltaic string or electrical connection to the pantograph is switched on, and only then after a time delay does the relay close shut down.

The switching device is preferably also designed to switch off the associated photovoltaic string, or disconnect the associated photovoltaic string from the

BE2017 / 5252

Current collector, first to open the relay and only after a time delay afterwards to open the semiconductor switching device, in particular the field effect transistor or transistors, preferably MOSFETs.

This ensures that the relay does not have to switch the full phase voltage, so that an arc that may not be extinguished due to the DC voltage can be avoided. Nevertheless, the relay relieves the

Semiconductor switching device in continuous operation, so that the permanent power loss can be kept in a range acceptable for the special installation conditions in a photovoltaic generator. Advantageously, no high current relay needs to be used, but a simple, small, standard relay can be used. The relay is protected, which is conducive to the longevity of the switchgear and which guarantees safety, reliability and longevity to the extent required for photovoltaic systems.

The switching device can be designed to carry out a test routine before the (re) switching on of the at least one photovoltaic string, to test at least one electrical characteristic of the associated photovoltaic string in the test routine and to maintain a predefined threshold value for the at least one electrical characteristic to switch on the at least one photovoltaic string if there is user authorization.

The switching device can also be designed to measure the photovoltaically generated current flow through the associated string line and to close the relay only when the photovoltaically generated current I flowing through the string line exceeds a predefined threshold value l_min, or after a time delay after that photovoltaically generated current I flowing through the string line has exceeded a predefined threshold value l_min.

The switching device can also contain a control device and a sensor device connected to the control device for measuring at least one electrical parameter on the associated photovoltaic string. In response to the at least one electrical characteristic measured with the sensor device, the control device can be designed to electrically connect the associated photovoltaic string to the current collector when a user release is present, the sensor device in particular comprising an input voltage sensor which detects the input voltage U1 on the string side Switching device measures and / or comprises an output voltage sensor, which the

BE2017 / 5252 measures the output voltage U2 at the switching point on the switching device. The

Control device can be designed in response to the measured strand-side

Input voltage U1 and / or to control the switching operations of the relay and / or the semiconductor switch on the measured output voltage U2 at the common point.

Advantageously, when switching on, a plurality of switching operations can first be carried out by the semiconductor switching device, e.g. the back-to-back MOSFET circuit are performed, e.g. until certain operating parameters are reached before the relay is closed. In other words, when switched on, the relay remains open until certain operating parameters are reached, even if several switching operations are carried out with the semiconductor switching device during this time. In this way the number of switching operations of the relay can be kept low. In production or continuous operation, especially after the desired operating parameters have been reached, the relay then relieves the load on the semiconductor switching device. Nevertheless, with the hybrid switch fully open, i.e. when both the semiconductor switches and the relay are open, bidirectional disconnection of the electrical connection is achieved, i.e. the flow of electricity will be interrupted in both directions if a back-to-back circuit is used.

The time delay when switching on and / or when switching off is preferably less than or equal to 2000 ms, preferably less than or equal to 700 ms, preferably less than or equal to 300 ms. At least the semiconductor switching device should not be closed for longer than this maximum delay time and should not be relieved by the relay, i.e. the semiconductor switching device should be closed and the relay should be open when the full (nominal) phase current or when a phase current greater than or equal to 5 A, greater than or equal to 8 A, greater than or equal to 10 A, or 12.5 A +/- 40% flows through the semiconductor switching device. I.e. the maximum delay time can be calculated from the point in time from which, at least theoretically, the nominal current could flow if the irradiation is correspondingly large. In other words, the hybrid switch is controlled so that a state in which the semiconductor switching device is closed, the relay is opened and at the same time the rated current can flow, i.e. the rated current can flow through the unloaded semiconductor circuit no longer than the maximum delay time. More preferably, the delay time is between 50 ms and 2000 ms, preferably between 100 ms and 1000 ms, preferably between 150 ms and 500 ms, preferably between 200 ms and 300 ms, at least if a string current flows in the photovoltaic string or

BE2017 / 5252 can flow at least, which essentially corresponds to the nominal current. Depending on which components are used, the semiconductor switching device can pass through the full strand power at least for a correspondingly short delay time even without relief from the relay, even if it is installed in a strand box without special cooling measures. The time delay of the switching process of the semiconductor switching device can accordingly be related to the previous switching process of the relay or vice versa or to reaching certain threshold values for the electrical parameters, e.g. for the input voltage U1, for the output voltage U2 and / or for the phase current I.

The part of the photovoltaic generator that is switched by the switching device, in particular the associated photovoltaic string, preferably has a DC nominal voltage of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V +/- 30% and / or a DC nominal current of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of 12.5 A +/- 40%.

The hybrid switch as a whole is accordingly for a DC switching voltage of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V +/- 30% and / or for a DC through current of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of 12.5 A +/- 40%. In particular, the hybrid switch as a whole is designed for a DC switching voltage of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V +/- 30%.

In particular, the semiconductor switching device or the field-effect transistors, preferably MOSFETs, preferably for a drain-source voltage (Vds) of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V +/- 30% trained.

The semiconductor switching device or the field effect transistors, preferably MOSFETs, are preferably for a drain current (Id) of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of 12.5 A. +/- 40% trained.

Due to the short duration of the current flow through the semiconductor switching device, the power loss that arises at the hybrid switch is still acceptable. Excessively large and expensive semiconductor switches need not be used.

BE2017 / 5252

Field-effect transistors, preferably MOSFETs, can be used which have an on-resistance (resistance-drain-source-on, or RDS-on) of greater than or equal to

100 mOhm, preferably greater than or equal to 300 mOhm, preferably greater than or equal to

500 mOhm, preferably of 690 mOhm +/- 40%.

Although this produces a relatively large loss line of possibly one watt, a few watts or more, this is acceptable in particular due to the relief provided by the relay connected in parallel. Such field effect transistors, in particular MOSFETs, are available inexpensively and have a small size.

The semiconductor switch or switches, field-effect transistors or MOSFETs can, based on a nominal current of 8.5 A or 10 A of the at least one photovoltaic string, even a calculated power loss of greater than or equal to 2 W, greater than or equal to 5 W, of greater than or equal to 10 W, in particular greater than or equal to 40 W, if the semiconductor switch or switches, field-effect transistors or MOSFETs are closed and the relay is open (intermediate switching state).

On the other hand, the hybrid switch generates based on a nominal current of

8.5 A or 10 A of the at least one photovoltaic string nevertheless only has a calculated power loss of preferably less than or equal to 10 W, preferably less than or equal to 5 W, preferably less than or equal to 2 W, preferably less than or equal to 1 W, if the semiconductor switching device and the relays are closed (continuous operation). In particular, the hybrid switch has a power loss of less than or equal to 1 W in production operation, for example at 1000 volts and 10 amperes (typically plus 25% reserve) per photovoltaic string when the semiconductor switching device and the relay are closed.

The relay is preferably for a DC through current of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of

12.5 A +/- 40% trained. On the other hand, it is preferably sufficient if the relay is designed for a DC switching current of less than or equal to 8 A, in particular less than or equal to 6 A, in particular less than or equal to 4 A, in particular of 2 A +/- 50%.

Furthermore, it is preferably sufficient if the relay has a maximum AC switching voltage of less than or equal to 800 V, in particular less than or equal to 500 V, in particular of 400 V +/- 50%.

This keeps the cost and size of the relay, especially for installation in a string box, also within reasonable limits.

BE2017 / 5252

Furthermore, the switching device can preferably be designed to check electrical parameters of the associated photovoltaic string in a test routine before the (re) switching on of the associated photovoltaic string and to close the switching device if predefined threshold values for the electrical parameters are maintained and after user approval. I.e. The switching device is only closed when both are present, i.e. if both the test conditions for the electrical parameters are met and the user is approved for (re) switching on. Only then is the associated photovoltaic string switched on again. In particular, the semiconductor switches can initially be closed as a test and, with the relay still open, electrical parameters such as input voltage, output voltage and / or the phase current can be measured. This process can be repeated several times before the relay is also closed, so that the relay can be protected.

In particular, the switching device thus comprises a current sensor, which measures the photovoltaically generated current flow through the associated string line. The switching device preferably closes the relay only when the photovoltaically generated current flowing through the string line exceeds a predefined threshold value. This can ensure that the associated photovoltaic string is only put into permanent production operation when it is fully operational.

The photovoltaically generated current preferably flows at least temporarily, in particular in the permanent production operation of the photovoltaic string, in the part of the photovoltaic string in which the full nominal voltage of the plurality of serial photovoltaic modules or of the entire photovoltaic string is present, preferably exclusively, through metallic conductors. e.g. Metal cables, metal connectors and the relay and at least not permanently through semiconductor components. As a result, the power loss can advantageously be kept low, so that the switching device can optionally be installed in existing housings without these overheating.

In a multistrand photovoltaic system, each parallel photovoltaic string preferably has such a switching device in front of the central collection point. The switching devices are cross-photovoltaic module, i.e. are each responsible for the entire photovoltaic string with several series-connected photovoltaic modules.

BE2017 / 5252

The switching devices have a positive pole input and a negative pole input for connecting the positive pole or negative pole of the string line on the input side (i.e. photovoltaic string or photovoltaic module side) and a positive pole output and a negative pole output for connecting the positive pole or negative pole on the output side (i.e. on the collecting point side) Continuation of the string line up to the central collection point of the photovoltaic strings or up to the DC input of the inverter. Accordingly, in particular the entire phase voltage is applied to the switching device and / or the entire phase current flows through the switching device

As already stated above, the present invention has particular advantages in combination with the reverse current protection according to DE 10 2016 117 049. If the switching device also acts as a reverse current protection device in a multi-strand photovoltaic system, this additionally prevents a cross current from becoming so large that the direction of the current flow in the associated photovoltaic string is reversed, ie a negative current flows back into the associated photovoltaic string. This can be done in particular with the back-to-back circuit comprising two semiconductor switches, in particular the back-to-back circuit consisting of two field effect transistors, e.g. MOSFETs can be achieved. In an advantageous manner, undesired reverse currents can be prevented, which could otherwise arise if the associated photovoltaic string should have a lower impedance than the inverter or corresponding pantograph downstream of the central collecting point. This can have a positive impact on the lifespan of the associated photovoltaic modules. Depending on the safety equipment of the photovoltaic system, the reverse current protection function can also increase the safety of the system, especially when switching off individual photovoltaic strings or the photovoltaic system, e.g. due to insufficient radiation, maintenance work or in the event of a hazard shutdown, in particular in which the reverse current protection function prevents the associated photovoltaic string from being switched off due to reverse current.

The switching device is preferably installed in an electrically insulating housing which has a positive pole connection for the positive pole of the string line and a negative pole connection for the negative pole of the string line of the associated photovoltaic string at the string-side input. Furthermore, the switching device preferably has a positive pole connection for the positive pole and a negative pole connection for the negative pole of the extension of the branch line, which leads to the central one, at the output on the common point

BE2017 / 5252

Collection point leads to. The connections on the housing are preferably as photovoltaic connectors, e.g. trained in accordance with the applicant's SUNCLIX® system. The housing with the switching device, which can be inserted with the connectors in the two lines of the string line of the associated photovoltaic module, can therefore form a separately pluggable unit in the form of a string box, which can also be used as a retrofit solution in existing string lines between the photovoltaic modules one photovoltaic string each and the central collection point or the common inverter can be inserted in order to retrofit an existing multistrand photovoltaic system.

The switching device preferably contains a sensor connected to the control device for measuring an electrical parameter on the associated photovoltaic string. In response to the electrical characteristic measured with the sensor, the control device can switch the switching device, but possibly only if there is also user authorization. In particular, in response to the electrical characteristic measured with the sensor, the control device prevents the switching device and / or at least the relay, e.g. if the measured electrical parameter lies outside a safety condition for the first electrical parameter that is relevant for the restart.

The sensor is preferably a current sensor or a voltage sensor, which measures at least one of the following electrical parameters:

- input voltage at the string-side input of the switching device,

- output voltage at the collector-side or inverter-side output of the switching device,

- string current of the associated photovoltaic string or through the switching device or string box,

- negative current flow.

A negative current flow means that the current in the photovoltaic string flows through the switching device counter to the flow direction of the current photovoltaically generated during operation. I.e. the current sensor is in particular designed to also be able to measure a negative current flow.

In response to one or more of these electrical parameters measured with the sensor or sensors, the hybrid switch can open and interrupt the connection of the associated photovoltaic string to the pantograph. The switching device thus contains

BE2017 / 5252 preferably a current sensor that can also measure negative currents and / or one if necessary

Input voltage sensor and / or an output voltage sensor.

Further details of an optional additional backflow prevention are in the

Described below.

According to a preferred embodiment of the invention, the sensor is a current sensor, which can also measure a negative current flow through the switching device. The switching device can connect the associated photovoltaic string to the central collection point, i.e. to the parallel connection with the other photovoltaic strings and to the direct current input of the inverter, at least if the current in the associated photovoltaic string is negative and / or exceeds a predefined threshold value for the amount of the negative current. However, a negative current is not a necessary prerequisite for the disconnection. Depending on which operating and safety parameters are specified, the switching device can also carry out the interruption even if the current is still positive but is below a predefined safety threshold value. This can e.g. then occur when the photovoltaic modules of the associated photovoltaic string are shaded considerably more than the photovoltaic modules of the other photovoltaic strings. In this case, the cross currents may not yet result in a negative total current flow in the associated photovoltaic string, but may reduce the current generated by the photovoltaic string from the associated photovoltaic string so far that the production operation of this associated photovoltaic string is no longer economically sensible, so that it is better to interrupt the connection of this associated photovoltaic string to the parallel connection with the other photovoltaic strings and to the common inverter. This can be particularly useful if the current measured by the switching device is still positive, but considerably below the maximum current of the photovoltaic string, e.g. is less than 10% of the maximum current of the photovoltaic string. In other words, the control device is preferably designed to switch the switching device automatically, or to interrupt the connection of the associated photovoltaic string to the parallel connection and to the inverter, if the condition occurs that the string current I becomes smaller than a predefined threshold value OK. The predefined threshold value IO can be between positive and considerably smaller than the maximum current of the associated photovoltaic string and one

BE2017 / 5252 negative safety value for the current flow can be selected. Expressed mathematically, the switching condition can be defined as l <IO, where IO is selected from an interval [11,12], where 11 is a negative safety value at which the associated photovoltaic string could be damaged and I2 is a positive value below which a economic operation no longer makes sense.

In particular, the switching device also electrically connects the associated photovoltaic k string to the parallel connection with the other photovoltaic k strings and to the common inverter if the operating and safety parameters permit this and the user release, e.g. in the form of a trigger signal, e.g. by a closed switch. For this purpose, the control device is connected to a sensor device for measuring at least one electrical parameter.

According to a preferred embodiment, the switching device switches the associated photovoltaic string, whose connection to the central collecting point is interrupted, back to the central collecting point with the other parallel ones in response to the measured string-side input voltage and / or to the measured collecting point-side or inverter-side output voltage Photovoltaic strings and thus to the DC input of the inverter electrically when the user approval is available.

According to a further preferred embodiment of the invention, the input voltage is compared with the output voltage and the control device controls the switching device in response to the comparison of the measured string-side input voltage and the measured pantograph-side output voltage, in particular to the extent that the associated photovoltaic k string, its connection to the Pantograph is interrupted, reapply to the pantograph when user approval is available. The voltage comparison can ensure that the desired operating and safety parameters are fulfilled after the relevant photovoltaic string has been switched on again, e.g. that no negative current flows back into the associated photovoltaic k string or that the positive production current exceeds a minimum value by the associated photovoltaic k string being switched on again electrically only when the difference between output voltage U2 minus input voltage U1 is less than one predefined threshold U0. If U0 = 0, this means that the output voltage U2 is lower than the input voltage U1. A certain tolerance can be present here, in particular the effect that the input voltage of the associated one can be exploited

BE2017 / 5252

The photovoltaic string whose connection to the central collection point is broken is the open circuit voltage, whereas the output voltage, which represents the voltage generated by the other parallel photovoltaic modules, already represents a load voltage, which is typically about 20% lower than the open circuit voltage because the inverter is already working. Accordingly, in response to the comparison of the open circuit voltage of the associated photovoltaic string with the load voltage of the other photovoltaic strings, the control device can return the associated photovoltaic string, whose connection to the central collecting point is interrupted, to the central collecting point with the other parallel photovoltaic strips. Connect the strings and thus to the DC input of the inverter if the user approval is available. In addition to the voltage comparison, it can also be checked whether the voltage of the associated photovoltaic string exceeds a predefined threshold value U_min, e.g. to ensure that the associated photovoltaic string can generate sufficient power at this time.

In the closed state, the switching device electrically connects the associated photovoltaic string to the pantograph and, in the open state, bi-directionally interrupts the current-carrying connection of the associated photovoltaic string to the pantograph within the string line.

The semiconductor switches and / or the relay used are preferably designed as NO contacts (normally off or normally open). At first glance, this might appear to be disadvantageous, since electrical power is required to maintain the on state. However, this is accepted in order to achieve the associated safety, namely that the connection of the associated photovoltaic string is interrupted in the normal state of the switching device to the parallel connection with the other photovoltaic strings and to the direct current input of the inverter.

The presently disclosed invention can be used particularly advantageously in photovoltaic systems in which the series-connected photovoltaic modules in at least one of the photovoltaic strings, preferably in all photovoltaic strings, each have protective circuits by means of which the photovoltaic modules are individually isolated from the associated one Photovoltaic string can be switched off, and the protective circuits of the individual photovoltaic modules short-circuit the output of the respective photovoltaic module at the connection points for the string line in order to generate a low-resistance bypass for the respective photovoltaic module. Such protective circuits for the photovoltaic modules

BE2017 / 5252 are described in more detail in WO2013 / 026539 A1, to which reference is hereby made and which in this regard is hereby incorporated by reference. Furthermore, the presently disclosed invention can be used particularly advantageously in photovoltaic systems in which the associated photovoltaic string has a start circuit which is designed to reactivate such or other protective circuits of the individual photovoltaic modules of the associated photovoltaic string. Such starting circuits for the photovoltaic strings are described in more detail in WO2014 / 122325 A1, to which reference is hereby made and which in this regard is hereby incorporated by reference.

Such a start circuit for starting the associated photovoltaic string and the switching device for the associated photovoltaic string can preferably be accommodated in a common housing, so that a string box with a combined on and off function for the associated photovoltaic string is created. The strand box is provided with positive pole and negative pole connections at the input and positive pole and negative pole connections at the output of the strand box between the series of photovoltaic modules of the associated photovoltaic string and the central assembly point with the other photovoltaic strings in the associated photovoltaic String switched. In this way, superfluous components, in particular plug connections, can be saved, which can have a positive effect on costs, service life and loss conduction of the photovoltaic system. The power loss of the switching device is so low in production with the relay closed that the thermal load is acceptable.

Each photovoltaic string is preferably equipped with the switching device or string box described above for the photovoltaic module.

The invention further relates to an electronically controlled direct current isolating switching device for the direct current part of a photovoltaic system for separating at least one photovoltaic string from a pantograph, e.g. an inverter, the DC isolating switching device being a hybrid switch consisting of a relay, in particular an electromechanical relay, and a relay connected in parallel with the relay

Semiconductor switching device includes.

The invention further relates to the use of such a switching device for the direct current part of a photovoltaic system.

BE2017 / 5252

The invention further relates to a method for user-controlled shutdown and

Reactivating at least one photovoltaic string of a photovoltaic system, comprising the following steps:

user-controlled triggering of the switching device of the at least one photovoltaic string by an electrical or electronic trigger signal in order to disconnect the at least one photovoltaic string from the pantograph, user-controlled triggering of the switching device of the at least one photovoltaic string by an electrical or electronic trigger signal to the at least one photovoltaic string to connect to the pantograph, possibly in response to the fulfillment of further test conditions.

It is obvious to the person skilled in the art that the invention can be used particularly advantageously for photovoltaic systems, but in principle can also be used for other DC generators. These should not be excluded.

The invention is explained in more detail below on the basis of exemplary embodiments and with reference to the figures, the same and similar elements being partially provided with the same reference numerals and the features of the different

Embodiments can be combined.

Brief description of the figures

Show it:

1 is a block diagram of a photovoltaic system with parallel photovoltaic strings,

2 shows a block diagram of a protective circuit for a photovoltaic module,

3 is a block diagram of a strand box with the switching device,

4 shows a circuit diagram of the control of the hybrid circuit comprising a relay and a MOSFET back-to-back circuit,

Fig. 5 is a circuit diagram for a switching power supply for driving the MOSFET back-to-back circuit, and

Fig. 6 is a flowchart for starting, checking and switching off the associated

Photovoltaic string.

Detailed description of the invention

BE2017 / 5252

Referring to FIG. 1, the multi-strand photovoltaic system 1 comprises one

A plurality of photovoltaic strings connected in parallel, of which only two photovoltaic strands 10, 10 'are shown for the sake of simplicity.

Each photovoltaic string comprises a plurality of photovoltaic modules or panels 12, 12 ', each of which is equipped with a protective circuit 14, 14', e.g. as described in WO 2013/026539 A1. The protective circuits 14, 14 'are each assigned to a photovoltaic module 12, 12' and the respective string line 16, 16 'leads through the protective circuit 14, 14' associated with the photovoltaic string 10, 10 'with two poles.

With reference to FIG. 2, each protective circuit 14, 14 ′ contains a short-circuit switch S3 for short-circuiting the associated photovoltaic module 12, 12 ′ as well as a serial isolating switch S4, with which the associated photovoltaic module 12, 12 ′ from the photovoltaic string 10 , 10 'can be separated. In the event of shading or failure of a photovoltaic module 12, 12 ', the short-circuit switch S3 closes and the serial isolating switch S4 opens, so that the respective photovoltaic module 12, 12' is disconnected from the photovoltaic line, runs idle and the photovoltaic line 10, 10 'nevertheless remains closed, so that the photovoltaically generated current of the other photovoltaic modules of this photovoltaic string 10, 10 'can continue to flow through the string line 16, 16', which is also closed in this protected state. For further details of the protective circuit 14, 14 ′ which is optional for the present invention, reference is made to WO 2013/026539, which in this regard is hereby made the subject of the present disclosure by reference.

Referring back to FIG. 1, a string box 20, 20 'is inserted into each photovoltaic string 10, 10', which can be designed as start boxes in accordance with WO 2014/122325 A1, and through which both string lines 16, 16 'pass .

On the inverter side of the string boxes 20, 20 'are continuations 17, 17' of the string lines 16,

16 'at a central collection point 22a, 22b, or its plus and minus pole, connected in parallel in order to connect the photovoltaically generated power of several photovoltaic strings 10, 10' etc. in this example to the DC input 24a, 24b of the feed common inverter 26. At the alternating current output 28 of the inverter 26, the alternating current is made available for feeding into a supply network.

BE2017 / 5252

In this example, the string boxes 20, 20 'are supplied by an external 24-volt power supply unit (FIG. 2) in order to carry out the desired switching operations. However, the supply can also be provided by a start photovoltaic module which does not have a protective circuit 14,

14 ″ and thus automatically supplies the respective photovoltaic string 10,10 ″ and thus also the associated string box 20,20 ″ with electrical power in the event of light. For further details, reference is made to WO 2014/122325 A1, which in this regard is hereby made the subject of the present disclosure by reference.

3, a string box 20 of one of the photovoltaic strings 10 is shown in more detail. All other photovoltaic strings 10, 10 'etc. connected in parallel, if present, are preferably constructed identically. However, the present invention can also be used in a single-strand photovoltaic system 1, that is to say with a DC generator 2, which consists of only one photovoltaic strand 10.

The photovoltaic modules 12 with a connected protective circuit 14, which is not shown separately in FIG. 3 for reasons of simplicity, form the photovoltaic string 10 in series connection. The positive pole 16a and the negative pole 16b of the string line 16 are connected to a positive pole input 34a and a negative pole input, respectively 34b of the strand box 20 connected in order to be fed into the strand box 20. Corresponding extensions 17 of the string line 16 to the positive pole 24a or to the negative pole 24b of the direct current input 24 of the inverter 26, which in this example forms the current collector for the photovoltaically generated current, are connected to a positive pole output 36a or a negative pole output 36b. The current photovoltaically generated by the photovoltaic modules 12 of the photovoltaic string 10 therefore flows through the string box 20 during production operation. At the inputs and outputs 34a, 34b; 36a, 36b, the module-side and assembly-side sections 16 of the strand line are preferably connected with plug connectors (not shown).

Further optional parallel photovoltaic strings 10 'are symbolized by the dashed lines which lead to the two poles of the central collecting point 22a, 22b.

The strand box 20 contains a switching device 38, which is integrated into the preferably waterproof plastic housing 21 of the strand box 20. The switching device 38 comprises a hybrid switch S1, which is connected in series in the photovoltaic string 10, in this example in a branch of the string line (in this example the positive pole). With the serial hybrid switch S1, the current-carrying connection of the associated photovoltaic string 10 to the inverter 26 can be interrupted in a user-controlled manner, and the associated one

BE2017 / 5252

Photovoltaic string 10 can thus be switched off. A control device 42 in the form of a

The microcontroller controls the serial hybrid switch S1, which can also be referred to as an isolating hybrid switch, and monitors a current sensor 44, one

Input voltage sensor 46 and an output voltage sensor 48 to electrical

To obtain parameters of the associated photovoltaic string 10.

The input voltage sensor 46 is connected in parallel to the input connections 34a, 34b of the string box 20 in order to measure the input voltage U1, which is the string voltage of the associated photovoltaic string 10. The output voltage sensor 48 is connected in parallel to the output connections 36a, 36b of the string box 20 in order to measure the output voltage U2, which is the voltage that is present at the inverter 26. In the case of a multi-strand photovoltaic system, the output voltage U2 is the voltage which is applied to the inverter 26 by the parallel connection of all other photovoltaic strings. In production operation, the current sensor 44 measures the string current which flows through the string line 16, the string box 20 and the continuation of the string line 17 into the inverter 26 in the normal direction, which is referred to here as positive, when the photovoltaic string 10 is producing current to be fed into the inverter 26. The current sensor 44 is optionally also designed to detect a current flow in the reverse direction, i.e. to measure a current which is negative with respect to the normal current direction of production of the photovoltaic string 10 (that is to say with the opposite polarity to the direct current inputs 24a, 24b of the inverter). Alternatively, however, two separate current sensors, one for the positive current flow and one for the negative current flow, can also be provided (not shown). If desired, the switching device 38 is accordingly designed to measure positive and / or negative current flow.

In the basic position of the string box 20 or the switching device 38, the serial hybrid switch S1 is open and is in its normal state (normally open). A main function of the serial hybrid switch S1 is to interrupt the current-carrying connection of the associated photovoltaic string 10 to the inverter 26. A short-circuit switch S2 is used to trigger string-side short-circuits in the associated photovoltaic string 10 and to activate the photovoltaic modules 12 of the associated photovoltaic string 10 via an impressed starting current. After sending the start pulse, the phase voltage U1 and the inverter voltage U2 are measured and compared in order to respond to the associated voltage response

BE2017 / 5252

To electrically connect the photovoltaic string 10 to the inverter 26, if necessary if there is a corresponding user release.

In this example, the serial hybrid switch S1 is closed in response to a comparison of the phase voltage U1 and the inverter voltage U2, i.e. the switching condition for the connection process of the serial hybrid switch S1 depends in this example on a comparison of the phase voltage U1 and the inverter voltage U2. The serial hybrid switch S1 is only closed when the string voltage U1 of the associated photovoltaic string 10 is either greater than the inverter voltage U2 or only by a predetermined threshold value U0 (slightly) less than the inverter voltage U2. In other words, a switching condition for the serial hybrid switch S1 for electrically switching on the photovoltaic string 10 to the parallel connection and to the inverter 26: U1> = U2-U0, where U0 is a predefined value for the maximum permissible voltage difference for the safe switching on of the associated photovoltaic string 10 to the inverter. The predefined switching value U0 stored in the microcontroller is accordingly (significantly) smaller than the maximum possible voltage of the associated photovoltaic string 10. Only when such a switching condition, which depends on electrical parameters of the associated photovoltaic string 10 and possibly the other photovoltaic strings , is fulfilled, the control device 42 controls the serial hybrid switch S1 in such a way that the hybrid switch S1 is closed and thus connects the associated photovoltaic string 10 to the inverter 26. In this special exemplary embodiment, it is thus possible to start the associated photovoltaic string 10 even without the risk of undesired reverse currents occurring.

In order to detect undesired reverse currents from the other photovoltaic strings present in this example in the associated photovoltaic string 10 in the production mode in which the serial hybrid switch S1 is closed, the current flow including the direction of current flow is monitored during the production mode. For this purpose, a current measurement is carried out using the current sensor 44. The current sensor 44 accordingly carries out permanent monitoring of the phase current, including the sign of the phase current, that is to say as to whether the phase current is negative. If the string current should become negative or a state close to that is reached, the microcontroller 42 controls the serial hybrid switch S1 to open and the

BE2017 / 5252 current-carrying connection of the photovoltaic string 10 to the central collection point 22a, 22b and to the inverter 26 is interrupted.

So that all string boxes 20 cleanly separate the associated photovoltaic string 10 from the inverter 26 when the entire photovoltaic system 1 shuts down, the serial hybrid switches S1 of all switching devices 38 of all photovoltaic strings are also opened, preferably and if available, as soon as the inverter voltage U2 is below a predefined minimum voltage U_min, U_min, for example can be in the range of about 30 volts.

3 and 4, the hybrid switch S1 comprises a parallel circuit comprising a back-to-back circuit 50 of two semiconductor switches, in this example two field-effect transistors, more precisely two MOS-FETs 52, and an electromechanical relay 54. The hybrid switch S1 as a whole is designed for the full nominal string voltage and the full nominal string current of the associated photovoltaic string 10, which are typically up to 1000 volts or even 1500 volts and, for example, 10 A. However, the MOS-FETs 52 have a typical switch-on resistance, the so-called resistance drain source-on or RDS-on for short, of 690 mOhm in this example. This can result in a power loss in the region of a few watts in a typical photovoltaic string 10 on the MOS-FETs 52. For example, with an RDS-on of 690 mOhm and a nominal phase current of lnom = 10 A, there is a calculated power loss Pvl = RDS-on * (lnom) ² , ie Pvl = 69 watts in this example. Since such a power loss is particularly undesirable for installation in existing (plastic) housings, the relay 54 relieves the back-to-back circuit 50 from the two MOS-FETs 52 in continuous operation. That is, the switch-on process is first carried out by the back-to-back circuit from the two MOS-FETs 52 and when the associated photovoltaic string 10 is in production operation for a certain minimum time, the parallel relay 54 is closed to the MOS-FETs Relieve 52. This on the one hand avoids the permanent generation of high power loss at the MOS-FETs 52 and on the other hand a relay 54 can be used which would not be suitable on its own.

Carry out switching operations at a nominal DC phase voltage of 1000 V or even 1500 V without the DC voltage causing an increased risk of a non-extinguishing arc.

BE2017 / 5252

The hybrid switch S1 can despite the high demands on nominal

String voltage, nominal string current and the direct current application can be built with commercially available, relatively small and inexpensive components.

E.g. the RT.3T and RTS3L relays from TE Connectivity Ltd. (see.

www.te.com) with the following properties:

Pole 16A,

Form A (NO) contact (AgSnO2 or W pre-make contact + AgSnO2) mono- or bistable coil 5kV / 10mm coil contact reinforced insulation

WG version: Product according to IEC60335-1

RTS3T: UL508 / NEMA410 electronic ballast rated RTS3T: 165 / 20ms inrush current

contact details

Contact arrangement

nominal voltage

Max. Switching voltage

Rated current

Limiting continuous current Limiting inrush current, max. 20ms (incandescent lamps) max. 200ps

Switching capacity max.

Contact material

Contact type

Operating frequency, with / without load Operating / tripping time max., DC coil

RT.3T

RTS3L

Operating / reset time max., Bistable version bounce time

Form A (NO) contact 250VAC 400VAC

16A

16A, UL: 20A (RTS3L)

165A peak 800A peak

4000VA

W (pre-make cont.) + AgSnO2 pre-make contact

360 / 3600h- ¹

10 / 5ms

120A peak

10 / 10ms max. 4ms

AgSnO2 single contact

BE2017 / 5252

For the back-to-back circuit 50, e.g. the STH12N120K5-2 type MOSFETs,

STP12N120K5, STW12N120K5, or STWA12N120K5 from ST (see www.st.com) with the following

Properties proven to be suitable:

2017/5252

Vos: 1200 V

RDS-on max. 690 mOhm Id 12A

Ptot 250 W.

Vgs gate-source voltage ± 30 V

Id drain current at Tc = 25 ° C 12 A.

Id drain current at Tc = 100 ° C 7.6 A.

Idm drain current (pulsed) 48 A

Ptot total dissipation at Tc = 25 ° C 250 W.

Iar Max current during repeated or single pulse avalanche 4 A

Eas single pulse avalanche energy 215 mJ dv / dt peak diode reset voltage drop 4.5V / ns dv / dt MOSFET dv / dt insensitivity 50 V / ns

With such a hybrid circuit S1 consisting of the relay 54 and the MOSFET back-to-back circuit 50, as well as the associated control electronics, the photovoltaic string can be switched on and off safely and in the long term.

The current-carrying connection between the associated photovoltaic string 10 or the part of the DC generator 2 connected therewith and the central collection point 22a, 22b or the inverter 26 is thus separated, in this example even bidirectionally, by means of the hybrid switch S1, i.e. a possible current flow, in this example in both directions, is interrupted.

If the user initiates a trigger signal to switch off, which is indicated here with the test condition “U ext. Start = Off ¹ , the control device 42 automatically opens the hybrid switch S1.

When the photovoltaic string 10 is switched off, the relay 54 is opened first and only after a time delay the back-to-back circuit 50 is opened in order to remove the associated one

BE2017 / 5252

Separate photovoltaic string 10 from the central collection point 22a, 22b. The

In this exemplary embodiment, the time delay when switching on and / or switching off is approximately 200 ms to 300 ms, which is short enough not to overload the MOSFET back-to-back circuit 50/52 without special cooling.

4 shows the hybrid switch S1 with a control circuit 60 for controlling the relay 54 and a more detailed illustration of the MOSFET back-to-back circuit 50/52.

At the control input 62 “relay”, the control circuit 60 receives a standard signal (0/1) as a trigger signal from the control device 42. A bipolar transistor 64 switches against ground 66 “GND”. A freewheeling element, in this example a freewheeling diode 68, is connected in parallel with the relay 54 to interrupt the spark. The gate voltage of the semiconductor switching device 50 or FET back-to-back circuit is potential-free against source.

5 shows a switching power supply 70 for driving the MOSFET back-to-back circuit 50/52. Up to 10 A flow via drain 72. A clock generator 74 outputs a 50/50 clock pulse at approximately 200 kHz to the switching transistors 76. This part of the control, which generates the control signal for the MOSFET back-to-back circuit 50/52 , is electrically isolated from the MOSFET back-to-back circuit 50/52. The electrical isolation is produced by means of a circuit board transformer 78.

The diodes V17, C35, C36 rectify and smooth the chopped voltage of 19.4 V.

Furthermore, the control for the MOSFET back-to-back circuit 50/52 includes an optocoupler 82, which effects a galvanic separation from the control device 42. The control signal is provided via the control output 84 and the voltage of the power supply unit is connected to the MOSFET back-to-back circuit 50/52 via the optocoupler 82.

The gate 86 and source 88 connections are the powers that are connected to the MOSFET back-to-back circuit 50/52.

6, the start and shutdown sequence of the switching device 38 proceeds, for example, as follows.

At system start at 102, the hybrid switch S1 is open in step 104 (semiconductor switching device 50 and relay 54 open). A query in step 106 checks whether the input voltage U1 falls below a minimum voltage U_min1. If the condition U1 <U_min1, in the present example U_min1 = 30 V DC, is fulfilled and the user is enabled to start (U ext. Start = on), in step 108 with the

BE2017 / 5252

Short-circuit switch S2 triggered the start pulses to start the associated photovoltaic string 10. The serial hybrid switch S1 remains open and the loop goes back to

Step 104.

If the associated photovoltaic string 10 has now started as a result of the start pulses, in that the associated protective circuits 14 have electrically connected the associated photovoltaic modules 12 to the photovoltaic string 10, the string voltage U1 should be significantly above the predefined minimum value U_min1 - provided there is no error is present - and the associated photovoltaic string 10 is not totally shaded. After the condition U1 <U_min1 is no longer fulfilled in normal irradiation and without interference in step 106 and the user is still enabled to start (U ext. Start = on), a further query is made in step 110 as to whether the input voltage U1 of the associated photovoltaic string 10 is greater than or equal to the output voltage U2 of the associated photovoltaic string 10 minus a predefined threshold value U0 (U1> = U2-U0), wherein U0 in this example is 20 V DC, but could also be zero. This condition should preferably be met for a predefined minimum time tO, which in this case is tO = 1s. Furthermore, it is checked again whether the voltage U1 is greater than or equal to a minimum value U_min2, in order to ensure that the associated photovoltaic string 10 is still electrically connected, U_min2 = 150 V DC in this example. Furthermore, it is checked again whether the user release (U ext. Start = on) is present. If at least one of these three test conditions is not met in query step 110, the loop goes back to step 104 and query 106.

If, however, all of these three test conditions in query 110 are met, it is checked in step 111 whether the phase current I is greater than a predefined threshold value l_min, l_min being 500 mA (in the positive direction) in this example. If this test condition is not met, the microcontroller 42 controls the serial hybrid switch S1 in step 112a, such that initially only the semiconductor switching device 50 or back-to-back circuit closes. If this test condition I> l_min is met, the microcontroller 42 controls the serial hybrid switch S1 in step 112b in such a way that the back-to-back circuit 50 remains closed and the relay 54 now also closes. In both cases 112a, 112b, the associated photovoltaic string 10 is connected to the central collection point 22a, 22b or the inverter 26, and the associated photovoltaic string 10 feeds electrical power into the inverter 26 via the central collection point 22a, 22b, but the hybrid switch S1 only after

BE2017 / 5252 closing relay 54 in step 112b, i.e. in the state for continuous production operation, works particularly low loss. Because the semiconductor switching device 50 or back-to-back circuit alone is already closed beforehand in step 112a, this routine in step 112b causes the relay 54 to close at different times only after a delay after the semiconductor switch back-to-back has closed. Circuit 50 in step 112a. The time delay in the present example is approximately 200 ms to 300 ms, which is short enough not to overload the MOSFET back-to-back circuit 50, even if the full nominal phase current should flow.

The relay 54 takes over the current flow in this example only from I> 500 mA and only needs to switch a low voltage of typically 1 volt, so that a relatively small, inexpensive and in particular not designed for switching 1000 V DC can be used, such as with the properties described above.

During production operation, a test step 114 then continuously or regularly checks whether a) there is a negative current greater than or equal to a predefined minimum value LReverse, specifically over a predefined minimum time t1 (t1 = 1s), or b) whether the input voltage U1 falls below a predefined minimum value U_min3 (here U1_min3 = 150V) or c) whether the user release is not available (U ext. Start = Off). The minimum value LReverse for the negative current is typically in the milliampere range. In this example, the corresponding test condition is therefore whether there is a negative current of at least 20 mA (l_Reverse <= - 20mA). As long as all three test results a), b), c) are negative, i.e. logical a) OR b) OR c) = NO, the hybrid switch S1 is kept closed.

A further test step 116 is then carried out by querying in an error monitor whether the temperature is <130 ° C. and whether the differential voltage between U1 and U2 is greater than 2V. If this error check is also negative, the loop to test step 111 is closed. Steps 111-116 accordingly form a permanent or continuous monitoring circuit for the associated photovoltaic string 10 to ensure that no undesired values of the monitored electrical parameters occur even in production operation.

If the query in step 114 shows that one of the three test conditions mentioned is positive, i.e. logical a) OR b) OR c) = YES, e.g. if there is an undesirably high negative reverse current because e.g. the associated photovoltaic k string 10 is shaded considerably more than the other photovoltaic k strands, or because the associated photovoltaic 32

BE2017 / 5252

String 10 has lost string voltage to such an extent that the threshold condition U1 <U_min3 is met, or because the user-controlled switch-off request is present at the control device 42 (U ext. Start = Off), the loop goes back to step 104, i.e. the hybrid switch S1 opens, the relay 54 only being opened and the semiconductor switching device 50 only after a time delay. The hybrid switch S1 or both the MOSFETs 52 and the relay 54 are preferably designed as normally open contacts, so that the hybrid switch S1 as a whole automatically falls into the open state unless the MOSFETs 52 and the relay 54 are kept in the closed state by the control device 42 (loop 111-116). If necessary, the time delay is also ensured here. Loop 111-116 accordingly represents the production operation of the associated photovoltaic string 10.

In step 114, the user can trigger the condition U ext. Start = Off, intervene in the loop 111-116 as desired in order to disconnect the current-carrying connection of the associated photovoltaic string 10 in a user-controlled manner from the inverter 26 or to switch off the associated photovoltaic string 10 in a user-controlled manner. If so user-controlled by triggering the condition U ext. Start = Off the query in step 114 is set to "yes", the loop 111-116 is interrupted and the path of the test / control routine goes to step 104, in which the hybrid switch S1 opens, even if all the electrical parameters meet predefined test conditions. The user thus has the possibility of triggering or triggering the shutdown of the associated photovoltaic string 10 in a user-controlled manner at his own discretion. If necessary, the time delay is also ensured here.

If the error monitoring in step 116 gives a positive result, i.e. If one of the two error conditions mentioned applies, the hybrid switch S1 is opened in a step 118 as in step 114 and the signaling output is additionally toggled, which emits an error message for the user. The cycle is then ended with step 120. This typically signals a malfunction.

With the present invention it is possible to switch off in a controlled manner any user-controlled photovoltaic string 10 equipped with such a switching device 38 or in production operation, i.e. to separate from the pantograph 26. This is achieved by means of the hybrid switch S1 from a parallel connection from a MOSFET back-to-back33

BE2017 / 5252

Circuit 50 and a relay 54 and a corresponding control e.g. 6 accomplished.

The hybrid switch S1 installed in the string box 20 is able to disconnect the photovoltaic string 10 and prevent the current flow. This causes the protective circuits 14 (e.g. Phoenix Contact SCK-RSD-100) installed on the photovoltaic modules 12 in the present example to also be switched off. In other words, in the present example, the protective circuits 14 installed on the photovoltaic modules 12 are then automatically deactivated and the individual photovoltaic modules 12 are switched off, so that the entire photovoltaic string 10 is not only electrical from the central collection point 22a, 22b is disconnected, but also no longer leads dangerous voltage.

To start the photovoltaic string 10, start pulses are sent via the string line 16 to the protective circuits 14 of the photovoltaic modules 12 of the associated photovoltaic string 10 (step 108) in order to reactivate the unloaded photovoltaic string 10, but not yet immediately to connect the central collection point 22a, 22b. The test routine is then carried out with steps 110-116 according to FIG. 6.

The present invention enables the at least one photovoltaic string 10 to be switched on and off via a (module) higher-level control unit and represents an advantageous function for the customer in order not only to act in an emergency, but also e.g. switch off photovoltaic strings or entire areas of a DC generator 2 for maintenance purposes.

In summary, the present switching device 38 can be used to switch a large output with a small power loss on a small construction volume. The nominal power of the photovoltaic string 10 is preferably at least 10 kW, which can be switched as a whole by the hybrid switch S1. The loss line of the hybrid switch S1, however, is nominally 1000 V and 10 A less than or equal to 10 W, preferably less than or equal to 5 W, preferably less than or equal to 2 W, preferably less than or equal to 1 W, when the relay 54 commutates the current. The advantages of the different switching types (electromechanical, semiconductors) are sensibly combined. When switching on, the semiconductor switching device 50 takes over the first switching operation in order to switch the up to 1000 V in the possibly small load range (for example up to 500 mA) on and off again. Here, the advantage of the semiconductor switching device 50, which is important in relation to the DC application, of being able to switch large voltages without sparkover is used. After switching the semiconductor switching device 50

BE2017 / 5252

2017/5252, however, is primarily about getting a grip on the power loss of the flowing current. The product parameters of a semiconductor are not ideally suited for this, since the internal through-resistance RDS-on increases with increasing voltage at UBS. The advantages of an electromechanical switch in the form of a relay 54 are used for this. Small relays are not able to separate high DC voltages, but large currents up to e.g. 16 amps unproblematic.

When switching on, the semiconductor switching device 50 is switched on, and then the relay is switched on with a time delay 54. When switching off, this is done in reverse, likewise with a time delay. Relay 54 thus only switches the remaining residual voltage both when switching on and when switching off, via semiconductor switching device 50 or MOSFETs 52, but commutates almost all of the current due to the low conduction resistance. The switching device 38 is thus suitable for switching 1000 V with 10 A direct voltage / direct current with a low loss line. Thus, with the invention, a photovoltaic string 10 or parts of the DC generator 2 can be switched on and off in a size-optimized and cost-optimized manner.

It will be apparent to those skilled in the art that those described above

Embodiments are to be understood as examples and the invention is not limited to these, but can be varied in many ways without leaving the scope of the claims. It can also be seen that the features regardless of whether they are in the

Description, the claims, the figures or otherwise disclosed also individually define essential components of the invention, even if they are described together with other features.

BE2017 / 5252

Claims (15)

Claims: 1. Photovoltaic system (1) comprising: at least one photovoltaic string (10), the at least one photovoltaic string being formed by photovoltaic modules (12) which are connected in series with one another by means of a string line and thus generate a string voltage, a switching device (38) which is connected serially into the String line is installed in order to switch the at least one photovoltaic string on and off with the switching device (38), the switching device (38) being a hybrid switch (S1) with a relay (54) and a semiconductor switching device connected in parallel with the relay (54) (50) with at least one semiconductor switch. 2. Photovoltaic system (1) according to claim 1, wherein the hybrid switch (S1) defines a closed and an open state and in the closed state passes photovoltaically generated electricity from the at least one photovoltaic string (10) to a current collector and in which opened state, the passage of photovoltaically generated current from the at least one photovoltaic string (10) is interrupted, and a control device (42) is included, which is designed to open the hybrid switch (S1) in a user-controlled manner in response to a user input. 3. Photovoltaic system (1) according to claim 1 or 2, wherein the semiconductor switch is a field effect transistor, preferably a MOSFET (52). 4. Photovoltaic system (1) according to one of the preceding claims, wherein the hybrid switch (S1) is designed to interrupt the current flow in both directions in the open state. BE2017 / 5252 5. Photovoltaic system (1) according to one of the preceding claims, wherein the hybrid switch (S1) is a parallel connection from the relay (54) and a back-to-back circuit (50) from two semiconductor switches, in particular a parallel connection from a relay (54) and a back-to-back circuit (50) comprising two field-effect transistors, preferably MOSFETs (52). 6. Photovoltaic system (1) according to one of the preceding claims, wherein the switching device (38) is designed, when switching on the associated photovoltaic k string (10), first the semiconductor switching device (50), in particular the field effect transistor or transistors, preferably to close MOSFETs (52) and then to close the relay (54) only after a time delay and / or to open the relay (54) when the associated photovoltaic string (10) is switched off and only after a time delay then open the semiconductor switching device (50), in particular the field-effect transistor (s), preferably MOSFETs (52). 7. The photovoltaic system (1) according to claim 6, wherein the time delay when switching on and / or when switching off is less than or equal to 2000 ms, preferably less than or equal to 700 ms, preferably less than or equal to 300 ms, at least if in the photovoltaic k Strand (10) a strand current flows which essentially corresponds to the nominal current. 8. Photovoltaic system (1) according to one of the preceding claims, wherein the switching device (38), a control device (42) and a sensor device (46, 48) connected to the control device (42) for measuring at least one electrical parameter on the associated photovoltaic contains k-string (10), the control device (42) being designed to electrically connect the associated photovoltaic k-string (10) to the current collector in response to the at least one electrical characteristic measured with the sensor device (46, 48), if there is a user release, the sensor device comprising in particular: an input voltage sensor (46), which the string-side BE2017 / 5252 Input voltage (U1) on the switching device (38) and / or an output voltage sensor (48) which measures the pantograph-side Output voltage (U2) measures at the switching device (38), and the control device (42) is designed to respond to the measured string-side input voltage (U1) and / or the measured pantograph-side output voltage (U2) the associated photovoltaic string ( 10) to be electrically connected to the central collection point (22a, b) if one User approval exists. 9. Photovoltaic system (1) according to one of the preceding claims, wherein the switching device (38) for a DC switching voltage of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V. +/- 30% and / or for a DC through current of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of 12.5 A +/- 40%, and / or wherein the hybrid switch (S1) generates a power loss of less than or equal to 10 W, preferably less than or equal to 5 W, preferably less than or equal to 2 W, preferably less than or equal to 1 W, calculated based on the nominal current of the at least one photovoltaic string, if the semiconductor switching device (50) and the relay (54) are closed, and / or wherein the semiconductor switching device (50) for a DC switching voltage of greater than or equal to 300 V, preferably greater than or equal to 600 V, before preferably greater than or equal to 800 V, preferably 1250 V +/- 30%. 10. photovoltaic system (1) according to any one of claims 3-9, wherein the or the field effect transistors, preferably MOSFETs (52), for a drain-source voltage (Vds) of greater than or equal to 300 V, preferably greater than or equal to 600 V, preferably greater than or equal to 800 V, preferably of 1250 V +/- 30% and / or for a drain current (Id) of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably from 12.5 A +/- 40% BE2017 / 5252 are trained. 11. The photovoltaic system (1) according to any one of claims 3-10, wherein the field effect transistor or transistors, preferably MOSFETs (52), a resistance drain source on of greater than or equal to 100 mOhm, preferably greater than or equal to 300 mOhm, preferably greater than or equal to 500 mOhm, preferably of 690 mOhm +/- 40% and / or wherein the field-effect transistors, preferably MOSFETs (52), have a power loss of greater than that calculated based on the nominal current of the at least one photovoltaic string (10) or equal to 2 W, greater than or equal to 5 W, greater than or equal to 10 W, in particular greater than or equal to 40 W, if the field effect transistor or transistors, preferably MOSFETs (52), are closed and the relay (54) is open . 12. Photovoltaic system (1) according to one of the preceding claims, wherein the relay (54) for a DC through current of greater than or equal to 5 A, preferably greater than or equal to 8 A, preferably greater than or equal to 10 A, preferably of 12, 5 A +/- 40% and / or for a DC switching current of less than or equal to 8 A, in particular less than or equal to 6 A, in particular less than or equal to 4 A, in particular of 2 A +/- 50%, and / or wherein the relay (54) has a maximum AC switching voltage of less than or equal to 800 V, in particular less than or equal to 500 V, in particular of 400 V +/- 50%. 13. Electronically controlled direct current hybrid switching device designed for the direct current part of a photovoltaic system (1), in particular according to one of the preceding claims, for switching off at least one photovoltaic string (10) from a pantograph, the direct current hybrid switching device comprises a hybrid switch (S1) comprising a relay (54) and a semiconductor switching device (50) connected in parallel with the relay (54). 14. Use of a switching device (38) comprising a hybrid switch (S1) comprising a relay (54) and a semiconductor switching device connected in parallel to the relay (54) BE2017 / 5252 2017/5252 (50), in particular according to one of the preceding claims, for switching on and off at least part of a photovoltaic generator (2) in the DC part of a photovoltaic system (1). 5 15. Procedure for user-controlled switching off and on again at least one Photovoltaic string (10) of a photovoltaic system (1), in particular according to one of the preceding claims, comprising the following steps: User-controlled triggering (U ext. Start = Off) of a switching device (38) of the at least one photovoltaic string (10) by a trigger signal to trigger the at least one 10 to disconnect the photovoltaic string (10) from the pantograph, user-controlled triggering (U ext. Start = On) of the switching device (38) of the at least one photovoltaic string (10) by a trigger signal to trigger the at least one photovoltaic string (10) connect to the pantograph again, possibly in response to the fulfillment of further test conditions. t rkk I AC grid ................ BE2017 / 5252 AG 77 ·; ν 'PVPane! I. ..... + J ....... t \ / ^z 12 ‘^ J! PV 12'-J 24b I ZZu 17 ″ -— i out 2O '~ ^ \ DC j LAC SCK RSD 100 i ...... I .. κ: ^17Ί7: .-22a • 5; -x · Υ ........ Out H-17 SCK-RSD4 i SCK-RSD- ^ 20 600! I 600 ΐ Ext j j Ext. J c *. ™ - î s .Start * ΐ ..Disrupt, I <....... f .......... t ·· 'l ·' t Pi6 ^; SCKRSD100 IPanei MscK-H I i jSCK-J (! RSD-p44 '! i pSDrt j Γ-4 WO 7: I j H'710 i 12 ' 12 \ / i PVPane !! fOl j PV- j j Panel I PV- I Panel! SCK- ⁵ îrsd4— ί where I. pZil • i PV [RSD-I 124p _sno f ί loo! ISCK-j BE2017 / 5252 BE2017 / 5252 BE2017 / 5252 BE2017 / 5252 Ed. 5 BE2017 / 5252 no BE2017 / 5252 2017/5252 Summary The invention relates to a photovoltaic system (1) with a switching device (38) for switching on and off at least one photovoltaic string (10), an electronically controlled direct current5 hybrid switching device for the user-controlled switching on and off of at least one photovoltaic string (10 ), the use of a hybrid switch (S1) for switching a photovoltaic string (10), and a method for switching off and on again at least one photovoltaic string (10) of the photovoltaic system (1). The photovoltaic system (1) includes: at least one photovoltaic string (10), the at least one 10 photovoltaic string is formed by photovoltaic modules (12) which are connected in series with one another by means of a string line and thus generate a string voltage, a switching device (38) which is installed in series in the string line around the at least one photovoltaic string the switching device (38) on and off, the switching device (38) a hybrid switch (S1) with a relay (54) 15 and a semiconductor switching device (50) connected in parallel to the relay (54) with at least one semiconductor switch.