DE102014104205A1 - Separating device for a DC circuit and photovoltaic system with a separator - Google Patents

Abstract

The invention relates to a separating device (10) for a DC circuit with two current-carrying DC lines (2, 3), comprising at least one switching element with at least one switching contact (11, 12) arranged in one of the DC lines (2, 3) of the DC circuit. The separating device (10) is characterized in that it has a transformer (13) with two magnetically coupled windings (14, 15) for transmitting a high-frequency signal, wherein the windings (14, 15) each with a capacitor (16, 17) are series-connected and wherein each of the series circuits of winding (14, 15) and capacitor (16, 17), the DC lines (2, 3) connects to each other and each connected to a terminal of the switching contact (11, 12). The invention further relates to a PV system with such a separating device (10).

Description

The invention relates to a separator for a DC circuit with two current-carrying DC lines, which has at least one switching element with at least one arranged in one of the DC lines of the DC circuit switching contact. The invention further relates to a photovoltaic system with such a separator.

In photovoltaic (PV) plants, power generating PV generators are often connected to one or more remotely mounted inverters via often very long DC power lines. In this case, generator-near devices such as protective devices or measuring devices are often provided, which communicate with the inverter or other inverters installed close control devices. In this case, in addition to conventional wired communication methods via separate signal lines or serial and / or parallel bus or network connections or radio communications, a communication via the DC cables, with which the PV generator is connected to the inverter, take place. Such a communication for data transmission via the DC lines for power transmission is also known as powerline communication (PLC). In this case, the communication signal is coupled as a high-frequency (RF) signal to the DC lines for energy transmission and coupled out again on the receiving side by appropriate decoupling and evaluated. The transmission can be unidirectional, for example, run from the inverter or a central control device to the PV generator when generator-near devices, such as protective devices are to be controlled via the PLC signal. Unidirectional data transmission from the PV generator or devices installed close to the generator to the inverter or to data acquisition stations near the inverter can be provided if measured data is to be transmitted from the PV generator to the inverter or to the central detection devices. If both control information is to be transmitted to the PV generator and measurement data from the PV generator, bidirectional execution of the PLC communication is also possible.

A PV system in which a communication between remote generator and generator-related devices via a PLC signal is performed, for example, from the document EP 2 243 208 B1 known. According to this publication, the PV generator is formed by a plurality of PV sub-generators, which are brought together in a near-generator terminal box, in which a circuit breaker is arranged, with which the inverter leading DC lines can be interrupted. It is intended to transmit PLC signals via the DC cables between the inverter and the terminal box and between the terminal box and the PV sub-generators, to control the disconnector and to transfer measured data from the PV sub-generators to the inverter. In order to enable a transfer of measurement data from the PV sub-generators to the inverter even when the circuit breaker is opened in the terminal box, a data signal coupler is arranged in the form of a capacitor parallel to the switching contacts of the circuit breaker. This capacitor allows transmission of high-frequency signals between PV sub-generators and the inverter even when the disconnector is open.

A disadvantage of using a capacitor arranged parallel to the switching contact as a data signal coupler is that this capacitor does not constitute a safe separation in the sense of a galvanically isolated connection. For a safe activation of the PV generator, such a data signal coupler is therefore not suitable.

Object of the present invention is to provide a separator for a DC circuit, which allows a completely galvanically isolated interruption of the DC circuit with simultaneous successful RF signal transmission.

This object is achieved by a separator or a PV system with the features of the respective independent claim. Advantageous embodiments and further developments are the subject of the respective dependent claims.

A separator according to the invention of the type mentioned has a transformer with two magnetically coupled windings, wherein the windings are each seriengeschaltet with a capacitor and wherein each of the series circuits of winding and capacitor connects the DC cables together and each connected to a terminal of the switch contact. The separator is characterized in that the transmitter is arranged for transmitting a high-frequency signal from an inverter to another separator with at least one switching element in one of the DC lines and / or to a short-circuit switch, wherein the further separator and / or the short-circuit switch the side facing away from the inverter side of the separator is arranged.

Opening the at least one switch contact in one of the two DC lines interrupts a DC current on the DC lines. Even when the switching contact is open, the transformer allows a transmission of the RF signals of a PLC communication or of RF signals that emits an arc across the separator. Since the windings are not traversed by the direct current flowing in the DC circuit due to the upstream capacitor, they can have a small cross section and be made according to material and cost. At the same time, a cost-effective construction of the core material of the transformer is possible because it does not saturate.

In an advantageous embodiment of the separator, at least one switching contact is arranged in each of the two DC lines. When the switch contacts are open, the DC circuit is then completely galvanically interrupted for direct current.

In a further advantageous embodiment of the separation device, the two windings have the same inductances and the two capacitors have the same capacitance. Equal inductances of the two windings and thus the same number of windings in the windings is particularly advantageous in the case of closed switch contacts, since in that case the alternating currents through the windings, e.g. that of the RF signals, cancel each other out and effectively no current flows across the transformer. Preferably, the series circuit of winding and capacitor each have a resonant frequency which is suitable for the transmission of PLC signals. Particularly preferably, the frequency of the PLC signals is in the range of 100 kilohertz (kHz) to 1 megahertz (MHz) and in particular in the range of 100 kHz to 300 kHz.

In a PV system according to the invention with at least one PV generator and at least one inverter for feeding electrical energy into a power supply network, the PV generator and the inverter are connected to one another via DC lines. The PV system is characterized in that an inverter-side section of the DC lines and a generator-side section of the DC lines are connected to each other via such a separator, wherein the inverter is adapted to the generator side arranged further separator and / or the shorting switch by means of the high frequency To drive signals. With regard to a transmission of HF signals, the advantages mentioned in connection with the separating device result.

In an advantageous embodiment of the PV system, a transmitting unit and / or a receiving unit for RF signals for PLC communication are provided on the inverter side and generator side of the separating device. Additionally or alternatively, on the inverter side, on the generator side or in the separation device, a device for arc detection can be provided based on RF signals. The separator according to the invention can be used for both applications within the PV system.

In a further advantageous embodiment of the PV system, a DC-DC converter is provided for the power supply of generator-related electrical components, wherein the DC-DC converter is supplied on the input side with a voltage applied across one of the capacitors voltage. Preferably, the voltage is tapped on the capacitor side arranged on the capacitor. This makes it possible to supply power to components close to the generator. Compared to a tapping of the input voltage for the DC-DC converter directly to the DC lines tapping the input voltage across the capacitor offers the advantage that strong voltage fluctuations or jumps are attenuated on the DC lines through the capacitor and the inductance of the winding and therefore the risk of overvoltage on DC converter is reduced.

The invention will be explained in more detail by means of exemplary embodiments with the aid of two figures. Show it:

1 a schematic representation of a PV system with a separator in a first embodiment and

2 a schematic representation of a PV system with separator in a second embodiment.

1 shows a PV system in a first embodiment in a schematic block diagram. A PV generator 1 is via DC power lines 2 . 3 with a remote inverter 5 connected. The inverter 5 is for feeding in electrical power from the PV generator 1 is generated, with an AC output to a power grid 6 coupled. Exemplary are the AC output and the power grid 6 shown here in single phase. As part of the registration, however, both the inverter 5 as well as the power supply network 6 have a different number of phases, for example be three-phase.

The PV generator 1 is symbolized here by the symbol of a single PV cell. It is understood that the PV generator 1 can be constructed from a plurality of PV modules, which in turn each consist of a plurality of PV modules. Cells can exist. The PV modules can be series-connected to a so-called string, several of which are connected in parallel and the PV generator 1 can form. In the schematic of the PV generator 1 is a series connection of a series resistor 1R , a series inductance 1L and a series capacitor 1C located. The series connection of these three elements symbolizes the small-signal equivalent circuit diagram of the PV generator 1 ,

Parallel to the outputs of the PV generator 1 is close to the generator a short-circuit switch 4 arranged. The short-circuit switch 4 , in the present example, a semiconductor power switch, is used in its operation of the voltage isolation of the DC cables 2 . 3 , Such a voltage release can be used, for example in a fire, to prevent that to the inverter 5 leading DC power lines 2 . 3 are subjected to a high PV voltage that can pose a life-threatening danger during firefighting.

Furthermore, a separator 10 provided, the at least one switching element with present two switching contacts 11 . 12 having. Each of the switch contacts 11 . 12 is in one of the DC power lines 2 . 3 - In this case, the switching contact 11 in the DC line 2 and the switching contact 12 in the DC line 3 - arranged to the PV generator 1 galvanically from the inverter 5 to be able to disconnect.

In the illustrated embodiment, both the shorting switch 4 as well as the separator 10 Generatornah arranged. In particular, the separator 10 However, it can also be near the inverter or in the inverter 5 be arranged. It is also conceivable, both inverter near or in the inverter 5 as well as generator close use such a separator.

The generator-near short-circuit switch 4 and, if likewise arranged close to the generator, the separating device 10 are via powerline communication (PLC) signals from the inverter 5 driven. For this purpose is in the inverter 5 a PLC transmitting unit arranged the DC lines 2 . 3 with a corresponding radio frequency (RF) signal applied. The frequency range of the PLC signal is preferably in the range of about 100 kilohertz (kHz) to about 1 megahertz (MHz), and more preferably in the range of 100 to 300 kHz. As an alternative to the illustrated arrangement, it may be provided that the PLC transmission unit is not in the inverter 5 but to arrange in a separate unit inverter near. For coupling the high-frequency signals to the PLC communication, for example, an inductively operating Einkoppelübertrager can be provided. Other coupling paths, for example capacitive or resistive, are possible.

For receiving and evaluating the PLC signal is generatornah a receiving unit 20 provided that a Auskoppelübertrager 21 which has a primary winding 22 in one of the DC lines, here for example the DC line 2 , is looped. The one DC in the DC line 2 superimposed PLC signal is applied to its secondary winding 23 of the decoupling transformer 21 transmitted and a receiver 24 fed. This amplifies and analyzes the PLC signal and outputs information contained in the PLC signal via a communication interface or via signal lines. The information concerns, for example, an actuation of the short-circuit switch 4 and / or an actuation of the separating device 10 to the switch contacts 11 . 12 to open or close. The decoupling unit 20 Alternatively, it can also consist of any combination of ohmic, capacitive and inductive elements.

It is understood that the receiving unit 20 can also be designed as a bidirectional transmitting / receiving unit to transmit information in the form of PLC signals to a PLC receiver in the inverter.

Even with open switch contacts 11 . 12 Signals from the inverter 5 to the receiving unit 20 (and vice versa), for example, to enable the PV generator 1 through the short-circuit switch 4 cancel and a restart of the switch contacts 11 . 12 to effect is the separator 10 According to the application, signal-transmitting executed. For this purpose, the separator 10 a transformer 13 on, the two preferably same windings 14 and 15 includes. The transformer 13 is completely galvanic isolated.

Each of the windings 14 . 15 is with a capacitor 16 respectively. 17 series-connected. The formed series circuit from the winding 14 and the capacitor 16 is between the DC lines 2 . 3 On the inverter side of the switch contacts 10 and 11 connected. The out of the winding 15 and the capacitor 17 formed series circuit contacted in the same way the DC lines 2 and 3 , but on the PV generator 1 facing side of the switch contacts 11 . 12 , The series connection of the windings 14 respectively. 15 and the capacitors 16 respectively. 17 is designed in terms of its resonance frequency and quality so that the PLC signals in the mentioned frequency range of, for example, 100 kHz to 1 MHz, and preferably in the range of 100 to 300 kHz can be well transferred.

Because the windings 14 and 15 can not be traversed by the DC current flowing in the DC circuit, they may have a small cross-section and be made in accordance with material and cost. At the same time, a cost-effective design of the core material of the transformer 13 possible, because this does not saturate. With opened switch contacts 11 . 12 are the DC cables 2 and 3 completely DC isolated for DC. A DC current on the DC lines 2 . 3 is interrupted.

An inverter-side impressed RF signal of a PLC communication can, however, via the series circuit of capacitor 16 and winding 14 still flow in this section of the DC circuit. It is advantageous if the series circuit of winding 14 and capacitor 16 has the lowest possible impedance for the typical frequencies of the PLC signal used. This is given, for example, when the resonance frequency of the series circuit is in the range of frequencies occurring in the case of the PLC signal.

Due to the magnetic coupling of the winding 14 and 15 in the transformer 13 a corresponding RF signal is also in the section of the DC circuit in which the PV generator 1 is induced. For the RF signal, this circuit is across the winding 15 and the capacitor 17 on the one hand, and the short-circuit element 4 and / or the PV generator 1 closed. For the impedance or the resonance frequency of the series circuit of winding 15 and capacitor 17 this applies previously for the winding 14 and the capacitor 16 called. Advantageously, the windings 14 and 15 with regard to the number of turns and the inductance designed the same, as well as the capacitors 16 and 17 preferably have the same capacity. Same number of turns in the windings 14 and 15 is especially with closed switch contacts 11 . 12 advantageous in that case the (AC) currents through the windings 14 . 15 cancel each other out and effectively no electricity through the transformer 13 flows.

With closed switch contacts 11 and 12 are the series circuits of winding 14 and capacitor 16 as well as the series connection of winding 15 and capacitor 17 connected in parallel. The winding sense of the windings 14 and 15 of the transformer 13 is preferably set up so that the communication signal in the transmitter almost completely canceled. Are the windings 14 and 15 for example, wound in the same direction, which in 1 through points on the windings 14 and 15 is indicated, and they have the same number of turns, then the RF signal flows almost completely through the DC lines in the circle between inverters 5 and PV generator 1 and / or short-circuit switch 4 ,

Especially with identically designed windings 14 . 15 is a transmission not only from the inverter side of the separator 10 on the generator side possible, but vice versa from the generator side to the inverter side. Such a case is relevant, for example, if a PLC communication from the generator side to the inverter side or a bidirectional PLC communication is provided.

Also in connection with a detection of arcs, a transmission of high frequency from the generator side to the inverter side of the separator 10 be desired. Arcs emit when they occur a broadband RF signal, by means of which their occurrence can be detected in a DC circuit. For example, in the inverter 5 or in a near-inverter monitoring device to be arranged on such an RF signal in a certain frequency range detection circuit for detecting arcing. To arcs regardless of the closing or opening state of the switching contacts 11 . 12 the separator 10 To be able to reliably detect and be able to initiate measures for their deletion, a transmission of the emanating from a burning arc RF signals to the detection unit is essential. Again, this is due to the coupling of high frequency signals through the transmitter 13 in the separator 10 guaranteed. Optionally, this can be done by resonant frequency and quality of the series circuits from the windings 14 respectively. 15 and the capacitors 16 respectively. 17 be designed so that on the one hand PLC signals are well transmitted in a defined narrow frequency band, and on the other hand, any arc signals that are detected by the detection circuit in a different frequency band, are only slightly attenuated.

2 shows a PV system with an according to the application separator 10 in a second embodiment. The same reference numerals in this figure denote the same or equivalent elements as in FIG 1 ,

In its basic structure, the PV system of the second embodiment corresponds to that of the first embodiment, and therefore to the descriptions of 1 is referenced. Deviating from the first embodiment is in the embodiment of the 2 at the separator 10 only one switching contact 11 provided, the example here in the DC line 2 is arranged. Also by such an embodiment of the separator 10 may be a break in the DC flow in the DC circuit, however no galvanic decoupling of the generator near and the inverter near part of the DC circuit takes place.

In addition, a DC-DC converter 25 , also called DC (direct current) / DC converter, for powering the receiving unit 20 and here in particular the recipient 24 and possibly further components close to the generator. The DC-DC converter 25 It uses its input voltage via the capacitor 16 in the separator 10 is arranged on the inverter side, from. With closed switching contact 11 is due to this capacitor 16 the PV voltage of the PV generator 1 from which the receiving unit 20 then via the DC / DC converter 25 is supplied. With opened switch contacts 11 is alternatively provided that the DC lines 2 . 3 from the inverter 5 is acted upon with respect to electric arcs or at the risk of electric shock harmless small DC voltage. The receiving unit 20 is then over the DC / DC converter 25 from this also via the capacitor 16 supplied small voltage supplied.

Compared to a tapping of the input voltage for the DC-DC converter 25 directly on the inverter side DC cables 2 . 3 provides tapping the input voltage across the capacitor 16 the advantage that strong voltage fluctuations or jumps on the DC cables 2 . 3 through the capacitor 16 and the inductance of the winding 14 be damped and therefore the risk of overvoltage on the DC-DC converter 25 is reduced.

Instead of a decoupling of the PLC signal via a DC coil through the primary coil 22 of the transformer 21 Alternatively, a decoupling of the PLC signal in a parallel to the PV generator 1 arranged in the series resonant circuit. In principle, in addition to an inductive and a capacitive or resistive coupling can be implemented.

LIST OF REFERENCE NUMBERS

1

 PV generator

1R

 Series resistance of the PV generator

1L

 Series inductance of the PV generator

1C

 Series capacity of the PV generator

2, 3

 DC line

4

 DC circuit switch

5

 inverter

6

 Power grid

10

 separator

11, 12

 switching contact

13

 exchangers

14, 15

 winding

16, 17

 capacitor

20

 receiver unit

21

 Auskoppelübertrager

22

 primary

23

 secondary winding

24

 receiver

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• EP 2243208 B1 [0003]

Claims (9)

Separating device ( 10 ) for a DC circuit with two live DC cables ( 2 . 3 ), wherein the separating device ( 10 ) at least one switching element with at least one in one of the DC lines ( 2 . 3 ) of the DC circuit arranged switching contact ( 11 . 12 ) and a transformer ( 13 ) with two magnetically coupled windings ( 14 . 15 ), wherein the windings ( 14 . 15 ) each with a capacitor ( 16 . 17 ) are series-connected and wherein each of the series circuits of winding ( 14 . 15 ) and capacitor ( 16 . 17 ) the DC cables ( 2 . 3 ) and each at a terminal of the switch contact ( 11 . 12 ), characterized in that the transformer ( 13 ) for transmitting a high-frequency signal from an inverter ( 5 ) to a further separating device with at least one switching element in one of the direct current lines ( 2 . 3 ) and / or to a short-circuit switch ( 4 ), wherein the further disconnecting device and / or the short-circuiting switch ( 4 ) on the inverter ( 5 ) facing away from the separator ( 10 ) is arranged. Separating device ( 10 ) according to claim 1, comprising at least one switching contact each ( 11 . 12 ) in each of the two DC lines ( 2 . 3 ). Separating device ( 10 ) according to claim 1 or 2, wherein the two windings ( 14 . 15 ) same inductors and the two capacitors ( 16 . 17 ) have the same capacities. Separating device ( 10 ) according to one of claims 1 to 3, in which the series circuit of winding ( 14 . 15 ) and capacitor ( 16 . 17 ) each having a resonant frequency which is suitable for the transmission of PLC signals. Separating device ( 10 ) according to claim 4, wherein the frequency of the PLC signals is in the range of 100 kHz to 1 MHz and in particular in the range of 100 kHz to 300 kHz. PV system with at least one PV generator ( 1 ) and at least one inverter ( 5 ) for feeding electrical energy into a power grid ( 6 ), the PV generator ( 1 ) and the inverter ( 5 ) via DC cables ( 2 . 3 ) are connected to one another, characterized in that an inverter-side section of the DC lines ( 2 . 3 ) and a generator side section of the DC lines ( 2 . 3 ) via a separating device ( 10 ) are connected to each other according to one of claims 1 to 5, wherein the inverter is adapted to the generator side arranged further separator and / or the short circuit switch ( 4 ) by means of the high-frequency signal. PV system according to claim 6, in which the inverter side and the generator side of the separating device ( 10 ) a transmitting unit and / or a receiving unit ( 20 ) are provided for high-frequency signals for PLC communication. PV system according to claim 6 or 7, wherein the device is provided on the inverter side, the generator side or in the separating device, a device for arc detection based on high-frequency signals. PV system according to one of claims 6 to 8, comprising a DC-DC converter ( 25 ) for the power supply of generator-related electrical components, wherein the DC-DC converter ( 25 ) on the input side with one above one of the capacitors ( 16 . 17 ) applied voltage is applied.

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