EP3210243A1

EP3210243A1 - A method to determine an installation error in a dc part of pv plant and a combiner box of the dc part for performing the method

Info

Publication number: EP3210243A1
Application number: EP14776845.1A
Authority: EP
Inventors: Markus Abplanalp; Rudolf Gati; Thomas Wulf; Thorsten STRASSEL
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2014-09-24
Filing date: 2014-09-24
Publication date: 2017-08-30
Also published as: WO2016045725A1; JP6211739B1; CN107112946A; JP2017532940A

Abstract

The method of the invention is performed in a combiner box of a DC part of a PV plant before start-up and forms a measuring circuit in which at least one of the direction of a DC current, the polarity of a voltage or a ground fault is measured and in which the result of the measurement is used to determine an installation error in the DC part.

Description

A method to determine an installation error in a DC part of PV plant and a combiner box of the DC part for performing the method

FIELD OF THE INVENTION

The invention relates to a method to determine an installation error in a DC (direct current) part of PV (photovoltaic) plant and to a combiner box of the DC part for performing the method.

BACKGROUND OF THE INVENTION A photovoltaic plant comprises a DC part with at least a combiner box which is realized as a string combiner box. The string combiner box combines DC currents which are generated in a plurality of strings. Each string represents a DC source and includes serially connected PV modules for generating a direct current which is fed into the string combiner box. If the DC part comprises a plurality of string combiner boxes each of these boxes is feeding combined DC currents directly into an inverter or into an array combiner box in which the combined direct currents are further combined. Each string is individually connected to one of a plurality of DC inputs of the string combiner box resp. each DC output of a string combiner box is individually connected to one of a plurality of DC inputs of the array combiner box. Thus the installation of the DC part includes a step in which the strings are electrically connected to the DC inputs of the string combiner boxes resp. in which the positive and the negative poles of the strings are electrically connected to power and return line terminals of the plurality of DC inputs of the string combiner box. The connection is realized with installation parts, which are installed independently between a pole of the strings and a power or return line terminal of the DC inputs. Thus installing the DC part can cause installation errors, like an inverted connection of the power and the return line or a wrong association of the poles of a string to a power and to a return line terminal of different DC inputs of the string combiner box. PV plants with combiner boxes which are realized as string combiner box and - if applicable - also as array combiner box are described in prior art documents, like EP 2282366 A1 or US 2013/0264883, resp. in a former International patent application PCT/EP2013/070258 filed September 27, 2013.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method which enables the determination of an installation error in the DC part of the PV plant before the DC part is operated and to provide a combiner box of the DC part which allows the performance of the method.

These and other objects are achieved with a method to determine an installation error in a DC part of a PV plant comprising a plurality of at least two DC sources, a combiner box with a plurality of at least two DC inputs and installation parts for connecting a positive and a negative pole of each DC source with a power and with a return line terminal of the DC inputs. The method performs steps as follows:

(a) closing at least one switching unit of a plurality of at least two first switching units being arranged either in a plurality of power line connections which are extended between the power line terminals of the DC inputs and a power line busbar of the combiner box or in a plurality of at least two return line connections which are extended between the return line terminals of the DC inputs and a return line busbar of the combiner box,

(b) closing one switching unit of a plurality of at least two second switching units being arranged in the plurality of power or return line connections, which connections do not comprise any of the first switching units, in order to identify one of the DC sources and to define a measuring circuit comprising the identified DC source, one closed first switching unit and one closed second switching unit,

(c) measuring at least one of the direction of a current, the polarity of a voltage and a ground fault in the measuring circuit, (d) opening the measuring circuit when at least one of a forward current, a correct polarity of the voltage or no ground fault is measured, and repeating the method steps (a) to (d) with another of the remaining DC sources, or signaling an installation error and blocking the combiner box for start-up when at least one of a reverse current, a wrong polarity of the voltage and a ground fault is measured, unblocking the combiner box after elimination of the installation error and repeating the method steps (a) to (d), and

(e) releasing the combiner box for operation in the absence of any installation error after performing the method steps (a) to (d) with each of the DC sources. The method according to the invention allows a fast localization and removal of an installation error in the DC part of the PV plant before the combiner box, which can be a string or an array combiner box, starts nominal operation. Thus the combiner box and its equipment are prevented from fatal damages due to installation errors. Since the method can be performed with remotely controllable components, like switching units and current, voltage or ground fault sensing means, the method according to the invention can be performed automatically and watched at a remote place.

In order to save performance time the method according to the invention can close in step (a) the plurality of first switching units when each of the first switching units is designed in a manner to make and break at least the nominal current of each of the DC sources and can open the closed first switching units and can signal an installation error when a short current is measured in a current circuit comprising one of the DC sources and two first switching units.

The method can electrically connect the power and the return line busbar before performing step (b). The method can electrically connect the power and the return line busbar after performing step (b) and before measuring the direction of the current according to step (c). The method can electrically connect the power and the return line busbar after measuring the polarity of a voltage between these two busbars according to step (c). The method further can disconnect the power and the return line busbar before opening the closed second switching unit when a reverse current according to step (d) is measured. The method can identify in step (b) a second of the installation parts which connects a second pole of the identified DC source to the second switching unit, can measure in step (c) the current in a section of the measuring circuit comprising the at least one closed first switching unit and a first of the installation parts, which connects the first of the two poles of the identified DC source to the closed first switching unit in order to identify the first installation part, and can store the identities of the first and the second installation part as a pair.

The method can screen the stored pairs associated to the DC sources and can check if for each of the DC sources a pair connecting this source to one of the DC inputs has been stored.

A combiner box for performing the method according to the invention can comprise:

a plurality of at least two DC inputs each of which being suited for electrical connection to one of a plurality of at least two DC sources ,

a DC output for electrical connection to a further combiner box of the DC part or to an inverter of the PV plant,

a power and a return line busbar,

a plurality of at least two first switching units being arranged either in a plurality of power line connections extended between power line terminals of the DC inputs and the power line busbar or in a plurality of return line connections extended between return line terminals of the DC inputs and the return line busbar, a plurality of at least two second switching units being arranged either in the plurality of the power or return line connections which do not comprise any first switching unit,

a plurality of at least two current sensors being associated to the plurality of first switching units,

a control and processing unit for receiving output signals from the first and the second switching units and the plurality of current sensors and for communicating signals to the first and second switching units, and

a bridging member which on the one side is electrically connected to the power and on the other side to the return line busbar, which is in data communication with the control and processing unit and which before start-up forms a section of a circuit for measuring at least one of the direction of a current, the polarity of a voltage and the presence of a ground fault.

The bridging member can comprise at least one of an auxiliary switch, a voltage polarity sensor and a ground fault detection sensor, wherein the at least one of the auxiliary switch, the voltage polarity sensor and the ground fault detection sensor with one end is electrically connected to the power and with the other end to the return line busbar. The ground fault detection sensor is kept on ground potential.

The bridging member can comprises the auxiliary switch and at least one of the voltage polarity sensor and the ground fault detection sensor. The bridging member can comprise merely either the auxiliary switch or the voltage polarity sensor.

The auxiliary switch can be designed as disconnector, and each of the first switching units can be designed as bidirectional hybrid switch. The auxiliary switch can be designed as bidirectional hybrid switch, and each of the first switching units can be designed as unidirectional hybrid switch.

In order to reduce the size of the auxiliary switch a resistor can be connected in series with the auxiliary switch.

BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments of a DC combiner box for performing the method according to the invention are shown in figures as follows: fig .1 is a schematic circuit diagram of a DC part of a PV plant

comprising combiner boxes according to the invention, fig.2 is an enlarged view of a combiner box according to fig.1 , fig.3 is a view of a current measuring and switching module of a

mechanical layout of the combiner box according to fig.2, fig.4 is a view of a control module of a mechanical layout of the combiner box according to fig.2, and figures 5 to 9 are DC circuit diagrams of five embodiments of the combiner box according to fig.2. The reference signs used in the figures and their meaning are summarized in a list of reference signs. Generally, alike or alike-functioning parts are given the same reference signs. The described embodiments are meant as examples and shall not confine the invention.

WAY TO IMPLEMENT THE INVENTION

The DC part of the PV plant shown in fig.1 comprises three pluralities of n strings S1 , S2, ... , Sn, three string combiner boxes SCB, three power cables C and an array combiner box ACB. Each of the three pluralities of n strings is electrically connected to one of n DC inputs IS1 , IS2, ... , ISn of one of the three string combiner boxes SCB. Each string is a DC source which feeds direct current in the string combiner box SCB. Each combiner box SCB combines the fed n direct currents generated in the n strings. The resulting direct current passes a DC output OS of each of the three string combiner boxes SCB. The DC output of each of the three string combiner boxes SCB is electrically connected to one of three DC inputs IA1 , IA2 and IA3 of the array combiner box ACB. Each string combiner box is a DC source which feeds the resulting direct current via one of the three power cables C in the array combiner box ACB. The combiner box ACB combines the fed direct currents. The resulting direct current passes a DC output OA of the array combiner box ACB which is electrically connected to an inverter of the PV plant.

The DC part can comprise more or less than three string combiner boxes SCB and more than one or no array combiner box ACB. n is an integer greater 2 and can be different in at least a first and a second of the combiner boxes SCB. The general design and the function of a string S1 , S2, .., Sn, a string combiner box SCB and an array combiner box ACB are already described in the aforementioned prior art.

Each string S1 , S2, ... Sn includes a plurality of serially connected PV modules PM for generating a direct current. Installation parts S1 +, S2+, Sn+ resp. S1 -, S2-, Sn- connect the positive resp. the negative pole of each of the strings S1 , S2, Sn to the n DC inputs IS1 , IS2, ... ISn of the combiner boxes SCB. Paired installation parts, for instance S1 + and S1 -, connect the positive and the negative pole of each of the n strings resp. DC source S1 , S2, ... Sn, such as S1 , to a power line terminal and a return line terminal of each of the n DC inputs IS1 , IS2, ISn. The installation parts S1 +, S2+, ... S1 -, ...Sn- can be designed as a flexible or rigid current conductor, which is attached to a pole of one of the DC sources, such as S1 , and to a power or return terminal of one of the DC inputs, such as IS1 , by means of at least one plug, screw or any further detachable current connection, or a detachable current connection, which directly connects a pole of the DC source to a terminal of the DC input of the combiner box.

Each string combiner box SCB comprises a positive and a negative pole, which are arranged in the DC output OS and which by means of one of the three power cables C are electrically connected to one of three DC inputs IA1 , IA2 and IA3 of the array combiner box ACB. Thus each string combiner box SCB acts on the array combiner box ACB as a DC source.

The designs of the four shown combiner boxes SCB and ACB are similar. Fig.2 shows one of the three string combiner boxes SCB in an enlarged view. Fig.2 illustrates that the string combiner box SCB beside the n DC inputs IS1 , IS2, ISn and the DC output OS comprises a power line busbar A+ and a return line busbar A-. The power line busbar A+ is electrically connected to power line terminals of the n DC inputs IS1 , ... by means of n power line connections L1 +, L2+,..., Ln+ and to a power line terminal of the DC output OS by means of a power line connection L0+. The return line bus bar A- is electrically connected to return line terminals of the n DC inputs by means of n return line connections L1 -, L2-, Ln- and to a return line terminal of the DC output OS by means of a return line connection L0-. In each of the n power line connections L1 +, L2+,..., Ln+ resp. in each of the n corresponding return line connections L1 -, L2-,..., Ln- is arranged a power line switching unit B1 +, B2+, Bn+ resp. a return line switching unit B1 -, B2-, Bn- and a current sensor CS1 +, CS2+, CSn+ resp. CS1 -, CS2-, CSn-. Each current sensor reaches an accuracy which is sufficient to detect the flow and the direction of a direct current, which flows in a current circuit comprising the associated power or return line connection. In the power line connection L0+ resp. in the return line connection L0- is arranged a switching unit of a main switch M.

The string combiner box SCB further comprises a bridging member D and a combiner control and processing unit CU. The bridging member D on the one side is electrically connected to the power A+ and on the other side to the return line busbar A- and makes at least one of electrically connecting or disconnecting the two busbars A+ and A- and measuring the voltage polarity between these two busbars or a ground fault. As shown in figures 1 and 2 the control unit CU receives output signals from the power and return line switching units B1 +, B2+, B1 -, Bn-, the current sensors CS1 +, CSn+, CS1 -, CSn-, a power and a return line switching unit of the main switch M and from the bridging member D. The control unit CU is enabled to process and to save the received signals and to generate signals, in particular for opening, closing, blocking or unblocking the switching units of the main switch M, the power and return line switching units B1 +, B2+, B1 -, Bn- and - if applicable - also for opening or closing a switch provided in the bridging device D. Thus all these switches can be controlled remotely.

The control and processing unit CU in combination with the remotely controllable switching units enable the associated combiner box, like SCB or ACB, to run an automatic start-up routine. The automatic start-up routine can detect an installation failure, like an inverting connection of power and return line or a faulty string S1 , S2, Sn resp. a faulty power cable C if run in the array combiner box ACB.

Before running the start-up routine in one of the three string combiner boxes SCB the n strings S1 , Sn are electrically connected to the inputs IS1 , ISn of this combiner box and the main switch M, all switching units B1 +, ..., Βη+, B1 -, Bn- and - if applicable - the switch being arranged in the bridging device D are open. Before running the start-up routine in the array combiner box ACB the three pluralities of strings are electrically connected to the inputs of the associated string combiner boxes SCB and the three power cables C electrically connect the outputs OS of the three combiner boxes SCB to the three inputs IA1 , IA2 and IA3 of the array combiner box ACB. The main switch M and all power and return line switching units B1 +, B2+, B1 -, ..., Bn-, and - if applicable - the switch being arranged in the bridging device D are open.

In order to determine an installation error in the DC part of the PV plant according to fig .1 in any of the four combiner boxes SCB and ACB largely identical method steps are performed. In an example which is typical for the invention in the string combiner box SCB according to fig.2 method steps are performed as follows:

(a) closing at least one switching unit, such as B1 +, of a plurality of first switching units which are either the power B1 +, Bn+ or the return line switching units B1 -, Bn- resp. which are arranged either in the power L1 +, L2+, Ln+ or in the return line connections L1 -, L2-, Ln -,

(b) closing one switching unit, such as B1 -, of a plurality of second switching units which are arranged in power or in return line connections that do not comprise any of the first switching units in order to identify one of the DC sources, such as S1 , and to define a measuring circuit comprising the identified DC source, here S1 , one closed first switching unit, here B1 +, and one closed second switching unit, here B1 -,

(c) measuring at least one of the direction of a current, the polarity of a voltage and a ground fault in the measuring circuit,

(d) opening the measuring circuit when at least one of a forward current, a correct polarity of the voltage or no ground fault is measured, and repeating the method steps (a) to (d) with another, here S2, of the remaining DC sources, or signaling an installation error and blocking the combiner box, here SCB, for start-up when at least one of a reverse current, a wrong polarity of the voltage and a ground fault is measured, unblocking the combiner box after elimination of the installation error and repeating the method steps (a) to (d), and (θ) releasing the combiner box for operation in the absence of any installation error after performing the method steps (a) to (d) with each of the DC sources, here S1 , S2, Sn.

"Closing at least one switching unit of a plurality of at least two first switching units" is achieved with a tripping signal which the control and processing unit CU communicates to one first switching unit, such as B1 + or B1 -, to two, such as B1 + and B2+ or B1 - and B2-, to more than two or to all first switching units, that means either to all the switching units B1 +, Bn+ or to all the switching units B1 -, Bn-. In each case the first switching units are arranged either in the power L1 +, Ln+ or in the return line connections L1 -, .... , Ln-.

"Closing one switching unit of a plurality of at least two second switching units," is achieved with a tripping signal which the control and processing unit CU

communicates to only one second switching units, such as B1 - or B1 +, being arranged in the plurality of power L1 +, Ln+ or return line connections L1 -, Ln, which do not comprise any of the first switching units. The closing of the second switching unit, such as B1 -, identifies one of the DC sources, here S1 , the identity of which is stored in the control and processing unit CU. The closing further defines a measuring circuit. An embodiment of the measuring circuit is shown in Fig.2 and comprises the identified DC source S1 , the installation part S1 +, the power line connection L1 + together with the power line switching unit B1 + and the current sensor CS1 +, the power line busbar A+, the bridging device, the return line busbar A-, the return line connection L1 - together with the return line switching unit B1 - and the current sensor CS1 - and the installation part S1 -.

"Measuring at least one of the direction of a current, the polarity of a voltage and a ground fault in the measuring circuit" is achieved with at least one of the aforementioned current sensors CS1 +,..., CSn- and with the afore-mentioned bridging device D that may contain an additional current sensor. The current sensors and the bridging device D communicate measuring signals to the control and processing unit CU. Opening the measuring circuit" is achieved with a tripping signal which the control and processing unit CU communicates to at least one interrupter of the measuring circuit, like a first or a second switching unit or a further switching unit, like an auxiliary switch AS, which on the one side is electrically connected to the power line busbar A+ and on the other side to the return line busbar A- and which typically is arranged in the bridging member D. "Blocking the combiner box", here SCB, is achieved with a signal which the control and processing unit CU communicates at least to the switching units B+1 , B2+, B1 -, Bn- and - if required - also to the main switch M and the auxiliary switch AS when at least one of the reverse current, the wrong polarity of the voltage and the ground fault is measured. This signal further causes the reverse current or any further error current to be interrupted.

"Unblocking the combiner box" and "releasing the combiner box for operation" are achieved with signals which the control and processing unit CU communicates to the afore-listed switches and switching units. If the combiner box, here SCB, does not comprise the main switch M the signals are communicated to a switch of the DC part which connects or disconnects the DC output, here OS, of the combiner box and the DC part.

The method step "releasing the combiner box for operation" can also be achieved manually, that means with an input command of an user: Such a command can confirm an automatically generated release signal and thus can initiate a connection between the strings and the DC part of the PV plant via the combiner box.

A basic design of a switching unit, for example B1 +, and of the control and process unit CU are shown in figures 3 resp. 4. These units are realized as modules MS and MC for installation on a mounting rail of a combiner box, here the string combiner box SCB. As shown in fig.3 the module MS comprises the power line switching unit B1 +, the power line connection L1 + and the current sensor CS1 + which is applied to the power line connection L1 +. The module MS further comprises a local control and processing unit LCU for receiving data signals from within the unit, in particular the switching unit B1 + (identity, status), the current sensor CS1 + and a manual operation switch MOD, and from outside, in particular from the control and processing unit CU, and for emitting data signals to the switching unit B1 + and to the unit CU. A data interface IOL communicates the data signals DS emitted from the local control unit LCU to the control unit CU and from the control unit CU to the local control unit LCU.

The manual operation switch MOD enables the input of manually generated signals and the display of manually requested data signals DS. The local control units LCU resp. the control unit CU typically is realized as microprocessor.

Fig.4 shows the module MC. This module comprises the combiner control unit CU, a manual operation switch MOS and a data interface IOS for communicating the data signals DS emitted from the control unit CU and the manual operation MOS to data receivers, like the local control units LCU of the modules MS or of modules comprising the switching units of the main switch M or - if applicable - the switch provided in the bridging member D. The data interface IOS further communicates the data signals DS between the local control units LCU and the manual operation switches MOD on the one side and the control unit CU on the other side. The manual operation switch MOS like the manual operation switch MOD enables the input of manually generated data signals and the display of manually requested data signals DS.

In the figures 5 to 9 are shown five embodiments of the combiner box SCB according to fig.2. In these five embodiment the power line switching units B1 +, B2+, Bn+ are designed as switches which are able to make and break at least the nominal DC current of a DC source, that means of each of the strings S1 , S2,

Sn, whereas the return line switching units B1 -, B2-, Bn- are typically designed as disconnectors and are only able to make current. In modified embodiments of the combiner box SCB the return line switching units B1 -, B2-, Bn- can be realized as the switches for making and breaking at least the nominal current of the DC source and the power line switching units B1 +, B2+, Bn+ as disconnectors. In a further embodiment all the power and return line switching units B1 +, Bn- can be realized as switches for making and breaking at least the nominal DC current. In the four embodiments according to figures 5, 6, 7 and 9 the afore-described current sensors CS1 +, CS2+, CSn+, CS1 -, CS2-, CSn- are applied in the power resp. in the return line connections L1 +, L2+, Ln-, whereas in the embodiment according to fig.8 only the current sensors CS1 +, CS2+, CSn+ are arranged in the power line connections L1 +, Ln+.

In the embodiment according to fig.5 the bridging member D comprises the afore- described auxiliary switch AS. Each of the power line switching units B1 +, B2+, Bn+ is designed as bidirectional hybrid switch and thus is able to make and break the nominal current of a DC in the forward and in the reverse direction. The auxiliary switch AS and each of the switching units B1 -, B2-, Bn- are realized as disconnectors. The bidirectional hybrid switches as well as unidirectional hybrid switches, which are shown in the figures 6, 7 and 9, are uniformly drafted as unidirectional hybrid switches.

In this embodiment of the combiner box SCB a start-up routine is performed as follows:

(1 ) The switches M and AS and the switching units B1 +, B2+,..., Bn+ and B1 -, B2-,..., Bn- are open.

(2) The control and processing unit CU (only shown in figures 1 , 2 and 4)

communicates a tripping signal to the auxiliary switch AS to close.

(3) The unit CU further communicates a tripping signal to all the power line

switching units B1 +, B2+, Bn+ to close.

(4) If for reason of a first installation error one of the strings S1 , S2, ... has a short, at least one of the current sensors CS1 +, CSn+ communicates the occurence of a short-circuit-current to the control and processing unit CU. The control and processing unit CU communicates a signal indicating the first installation error and causes the blocking of the combiner box SCB. The blocking includes the reopening of the closed switching units B1 +, Bn+ in order to break the short-circuit-current. Such a short-circuit can occur when the installation parts S1 +,..., Sn- are erroneously installed, such as connecting the positive pole of a DC source, like S1 , to the power line terminal of the DC input IS1 by a first installation part, like S1 +, and the negative pole of the DC source, here S1 , to the power line terminal of the DC input IS2 by a second installation part, like S1 -. (5) After eliminating the first installation error the unit CU communicates a signal to the combiner box to unblock and causes the combiner box to repeat the afore-listed method steps.

(6) In the absence of the first installation error the control unit CU communicates a tripping signal to the switching unit B1 - to close.

(7) The unit CU identifies the closed switching unit B1 - and the DC source, here string S1 , the first pole of which being electrically connected to the identified switching unit B1 - across an identified first installation part, here S1 -.

(8) The unit CU stores the identities of the switching unit B1 -, the string S1 and the installation part S1 -.

(9) The closing of B1 - forms a measuring circuit which extends from the first pole of the identified string S1 across the first installation part S1 -, the return line connection L1 - with the current sensor CS1 - and the return line switching unit B1 -, the return line busbar A-, the auxiliary switch AS, the power line busbar A+, one of the power line connections L1 +, Ln, here L2+, with one of the current sensors CS1 +, CSn+, here CS2+, and with one of the power line switching units B1 +, Bn+, here B2+, and a second of the installation parts, here S2+, to the second pole of the identified string S1 .

(1 0) If the first pole is the negative pole of the string S1 the current sensors detect a forward current in the measuring circuit, which flows from the installation part S2+ to the installation part S1 -.

(1 1 ) The control and processing unit CU notices the forward current and identifies the two installation parts S1 - and S2+ as a pair which is associated to the string S1 . The identity of this pair is stored in the control and processing unit CU.

(1 2) The unit CU then communicates a tripping signal to the closed switching unit B2+ to open. This tripping signal is communicated to the switching unit B1 - to open with a time delay in which the forward current is interrupted. The switching unit B2+ can be reclosed once the switching unit B1 - is open.

(1 3) The control and processing unit CU communicates a tripping signal to the switching unit B2- in order to identify a further of the pluralities of DC sources, such as string S2, and to repeat the method steps (1 ) to (12) with the switching unit B2- and the string S2.

(14) In the same manner the remaining strings are checked.

(1 5) If the poles of the string 1 are inverted resp. if the installation part S1 - is

connected to the positive and the installation part S2+ to the negative pole of the string S1 the control and processing unit CU notices a reverse current flow in the measuring circuit. The unit CU then signalizes a second installation error and communicates a tripping signal to open the measuring circuit, that means to open the power line switching unit B2+. Furthermore the unit CU causes the blocking of the combiner box SCB for operation, which enables the elimination of the installation error.

(1 6) The control and processing unit CU communicates an unblocking signal to the combiner box after the elimination of the second installation error and initiates the repetition of the method steps (1 ) to (16).

(1 7) In the absence of any installation error after performing the method steps (1 ) to (16) a release signal is automatically (from the unit CU) and/or manually (from a user) communicated to the combiner box for operation resp. for opening the auxiliary switch AS and for closing the main switch M or any other switching unit with a time delay, wherein the other switching unit connects the DC output OS of the combiner box SCB to the DC part of the

PV plant.

In the embodiments of the invention according to figures 6, 7 and 9 the auxiliary switch AS is implemented as bidirectional hybrid switch and each of the power line switching units B1 +, B2+, Bn+ are implemented as unidirectional hybrid switch. The comparatively cheap and simple unidirectional hybrid switches can switch-off the direct current only in one predefined direction, whereas the more expensive bidirectional hybrid switch can switch-off a current flowing in either direction, that means a forward and a reverse current.

Each of these three combiner boxes SCB performs the same method steps (1 ), (3) to (8) as the combiner box according to fig.5. Other than in the combiner box according to fig.5 in each of the three combiner boxes according to figures 6, 7 and 9 the auxiliary switch AS can close resp. can open the measuring circuit in order to make or break the current in the measuring circuit. Thus in step (1 2) resp. step (1 5) instead of the switching units B1 +, B2+,.... the auxiliary switch AS can be closed resp. opened in order to make or break the current in the measuring circuit.

Other than in the combiner box according to fig.5 in the combiner box according to fig.6 the method step (2) (closing the auxiliary switch AS) is performed between the method steps (8) and (9). Afterwards the method steps (10) and (1 1 ) are performed. The further method steps are similar or identical to the method steps (1 2) to (1 7) performed with the string combiner box SCB according to fig.5 and are as follows:

(1 2) The unit CU communicates a tripping signal to the closed auxiliary switch AS to open. This tripping signal is communicated to the switching unit B1 - to open with a time delay in which the forward current is interrupted. The auxiliary switch can be reclosed once the switching B1 - is open.

(1 3) The control and processing unit CU communicates a tripping signal to the switching unit B2- in order to identify a further of the pluralities of DC sources, such as string S2, and to repeat the method steps (1 ), (3) to (8), (2), (9) to (12) with the switching unit B2- and the string S2.

(14) In the same manner the remaining strings are checked.

connected to the positive and the installation part S2+ to the negative pole of the string S1 the control and processing unit CU notices a reverse current flow in the measuring circuit. The unit CU then signalizes a second

installation error and communicates a tripping signal to open the measuring circuit, that means to open the auxiliary switch AS. Furthermore the unit CU causes the blocking of the combiner box SCB for operation, which enables the elimination of the installation error.

(1 6) The control and processing unit CU communicates an unblocking signal to the combiner box after the elimination of the second installation error and initiates the repetition of the method steps (1 ), (3) to (8), (2), (9) to (16). (1 7) In the absence of any installation error after performing the method steps (1 ), (3) to (8), (2), (9) to (16) a release signal is automatically (unit CU) and/or manually (user) communicated to the combiner box for operation resp. for opening the auxiliary switch AS and for closing the main switch M or any other switching unit with a time delay, wherein the other switching unit connects the DC output OS of the combiner box SCB to the DC part of the PV plant.

Other than in the combiner according to fig.6 the combiner box according to fig.7 further comprises a voltage polarity sensor VPS which measures the polarity of the voltage between the busbars A+ and A- when the auxiliary switch AS is open.

The combiner box SCB performs the afore-described method steps (1 ) and (3) to

(8) and further method steps as follows:

(9) The closing of the switching B1 - according to step (6) forms a first measuring circuit which extends from the first pole of the identified string S1 across the first installation part S1 -, the return line connection L1 - with the current sensor CS1 - and the return line switching unit B1 -, the return line busbar A-, the voltage polarity sensor VPS, the power line busbar A+, one of the power line connections L1 +, Ln+, with one of the current sensors CS1 +, CSn+, and with one of the power line switching units B1 +, Bn+ and a second of the installation parts to the second pole of the identified string S1 .

(1 0) If the first pole is the negative pole of the string S1 the voltage polarity sensor VPS measures a correct polarity of the voltage between the two busbars A+ and A-.

(1 1 ) The control and processing unit CU communicates a tripping signal to the auxiliary switch AS to close.

(1 2) The closing of the auxiliary switch AS forms a second measuring circuit

which extends from the first pole of the identified string S1 across the first installation part S1 -, the return line connection L1 - with the current sensor CS1 - and the return line switching unit B1 -, the return line busbar A-, the auxiliary switch AS, the power line busbar A+, one of the power line connections L1 +, Ln, here L2+, with one of the current sensors CS1 +, CSn+, here CS2+, and with one of the power line switching units B1 +, Bn+, here B2+, and a second of the installation parts, here S2+, to the second pole of the identified string S1 .

(1 3) For reason of the correct polarity of the voltage between the two busbars A+ and A- the current sensors detect a forward current in the second measuring circuit, which flows from the installation part S2+ to the installation part S1 -.

(14) The control and processing unit CU notices the forward current and identifies the two installation parts S1 - and S2+ as a pair which is associated to the string S1 . The identity of this pair is stored in the control and processing unit CU.

(1 5) The unit CU then communicates a tripping signal to the closed auxiliary

switch AS to open. This tripping signal is communicated to the switching unit B1 - to open with a time delay in which the forward current is interrupted. The auxiliary switch can be reclosed once the switching B1 - is open.

(1 6) The control and processing unit CU then communicates a tripping signal to the switching unit B2- in order to identify a further of the pluralities of DC sources, such as string S2, and to repeat the method steps (1 ), (3) to (16) with the switching unit B2- and the string S1 .

(1 7) In the same manner the remaining strings are checked.

(1 8) If the poles of the string 1 are inverted resp. if the installation part S1 - is connected to the positive and the installation part S2+ to the negative pole of the string S1 the control and processing unit CU notices a wrong polarity of the voltage in the first measuring circuit. The unit CU then signalizes a second installation error and communicates a tripping signal to open the first measuring circuit resp. to open the switching unit B1 -. Furthermore the unit

CU causes the blocking of the combiner box SCB for operation, which enables the elimination of the installation error.

(1 9) The control and processing unit CU communicates an unblocking signal to the combiner box after the elimination of the second installation error and initiates the repetition of the method steps (1 ), (3) to (19). (20) In the absence of any installation error after performing the method steps (1 ), (3) to (1 9) a release signal is automatically (unit CU) and/or manually (user) communicated to the combiner box for operation resp. for opening the auxiliary switch AS and for closing the main switch M or any other switching unit with a time delay, wherein the other switching unit connects the DC output OS of the combiner box SCB to the DC part of the PV plant.

In the embodiment according to fig.8 the bridging member D merely comprises the voltage polarity sensor VPS for measuring the polarity of the voltage between the busbars A+ and A-. The combiner box SCB performs the afore-described method steps (1 ) and (3) to (8) and then further method steps as follows:

(9) The closing of the switching B1 - according to step (6) forms a measuring circuit which extends from the first pole of the identified string S1 across the first installation part S1 -, the return line connection L1 - with the switching unit B1 -, the return line busbar A-, the voltage polarity sensor VPS, the power line busbar A+, one of the power line connections L1 +, Ln+, with one of the current sensors CS1 +, CSn+ and with one of the power line switching units B1 +, Bn+ and a second of the installation parts to the second pole of the identified string S1 .

(1 1 ) The control and processing unit CU notices the correct polarity of the voltage and communicates a tripping signal to the plurality of switching units B1 +,..., Bn+ to open and then to close these switching units sequently in order to measure the correct polarity of the voltage in a measuring circuit in which one of the sequently closed switching units, here B2+, identifies the second pole of the string S1 resp. the second installation part, here S2+.

(1 2) The control and processing unit CU stores the identities of the first, here S-, and the second installation part, here S2+, as a pair.

(1 3) The unit CU communicates a tripping signal to the closed switching unit B1 - open and to the plurality of switching units B1 +, B2+, to close. (14) The control and processing unit CU communicates a tripping signal to the switching unit B2- to close in order to identify a further of the pluralities of DC sources, such as string S2, and to repeat the method steps (1 ) and (3) to (14) with the switching unit B2- and the string S2.

(1 5) In the same manner the remaining strings are checked.

(1 6) If the poles of the string 1 are inverted resp. if the installation part S1 - is

connected to the positive and the installation part S2+ to the negative pole of the string S1 the control and processing unit CU notices a wrong polarity of the voltage in the measuring circuit. The unit CU then signalizes a second installation error and communicates a tripping signal to open the measuring circuit, that means to open the switching unit B1 - resp. the plurality of the switching units B1 +, , Bn+. Furthermore the unit CU causes the blocking of the combiner box SCB for operation, which enables the elimination of the installation error.

(1 7) The control and processing unit CU communicates an unblocking signal to the combiner box after the elimination of the second installation error and causes the repetition of the method steps (1 ), (3) to (17).

(1 8) In the absence of any installation error after performing the method steps (1 ), (3) to (1 7) a release signal is automatically (unit CU) and/or manually (user) communicated to the combiner box for operation resp. for closing the main switch M or any other switching unit with a time delay, wherein the other switching unit connects the DC output OS of the combiner box SCB to the DC part of the PV plant.

In the embodiment according to fig.9 the bridging member D comprises a resistor R which is connected in series with the auxiliary switch AS. The resistor R reduces the current in the measuring circuit and thus in the auxiliary switch AS. This results in a cost reduction for the auxiliary switch AS. The bridging member D further comprises a ground fault detection sensor GF which with one end is electrically connected to the power (A+) and with the other end to the return line busbar (A-) and which is kept on ground potential. The sensor GF signals the presence of a ground fault. In the combiner box according to fig.9 the method according to the invention can perform the method steps described in the combiner box according to fig.7, however, in which the unit CU instead of a correct or a wrong polarity of the voltage between the busbars A+ and A- notices the presence or the absence of a ground fault signaled from the ground fault detection sensor GF.

In the afore-described embodiments of the combiner box according to figures 5 to 9 the plurality of the first switching units B1 +, Bn+ resp. B1 -, Bn- is closed before defining the measuring circuit. This saves execution time when before startup the method according to the invention is performed in the DC part. If only one of the first switching units is closed before defining the measuring circuit the method according to the invention can be performed such that after closing one of the first switching units the plurality of second switching units is closed and opened sequently in order to form measuring circuits which comprise each DC source of the plurality of DC sources and each combination of switching units comprising one first and one second switching unit. This needs more time but avoids additional effort to determine the first installation error (shorting of the plurality of first switching units) with additional method steps. The first kind of installation error is still found as no pair of switching units will be found for the corresponding string.

List of Reference Signs

A+ power line busbar

A- return line busbar

ACB array combiner box

B1 +, B2+..., Bn+ power line switching units B1 -, B2-..., Bn- return line switching units C power cables

CU control and processing unit

CS1 +, CS2+..., CSn+,

CS1 -, CS2-..., CSn- current sensors

D bridging member

DS data signals

GF ground fault detection sensor

IA1 , IA2, ..., lAn DC inputs of array combiner box

IOL, IOS data interfaces

IS1 , IS2, ISn DC inputs of string combiner box

L0+, L1 +. L2+, Ln+ power line connections

L0-, L1 -. L2-, Ln- return line connections

LCU local control and processing unit

M main switch

MC, MS modules

MOD, MOS manual operation switches OA DC output of array combiner box OS, DC output of string combiner box PM photovoltaic modules

R resistor

S1 , S2,... , Sn strings, DC sources

S1 +, S2+,... , Sn+ installation parts

S1 -, S2-,..., Sn- SCB string combiner box, DC source VPS voltage polarity sensor

PM PV modules

Claims

A method to determine an installation error in a DC part of a PV plant comprising a plurality of at least two DC sources (S1 , S2, ...), a combiner box (SCB, ACB) with a plurality of at least two DC inputs (IS1 , IS2, ... IA1 , IA2, ...) and with installations parts (S1 +, S2+, S1 -, S2-, ...) for connecting a positive and a negative pole of each DC source with a power and with a return line terminal of the DC inputs, characterized in method steps as follows:

(a) closing at least one switching unit (B1 +) of a plurality of at least two first switching units (B1 +, B2+, ..., B1 -, Bn-) being arranged either in a plurality of power line connections (L1 +, L2+,...) which are extended between the power line terminals of the DC inputs (IS1 , ...) and a power line busbar (A+) of the combiner box or in a plurality of at least two return line connections (L1 -, L2-, ..) which are extended between the return line terminals of the DC inputs (IS1 ,..) and a return line busbar (A-) of the combiner box (SCB),

(b) closing one switching unit (B1 -) of a plurality of at least two second

switching units (B1 -, B2-, ..., B1 +, Bn+) being arranged in the plurality of power or return line connections ( L1 -, L2-,..., L1 +, ..), which connections do not comprise any of the first switching units (B1 +, B1 - , ..), in order to identify one (S1 ) of the DC sources and to define a measuring circuit comprising the identified DC source (S1 ), one closed first switching unit (B1 +) and one closed second switching unit (B1 -),

(c) measuring at least one of the direction of a current, the polarity of a

voltage and a ground fault in the measuring circuit,

(d) opening the measuring circuit when at least one of a forward current, a correct polarity of the voltage or no ground fault is measured, and repeating the method steps (a) to (d) with another (S2) of the remaining DC sources, or

signaling an installation error and blocking the combiner box (SCB) for start-up when at least one of a reverse current, a wrong polarity of the voltage and a ground fault is measured, unblocking the combiner box (SCB) after elimination of the installation error and repeating the method steps (a) to (d), and

(e) releasing the combiner box (SCB) for operation in the absence of any installation error after performing the method steps (a) to (d) with each of the DC sources (S1 , S2, ...).

The method according to claim 1 , characterized in

closing in step (a) the plurality of first switching units (B1 +, ...) when each of the first switching units is designed in a manner to make and break at least the nominal current of each of the DC sources (S1 , S2, ...) and opening the closed first switching units (B1 +, B2+, ...) and signaling an installation error when a short current is measured in a current circuit comprising one of the DC sources (S1 ) and two first switching units (B1 +, B2+, ...).

The method according to any of claims 1 or 2, characterized in

electrically connecting the power (A+) and the return line busbar (A-) before performing step (b).

The method according to any of claims 1 or 2, characterized in

electrically connecting the power (A+) and the return line busbar (A-) after performing step (b) and before measuring the direction of the current according to step (c).

The method according to claim 4, characterized in

electrically connecting the power (A+) and the return line busbar (A-) after measuring the polarity of the voltage according to step (c).

6. The method according to any of claims 3 to 5, characterized in disconnecting the power (A+) and the return line busbar (A-) before opening the closed second switching unit (B1 -) when a reverse current according to step (d) is measured.

The method according to any of claims 1 to 6, characterized in

identifying in step (b) a second (S1 -) of the installation parts which connects a second pole of the identified DC source (S1 ) to the second switching unit

(B1 -).

measuring in step (c) the current in a section of the measuring circuit comprising the at least one closed first switching unit (B1 +) and a first (S1 +) of the installation parts, which connects the first of the two poles of the identified DC source (S1 ) to the closed first switching unit (B1 +), in order to identify the first (S1 +) installation part, and

storing the identities of the first (S1 +) and the second installation part (S1 -) as a pair. 8. The method according to claim 7, characterized in

screening the stored pairs associated to the DC sources (S1 , S2, ...), and checking if for each of the DC sources (S1 , ...) a pair (S1 +, S1 -) connecting this source to one of the DC inputs (IS1 , IS2, ...) has been stored.

9. A combiner box (SCB, ACA) for performing the method according to claim 1 in a DC part of a PV plant comprising:

a plurality of at least two DC inputs (IS1 , IS2, ... ; IA1 , IA2, ...) each (IS1 ) of which being suited for electrical connection to one (S1 ) of a plurality of at least two DC sources (S1 , S2, ...),

a DC output (OS, OA) for electrical connection to a further combiner box (ACA) of the DC part or to an inverter of the PV plant,

a power (A+) and a return line busbar (A-),

a plurality of at least two first switching units (B1 +, B2+, ...) being arranged either in a plurality of power line connections (L1 +, L2+,...) extended between power line terminals of the DC inputs (IS1 , IS2, ...) and the power line busbar (A+) or in a plurality of return line connections (L1 -, L2-, ...) extended between return line terminals of the DC inputs (IS1 , ...) and the return line busbar (A-),

a plurality of at least two second switching units (B1 -, B2-, ...) being arranged either in the plurality of the power or return line connections (L1 -, L2-,...) which do not comprise any first switching unit (B1 +),

a plurality of at least two current sensors (CS1 +, CS2+, ...) being associated to the plurality of first or to the plurality of second switching units, and a control and processing unit (CU) for receiving output signals from the first and the second switching units (B1 +, ..., B1 -, ...) and the plurality of current sensors (CS1 +, CS2+, ...) and for communicating signals to the first and second switching units, characterized in

that the combiner box further comprises a bridging member (D) which on the one side is electrically connected to the power (A+) and on the other side to the return line busbar (A-), which is in data communication with the control and processing unit (CU) and which before start-up forms a section of a circuit for measuring at least one of the direction of a current, the polarity of a voltage and the presence a ground fault.

10. The combiner box according to claim 9, characterized in

that the bridging member (D) comprises at least one of an auxiliary switch (AS), a voltage polarity sensor (VPS) and a ground fault detection sensor (GF), wherein the at least one of the auxiliary switch, the voltage polarity sensor and the ground fault detection sensor with one end is electrically connected to the power (A1 ) and with the other end to the return line busbar (A-). 1 1 . The combiner box according to claim 10, characterized in

that the bridging member (D) comprises the auxiliary switch (AS) and at least one of the voltage polarity sensor (VPS) and the ground fault detection sensor (GF).

12. The combiner box according to any of claims 10 or 1 1 , characterized in

that the bridging member (D) comprises merely either the auxiliary switch or the voltage polarity sensor.

13. The combiner box according to any of claims 10 to 12, characterized in that the auxiliary switch (AS) is designed as disconnector, and that each (B1 +) of the first switching units (B1 +, ...) is designed as birectional hybrid switch. 14. The combiner box according to any of claims 1 0 to 13, characterized in

that the auxiliary switch (AS) is designed as bidirectional hybrid switch, and that each (B1 +) of the first switching units is designed as unidirectional hybrid switch.

15. The combiner box according to any of claim 10 to 14, characterized in

that a resistor (R) is connected in series with the auxiliary switch.