WO2013008084A1

WO2013008084A1 - System for placing solar power plants into a safe condition

Info

Publication number: WO2013008084A1
Application number: PCT/IB2012/001363
Authority: WO
Inventors: Harald Hauf; Didier Rossi; Enrico Bianconi
Original assignee: Ehw-Research S.A.S.
Priority date: 2011-07-13
Filing date: 2012-07-11
Publication date: 2013-01-17
Also published as: ITTO20110616A1; EP2732472A1

Abstract

A system for placing into a safe condition one or more solar systems "I", each system comprising a plurality of solar panels "P", which are electrically connected in series, so as to form one or more strings "S". Said system comprises at least one central unit 3, which is electrically connected to one or more strings "S" and to a power supply source 2, and comprises at least one control unit 32; at least one peripheral unit 4, which is electrically connected to at least one string "S" and to said central unit 3, and comprises a plurality of switches (43, 33), which are properly connected to one or more panels "P" comprised in said string "S". The central unit 3 is adapted, when the voltage of the power supply source 2 in interrupted, to isolate at least one of the strings "S" by interrupting the current in said string "S" and by disconnecting it opening said plurality of switches 43, so that it is galvanically isolated and presents, at its ends, at most a predetermined safety low voltage.

Description

SYSTEM FOR PLACING SOLAR POWER PLANTS INTO A SAFE CONDITION

The present invention is relative to a system for placing into a safe condition one or more solar plants, preferably photovoltaic systems, adapted to electrically isolate portions of said system, so as to obtain, at the ends of said panels, a safety low voltage, which perfectly complies with electrical safety regulations.

In the photovoltaic power generation field, photovoltaic modules or panels are normally used, which feature a relatively low voltage and are connected in series, thus obtaining strings. Typically, the voltage of one single module or panel is sufficiently low to be considered safe. Indeed, each photovoltaic module complies with safety regulation, thus generating, in use, a voltage, at its ends, which is normally lower than 40Vdc.

The fact that different modules are connected in series so as to obtain a string causes high voltages to be reached, in use, at the ends of said string. The values of said high voltages are directly proportional to the number of panels connected in series. For example, in domestic implementations, the creation of a typical 3kWp photovoltaic system requires the connection in series of approximately twelve photovoltaic modules, thus obtaining a string, which, in use, features, at its ends, a voltage that is approximately equal to 420Vdc.

In traditional systems, when the string is irradiated by sun rays, said string always features a high voltage at its ends, without the possibility of safely disabling the generation of the voltage itself, for example in case of danger . Electrical safety regulations, nowadays, provide for the insertion of a direct current "DC" switch between the photovoltaic system, consisting of said modules, and the input of an inverter for the generation of an alternating voltage, which is comprised in photovoltaic systems. This solution is merely adapted to guarantee the safety of the inverter, but leaves the used photovoltaic system energized.

In the event of a daytime fire of a building provided with a photovoltaic system, even though the network power supply is disconnected and the safety of the inverter is guaranteed, said system still presents, at its ends, a high voltage. As a matter of fact, said voltage is potentially dangerous for firefighters since, for example, it can generate an electric current through the water used to put out the fire itself.

In the event that the photovoltaic system has to be accessed by an operator for maintenance purposes, the operator has to make sure that the system itself is completely de-energised, in order to avoid, in case of an accidental contact with the system, being subject to a voltage that is potentially dangerous for his health.

A safety system is known, adapted to isolate the photovoltaic system at a module level . Said system comprises a control unit, to which all the panels or modules comprised in the system itself are electrically connected.

This solution, for systems with a number of modules higher than ten, requires a high number of cables to be laid. Therefore, this solution generates a bundle of cables with large dimensions, which is very difficult to handle and lay. Furthermore, the cable connecting each single panel to said control unit is, on an average, very long, thus increasing the costs for the creation of the system. As a matter of fact, said connection cable is very expensive because, in order to guarantee the correct coupling to the panel, is made of low-resistance alloys.

Switch systems are also known, adapted to isolate a circuit. Said systems comprise switches of the semiconductor type, which interrupt or at least reduce the flow of a current inside said circuit, though, without guaranteeing a galvanic isolation of the contacts; therefore, said type of switches cannot be used in safety systems .

Moreover, the use of relays in safety systems is known, since they guarantee a galvanic isolation of the contacts. In order to guarantee the opening of a "DC" electrical load, said relays are manufactured with oversize contacts, which are very expensive, and with high- consumption excitation coils.

The object of the present invention is to solve the above-mentioned problems by providing a system for guaranteeing the safety of photovoltaic systems, which comprises at least one central unit and at least one peripheral unit, so as to guarantee the safety of photovoltaic system, even of large dimensions, by isolating at least one string comprised in said system at the level of the single modules or panels comprised in said string.

An aspect of the present invention relates to a system for guaranteeing the safety of photovoltaic systems with the features set forth in appended claim 1.

Further accessory features are set forth in the appended dependent claims . The additional features and advantages of the system according to the present invention will be best understood upon perusal of the following detailed description of different embodiments with reference to the accompanying drawings, which respectively illustrate what follows:

• figure 1 shows a flowchart of the system according to the present invention;

• figure 2 shows an embodiment of the circuit diagram of the system of figure 1 ;

· figure 3 shows a further embodiment of the general circuit diagram of the system of figure 1;

• figure 4 shows, in detail, the circuit diagram of figure 3.

With reference to the figures mentioned above, the safety system according to the present invention can be applied to one or more solar systems "I" for the generation of power comprising, in each case, a plurality of modules or solar panels "P", which, in use, are electrically connected in one or more series called strings "S" .

Said system comprises at least one central unit 3 and at least one peripheral unit 4.

Said at least one central unit 3 comprises at least one control unit 32 and is electrically connected to one or more strings "S" and to a power supply source 2, adapted to supply said safety system with power.

Said at least one peripheral unit 4 is electrically connected to at least one string "S" and to said central unit 3 and comprises a plurality of switches (43, 33), which are electrically controlled and properly connected to one or more panels "P" comprised in said string "S" .

Said at least one central unit 3 is adapted, when the voltage of the power supply source 2 is interrupted, by means of said control unit 32, to isolate at least one string "S" by interrupting the current in said string "S" and to disconnect said string "S" by opening said plurality of switches (43, 33), so that said string "S" is galvanically isolated and presents, at its ends, at most a predetermined safety low voltage.

For the purpose of the present invention, the expression "presents, at its ends, at most a predetermined safety low voltage" means that at the ends of string "S" there is a voltage ranging from OVdc to a predetermined safety voltage as per Safety Extra Low Voltage definition. As shown in figure 1, central unit 3 is connected to power supply 2, which preferably is the network voltage (240Vac 400Vac) . Furthermore, said central unit 3 is connected to an inverter 10, which is generally comprised in photovoltaic systems, so as to introduce the power produced by system "I" in direct current into the alternating energy distribution network.

Said central unit 3 is connected to one or more peripheral units 4, which are properly connected to one another, e.g. in parallel or in series, as a function of the features of system "I".

Each peripheral unit 4 is connected to one or more strings "S" of panels "P", each one of said strings "S" comprising at least one panel "P" .

During the normal use of system "I", each peripheral unit 4 connects in series the different panels "P" comprised in each string "S" connected thereto, so as to allow the production of power, which is introduced into the network by inverter 10. The ends of one or more strings "S", which are connected to the respective peripheral units 4, arrive at central unit 3.

Each peripheral unit 4 is connected to central unit 3 by means of at least one data line 5, preferably a serial line, for example implementing the RS-485 standard.

By means of said data line 5, central unit 3 and in particular control unit 32 can communicate with the single peripheral units 4, so as to isolate one or more portions of system "I" in case of danger of for maintenance purposes .

In the embodiment shown in figure 2, control unit 32 is adapted to manage a plurality of switches 33, which are closed while in use, comprised in peripheral unit 4, and adapted to open so that at least one string "S" or a section "S¹" thereof is galvanically isolated and features, at its ends, a predetermined safety low voltage, for example in case the voltage of power supply source 2 is interrupted .

For the purpose of the present invention, the term

"switch" indicates an electromechanical device, which is adapted to interrupt the current in at least one portion of an electrical circuit, thus creating a galvanic isolation between the contacts.

In the embodiment of figure 2, said switches 33 are electromechanical relays, which are normally open. Said relays comprise a coil, through which current has to flow in order to allow said switch 33 to close the contact, so as to create string "S". The use of relays allows the creation of a galvanic isolation between the contacts by means of air gap and, therefore, they can be applied in safety systems. The removal of the power supply voltage of the relays causes their opening, thus opening the electrical contact.

The substantially simultaneous opening of switches 33 causes the interruption and isolation capacity requested to each single switch 33 to be reduced. This solution allows the use of relays featuring contacts of reduced dimensions, which, therefore, can be easily inserted into an electronic system, as well as low-consumption excitation coils.

The opening of switches 33 comprised in a string "S" allows the isolation of string "S" itself, for example at the level of each single panel "P", thus intrinsically guaranteeing the safety of at least said portion of system "I" that has been isolated.

Preferably, each panel "P" comprised in string "S" is connected to two switches 33, a first switch being connected to the cathode terminal and a second switch being connected to the anode terminal of each panel "P" respectively.

Preferably, the interruption of power supply 2 takes place after an emergency button 1 has been pushed. Said emergency button 1, according to electrical safety regulations, is a DC ^'switch, preferably a push-button, so that, in case of danger, for example in the event of a fire, power supply 2 is disconnected from system "I" by simply pushing button 1.

Said emergency button 1, besides being pushed in case of danger, can be pushed by an operator performing the maintenance of the system before beginning the maintenance work on the system itself.

In the alternative embodiment shown in figure 3, peripheral unit 4 comprises a plurality of switches (43, 33) , said switches comprising, in particular, at least one switch 33, adapted to interrupt a direct current, for example inside a string "S", and one or more isolator switches 43, adapted to isolate said string "S" creating a plurality of sections "S'^M , which are galvanically isolated from the rest of system "I".

Said switch 33 is a relay, adapted to open a DC electrical contact, thus interrupting the current flow inside string "S", and to switch off the electric arc generated during the opening of the contacts, thus guaranteeing an electrical isolation.

Preferably, each switch 33 is arranged in series with respect to a string "S" and presents structural features that are adapted to interrupt the current flowing inside string "S" itself. In particular, said switch 33 is a relay, which comprises an electromechanical switch and a solid state switch, which are arranged in parallel, so as to increase the performances of switch 33.

The system according to the present invention, thanks to a plurality of peripheral units 4, allows the number of panels "P" comprised in each string "S" to be reduced, thus allowing the use of switches 33 with reduced dimensions, since the interruption capacity is lower.

According to a further method for reducing the interruption capacity requested to switch 33 in order to open the contacts and consequently interrupting the current in string "S", more than one switch 33, for example two switches, can be arranged in series.

Said one or more isolator switches 43, on the other hand, are adapted to isolate said string creating a plurality of string sections "S^{, n}.

For the purpose of the present invention, the term "isolator switch" indicates a switch, which is able to open a line guaranteeing a galvanic isolation between the contacts, when the current is substantially absent in that line .

For the purpose of the present invention, the expression "the current is substantially absent" means that the current is lower than 1/10 of the nominal current flowing in the string "S" while in use.

In particular said isolator switches 43 have technical and functional features that allow an air gap isolation, though without the need for a current interruption power.

In case power supply 2 is interrupted, switch 33 is opened, thus stopping the current flow in at least one string "S". After the current has been interrupted in string "S", the plurality of isolator switches 43 are adapted to isolate said string "S", thus guaranteeing a galvanic isolation.

Said isolator switches 43 are preferably adapted to isolate string "S" at the level of each single panel "P" comprised in the string itself. In particular, said isolator switches 43 can be, for example, two-step relays.

Preferably, each panel "P" comprised in string "S" is connected to two isolator switches 43, a first isolator switch being connected to the cathode terminal and a second isolator switch being connected to the anode terminal of each panel "P" respectively.

In the embodiment shown in detail in figure 4, said central unit 30 comprises at least one energy storage device 34, adapted to temporarily supply power to said safety system in case power supply 2 is interrupted.

Said energy storage device 34, in a preferred embodiment, comprises a capacitor, adapted to guarantee a predetermined voltage value, a capacitor charging device, adapted to stabilize the energy coming from an energy source, e.g. the energy distribution network, for the purpose of charging said capacitor, and at least one control device, adapted to manage the charging of the capacitor itself, so as to preserve its performances.

Said energy storage device 34, in an embodiment, is supplied with power by means of one or more panels "P".

Said control unit 32 comprises, furthermore, at least one monitoring device 321, adapted to detect the interruption of power supply 2.

Said monitoring device 321 monitors power supply line 2, so as to detect, for example, a decrease in voltage, said voltage falling below a predetermined voltage threshold.

Said predetermined voltage threshold corresponding, for example, to 1/10 of the nominal voltage of power supply 2. In the preferred embodiment, said monitoring device is, for example, a voltmeter, which is suited to measure the voltage at the ends of power supply 2.

Said solution allows the use of isolator switches 43 instead of switches 33, thus requiring a reduced interruption capacity and reduced current consumptions for the management of the system according to the present invention .

Said control unit 32 comprises, furthermore, a data processor 322, adapted to process the data coming from said monitoring device 321 and to transmit the proper signals to peripheral units 4.

In particular, said data processor 322 is adapted to compare the voltage measured by monitoring device 321 with the predetermined threshold voltage. If the voltage measured by monitoring device 321 is below the above- mentioned threshold voltage, data processor 322 causes the system according to the present ^' invention to guarantee the safety of system "I" or at least of a portion thereof.

Said control unit 32, furthermore, is adapted to run a computer program, which is duly stored on a non-volatile memory medium and is adapted to perform a series of operating steps, preferably consecutive, which are adapted to guarantee the safety of solar systems "I" for generating electrical energy.

Said program performs the following operating steps:

• monitoring power supply 2 ;

• detecting a reduction of power supply 2 below a predetermined threshold;

• opening an electrical circuit of one or more strings "S" ;

• isolating a string "S" creating string sections

"S"';

• galvanically isolating string section "S'" with a predetermined safety low voltage at its ends.

During the power supply monitoring step, monitoring device 321 monitors power supply 2, so as to detect, for example, a reduction of the voltage of power supply 2 below a predetermined threshold.

Said monitoring device 321 keeps monitoring line 2 and sends, for example at regular intervals, the voltage measure to control unit 32 and, in particular, to data processor 322. In case of a reduction, by way of example, of the voltage of power supply 2, the value measured by monitoring device 321 and sent to data processor 322 is lower than the predetermined threshold. During the step for detecting a reduction of power supply 2 below a predetermined threshold, data processor 322 detects that the voltage measured by the monitoring device has fallen below the predetermined threshold. Subsequently, the step for opening an electrical circuit of one or more strings "S" is performed. During this step, control unit 32, preferably data processor 322, sends the opening command to switches 33, whose oil, in the preferred embodiment, is de- energized, thus opening the contacts of the relay.

The step for isolating a string "S" creating string sections "S¹", in the embodiment shown in figure 2, is performed simultaneously to the electrical circuit opening step mentioned above. Control unit 32, preferably data processor 322, simultaneously sends the opening signal to all switches 33.

In the embodiment shown in figures 3 and 4, the isolation takes place after the electrical circuit opening step, after a predetermined amount of time. Indeed, control unit 32, preferably data processor 322, initially sends the opening signal to switch 33 and subsequently, after a predetermined amount of time, it sends the opening signal to isolator switches 43. Said predetermined amount of time substantially is the average time needed by switch 33 to reduce the current flowing inside string "S", so as to cause it to reach a predetermined threshold close to zero. Thus, said amount of time corresponds on an average to the reaction time of switch 33. Therefore, the time between the opening signal of switch 33 and the opening signal of isolator switches 43 can be adjusted as a function of the technical features both of switch 33, in particular the switching time, and of isolator switches 43, for example dimensions of the contacts. Preferably, said step for isolating string "S" is performed after the complete removal of the current from string "S" following the electrical circuit opening step.

Subsequently, the step for galvanically isolating string section "S¹" with a predetermined safety low voltage at its ends is performed. During this step, after the isolating step, a galvanic isolation is guaranteed at the ends of said string sections "S^{, M}. Said string sections ⁱⁱ g ^{i ii} present, at their ends, a low voltage that complies with electrical safety regulations. Preferably, said string section "S^{, M} comprises one single panel "P", since the isolation of string "S" takes place at the level of each single panel "P", which, while in use, presents, at its ends, a voltage that fully complies with the regulations on electrical safety.

In the preferred embodiment, the central unit is arranged close to safety button 1, for example close to the distribution boards of system "I", while each peripheral unit 4 is arranged close to one or more strings "S" connected thereto.

The different peripheral units 4 are preferably connected in series to one another. Peripheral unit 4 comprises a protective casing, adapted to protect the electronic devices comprised therein against bad weather, since said peripheral unit 4 is normally arranged close to the string in non- insulated places.

Both central unit 3 and each peripheral unit 4 are fully compliant with the regulations on electromagnetic compatibility.

In the embodiment shown in figures 3 and 4, each peripheral unit 4 is connected to one single string "S", which is made up of a plurality of panels "P" and comprises a switch 33 and a plurality of isolator switches 43, preferably two isolator switches 43 for each panel "P" comprised in string "S".

The system according to the present invention can be connected to a processor or to a personal computer, so as to remotely control the system through a connection implementing, for example, the Ethernet protocol. In particular, central unit 3 can be connected to a computer network and the system according to the present invention can be remotely activated.

Central unit 3 is connected to the inverter 10 by means of a second data line 51, so as to obtain supplementary items of information on system "I" and on the energy distribution network, so as to be able to promptly intervene and guarantee the safety of system "I" or at least of a portion thereof in case of danger or fault of the system itself.

Claims

CLAIMS :

1. System for placing into safe condition one or more solar systems (I) for the generation of electrical power, each system comprising a plurality of solar panels (P) , which, in use, are electrically connected in series, so as to form one or more strings (S) ;

characterized in that it comprises:

• at least one central unit (3) , which is electrically connected to one or more of said strings (S) of panels (P) and to a power supply source (2) for supplying said safety system with power, and comprises at least one control unit (32) ;

• at least one peripheral unit (4) , which is electrically connected to at least one string (S) and to said central unit (3), comprising a plurality of switches (43, 33), which are electrically controlled and properly connected to one or more panels (P) comprised in said string (S) ;

said at least one central unit (3) is adapted, when the voltage of the power supply source (2) is interrupted, by means of said control unit (32) , to isolate at least one of the strings (S) connected thereto by interrupting the current in said string (S) and by disconnecting said string (S) opening said plurality of switches (43, 33), so that said string is galvanically isolated and presents, at its ends, at most a predetermined safety low voltage.

2. System according to claim 1, wherein said plurality of switches (43, 33) comprises:

^■ at least one switch (33), for interrupting a direct current , ^■ one or more isolator switches (43) , for isolating said string (S) creating a plurality of sections (S') thereof, which are galvanically isolated.

3. System according to claim 1, wherein said central unit (30) comprises at least one energy storage device (34) , for temporarily supplying power to said safety system in case the power supply (2) is interrupted.

4. System according to claim 1, wherein said control unit (32) comprises at least one monitoring device (321) , for detecting the interruption of the power supply (2), and a data processor (322) , for processing the data coming from said monitoring device (321) and for transmitting the proper signals to the peripheral unit (4) .

5. System according to claim 1, wherein the system comprises a plurality of switches (33) , each of which is adapted to isolate one single string (S) .

6. System according to claim 1 or 5, wherein each peripheral unit (4) is connected to one single string (S) and comprises a plurality of isolator switches (43), for isolating the string (S) by isolating each single panel (P) comprised in the string (S) .

7. System according to claim 1, wherein the interruption of the power supply (2) takes place after an emergency button (1) has been pushed.

8. System according to claim 3, wherein the energy storage device (34) is supplied with power by means of one or more panels (P) .

9. System according to claim 7, wherein said emergency button (1) is a DC switch.