ITTV20130015A1 - METHOD AND AUTOMATIC SYSTEM OF CURRENT INTERRUPTION CONFIGURED TO ISOLATE ELECTRICALLY, IN A SELECTIVE WAY, OF PHOTOVOLTAIC PANELS IN A STRING OF PHOTOVOLTAIC PANELS - Google Patents

Description

DESCRIPTION

â € œMETHOD AND AUTOMATIC CURRENT BREAKAGE SYSTEM CONFIGURED TO ELECTRICALLY SELECTIVE ISOLATION OF PHOTOVOLTAIC PANELS IN A STRING OF PHOTOVOLTAIC PANELSâ €

The present invention relates to a method and an automatic current interruption system configured to electrically and selectively isolate photovoltaic panels in a string of photovoltaic panels of a photovoltaic system.

In particular, the present invention relates to an automatic current interruption system configured in such a way as to selectively carry out an electrical disconnection of two or more photovoltaic panels of a string from the remaining panels of the string itself, when a critical condition of associated danger occurs. , for example, to a fire / start of fire; to which the following discussion will explicitly refer without losing generality.

It is known that photovoltaic systems generally comprise a photovoltaic generator equipped with a plurality of strings of panels connected in series with each other, and an inverter which is connected to the photovoltaic generator, through a current switch device, and is configured to convert the direct current generated by the photovoltaic generator in an alternating current suitable for powering loads or electrical networks.

In particular, the current switch device is typically structured to interrupt high direct currents while simultaneously preventing the formation of electric arcs during the opening of its electrical contacts.

Patent US 8 213 133 B2 describes a current switch device used in a photovoltaic system, which is configured in such a way as to automatically switch from a closed state to an open state to electrically isolate the photovoltaic generator from the inverter based on a fault signal indicating for example the detection of a fault / fire. In the event of a fire, in fact, the current switch device described in US 8 213 133 B2 switches automatically to electrically separate the inverter from the strings of photovoltaic panels which, however, remain connected together, thus continuing to generate in the strings, in the presence of sunlight, high currents / voltages.

In this case, the presence of high voltage / currents is particularly dangerous as, on the one hand, it can cause the electrocution of people who accidentally or necessarily come into contact with the strings during fire extinguishing operations and from other (simultaneously with other conditions e.g. shading of a string in parallel, damage to the bypass diodes) can determine, if not checked promptly, critical electrical and thermal conditions capable of irreversibly damaging the panels and the remaining components, and / or the electrical wiring of the string, in addition to starting a possible fire.

The Applicant has therefore conducted an in-depth study with the aim of identifying a solution that allows to specifically achieve the goal of creating a simple and economical system that is able to selectively and automatically isolate the panels present in the string electrically, when a critical condition of danger occurs, caused for example by a malfunction of the panel due to overheating and / or overcurrent and / or in the event of fire, so as to reduce the risk of electrocution and / or damage to the panels themselves.

The object of the present invention is therefore that of providing a solution that allows to achieve the above indicated objective.

This object is achieved by the present invention as it relates to an automatic current interruption method and system in at least one string of panels of a photovoltaic system, as defined in the attached claims.

The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of embodiment, in which:

Figure 1 schematically shows a photovoltaic system provided with an automatic current interruption system realized according to the dictates of the present invention;

Figure 2 schematically shows an automatic current switch device present in the automatic current interruption system shown in Figure 1; while

Figures 3 and 4 schematically show an electronic circuit included in the current drain device used in the disconnection device shown in Figure 2, two different operating conditions.

The present invention will now be described in detail with reference to the attached Figures to allow a skilled person to make and use it. Various modifications to the embodiments described will be immediately evident to those skilled in the art and the generic principles described can be applied to other embodiments and applications without thereby departing from the protective scope of the present invention, as defined in the attached claims. Therefore, the present invention should not be considered limited to the embodiments described and illustrated, but should be accorded the widest protective scope in accordance with the principles and characteristics described and claimed herein.

With reference to figure 1, the number 1 indicates as a whole a photovoltaic system comprising a photovoltaic generator 2 and an electronic converter device 3. The photovoltaic generator 2 is able to convert solar energy into electrical energy thus to generate a direct voltage and a direct current I, while the electronic converter device 3 is connected to the photovoltaic generator 2 to receive the direct current I in input and converts the direct current I received into an alternating current suitable to power a load electrical (not shown) and / or an electrical network 100.

According to a preferred embodiment shown in Figure 1, the photovoltaic generator 2 comprises a series of strings of photovoltaic panels 4 (only two of which are shown in Figure 1 by way of example only) preferably, but not necessarily, connected in parallel with each other through some power lines, and in which each string 4 comprises a plurality of photovoltaic panels 5 connected in series with each other, through connection terminals 6.

The converter electronic device 3 and the photovoltaic panels 5 are of a known type and therefore will not be further described, except to specify that the converter electronic device 3 can comprise one or more inverters suitably connected to the panels 5, while each panel photovoltaic 5 is structured to convert the light rays received into a direct electric current which outputs to the string 4 through the two connection terminals 6.

The photovoltaic system 1 is also equipped with an automatic current interruption system 7, which is configured in such a way as to determine a damage-danger condition of the system (described in detail below) and, when the latter is determined, it selectively disconnects a series of photovoltaic panels 5 from string 4 so as to interrupt the current in several points of the string 4 itself.

According to the preferred embodiment shown in Figures 1 and 2, the system 7 comprises a plurality of automatic current switch devices 8, which are arranged along the strings 4 and are configured in such a way as to electrically disconnect / isolate the panels 5 from the string. 4 in one or more pre-established electrical points / sections of the same.

From what has been described above, it is appropriate to specify that the number and / or position of the automatic current switch devices 8 along string 4 is determined / established on the basis of the number of panels 5 present in string 4 and / or the voltage and direct current generated by the panels 5 themselves. For example, it may be advantageous to install an automatic current switch device 8 immediately downstream of a portion of string 4 comprising a number of panels capable of generating an overall electrical voltage lower than or equal to a voltage considered dangerous for the purposes of electrocution, for example a voltage of about 120 V.

With reference to the example shown in figure 1, each automatic current switch device 8 is connected to one of the two connection terminals 6 of a photovoltaic panel 5 positioned at the point of the string 4 to be sectioned, preferably the connection terminal 6 of the panel 5 intended to be crossed by the current generated at the output of the panel 5 itself.

According to a preferred embodiment shown in Figure 2, the automatic current switch device 8 comprises a first and second terminal 9 connected to the terminal 6 of a panel 5 to be insulated and respectively to the terminal 6 of a panel 5 arranged in series with the panel 5 to be insulated. isolate in a position adjacent / consecutive to it, for example downstream.

According to a possible embodiment, instead of being connected to terminal 6, the automatic current switch device 8 could be arranged along the connection terminal 6 and in this case, the first and second terminal 9 are connected to two respective portions / sections of the same connection terminal 6.

With reference to Figure 2, the automatic current switch device 8 can also comprise: a connection line 10 connected between the two connectors 9 to be crossed by the current I, and a switch module 11 which is arranged along the connection line 10 and is adapted to switch between a closed state in which the connection line 10 closes so as to allow the passage of current I through the terminal 6 of the panel 5, and an open state in which the connection line 10 opens and it interrupts the current I circulating in the terminal 6 of the panel 5 itself, electrically isolating the latter from the panel 5 immediately adjacent along the string 4.

The current switch device 8 also comprises an electronic control unit 12 which is configured in such a way as to receive at its input an electrical signal indicative of a control quantity and / or a disconnection command, and determines a condition of Risk of damage to the string on the basis of the control variable and / or the disconnection command received.

The electronic control unit 12 is also configured in such a way as to transit, when it determines the dangerous condition, from a normal operating state, in which it keeps the switch module 11 in the closed state so as to electrically connect the panel 5 to string 4, to an operational state of current interruption, in which it switches the switch module 11 from the closed state to the open state to electrically isolate the panel 5 from the string 4, and at the same time, it generates a disconnection command and communicates this last, through a communication system 13, to a series of pre-established automatic current switching devices 8 arranged along the string 4 to ensure that the switching modules 11 of the pre-established automatic current switching devices 8 automatically pass from the closed state to the closed state opening.

According to a preferred embodiment shown in Figures 1 and 2, the control quantity received by the electronic control unit 12 corresponds to the temperature. For this purpose, the automatic current switch system 8 can advantageously comprise at least one temperature sensor device 14, which is configured in such a way as to detect / measure the temperature preferably in correspondence with the panel 5 to be insulated in order to output the signal indicative of the temperature. measured / determined, while the electronic control unit 12 can be configured so as to pass into the operating state of current interruption when the measured temperature exceeds a predetermined temperature threshold.

With reference to Figure 2, the temperature sensor device 14 can be advantageously included in the automatic current switch device 8 or, alternatively, it can be arranged at the panel 5 or at any point of the photovoltaic system 1 (or in adjacent areas where a possible fire can spread to the system itself) and can include at least one thermal probe, or any similar known temperature detector / measuring device.

According to a preferred embodiment shown in Figures 1 and 2, the control quantity received by the electronic control unit 12 can correspond to the current flowing through the terminal 6 of the panel 5. For this purpose, the automatic current interruption system 7 can comprise advantageously, a current measuring device 15 suitable for measuring the current I which passes through the terminal 6 of the panel 5, while the electronic control unit 12 can be configured in such a way as to pass into the operating state of current interruption on the basis of the determined current / measured, for example, when the determined current exceeds a predetermined current threshold.

The automatic current interruption system 7 could advantageously comprise a voltage measuring device (not shown) suitable for measuring the voltage between the terminals 9 of the device 8, while the electronic control unit 12 can be configured in such a way as to pass through the current interruption operating state based on the determined / measured voltage, for example, when the determined voltage exceeds a predetermined voltage threshold.

According to a preferred embodiment shown in Figures 1 and 2, the control quantity received at the input by the electronic control unit 12 can correspond to, or be indicative of: a presence / detection of smoke, and / or a presence / detection of a flame, and / or a heat detection presence in correspondence with one or more photovoltaic panels 5 (or in rooms adjacent to them). For this purpose, the automatic current interruption system 7 can comprise one or more smoke detector devices 21 arranged in correspondence with a panel 5 and configured so as to detect the presence / absence of smoke, and / or the flame detection devices 22 arranged at a panel 5 and configured so as to detect the presence / absence of a flame, and / or infrared sensor devices 23 arranged at a photovoltaic panel 5 to detect the presence of heat. Obviously the devices 14, 21, 22 and 23 are connected to the electronic control unit to supply it with the determined quantities at the input.

The electronic control unit 12 can be configured to transition into the power failure operating state based on smoke detection, and / or flame detection, and / or heat detection.

From what has been described above, it is appropriate to specify that the automatic switching of the automatic current switch devices 8 present in the string 4 on the basis of the temperature and / or current and / or smoke and / or heat and / or the presence of flames allows to rapidly and selectively isolate the panels 5 of the string 4 in the event of a fire and / or short circuit, thus determining advantages in terms of reducing the risk of electrocution and / or reducing the risk of ignition / propagation of a fire.

With reference to a preferred embodiment shown in Figure 2, the switch module 11 comprises a first mechanical switch 16, and at least one second mechanical switch 17, which are connected in series to each other along the connection line 10 and are each suitable for selectively switching on the basis of a respective command signal S1 and S2, between an open state and a closed state.

According to a preferred embodiment shown in Figure 2, the switch module 11 further comprises a current drain device 18, which is connected in parallel to the first mechanical switch 16 and can be operated on the basis of a command signal S3 for drain the current I which passes through the first mechanical switch 16 during the transition of the latter.

Preferably, the electrically controllable mechanical switches 16 and 17 can correspond, for example, to switch relays each provided with a moving contact and a coil capable of generating a magnetic field, when it receives the command signal S1 or S2, which moves the contact into opening / closing of the circuit-breaker, or to contactors, or to any other type of circuit-breaker equipped with a similar mechanical operation that can be electrically controlled.

On the other hand, as regards the current drain device 18, it can comprise at least one semiconductor switch device, indicated hereinafter with the same number 18, which can be selectively controlled in the open state or alternatively in the closed state by means of the signal command S3.

The transition of the automatic current switch device 8 from the connected state, in which it connects the panel 5 to the string 4, to the disconnected state in which it galvanically isolates the panel 5 from the string 4, is obtained on the basis of a series of control operations of the mechanical switches 16 and 17 and of the semiconductor switch device 18 performed by the electronic control unit 12. For this purpose the electronic control unit 12 is configured in such a way as to: generate the command signal S3 so to cause the semiconductor switch device 18 to switch from the open state to the closed state and subsequently generate the command signal S1 to cause the first mechanical switch 16 to switch from the closed state to the open state. It should be noted that in this phase, as soon as the first mechanical switch 16 begins to open, the current tends to deviate and flow progressively through the semiconductor switch device 18 thanks to the reduced impedance presented by the latter, thus determining the progressive zeroing of the current flowing through the first mechanical switch 16.

Following the state transition of the first mechanical switch 16, the electronic control unit 12 generates the command signal S3 so as to cause the semiconductor switch device 18 to switch from the closed state to the open state, and following the state transition of the semiconductor switch device 18, it generates the command signal S2 so as to cause the second mechanical switch 17 to switch from the closed state to the open state.

From what has been described above, it should be noted that the passage of the automatic current switch device 8 from the disconnected state to the connected state is performed by implementing the operations described above in an inverse sequential order with respect to that described above, i.e. it is operated in closing the second mechanical switch 17, the semiconductor switch device 18 is actuated to close, the first mechanical switch 16 is actuated to close, and the semiconductor switch device 18 is actuated to open.

From what has been described above, it is appropriate to specify that the use of the semiconductor switch device 18 in parallel to the first mechanical switch 16 allows, during the disconnection of the panel 5, to preventively absorb the energy of formation of the electric arc and open the first main switch 16 in safety without the risk of damaging the latter. Furthermore, the use of the second mechanical switch 17 along the connection line 10 and the opening of the same only after the opening of the semiconductor switch device 18 and the opening of the first mechanical switch 16 ensures a high degree of and adequate dielectric stiffness in air.

According to a possible embodiment not shown, the semiconductor switching device 18 can comprise at least one MOSFET metal-oxide-semiconductor field effect transistor, having the drain terminal connected to the connection line 10 between the first 16 and the second mechanical switch 17, a source terminal connected to the section of connection line 10 connecting the first mechanical switch 16 to terminal 9, and the control terminal (door / gate) connected to the electronic control unit 12 for receive the command signal S3.

In particular, the field-effect transistor is able to pass from an off state (open) to a conduction state (closed) on the basis of the command signal S3.

The Applicant has found that the use of the single field-effect transistor according to the configuration described above is, on the one hand, effective for draining an electric current circulating in a first direction (towards), hereinafter referred to as direct current, which it passes through the well terminal and the source terminal in order, and therefore allows the first switch 16 to be opened safely without the formation of an electric arc, on the other it does not allow an electric current circulating in a second direction (towards) opposite to the first, indicated below with reverse current. In this case, the reverse current can be generated, for example, when strings of panels connected in parallel to each other are subjected to high differences in irradiation / shading and / or the safety devices that protect the panels from reverse currents, for example by diodes. -pass, are damaged.

In fact, the field effect transistor has a unipolar electrical behavior, in which the drain and the source can be crossed by the current only in a single direction and not in the opposite direction. Therefore, in case of generation of an inverse current, the actuation of the single field effect transistor does not determine a drainage of the same. Consequently, the reverse current continues to flow through the first mechanical switch 16 with the risk of arcing during the opening of the first mechanical switch 16 itself.

In order to overcome this drawback, the Applicant has devised a possible variant embodiment shown in Figures 3 and 4, in which the semiconductor switch device 18 comprises a first semiconductor switch 18a adapted to specifically drain the direct current IDir, and a second switch semiconductor 18b which is connected in series to the first semiconductor switch 18a and is adapted to drain the reverse current Iinv circulating in the connection terminal 6. In other words, the semiconductor switch device 18 comprises a first 18a and a second switch semiconductor 18b connected in anti-series to each other. In particular, the first semiconductor switch 18a comprises a first MOS field effect transistor having the drain terminal D (Drain) connected to the connection line 10 between the first 16 and the second mechanical switch 17, and the control terminal ( gate / gate) connected to the electronic control unit 12 to receive the command signal S3, while the second semiconductor switch 18b comprises a second MOS field effect transistor having the drain terminal D (Drain) connected to the connection line 10 connecting the first mechanical switch 16 to terminal 9, the source terminal S (Source) connected to the source terminal S of the first MOS transistor and the command terminal (gate / gate) connected to the electronic control unit 12 to receive the command signal S3.

The semiconductor switching device 18 further comprises a recirculation diode 18c having the anode and cathode connected to the source and drain terminals respectively of the first semiconductor switch 18a, and a recirculation diode 18d having the anode and the cathode connected to the source and drain terminal respectively of the second semiconductor switch 18b.

With reference to Figure 3, in use the direct current IDir is drained, during the opening of the switch 16, by the first semiconductor switch 18a and by the diode 18d connected in parallel to the second semiconductor switch 18b, while the reverse current Iinv (Figure 4) It is drained, during the opening of the switch 16, by the second semiconductor switch 18b and by the diode 18c connected in parallel to the first semiconductor switch 18a.

The electronic control unit 12 can be configured to actuate simultaneously the first 18a and the second semiconductor switch 18b in the closed state through the command signal S3 or to switch them off simultaneously to switch them into the open state.

According to a variant, the electronic control unit 12 can be configured to operate through the command signal S3 the first 18a or the second semiconductor switch 18b in the closed state on the basis of the presence of the direct current Idir or the reverse current Iinv . For this purpose the system 7 can comprise means for detecting the direction of the current passing through the terminals 6.

According to a preferred embodiment shown in Figure 2, each automatic current switching device 8 can further comprise a current measuring device 25 arranged in series with the current drain device 18 for measuring the current flowing through the latter. The electronic control unit 12 can be conveniently configured to determine the current I flowing through the current measuring device 25, in order to detect a possible fault status of the current drain device 18 if the measured current I is different from zero while device 18 is disabled. The electronic control unit 12 can be conveniently configured to detect an excessive voltage between the terminals 9 of the device 8 on the basis of the voltage measured between them, in order to establish a state of failure due to the deterioration of switches 16 and 17 when device 8 is in the connected state. The electronic control unit 12 therefore determines the condition of danger / damage on the basis of the current / voltage measured so as to detect the fault state, and in this case it transits the pre-set devices 8 of the system 7 in the state of disconnection.

According to a preferred embodiment shown in Figure 1, the communication system 13 comprises a bus also indicated by 13 in Figures 1 and 2, which connects the electronic control units 12 of the automatic current switching devices 8 to each other. It should be pointed out that the bus 13 could connect the electronic control units 12 of all or some of the automatic current switch devices 8 installed in the strings 4 to each other.

The electronic control unit 12 of each automatic current switch device 8 is also configured so as to communicate the electrical signal indicative of the disconnection signal to the electronic control units 12 of the automatic current switch devices 8 present in the same string 4 and / or in other pre-established strings 4, through the bus 13, in such a way as to cause the automatic transition of the electronic control unit 12 into the operating state of current interruption.

According to a different embodiment, the communication system 13 can comprise, as an alternative to the bus 13, wireless communication systems (not shown) suitable for allowing the automatic current-switching devices 8 to communicate the disconnection commands with each other.

According to the embodiment shown in Figure 1, the automatic current interruption system 7 can also comprise a bus management device 19 which is connected to bus 13 and is configured in such a way as to transmit signals containing the disconnection command to a or more automatic current switch devices 8, through the bus 13 itself.

According to a possible embodiment, the bus manager apparatus 19 comprises a bus-gateway capable of generating / communicating the disconnection command on the basis of a fire alarm generated by a fire prevention system 26, and / or on the basis of a command generated by a user control device 27 (for example a button or a graphical user control interface), and / or on the basis of the detection of a pre-established emergency condition carried out through a local or remote emergency system 28.

The automatic current switching devices 8 of each string 4 can be powered by common low voltage power lines 31 or, alternatively, by respective electric batteries (not shown) or, alternatively, by the photovoltaic panel itself, and are each structured so that they can be installed in the panel 5 to be insulated, for example at the bottom of the same, or it can be housed inside the junction box (not shown) possibly present in the panel (or in the support structure of the panels themselves ).

According to a possible embodiment, the control quantity can comprise an electrical quantity (current / voltage / power) indicative of the power supply status of the source / line 31 which powers the automatic current switching devices 8, while the electronic control unit 12 of each device 8 can also be configured in such a way as to determine a condition of danger of damage to the system when the power supply status corresponds to an absence / interruption / wrong power supply to the automatic current switch device 8.

The method for electrically and reciprocally insulating the photovoltaic panels 5 of a string of photovoltaic panels 4 essentially comprises the following steps: providing a plurality of automatic current switching devices 8 along the string of panels 4, so that each automatic switch device current 8 is installed between two consecutive photovoltaic panels 5 of string 4; receive, through at least one automatic current switch device 8, an electrical signal indicative of a control quantity and / or a disconnection command, determine a system-danger condition on the basis of the received control quantity and / or disconnect command ; if a system-danger condition is determined, command the switch module 11 of the automatic current switch device 8 from the closed state to the open state, and simultaneously communicate through the communication system 13, a disconnection command to one or more devices pre-established automatic current switches 8, to cause the switch modules 11 of the pre-established automatic current switch devices 8 to automatically pass from the closed state to the open state.

The method and protection system described above have the advantage of automatically cutting / isolating the string of panels in several points when a critical condition of danger occurs, for example due to a malfunction of the panel due to overheating and / or overcurrent and / or in the event of fire, so as to reduce the risk of electrocution and / or damage to the panels themselves.

Furthermore, the realization of a current drainage device comprising the two MOS transistors connected in anti-series and the two diodes in parallel to the relative transistors, allows to ensure the drainage of the current regardless of its direction, thus eliminating the possibility of arcing. electrical switches during opening or closing of mechanical switches which are known to present the problem of contact bouncing when closing.

Finally, it is clear that modifications and variations may be made to the method and to the automatic current interruption system described and illustrated without thereby departing from the scope of the present invention defined by the attached claims.

Claims (11)

R I V E N D I C A Z I O N I 1. Automatic current interruption system (7) configured so as to selectively isolate a plurality of photovoltaic panels (5) from each other; said photovoltaic panels (5) being connected in series by means of connection terminals (6) so as to form at least one string of panels (4) of a photovoltaic system (1); said system (7) being characterized in that it comprises: - a plurality of automatic current switching devices (8) arranged along the string of panels (4) in predetermined positions, and - a communication system (13) configured in such a way as to allow the automatic current switching devices to reciprocally exchange signals; each automatic current switch device (8) being installed between two consecutive photovoltaic panels (5) of the string (4) and comprising: a switch module (11) configured in such a way as to selectively switch between a closed state and an open state, in which it allows and, respectively, interrupts the passage of current through the connection terminals (6) of the two photovoltaic panels (6 ) consecutive; And electronic control means (12), which are configured in such a way as to: receiving an electrical signal indicative of a control quantity and / or a disconnection command, determining a system-danger condition on the basis of said received control quantity and / or said disconnection command; if a system danger condition is determined, transition from a normal operating state to a current interruption operating state, in which the electronic control means (12) command the switching of said switch module (11) from the closed state to the open state and at the same time communicate, through said communication system (13), a disconnection command to one or more pre-established automatic current switching devices, to ensure that the switch modules (11) of the pre-established automatic switching devices closing in the open state. 2. System according to claim 1, wherein said electronic control means (12) of each automatic current switch device (8) are further configured in such a way as to compare said control quantity with a predetermined threshold and determine said danger condition -plant on the basis of the outcome of said comparison. System according to claim 2, wherein said control quantity is indicative of: a measured temperature, and / or the presence of smoke, and / or the presence of heat, and / or flame, and / or a measured current in said string (4) and / or a voltage measured in said string (4). 4. System according to claim 3, comprising sensor / detector means (14) (15) (21) (22) (23) (25), which are arranged in, at the said photovoltaic system (1) to measure / detect at least one predetermined physical quantity and are configured to generate said control quantity on the basis of the measurement / detection carried out. 5. System according to any one of the preceding claims, wherein each automatic current switch device (8) is configured in such a way that it can be connected to an electric power source (31) so as to receive a necessary electric power supply to its own functioning; said control quantity comprising an electrical quantity indicative of an interruption of the electric power supply to said automatic current switch device (8), and / or an incorrect power supply voltage. System according to any one of the preceding claims, wherein: said switch module (11) comprises at least a first mechanical switch (16) that can be electrically controlled to switch between a closed state and an open state in which it interrupts the current circulating in said connection terminal (6), and current drain means (18), which are connected in parallel to said first mechanical switch (16) and can be operated to drain the current flowing through said first mechanical switch (16); said electronic control means (12) being configured in such a way as to activate said current drain means (18) and, subsequently, to command the switching of said first switch means (16) in the open state in such a way as to interrupt the passage of current in said connection terminal (6). 7. System according to claim 6, wherein said switch module (11) comprises at least a second mechanical switch (17) which is connected in series to said first mechanical switch (16) and is electrically controllable to switch between a state closing and an open state, in which it interrupts the current circulating in said connection terminal (6); said current drain means (18) comprising at least one semiconductor switch device (18) (18a) (18b) configured to transit between an open state and a closed state, on the basis of an electrical control signal (S3). System according to claim 7, wherein said semiconductor switch device (18) comprises at least a first semiconductor switch (18a), which is specifically structured so as to be able to be traversed by a current flowing in said connection terminal ( 6) in a first direction, and a second semiconductor switch (18b) which is connected in antiseries to the first semiconductor switch (18a) and is specifically structured so as to be able to be crossed by a current flowing through said connection terminal (6) in a second direction opposite to the first direction, a first (18c) and a second diode (18d) connected to said first (18a) and second semiconductor switch (18b) respectively, in parallel. System according to claim 8, wherein said automatic current switching device (8) comprises current measuring means (25) arranged in series with said semiconductor switching device (18) for measuring the current flowing through the latter; said electronic control means (12) being furthermore configured so as to determine said plant danger condition when the measured current circulating through semiconductor switching device (18) placed in the open state, turns out to be non-zero. System according to claim 9, wherein said automatic current switch device (8) comprises voltage measuring means adapted to measure a potential difference between the terminals (9) of the device (8); said electronic control means (12) being furthermore configured so as to determine said plant danger condition when said voltage measured in a condition in which the device (8) is in the connected state, is higher than a predetermined threshold. 11. Method for selectively isolating a plurality of photovoltaic panels (5) from each other; said photovoltaic panels (5) being connected in series by means of connection terminals (6) so as to form at least one string of panels (4) of a photovoltaic system (1); said method being characterized by the fact that it includes the steps of: arranging a plurality of automatic current switch devices (8) along the string of panels (4), so that each automatic current switch device (8) is installed between two consecutive photovoltaic panels (5) of the string (4); each automatic current switch device (8) comprising a switch module (11) configured in such a way as to selectively switch between a closed state and an open state, in which it allows and, respectively, interrupts the passage of current through the connection (6) of the two consecutive photovoltaic panels (5); - receiving, through at least one automatic current switch device (8), an electrical signal indicative of a control quantity and / or a disconnection command; - determining a plant-danger condition on the basis of said control quantity and / or said disconnection command received; - if a system danger condition is determined, command the switch module (11) of said automatic current switch device (8) from the closed state to the open state, and simultaneously communicate through a communication system (13), a disconnection to one or more pre-established automatic current switch devices (8), to ensure that the switch modules (11) of the pre-established automatic current switch devices (8) automatically pass from the closed state to the open state.