"MONITORING SYSTEM FOR A PHOTOVOLTAIC SOLAR PLANT" Technical field

The present invention relates to a monitoring system for a photovoltaic solar plant.

In particular, the present invention relates to a monitoring system for a photovoltaic solar plant which is intended to impede the frequent attempts to steal the panels of the plant.

The system of the invention is mainly applied to impede the theft of photovoltaic solar panels, above all during the nighttime and mainly in plants of large size positioned on the ground, but also to detect failures and malfunctions.

Background art

Up to today, it has been possible to protect the panels in photovoltaic plants against theft with various techniques, for example by using conventional protection and alarm systems such as IR perimeter barriers and fencing, seismic sensors, video surveillance, anti-tamper fasteners, etc., or else by using dedicated anti-theft systems, for example fibre optic systems.

These systems are costly and complex, since they represent veritable autonomous dedicated protection systems and require additional equipment and wiring which increase installation and maintenance costs; in addition, some passive components (e.g. anti-tamper fasteners) can preclude or complicate maintenance work on the plant.

Other rarer systems are made with dedicated components which can be disabled if the system is not correctly installed.

These systems, too, are costly and complex and in addition greatly limit the flexibility of installation and procurement of components for the whole plant, as they are tied to a specific model of panels or inverters.

Other systems of a different conception are integrated into the photovoltaic solar plant and exploit the conductors already present in the plant itself. The main disadvantage of these systems is the strong limitation in the type of tampering that can be detected, which makes the use thereof unreliable.

The object of the present invention is to provide a monitoring system for a photovoltaic solar plant which can reliably detect all types of tampering and/or malfunctioning.

A particular object of the invention is to provide a monitoring system for a photovoltaic solar plant which can efficiently detect thefts of panels of the plant itself.

A further object of the invention is to provide a monitoring system for a photovoltaic solar plant which guarantees continuous and constant monitoring of the panels of the plant.

Summary of the invention

These and other objects are achieved by a monitoring system for a photovoltaic solar plant as described in claims 1 to 8.

These and other objects are likewise achieved by a photovoltaic solar system comprising a photovoltaic solar plant and a system for the monitoring thereof, as described in claims 9 to 1 1.

The invention as described achieves the following technical effects:

· it enables reliable detection of the presence or absence of solar panels based on predefined conditions;

it enables constant daytime and nighttime monitoring of a plant for the production of electricity from a photovoltaic solar source;

it can be installed for all types of plants, irrespective of which brand of panels or inverters the system is connected to.

it provides indications as to the status of the electrical network the plant is connected to;

it provides indications of any deficits in the plant's production which are not ascribable to the absence of components but rather to their malfunctioning.

The aforementioned technical effects and other technical effects of the invention will appear in greater detail from the following description of an example embodiment given by way of illustration and not by way of limitation with reference to the appended drawings.

Brief description of drawings

Figure 1 shows a block diagram of a monitoring system for a photovoltaic solar plant and the corresponding monitored photovoltaic solar plant, according to the invention.

Figure 2 shows a detailed block diagram solely of the monitoring system, according to the invention.

Figure 3 shows a circuit diagram of a string of photovoltaic panels of the plant in figure 1.

Figure 4 shows a circuit detail of a component of the monitoring system.

Detailed description

The invention describes a monitoring system for a photovoltaic solar plant having at least one string of photovoltaic panels.

With reference to figure 1 , two strings 1 , 2 comprising respective panels 10, 11 and 20, 21 are shown.

In general, every string 1 , 2 can comprise at least one photovoltaic panel in which a by-pass diode D _b is associated with each panel.

In the example embodiment shown, two strings 1 ,2 of photovoltaic panels will be considered.

Hereinafter, for the sake of simplicity, the strings of photovoltaic panels will be more briefly defined "strings" and the terms "panels" and "modules" will be used as synonyms.

According to the invention, a by-pass diode D _bp is associated with each panel 10, 11 , 20, 21 and disposed in parallel to the panel itself; as is well known, the by-pass diode allows charges to pass between successive panels when the panel associated with the by-pass diode is not working. The photovoltaic solar plant further comprises inverters 12, 22 connected downstream of the respective strings 1 ,2.

With reference to figures 1 and 2, the monitoring system of the invention comprises at least one primary control device 15, 25 configured to monitor the strings 1 ,2 of photovoltaic panels 10, 11 , 20, 21.

The primary control device 5, 25 is interposed between the inverter 12,

22 and the strings 1 , 2.

Again with reference to figures 1 and 2, the monitoring system of the invention comprises a master control device 50, connected for data passage with the at least one primary control device 15, 25.

The master control device 50 is configured to receive from the at least one primary control device 5, 25 data representative of a state Si of the string 1 ,2 of the photovoltaic panels 10, 11 , 20, 21.

Thanks to the presence of by-pass diodes in parallel to the photovoltaic panels, and via a signal measurement downstream of the photovoltaic strings, it is possible to determine states of tampering of the string.

In particular, if the amplitude of the signal sent to the string is known, the following states can be determined:

S1 : circuit open, since no signal will be measured downstream of the string;

S2: complete short circuit, since the downstream signal will be measured as identical to the one sent;

S3: partial short circuit, i.e. absence of several panels, since the amplitude of the signal will not correspond to the drop over the entire string.

In order to determine the state Si of the string, the primary control device

15, 25 comprises a current pulse generator, hereinafter described as a pulse generating module 40, and a certain number of sensing circuits, one for each string under surveillance, comprised in a sensing module 33

(described below) for detecting the signal downstream of the string.

More precisely, the primary control device 15, 25 comprises a processing unit 30.

In general it should be noted that in the present context and in the claims below, the processing unit 30, and all processing units in general, are presented as divided into distinct functional modules (memory modules or operating modules) solely for the purpose of describing the functions of the units themselves in a clear and complete manner.

In reality these units can consist in a single electronic device, duly programmed to perform the functions described, and the various modules can correspond to hardware and/or routine software elements belonging to the programmed device.

Alternatively, or in addition, these functions can be performed by a plurality of electronic devices over which the aforesaid functional modules can be distributed.

The processing units can moreover rely on one or more processors in order to carry out the instructions contained in the memory modules.

The aforesaid functional modules can moreover be distributed over different local or remote computers based on the architecture of the network they reside in.

Advantageously, according to the invention, the primary control device 15, 25 checks the presence of the strings connected to the inverter at regular intervals (or alternatively receives it at regular intervals) and it determines and updates the state Si of the strings via the modules comprised in the processing unit 30, in particular the pulse generating module 40 and the sensing module 33.

The pulse generating module 40 is configured to generate a pulse train li to be sent to the strings 1 ,2 of photovoltaic panels to verify the presence and connection continuity thereof.

Advantageously, according to the invention, in order to generate the pulse train li, the pulse generating module 40 comprises a DC-DC converter, suitably controlled, and a high-frequency transformer.

The DC-DC converter used is in a half-bridge configuration, (fig. 4)

Among the possible DC-DC converters that can be used, the half-bridge architecture is suited to the purpose; it is simple to construct and has a modest cost.

As noted previously, the operation of the monitoring system envisages the presence of by-pass diodes present on the photovoltaic panels: by sending the pulse train li to the negative pole of the strings via the pulse generating module 40, it is possible to monitor, via the photocouplers comprised in the sensing modules 33, whether the pulses cross the string, so as to verify the presence and continuity of the connection.

By controlling the half bridge with a PWM modulation it is possible to obtain a pulse train of suitable amplitude with a duty cycle of 50%.

This type of system makes it possible to detect three types of tampering, corresponding to the above-mentioned system states Si:

· S1 : opening of the electrical circuit: if one or more strings are disconnected, the pulse train will not be detected by the respective sensing circuit.

• S2: total replacement with a short circuit; in the event of a bypass of the entire string with a short circuit, the load will be unbalanced and the shorted string will have an anomalous current draw while the current draw on the other strings will practically fall to zero. As a result, the pulse train will be detected only on the strings tampered with.

S3: partial removal with a short circuit; this case is analogous to the previous one, the difference being that only a portion of the string is bypassed, rather than the whole string. In this case as well, the load is unbalanced toward the string with fewer panels connected and the current draw on the string tampered with is predominant.

The system also makes it possible to detect a state

S4: normal operation within the preset thresholds As previously noted, according to the invention the processing unit 30 comprises a sensing module 33 (fig 2) configured to detect parameters Ps representative of the presence of the strings 1 , 2 of photovoltaic panels. According to the invention, the sensing module 33 is configured to detect parameters Ps representative of the presence of the strings 1 ,2 of photovoltaic panels 10, 11 , 20, 21 as a function of the pulses li sent by the pulse generating module 40.

These representative parameters can be electrical parameters such as, for example, voltage, current, frequency and impedance detected by the sensing module under the particular conditions.

According to the invention, the sensing module 33 is a linear-response module.

The sensing module 33 comprises one or more:

^■ linear opto-couplers;

■ resistive shunts;

^■ Hall effect probes;

^■ or the like

Preferably, the sensing module is made up of several branches, each of which is connected to the positive terminal of a photovoltaic string.

The pulse train sent to the negative terminal of the strings, connected in parallel, crosses them by exploiting the by-pass diodes present on every panel and closes back on the sensing branch.

The signal that is picked up via a linear opto-coupler contains the information Ps representative of the presence of the photovoltaic string, since the amplitude of the pulses is determined by the voltage drop on the diodes encountered.

The main part of the circuit is formed by the linear sensing circuit and the sensing resistor, which determines the current circulating over the branch.

This point is very important, since the sensing circuit saturates with currents exceeding a predefined current threshold.

On the sensing branch there are also safety devices (e.g. zener diodes) set in parallel to the sensing circuit in such a way as to prevent high incoming voltages from damaging the sensing circuit.

A high voltage capacitor is also present to prevent the continuous component from ending up on the secondary windings of the transformer with the risk of damaging it. Advantageously, according to the invention, the processing unit 30 comprises a configuration module 31 (figs. 1 and 2) configured to detect the number of strings 1 , 2 of photovoltaic panels connected to the respective inverters 12, 22.

In this manner, the configuration module 31 determines a first reference threshold I for identification of the state Si of the strings.

This detection is characteristic of daytime monitoring when the system is off, since there is no need to signal the presence of the panels and it is sufficient to verify the production of energy and the information sent by the inverter.

However, the monitoring device is always connected to the photovoltaic strings, even during the day; hence the device must also be capable of tolerating high incoming voltages without being damaged.

For this reason, zener diodes are placed in such a way as to limit the voltage input to the linear opto-couplers. As a result, the linear opto- coupler will always detect the maximum value and this information can be used to verify whether or not the string is present also during the day.

Summing up, therefore, in the daytime mode, the system detects:

- correct functioning;

- opening of the circuit of a string of photovoltaic panels;

- short circuit of a string of panels via a bridge at the start of the string in the attempt to cut out the panels;

The configuration module 31 is moreover configured to determine a threshold value of the presence of the strings 1 , 2 of photovoltaic panels. In particular, the configuration module 31 is configured to determine a reading value of the sensing module corresponding to a presence threshold for the strings 1 ,2 of photovoltaic panels.

In other words, there is also detected a threshold determined by

- a partial short circuit of a string via a bridge halfway along the string in the attempt to cut out only some panels of the string.

The configuration module 31 thus determines a second reference threshold II for identification of the state Si of the string.

This detection is characteristic of nighttime monitoring.

The technical effect of the daytime and nighttime operating configurations is continuous and constant monitoring of the state Si of the strings 1 , 2 of photovoltaic panels 10, 11 , 20, 21.

Consequently, the detection will give very reliable results.

According to the invention, the processing unit 30 further comprises a comparison module 32 configured to compare the representative parameters Ps with the reference thresholds l;ll so as to identify a possible state Si of the string, which corresponds to one of the states described above.

According to the invention, the primary control device 15, 25 comprises a communication module 34 configured to communicate the state Si detected by the comparison module 32 to the master control device 50. For this purpose, the master control device 50 comprises a first auxiliary communication module 51 configured for communication with at least one primary control device 15, 25.

The master control device 50 further comprises a second auxiliary communication module 52 configured for communication with a network module 61 configured for a transmission of data, e.g. the state Si, to a remote user base.

More specifically, a wireless module or a RS485 module is preferably used as the first auxiliary communication module 51 , while a TCP/IP module is preferably used as the second auxiliary communication module 52.

Inside the master control device 50 a control unit can be provided to assure an interface between the communication devices in the event that some problems related to the compatibility of communication arise.

The invention likewise describes a photovoltaic solar system comprising a photovoltaic solar plant monitored by a monitoring system.

The photovoltaic solar plant comprises at least one string 1 , 2 of photovoltaic panels 10, 11 , 20, 21 , in which each panel comprises a by- pass diode D _bp , the plant further comprising an inverter 12, 22 connected downstream of the string 1 , 2. Advantageously, according to the invention, the photovoltaic solar system comprises a monitoring system for the photovoltaic solar plant, with the above-described features.

According to the invention, the photovoltaic solar plant further comprises a monitoring point 60 (fig. 1 ).

The monitoring system comprises a network module 61 , associated with the monitoring point 60, and configured for a transmission of the state Si of the strings to a remote user base.