SENSOR FOR DETECTING THE ABNORMAL CONDITIONS OF A CONTAINER ELEMENT AND IN THE VOLUME INCLUDED IN SAID CONTAINER ELEMENT, AND RELATED METHOD OF DETECTION

Field of the invention

The present invention relates to a sensor for detecting abnormal conditions of a container element and within the volume defined by the container element itself. The present invention is specifically conceived to detect abnormal conditions of and within container elements intended to contain electrical and electronic equipment, such as container elements of inverters.

Background art

In the field of power electronics, components are designed and manufactured to achieve high operating voltages and currents. These components are accommodated in appropriate containers for reasons of electromagnetic compatibility with other components of the system, and for electrical safety.

In the event of a malfunction, the high operating voltages and currents may cause phenomena that are harmful to the components themselves, and such as to trigger even more harmful and hazardous phenomena, such as fire or the like. In the case of network inverters, the electrical and electronic components that make them up (including: a DC/AC converter and annexed control electronics) are usually accommodated in a container, for example placed close to the solar panel by means of which said inverter is powered. In operation, such a container is closed and the opening thereof is only envisioned if maintenance is required. Said electrical and electronic components must be protected from the outside weather and for this purpose, the container closes them tightly.

In many cases, the phenomenon indicative of incipient malfunction (such as the smoke produced by some overheated components or flashes of light of photovoltaic arcs produced due to an excess in electrostatic current accumulated or loss of insulation between components or due to wiring subjected to too high potential differences) must be detected as early as possible to take appropriate countermeasures.

The control and detection systems within containers of the type described are distinguished according to the type of detection they carry out. The container may for example be provided with sensor means in contact with the closing portions of the container itself so that, in case of opening, such means report it accordingly. In addition, temperature sensor means may be provided inside the container so that a temperature excess, potentially indicative of malfunction situations, may be reported.

The known prior art solutions partly described above therefore involve the use of different sensor means within the subject container, each designed to perform its specific function. In addition, although there are several detection means for different abnormal conditions, the measurements taken are not always indicative of a specific incipient malfunction. For example, an increase in temperature inside the subject container does not always represent the onset of a potential malfunction. Finally, some very hazardous phenomena such as lightning generated by electric arcs are not even detected.

Also the structural and electrical constraints imposed by the configuration and the spaces available in such containers and by the electrical and electromagnetic features of the components contained should be taken into account. Such constraints impose stringent features to the detection means employed and employable. It is therefore not feasible to install devices or sensors already developed, or to simply modify them to get something suitable.

The general object of the present invention therefore is to implement a sensor for detecting abnormal conditions of a container element (such as the undesired opening thereof) and within the volume defined by the container element itself (such as smoke and flashes produced by arcing) which can overcome in a simple and cost-effective manner the drawbacks of the known prior art solutions.

Therefore, it is a first object of the present invention to implement a sensor and a method associated therewith for the detection of abnormal conditions of a container element and within the volume defined by the container element itself. It is a second object of the present invention to provide a sensor which can be easily installed in container elements, in particular container elements suitable to contain electrical and electronic components.

It is a third object of the present invention to provide a container element, in particular a container element suitable for containing electrical and electronic components, comprising a sensor for detecting abnormal conditions according to the present invention.

It is a fourth object of the present invention to provide an inverter apparatus for the conversion of direct electrical energy into alternating electrical energy comprising a container element in turn comprising a sensor for detecting abnormal conditions according to the present invention.

According to the present invention, the abnormal conditions of a container element and/or of the volume defined by the container element adapted to be accommodated within said volume, includes:

- emitter means configured to generate a first light beam, said first light beam being adapted to perform a propagation within the volume;

- receiver means configured to receive a second light beam comprising at least one of said first light beam upon said propagation and a possible further light beam present within said volume and caused, for example, by an electric arc, a flame or by the light entering into said volume from the outside upon the undesired opening of said container element;

- a processing unit associated with the emitter means and with the receiver means;

wherein the processing unit is configured to detect abnormal conditions of the container element and/or in the volume on the basis of the analysis of said second light beam.

Again according to the present invention, the method for detecting abnormal conditions of a container element 50 and of volume V defined by said container element 50 includes the steps of:

- providing emitter means adapted to generate a light beam;

- providing receiver means adapted to receive said light beam;

- configuring said emitter means for generating said light beam so that it performs a propagation in said volume (V);

- configuring said receiver means so that they receive a second light beam comprising at least one of said first light beam upon said propagation and a further light beam present within said volume;

- providing a processing unit associated with said emitter means and said receiver means, said processing unit being adapted to detect one or more abnormal conditions of said container element 50 and/or of said volume V on the basis of the analysis of said second light beam.

Further objects, features and advantages of the present invention will become more apparent from the following detailed description, given by way of non-limiting example and shown in the accompanying figures, in which:

Figure 1 shows a container element provided with a sensor according to the present invention;

figure 2 shows a schematic representation of an embodiment of a sensor according to the present invention;

figure 3 shows a diagram of some characteristic quantities of an embodiment of the sensor according to the present invention in the absence of detection of abnormal conditions;

figure 4 shows a diagram of some characteristic quantities of an embodiment of the sensor according to the present invention in the presence of detection of abnormal conditions;

figure 5 shows a flow chart of a mode of operation of an embodiment of the sensor according to the present invention.

Detailed description of the invention

The present description and the accompanying drawings are to be deemed as illustrative and not limiting of the present invention, which may be implemented according to other and different embodiments, still falling within the annexed claims, which also are an integral part of the text.

With reference to the accompanying figure 1 , it is possible to see a container element 50 which defines a containment volume V. Element 50 is intended to contain electrical and electronic components and related wiring. In particular, according to an embodiment of the present invention, element 50 is the outer container of a network inverter suitable for being connected to a photovoltaic panel, and the related electrical and electronic components are those of the inverter itself. Connectors 51 are shown, with which the inverter is connected to the photovoltaic panel and to the remaining modules of the photovoltaic system for which it is intended. According to an embodiment, sensor 10 of abnormal conditions of the containing element 50 and/or of volume V defined by said container element 50, is adapted to be accommodated within said volume V, and comprises:

- emitter means 11 configured to generate a first light beam 13 adapted to perform a propagation within volume V;

- receiver means 12 configured to receive a second light beam comprising at least one of said first light beam 13 upon said propagation and a further light beam present within said volume V;

- a processing unit 14 associated with the emitter means 11 and with the receiver means 12 configured to detect abnormal conditions of the container element and/or in volume V on the basis of the analysis of said second light beam.

For the purposes of the present invention, the term "abnormal conditions" means, for example, the presence of smoke released by the components contained in element 50 upon excessive heating or other type of malfunction; the presence of light sources produced by electric arcs or flames generated by the same components; undesired opening of the containing element 50 such as to make volume V contained in the container element 50 accessible from the outside.

According to a preferred embodiment, the emitter means 11 comprise at least one LED, and the receiver means 12 comprise at least one photo-transistor. Said first light beam 13 therefore is a photon beam. The processing unit 14 may comprise various embodiments within the reach of the man skilled in the art.

With reference to figure 2, an embodiment of a sensor 10 according to the present invention is shown. The installation of sensor 10 within volume V of the container element 50 is such as to ensure a propagation of said first light beam 13 effective for the purposes of the present invention. In other words, the emitter means 11 and receiver means 12 are installed so that from the resulting propagation of said first light beam 13 it is possible to obtain information about (any) abnormal conditions, of the above-described type. According to a preferred embodiment, the propagation of said first beam 13 further includes a reflection on at least one surface opposite to the emitting source, which surface can consist of a portion of the container element 50. For example, said emitter means (11 ) and (12) said receivers means may be placed within said container element so that said surface comprises a portion of the inner wall of said container element 50 or of the lid 52 associated with said container element 50.

With reference to figures 1 a and 1 b, the portion of element 50 may be part of the inner wall of lid 52 for opening/closing said container element 50. Thereby, it is advantageously possible to simultaneously detect abnormal conditions within volume V, the container element of said volume V and lid 52 of said container element. It is therefore possible to detect the presence of smoke, electrical arcs or flame within volume V and the undesired opening of lid 52.

In this preferred embodiment, the emitter means 1 1 are configured so that said first light beam 13 propagates from said emitter means 1 1 themselves to the inner wall of lid 52, thus traveling part of the containment volume V. Said first light beam 13 is reflected on the inner wall of lid 52, the corresponding reflected beam 13b propagates to a different region of volume V up to the receiver means 12, by means of which it is received.

An operating mode of a preferred embodiment of the present invention provides for the simple evaluation of said second light beam received by said receiver means 12 if said emitter means are deactivated. The presence of a possible detection by said receiver means 12 of said second light beam will indicate the presence, within said volume V, of a light source produced, for example, by an electric arc or by a flame upon a strong overheating or upon undesired opening of said container element or by a breakage of the walls thereof such as to allow the light to enter from the outside.

In this case, said processing unit 4 can simply consist of a comparator adapted to compare the current IRX emitted by said receiver means 12 to a reference value or a range of reference values.

An operating mode associated with the preferred embodiment of the present invention shown in the accompanying figure 1 b provides for the simple evaluation of said second light beam received by said receiver means 12 upon the propagation of said first light beam 13, which evaluation can be carried out, for example, by measuring the current l _RX produced by said receiver means 12 in response to the light beam received and proportional to the intensity thereof.

In case of abnormal conditions such as the presence of smoke, flames or electric arcs within volume V and as the undesired opening of lid 52, the luminous flux of said second light beam received by said receiver means 12 will be different than the nominal case in the absence of abnormal conditions and, accordingly, the current IRX produced will be different from that in standard conditions. By simply measuring the current IRX and comparing it to a reference value or a range of reference values, it is possible to detect abnormal conditions within volume V. Also in this case, said processing unit 14 can simply consist of a comparator adapted to compare the current IRX emitted by said receiver means 12 to a reference value or a range of reference values.

Another operating mode associated with the present invention provides for said emitter means 1 1 being selectively configurable between a first operating condition, in which said emitter means 1 1 generate the light beam 13 and a second operating condition, in which said emitter means 1 1 are deactivated. In the practice, the operation of the emitter means is intermittent, set to a certain operating frequency by the processing unit 14.

As will become apparent from the following description, said first operating condition of the emitter means 1 1 is adapted to detect abnormal conditions within volume V such as, for example, the presence of smoke, and abnormal conditions of element 50, such as the undesired opening of lid 52.

Said second operating condition of the emitter means 1 1 is instead adapted to detect abnormal conditions within volume V such as, for example, the presence of light sources produced by electric arcs.

According to a preferred embodiment of the present invention, shown in the accompanying figure 2, sensor 10 includes a feedback block 15, possibly integrated in said processing unit 14, which activates in feedback the emitter means 1 1 on the basis of the intensity of said second light beam received by the receiver means 12. In particular, the feedback block 15 is adapted to update said first light beam 13 generated by said emitter means 1 1 so that said second light beam, comprising, in conditions of absence of faults, only the reflected light beam 13b in the absence of disturbances, has a predetermined light intensity.

Said emitter means 1 1 preferably comprise an LED, said receiver means preferably comprise a photo-transistor and the feedback block 15 comprises an electronic circuit connected to the LED and to the photo-transistor. The LED is powered by the feedback circuit 15 with a current l _T x and produces a corresponding first light beam 13. Photo-transistor 12, in response to receiving beam 13b (due to propagation of said first light beam 13), produces a current IRX. According to this embodiment, the feedback block drives the LED with a current Ιτχ so that current l _RX in output from the photo-transistor corresponds to a predetermined value. Therefore, as the conditions within volume V (such as smoke and/or electrical arcs) and/or element 50 (opening of lid 52) vary, the conditions of propagation of said first light beam 13 vary. The variation of the propagation conditions correspond to a second light beam received by said receiver means 12 having a different light intensity than the same light beam in propagation conditions considered as normal. This effect results in a change compared to the predetermined value of current IRX in output from the photo- transistor. In response to the variation of the current value l _RX , the feedback circuit 15 updates the value of current l _TX in input to the LED, so that it produces a first light beam 13 such as to produce the predetermined current value IR _X in output from the photo-transistor.

In said preferred embodiment, the emitter means 1 1 can be configured according to the "intermittent" mode described and sensor 10 can be adapted, for example, to detect an electric arc and the corresponding light phenomenon generated within volume V. In the embodiment shown in figure 2, the emitter means 1 comprise a LED and the receiver means 12 a photo-transistor, the feedback block 15 is connected to the processing unit 14. Said processing unit 14 further comprises switching means adapted to switch the LED between the first and second operating conditions.

In the absence of abnormal conditions of the container element 50 and of volume V contained therein, the pattern of currents Ι _Τ χ and IRX is shown in figure 3. As can be seen from the graph, the LED operation is intermittent, in fact it is active (ON) for a time T1 and inactive (OFF) for a time T2. The "duty cycle" of the LED, i.e. the ratio between the active time T1 and the switching period, T1 + T2, is configurable as desired. The value of current IRX in output from the photo-transistor remains constant - at the operating intervals of the LED - since no abnormal conditions occur. Current l _RX) as said, is kept to the same value by the feedback circuit 15. The processing unit 14 reads the values of current IRX and of current Ιτχ during the observation time span. During the ON phases, it calculates the actual value of Current Transfer Ratio (CTR) between currents l _RX and Ι _Τ χ (CTR = IRX/ITX) that, in the absence of abnormalities detected, will be equal to the nominal reference value CTRREF, during the OFF phases it measures the value of current IRX that, in conditions of absence of faults, will be equal to the reference value IRX _OF F- When the sensor 10 does not detect abnormal conditions, the LED is active, i.e. generates said first light beam 13, and the photo-transistor receives beam 13b upon the propagation within volume V and the reflection on lid 52 of element 50. When, instead, inside volume V there is a further light source 20 that produces a corresponding external light beam 21 (the light source 20 that can be produced as a result of abnormal phenomena of the electrical and electronic components contained within element 50, such as for example, an electrical arc), the value of IR _X remains fixed as it is kept constant by the feedback block 15 and, consequently, there is a decrease in current Ι _Τ χ because of the contribution provided by said further light source 20. Value CTR will therefore be greater than the nominal reference one CTRREF-

The accompanying figure 4 shows the pattern of currents l _RX and Ιτχ in the detection conditions after another abnormal condition of the container element 50th. In particular, the behavior of sensor 10 is shown when opening lid 52 of the container element 50.

The embodiment of sensor 10 is the same described above, therefore it includes a photo-transistor 12, a LED 11 , a control unit 14 and a feedback block 15. Following the opening of lid 52 of the container element 50, in order to ensure the predetermined current value l _RX in output from photo-transistor 12, the feedback circuit 15 imposes a constant increase in current Ιτχ so as to generate a corresponding first light beam 13. Such a behavior is clearly visible from the progressive increase in the levels of current l _TX in the conduction periods that follow one another after the occurrence of the abnormal condition, as shown in the accompanying figure 4. The processing unit 14, reading the values of currents l _T x and IR _X , calculating the current value of Current Transfer Ratio (CTR) between currents IRX and Ιτχ and comparing it to the reference value CTRREF is also in this case able to determine the present fault condition.

In a further embodiment and mode of operation of the present invention, said sensor 10 will simply check the values of currents Ι _Τ χ and l _R x.

This operating mode, which can be combined and integrated with that described above, allows faults related to an abnormal condition of the container element 50 to be detected, in particular faults related to the opening of lid 52 of the container element 50. Indeed, in if lid 52 is fully open and in the total absence of outside lighting (i.e., the box is in the dark), there is no optical coupling between LED 1 1 and photo-transistor 12, the latter does not perceive light and the feedback circuit 15 will try to restore the reference level of l _RX by forcing LED 1 1 to emit the maximum amount, so IRX will be almost null, and Ι _Τ χ very high. Conversely, in the absence of lid 52 and in the presence of a lighted environment, IRX will be high and the feedback circuit 15 will try to turn off LED 1 1 in a vain attempt to bring IRX back to the reference value; in this case, then, there will be a high l _RX with a null Ιτχ. Therefore, the faults related to the position of the lid can be detected by simply checking whether the current values IRX and I τχ are outside certain reference intervals Al _R x and ΔΙ _Τ χ.

The above-described reference values, IRX OFF and CTR _REF depend on the temperature and on the wear of the electronic components that make up sensor 10 according to the present invention and can thus be variable. These variations should not be construed as a fault and they must be made harmless for the purposes of detecting faults according to the present invention, through the introduction of an appropriate filtering which, in the case of "slow" variations such as parametric drifts with time and/or temperature, may for example include the calculation of time averages of the subject parameters.

In addition to that, some abnormal conditions, such as the presence of smoke inside the container element 50, may give rise to a variation of parameter CTR which is much less clear and steady than the corresponding variation in the case of fault due to open lid and more similar to an injection of noise that causes apparently random variations. Also in this case, the fault must be properly detected through the introduction of an appropriate filtering which, in the case of apparently random variations, may for example include the calculation of the temporal variance of the subject parameters.

The method of detection of abnormal conditions of a container element and of the volume included in said container element according to a preferred embodiment of the present invention therefore uses an algorithm based on the statistics of variables CTR (with emitter on) and l _RX (with emitter off).

In further detail, alternating on phase with off phases of said LED 1 1 as described and measuring the quantities of interest of each phase, said algorithm calculates the standard deviation, and in general the statistical trend, for a population of values detected and belonging to a certain range, both for calculating the reference values and for calculating the current values. If the standard deviation of the current values exceeds a certain threshold σ-m - calculated in advance by evaluating typical operating conditions, in the absence and in the presence of abnormal or alert conditions, and having different values in the conditions in which the emitter LED is turned on (OTH_ON) or off (O _T H_OFF) - then a fault is reported.

Being T _c the duration of an on phase plus an off phase, for example, the range for the calculation of the current values is T _s =NTc, where N is the number of samples used to calculate the standard deviation of the current values, and TM = MTc where M is the number of samples used to calculate the reference average, and where M » N.

Assuming that the device had already been working for some time in which it detected no faults and that therefore the 1 on/off cycles have already passed, the algorithm follows the following steps:

a) LED on (cycle i);

b) Measuring currents ITX_ON J and IRX ON i and calculating CTRi = IRX ONJ / ITXJDN J; c) Updating the mean (CTRREFJ) on the last M samples: d) Calculating the corresponding current standard deviation OON_ACTJ of the population of N samples: CTR,, CTR CTR-N: (for the same purpose it is possible to calculate the standard deviation instead of the corresponding standard deviation);

e) If cJoN_ACT_i >∑ON_TH there is a fault, otherwise proceed with the next step;

f) LED off;

g) Measuring IRX OFFJ;

h) Updating the mean value of lRx_oFF_Av on the last M samples; i) Calculating the current standard deviation O ₀ FF_ACT of the population of N samples: IRX OFFJ, IRX_OFF_ Μ , · - · , IRX_OFFJ-N: (for the same purpose it is possible to calculate the standard deviation instead of the corresponding standard deviation);

If OOFF_ACTJ > ∑ 0FF_TH there is a fault, otherwise proceed back to step a) after increasing the index from i to i+1.

A preferred embodiment of the method for detecting abnormal conditions of a container element 50 and of volume V defined by said container element 50 shown in the flow chart in the accompanying figure 7, where:

blocks 701 to 705 represent the initialization phase of the processing unit 14 in which the values of IRX and Ι _Τ χ are sampled 702, comparing 703 to appropriate values or reference ranges to verify that the sensor is properly installed and that it is not faulty. If a fault is found, such as if the values of l _RX and l _T x are found to be outside the reference ranges for a certain number of times in a row, the reset condition 704 is enabled and the algorithm is blocked, signaling the detected fault. If the above fault is not detected, the initial reference statistical parameters are calculated 705 to make comparisons in the next detection step.

Blocks 706 and 709 are the actual detection step in which the processing unit 14 controls the activation and deactivation of LED 1 1 , measures the values of currents ITX_ONJ, IRX_ONJ, 706 and IRX OFFJ 709, calculates parameters CTRi, CTRREFJ 706, IRX_OFF_AV 709, and the standard deviations a ₀ N_ACTj 706 e O ₀ FF_ACTJ 709.

Finally, blocks 707, 708, 710 and 71 1 represent the protection step implemented by the processing unit 14 in which, if a fault of element 50 or within the container element 50 is detected, said fault is reported and appropriate countermeasures are taken. In this step, the values sampled both during the LED on step 707, 708 and in the LED off step 710, 71 1 are compared to the previously calculated, corresponding reference values.

If faults are detected, the algorithm described carries out the cycle which involves the repetition of the actions relating to blocks 706 to 71 1. If faults are detected, they are reported 712 and an alarm is provided together with the reset 704 of the algorithm.

In greater detail, block 701 represents the initial reading block from which operations begin. Then, they go to block 702 in which the values of currents Ιτχ (ίη input to LED 1 1 ) and lRx (in output from photo-transistor 12) are sampled. In output from block 702, next is the test block 703 where a check is made as to whether the values of Ιτχ and IRX are around a value or within a predetermined reference range to determine whether the sensor has been installed correctly. If not so, following the NO branch in output from the test block 702, next is block 704 in which an abnormal condition is indicated and the algorithm is reset.

If so, i.e. if the values of Ιτχ and IRX are around a predetermined value, the YES branch in output from block 703 is followed. Block 705 is next, where the initial reference statistical parameters are calculated to make comparisons in the next detection step.

Module 706 is next, where LED 1 1 is kept on, the current value of CTR, CTRi is calculated, the reference value CTR _REF is updated on the basis of the last M samples, the standard deviation σοΝ_Αοτ of a plurality N of samples CTR is calculated. Thereafter, in test block 707, it is checked whether more than three samples (settable value depending on the circumstances) of Ιγχ and IRX are not around said predetermined value. If so, following branch YES in output from block 707 goes to block 7 2 in which the processing unit indicates a malfunction. If not so, branch NO in output from block 707 is followed to get to the test block 708 where it is assessed whether the standard deviation OON_ACT of a plurality N of samples of the ratio CTR calculated at block 706 is greater than the reference standard deviation value OQN_TH- If so, branch YES in output to the block 708 is followed, which leads to block 712 in which the processing unit indicates a malfunction. If not so, in output from the test block 708 next is block 709 in which LED 11 is kept off, the current value of IRX, IRX _O FFJ is calculated, the reference value x_oFF_A is updated on the basis of the last M samples, the standard deviation OOFF_ _AC T of a plurality N of samples of current IRX is calculated. Thereafter, in test block 710, it is checked whether more than three samples (settable value depending on the circumstances) of IRX are not around said predetermined value. If so, following branch YES in output from block 710 goes to block 712 in which the processing unit indicates a malfunction. If not so, branch NO in output from block 710 is followed to get to the test block 711 , where it is assessed whether the standard deviation OOF _F _A _C T of 3 plurality N of samples of the ratio CTR calculated at block 709 is greater than the reference standard deviation value O ^" O _FF _T _H - If so, following branch YES in output from block 711 goes to block 712 in which the processing unit indicates a malfunction. If not so, in output from test block 7 1 the procedure goes back to block 706 to restart the check described.