CN109546966B - Hot spot diagnosis method and device for photovoltaic module - Google Patents

Hot spot diagnosis method and device for photovoltaic module Download PDF

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CN109546966B
CN109546966B CN201811425755.0A CN201811425755A CN109546966B CN 109546966 B CN109546966 B CN 109546966B CN 201811425755 A CN201811425755 A CN 201811425755A CN 109546966 B CN109546966 B CN 109546966B
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bypass diode
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CN109546966A (en
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云平
徐君
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Sungrow Power Supply Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
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Abstract

According to the hot spot diagnosis method and device for the photovoltaic module, the hot spot problem is judged through the linearity of the curve of the specific interval of the IV curve, the bypass diode conduction type hot spot problem with steps on the IV curve can be judged, the bypass diode non-conduction type hot spot problem with distortion characteristics and without steps on the IV curve can be effectively judged, and the diagnosis problem of the step-free hot spot module in the prior art is solved.

Description

Hot spot diagnosis method and device for photovoltaic module
Technical Field
The invention relates to the technical field of hot spot diagnosis of photovoltaic modules, in particular to a hot spot diagnosis method and device of a photovoltaic module.
Background
In a photovoltaic power generation system, in order to avoid hot spots of a photovoltaic module and further influence the performance of the photovoltaic module, hot spot diagnosis is generally required. Among the numerous diagnostic methods for hot spots, the IV curve method is the preferred choice because of its low cost and high accuracy.
The IV curve method mainly makes full use of IV characteristic change when hot spots occur to judge various failure types, and can decouple different failure types through transverse and longitudinal comparison, thereby not only diagnosing the hot spots, but also diagnosing other failure types.
However, since the bypass diode non-conduction type hot spot is not clearly characterized on the IV curve, the determination of the hot spot by the IV curve method in the related art is limited to the bypass diode conduction type hot spot, and the bypass diode non-conduction type hot spot cannot be diagnosed.
Disclosure of Invention
The invention provides a hot spot diagnosis method and device of a photovoltaic module, and aims to solve the problem that a bypass diode non-conduction type hot spot cannot be diagnosed in the prior art.
In order to achieve the purpose, the technical scheme provided by the application is as follows:
a method of diagnosing hot spots of a photovoltaic module, comprising:
acquiring IV curve scanning data of the photovoltaic module;
judging whether steps exist in an IV curve formed by the IV curve scanning data;
if the IV curve has steps, performing linearity fitting on a first preset interval curve of the IV curve, and judging whether bypass diode conduction type hot spots exist according to the fitting degree;
and if the IV curve has no step, performing linearity fitting on a second preset interval curve of the IV curve, and judging whether the bypass diode non-conducting hot spot exists according to the fitting degree.
Preferably, the determining whether there is a step in the IV curve formed by the IV curve scan data includes:
searching a local maximum power point and a local minimum power point on the IV curve;
judging whether the number of the local maximum power points is more than 1;
if the number of the local maximum power points is more than 1, judging that a step exists in the IV curve;
and if the number of the local maximum power points is not more than 1, judging that no step exists in the IV curve.
Preferably, the first preset interval curve is as follows: a step section curve from the ith local minimum power point to the (i + 1) th local maximum power point; i is a positive integer, wherein i is less than N, and N is the number of the local maximum power points;
the second preset interval curve is as follows: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vmIs the voltage of the local maximum power point.
Preferably, the determining whether there is a step in the IV curve formed by the IV curve scan data includes:
judging whether the slope change rate of the IV curve meets a no-step condition or not;
if the slope change rate of the IV curve meets the no-step condition, judging that no step exists in the IV curve;
and if the slope change rate of the IV curve does not meet the no-step condition, judging that a step exists in the IV curve.
Preferably, the first preset interval curve is as follows: a step section curve between the ith step change of the slope of the IV curve and the (i + 1) th step change of the slope of the IV curve; i is a positive integer, wherein i is less than M, and M is the total number of step changes of the slope of the IV curve;
the second preset interval curve is as follows: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vmIs the local maximumVoltage of a high power point.
Preferably, the step of fitting the linearity of the first preset interval curve of the IV curve and judging whether the bypass diode conducting hot spot exists according to the degree of fitting includes:
performing linearity fitting on the first preset interval curve to obtain N-1 fitting degrees;
judging whether the N-1 fitting degrees are all smaller than a first threshold value; the first threshold is less than 1;
if the N-1 fitting degrees are all smaller than a first threshold value, judging that the bypass diode conduction type hot spot does not exist;
and if at least one fitting degree is larger than or equal to a first threshold value, judging that the bypass diode conduction type hot spot exists.
Preferably, after determining that the bypass diode conducting type hot spot exists, the method further includes:
judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
if the absolute values of the slopes of all the fitting straight lines are smaller than a second threshold value, judging that the existing bypass diode conduction type hot spots are light hot spots;
if the absolute value of the slope of at least one fitting straight line is greater than or equal to a second threshold, judging whether the fitting degree of the fitting straight line with the absolute value of the slope greater than or equal to the second threshold is smaller than a third threshold; the third threshold is greater than the first threshold and less than 1;
if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is smaller than a third threshold, judging that the existing bypass diode conduction type hot spot is a moderate hot spot;
and if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is larger than or equal to a third threshold, judging that the existing bypass diode conduction type hot spot is a heavy hot spot.
Preferably, the step of fitting the linearity of the second preset interval curve of the IV curve and judging whether the bypass diode non-conducting hot spot exists according to the degree of fitting includes:
performing linearity fitting on the second preset interval curve to obtain two fitting degrees;
judging whether the fitting degrees are both smaller than a first threshold value;
if the fitting degrees are both smaller than the first threshold value, judging that the bypass diode non-conduction type hot spot does not exist;
and if at least one fitting degree is larger than or equal to a first threshold value, judging that the bypass diode non-conducting hot spot exists.
Preferably, after determining that there is the bypass diode non-conductive hot spot, the method further includes:
judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
if the absolute values of the slopes of all the fitting straight lines are smaller than a second threshold value, judging that the existing bypass diode non-conducting hot spots are light hot spots;
if the absolute value of the slope of at least one fitting straight line is greater than or equal to a second threshold, judging whether the fitting degree of the fitting straight line with the absolute value of the slope greater than or equal to the second threshold is smaller than a third threshold;
if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is smaller than a third threshold, judging that the existing bypass diode non-conducting hot spot is a moderate hot spot;
and if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is larger than or equal to the third threshold, judging that the existing bypass diode non-conducting hot spot is a severe hot spot.
A hot spot diagnostic apparatus of a photovoltaic module, comprising: a processor and a memory; wherein:
the processor is used for executing all steps stored in the memory;
each step stored in the memory comprises the hot spot diagnosis method of the photovoltaic module.
According to the hot spot diagnosis method for the photovoltaic module, the hot spot problem is judged through the linearity of the curve of the specific interval of the IV curve, so that not only can the conduction type hot spot problem of the bypass diode with the step in the IV curve be judged, but also the non-conduction type hot spot problem of the bypass diode with the distortion characteristic and without the step in the IV curve can be effectively judged, and the diagnosis problem of the step-free hot spot module in the prior art is solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart of a hot spot diagnosis method for a photovoltaic module according to an embodiment of the present invention;
FIG. 2 is a partial flow diagram of a method for diagnosing hot spots of a photovoltaic module according to another embodiment of the present invention;
FIG. 3 is a partial flow diagram of a method for diagnosing hot spots of a photovoltaic module according to another embodiment of the present invention;
FIG. 4 is a partial flow diagram of a method for diagnosing hot spots of a photovoltaic module according to another embodiment of the present invention;
fig. 5a and 5b are schematic diagrams of two IV curve waveforms of a photovoltaic module according to another embodiment of the present invention;
fig. 6a and 6b are infrared thermal imaging diagrams of a photovoltaic module according to another embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The invention provides a hot spot diagnosis method of a photovoltaic module, which aims to solve the problem that a bypass diode non-conduction type hot spot cannot be diagnosed in the prior art.
Referring to fig. 1, the method for diagnosing hot spots of a photovoltaic module specifically includes:
s101, acquiring IV curve scanning data of the photovoltaic module;
in practical application, the photovoltaic module to be tested can be subjected to IV curve scanning through the electrical parameter extraction device such as the intelligent junction box or the optimizer, IV curve scanning data is obtained, and IV curve scanning data of the single photovoltaic module in the system string is obtained.
In addition, the data acquired when the photovoltaic module is subjected to IV scanning needs to be subjected to processing such as de-duplication and sequencing, so that the IV curve scanning data beneficial to application can be obtained; the specific processing procedure is the same as that in the prior art, and is not described herein again.
S102, judging whether steps exist in an IV curve formed by the IV curve scanning data;
specifically, the steps can be identified by comparing with a theoretical IV curve, but because the solution of the theoretical IV curve requires the selection and determination of irradiance, temperature data and model parameters, the accuracy is low, so in practical application, the steps can also be identified by deriving the IV curve, or the steps can also be identified by the slope change between characteristic points on the IV curve; it is not specifically limited herein, and may be within the scope of the present application depending on the specific application environment.
If the IV curve has a step, the curve characteristic of the bypass diode conduction type hot spot is met, and the step S103 needs to be executed; if there is no step in the IV curve, it is determined whether it conforms to the distortion characteristic of the bypass diode non-conduction type hot spot through step S104.
S103, performing linearity fitting on a first preset interval curve of the IV curve, and judging whether bypass diode conduction type hot spots exist according to the fitting degree;
and S104, performing linearity fitting on a second preset interval curve of the IV curve, and judging whether the bypass diode non-conducting hot spot exists according to the fitting degree.
The applicant finds that when the photovoltaic module generates hot spots, the voltage of the hot spot cell is in a reverse bias state, the parallel resistor of the hot spot cell is connected into the circuit and is influenced by the parallel resistor, the curve in the specific interval of the IV curve can change, and the change can be identified through the linearity of the curve, so that the hot spot problem can be diagnosed. The straightness refers to the fitting degree of a fitting straight line corresponding to an interval curve, and high straightness represents a high-probability hot spot problem.
For the bypass diode conduction type hot spot, the IV curve shows the characteristic of step appearance; the non-conducting hot spot of the bypass diode is characterized in that the IV curve has no steps but has distortion, namely, a straight line part with high linearity exists in a specific section of the IV curve. Therefore, according to whether a step exists in the IV curve, linearity fitting is carried out on the corresponding preset interval curve, the higher the fitting degree is, the higher the possibility of existence of hot spots is, and further whether the bypass diode conduction type hot spots or the bypass diode non-conduction type hot spots exist can be judged according to the fitting degree.
According to the hot spot diagnosis method for the photovoltaic module, the hot spot problem is judged through the linearity of the curve of the specific interval of the IV curve, so that not only can the conduction type hot spot problem of the bypass diode with the step in the IV curve be judged, but also the non-conduction type hot spot problem of the bypass diode with the distortion characteristic and without the step in the IV curve can be effectively judged, and the diagnosis problem of the step-free hot spot module in the prior art is solved.
Preferably, the step S102, namely, determining whether there is a step in the IV curve formed by the IV curve scan data, as shown in fig. 2, specifically includes:
s201, searching a local maximum power point and a local minimum power point on an IV curve;
the local maximum power point and the local minimum power point can be searched by adopting the slope change characteristics of all points of the VP curve corresponding to the IV curve. The local maximum power point and the local minimum power point are identified by the positive and negative relationship of the slope of the VP curve being 0 and the left and right slopes.
Taking fig. 5a and 5B as an example, fig. 5a can obtain that there are two local maximum power points a and C and one local minimum power point B on its IV curve according to its VP curve; fig. 5b shows that only one local maximum power point a is present on the IV curve from the VP curve.
S202, judging whether the number of the local maximum power points is more than 1;
the number N of local maximum power points in fig. 5a is 2, and the number N of local maximum power points in fig. 5b is 1.
If the number of the local maximum power points is greater than 1, executing step S203; if the number of the local maximum power points is not greater than 1, step S204 is executed.
And S203, judging that the IV curve has a step.
And S204, judging that no step exists in the IV curve.
In fig. 5a, the number N of local maximum power points is 1, and as can be seen from the figure, the IV curve does not have a step. While the number N of local maximum power points in fig. 5b is greater than 1, it can be seen that the IV curve does have steps.
Correspondingly, the first preset interval curve in step S103 is: a step section curve from the ith local minimum power point to the (i + 1) th local maximum power point; i is a positive integer, i is one of the N local maximum power points, i is less than N, and N is the number of the local maximum power points. Taking fig. 5a as an example, the number N of local maximum power points is 2, so the corresponding first preset interval curve is a step curve between the 1 st local minimum power point B and the 2 nd local maximum power point C.
The second preset interval curve in step S103 is: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vmIs the voltage at the local maximum power point. Taking fig. 5b as an example, if the voltage of the local maximum power point a is 25, the second preset interval curve is: the first interval (12.5, 17) and the second interval (17, 25) correspond to a curve.
Alternatively, step S102 may also be implemented in the following form, specifically including:
judging whether the slope change rate of the IV curve meets a no-step condition or not;
if the slope change rate of the IV curve meets the condition of no step, judging that the IV curve has no step;
and if the slope change rate of the IV curve does not meet the no-step condition, judging that a step exists in the IV curve.
At this time, correspondingly, the first preset interval curve in step S103 is: a step section curve from the slope of the IV curve after the step change occurs for the ith time to before the step change occurs for the (i + 1) th time; i is a positive integer, wherein i is less than M, and M is the total number of step change of the slope of the IV curve;
the second preset interval curve in step S103 is: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vmIs the voltage at the local maximum power point.
The specific implementation manner of step S102 and the setting of the two preset intervals may be determined according to a specific application environment, and are not limited herein and are within the protection scope of the present application.
Based on the above embodiment, preferably, as shown in fig. 3, step S103 is to perform linearity fitting on a first preset interval curve of an IV curve, and determine whether there is a bypass diode conducting hotspot according to a degree of fitting, where the method includes:
s301, performing linearity fitting on the first preset interval curve to obtain N-1 fitting degrees;
after fitting, the function is y ═ k1x+b1The degree of fitting is R2 1The closer the value is to 1, the higher the straightness.
Taking fig. 5a as an example, the number N of local maximum power points is determined to be 2, and the IV curve has a step, and the local maximum power point a corresponds to the voltage V1Its local minimum power point B corresponds to the voltage V29.2, voltage V corresponding to local maximum power point C3Thus, the first preset interval is determined to be (V) 292，V3) The first preset interval curve is a step section curve between BC. And performing linearity fitting on the step section curve, wherein the fitted function is that y is-0.0058 x +4.0741, and the fitting degree is R2 1＝0.9145。
S302, judging whether the fitting degrees of the N-1 are all smaller than a first threshold value;
if the N-1 fitting degrees are all smaller than the first threshold value, which indicates that the linearity is poor, executing step S303; the specific value of the first threshold may be determined according to the application environment, for example, 0.9, which is only an example, and other values that can show poor linearity are also within the protection scope of the present application.
If there is at least one degree of fit greater than or equal to the first threshold, the degree of fit R is shown in FIG. 5a2 1When the linearity is high, 0.9145 ≧ 0.9, step S304 is executed.
S303, judging that no bypass diode conduction type hot spot exists;
and S304, judging that the bypass diode conducting type hot spot exists.
Fig. 6a is an infrared thermal imaging diagram of the photovoltaic module corresponding to the IV curve shown in fig. 5a, and it can be seen from fig. 6a that hot spot cells exist in two sub-strings in the photovoltaic module, and the temperatures of the hot spot cells are substantially the same, and the temperature of the hot spot cells is-30 ℃ higher than that of the conventional cells.
Preferably, as shown in fig. 4, the step S104 of performing linearity fitting on the second preset interval curve of the IV curve and determining whether there is a bypass diode non-conducting hot spot according to the degree of fitting includes:
s401, performing linearity fitting on a second preset interval curve to obtain two fitting degrees;
for the first interval (V)m/2，2Vm/3), the fitted function is y ═ k2x+b2The degree of fitting is R2 2(ii) a For the second interval (2V)m/3，Vm) The function after fitting is y ═ k3x+b3The degree of fitting is R2 3. Two intervals are selected based on the fact that the existing photovoltaic assembly junction box is connected with 3 bypass diodes in parallel, and the photovoltaic assembly is connectedThe parts are divided into 3 sub-strings, and each sub-string contains 20 or 24 battery pieces. When 1 or 2 of the sub-strings are mismatched, it is possible to change between two intervals of the IV curve. And identifying the hot spots of each substring by selecting the two intervals. The practical application may depend on the specific application environment, and is not limited to this.
Taking fig. 5b as an example, according to the previous embodiment, the second preset interval in the IV curve shown in fig. 5b includes a first interval (12.5, 17) and a second interval (17, 25); the second preset interval curve is as follows: the first interval (12.5, 17) and the second interval (17, 25) correspond to a curve.
And performing linearity fitting on the curve corresponding to the first interval (12.5, 17), wherein the fitted function is-0.0869 x +8.2072, and the fitting degree is R2 20.9933. And performing linearity fitting on the curve corresponding to the second interval (17, 25), wherein the fitted function is-0.0821 x +8.1037, and the fitting degree is R2 3＝0.9971。
S402, judging whether the fitting degrees are both smaller than a first threshold value;
if both the fitting degrees are smaller than the first threshold value, executing step S403; if there is at least one degree of fit equal to or greater than a first threshold, for example 0.9, as shown by the two degrees of fit R of FIG. 5b2 2And R2 3Are both greater than 0.9, step S404 is executed.
S403, judging that the bypass diode non-conduction type hot spot does not exist;
s404, judging that the bypass diode non-conducting type hot spot exists.
Fig. 6b is an infrared thermal imaging diagram of the photovoltaic module corresponding to the IV curve shown in fig. 5b, and it can be seen from fig. 6b that hot spot cells exist in two sub-strings in the photovoltaic module, and the temperature of the hot spot cells is different, and the temperature of the most serious hot spot cells is-30 ℃ higher than that of the conventional cells.
Based on the above embodiment, the present embodiment provides a specific implementation process of performing linearity fitting on a corresponding preset interval curve of an IV curve, and determining whether a bypass diode conduction hot spot or a bypass diode non-conduction hot spot exists according to the degree of fitting, and the remaining principles are the same as those in the above embodiment, and are not described herein again.
In addition to the above, the applicant also found that the slope of the fitted function obtained in the above embodiment represents the parallel resistance of the hot spot cell, and the severity of the hot spot can be determined by the magnitude of the resistance.
That is, on the basis of the above embodiment, as shown in fig. 3, after determining that there is the bypass diode conducting type hot spot in step S304, it is preferable that the method further includes:
s305, judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
when the fitting degree is greater than or equal to the first threshold, the straightness is high, and at the moment, the absolute value of the slope of the fitting straight line needs to be judged; the absolute value of the slope is the reciprocal of the parallel resistance of the hotspot battery piece, and the parallel resistance can be judged through the absolute value.
Based on the measured IV data of a large number of hot spot batteries and the fact that the reverse bias power consumption of the battery plate in the literature is larger than 25W, the service life and the safety of the component are seriously influenced, the threshold value of the absolute value of the slope is obtained to be 0.07, therefore, the absolute value of the slope of the fitting straight line with the fitting degree larger than or equal to the first threshold value can be compared with 0.07 by taking 0.07 as the second threshold value. In practical application, the second threshold may also take other values, such as 0.069 or 0.071, and values capable of representing influences on the component life and safety are all within the protection range of the present application.
If the absolute values of the slopes of all the fitting straight lines are less than 0.07, which indicates that the parallel resistance is large and the service life and the safety of the component are not seriously affected, executing a step S306; if there is at least one fitted straight line with a slope absolute value greater than or equal to 0.07, indicating that the parallel resistance is small, the lifetime and safety of the component will be seriously affected, and therefore, the step S307 needs to be further executed.
S306, judging that the existing bypass diode conduction type hot spot is a mild hot spot;
s307, judging whether the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is smaller than a third threshold;
the third threshold is a value which is greater than the first threshold and smaller than and close to 1, for example, 0.99, and values which can represent that the fitting linearity is relatively high are all within the protection range of the application.
If the fitting degree of the fitting straight line with the absolute value of the slope being greater than or equal to the second threshold is smaller than the third threshold, which indicates that the fitting straight line is higher in degree and the parallel resistance is small, and the service life and the safety of the component will be seriously affected, the step S308 is executed; if the fitting degree of the fitting straight line with the absolute value of the slope being greater than or equal to the second threshold is greater than or equal to the third threshold, which indicates that the fitting straight line is very high in linearity and small in parallel resistance, and the service life and safety of the component will be seriously affected, the step S309 is executed;
s308, judging that the existing bypass diode conduction type hot spot is a moderate hot spot;
s309, judging that the existing bypass diode conduction type hot spot is a severe hot spot.
In FIG. 5a, the degree of fit is R2 10.9145, although greater than 0.9, the function of the fitted line is y k1x+b1-0.0058x +4.0741, i.e. its absolute value of slope | k10.0058 < 0.07, so the IV curve in FIG. 5a is mild hot spots.
Correspondingly, on the basis of the above embodiment, as shown in fig. 4, after the step S404 of determining that the bypass diode non-conducting type hot spot exists, the method further includes:
s405, judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
if the absolute values of the slopes of all the fitting straight lines are smaller than the second threshold, executing step S406; if the absolute value of the slope of at least one fitting straight line is greater than or equal to the second threshold, step S407 is executed.
S406, judging that the existing bypass diode non-conducting hot spots are mild hot spots;
s407, judging whether the fitting degree of the fitting straight line with the slope absolute value greater than or equal to the second threshold is smaller than a third threshold;
if the fitting degree of the fitting straight line with the slope absolute value greater than or equal to the second threshold is smaller than the third threshold, executing step S408; if the fitting degree of the fitting straight line with the absolute value of the slope being greater than or equal to the second threshold is greater than or equal to the third threshold, step S409 is executed.
S408, judging that the existing bypass diode non-conducting hot spot is a moderate hot spot;
and S409, judging that the existing bypass diode non-conduction type hot spot is a severe hot spot.
The following description will be given by taking as examples a first threshold value of 0.9, a second threshold value of 0.07, and a third threshold value of 0.99:
in practical application, the two fitting straight lines of the curve of the second preset interval can be respectively judged according to the sequence, and when the degree of fitting R corresponding to the first interval is obtained2 2If < 0.9, it means that the linearity of the curve in the first interval is low, and the fitting degree R corresponding to the second interval is low2 3Making a judgment if R2 3If the value is less than 0.9, the situation is that the bypass diode non-conduction type hot spot does not exist.
When the first interval corresponds to the fitting degree R2 2When the absolute value of the slope | k of the curve is more than or equal to 0.9, the linearity of the curve in the first interval is high, and the absolute value | k of the slope of the straight line needs to be fitted2Judging | the absolute value; if k2If | ≧ 0.07, it means that the parallel resistance is small, and further comparison of R is required2 2And 0.99; when R is2 2When the temperature is more than or equal to 0.99, the corresponding fitting linearity of the first interval is very high, and the parallel resistance is small, which belongs to the severe hot spot condition; when R is2 2If the value is less than 0.99, the fitting linearity corresponding to the first interval is higher, the parallel resistance is small, and the condition belongs to the condition of moderate hot spots.
When the second interval corresponds to the fitting degree R2 3When the absolute value of the slope | k of the curve is more than or equal to 0.9, the linearity of the curve in the second interval is high, and the absolute value | k of the slope of the straight line needs to be fitted3Judging | the absolute value; if when | k3If | ≧ 0.07, it means that the parallel resistance is small, and further comparison of R is required2 3And 0.99; when R is2 3When the temperature is more than or equal to 0.99, the corresponding fitting linearity of the second interval is very high, and the parallel resistance is small, which belongs to the severe hot spot condition; when R is2 3If the value is less than 0.99, the fitting linearity corresponding to the second interval is higher, the parallel resistance is small, and the condition belongs to the condition of moderate hot spots.
In fig. 5b, the curve corresponding to the first interval (12.5, 17) is fitted with linearity, and the fitted function is y ═ k2x+b2-0.0869x +8.2072 with absolute value of slope | k20.0869 ≥ 0.07 and degree of fit R2 2Since 0.9933 is equal to or greater than 0.99, the presence of bypass diode non-conduction hot spots can be determined as severe hot spots. The interval has hot spot characteristics, which can be the problem that one substring in the assembly generates hot spots, and can also be the problem that two substrings generate hot spots. And in combination with the infrared thermal imaging graph shown in fig. 6b, the existence of the hot spot cell pieces in the two sub-strings in the photovoltaic module can be confirmed.
In fig. 5b, the curve corresponding to the second section (17, 25) is fitted with linearity, and the fitted function is y ═ k3x+b3-0.0821x +8.1037 with absolute value of slope | k30.0821 ≥ 0.07 and its fitting degree R2 3Since 0.9971 is equal to or greater than 0.99, the presence of bypass diode non-conduction hot spots can be determined to be severe hot spots.
From the above, a specific classification for diagnosis of hot spots can be obtained as follows:
N＝1，0.9≤R2less than 0.99, | k | < 0.07, there are bypass diode non-conducting type hot spots, and it is a mild hot spot;
N＝1，0.9≤R2less than 0.99, | k | > 0.07, bypass diode non-conduction type hot spot exists, and the hot spot is moderate;
N＝1，0.99≤R2the | k | > is more than or equal to 0.07, bypass diode non-conduction type hot spots exist, and the hot spots are serious hot spots;
N＝1，0.99≤R2if k is less than 0.07, bypass diode non-conduction type hot spots exist, and the hot spots are light hot spots;
N＝1，R2less than 0.9, no hot spot;
N＞1，0.9≤R2less than 0.99, | k | < 0.07, bypass diode conduction type hot spots exist, and the hot spots are mild hot spots;
N＞1，0.9≤R2less than 0.99, | k | > 0.07, bypass diode conduction type hot spot exists, and the hot spot is moderate;
N＞1，0.99≤R2the | k |, is more than or equal to 0.07, bypass diode conduction type hot spots exist, and the hot spots are serious hot spots;
N＞1，0.99≤R2if k is less than 0.07, bypass diode conduction type hot spots exist, and the hot spots are mild hot spots;
N＞1，R2less than 0.9, no hot spots.
In practical application, the hot spot type can be respectively defined as three grades of no hot spot, hot spot and serious hot spot according to the severity degree of the hot spot type, and the three grades are mainly based on the number N of local maximum power points and the linearity fitting degree R2And comprehensively judging the absolute value | k | of the slope of the fitting straight line, wherein the grade of the hot spot can be further divided into a light hot spot and a medium hot spot according to the absolute value | k | of the slope of the fitting straight line, and the grade of the severe hot spot comprises the severe hot spot.
The method can effectively diagnose the conduction hot spots of the bypass diode and the non-conduction hot spots of the bypass diode, solve the fitted straight line slope of the specific interval of the IV curve, calculate the parallel resistance, evaluate the severity of the hot spots according to the magnitude of the parallel resistance, improve the fire early warning accuracy caused by the hot spots and further improve the safety of the photovoltaic power station.
And the straightness of the curve of the specific interval can be used as a core characteristic value of the hot spot problem and used for decoupling with other failure types or distinguishing the hot spot component from various failure components.
The rest of the principle is the same as the above embodiments, and is not described in detail here.
Another embodiment of the present invention further provides a hot spot diagnosis apparatus for a photovoltaic module, including: a processor and a memory; wherein:
the processor is used for executing all steps stored in the memory;
each step stored in the memory includes the hot spot diagnosis method for the photovoltaic module according to any one of the above embodiments.
The hot spot diagnosis method can be referred to the above embodiments, and is not described in detail here.
The hot spot diagnosis device may be a device capable of implementing IV scanning, such as a component-level optimizer or an intelligent junction box, or may also be a terminal communicatively connected to the device capable of implementing IV scanning, which is not limited herein and is within the scope of the present application depending on the specific application environment.
The embodiments of the invention are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make numerous possible variations and modifications to the present teachings, or modify equivalent embodiments to equivalent variations, without departing from the scope of the present teachings, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims (10)

1. A hot spot diagnosis method for a photovoltaic module is characterized by comprising the following steps:
acquiring IV curve scanning data of the photovoltaic module;
judging whether steps exist in an IV curve formed by the IV curve scanning data;
if the IV curve has steps, performing linearity fitting on a first preset interval curve of the IV curve, and judging whether bypass diode conduction type hot spots exist according to the fitting degree;
and if the IV curve has no step, performing linearity fitting on a second preset interval curve of the IV curve, and judging whether the bypass diode non-conducting hot spot exists according to the fitting degree.
2. The hot spot diagnosis method of a photovoltaic module according to claim 1, wherein the step of the IV curve formed by the IV curve scan data is determined to exist, and the step of the IV curve scan data includes:
searching a local maximum power point and a local minimum power point on the IV curve;
judging whether the number of the local maximum power points is more than 1;
if the number of the local maximum power points is more than 1, judging that a step exists in the IV curve;
and if the number of the local maximum power points is not more than 1, judging that no step exists in the IV curve.
3. The method for diagnosing hot spots of a photovoltaic module according to claim 2, wherein the first preset interval curve is: a step section curve from the ith local minimum power point to the (i + 1) th local maximum power point; i is a positive integer, wherein i is less than N, and N is the number of the local maximum power points;
the second preset interval curve is as follows: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vm is the voltage of the local maximum power point.
4. The hot spot diagnosis method of a photovoltaic module according to claim 1, wherein the step of the IV curve formed by the IV curve scan data is determined to exist, and the step of the IV curve scan data includes:
judging whether the slope change rate of the IV curve meets a no-step condition or not;
if the slope change rate of the IV curve meets the no-step condition, judging that no step exists in the IV curve;
and if the slope change rate of the IV curve does not meet the no-step condition, judging that a step exists in the IV curve.
5. The method for diagnosing hot spots of a photovoltaic module according to claim 4, wherein the first preset interval curve is: a step section curve between the ith step change of the slope of the IV curve and the (i + 1) th step change of the slope of the IV curve; i is a positive integer, wherein i is less than M, and M is the total number of step changes of the slope of the IV curve;
the second preset interval curve is as follows: first interval (V)m/2，2Vm/3) and a second interval (2V)m/3，Vm) The corresponding curve; vmIs the voltage at the local maximum power point.
6. The hot spot diagnosis method of a photovoltaic module according to any one of claims 1 to 5, wherein the step of fitting the linearity of the first preset interval curve of the IV curve and judging whether the bypass diode conducting hot spot exists according to the fitting degree comprises the following steps:
performing linearity fitting on the first preset interval curve to obtain N-1 fitting degrees;
judging whether the N-1 fitting degrees are all smaller than a first threshold value; the first threshold is less than 1;
if the N-1 fitting degrees are all smaller than a first threshold value, judging that the bypass diode conduction type hot spot does not exist;
and if at least one fitting degree is larger than or equal to a first threshold value, judging that the bypass diode conduction type hot spot exists.
7. The method for diagnosing hot spot of photovoltaic module according to claim 6, further comprising, after determining that there is a bypass diode conducting hot spot:
judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
if the absolute values of the slopes of all the fitting straight lines are smaller than a second threshold value, judging that the existing bypass diode conduction type hot spots are light hot spots;
if the absolute value of the slope of at least one fitting straight line is greater than or equal to a second threshold, judging whether the fitting degree of the fitting straight line with the absolute value of the slope greater than or equal to the second threshold is smaller than a third threshold; the third threshold is greater than the first threshold and less than 1;
if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is smaller than a third threshold, judging that the existing bypass diode conduction type hot spot is a moderate hot spot;
and if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is larger than or equal to a third threshold, judging that the existing bypass diode conduction type hot spot is a heavy hot spot.
8. The hot spot diagnosis method of a photovoltaic module according to any one of claims 1 to 5, wherein the step of fitting the linearity of the second preset interval curve of the IV curve and judging whether the bypass diode non-conducting hot spot exists according to the fitting degree comprises the following steps:
performing linearity fitting on the second preset interval curve to obtain two fitting degrees;
judging whether the fitting degrees are both smaller than a first threshold value;
if the fitting degrees are both smaller than the first threshold value, judging that the bypass diode non-conduction type hot spot does not exist;
and if at least one fitting degree is larger than or equal to a first threshold value, judging that the bypass diode non-conducting hot spot exists.
9. The method for diagnosing hot spots of a photovoltaic module according to claim 8, further comprising, after determining that there is a bypass diode non-conducting hot spot:
judging whether the absolute value of the slope of the fitting straight line with the fitting degree greater than or equal to the first threshold is smaller than a second threshold;
if the absolute values of the slopes of all the fitting straight lines are smaller than a second threshold value, judging that the existing bypass diode non-conducting hot spots are light hot spots;
if the absolute value of the slope of at least one fitting straight line is greater than or equal to a second threshold, judging whether the fitting degree of the fitting straight line with the absolute value of the slope greater than or equal to the second threshold is smaller than a third threshold;
if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is smaller than a third threshold, judging that the existing bypass diode non-conducting hot spot is a moderate hot spot;
and if the fitting degree of the fitting straight line with the slope absolute value larger than or equal to the second threshold is larger than or equal to the third threshold, judging that the existing bypass diode non-conducting hot spot is a severe hot spot.
10. A hot spot diagnosis apparatus for a photovoltaic module, comprising: a processor and a memory; wherein:
the processor is used for executing all steps stored in the memory;
the steps stored in the memory include a method of diagnosing hot spots of a photovoltaic module according to any one of claims 1 to 9.
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