Photovoltaic junction box diode thermal runaway outdoor test method

Abstract

The invention discloses a photovoltaic junction box diode thermal runaway outdoor test method, and relates to the technical field of photovoltaic module testing, and the method comprises the steps: S1, selecting a battery piece, and pasting a thermocouple on the outer side of a junction box housing corresponding to the battery piece; s2, preparing shielding sheets with different shielding proportions; s3, confirming that the test environment is in a specific environment condition; s4, sequentially shielding the battery pieces and recording the temperature until the temperature drops for the first time, and recording the shielding proportion corresponding to the highest temperature as the hot spot proportion of the battery pieces; s5, continuously shielding for 1 hour under the hot spot proportion; s6, quickly removing the shielding sheet to allow the current to flow through; s7, testing the performance of the assembly after 1 minute; and S8, judging whether thermal runaway occurs or not according to a test result. According to the test method, the working state of the photovoltaic module under the hot spot condition is simulated and tested, so that the safety and reliability of the photovoltaic module can be effectively evaluated and improved, thermal runaway events are reduced, the service life of the module is prolonged, and the power generation efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of photovoltaic component testing, and in particular relates to an outdoor testing method for thermal runaway of a photovoltaic junction box diode. Background Art

[0002] In solar panels, the main function of bypass diodes is to prevent the hot spot effect from damaging the battery components. When a battery cell in the component cannot generate electricity normally due to shading or other reasons, the battery cell will consume the energy generated by other normal batteries, resulting in local overheating, i.e., the hot spot effect. To prevent this, bypass diodes are connected in parallel between the positive and negative electrodes of the battery component. Under normal working conditions, the bypass diode is in a reverse cutoff state and will not affect the circuit. When the battery cell cannot generate electricity due to the hot spot effect, the bypass diode will be turned on, allowing the current generated by other batteries to flow out of the diode, protecting the battery cell from damage.

[0003] The following risks may exist in the process of state switching of the diode: when the diode switches from the forward conduction state to the reverse bias state, the temperature rise caused by the previous forward current may cause the reverse leakage of the diode to increase, thereby increasing the temperature; if continuous leakage current is generated during reverse bias, the junction temperature of the diode will increase. In the worst case, the temperature rise exceeds the cooling capacity of the junction box, which may cause the diode to be damaged. Therefore, when selecting a bypass diode, it is necessary to consider its withstand voltage capacity, current capacity, junction temperature, thermal resistance and voltage drop parameters to ensure that the diode can operate stably under various working conditions and can effectively protect the solar cell module.

[0004] The existing technology usually uses the following method to simulate the working state of the bypass diode of the solar module under extreme working conditions: first, place the junction box in an indoor environmental chamber and set the temperature of the environmental chamber to 75°C; then, pass 1 times the maximum power point current (Isc) through the module and maintain this current for 1 hour to simulate the thermal stability of the module under long-term operation; after 1 hour, switch the current to 1 / 3 of the open circuit voltage (Voc) of the module, and observe whether the diode is broken down during this process. The above method is carried out in a fixed place and under the regulation of special equipment, which cannot meet the testing requirements of power stations or outdoor. Summary of the invention

[0005] The purpose of the present invention is to provide an outdoor test method for thermal runaway of a photovoltaic junction box diode, by adopting different shielding area ratios for photovoltaic modules under outdoor lighting conditions to verify the thermal runaway resistance of the diode of the module when a hot spot occurs.

[0006] To achieve the above object, the present invention provides the following solution: a photovoltaic junction box diode thermal runaway outdoor testing method, comprising the following steps:

[0007] Step S1, randomly selecting a battery cell from the sample assembly, and pasting a thermocouple on the outer side of the junction box housing corresponding to the selected battery cell;

[0008] Step S2, preparing shielding sheets with different shielding ratios;

[0009] Step S3: Confirm that the test environment meets the outdoor light intensity of 800-1000W / m 2 , temperature 20±2℃, wind speed less than 1m / s;

[0010] Step S4, selecting shielding sheets in order from large to small according to the shielding ratio to shield the shielded battery cell for a preset time, recording the temperature of the junction box shell after each shielding, until the temperature of the junction box shell drops for the first time, and recording the shielding ratio corresponding to the highest temperature at this time as the battery cell hot spot ratio;

[0011] Step S5, under the condition of proportional shielding of the hot spots of the battery cell, shielding is continued for 1 hour, and the temperature of the junction box housing is recorded;

[0012] Step S6: After the shielding is completed, the shielding sheet is quickly removed to allow the power station string current or the component maximum power point current to flow quickly;

[0013] Step S7: After 1 minute, perform a performance test on the sample assembly and record the test results;

[0014] Step S8: Determine whether thermal runaway has occurred in the sample component according to the test results.

[0015] In some possible implementations of the testing method of the present invention, in step S2, a plurality of shielding sheets with corresponding shielding ratios decreasing in steps of 10% from 100% to 10% are prepared according to the area of ​​the selected shielding cell sheet.

[0016] In some possible implementations of the testing method of the present invention, in step S4, the shielding sheet is used to shield the shielding cell sheet for a preset time in a manner where the shielding ratio decreases in sequence by 10%.

[0017] In some possible implementations of the testing method of the present invention, in step S4, the shielded solar cell is shielded for a preset time, and each shielding time is 30 minutes.

[0018] In some possible implementations of the testing method of the present invention, the sample component is selected from a power plant operating component. When the performance test is performed on the sample component in step S7, the connection between the sample component under test and the string is disconnected, and the open circuit voltage of the sample component is tested with a multimeter and recorded as Uk1.

[0019] In some possible implementations of the testing method of the present invention, in step S8, the open circuit voltage Uk1 of the sample assembly should be no less than 2 / 3Voc, indicating that the diode is working properly; otherwise, it indicates that the diode is broken down and thermal runaway occurs.

[0020] In some possible implementations of the testing method of the present invention, the sample component is an independent photovoltaic component. In the step S1, the component is installed at the local optimal inclination angle, the sample component is connected to the MPPT load, the sample component is at the maximum power point, and the power W1 of the sample component is recorded; then, a shielding cell is randomly selected, and a thermocouple is pasted on the outer side of the corresponding junction box shell of the selected shielding cell.

[0021] In some possible implementations of the testing method of the present invention, when the performance test is performed on the sample component in step S7, the power value displayed by the MPPT load is observed and the component power W2 is recorded.

[0022] In some possible implementations of the testing method of the present invention, in step S8, the sample component power W2 should be no less than 2 / 3 W1, indicating that the diode is working normally; otherwise, it indicates that the diode is broken down and thermal runaway occurs.

[0023] The present invention has the following beneficial effects:

[0024] The testing method of the present invention can effectively evaluate and improve the safety and reliability of photovoltaic modules, reduce thermal runaway events, extend module life, and improve power generation efficiency by simulating and testing the working state of photovoltaic modules under hot spot conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 The present invention is a flow chart of the outdoor test method for thermal runaway of a photovoltaic junction box diode. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In a photovoltaic module, the reverse current of the bypass diode increases with the increase of temperature when it is reverse biased. If the diode is already in a high temperature environment when it changes to reverse bias, there may be a large reverse current, causing the diode temperature to rise further. When the temperature rise exceeds the heat dissipation capacity of the junction box, this phenomenon of temperature rise and leakage current causing the bypass diode to be damaged is called thermal runaway. Thermal runaway of the diode in the junction box of a photovoltaic module is a serious reliability issue. Thermal runaway will not only reduce the working efficiency of the module, but also accelerate the degradation and failure of the polymer packaging material, and even directly break down the diode after exceeding the leakage current limit. Therefore, thermal runaway of the diode in the junction box of a photovoltaic module is a complex phenomenon involving multiple factors, which needs to be prevented and controlled through rigorous testing and optimized design.

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Reference Figure 1 As shown, an embodiment of the present invention provides a method for outdoor testing of thermal runaway of a photovoltaic junction box diode, comprising the following steps:

[0031] Step S1: randomly select a battery cell from the sample assembly, and paste a thermocouple on the outer side of the junction box shell corresponding to the selected battery cell.

[0032] Step S2: according to the area of ​​the selected shielding battery sheet, prepare shielding sheets with corresponding shielding ratios of 100%, 90%, 80% ... 10%, and the area of ​​the shielding sheets decreases gradually by 10%.

[0033] Step S3: outdoor light intensity 800-1000W / m 2 The test was carried out in an environment with an ambient temperature of 20±2℃ and a wind speed less than 1m / s.

[0034] Step S4, use shielding sheets with shielding ratios of 100%, 90%, 80%...10%, and shield the battery cells for 30 minutes in a manner that the shielding ratio decreases in sequence by 10%. Record the temperature of the junction box shell after each shielding until the temperature of the junction box shell drops for the first time, and record the shielding ratio corresponding to the highest temperature of the junction box shell. At this time, the shielding ratio corresponding to the highest temperature of the junction box shell is the hot spot ratio of the battery cell.

[0035] Step S5: Under the condition of proportional shielding of the hot spots of the battery cell, shielding is continued for 1 hour, and the temperature of the junction box housing is recorded.

[0036] Step S6: After the shielding is completed, the shielding sheet is quickly removed to allow the power station string current or the component maximum power point current to flow quickly.

[0037] Step S7: After 1 minute, perform a performance test on the sample assembly and record the test results.

[0038] Step S8: Determine whether thermal runaway has occurred in the sample component according to the test results.

[0039] Example 1

[0040] In a specific embodiment, the sample component selects a power station operating component, and the photovoltaic junction box diode thermal runaway outdoor test method of this embodiment includes the following steps:

[0041] Step S1: randomly select a battery cell on the sample assembly, and stick a thermocouple on the outer side of the corresponding junction box shell of the selected shielding battery.

[0042] Step S2: according to the area of ​​the selected shielding battery sheet, prepare shielding sheets with corresponding shielding ratios of 100%, 90%, 80% ... 10%, and the area of ​​the shielding sheets decreases gradually by 10%.

[0043] Step S3: outdoor light intensity 800-1000W / m 2 The test was carried out in an environment with an ambient temperature of 20±2℃ and a wind speed less than 1m / s.

[0044] Step S4, use shielding sheets with shielding ratios of 100%, 90%, 80%...10%, and shield the battery cells for 30 minutes in a manner that the shielding ratio decreases in sequence by 10%. Record the temperature of the junction box shell after each shielding until the temperature of the junction box shell drops for the first time, and record the shielding ratio corresponding to the highest temperature of the junction box shell. At this time, the shielding ratio corresponding to the highest temperature of the junction box shell is the hot spot ratio of the battery cell.

[0045] Step S5: Under the condition of proportional shielding of the hot spots of the battery cell, shielding is continued for 1 hour, and the temperature of the junction box housing is recorded.

[0046] Step S6: After the shielding is completed, the shielding sheet is quickly removed to allow the power station string current or the component maximum power point current to flow quickly.

[0047] Step S7, after 1 minute, perform a performance test on the sample component and record the test results, specifically including: disconnecting the sample component under test from the string, using a multimeter to test the open circuit voltage of the sample component and record it as Uk1.

[0048] Step S8, determine whether thermal runaway has occurred in the sample component based on the test results. If the open circuit voltage Uk1 of the sample component is not less than 2 / 3Voc (nominal open circuit voltage of the component), it means that the diode is working normally; otherwise, it means that the diode is broken down and thermal runaway has occurred.

[0049] Example 2

[0050] In a specific embodiment, the sample assembly is an independent photovoltaic assembly. The photovoltaic junction box diode thermal runaway outdoor test method of this embodiment includes the following steps:

[0051] Step S1, install the sample assembly at the local optimal inclination angle, connect the sample assembly to the MPPT load, make the sample assembly at the maximum power point, and record the power W1 of the sample assembly; then randomly select a shielding cell and stick the thermocouple on the outer side of the corresponding junction box shell of the selected shielding cell.

[0052] Step S2: according to the area of ​​the selected shielding battery sheet, prepare shielding sheets with corresponding shielding ratios of 100%, 90%, 80% ... 10%, and the area of ​​the shielding sheets decreases gradually by 10%.

[0053] Step S3: outdoor light intensity 800-1000W / m 2 The test was carried out in an environment with an ambient temperature of 20±2℃ and a wind speed less than 1m / s.

[0054] Step S4, use shielding sheets with shielding ratios of 100%, 90%, 80%...10%, and shield the battery cells for 30 minutes in a manner that the shielding ratio decreases in sequence by 10%. Record the temperature of the junction box shell after each shielding until the temperature of the junction box shell drops for the first time, and record the shielding ratio corresponding to the highest temperature of the junction box shell. At this time, the shielding ratio corresponding to the highest temperature of the junction box shell is the hot spot ratio of the battery cell.

[0055] Step S5: Under the condition of proportional shielding of the hot spots of the battery cell, shielding is continued for 1 hour, and the temperature of the junction box housing is recorded.

[0056] Step S6: After the shielding is completed, the shielding sheet is quickly removed to allow the power station string current or the component maximum power point current to flow quickly;

[0057] Step S7: After 1 minute, perform a performance test on the sample component, observe the power value displayed by the MPPT load, and record the component power W2.

[0058] Step S8, judging whether thermal runaway has occurred in the sample component according to the test results. If the sample component power W2 is ≥ 2 / 3W1, it indicates that the diode is working normally; otherwise, it indicates that the diode is broken down and thermal runaway has occurred.

[0059] Compared with the prior art, the testing method of the present invention discloses at least the following beneficial effects:

[0060] 1. Improve safety: Through outdoor hot spot temperature testing, the thermal runaway resistance of the junction box diode can be effectively verified, thereby improving the safety of the power station components. By timely discovering and handling the thermal runaway problem of the diode, the service life of the photovoltaic module can be extended and the replacement cost can be reduced.

[0061] 2. Accurate detection: This solution can accurately determine the proportion of hot spots on the battery cell. By recording the maximum temperature of the junction box shell at different shading ratios, the specific shading ratio that causes the hot spot can be found.

[0062] 3. Real-time monitoring: Through a 1-hour continuous shielding test, the temperature changes of the junction box shell can be monitored in real time to ensure the working status of the diode under hot spot conditions.

[0063] 4. Fast response: After the shielding ends, the solution requires that the shielding sheet be removed quickly to allow current to flow through, in order to simulate the current changes under actual working conditions and evaluate the response speed of the diode.

[0064] 5. Performance evaluation: By testing the open circuit voltage of the power station components and the power of the independent photovoltaic components, it is possible to evaluate whether the diode is working properly and find out whether the diode is broken down in time.

[0065] 6. Prevention of thermal runaway: By simulating the hot spot phenomenon under actual working conditions, the occurrence of thermal runaway events can be prevented and reduced, protecting photovoltaic modules from damage.

[0066] 7. Easy maintenance: This solution provides a simple test method that can quickly determine the working status of the diode, making it easier for maintenance personnel to diagnose and repair faults. By ensuring the normal operation of the diode, the power generation efficiency of the photovoltaic module can be improved and energy output can be increased.

[0067] 8. Environmental adaptability: This solution is suitable for outdoor environments and can simulate the hot spot phenomenon under actual working conditions, thus improving the reliability and practicality of the test results.

[0068] The details not described in detail in the present invention are all conventional technical means known to those skilled in the art.

[0069] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0070] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A photovoltaic junction box diode thermal runaway outdoor test method, characterized in that: The following steps are involved: Step S1, randomly selecting a battery cell from the sample assembly, and pasting a thermocouple on the outer side of the junction box housing corresponding to the selected battery cell; Step S2, preparing shielding sheets with different shielding ratios; Step S3: Confirm that the test environment meets the outdoor light intensity of 800-1000W / m 2 , temperature 20±2℃, wind speed less than 1m / s; Step S4, selecting shielding sheets in order from large to small according to the shielding ratio to shield the shielded battery cell for a preset time, recording the temperature of the junction box shell after each shielding, until the temperature of the junction box shell drops for the first time, and recording the shielding ratio corresponding to the highest temperature at this time as the battery cell hot spot ratio; Step S5, under the condition of proportional shielding of the hot spots of the battery cell, shielding is continued for 1 hour, and the temperature of the junction box housing is recorded; Step S6: After the shielding is completed, the shielding sheet is quickly removed to allow the power station string current or the component maximum power point current to flow quickly; Step S7: After 1 minute, perform a performance test on the sample assembly and record the test results; Step S8: Determine whether thermal runaway has occurred in the sample component according to the test results.

2. The photovoltaic junction box diode thermal runaway outdoor test method according to claim 1, characterized in that: In the step S2, a plurality of shielding sheets are prepared, with corresponding shielding ratios decreasing in steps of 10% from 100% to 10%, according to the area of ​​the selected shielding cell sheet.

3. The photovoltaic junction box diode thermal runaway outdoor test method according to claim 2, characterized in that: In the step S4, the shielding sheet is used to shield the shielding cell sheet for a preset time in a manner where the shielding ratio decreases in sequence by 10%.

4. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 1, characterized in that: In the step S4, the shielding cell is shielded for a preset time, and each shielding time is 30 minutes.

5. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 1, characterized in that: The sample component is selected from a power station operating component. When the performance test is performed on the sample component in step S7, the connection between the sample component under test and the string is disconnected, and the open circuit voltage of the sample component is tested with a multimeter and recorded as Uk1.

6. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 5, characterized in that: In step S8, the open circuit voltage Uk1 of the sample assembly should be no less than 2 / 3Voc, indicating that the diode is working normally; otherwise, it means that the diode is broken down and thermal runaway occurs.

7. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 1, characterized in that: The sample assembly is an independent photovoltaic assembly. In step S1, the assembly is installed at the local optimal inclination angle, the sample assembly is connected to the MPPT load, the sample assembly is at the maximum power point, and the power W1 of the sample assembly is recorded; Then, a shielded battery cell is randomly selected, and a thermocouple is pasted on the outer side of the corresponding junction box shell of the selected shielded battery cell.

8. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 7, characterized in that: When the performance test of the sample component is performed in step S7, the power value displayed by the MPPT load is observed and the component power W2 is recorded.

9. The photovoltaic junction box diode thermal runaway outdoor testing method according to claim 8, characterized in that: In step S8, the sample component power W2 should be no less than 2 / 3W1, indicating that the diode is working normally; otherwise, it means that the diode is broken down and thermal runaway occurs.

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