A method and system for analyzing temperature rise distribution of parallel photovoltaic modules

Abstract

The application discloses a temperature rise distribution analysis method and system of a parallel photovoltaic module, wherein the analysis method comprises the following steps: acquiring the appearance state of each cell in the parallel photovoltaic module; determining the performance state of each cell according to the appearance state of the cell; and determining the additional temperature rise of each cell in the parallel photovoltaic module by using an equivalent circuit model of the parallel photovoltaic module according to the performance state of each cell. The application can evaluate the additional temperature rise of each cell in the parallel photovoltaic module.

Description

Technical Field

[0001] This invention relates to a method and system for analyzing the temperature rise distribution of parallel photovoltaic modules, belonging to the field of photovoltaic power generation technology. Background Technology

[0002] With the development of new energy sources, more and more photovoltaic (PV) modules are being used in daily life, making research on their reliability increasingly important. When cells are interconnected to form modules, mismatch losses occur due to differences in cell performance, and the losses caused by mismatch in PV modules cannot be ignored. Parallel mismatch, in particular, is caused by voltage mismatch between parallel modules, which can lead to reverse current flow. Research on PV module temperature has found that mismatch in the PV array caused by factors such as cell defects and malfunctions can further increase cell temperature. High temperatures not only reduce cell output but can also cause irreversible damage to the cells in severe cases, greatly impairing the safe and efficient operation and maintenance of PV modules.

[0003] Regarding the impact of parallel mismatch in photovoltaic modules, the mismatch is generally caused by voltage differences between parallel modules, resulting in forward bias and reverse current flowing into the branches, leading to temperature increases and affecting overall power generation. Therefore, it is necessary to calculate the temperature rise caused by parallel mismatch. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and system for analyzing the temperature rise distribution of parallel photovoltaic modules, which can assess the additional temperature rise of each cell in the parallel photovoltaic module.

[0005] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0006] On one hand, the present invention provides a method for analyzing the temperature rise distribution of parallel photovoltaic modules, comprising the following steps:

[0007] Obtain the appearance status of each cell in a parallel photovoltaic module;

[0008] Determine the performance status of each battery based on its appearance;

[0009] Based on the performance status of each battery, the additional temperature rise of each battery in the parallel photovoltaic module is determined using the equivalent circuit model of the parallel photovoltaic module.

[0010] Furthermore, the equivalent circuit model is established based on the linear source characteristics of the parallel photovoltaic modules in the working state;

[0011] Each branch of the parallel photovoltaic module includes several cells connected in series.

[0012] Furthermore, determining the performance state of each battery based on its appearance includes:

[0013] When the battery's appearance is undamaged, its performance is good;

[0014] In a preferred embodiment, determining the performance state of each battery based on its appearance includes: when the battery has microcrack defects, the battery performance decreases and the heat distribution is uneven.

[0015] In a preferred embodiment, determining the performance state of each battery based on its appearance includes: when the battery has surface defects, the battery performance decreases and the heat distribution is uniform.

[0016] In a preferred embodiment, determining the performance state of each battery based on its appearance includes: when the battery's appearance is obstructed, the battery performance decreases and the heat distribution is uniform.

[0017] Furthermore, the battery performance status includes: good and degraded;

[0018] Furthermore, determining the additional temperature rise of each cell in the parallel photovoltaic module using the equivalent circuit model of the parallel photovoltaic module based on the performance state of each cell includes:

[0019] If the performance of each cell in the branch of the parallel photovoltaic module is good, then the additional temperature rise of each cell in the branch is 0.

[0020] In a preferred embodiment, if the performance of each cell in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch is determined based on the cell's current-voltage characteristics.

[0021] In a preferred embodiment, if the performance of some cells in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch is determined based on the current-voltage characteristics of the main circuit, the branch circuit, and the cells.

[0022] Furthermore, if the performance of each cell in a branch of the parallel photovoltaic module degrades, the determination of the additional temperature rise of each cell in the branch based on the cell's current-voltage characteristics includes:

[0023] When the performance of each battery in the branch decreases, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch, and the voltage of each battery is determined according to the voltage of the branch.

[0024] Based on the volt-ampere characteristics of the main circuit, branch circuit and battery, the voltage and current of each battery are determined. When the current of a battery is less than 0, the performance of the battery deteriorates. Let the absolute value of the current of the battery with deteriorated performance be the reverse current of the battery with deteriorated performance.

[0025] Based on a preset temperature rise strategy, the additional temperature rise of each degraded battery is determined according to its voltage, reverse current, and appearance condition.

[0026] Furthermore, if the performance of some cells in a branch of a parallel photovoltaic module degrades, determining the additional temperature rise of each cell in the branch based on the current-voltage characteristics of the main circuit, branch circuit, and cells includes:

[0027] When the performance of some cells in the middle of a branch of a parallel photovoltaic module degrades, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch.

[0028] Based on the volt-ampere characteristics of the main circuit, branch circuit and battery, determine the voltage and current of each battery, and let the absolute value of the battery current be the reverse current of the battery.

[0029] The additional temperature rise of a high-performance battery is set to 0, and based on a preset temperature rise strategy, the additional temperature rise of each degraded battery is determined according to its voltage, reverse current, and appearance condition.

[0030] Furthermore, determining the voltage and current of each degraded battery based on the volt-ampere characteristics of the main circuit, branch circuit, and battery includes:

[0031] Based on the fact that the voltage and current of the battery conform to the volt-ampere characteristics of the battery, and according to the fact that the current of the main circuit is the sum of the currents of each branch, the voltage of the branch is the sum of the voltages of each battery, and the current of the branch is equal to the current of each battery in the branch, the voltage and current of each battery are determined.

[0032] Furthermore, the temperature rise strategy includes:

[0033] Obtain environmental and battery parameters for parallel photovoltaic module operation;

[0034] The heat flow rate of each battery is determined by multiplying the voltage and reverse current of the battery with degraded performance by a preset coefficient for converting reverse current into heat energy.

[0035] The temperature of each battery is determined using environmental parameters, battery parameters, and the heat flow received by the battery.

[0036] The additional temperature rise of each degraded battery is obtained by subtracting the temperature of the good-performing battery from the temperature of the degraded battery in the same branch.

[0037] The additional temperature rise of each high-performance battery is 0;

[0038] Among them, batteries with different appearances have different coefficients for converting reverse current into heat energy.

[0039] Furthermore, determining the temperature of each battery using environmental parameters, battery parameters, and battery heat flow includes:

[0040] P=αηS+kI re V f

[0041]

[0042] A1·T PV 4 +B1·T PV +C1=0

[0043] In the formula, P is the heat flux received by the battery, α is the battery absorptivity, η is the battery photoelectric conversion efficiency, S is the irradiance received by the battery during operation, k is the coefficient for converting reverse current into heat energy, and I... re V is the reverse current of the battery. f Where A1, B1, and C1 are the battery voltages, σ is the Stefan-Boltzmann constant, and ε is the temperature coefficient. g ε b The emissivity of the front and back of the battery, respectively, h g,air h g,air The convective heat transfer coefficients between the front and back of the battery and the air are respectively, P is the heat flux received by the battery, A is the battery area, and T is the heat transfer coefficient between the front and back of the battery and the air. a For ambient temperature, T sky For sky temperature, T gro For ground temperature, ε sky For sky emissivity, ε gro For ground emissivity, T PV This refers to the battery temperature.

[0044] On the other hand, the present invention provides a temperature rise distribution analysis system for parallel photovoltaic modules, comprising:

[0045] The acquisition module is used to acquire the appearance status of each cell in the parallel photovoltaic module.

[0046] The determination module is used to determine the performance status of each battery based on its appearance.

[0047] The evaluation module is used to determine the additional temperature rise of each cell in the parallel photovoltaic module based on the performance status of each cell and using the equivalent circuit model of the parallel photovoltaic module.

[0048] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0049] Based on the appearance of each battery, this invention determines the additional temperature rise of undamaged batteries and batteries with different defects when operating in parallel photovoltaic modules. Attached Figure Description

[0050] Figure 1 The diagram shown is a flowchart of an embodiment of the temperature rise distribution analysis method for parallel photovoltaic modules of the present invention.

[0051] Figure 2The diagram shown is a circuit diagram of one embodiment of the single-cell battery model of the present invention;

[0052] Figure 3 The diagram shown is a schematic representation of an embodiment of the equivalent circuit model of the present invention.

[0053] Figure 4 The figure shown is the current-voltage characteristic curve of one embodiment of the single-cell battery model of the present invention;

[0054] Figure 5 The diagram shown is a structural schematic of one embodiment of the battery with cracks according to the present invention.

[0055] Figure 6 The figure shows the current-voltage characteristic curve of a single-cell battery model in Embodiment 4 of the present invention. Detailed Implementation

[0056] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0057] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0059] Example 1

[0060] This embodiment introduces a method for analyzing the temperature rise distribution of parallel photovoltaic modules.

[0061] The method for analyzing the temperature rise distribution of parallel photovoltaic modules in this embodiment includes:

[0062] S1 acquires the appearance status of each cell in the parallel photovoltaic module;

[0063] S2 determines the performance status of each battery based on its appearance.

[0064] Based on the performance status of each battery, S3 uses the equivalent circuit model of the parallel photovoltaic module to determine the additional temperature rise of each battery in the parallel photovoltaic module.

[0065] Based on the appearance of each battery, this invention determines the additional temperature rise of undamaged batteries and batteries with different defects when operating in parallel photovoltaic modules.

[0066] Example 2

[0067] Based on Example 1, this example details a method for analyzing the temperature rise distribution of parallel photovoltaic modules:

[0068] S1 acquires the appearance status of each cell in the parallel photovoltaic module.

[0069] When in use, the appearance of the battery includes undamaged, micro-cracked defects, surface defects, and surface obstruction.

[0070] S2 determines the performance status of each battery based on its appearance.

[0071] When in use, the battery's appearance may include the following:

[0072] State 1: When the battery is undamaged, its performance is good and the heat distribution is uniform.

[0073] State 2: When the battery has microcracks or defects on its surface, the battery performance deteriorates and the heat distribution of the battery becomes uneven.

[0074] State 3: When the battery has surface defects, the battery performance decreases and the heat distribution of the battery becomes more uniform.

[0075] State 4: When the battery's appearance is obstructed, the battery performance decreases and the heat distribution of the battery becomes more uniform.

[0076] Based on the performance status of each battery, S3 uses the equivalent circuit model of the parallel photovoltaic module to determine the additional temperature rise of each battery in the parallel photovoltaic module.

[0077] When applied, step S3 includes the following scenarios:

[0078] Scenario 1: If the performance of each cell in the branch of the parallel photovoltaic module is good, then the additional temperature rise of each cell in the branch is 0.

[0079] Scenario 2: If the performance of each cell in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch is determined based on the cell's current-voltage characteristics.

[0080] Specifically, the processing steps for Scenario 2 are as follows:

[0081] S321 When the performance of each battery in the branch decreases, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch, and the voltage of each battery is determined according to the voltage of the branch.

[0082] Those skilled in the art will use the preset voltage value of the parallel photovoltaic modules as the voltage of the branch to which the performance degradation battery belongs, and determine the voltage of each performance degradation battery based on the voltage of the branch to which the performance degradation battery belongs.

[0083] S322 determines the voltage and current of each battery based on the volt-ampere characteristics of the main circuit, branch circuit and battery. When the current of a battery is less than 0, the performance of the battery deteriorates. The absolute value of the current of the battery with deteriorated performance is set as the reverse current of the battery with deteriorated performance.

[0084] Among them, the voltage and current of each degraded battery conform to its volt-ampere characteristics, that is, the voltage and current of the battery with microcrack defects conform to the volt-ampere characteristics of the battery with microcrack defects, the voltage and current of the battery with surface defects conform to the volt-ampere characteristics of the battery with surface defects, and the voltage and current of the battery with surface shielding conform to the volt-ampere characteristics of the battery with surface shielding.

[0085] S323 determines the additional temperature rise of each degraded battery based on a preset temperature rise strategy, taking into account the voltage, reverse current, and appearance of the degraded battery.

[0086] The temperature rise strategy for scenario 2 includes the following:

[0087] Obtain environmental and battery parameters for parallel photovoltaic module operation;

[0088] The heat flow rate of each degraded battery is determined by multiplying the voltage, reverse current, and a preset coefficient for converting reverse current into heat energy.

[0089] The temperature at which each battery's performance degrades is determined by using environmental parameters, battery parameters, and the heat flow received by the battery.

[0090] The temperature of the degraded battery is subtracted from the temperature of the good-performing batteries in other branches to obtain the additional temperature rise of each degraded battery.

[0091] Among them, batteries with different appearances have different coefficients for converting reverse current into heat energy.

[0092] Scenario 3: If the performance of some cells in the branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch is determined based on the current-voltage characteristics of the main circuit, the branch circuit, and the cells.

[0093] Specifically, the processing steps for scenario 3 are as follows:

[0094] S331 When the performance of some cells in the middle of the branch of the parallel photovoltaic module deteriorates, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch.

[0095] S332 determines the voltage and current of each battery based on the volt-ampere characteristics of the main circuit, branch circuit and battery. When the current of a battery is less than 0, the performance of the battery deteriorates. The absolute value of the current of the battery with deteriorated performance is set as the reverse current of the battery with deteriorated performance.

[0096] Since the current of the battery whose performance has degraded is negative at this time, let the absolute value of the current of the battery whose performance has degraded be its reverse current.

[0097] The volt-ampere characteristics of the main circuit are as follows: the current in the main circuit is the sum of the currents in each branch circuit, and the voltage in the main circuit is equal to the voltage in each branch circuit.

[0098] The volt-ampere characteristics of the branch are: the voltage of the branch is the sum of the voltages of each battery, and the current of the branch is equal to the current of each battery in the branch.

[0099] The voltage and current characteristics of a battery are as follows: the voltage and current of a battery with microcrack defects conform to the voltage and current characteristics of a battery with microcrack defects; the voltage and current of a battery with surface defects conform to the voltage and current characteristics of a battery with surface obstruction conform to the voltage and current characteristics of a battery with surface obstruction; and the voltage and current of a battery without damage conform to the voltage and current characteristics of a battery without damage.

[0100] S333 ensures that the additional temperature rise of a high-performance battery is 0, and determines the additional temperature rise of each battery based on the voltage, reverse current, and appearance condition of the battery with degraded performance, according to a preset temperature rise strategy.

[0101] The temperature rise strategy for scenario 3 includes the following:

[0102] a. Obtain environmental parameters and battery parameters for parallel photovoltaic module operation.

[0103] b. Determine the heat flow rate of each degraded battery by multiplying the voltage, reverse current, and a preset coefficient for converting reverse current into heat energy. Specifically, this includes the following formula:

[0104] P=αηS+kI re V f ;

[0105] In the formula, P is the heat flux received by the battery, α is the battery absorptivity, η is the battery photoelectric conversion efficiency, S is the irradiance received by the battery during operation, k is the coefficient for converting reverse current into heat energy, and I... re V is the reverse current of the battery. f This refers to the battery voltage.

[0106] Batteries with different appearances have different coefficients for converting reverse current into heat energy. Since the coefficient for converting reverse current into heat energy of a damage-free battery is 0, the reverse current of a damage-free battery does not need to be considered.

[0107] In addition, those skilled in the art generally will Damage-free battery The heat flow received is considered to be 0.

[0108] c. The temperature of each battery is determined using environmental parameters, battery parameters, and the heat flow received by the battery, specifically including the following formula;

[0109]

[0110] A1·T PV 4 +B1·T PV +C1=0

[0111] In the formula, P is the heat flux received by the battery, A1, B1, and C1 are temperature coefficients, σ ​​is the Stefan-Boltzmann constant, and ε is the heat flux received by the battery. g ε b The emissivity of the front and back of the battery, respectively, h g,air h g,air The convective heat transfer coefficients between the front and back of the battery and the air are respectively, P is the heat flux received by the battery, A is the battery area, and T is the heat transfer coefficient between the front and back of the battery and the air. a For ambient temperature, T sky For sky temperature, T gro For ground temperature, ε sky For sky emissivity, ε gro For ground emissivity, T PV This refers to the battery temperature.

[0112] The additional temperature rise of each degraded battery is obtained by subtracting its temperature from the temperature of the good-performing battery in the same branch.

[0113] In addition, those skilled in the art generally consider the coefficient of converting reverse current of a non-destructive battery into heat energy as 0, and the additional temperature rise of each high-performance battery as 0.

[0114] Example 3

[0115] Based on Example 1 or 2, this example details the method for constructing the equivalent circuit model.

[0116] (1) Based on the electrical characteristics of photovoltaic cells, a model of a single cell is established, referring to... Figure 1 .

[0117] In this embodiment, the single-cell battery model is a dual-diode model, which involves connecting the photocurrent source, the first diode, and the second diode in parallel, along with the equivalent parallel resistance, and then connecting them in series with the equivalent series resistance. (Refer to...) Figure 2 .

[0118] Because different appearance conditions have different effects on the output capability of photovoltaic cells, cells with different appearance conditions have different volt-ampere characteristics: the voltage and current of cells with microcrack defects conform to the volt-ampere characteristics of cells with microcrack defects, the voltage and current of cells with surface defects conform to the volt-ampere characteristics of cells with surface defects, the voltage and current of cells with surface shading conform to the volt-ampere characteristics of cells with surface shading, and the voltage and current of undamaged cells conform to the volt-ampere characteristics of undamaged cells.

[0119] In application, those skilled in the art can adjust the current of the photogenerated current source, the reference illumination, the dark saturation current and quality factor of the first and second diodes, the equivalent parallel resistance, and the equivalent series resistance to adjust the error between the current-voltage characteristics of the single-cell model and the actual measured value of the photovoltaic cell. When the error is less than the preset error, the current single-cell model is determined to be the optimal model.

[0120] The current-voltage characteristics of a single-cell battery model include the following formula:

[0121]

[0122] In the formula, I is the battery current, and R... s R is the equivalent series resistance. sh For the equivalent parallel resistance, I ph For the current of the photogenerated current source, I s1 I is the saturation current of the first diode. s2 Let n1 be the saturation current of the second diode, n2 be the quality factor of the first diode, n3 be the quality factor of the second diode, q be the elementary charge of an electron, and k be the saturation current of the second diode. b V is the Boltzmann constant. f This refers to the battery voltage.

[0123] Those skilled in the art can plot the current-voltage characteristic curves of batteries with different appearance states based on the model of a single battery cell, for reference. Figure 4 .

[0124] (2) Based on the number of branches in the parallel photovoltaic module, the number of photovoltaic cells in each branch, and the linear source characteristics of the parallel photovoltaic module under working conditions, the equivalent circuit model of the parallel photovoltaic module is constructed using the model of a single cell.

[0125] In this embodiment, each photovoltaic cell in the parallel photovoltaic module has a bypass diode, but there are no blocking diodes on the branches. (Refer to...) Figure 3 Furthermore, in the effective circuit model of this embodiment, the number of parallel branches is n, and the number of single batteries connected in series in each branch is m.

[0126] Parallel failure occurs when voltage mismatch in parallel branches causes the high-voltage side to exert pressure on the low-voltage side, resulting in a reverse current flowing into the photovoltaic cell in the low-voltage branch. Within a preset error range, except for cells whose performance is significantly degraded due to appearance, all other cells are considered to be in good performance.

[0127] 1. For a branch containing photovoltaic cells that are all in perfect physical condition, the branch voltage is considered to be the superposition of the voltages of m identical photovoltaic cells under equal current. The normal branch voltage-current characteristic in this case includes the following formula:

[0128]

[0129] In the formula, I norm For the current in a normal branch, I ph For the current of the photogenerated current source, I s1 I is the saturation current of the first diode. s2 The saturation current of the second diode is q, where q is the elementary charge of the electron, and k is the saturation current of the second diode. b V is the Boltzmann constant. norm The voltage of the normal branch is given by R, where I is the battery current and R is the voltage of the normal branch. s R is the equivalent series resistance. sh The equivalent parallel resistance is n1, where n1 is the quality factor of the first diode and n2 is the quality factor of the second diode.

[0130] 2. For a branch containing a photovoltaic cell with degraded performance (a) and a photovoltaic cell with good performance (ma), the branch voltage is considered as the sum of the voltages of the good-performing (ma) photovoltaic cells and the voltage of the degraded (a) cell under equal current. The current-voltage characteristic of this mismatched branch includes the following formula:

[0131]

[0132] In the formula, I de For the current in the mismatched branch, V de I is the voltage of the mismatched branch. phde It is the current of the photogenerated current source in the mismatched branch, I s1de I is the saturation current of the first diode in the mismatched branch. s2de n is the saturation current of the second diode in the mismatched branch. 1de n is the quality factor of the first diode in the mismatched branch. 2deR is the quality factor of the second diode in the mismatched branch. sde R is the equivalent series resistance of the mismatched branch. shde This is the equivalent parallel resistance of the mismatched branch.

[0133] 3. Determining the magnitude of the reverse current in the mismatched branch when there is a parallel mismatch:

[0134] For a branch containing one degraded photovoltaic cell and one good photovoltaic cell, when reverse current occurs due to parallel mismatch, the current-voltage characteristics of the branch and the degraded cell are determined through the aforementioned steps. The total voltage of the branch is the preset voltage V of the photovoltaic array. PV V PV If the current obtained by substituting into equation (3) is negative, let its absolute value be the magnitude of the reverse current. Substituting the reverse current into equation (1) will give the forward bias voltage of the single cell on that branch.

[0135] Example 4

[0136] Based on Example 1 or 2, this example details the temperature rise distribution of parallel photovoltaic modules.

[0137] For batteries with surface defects or surface shading, the reverse current flows through the battery evenly, resulting in the increased heat being evenly distributed across the battery.

[0138] For batteries with microcrack defects, reverse current is generally concentrated at the crack, causing uneven distribution of increased heat across the battery. (Refer to...) Figure 5 In application, the area of ​​microcracks is generally less than 1cm × (1-10)cm.

[0139] The photovoltaic cell used in this example is a Trina Solar TSM-DD06M.05(II) crystalline silicon monocrystalline module. Specific performance parameters are shown in Table 1.

[0140] Table 1 Performance parameters of crystalline silicon solar cells

[0141]

[0142] In this embodiment, the parallel photovoltaic modules are installed on a rooftop concrete floor. The ambient temperature is 27.60℃, the wind speed is 1.18m / s, the average temperature of the rooftop concrete floor is 32℃, and the sky temperature is T. sky The temperature was 14.85℃, and the solar radiation intensity received on the upper surface of the parallel photovoltaic module was 1000W / m. 2 The absorptivity α of the component's front side is 0.9, and the emissivity ε of the glass cover is... g The emissivity ε of the module backsheet is 0.92. b The emissivity ε of the roof concrete floor is 0.88. groThe convective heat transfer coefficient h between the glass cover and the air is 0.95. g,air 10.20 W / (m 2 ·K), the convective heat transfer coefficient h between the component backplate and the air. b,air It is 5.70 W / (m 2 ·K). Then, when the battery is operating normally, the heat flow it experiences is:

[0143] P=αηS+kI re V f =0.9 × 0.18 × 1000 = 162 W / m 2 (4)

[0144] Substitute the above parameters into equation (5):

[0145]

[0146] The temperature of the crystalline silicon cell is determined using equation (6):

[0147] A1·T PV 4 +B1·T PV +C1=0 (6)

[0148] In summary, the normal operating temperature of a crystalline silicon solar cell is 49.62℃.

[0149] In this embodiment, the parallel photovoltaic module consists of two identical crystalline silicon cells connected in parallel. One of the crystalline silicon cells is completely shaded, resulting in a performance degradation, while the other operates normally.

[0150] Using the trained equivalent circuit model, the current-voltage characteristics of the two crystalline silicon solar cells were determined, with reference to... Figure 6 .

[0151] In this embodiment, when the battery is fully charged, the reverse current flowing into the completely shielded crystalline silicon cell is at its maximum. The preset voltage is set to the voltage in the open circuit state, resulting in a reverse current of 2.59A and a forward bias voltage of 39.6V for the completely shielded crystalline silicon cell.

[0152] Given that the battery is in a shaded state, the thermal energy conversion coefficient k of the battery is 0.95. Therefore, the heat flux density generated by the module under parallel mismatch is...

[0153] P=αηS+kI re V f =0.92×2.59×39.6=58.00W / m 2 (7)

[0154] Substituting the obtained heat flow to the battery into the above formula, the temperature of the completely shaded crystalline silicon battery can be obtained as 51.58℃.

[0155] Comparing the two temperatures, it can be seen that the temperature rise of the crystalline silicon cell in this embodiment, which is completely shielded, is about 2°C.

[0156] Example 5

[0157] This embodiment introduces a temperature rise distribution analysis system for parallel photovoltaic modules.

[0158] The temperature rise distribution analysis system for parallel photovoltaic modules implemented in this paper includes:

[0159] The acquisition module is used to acquire the appearance status of each cell in the parallel photovoltaic module.

[0160] The determination module is used to determine the performance status of each battery based on its appearance.

[0161] The evaluation module is used to determine the additional temperature rise of each cell in the parallel photovoltaic module based on the performance status of each cell and using the equivalent circuit model of the parallel photovoltaic module.

[0162] The specific implementation of each of the above functional modules is described in the temperature rise distribution analysis method of parallel photovoltaic modules as described in Examples 1-4.

[0163] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0164] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0165] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0166] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0167] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for analyzing the temperature rise distribution of parallel photovoltaic modules, characterized in that, include: Obtain the appearance status of each cell in a parallel photovoltaic module; Determine the performance status of each battery based on its appearance; Based on the performance status of each battery, the additional temperature rise of each battery in the parallel photovoltaic module is determined using the equivalent circuit model of the parallel photovoltaic module. The step of determining the additional temperature rise of each cell in the parallel photovoltaic module using the equivalent circuit model of the parallel photovoltaic module based on the performance status of each cell includes: If the performance of some cells in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in that branch is determined based on the current-voltage characteristics of the main circuit, the branch circuit, and the cells. Wherein, if the performance of some cells in a branch of a parallel photovoltaic module degrades, determining the additional temperature rise of each cell in the branch based on the current-voltage characteristics of the main circuit, branch circuit, and cells includes: When the performance of some cells in a branch of a parallel photovoltaic module degrades, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch. Based on the volt-ampere characteristics of the main circuit, branch circuit and battery, the voltage and current of each battery are determined. When the current of a battery is less than 0, the performance of the battery deteriorates. Let the absolute value of the current of the battery with deteriorated performance be the reverse current of the battery with deteriorated performance. The additional temperature rise of the high-performance battery is set to 0, and the additional temperature rise of each degraded battery is determined based on the voltage, reverse current and appearance of the degraded battery according to the preset temperature rise strategy. The determination of the voltage and current of each battery based on the volt-ampere characteristics of the main circuit, branch circuit, and battery includes: Based on the fact that the voltage and current of the battery conform to the volt-ampere characteristics of the battery, and according to the fact that the current of the main circuit is the sum of the currents of each branch, the voltage of the branch is the sum of the voltages of each battery, and the current of the branch is equal to the current of each battery in the branch, the voltage and current of each battery are determined. The temperature rise strategy includes: Obtain environmental and battery parameters for parallel photovoltaic module operation; The heat flow rate of each battery is determined by multiplying the battery voltage, reverse current, and a preset coefficient for converting reverse current into heat energy. The temperature of each battery is determined using environmental parameters, battery parameters, and the heat flow received by the battery. Subtract the temperature of the degraded battery from the temperature of the good-performing battery to obtain the additional temperature rise of each degraded battery; Among them, batteries with different appearances have different coefficients for converting reverse current into heat energy.

2. The method for analyzing the temperature rise distribution of parallel photovoltaic modules according to claim 1, characterized in that, The equivalent circuit model is established based on the linear source characteristics of the parallel photovoltaic modules in operation. Each branch of the parallel photovoltaic module includes several cells connected in series.

3. The method for analyzing the temperature rise distribution of parallel photovoltaic modules according to claim 1 or 2, characterized in that, Determining the performance status of each battery based on its appearance includes: When the battery's appearance is undamaged, its performance is good; And / or, when the battery has microcrack defects on its surface, the battery performance deteriorates and the heat distribution becomes uneven; And / or, when the battery has surface defects, battery performance deteriorates and heat distribution becomes uneven; And / or, when the battery's appearance has surface obstruction, battery performance degrades and heat distribution becomes more uniform.

4. The method for analyzing the temperature rise distribution of parallel photovoltaic modules according to claim 1, characterized in that, The battery performance status includes: good and deteriorated; The step of determining the additional temperature rise of each cell in the parallel photovoltaic module using the equivalent circuit model of the parallel photovoltaic module based on the performance status of each cell also includes: If the performance of each cell in the branch of the parallel photovoltaic module is good, then the additional temperature rise of each cell in the branch is 0. If the performance of each cell in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch is determined based on the cell's current-voltage characteristics.

5. The method for analyzing the temperature rise distribution of parallel photovoltaic modules according to claim 4, characterized in that, If the performance of each cell in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in the branch, determined based on the cell's current-voltage characteristics, includes: When the performance of each battery in the branch decreases, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch, and the voltage of each battery is determined according to the voltage of the branch. Based on the battery's volt-ampere characteristics, the battery current is determined according to the battery voltage, and the absolute value of the battery current is set as the battery's reverse current. Based on a preset temperature rise strategy, the additional temperature rise of each degraded battery is determined according to its voltage, reverse current, and appearance condition.

6. The method for analyzing the temperature rise distribution of parallel photovoltaic modules according to claim 1, characterized in that, The process of determining the temperature of each battery using environmental parameters, battery parameters, and battery heat flow includes: In the formula, The heat flow received by the battery. For battery absorption rate, For battery photoelectric conversion efficiency, Where is the radiation intensity received by the battery during operation, and k is the coefficient for converting reverse current into heat energy. This is the reverse current of the battery. This refers to the battery voltage. , , All are temperature coefficients. It is the Stefan-Boltzmann constant. The emissivity is shown for the front and back of the battery, respectively. These are the convective heat transfer coefficients between the front and back of the battery and the air, respectively. The heat flow received by the battery. For battery area, For ambient temperature, For the sky temperature, Ground temperature, For sky emission rate, For ground-based emission rate, This refers to the battery temperature.

7. A temperature rise distribution analysis system for parallel photovoltaic modules, characterized in that, include: The acquisition module is used to acquire the appearance status of each cell in the parallel photovoltaic module. The determination module is used to determine the performance status of each battery based on its appearance. The evaluation module is used to determine the additional temperature rise of each cell in the parallel photovoltaic module based on the performance status of each cell and using the equivalent circuit model of the parallel photovoltaic module. The step of determining the additional temperature rise of each cell in the parallel photovoltaic module using the equivalent circuit model of the parallel photovoltaic module based on the performance status of each cell includes: If the performance of some cells in a branch of a parallel photovoltaic module degrades, the additional temperature rise of each cell in that branch is determined based on the current-voltage characteristics of the main circuit, the branch circuit, and the cells. Wherein, if the performance of some cells in a branch of a parallel photovoltaic module degrades, determining the additional temperature rise of each cell in the branch based on the current-voltage characteristics of the main circuit, branch circuit, and cells includes: When the performance of some cells in a branch of a parallel photovoltaic module degrades, the preset voltage value of the parallel photovoltaic module is used as the voltage of the branch. Based on the volt-ampere characteristics of the main circuit, branch circuit and battery, the voltage and current of each battery are determined. When the current of a battery is less than 0, the performance of the battery deteriorates. Let the absolute value of the current of the battery with deteriorated performance be the reverse current of the battery with deteriorated performance. The additional temperature rise of the high-performance battery is set to 0, and the additional temperature rise of each degraded battery is determined based on the voltage, reverse current and appearance of the degraded battery according to the preset temperature rise strategy. The determination of the voltage and current of each battery based on the volt-ampere characteristics of the main circuit, branch circuit, and battery includes: Based on the fact that the voltage and current of the battery conform to the volt-ampere characteristics of the battery, and according to the fact that the current of the main circuit is the sum of the currents of each branch, the voltage of the branch is the sum of the voltages of each battery, and the current of the branch is equal to the current of each battery in the branch, the voltage and current of each battery are determined. The temperature rise strategy includes: Obtain environmental and battery parameters for parallel photovoltaic module operation; The heat flow rate of each battery is determined by multiplying the battery voltage, reverse current, and a preset coefficient for converting reverse current into heat energy. The temperature of each battery is determined using environmental parameters, battery parameters, and the heat flow received by the battery. Subtract the temperature of the degraded battery from the temperature of the good-performing battery to obtain the additional temperature rise of each degraded battery; Among them, batteries with different appearances have different coefficients for converting reverse current into heat energy.

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