A method for calculating the parameters of a single-diode model of a photovoltaic module

Abstract

The present invention discloses a method for calculating the parameters of a single-diode model of a photovoltaic module. First, according to the equivalent circuit of the single-diode model, a model under standard test conditions is obtained, and a model under any test environment is obtained by correlating the model parameters and the test environment parameters. Then, the performance parameters of the photovoltaic module are obtained, including short-circuit current, open-circuit voltage, maximum power point current, maximum power point voltage, short-circuit current temperature coefficient, and open-circuit voltage temperature coefficient, and the model parameters are obtained by constructing and solving a system of equations. The present invention does not require a complete I-V curve and can achieve modeling and parameter identification of the model only with the product description information provided by the component manufacturer, so it has strong guiding significance for simulation and production practice.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic module system calculations, and specifically refers to a method for calculating the parameters of a single-diode model of a photovoltaic module. Background Art

[0002] In order to address global warming and achieve the "dual carbon" goal, a large number of photovoltaic power generation systems have been put into operation. As a component of the photovoltaic system, the modeling and parameter identification of photovoltaic cells are of great significance for conducting research on battery structure optimization, operating state prediction, etc.

[0003] The models used to measure the performance characteristics of photovoltaic modules include single-diode models, double-diode models, triple-diode models, etc. Among these models, the single-diode model has been widely used due to its simple model, strong interpretability, and good applicability. Currently, although certain achievements have been made in the parameter identification of the single-diode model, most rely on the sampling points of the I-V curve, and there are still challenges in completing parameter identification only using the information provided by the manufacturer. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for calculating the parameters of a single-diode model of a photovoltaic module, which can obtain the numerical values of the parameters of the single-diode model of the photovoltaic module with only very little information of the product, and has important guiding significance for simulation and production practice.

[0005] The above object of the present invention is achieved through the following technical solutions: A method for calculating the parameters of a single-diode model of a photovoltaic module, characterized in that the calculation method includes the following steps:

[0006] Step 1: Establish a single-diode model under any test conditions;

[0007] Step 2: Obtain the product information of the photovoltaic module;

[0008] Step 3: Establish and solve a system of equations to obtain the numerical values of the parameters of the model.

[0009] In the present invention, the specific content of the above Step 1 includes:

[0010] Step 1.1: Obtain the single-diode model under standard test conditions (STC) according to the equivalent circuit of the photovoltaic module:

[0011] (1)

[0012] Wherein, is the port current, is the port voltage, is the standard value of the series resistance, is the standard value of the parallel resistance, is the standard value of the photocurrent of the battery, is the standard value of the reverse saturation current of the diode D, and exp is the exponential power of e, is the standard value of the diode ideality factor, is the standard value of the temperature potential.

[0013] Step 1.2: Import the key test environment variables into the model parameters, and derive the display expression of voltage and current to obtain the single diode model under any test conditions:

[0014] (2)

[0015] Among them, is the Lambert W function, , , , , and are the photocurrent, reverse saturation current, ideality factor, series resistance, parallel resistance, and temperature potential of any test environment respectively. When the radiation amount of the test environment is and the battery temperature is , the expression of the model parameters is:

[0016] ( )

[0017] ( )

[0018] ( )

[0019] ( )

[0020] ( )

[0021] Among them, is the radiation amount of STC, is the battery temperature of STC, is the standard value of the energy band width of the p-n junction of the photovoltaic cell, is the Boltzmann constant, represents the temperature coefficient of the short-circuit current, represents the temperature coefficient of the material energy band width.

[0022] In the present invention, in the step 2, the product information of the photovoltaic module includes the short-circuit current , the open-circuit voltage , the maximum power point current , maximum power point voltage , short - circuit current temperature coefficient and open - circuit voltage temperature coefficient . These parameters can be obtained by referring to the product manual, asking the manufacturer, or conducting active tests.

[0023] In the present invention, step 3 specifically includes:

[0024] Step 3.1: Establish a system of equations consisting of five equations:

[0025] ( )

[0026] Among them, represents the functional relationship between voltage and current, represents the derivative of the function with respect to current, represents the functional relationship between open - circuit voltage and temperature, represents the derivative of the function with respect to temperature, is the battery temperature at STC, is the temperature change, represents the open - circuit voltage temperature coefficient, , and The expressions of are as follows:

[0027] ( )

[0028] ( )

[0029] ( )

[0030] Among them, the current and the temperature are both function variables, , , and are all intermediate variables, and the expressions are:

[0031] ( )

[0032] ( )

[0033] ( )

[0034] ( )

[0035] Step 3.2: Solve for the values of each parameter in the equations using the trust region reflection method.

[0036] The present invention can be improved as follows: The method further includes Step 4: Simulate the performance indicators of the photovoltaic module using the single-diode model expression obtained in Step 1.2 and the model parameters obtained in Step 3.2, and calculate the relative error between the simulated performance indicators and the actual performance indicators of the photovoltaic module, which is used to evaluate whether the calculation method can be used for actual simulation.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] First, a single-diode model for any test environment is established, which can be used to calculate the performance of the module under different radiation levels and different temperatures;

[0039] Second, six key indicators including short-circuit current, open-circuit voltage, maximum power point current, maximum power point voltage, short-circuit current temperature coefficient, and open-circuit voltage temperature coefficient are extracted from the product information for parameter identification;

[0040] Third, the parameter identification method is simple, and the model parameters can be directly obtained by only solving the established equations;

[0041] Fourth, the present invention can complete the parameter identification of the model only relying on the product information, without the need for a complete I-V curve, avoiding the inconvenience of additional data collection. Brief Description of the Drawings

[0042] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0043] Figure 1 is a schematic diagram of the equivalent circuit of a single-diode under standard test conditions provided in an embodiment of the present invention;

[0044] Figure 2 is a schematic diagram of the flow of the method for calculating the parameters of the single-diode model of a photovoltaic module of the present invention. Detailed Embodiments

[0045] As Figure 2 shown, a method for calculating the parameters of a single-diode model of a photovoltaic module includes the following steps:

[0046] Step 1: Establish a single-diode model for any test conditions;

[0047] Step 2: Obtain the product information of the photovoltaic module;

[0048] Step 3: Establish and solve the equations to obtain the model parameters;

[0049] Step 4: Simulate and calculate the relative error of the performance index.

[0050] The specific processes of each step are as follows:

[0051] In Step 1, the steps for establishing the single-diode model include:

[0052] Step 1.1, establish the single-diode model under standard test conditions: The single-diode equivalent circuit is as Figure 1 shown.

[0053] Figure 1 In, the port current-voltage function relationship corresponding to the equivalent circuit is:

[0054] (1)

[0055] Among them, is the port current, is the port voltage, is the standard value of the series resistance, is the standard value of the parallel resistance, is the standard value of the photocurrent of the battery, is the standard value of the reverse saturation current of the diode D, exp is the exponential power of e, is the standard value of the ideality factor of the diode, is the standard value of the temperature potential. The model under standard test conditions has a narrow scope of application and cannot cope with the actual diverse test environments, so it is necessary to further establish a model for general test environments.

[0056] Step 1.2, establish the single-diode model under any test conditions:

[0057] The solar radiation and temperature in the test environment will affect the values of the model parameters, and thus change the component performance. Therefore, expanding the model under standard test conditions (STC) to any test environment gives:

[0058] (2)

[0059] Among them, and are the port voltage and current respectively, is the temperature potential of the test environment, 、 、 、 and are the photocurrent, reverse saturation current, ideality factor, series resistance and parallel resistance of the single-diode model respectively. This formula is not convenient for visually showing the relationship between voltage and current, and can be further converted to:

[0060] (3)

[0061] Among them, is the Lambert W function, is the intermediate variable.

[0062] STC is a special case of any test condition. There is a certain relationship between the two environmental model parameters. Establish , , , , and , , , , to obtain:

[0063] (4)

[0064] (5)

[0065] (6)

[0066] (7)

[0067] (8)

[0068] Among them, is the radiation amount of STC, is the cell temperature of STC, is the standard value of the energy band width of the p-n junction of the photovoltaic cell. For monocrystalline silicon cells, this value is 1.12 eV, is the Boltzmann constant, represents the radiation amount of the test environment, represents the module temperature of the test environment, represents the temperature coefficient of the short-circuit current, represents the temperature coefficient of the material energy band width. For monocrystalline silicon cells, this value is -0.02677% / K.

[0069] In step 2, the steps of obtaining the product information of the photovoltaic module include:

[0070] Consult the product manual to obtain the performance indicators of the photovoltaic module in the STC environment, including the short-circuit current , open-circuit voltage , maximum power point current , maximum power point voltage , short-circuit current temperature coefficient and open-circuit voltage temperature coefficient . When and When expressed as percentages, their values are respectively converted to and . All specific performance indicators are shown in the given values in Table 2.

[0071] In step 3, the steps to obtain the model parameters include:

[0072] Step 3.1, establish a system of equations.

[0073] SDM has five parameters. By constructing five equations and solving the corresponding system of equations, the parameter values can be obtained. The voltage-current relationship in the standard test environment is:

[0074] (9)

[0075] where is a function symbol, is an intermediate variable.

[0076] Using the short-circuit point value to obtain the first equation:

[0077] (10)

[0078] Similarly, using the open-circuit point and the maximum power point respectively to obtain the second and third equations:

[0079] (11)

[0080] (12)

[0081] For the maximum power point, it also satisfies the condition that the power is an extreme point. Therefore, the fourth equation can be obtained:

[0082] (13)

[0083] where represents the derivative of power with respect to current, represents the derivative of the function with respect to current, the derivative of The expression is:

[0084] (14)

[0085] In the test environment, when the radiation dose is fixed at , and the temperature is regarded as a variable, the expression of the open-circuit voltage at this time is:

[0086] (15)

[0087] Among them, is the function symbol, is the intermediate variable. , and The expressions of

[0088] (16)

[0089] (17)

[0090] (18)

[0091] Among them, represents the temperature coefficient of the reverse saturation current at the temperature of , and its expression is:

[0092] (19)

[0093] Then the open-circuit voltage temperature coefficient is obtained:

[0094] (20)

[0095] Among them, represents the derivative of the function , and are both intermediate variables, and the expressions are:

[0096] (21)

[0097] (22)

[0098] Thus, the fifth equation can be obtained:

[0099] (23)

[0100] Among them, is the STC temperature, represents the temperature change, and is preferably taken as 1K.

[0101] Combining the above five equations gives a system of equations:

[0102] (24)

[0103] Step 3.2, Use the trust region dogleg method to solve equation (24) to obtain the numerical values of the various parameters of the model.

[0104] In step 4, the steps for simulating the relative error of the performance index include:

[0105] Step 4.1: Simulate the performance index of the photovoltaic module using the single-diode model expression obtained in step 1.2 and the model parameters obtained in step 3.2. The specific process is as follows:

[0106] S1. Substitute the model parameters into Equation (9) and solve using the trust-region dogleg method to obtain the simulated short-circuit current value ;

[0107] S2. Substitute the model parameters into Equation (9) and calculate to obtain the simulated open-circuit voltage value ;

[0108] S3. The irradiance , temperature in the non-standard test environment, and use the model parameters and formula (4-8) to obtain the parameters of the non-standard test environment;

[0109] S4. Change the model parameters to the parameters of the non-standard test environment, and use S1 to obtain the simulated short-circuit current value in the non-standard test environment , use S2 to obtain the simulated short-circuit current value in the non-standard test environment , then the short-circuit current temperature coefficient , the open-circuit voltage temperature coefficient .

[0110] Step 4.2: Calculate the relative error between the simulated performance index and the actual performance index of the photovoltaic module. If the relative error between the two is within the range of ±6%, it means that this calculation method can be used for actual simulation.

[0111] In this embodiment, according to the relevant data in the product manual of the monocrystalline silicon photovoltaic module obtained, parameter estimation is performed through a formula, and the model parameters of the photovoltaic module under the STC environment are shown in Table 1.

[0112] Table 1: Estimated values of the model parameters of the monocrystalline silicon module

[0113]

[0114] Among them, the reference method is from the method disclosed in the patent document with the patent number CN202311237791.5 and the invention name "Photovoltaic Module Parameter Estimation Method and System Based on Newton-Raphson Method".

[0115] The simulated values of the component performance index calculated using the model expression and model parameters, as well as the comparison results between the given value and the simulated value, are shown in Table 2.

[0116] Table 2: Given values and simulation results of the performance indicators of monocrystalline silicon modules

[0117]

[0118] Among them, the simulation values and relative errors marked (1) are the simulation results obtained by the reference method.

[0119] As can be seen from Table 2, the simulation results of the short-circuit current, maximum power point voltage and short-circuit current temperature coefficient of the present invention are slightly weaker than those of the reference method, but the simulation results of the remaining three indicators are better, and the relative error of the open-circuit voltage temperature coefficient is much lower than that of the reference method. Overall, the performance indicators obtained by simulation of the present invention are all within the ±6% range allowed by the project and can be used for actual simulation.

Claims

1. A method for calculating the parameters of a single-diode model of a photovoltaic module, characterized in that, The calculation method includes the following steps: Step 1: Establish a single-diode model under any test conditions. Specifically, Step 1 includes: Step 1.1: Obtain the single-diode model under standard test conditions (STC) according to the equivalent circuit of the photovoltaic module: where I is the port current, V is the port voltage, and R s,ref is the standard value of the series resistance, and R sh,ref is the standard value of the parallel resistance, I ph,ref is the standard value of the photocurrent of the battery, I o,ref is the standard value of the reverse saturation current of the diode D, exp is the exponential power of e, and n ref is the standard value of the ideality factor of the diode, and V t,ref = 25.7 mV is the standard value of the temperature potential; Step 1.2: Import key test environment variables into the model parameters, and derive the explicit expression of voltage and current to obtain the single-diode model under any test conditions: where W is the Lambert W function, I ph , I o , n, R s , R sh and V t are the photocurrent, reverse saturation current, ideality factor, series resistance, shunt resistance, and thermal voltage of an arbitrary test environment, respectively; when the radiation dose of the test environment is G and the cell temperature is T, the expressions for the model parameters are: n = n ref (5) Among them, G ref = 1000 W / m 2 is the radiation amount under STC, T ref = 298.15 K is the battery temperature under STC, E g,ref is the standard value of the energy band width of the p-n junction of the photovoltaic cell, k = 1.38×10 -23 J / K is the Boltzmann constant, α represents the temperature coefficient of the short-circuit current, and γ represents the temperature coefficient of the material energy band width; Step 2: Obtain the product information of the photovoltaic module. In Step 2, the product information of the photovoltaic module includes the short-circuit current I sc,ref , open-circuit voltage V oc,ref , maximum power point current I m,ref , maximum power point voltage V m,ref , short-circuit current temperature coefficient α, and open-circuit voltage temperature coefficient β; Step 3: Establish and solve a system of equations to obtain the numerical values of each parameter of the model. Specifically, Step 3 includes: Step 3.1: Establish a system of equations consisting of five equations: where f represents the functional relationship between voltage and current, f′ represents the derivative of the function f with respect to current, g represents the functional relationship between open-circuit voltage and temperature, g′ represents the derivative of the function g with respect to temperature, T ref = 298.15 K is the battery temperature under STC, ΔT = 1 K is the temperature change, β represents the open-circuit voltage temperature coefficient, and the expressions of f(I), f′(I) and g′(T) are respectively: f(I) = R sh,ref (I ph,ref + I o,ref ) - (R sh,ref + R s,ref )I - n ref V t,ref W(X ref )(9) wherein, both the current I and the temperature T are function variables, and X ref , A(T), C(T), and D(T) are all intermediate variables, and the expressions are as follows: Step 3.2: Use the trust-region dogleg method to solve the values of each parameter in the system of equations.

2. The method for calculating the parameters of the single-diode model of a photovoltaic module according to claim 1, wherein, The method further includes Step 4: Simulate the performance indicators of the photovoltaic module using the single-diode model expression obtained in Step 1.2 and the model parameters obtained in Step 3.2, and calculate the relative error between the simulated performance indicators and the actual performance indicators of the photovoltaic module, which is used to evaluate whether the calculation method can be used for actual simulation.

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