Parameter calculation method for single-diode model for photovoltaic module

Abstract

Disclosed in the present invention is a parameter calculation method for a single-diode model for a photovoltaic module. The method comprises: firstly, on the basis of an equivalent circuit of a single-diode model, obtaining a model under standard test conditions, and associating model parameters with test environment parameters to obtain a model for any test environment; and then acquiring performance parameters of a photovoltaic module, which comprise a short-circuit current, an open-circuit voltage, the maximum power-point current, the maximum power-point voltage, a short-circuit current temperature coefficient and an open-circuit voltage temperature coefficient, and constructing a system of equations and solving same to obtain model parameters. The present invention can realize the modeling and parameter identification of a model only on the basis of product specification information provided by a module manufacturer, without a complete I-V curve, thereby achieving a strong guiding significance for simulation and production practices.

Description

A photovoltaic module single diode model parameter calculation method TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaic module system calculation, and particularly refers to a photovoltaic module single diode model parameter calculation method. BACKGROUND

[0002] In order to cope with global warming and achieve the "double carbon" target, photovoltaic power generation systems are widely put into operation. Photovoltaic cells, as a component of photovoltaic systems, their modeling and parameter identification are of great significance for the research of battery structure optimization, operation state prediction, etc.

[0003] Models for measuring the performance characteristics of photovoltaic modules include single diode models, double diode models, and triple diode models. Among these models, the single diode model is widely used because of its simple model, strong interpretability, and good applicability. At present, although the single diode model parameter identification has made certain achievements, it still faces challenges to rely on the sampling points of I-V curves and only use the information provided by manufacturers to complete parameter identification.

[0004] SUMMARY

[0005] The purpose of the present application is to provide a photovoltaic module single diode model parameter calculation method, which can obtain the numerical values of each parameter of the photovoltaic module single diode model with only a small amount of product information, and has important guiding significance for simulation and production practice.

[0006] The above-mentioned purpose of the present application is realized by the following technical scheme: a photovoltaic module single diode model parameter calculation method, characterized in that the calculation method comprises the following steps:

[0007] Step 1: Establish a single diode model under any test condition;

[0008] Step 2: Obtain product information of the photovoltaic module;

[0009] Step 3: Establish and solve the equation set to obtain the numerical values of each parameter of the model.

[0010] In the present application, step 1 specifically comprises:

[0011] Step 1.1: Obtain a single diode model under standard test conditions (STC) according to the equivalent circuit of the photovoltaic module:

[0012] Where I is the port current, V is the port voltage, R s,ref is the standard value of series resistance, R sh,ref is the standard value of parallel resistance, I ph,refI is the standard value of the light-generated current o,ref exp is the exponential power of e, n is the standard value of the reverse saturation current ref V is the standard value of the ideality factor t,ref =25.7 mV is the standard value of the temperature potential.

[0013] Step 1.2: Introducing the key test environment variables into the model parameters, deriving the explicit expression of V with respect to I to obtain the single diode model of any test condition:

[0014] wherein W is the Lambert W function, V t is the temperature potential of any test environment, I ph , I o , n, R s and R sh are the light-generated current, the reverse saturation current, the ideality factor, the series resistance and the parallel resistance of the model in any test environment, respectively. When the radiation of the test environment is G and the battery temperature is T, the expression of the model parameters is: n=n ref (5)

[0015] wherein G ref =1000 W / m 2 is the radiation of STC, T ref =298.15 K is the battery temperature of 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, and α represents the temperature coefficient of the short-circuit current, and γ represents the temperature coefficient of the material energy band width.

[0016] In the present application, in step 2, the product information of the photovoltaic module includes the short-circuit current I sc,ref , the open-circuit voltage V oc,ref , the maximum power point current I m,ref , the maximum power point voltage V m,ref , the short-circuit current temperature coefficient α and the open-circuit voltage temperature coefficient β, which can be obtained by consulting the product manual or inquiring the manufacturer or active test.

[0017] In the present application, step 3 specifically comprises:

[0018] Step 3.1: establishing an equation group composed of five equations:

[0019] Wherein, f represents the functional relationship between the port voltage and the port current, f' represents the derivative of the function f to the port current, g represents the functional relationship between the open circuit voltage and the battery temperature, g' represents the derivative of the function g, T ref = 298.15K is the battery temperature of STC, ΔT is the battery temperature change, β represents the open circuit voltage temperature coefficient, 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)

[0020] Wherein, I is the port current, T is the battery temperature, X ref , A(T), C(T) and D(T) are all intermediate variables, and the expressions are:

[0021] Step 3.2: the values of each parameter in the equation set are solved by using the trust region polyline method.

[0022] The present application can be improved as follows: the method further comprises step 4: simulating the performance indicators of the photovoltaic module by using the single diode model expression obtained in step 1.2 and the model parameters obtained in step 3.2, and calculating the relative error between the simulation performance indicators of the photovoltaic module and the actual performance indicators, for evaluating whether the calculation method can be used for actual simulation.

[0023] Compared with the prior art, the present application has the beneficial effects as follows:

[0024] Firstly, the single diode model of any test environment is established, which can be used to calculate the performance of the module under different radiation and different temperature conditions;

[0025] Secondly, the short circuit current, the open circuit voltage, the maximum power point current, the maximum power point voltage, the short circuit current temperature coefficient and the open circuit voltage temperature coefficient are extracted from the product information to perform parameter identification;

[0026] Thirdly, the parameter identification method is simple, and the model parameters can be directly obtained by solving the established equation set;

[0027] Fourthly, the parameter identification of the model can be completed only by relying on the product information, without the need of complete I-V curve, so that the inconvenience of additional data collection is avoided. Attached Figure Description

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] 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;

[0030] Figure 2 is a flowchart illustrating the method for calculating the parameters of a single diode model for a photovoltaic module according to the present invention. Detailed Implementation

[0031] As shown in Figure 2, a method for calculating the parameters of a single diode model of a photovoltaic module includes the following steps:

[0032] Step 1: Establish a single diode model under arbitrary experimental conditions;

[0033] Step 2: Obtain product information for photovoltaic modules;

[0034] Step 3: Establish and solve the system of equations to obtain the model parameters;

[0035] Step 4: Simulate and calculate the relative error of performance indicators.

[0036] The specific process for each step is as follows:

[0037] Step 1, the steps for establishing a single diode model include:

[0038] Step 1.1, establish a single diode model under standard test conditions: the equivalent circuit of a single diode is shown in Figure 1.

[0039] In Figure 1, the current and voltage functions corresponding to the equivalent circuit are as follows:

[0040] Where I is the port current, V is the port voltage, and R... s,ref R is the standard value of the series resistance. sh,ref I is the standard value of the parallel resistance. ph,ref The standard value of photocurrent, I o,ref Let n be the standard value of the reverse saturation current, exp be the power of e, and n ref V is the ideal factor standard value. t,ref =25.7mV is the standard value of temperature potential. The model under standard test conditions has a narrow range of applicability and cannot cope with the diverse test environments in reality. It is necessary to further develop a model for general test environments.

[0041] Step 1.2, establish a single diode model under arbitrary experimental conditions:

[0042] The solar irradiance and temperature in the test environment affect the values of the model parameters and thus change the performance of the component, so the model under standard test conditions (STC) is extended to any test environment:

[0043] where V and I are the port voltage and port current, respectively, V t is the temperature potential of the test environment, I ph , I o , n, R s , and R sh are the photo-generated current, the reverse saturation current, the ideality factor, the series resistance, and the parallel resistance of the model in the test environment, respectively. This formula is not convenient for intuitively displaying the relationship between voltage and current, and can be further converted to: V = R sh (I ph + I o ) - (R sh + R s )I - nV t W(X) (3)

[0044] where W is the Lambert W function, and X is an intermediate variable.

[0045] STC is a special case of any test condition, and there is a certain relationship between the parameters of the two environment models. The correlation between I ph , I o , n, R s , and R sh and I ph,ref , I o,ref , n ref , R s,ref , and R sh,ref is established as: n = n ref (6)

[0046] where G ref = 1000 W / m 2 is the irradiance of STC, T ref = 298.15 K is the cell temperature of STC, E g,ref is the standard value of the energy band width of the p-n junction of the photovoltaic cell, which is 1.12 eV for a single-crystal silicon cell, k = 1.38 × 10 -23 J / K is the Boltzmann constant. G represents the irradiance of the test environment, T represents the cell temperature of the test environment, a represents the temperature coefficient of the short-circuit current, and γ represents the temperature coefficient of the material energy band width, which is -0.02677% / K for a single-crystal silicon cell.

[0047] In step 2, the step of obtaining the photovoltaic module product information includes:

[0048] The performance indices of the photovoltaic module in STC environment are obtained from the product manual, including 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. When α and β are expressed in percentage, their values are converted to αI sc,ref and βV oc,ref respectively. All the performance indices are given in Table 2.

[0049] In step 3, the step of obtaining the model parameters includes:

[0050] Step 3.1, establishing the equation set.

[0051] The SDM has five parameters, and five equations are constructed to solve the corresponding equation set to obtain the parameter values. The voltage and current relationship in the standard test environment is: V = 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)

[0052] Wherein, f is a function symbol, is an intermediate variable.

[0053] The short-circuit point value (I sc,ref , 0) is used to obtain the first equation: f(I sc,ref ) = 0 (10)

[0054] Similarly, the open-circuit point and the maximum power point are used to obtain the second and third equations respectively: f(0) = V oc,ref (11) f(I m,ref ) = V m,ref (12)

[0055] For the maximum power point, it also satisfies the condition that the power is the extreme point, so the fourth equation can be obtained: P'(I m,ref ) = f(I m,ref ) + f ′ (I m,ref )I m,ref = 0 (13)

[0056] Wherein, P' represents the derivative of power P with respect to the port current, f' represents the derivative of function f, f ′(I) Expression is:

[0057] In the test environment, the radiation amount is fixed at 1000W / m 2 , and the battery temperature T is taken as a variable, at which time the expression of open circuit voltage is: oc = g(T) = R sh,ref (I ph (T) + I o (T))-n ref V t (T)W(X(T))(15)

[0058] Wherein, g is a function symbol, is an intermediate variable. V t (T), I ph (T) and I o (T) are expressed as: I ph (T) = I ph,ref + α(T-T ref )(17) I o (T) = I o,ref + A(T)(T-T ref )(18)

[0059] Wherein, A(T) represents the temperature coefficient of the reverse saturation current at temperature T, and its expression is:

[0060] Then the open circuit voltage temperature coefficient β is obtained:

[0061] Wherein, g'(T) represents the derivative of function g, and C(T) and D(T) are both intermediate variables, and their expressions are:

[0062] From this, the fifth equation is obtained: g'(T ref + ΔT) = β (23)

[0063] Wherein, T ref = 298.15K is the STC temperature, and ΔT represents the temperature change, preferably 1K.

[0064] An equation group is obtained by combining the above five equations:

[0065] Step 3.2, the model parameters are obtained by solving equation (24) using the trust region polyline method.

[0066] In step 4, the steps of simulating the relative error of performance indicators include:

[0067] Step 4.1: Simulate the performance indicators of the photovoltaic module by 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:

[0068] S1, substitute the model parameters into equation (9), and solve f(I sc ) = 0 to obtain the short-circuit current simulation value I sc ;

[0069] S2, substitute the model parameters into equation (9), and calculate f(0) to obtain the open-circuit voltage simulation value V oc ;

[0070] S3, the irradiance G = 1000 W / m 2 and the cell temperature T = 299.15 K in the non-standard test environment, and the parameters in the non-standard test environment are obtained using the model parameters and equations (4-8);

[0071] S4, the model parameters are changed to the parameters in the non-standard test environment, and the short-circuit current simulation value in the non-standard test environment is obtained using S1 The short-circuit current simulation value in the non-standard test environment is obtained using S2 The short-circuit current temperature coefficient is The open-circuit voltage temperature coefficient is

[0072] Step 4.2: Calculate the relative error between the simulation performance indicators of the photovoltaic module and the actual performance indicators. If the relative error between the two is within ±6%, it means that the calculation method can be used for actual simulation.

[0073] In this embodiment, according to the relevant data obtained from the product manual of the monocrystalline silicon photovoltaic module, the model parameters in the STC environment of the photovoltaic module are obtained by parameter estimation through the formula, as shown in Table 1.

[0074] Table 1: Model parameter estimation value of monocrystalline silicon module

[0075] The reference method is derived 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".

[0076] The simulation value of the module performance indicators calculated using the model expression and the model parameters, and the comparison results of the given value and the simulation value are shown in Table 2.

[0077] Table 2: Given value and simulation result of monocrystalline silicon module performance indicators

[0078] Wherein, the simulation value and relative error of mark (1) are simulation results obtained by using the reference method.

[0079] From Table 2, it can be seen that the absolute value of relative error of short-circuit current, maximum power point voltage and short-circuit current temperature coefficient of the present application is larger, the simulation result is slightly weaker than the reference method, but the simulation result of the remaining three indexes is better, wherein the relative error of open-circuit voltage temperature coefficient is far lower than the reference method. Comprehensive comparison shows that the performance indexes obtained by simulation of the present application are all within the engineering allowable range of ± 6%, which can be used for actual simulation.

Claims

1. A method of calculating parameters of a single-diode model of a photovoltaic module, characterized in that, The calculation method comprises the following steps: Step 1: establishing a single-diode model of any test condition; Step 2: obtaining product information of the photovoltaic module; Step 3: establishing and solving an equation set to obtain numerical values of various parameters of the model.

2. The photovoltaic module single-diode model parameter calculation method of claim 1, wherein, The step 1 specifically comprises: Step 1.1: Single diode model under standard test conditions (STC) from the equivalent circuit of a photovoltaic module: where I is the port current, V is the port voltage, R s,ref is the series resistance standard value, R sh,ref is the parallel resistance standard value, I ph,ref is the photocurrent standard value, I o,ref is the reverse saturation current standard value, exp is the exponential power of e, n ref is the ideality factor standard value, V t,ref = 25.7 mV is the temperature potential standard value; Step 1.2: Importing the key experimental environmental variables into the model parameters, deriving the explicit expression of V as a function of I for the single diode model under arbitrary experimental conditions: where W is the Lambert W function, V t is the temperature potential of any test environment, I ph , I o , n, R s and R sh are the photo-generated current, the reverse saturation current, the ideality factor, the series resistance and the parallel resistance of the model in any test environment, respectively; when the radiation of the test environment is G and the battery temperature is T, the expression of the model parameters is: n = n ref (5) Among them, G ref =1000W / m 2 T represents the radiation dose of STC. ref =298.15K is the STC battery temperature, E g,ref The standard value for the bandgap of the pn junction in a photovoltaic cell is k = 1.38 × 10⁻⁶. -23 J / K is the Boltzmann constant, and α represents the short-circuit current. A temperature coefficient of the flow, γ, represents a temperature coefficient of a material band width.

3. The photovoltaic module single-diode model parameter calculation method of claim 2, wherein, The product information of the photovoltaic module in step 2 includes 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 a, and open-circuit voltage temperature coefficient β.

4. The photovoltaic module single-diode model parameter calculation method of claim 3, wherein, The step 3 specifically comprises: Step 3.1 : Set up a system of equations consisting of five equations: where f represents a functional relationship of the port voltage and the port current, f' represents a derivative of the function f, g represents a functional relationship of the open circuit voltage and the battery temperature, g' represents a derivative of the function g, T ref = 298.15 K is the battery temperature at STC, ΔT = 1 K is the battery 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) where I is the port current, T is the battery temperature, X ref , A(T), C(T), and D(T) are all intermediate variables, expressed as: Step 3.2: solving values of various parameters in the equation set by using a trust region broken line method.

5. The photovoltaic module single-diode model parameter calculation method of claim 4, wherein, The method further comprises a step 4: simulating a performance index of the photovoltaic module by using the single-diode model expression obtained in the step 1.2 and the model parameters obtained in the step 3.2, and calculating a relative error between a simulated performance index and an actual performance index of the photovoltaic module, which is used to evaluate whether the calculation method can be used for actual simulation.

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