A method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters

Abstract

The present invention relates to a method for dynamically generating photovoltaic array working conditions considering random differences in multivariate shading parameters, belonging to the technical field of new energy photovoltaic power generation, including setting photovoltaic array parameters under shading conditions, including short-circuit current, open-circuit voltage, optimal voltage value and optimal current value; setting the value range of a random shading parameter generator, and the number of random local shading condition generation times N set ; Randomly generate shading parameters, import the PV array model considering the difference of PV local shading parameters; output the P-V characteristic curve of the PV array under local shading conditions until N is reached set The present invention can accurately and quickly output the photovoltaic partial shading working condition and obtain the photovoltaic output characteristic curve.

Description

Technical Field

[0001] The invention relates to a method for dynamically generating photovoltaic array working conditions taking into account random differences in multivariate shielding parameters, and belongs to the technical field of new energy photovoltaic power generation. Background Art

[0002] With the continuous development of photovoltaic power generation technology, the performance analysis of photovoltaic arrays has become a hot topic in the field of photovoltaic power generation. However, in practical applications, photovoltaic arrays are often shielded by the surrounding environment, causing local shading effects and thus affecting the overall power generation. In order to more accurately evaluate the performance of photovoltaic system control strategies, it is necessary to consider scenarios with differences in shading parameters. Therefore, it is particularly important to establish a photovoltaic array power analysis model that takes into account differences in photovoltaic shading parameters.

[0003] Existing photovoltaic array models lack consideration of the output characteristics of photovoltaic arrays under extreme environments, including local shading environments and ice and snow coverage. Traditional photovoltaic array analysis models are based on ideal environments without shadows, which is different from the actual situation, resulting in low prediction accuracy of photovoltaic array power analysis models. In actual working conditions, sudden changes in light or shading by foreign objects will affect the photocurrent of photovoltaic modules. In order to accurately reflect the response characteristics of photovoltaic modules under actual working conditions, it is more critical to build a photovoltaic array model that takes into account the local shading effect. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method for dynamically generating photovoltaic array working conditions taking into account the random differences of multivariate shading parameters, which can accurately and quickly output photovoltaic local shading conditions and obtain photovoltaic output characteristic curves.

[0005] The technical solution of the present invention is as follows:

[0006] A method for dynamically generating photovoltaic array working conditions that considers random differences in multivariate shading parameters. The engineering mathematical model of the photovoltaic array analyzes the output characteristics of the photovoltaic array under local shading. Photovoltaic modules that receive different light radiation will produce different photocurrents. At the same time, in order to reduce the hot spot effect of the photovoltaic array module, the photovoltaic module is anti-parallel connected with a diode. By judging the size of the photocurrent of the photovoltaic module and the output current of the photovoltaic array, the conduction state of the photovoltaic module can be obtained and the characteristic curve of the photovoltaic array can be output. Shading intensity, shading difference, and shading dispersion are introduced to measure the shading working conditions. The corresponding local shading working conditions are generated by the random values ​​of the three shading parameters. The local shading working conditions are reflected by the output characteristic curve of the photovoltaic array.

[0007] Through the dynamic generation method of photovoltaic array working conditions, the optimal voltage and maximum output power corresponding to the maximum power point can be obtained from the photovoltaic array output characteristic curve.

[0008] The specific steps include:

[0009] S1: Set the photovoltaic array parameters under the shade condition, including short-circuit current, open-circuit voltage, optimal voltage value and optimal current value;

[0010] S2: Set the value range of the random shading parameter generator and the number of random local shading conditions generated N set ;

[0011] S3: Randomly generate shading parameters and import the PV array model that takes into account the differences in PV local shading parameters;

[0012] S4: Output the PV characteristic curve of the photovoltaic array under partial shading conditions until N is reached set ,Finish.

[0013] The present invention first builds a photovoltaic array model that considers the differences in multivariate shielding parameters, collects four parameters of the photovoltaic module, and introduces three shielding parameters through the engineering mathematical model of the photovoltaic array, including shielding intensity, shielding difference, and shielding dispersion to simulate the shielding conditions on the surface of the photovoltaic power generation component. The model can take into account the impact of local shielding effects on the performance of the photovoltaic system, including factors such as shielding area, shielding position and shielding degree, and more realistically reflect the working state of the photovoltaic array in local shielding in the actual environment. A method for dynamically generating photovoltaic array working conditions that considers the differences in multivariate shielding parameters is proposed, and multiple photovoltaic local shielding working conditions are simulated by multiple random values ​​of multivariate shielding parameters. These working conditions can be applied to the simulation verification and comparison of the performance of the photovoltaic maximum power point tracking control strategy under local shielding working conditions. Different from traditional methods, the present invention can output multiple local shielding working conditions of the photovoltaic power generation system, distinguish different types of local shielding working conditions, and randomly generate local shielding working conditions that the photovoltaic power generation system may face in the actual environment. The analysis based on this model will provide strong support for the design and operation of photovoltaic arrays. By accurately simulating the impact of local shading conditions on photovoltaic systems, it will guide the optimization of control strategies, adjust the arrangement of photovoltaic components, and improve the overall performance of photovoltaic power generation systems. At the same time, this model can also provide a scientific basis for the operation and maintenance management of photovoltaic power generation systems, and ensure the stable operation of photovoltaic power generation systems to the greatest extent.

[0014] Preferably, in step S1, the corresponding environmental parameters are changed to obtain output characteristics under different environments. In the open circuit voltage test, the open circuit voltage at both ends of the module is obtained. The open circuit voltage is related to the irradiation intensity and has nothing to do with the area of ​​the photovoltaic module. The external characteristics of the photovoltaic module, i.e. the output characteristics, are an important basis for the design of photovoltaic modules. Light radiation intensity and temperature are two important parameters for determining the output characteristics of photovoltaic modules. When the voltage reaches a certain value, the power can reach the maximum. The point where the output power of the photovoltaic module assembly reaches the maximum is called the maximum power point (MPP) of the photovoltaic array; the voltage U corresponding to this point m , called the maximum power point voltage; the current corresponding to this point is I m , called the maximum power point current, the power at this point is the maximum power P m .

[0015] Analyze the engineering calculation method of photovoltaic array output characteristics under general dynamic conditions. Formula (1) describes the characteristic curve under standard conditions. Take the standard illumination S ref =1000W / m 2 , standard temperature T ref =25℃. When the irradiance and reference temperature change, the irradiance and reference temperature need to be modified to describe the new characteristic curve. According to the standard sunshine intensity and standard temperature I sc , U oc ,I m , U m Calculate the I' of general working conditions under irradiance S and temperature T sc , U' oc , I' m , U' m , then we can still use formula (1) to perform engineering calculations on the output characteristics of the photovoltaic array under non-standard conditions.

[0016] Formula (1) is used to calculate the output characteristics of the photovoltaic array under standard conditions. Formula (2) represents the current at the maximum power point under standard conditions:

[0017]

[0018] Among them, I L Indicates the load current, I sc represents the photon-induced current; U L Indicates the load voltage; I m Indicates the current corresponding to the maximum power point, that is, the optimal current under standard working conditions; U oc Indicates the open circuit voltage under standard working conditions; U m Indicates the voltage corresponding to the maximum power point, that is, the optimal voltage under standard conditions; C 1 , C 2represents a constant, which is determined by equations (3) and (4):

[0019]

[0020] In step S1, the temperature difference and irradiance difference between the shielding condition and the standard condition are first calculated:

[0021] ΔT=TT re f (5)

[0022]

[0023] Wherein, ΔT represents the temperature difference between the shielding condition and the standard condition; ΔS represents the irradiance difference between the shielding condition and the standard condition; T represents the temperature of the shielding condition; T ref represents the temperature of the standard working condition; S represents the irradiance of the shielding working condition; S ref Indicates the irradiance under standard working conditions;

[0024] Then, the short-circuit current, open-circuit voltage, optimal current and optimal voltage under the shading condition are calculated by the photovoltaic array model, as shown in equations (5) to (9):

[0025]

[0026] U' oc =U oc (1-γΔT)(1+βΔT) (9)

[0027]

[0028] U' m =U m (1-γΔT)(1+βΔS) (11)

[0029] Among them, I' sc Indicates the photon-induced current under shielding conditions, i.e., the short-circuit current; U' oc Indicates the open circuit voltage under shielding conditions; I' m represents the current corresponding to the maximum power point under shading conditions, that is, the optimal current; U' m It represents the voltage corresponding to the maximum power point under the shading condition, that is, the optimal voltage; α, β, and γ are all constants, α is 0.0025 / ℃, β is 0.5, and γ is 0.00288 / ℃.

[0030] The open circuit voltage value, short circuit current value, optimal voltage value and optimal current value are the four parameter values ​​of the photovoltaic module. Different photovoltaic module models have different parameter values.

[0031] Preferably, the temperature T under standard working conditions ref=25℃, irradiance S under standard working conditions ref =1000W / m 2 .

[0032] Preferably, in step S2, a random shielding parameter generator is built into the photovoltaic array model to randomly generate shielding parameters of the photovoltaic array, the shielding parameters including shielding intensity χ, shielding difference γ and shielding dispersion δ;

[0033] The photovoltaic array includes a plurality of photovoltaic modules N connected in series. s The photovoltaic modules include standard modules and shielding modules. The photovoltaic modules that receive standard light radiation are set as standard modules. The number of standard modules is N. uic , the photovoltaic modules with low irradiance after being shaded are shaded modules, and the number of shaded modules is N psc :

[0034] N s =N psc +N uic (10)

[0035] The shielding intensity χ measures the degree of shielding of the shielding module and is expressed by formula (11), with the value range set to (0,1):

[0036]

[0037] x j =rand(0,1) (12)

[0038] Among them, x j represents the shielding strength of the jth shielding module; S psc_j represents the irradiance of the jth shading module;

[0039] The shading difference γ is the number of different shading intensity values ​​χ, which indicates the number of photovoltaic modules that receive different light radiation intensities and thus generate different photocurrents. The value range of the shading difference γ is [0, N s ];

[0040] Number of shielding modules N psc It is equal to the sum of the number of shading modules corresponding to each different shading difference, and the number of shading modules is not greater than the total number of series-connected photovoltaic modules;

[0041] N psc =N psc_1 +…+N psc_j +…+N psc_r (j=1,…,γ)(13)

[0042] N psc_j =rand(1,N psc ) (14)

[0043]

[0044] N psc_j represents the number of PV modules with the same light irradiance as the jth shaded module;

[0045] The shading dispersion δ refers to the proportion of the shading intensity corresponding to the shading difference in all shading modules:

[0046]

[0047] Among them, δ j represents the shielding dispersion corresponding to the jth shielding intensity; x j represents the jth shielding intensity. When the shielding condition is determined, the γ value is also determined;

[0048] Shielding equivalent area A psc A represents the sum of the products of the shielding intensity corresponding to each shielding difference and the number of corresponding shielding modules. psc_j is the equivalent shielding area of ​​the jth group:

[0049] A psc_j =x j ×N psc_j (17)

[0050]

[0051] The value range of the number of shielding modules is set according to the number of photovoltaic modules. For example, if the number of modules in series in the photovoltaic power generation system is 30, the number of shielding modules is between 0 and 30. The three parameters of shielding intensity χ, shielding difference γ, and shielding dispersion δ are used to equivalently measure the shielding situation of the photovoltaic array, which are used to adjust the irradiance S of the shielding condition.

[0052] Set the number of random local occlusion conditions to be generated N set 10 to 30 times, preferably 20 times.

[0053] Preferably, in step S3, the total number of photovoltaic modules N is set s , the number of photovoltaic shading modules N psc , and the number of standard modules N is obtained uic . Set the shielding strength x of the shielding module j The larger the shielding intensity value, the less irradiance the photovoltaic module receives. Assuming that the photovoltaic array under partial shielding receives different light radiation intensities, the shielding intensity is used to quantify the light radiation intensity lost by shielding. The difference between the standard radiation intensity and the light radiation intensity received by the partially shielded photovoltaic is equal to the shielding intensity multiplied by the standard irradiance intensity.

[0054] Randomly select a value within the numerical range of the random masking parameter generator in step S2 to generate a masking parameter;

[0055] Assuming that the same type of photovoltaic modules have consistent output characteristics, the output characteristics of photovoltaic modules receiving different light radiation intensities are different. The four photovoltaic array parameters under the shaded condition are re-described according to the sunlight radiation intensity and standard temperature under the standard working condition.

[0056] The shielding modules with the same shielding parameters are divided into the same group. The shielding modules are arranged in ascending order according to the light irradiance intensity: normal light, shielding 1, shielding 2, ..., shielding γ. The output characteristic engineering calculation under the shielding condition is calculated according to formula (1), and the photovoltaic array characteristic curve is output; first, the shielding module with the largest shielding intensity value is put into use, and the current switching node under the currently put into use shielding module is calculated. When the output current is greater than the current current switching node, the shielding module is bypassed, otherwise, the standard module continues to be put into use;

[0057] The photovoltaic modules in normal working state are put into operation. As the current decreases, the shielded module groups are put into operation in sequence from low to high according to the shielding intensity, and the remaining shielded photovoltaic modules that are not put into operation are bypassed through diodes; when the voltage reaches the inflection point, the next shielded module group is put into operation in sequence, and the corresponding photovoltaic shielding module switching state changes.

[0058] Preferably, in step S4, the short-circuit current, open-circuit voltage, optimal current and optimal voltage of the photovoltaic array under the shielding condition are calculated again according to the photovoltaic array model, that is, formulas (5) to (9), the optimal current and the optimal voltage are multiplied to obtain the maximum output power, and the IV and PV characteristic curves of the photovoltaic array are plotted.

[0059] For any details not provided in the present invention, please refer to the prior art.

[0060] The beneficial effects of the present invention are:

[0061] The present invention's method for dynamically generating photovoltaic array operating conditions that considers random differences in multivariate shielding parameters introduces shielding parameters to describe local shielding conditions, and the random values ​​of multivariate shielding parameters simulate randomly occurring photovoltaic array operating conditions. This method can simulate different photovoltaic array local shielding environments, and then can set the maximum number of cycles according to research needs and practical applications to generate local shielding conditions multiple times, ensuring the comprehensiveness and representativeness of the model. This method covers various shielding conditions that may be encountered by photovoltaic power generation systems, and is of great significance for the study of control strategies for photovoltaic power generation systems under local shielding. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0063] Figure 1 This is the principle diagram of the photovoltaic effect;

[0064] Figure 2 is the single diode equivalent circuit diagram of the photovoltaic module;

[0065] Figure 3 (a) is a schematic diagram of the parallel diode structure of the photovoltaic module under normal illumination. Figure 3 (b) is a schematic diagram of the parallel diode structure of the photovoltaic module under partial shading;

[0066] Figure 4 (a) is a photovoltaic array structure diagram of photovoltaic modules of the same model connected in series. Figure 4 (b) is the array structure of N groups of photovoltaic modules connected in series.

[0067] Figure 5 This is the photovoltaic array series structure for partial shading condition 1.

[0068] Figure 6 (a) is the PV output characteristic curve of the photovoltaic array under partial shading condition 1, Figure 6 (b) is the IV output characteristic curve of the photovoltaic array under partial shading condition 1, Figure 6 (c) is the output voltage variation curve of the photovoltaic module under partial shading condition 1, Figure 6 (d) is the output current variation curve of the photovoltaic module under partial shading condition 1.

[0069] Figure 7 This is the photovoltaic array series structure for partial shading condition 2.

[0070] Figure 8 (a) is the PV output curve of the photovoltaic array under partial shading condition 2, Figure 8 (b) is the IV output curve of the photovoltaic array under partial shading condition 2, Figure 8 (c) is the output voltage variation curve of the photovoltaic module under partial shading condition 2. Figure 8 (d) is the output current variation curve of the photovoltaic module under partial shading condition 2.

[0071] Fig. 9 (a) is the PV output curve for the simulation verification of partial shading condition 3, Fig. 9 (b) The IV output curve for the simulation verification of partial shading condition 3;

[0072] Fig.10 (a) is the PV output curve for the simulation verification of partial shading condition 4, Fig.10 (b) IV output curve for partial shading condition 4 simulation verification;

[0073] Fig.11(a) is the PV output curve of the photovoltaic array under partial shading conditions generated randomly 4 times. Fig.11 (b) is the IV output curve of the photovoltaic array characteristic under partial shading conditions generated randomly 4 times.

[0074] Fig.12 Flowchart of the method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters. DETAILED DESCRIPTION

[0075] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in the art.

[0076] Example 1

[0077] A method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters, such as Fig.12 As shown, the following steps are included:

[0078] S1: Set the photovoltaic array parameters under the shade condition, including short-circuit current, open-circuit voltage, optimal voltage value and optimal current value;

[0079] S2: Set the value range of the random shading parameter generator and the number of random local shading conditions generated N set ;

[0080] S3: Randomly generate shading parameters and import the PV array model that takes into account the differences in PV local shading parameters;

[0081] S4: Output the PV characteristic curve of the photovoltaic array under partial shading conditions until N is reached set ,Finish.

[0082] Establish shielding parameters, generate random values ​​based on shielding parameters based on historical and current moment quantities for sampling, better distinguish fault types, and make prediction results more accurate. According to the random values ​​of three shielding parameters, simulate the local shielding conditions faced by the photovoltaic array, and use the characteristic output curve of the photovoltaic array under the shielding condition to reflect the impact of local shielding on the output characteristics of the photovoltaic array.

[0083] This embodiment first builds a photovoltaic array model that considers the difference in multivariate shielding parameters, collects four parameters of the photovoltaic module, and introduces three shielding parameters through the engineering mathematical model of the photovoltaic array, including shielding intensity, shielding difference, and shielding dispersion to simulate the shielding situation on the surface of the photovoltaic power generation component. The model can take into account the impact of local shielding effects on the performance of the photovoltaic system, including factors such as shielding area, shielding position and shielding degree, and more realistically reflect the working state of the photovoltaic array in local shielding in the actual environment. A method for dynamically generating photovoltaic array working conditions that considers the difference in multivariate shielding parameters is proposed, and multiple photovoltaic local shielding working conditions are simulated by multiple random values ​​of multivariate shielding parameters. These working conditions can be applied to the performance simulation verification and comparison of photovoltaic maximum power point tracking control strategies under local shielding working conditions. Different from traditional methods, the present invention can output multiple local shielding working conditions of photovoltaic power generation systems, distinguish different types of local shielding working conditions, and randomly generate local shielding working conditions that photovoltaic power generation systems may face in actual environments. The analysis based on this model will provide strong support for the design and operation of photovoltaic arrays. By accurately simulating the impact of local shading conditions on photovoltaic systems, it will guide the optimization of control strategies, adjust the arrangement of photovoltaic components, and improve the overall performance of photovoltaic power generation systems. At the same time, this model can also provide a scientific basis for the operation and maintenance management of photovoltaic power generation systems, and ensure the stable operation of photovoltaic power generation systems to the greatest extent.

[0084] Figure 1 This is a schematic diagram of the photovoltaic effect. The principle of the photovoltaic module is the energy conversion of the photovoltaic effect. When the semiconductor material is exposed to light, electron-hole pairs are formed. Under the influence of the electric field, these electron-hole pairs will separate and move. Specifically, the electrons will migrate toward the N region, and the holes will move toward the P region. Therefore, a voltage difference will appear at the external terminals, and a current will be generated after a complete circuit is formed, thereby realizing the process of converting solar energy into electrical energy. This process is used to make photovoltaic modules.

[0085] Figure 2 is the equivalent circuit diagram of a single diode of a photovoltaic module, where P represents the region to which positively charged holes move, and N represents the region to which electrons move; R s Represents the series resistance; R sh Represents parallel resistance; R L The following calculation methods are all based on this topological structure, and the present invention can be applied to the simulation and generation of random local shading conditions of photovoltaic arrays, which are composed of photovoltaic modules connected in series and parallel.

[0086] Figure 3 (a) is a schematic diagram of the parallel diode structure of the photovoltaic module under normal illumination. Figure 3 (b) is a schematic diagram of the parallel diode structure of a photovoltaic module under partial shading, where I represents the photocurrent; I ph Represents the current flowing into the photovoltaic module; IVD Represents the total diffusion current through the PN junction. As shown in the photovoltaic module under normal illumination, the bypass diode output voltage is forward biased, which does not affect the normal operation of the photovoltaic module. Under partial shading, when the photovoltaic module is shaded, the shaded photovoltaic module becomes a load, the output current becomes smaller, and the power generated by the remaining photovoltaic modules begins to be consumed, and the diode is reverse biased. If the conduction threshold of the diode is lower than the reverse bias voltage, the diode is turned on.

[0087] Figure 4 (a) is a photovoltaic array structure diagram of photovoltaic modules of the same model connected in series, PV module refers to photovoltaic module; ph1 Represents the photocurrent of the first module; I ph2 represents the photocurrent of the second module; D 1 , D 3 is a diode, D 2 , D 4 It is an anti-parallel diode. Figure 4 (b) is the array structure of N groups of photovoltaic modules connected in series, I pv Represents photocurrent; I out Represents the output current of the photovoltaic module; I d Indicates the current flowing through the reverse diode; U pv1 Indicates the output voltage of the first photovoltaic module; U pv2 Indicates the output voltage of the second photovoltaic module; U pv3 Represents the output voltage of the third photovoltaic module; U out Represents the output voltage of the photovoltaic array. The power consumed by the shaded photovoltaic module is related to the shaded area and shaded intensity. When the output current of the shaded photovoltaic module is determined, the output current value of the entire series branch is also determined.

[0088] Example 2

[0089] A method for dynamically generating photovoltaic array operating conditions taking into account random differences in multivariate shielding parameters, as described in Example 1, except that in step S1, the corresponding environmental parameters are changed to obtain output characteristics under different environments. In the open circuit voltage test, the open circuit voltage at both ends of the module is obtained. The open circuit voltage is related to the irradiation intensity and has nothing to do with the area of ​​the photovoltaic module. The external characteristics of the photovoltaic module, namely the output characteristics, are an important basis for the design of photovoltaic modules. Light radiation intensity and temperature are two important parameters for determining the output characteristics of photovoltaic modules. When the voltage reaches a certain value, the power can reach the maximum. The point where the output power of the photovoltaic module assembly reaches the maximum is called the maximum power point (MPP) of the photovoltaic array; the voltage U corresponding to this point m , called the maximum power point voltage; the current corresponding to this point is I m, called the maximum power point current, the power at this point is the maximum power P m .

[0090] Analyze the engineering calculation method of photovoltaic array output characteristics under general dynamic conditions. Formula (1) describes the characteristic curve under standard conditions. Take the standard illumination S ref =1000W / m 2 , standard temperature T ref =25℃. When the irradiance and reference temperature change, the irradiance and reference temperature need to be modified to describe the new characteristic curve. According to the standard sunshine intensity and standard temperature I sc , U oc ,I m , U m Calculate I' under general working conditions (irradiance S and temperature T) sc , U' oc , I' m , U' m , then we can still use formula (1) to perform engineering calculations on the output characteristics of the photovoltaic array under non-standard conditions.

[0091] Formula (1) is used to calculate the output characteristics of the photovoltaic array under standard conditions. Formula (2) represents the current at the maximum power point under standard conditions:

[0092]

[0093] Among them, I L Indicates the load current, I sc represents the photon-induced current; U L Indicates the load voltage; I m Indicates the current corresponding to the maximum power point, that is, the optimal current under standard working conditions; U oc Indicates the open circuit voltage under standard working conditions; U m Indicates the voltage corresponding to the maximum power point, that is, the optimal voltage under standard conditions; C 1 , C 2 represents a constant, determined by equations (3) and (4), C 1 and C 2 After determination, the photovoltaic characteristic output curve under standard test conditions can be calculated:

[0094]

[0095] In step S1, the temperature difference and irradiance difference between the shielding condition and the standard condition are first calculated:

[0096] ΔT=TT re f (5)

[0097]

[0098] Wherein, ΔT represents the temperature difference between the shielding condition and the standard condition; ΔS represents the irradiance difference between the shielding condition and the standard condition; T represents the temperature of the shielding condition; T ref represents the temperature of the standard working condition; S represents the irradiance of the shielding working condition; S ref Indicates the irradiance under standard working conditions;

[0099] Then, the short-circuit current, open-circuit voltage, optimal current and optimal voltage under the shading condition are calculated by the photovoltaic array model, as shown in equations (5) to (9):

[0100]

[0101] U' oc =U oc (1-γΔT)(1+βΔT) (9)

[0102]

[0103] U' m =U m (1-γΔT)(1+βΔS) (11)

[0104] Among them, I' sc Indicates the photon-induced current under shielding conditions, i.e., the short-circuit current; U' oc Indicates the open circuit voltage under shielding conditions; I' m represents the current corresponding to the maximum power point under shading conditions, that is, the optimal current; U' m It represents the voltage corresponding to the maximum power point under the shading condition, that is, the optimal voltage; α, β, and γ are all constants, α is 0.0025 / ℃, β is 0.5, and γ is 0.00288 / ℃.

[0105] The open circuit voltage value, short circuit current value, optimal voltage value and optimal current value are the four parameter values ​​of the photovoltaic module. Different photovoltaic module models have different parameter values.

[0106] Example 3

[0107] A method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters, as described in Example 2, except that in step S2, a random shading parameter generator is built into the photovoltaic array model to randomly generate shading parameters of the photovoltaic array, the shading parameters including shading intensity χ, shading difference γ and shading dispersion δ;

[0108] The photovoltaic array includes a plurality of photovoltaic modules N connected in series. sThe photovoltaic modules include standard modules and shielding modules. The photovoltaic modules that receive standard light radiation are set as standard modules. The number of standard modules is N. uic , the photovoltaic modules with low irradiance after being shaded are shaded modules, and the number of shaded modules is N psc :

[0109] N s =N psc +N uic (10)

[0110] The shielding intensity χ measures the degree of shielding of the shielding module and is expressed by formula (11), with the value range set to (0,1):

[0111]

[0112] x j =rand(0,1) (12)

[0113] Among them, x j represents the shielding strength of the jth shielding module; S psc_j represents the irradiance of the jth shading module;

[0114] The shading difference γ is the number of different shading intensity values ​​χ, which indicates the number of photovoltaic modules that receive different light radiation intensities and thus generate different photocurrents. The value range of the shading difference γ is [0, N s ];

[0115] Number of shielding modules N psc It is equal to the sum of the number of shading modules corresponding to each different shading difference, and the number of shading modules is not greater than the total number of series-connected photovoltaic modules;

[0116] N psc =N psc_1 +…+N psc_j +…+N psc_r (j=1,…,γ)(13)

[0117] N psc_j =rand(1,N psc ) (14)

[0118]

[0119] N psc_j represents the number of PV modules with the same light irradiance as the jth shaded module;

[0120] The shading dispersion δ refers to the proportion of the shading intensity corresponding to the shading difference in all shading modules:

[0121]

[0122] Among them, δ j represents the shielding dispersion corresponding to the jth shielding intensity; x j represents the jth shielding intensity. When the shielding condition is determined, the γ value is also determined;

[0123] Shielding equivalent area A psc A represents the sum of the products of the shielding intensity corresponding to each shielding difference and the number of corresponding shielding modules. psc_j is the equivalent shielding area of ​​the jth group:

[0124] A psc_j =x j ×N psc_j (17)

[0125]

[0126] The value range of the number of shielding modules is set according to the number of photovoltaic modules. For example, if the number of modules in series in the photovoltaic power generation system is 30, the number of shielding modules is between 0 and 30. The three parameters of shielding intensity χ, shielding difference γ, and shielding dispersion δ are used to equivalently measure the shielding situation of the photovoltaic array, which are used to adjust the irradiance S of the shielding condition.

[0127] Set the number of random local occlusion conditions to be generated N set For 20 times.

[0128] Example 4

[0129] A method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters is as described in Example 3, except that in step S3, the total number of photovoltaic modules N is set s , the number of photovoltaic shading modules N psc , and the number of standard modules N is obtained uic . Set the shielding strength x of the shielding module j The larger the shielding intensity value, the less irradiance the photovoltaic module receives. Assuming that the photovoltaic array under partial shielding receives different light radiation intensities, the shielding intensity is used to quantify the light radiation intensity lost by shielding. The difference between the standard radiation intensity and the light radiation intensity received by the partially shielded photovoltaic is equal to the shielding intensity multiplied by the standard irradiance intensity.

[0130] Randomly select a value within the numerical range of the random masking parameter generator in step S2 to generate a masking parameter;

[0131] Assuming that the same type of photovoltaic modules have consistent output characteristics, the output characteristics of photovoltaic modules receiving different light radiation intensities are different. The four photovoltaic array parameters under the shaded condition are re-described according to the sunlight radiation intensity and standard temperature under the standard working condition.

[0132] The shielding modules with the same shielding parameters are divided into the same group. The shielding modules are arranged in ascending order according to the light irradiance intensity: normal light, shielding 1, shielding 2, ..., shielding γ. The output characteristic engineering calculation under the shielding condition is calculated according to formula (1), and the photovoltaic array characteristic curve is output; first, the shielding module with the largest shielding intensity value is put into use, and the current switching node under the currently put into use shielding module is calculated. When the output current is greater than the current current switching node, the shielding module is bypassed, otherwise, the standard module continues to be put into use;

[0133] The photovoltaic modules in normal working state are put into operation. As the current decreases, the shielded module groups are put into operation in sequence from low to high according to the shielding intensity, and the remaining shielded photovoltaic modules that are not put into operation are bypassed through diodes; when the voltage reaches the inflection point, the next shielded module group is put into operation in sequence, and the corresponding photovoltaic shielding module switching state changes.

[0134] Example 5

[0135] A method for dynamically generating photovoltaic array operating conditions taking into account random differences in multivariate shading parameters is as described in Example 4, except that in step S4, the short-circuit current, open-circuit voltage, optimal current and optimal voltage of the photovoltaic array under shading conditions are calculated again according to the photovoltaic array model, that is, formulas (5) to (9), the optimal current and the optimal voltage are multiplied to obtain the maximum output power, and the IV and PV characteristic curves of the photovoltaic array are plotted.

[0136] Method Validation:

[0137] The present invention builds a photovoltaic array series structure in MATLAB / Simulink. The photovoltaic array structure is composed of photovoltaic modules connected in series. The wiring diagram is as follows Figure 5 As shown, two working conditions are set up to verify the feasibility of the proposed photovoltaic array model considering the influence of local shading, and to prove the accuracy of the photovoltaic array output characteristics under the local shading.

[0138] Figure 5 The PV array series structure of partial shading condition 1 is shown, which includes 30 shaded modules and 60 standard modules. The irradiances received by the standard modules and the shaded modules are S 1 and S 2 , and S 1 >S 2 . The IV and PV characteristics of the photovoltaic array are demonstrated. Figure 6 (a) Figure 6 (b) shows the changes in output voltage and output current under partial shading condition 1. Figure 6 (c) Figure 6(d) is the output voltage and output current curve of the photovoltaic module. First, the output characteristics of the photovoltaic module are analyzed from the PV and IV. Figure 6 (b), the voltage inflection point is the boundary between region 1 and region 2. When the working position is in region 1, the standard module works, the light radiation intensity is low, the short-circuit current is lower than the current of the photovoltaic array, and the bypass diode of the shaded module is turned on. The bypass diode of the shaded module will conduct additional current and cause the voltage across the two ends to be approximately -0.7 to -1V. In this case, the total output voltage of the photovoltaic array is evenly distributed only among the standard modules. When the working position is in region 2, the standard module and the shaded module work. When the output current of the photovoltaic array decreases and the photovoltaic array current is lower than the short-circuit current of the shaded module, the total output voltage of the photovoltaic array begins to be distributed on the shaded modules. The voltage on these shaded modules will gradually increase. The standard module voltage operates in an approximately constant voltage region. Therefore, the voltage of each of the shaded modules will be greater than the photovoltaic array voltage at the maximum power point (MPP) under standard illumination and close to the total photovoltaic series voltage at the maximum power point under standard illumination. There are two extreme points on this P–V characteristic curve.

[0139] Combination Figure 7 Analysis of partial shading condition 2 shows that there are two types of shading modules in the photovoltaic array, each including 30 photovoltaic array modules, among which the light radiation intensity received by shading module 1 is greater than that of shading module 2. Figure 8 When the PV array is in region 1, the standard module works. The light radiation intensity is low, the short-circuit current is lower than the current of the PV array, and the bypass diode of the shading module is turned on. When the working position is in region 2, the standard module and shading module 1 work, and the bypass diode of shading module 2 is turned on. When the working position is in region 3, the PV array current is further reduced, the short-circuit current of the shading module is greater than the PV output current, and the standard module and shading modules 1 and 2 work. There are three inflection points on the I–V characteristic curve, so there are three extreme points on the P–V characteristic curve.

[0140] The power analysis model needs to input the parameters of the corresponding photovoltaic array module, and calculate the output characteristics of the photovoltaic module under partial shading through the parameters. The specific photovoltaic parameters used in the power analysis model are: open circuit voltage 62.8V, short circuit current 9.34A, optimal voltage 53.2V, optimal current 8.83A, and the maximum output power of a single module is 469.72W. The solid line represents the photovoltaic array output characteristic waveform curve obtained by the power analysis model, and the dotted line represents the photovoltaic array output characteristic waveform curve obtained by simulation. The photovoltaic characteristic output curve obtained by the power analysis model proposed in the present invention is consistent with the simulation waveform obtained in Simulink. By changing the shading intensity of the photovoltaic array module, it can be concluded that Fig. 9 , Fig.10The comparison of the photovoltaic array output characteristics of working conditions 3 and 4 respectively shows that the photovoltaic output curve obtained by the model proposed in the present invention is still consistent with the simulation waveform.

[0141] The three parameters are randomly selected within the constraints. The masking intensity ranges from 0 to 1, and the masking difference ranges from 0 to N. s The total number of shading modules corresponding to all shading differences does not exceed the total number of series-connected photovoltaic modules. The photovoltaic characteristic curve shows more obvious randomness and volatility. For a photovoltaic array with 10 series-connected photovoltaic modules, the model randomly generates 4 shading parameters. Fig.11 (a) Fig.11 (b) shows the characteristic output voltage curve and output current curve of the photovoltaic array under four random partial shading conditions.

[0142] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters, characterized in that: The steps include: S1: Set the photovoltaic array parameters under the shade condition, including short-circuit current, open-circuit voltage, optimal voltage value and optimal current value; S2: Set the value range of the random shading parameter generator and the number of random local shading conditions generated N set ; S3: Randomly generate shading parameters and import the PV array model that takes into account the differences in PV local shading parameters; S4: Output the PV characteristic curve of the photovoltaic array under partial shading conditions until N is reached set ,Finish; Formula (1) is used to calculate the output characteristics of the photovoltaic array under standard conditions. Formula (2) represents the current at the maximum power point under standard conditions: Among them, I L Represents the load current, I sc represents the photon-induced current; U L Indicates the load voltage; I m Indicates the current corresponding to the maximum power point, that is, the optimal current under standard working conditions; U oc Indicates the open circuit voltage under standard working conditions; U m represents the voltage corresponding to the maximum power point, that is, the optimal voltage under standard conditions; C1 and C2 represent constants, which are determined by equations (3) and (4): In step S1, the temperature difference and irradiance difference between the shielding condition and the standard condition are first calculated: ΔT=T-T ref (5) Wherein, ΔT represents the temperature difference between the shielding condition and the standard condition; ΔS represents the irradiance difference between the shielding condition and the standard condition; T represents the temperature of the shielding condition; T ref represents the temperature of the standard working condition; S represents the irradiance of the shielding working condition; S ref Indicates the irradiance under standard working conditions; Then, the short-circuit current, open-circuit voltage, optimal current and optimal voltage under the shading condition are calculated by the photovoltaic array model, as shown in equations (5) to (9): U' oc =U oc (1-γΔT)(1+βΔT) (9) U' m =U m (1-γΔT)(1+βΔS) (11) Among them, I' sc Indicates the photon-induced current under shielding conditions, i.e., the short-circuit current; U' oc Indicates the open circuit voltage under shielding conditions; I' m represents the current corresponding to the maximum power point under shading conditions, that is, the optimal current; U' m It represents the voltage corresponding to the maximum power point under the shading condition, that is, the optimal voltage; α is 0.0025 / ℃, β is 0.5, and γ is 0.00288 / ℃; In step S2, a random shading parameter generator is built into the photovoltaic array model to randomly generate shading parameters of the photovoltaic array, and the shading parameters include shading intensity χ, shading difference γ and shading dispersion δ; The photovoltaic array includes a plurality of photovoltaic modules N connected in series. s The photovoltaic modules include standard modules and shielding modules. The photovoltaic modules that receive standard light radiation are set as standard modules. The number of standard modules is N. uic , the photovoltaic modules with low irradiance after being shaded are shaded modules, and the number of shaded modules is N psc : N s =N psc +N uic (12) The shielding intensity χ measures the degree of shielding of the shielding module and is expressed by formula (13), with the value range set to (0,1): x j =rand(0,1) (14) Among them, x j represents the shielding strength of the jth shielding module; S psc_j represents the irradiance of the jth shading module; The shading difference γ is the number of different shading intensity values ​​χ, which indicates the number of photovoltaic modules that receive different light radiation intensities and thus generate different photocurrents. The value range of the shading difference γ is [0, N s ]; Number of shielding modules N psc It is equal to the sum of the number of shielding modules corresponding to each different shielding difference degree; N psc =N psc_1 +…+N psc_j +…+N psc_r (j=1,…,γ) (15) N psc_j =row(1,N psc ) (16) N psc_j represents the number of photovoltaic modules with the same light irradiance as the jth shading module; the shading dispersion δ refers to the proportion of the shading intensity corresponding to the shading difference in all shading modules: Among them, δ j represents the shielding dispersion corresponding to the jth shielding intensity; x j represents the jth shielding intensity; Shielding equivalent area A psc A represents the sum of the products of the shielding intensity corresponding to each shielding difference and the number of corresponding shielding modules. psc_j is the equivalent shielding area of ​​the jth group: A psc_j =x j ×N psc_j (19) The value range of the number of shielding modules is set according to the number of photovoltaic modules, and the three parameters of shielding intensity χ, shielding difference γ, and shielding dispersion δ are used to equivalently measure the shielding situation of the photovoltaic array, which is used to adjust the irradiance S of the shielding condition; Set the number of random local occlusion conditions to be generated N set 10 to 30 times; In step S4, the short-circuit current, open-circuit voltage, optimal current and optimal voltage of the photovoltaic array under the shaded condition are calculated again according to the photovoltaic array model, that is, formulas (5) to (9). The maximum output power is obtained by multiplying the optimal current and the optimal voltage, and the IV and PV characteristic curves of the photovoltaic array are plotted.

2. The method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters according to claim 1, characterized in that: Temperature T under standard conditions ref =25℃, irradiance S under standard working conditions ref =1000W / m 2 .

3. The method for dynamically generating photovoltaic array operating conditions considering random differences in multivariate shading parameters according to claim 2, characterized in that: In step S3, randomly taking a value within the numerical range of the random masking parameter generator in step S2 to generate a masking parameter; Assuming that the same type of photovoltaic modules have consistent output characteristics, the output characteristics of photovoltaic modules receiving different light radiation intensities are different. The four photovoltaic array parameters under the shaded condition are re-described according to the sunlight radiation intensity and standard temperature under the standard working condition. The output characteristic engineering calculation under the shading condition is calculated according to formula (1), and the characteristic curve of the photovoltaic array is output; first, the shading module with the largest shading intensity value is put into use, and the current switching node under the currently put into use shading module is calculated. When the output current is greater than the current current switching node, the shading module is bypassed, otherwise, the standard module continues to be put into use.

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