Satellite photovoltaic array design method considering parallel mismatch temperature rise

Abstract

The application provides a satellite photovoltaic array design method considering parallel mismatch temperature rise, and belongs to the photovoltaic power generation technical field.The method comprises the following steps: S1, a controller acquires information in an actual operation process of a satellite and design data of a battery; S2, the controller establishes a thermal balance equation according to the information in the actual operation process of the satellite and the design data of the battery acquired in S1; S3, a photovoltaic array model is established, and the size of reverse current and the forward voltage of the battery under parallel mismatch are simulated; S4, the size of the reverse current under parallel failure is corrected according to the influence of the battery temperature on the volt-ampere characteristic of the battery, the stable corrected reverse current is obtained, and the stable battery temperature is calculated; and S5, the number of parallel branches of the photovoltaic array model in S3 is changed, and the maximum parallel number of the parallel branch Z without the anti-reverse diode is calculated.The method corrects the reverse current, obtains the corrected battery temperature, and obtains the maximum number of batteries that can be connected in parallel according to the corrected battery temperature.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology, specifically relating to a design method for satellite photovoltaic arrays that takes into account the temperature rise due to parallel mismatch. Background Technology

[0002] Satellite photovoltaic arrays are an important component of satellites and their primary energy source. In outer space, these arrays convert solar energy into electrical energy, providing a stable power output for satellite operation.

[0003] Most battery series mismatches and parallel mismatches are inextricably linked. However, each satellite battery has two bypass diodes, so series mismatches are not an issue. Yet, parallel mismatches still exist in satellite batteries. Parallel mismatch is a loss caused by voltage mismatch between parallel components. Parallel mismatch leads to reverse current flowing into the lower-voltage branch battery, further increasing battery temperature, affecting power output, and in severe cases causing irreversible damage to the battery.

[0004] Existing photovoltaic (PV) array design methods, such as the Chinese patent with publication number CN115549205A, disclose methods for locating and optimizing series and parallel mismatches in PV power plant modules. These methods primarily focus on terrestrial PV arrays, taking series mismatch into account. However, existing terrestrial PV array design methods differ from satellite PV array design methods, which do not require consideration of series mismatch. Furthermore, satellite PV arrays are constantly moving in space, and their position and angle affect their temperature. Therefore, the temperature rise calculation methods for satellite PV arrays differ from those for terrestrial PV arrays.

[0005] For the two reasons mentioned above, the existing design methods for ground-based photovoltaic arrays cannot be directly applied to the design methods for satellite photovoltaic arrays; there are significant differences between the two. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention proposes a design method for satellite photovoltaic arrays that considers the temperature rise due to parallel mismatch, in order to solve the technical problem of how to study the temperature rise due to parallel mismatch in satellite photovoltaic arrays.

[0007] To achieve the above objectives, the present invention provides a satellite photovoltaic array design method considering the temperature rise due to parallel mismatch, comprising the following steps: S1: The controller acquires information from the actual operation of the satellite and the battery design data; S2: The controller establishes a thermal balance equation based on the information from the actual operation of the satellite and the battery design data acquired in S1; S3: A photovoltaic array model is established to simulate the magnitude of the reverse current and the forward voltage of the battery under parallel mismatch; S4: The magnitude of the reverse current under parallel failure is corrected according to the influence of battery temperature on the battery's volt-ampere characteristics to obtain a stable corrected reverse current, and a stable battery temperature is calculated; S5: The number of parallel branches in the photovoltaic array model in S3 is changed to calculate the maximum number of parallel branches Z without anti-reverse diodes.

[0008] Furthermore, in step S1, the information on the actual operation of the satellite includes the solar constant; the design data of the battery includes the battery area, battery absorptivity and emissivity, photoelectric conversion efficiency, battery components and the thermal conductivity of each component.

[0009] Furthermore, in step S2,

[0010] The heat balance equation is: q = q c +q b =αG-ηG-E cell (T)+α b G b -E back (T) (1)

[0011] The heat flux densities on the front and back of the battery are q, respectively. c q b The total heat flux density of the battery is q; α is the front absorptivity of the battery; η is the photoelectric conversion efficiency of the battery; G is the total radiant energy received by the battery from the outside environment; G b The total radiant energy received from the outside environment on the back of the battery; α b The absorption rate at the back of the battery; E cell E represents the radiant energy emitted from the front of the battery. back E is the radiation energy emitted from the back of the battery. cell and E back Both are functions of the battery's steady-state temperature T, and the calculation formulas are as follows:

[0012] E cell =σε cell T 4 (2)

[0013] E back =σε back T 4 (3)

[0014] Where σ is the Stefan-Boltzmann constant, ε cell ε back These are the emissivity of the front and back sides of the battery, respectively; T is the temperature of the battery in steady state.

[0015] When q is 0, the steady-state temperature of the battery can be obtained.

[0016] Further, step S3 includes the following steps:

[0017] S31: In the simulation software, build a battery module based on the battery to be analyzed, and determine the battery's current-voltage characteristics by inputting the parameters of the equivalent circuit model of the battery; simulate the current-voltage characteristics of the battery through Simulink, compare the simulated current-voltage characteristic curve with the measured value of the battery, and continuously adjust the variable parameter values ​​in the equivalent circuit model to make the error between the two less than or equal to 5%. Set the irradiance and steady-state temperature as the input terminals of the battery module, and the forward bias voltage V and reverse current I of the battery as the output terminals of the battery module.

[0018] S32: Set the number of parallel branches z in the photovoltaic array and the number of series battery modules w on each branch; set the corresponding number of battery modules in S31 to build the photovoltaic array modules, input the solar constant obtained in step S1 to the battery irradiation input terminal, and input the steady-state temperature calculated in step S2 to the battery temperature input terminal.

[0019] By employing simulation, the error between the simulated volt-ampere characteristic curve and the measured value of the battery is controlled within 5%. This allows the battery characteristics shown in the simulation to be considered as actual battery characteristics. Through simulation, the forward bias voltage V and reverse current I of the battery can be obtained.

[0020] Furthermore, in step S4, the formula for calculating the battery temperature is:

[0021] Q = J re V = AT cell 4 +BT cell +C (4)

[0022] Q represents the heat power generated by the reverse current; J re V is the reverse current density obtained in step S3; V is the forward bias voltage of the battery obtained in step S3, which is considered constant; A, B, and C are the corresponding parameter values, and I is the corrected current of the battery. c The calculation formula is:

[0023]

[0024] Among them, I ph The photocurrent generated by the battery; R sR is the series resistance of the battery. sh The parallel resistance of the battery; V c n is the output voltage of the battery; n1 and n2 are the quality factors of diodes 1 and 2, respectively; q is the elementary charge of an electron; and k is the Boltzmann constant.

[0025] in,

[0026] I s1 I s2 The dark saturation currents of diodes 1 and 2 are provided by the battery manufacturer; T meas X is the standard temperature for the dark saturation current density of diodes 1 and 2 in equation (5); i V is the temperature coefficient; EG is the bandgap of the battery; V t Thermoelectric voltage is equal to T cell For the battery temperature; I si (T cell ) represents the corrected dark saturation current of the two diodes 1 and 2.

[0027] Furthermore, the relationship between the number of parallel connections Z and the battery temperature is established as follows:

[0028]

[0029] Beneficial effects

[0030] This method approximates the characteristics of a battery through simulation. The solar constant is input to the battery irradiance input terminal, and the steady-state temperature is input to the battery temperature input terminal. The forward bias voltage V and reverse current I of the battery are obtained through simulation. The reverse current I is then corrected, and the steady-state temperature of the battery is calculated using the corrected reverse current. By changing the number of parallel connections in the simulation software, the maximum number of parallel batteries Z can be determined, thus achieving the purpose of photovoltaic array design. Attached Figure Description

[0031] Figure 1 This is a diagram showing the energy balance of the satellite's batteries;

[0032] Figure 2 This is a temperature change graph of a 300km satellite battery over one cycle;

[0033] Figure 3 This is a schematic diagram of the battery module created through simulation;

[0034] Figure 4 This is a schematic diagram showing the simulated and experimental values ​​of the battery's current-voltage characteristics;

[0035] Figure 5 It is a simulated page layout;

[0036] Figure 6 This is a schematic diagram of the photovoltaic array module;

[0037] Figure 7 This is a schematic diagram of the battery temperature correction steps in this embodiment. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] A design method for satellite photovoltaic arrays that considers the temperature rise due to parallel mismatch includes the following steps:

[0040] S1: The controller acquires information about the actual operation of the satellite and the design data of the battery.

[0041] The information obtained during actual satellite operation includes satellite orbital altitude, solar constant, solar radiation energy, Earth's emitted radiation, Earth's reflected radiation, space cold background temperature, angular coefficient with respect to the Sun, and angular coefficient with respect to the Earth.

[0042] The design data of a battery includes battery area, battery absorptivity and emissivity, photoelectric conversion efficiency, battery components and the thermal conductivity of each component.

[0043] S2: Based on the information obtained from S1 regarding the actual operation of the satellite and the design data of the battery, the controller establishes a thermal balance equation and calculates the steady-state temperature of the battery when it orbits the Earth once with the satellite.

[0044] like Figure 1 As shown, the heat balance equation in this step is:

[0045] q = q c +q b =αG-ηG-E cell (T)+α b G b -E back (T) (1)

[0046] The heat flux densities on the front and back of the battery are q, respectively. c q b The total heat flux density of the battery is q; α is the front absorptivity of the battery; η is the photoelectric conversion efficiency of the battery; G is the total radiant energy received by the battery from the outside environment; G b The total radiant energy received from the outside environment on the back of the battery; αb The absorption rate at the back of the battery; E cell E represents the radiant energy emitted from the front of the battery. back E is the radiation energy emitted from the back of the battery. cell and E back Both are functions of the battery's steady-state temperature T, and the calculation formulas are as follows:

[0047] E cell =σε cell T 4 (2)

[0048] E back =σε back T 4 (3)

[0049] Where σ is the Stefan-Boltzmann constant, ε cell ε back , where are the emissivity of the front and back of the battery, respectively, and T is the temperature of the battery in steady state.

[0050] Taking the external radiation energy received by the front of the battery as an example, the calculation is shown in formula (4):

[0051] G=X c,s E sun +X c,e E earth +X c,r E refl ec t (4)

[0052] In the formula, X c,s X is the angular factor of the battery facing the sun; c,e X is the angular factor of the battery facing the Earth; c,r E represents the angular coefficient of the area reflecting the Earth's surface from the front of the battery; sun E earth E reflect These are solar radiation energy, Earth's emitted radiation, and Earth's reflected radiation, respectively.

[0053] When q is 0, the battery is in a stable thermal equilibrium state, and the steady-state temperature T of the battery can be calculated. Taking 300km as an example, this embodiment plots a curve of the steady-state temperature of the satellite during one orbit around the Earth, as shown below. Figure 2 As shown.

[0054] S3: Establish a photovoltaic array model and simulate the magnitude of the reverse current and forward voltage of the cells under parallel mismatch.

[0055] Specifically, step S3 includes the following steps:

[0056] S31, see Figure 3In the simulation software, a battery module is built based on the battery to be analyzed. The battery module corresponding to the battery selected in this embodiment is as follows: Figure 3 As shown. The battery's volt-ampere characteristics are determined by inputting the parameters of the battery's equivalent circuit model; see... Figure 4 and Figure 5 The battery's volt-ampere characteristics were simulated using Simulink. The simulated volt-ampere characteristic curve was compared with the measured values ​​of the battery. By continuously adjusting the variable parameter values ​​in the equivalent circuit model, such as parallel resistance, series resistance, diode quality factor, and dark saturation current, the error between the two was made less than or equal to 5%. Irradiance and steady-state temperature were set as the input terminals of the battery module, and the battery's forward bias voltage V and reverse current I were set as the output terminals of the battery module.

[0057] S32. According to user needs, see Figure 6 Set the number of parallel branches z in the photovoltaic array, and the number of series battery modules w on each branch; set the corresponding number of battery modules in S31 to build the photovoltaic array module. The completed photovoltaic array module is as follows: Figure 6 As shown; the solar constant obtained in step S1 is input to the battery irradiation input terminal, and the steady-state temperature calculated in step S2 is input to the battery temperature input terminal.

[0058] S4: Correct the magnitude of the reverse current under parallel failure based on the effect of battery temperature on the battery's volt-ampere characteristics, and obtain a stable corrected reverse current.

[0059] In step S4, the corrected battery current I c The calculation formula is as follows:

[0060]

[0061] In equation (5), I ph The photocurrent generated by the battery; R s R is the series resistance of the battery. sh The parallel resistance of the battery; V c n is the output voltage of the battery; n1 and n2 are the quality factors of diodes 1 and 2, respectively; q is the elementary charge of an electron; and k is the Boltzmann constant.

[0062] In equation (5):

[0063]

[0064] I s1 I s2 The dark saturation currents of diodes 1 and 2 are provided by the battery manufacturer; T meas X is the standard temperature for the dark saturation current density of diodes 1 and 2 in equation (5); iV is the temperature coefficient; EG is the bandgap of the battery; V t Thermoelectric voltage is equal to T cell The temperature of the battery. si (T cell ) represents the corrected dark saturation current of the two diodes 1 and 2.

[0065] Q = J re V = AT cell 4 +BT cell +C (7)

[0066] In formula (7), Q represents the heat power generated by the reverse current; J re V is the reverse current density obtained in step S3; V is the forward bias voltage of the battery obtained in step S3, which is assumed to be constant; A, B, and C are the corresponding parameter values, which need to be analyzed according to different environmental conditions.

[0067] See Figure 7 The operation process for step S4 is as follows:

[0068] The forward bias voltage V and reverse current density J of the battery obtained in step S3 re Substitute into equation (7), where

[0069] J re =I / A (8)

[0070] Where A is the cross-sectional area of ​​the battery; I is the reverse current in S3. The corresponding battery temperature T can be obtained by solving equation (7). cell1 Then put T cell1 Substituting into equations (5) and (6), we obtain the battery-corrected current I. c The corrected current I is obtained by calculating from equation (8). c Corresponding current density J re2 Then the corrected current density J re2 Substituting into formula (7), since the forward bias voltage V remains constant, the corrected battery temperature T can be obtained. cell2 .

[0071] The above current I c Substituting into formula (5) for iterative calculation, the corrected current I of the other battery is calculated. c2 Following the steps above, I c2 Substituting into formula (7), another corrected battery temperature T is calculated. cell3 And so on. Until the temperature T is obtained. celln The temperature T obtained in the previous step cell(n-1)If the difference is less than the given allowable iteration error, which is 0.2K in this embodiment, the battery temperature can be considered to be close to constant. At this point, with Z parallel branches, the constant battery temperature is considered to be T. cell(z)， T cell(z) With T cell(n-1) equal.

[0072] S5: Calculate the maximum number of parallel branches Z without anti-reverse diodes.

[0073] Based on the battery selected in S3, its maximum withstand temperature T can be determined from the battery specifications. max Increase the number of parallel branches z in S3 to z+1. Simulate the magnitude of the reverse current and forward voltage under parallel mismatch with z+1 parallel branches. Calculate T with z+1 parallel branches using the steps in S4. cell(z+1) The relationship between the number of parallel batteries Z and the constant battery temperature is established as follows:

[0074]

[0075] The number of parallel connections can be calculated as Z from equation (9).

[0076] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A design method for satellite photovoltaic arrays considering parallel mismatch temperature rise, characterized in that, Includes the following steps, S1: The controller acquires information about the actual operation of the satellite and the design data of the battery; S2: The controller establishes a thermal balance equation based on the information obtained from S1 regarding the actual operation of the satellite and the battery design data. S3: Establish a photovoltaic array model and simulate the magnitude of the reverse current and forward bias voltage of the cells under parallel mismatch. S4: Correct the magnitude of the reverse current under parallel failure based on the effect of battery temperature on battery volt-ampere characteristics, obtain a stable corrected reverse current, and calculate the stable battery temperature. The formula for calculating the heat power caused by reverse current is: ； In the formula, The heat power generated by the reverse current; The reverse current density obtained in step S3; The forward bias voltage of the battery obtained in step S3 is considered constant; For the corresponding parameter values, The temperature of the battery; Battery corrected current The calculation formula is: ； in, The photocurrent generated by the battery; This is the series resistance of the battery; This is the parallel resistance of the battery; This refers to the output voltage of the battery. These are the quality factors of diodes 1 and 2, respectively. The fundamental charge of an electron; Boltzmann's constant; in, ; The dark saturation currents of diodes 1 and 2 are provided by the battery manufacturer. The standard temperature for the dark saturation current density of diodes 1 and 2; Temperature coefficient; The bandgap of the battery; Thermoelectric voltage is equal to ; The temperature of the battery; This is represented by the corrected dark saturation current of diodes 1 and 2; S5: Change the number of parallel branches in the photovoltaic array model in S3, and calculate the maximum number of parallel branches Z without anti-reverse diodes.

2. The satellite photovoltaic array design method considering parallel mismatch temperature rise according to claim 1, characterized in that, In step S1, the information on the actual operation of the satellite includes the solar constant; the design data of the battery includes the battery area, battery absorptivity and emissivity, photoelectric conversion efficiency, battery components and the thermal conductivity of each component.

3. The satellite photovoltaic array design method considering parallel mismatch temperature rise according to claim 1, characterized in that, In step S2, the heat balance equation is: The heat flux densities experienced by the front and back sides of the battery are respectively... ; This represents the total heat flux density of the battery; The front absorption rate of the battery; The photoelectric conversion efficiency of the battery; The total radiant energy received from the outside environment by the front of the battery; The total radiant energy received from the outside environment at the back of the battery; The absorption rate on the back of the battery; The radiation energy emitted from the front of the battery; This refers to the radiation energy emitted from the back of the battery. and All about battery temperature The function is calculated using the following formula: ； ； in, It is the Stefan-Boltzmann constant. The emissivity is shown for the front and back of the battery, respectively. The temperature at which the battery is in steady state, when When the value is 0, the steady-state temperature of the battery can be obtained.

4. The satellite photovoltaic array design method considering parallel mismatch temperature rise according to claim 1, characterized in that, Step S3 Includes the following steps, S31: In the simulation software, build a battery module based on the battery to be analyzed. Determine the battery's volt-ampere characteristics by inputting the parameters of the equivalent circuit model. Simulate the battery's volt-ampere characteristics using Simulink, compare the simulated volt-ampere characteristic curve with the measured values ​​of the battery, and continuously adjust the variable parameter values ​​in the equivalent circuit model to ensure that the error between the two is less than or equal to 5%. Set the irradiance and steady-state temperature as the input terminals of the battery module, and the forward bias voltage of the battery. and reverse current As the output terminal of the battery module; S32: Set the number of parallel branches in the photovoltaic array And the number of series-connected battery modules on each branch. Set the corresponding number of battery modules in S31 to establish a photovoltaic array module. The solar constant obtained in step S1 is input to the battery irradiation input terminal, and the steady-state temperature calculated in step S2 is input to the battery temperature input terminal.

5. A satellite photovoltaic array design method considering parallel mismatch temperature rise according to claim 1, characterized in that, Establish parallel quantity The relationship with battery temperature is as follows: 。

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