Intelligent control method and system for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance

Abstract

The present invention relates to the field of battery management technology, and specifically to an intelligent control method and system for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant. The present invention divides the batteries to be charged each time into low internal resistance batteries and high internal resistance batteries, matches the two batteries according to the difference between the voltage of the high internal resistance battery and the voltage of the low internal resistance battery after photovoltaic charging power adjustment, and obtains a matching battery for the high internal resistance battery; selects a battery to be balanced according to the difference between the voltage of the high internal resistance battery and the voltage of its matching battery after photovoltaic charging power adjustment and the voltage of the high internal resistance battery, and balances the battery to be balanced with its matching battery, thereby obtaining the actual discharge power of each charge and participating in the control of the operation and maintenance of the virtual power plant. The present invention selects the battery to be balanced, and considers the unstable factor of light in the selection process, thereby improving the balancing efficiency, extending the battery life, and dynamically adapting to photovoltaic fluctuations.

Description

Technical Field

[0001] The present invention relates to the field of battery management technology, and in particular to an intelligent control method and system for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant. Background Art

[0002] Solar-plus-storage charging and discharging stations, with their ability to absorb clean energy locally and their flexible regulation, are key enablers of new power system development. As a key component of virtual power plants (VPPs), these stations participate in the intelligent regulation of VPPs, collaboratively optimizing the operation of distributed energy resources and energy storage facilities, effectively balancing grid loads and improving system stability and flexibility.

[0003] When a photovoltaic charging and discharging station participates in virtual power plant regulation, unstable light intensity causes fluctuations in the charging power of the photovoltaic storage batteries. This, in turn, leads to inconsistent performance among different batteries due to differences in battery manufacturing processes, causing imbalanced charge levels between batteries. The specific impact mechanism is as follows: when sunlight is sufficient, meaning the photovoltaic charging power is high, the charging needs of batteries of varying performance can be met, and internal resistance differences have little impact on the charge capacity. When sunlight is insufficient, low-resistance batteries absorb more energy due to lower energy losses, while high-resistance batteries (i.e., batteries with lower performance) experience greater energy losses. Consequently, within the same amount of sunlight charging time, low-resistance batteries receive far more energy than high-resistance batteries, exacerbating charge imbalances between batteries. Charge balancing can fully utilize the battery pack's total energy storage potential, reduce accelerated aging caused by inconsistent battery charge levels, and extend the battery life of the photovoltaic charging and discharging station.

[0004] Existing balancing technology usually detects the voltage difference between batteries and transfers the power of high-voltage batteries to low-voltage batteries to achieve power balancing between batteries. However, unstable light intensity will cause the corresponding relationship between battery voltage and power to shift, resulting in the voltage difference between batteries not accurately reflecting the actual power difference. During the power balancing process, the higher-voltage battery consumes insufficient power due to internal resistance consumption, resulting in insufficient power to balance the lower-voltage battery. The balancing circuit continues to consume energy but fails to achieve power transfer, resulting in low power balancing efficiency of the batteries in the solar storage charging and discharging station. Summary of the Invention

[0005] In order to solve the technical problem of low battery charge balancing efficiency due to unstable light intensity, the purpose of the present invention is to provide an intelligent control method and system for photovoltaic storage charging and discharging stations to participate in the operation and maintenance of virtual power plants. The technical solutions adopted are as follows:

[0006] In a first aspect, an embodiment of the present invention provides an intelligent control method for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant, the method comprising:

[0007] Obtain the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charge and the battery voltage after each charge;

[0008] Based on the battery voltage after each charge, the batteries are divided into low internal resistance batteries and high internal resistance batteries; based on the difference between the voltage of the high internal resistance battery after each charge and the voltage of the low internal resistance battery after adjustment by the photovoltaic charging power, the low internal resistance battery and the high internal resistance battery of each charge are matched to obtain matching batteries for the high internal resistance battery;

[0009] Based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after photovoltaic charging power adjustment, as well as the voltage of the high-resistance battery, a battery to be balanced is selected from the high-resistance batteries charged each time, and the battery to be balanced and its matching battery are charged and balanced;

[0010] The battery after power balancing is discharged, and the actual discharge power of the photovoltaic storage charging and discharging station after each charge is obtained according to the current change of the battery during the power discharge process, and participates in the regulation of virtual power plant operation and maintenance.

[0011] Furthermore, obtaining a matching battery for the high internal resistance battery includes:

[0012] Based on the photovoltaic charging power of each charge, the battery power separation degree of each charge is obtained;

[0013] The battery charge separation degree is used to adjust the voltage of the low internal resistance battery after each charge to obtain a corrected voltage; the corrected voltage of the low internal resistance battery and the voltage of the high internal resistance battery after each charge are arranged in sequence to obtain a low internal resistance voltage sequence and a high internal resistance voltage sequence; a target balancing voltage is obtained for each charge, where the elements in the low internal resistance voltage sequence are greater than the target balancing voltage, and the elements in the high internal resistance voltage sequence are less than the target balancing voltage;

[0014] Set the initial subscript to be measured to 0, and use the low internal resistance voltage sequence as the initial voltage sequence to be measured; determine whether the element corresponding to the subscript to be measured in the voltage sequence to be measured is smaller than the element corresponding to the subscript to be measured in the high internal resistance voltage sequence; if so, delete the element corresponding to the subscript to be measured in the voltage sequence to be measured to obtain a new voltage sequence to be measured; if not, determine a new subscript to be measured, and determine whether the element corresponding to the new subscript to be measured in the new voltage sequence to be measured is smaller than the element corresponding to the new subscript to be measured in the high internal resistance voltage sequence, and stop updating the voltage sequence to be measured until the new subscript to be measured is greater than the subscript corresponding to the last element in the high internal resistance voltage sequence, and use the updated voltage sequence to be measured as the voltage sequence that meets the equilibrium condition;

[0015] The matching battery of each high internal resistance battery in each charge is determined, and the subscript of the corresponding element of each high internal resistance battery in the high internal resistance voltage sequence is equal to the subscript of the corresponding element of the matching battery in the balanced voltage sequence.

[0016] Furthermore, obtaining the battery power separation degree of each charge includes:

[0017] Select a full-charge charging power from the photovoltaic charging powers of several charging times before each charging, and the voltage of the battery after the corresponding full-charge charging power is within the full-charge voltage range;

[0018] The cumulative sum of the differences between all full-charge charging powers and the photovoltaic charging power of each charge is normalized to obtain the battery power separation degree of each charge.

[0019] Furthermore, the step of selecting batteries to be balanced from the high internal resistance batteries charged each time includes:

[0020] Normalizing the difference between the voltage of each high internal resistance battery after each charge and the target balancing voltage to obtain a balancing reference deviation;

[0021] The matching and balancing requirement of the corresponding high-internal-resistance battery is obtained based on the difference between the voltage of each high-internal-resistance battery and the corrected voltage of its matching battery after each charge, as well as the balancing reference deviation. The high-internal-resistance battery corresponding to the matching and balancing requirement less than a preset requirement threshold is selected from the high-internal-resistance batteries charged each time as the battery to be balanced.

[0022] Furthermore, the target balancing voltage is equal to the product of the sum of the battery charge separation degree and a constant 1 and the concentrated value of the voltage of all batteries after each charging.

[0023] Furthermore, the method for obtaining the actual discharged power includes:

[0024] Obtain the discharge current of all batteries at each moment in the power release time period, calculate the average of the discharge currents at the same moment, perform curve fitting on the average values ​​corresponding to all moments in the power release time period, and obtain a discharge current function; integrate the discharge current function within the discharge time period, and take the product of the integral result and the total number of batteries as the actual discharge capacity of the solar storage charging and discharging station after each charge.

[0025] Furthermore, performing battery balancing on the battery to be balanced and its matching battery includes:

[0026] For each battery to be balanced, the matching battery of the battery to be balanced is discharged, and the excess power is transferred to the battery to be balanced. The discharge voltage of the battery to be balanced and its matching battery at each moment during the power transfer process is obtained. If the discharge voltage difference between the battery to be balanced and its matching battery at the same moment is not within the balancing requirement range, the power transfer continues until the discharge voltage difference is within the balancing requirement range, and the power transfer is stopped, completing the power balancing of the batteries after each charge.

[0027] Furthermore, the division of batteries into low internal resistance batteries and high internal resistance batteries includes:

[0028] For each battery after charging, the centralized value of the voltage of all batteries is calculated, and batteries with voltages less than the centralized value are classified as high internal resistance batteries, and batteries with voltages greater than or equal to the centralized value are classified as low internal resistance batteries.

[0029] Furthermore, the battery power separation degree is negatively correlated with the correction voltage.

[0030] Furthermore, the number of low internal resistance batteries charged each time is greater than the number of high resistance batteries.

[0031] Furthermore, the arrangement order of elements in the low internal resistance voltage sequence is opposite to that in the high internal resistance voltage sequence.

[0032] In a second aspect, another embodiment of the present invention provides an intelligent control system for photovoltaic storage charging and discharging stations to participate in the operation and maintenance of a virtual power plant, the system comprising:

[0033] The data acquisition module is used to obtain the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charge and the battery voltage after each charge;

[0034] A battery matching module is used to classify batteries into low-internal-resistance batteries and high-internal-resistance batteries based on the voltage of the batteries after each charge; and to match the low-internal-resistance batteries with the high-internal-resistance batteries after each charge based on the difference between the voltage of the high-internal-resistance batteries after each charge and the voltage of the low-internal-resistance batteries after adjustment by the photovoltaic charging power, to obtain matching batteries for the high-internal-resistance batteries;

[0035] The battery balancing module is used to select a battery to be balanced from the high-resistance batteries charged each time based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after adjustment by photovoltaic charging power, as well as the voltage of the high-resistance battery, and perform battery balancing on the battery to be balanced and its matching battery;

[0036] The virtual power plant control module is used to release the power of the battery after the power balancing is completed. According to the current changes of the battery during the power release process, the actual discharge power of the photovoltaic storage charging and discharging station after each charging is obtained, and it participates in the control of the virtual power plant operation and maintenance.

[0037] The present invention has the following beneficial effects:

[0038] First, batteries charged each time are divided into high- and low-internal-resistance batteries, and the two types of batteries are matched for battery balancing. Considering that unstable light intensity and differences in battery performance can lead to battery imbalance, the low-internal-resistance battery may consume insufficient power to balance the high-internal-resistance battery due to internal resistance consumption during the balancing process. The two types of batteries are matched based on the difference between the voltage of the high-internal-resistance battery and the voltage of the low-internal-resistance battery adjusted by photovoltaic charging power. Matching batteries that can support battery balancing for the high-internal-resistance battery are selected to ensure effective balancing. Subsequently, through a two-dimensional assessment of the difference between the voltage of the high-internal-resistance battery and its matching battery, namely dynamic deviation detection, and the voltage of the high-internal-resistance battery, namely baseline deviation calibration, the balancing requirement of the high-internal-resistance battery can be accurately analyzed. Batteries with higher balancing requirements can be selected from the high-internal-resistance batteries for balancing, improving balancing efficiency and extending battery life.

[0039] Second, photovoltaic charging power can measure the difference in charge between batteries. The voltage of the low-resistance battery after adjustment by photovoltaic charging power reflects its voltage after the internal resistance energy consumption of the high-resistance battery. The matching battery of the high-resistance battery determined based on this voltage is effectively matched according to the fluctuation of light intensity. The difference between the voltage of the high-resistance battery and the voltage of its matching battery after adjustment by photovoltaic charging power reflects the energy distribution imbalance caused by the internal resistance difference, reflects the significant degree of dynamic deviation of the high-resistance battery, and indicates the degree of demand for charge balancing, so that the selected battery to be balanced can dynamically adapt to the fluctuation of light intensity.

[0040] This solution balances the energy between the battery to be balanced and its matching battery, and takes light fluctuations into consideration when selecting the battery to be balanced and its matching battery. This effectively improves the efficiency of energy balancing between batteries in photovoltaic charging and discharging stations and reduces the impact of light intensity fluctuations. This makes the actual discharge energy more accurate, reduces virtual power plant scheduling errors, and improves the grid's ability to absorb fluctuating power sources caused by light intensity fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 A flowchart of the steps of an intelligent control method for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant, provided by one embodiment of the present invention;

[0043] Figure 2A flow chart of a method for obtaining a matching battery for a high internal resistance battery provided by one embodiment of the present invention;

[0044] Figure 3 This is a system structure diagram of an intelligent control system for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant, provided by one embodiment of the present invention;

[0045] Figure 4 A schematic diagram of a computer device for an intelligent control device for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant, provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0046] To further illustrate the technical means and effectiveness of the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation, structure, features, and effectiveness of a method and system for intelligently controlling a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant, as proposed by the present invention. In the following description, different references to "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0047] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0048] The following describes in detail with reference to the accompanying drawings a specific solution of an intelligent control method and system for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant provided by the present invention.

[0049] Example 1:

[0050] This invention proposes an intelligent control method for photovoltaic storage charging and discharging stations to participate in the operation and maintenance of virtual power plants. Figure 1 , which shows a flowchart of the steps of an intelligent control method for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant provided by an embodiment of the present invention, the method comprising:

[0051] Step S1: Obtain the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charging and the battery voltage after each charging.

[0052] A photovoltaic monitor is installed on the DC side of the photovoltaic array in the photovoltaic storage charging and discharging station to collect the voltage and current output by the junction box at each moment during the charging cycle of each battery. The product of the voltage and current at the same moment is used as the charging power, and the average of the charging power at all moments is used as the photovoltaic charging power for each charge. At the same time, a voltage sensor and a current sensor are configured for each battery, and the sensor probes are connected to the battery poles. The voltage sensor is used to measure the terminal voltage of each battery at the last moment of the charging cycle and record it as the voltage of the battery after each charge.

[0053] In one implementation of an embodiment of the present invention, the data acquisition frequency of the photovoltaic monitor is set to 5 Hz, and the data acquisition frequencies of the pressure sensor and the current sensor are both set to 10 Hz. The duration of the charging cycle is the time required to fully charge a normal battery with the same specifications as the battery in the power station. The implementer can set it according to the specific situation.

[0054] It should be noted that since the batteries in the power station adopt a centralized power supply mode of a single charger, all batteries operate in parallel and there is no group control, so the photovoltaic charging power of all batteries in the same charge is the same; the specifications of all batteries in the photovoltaic storage charging and discharging station are the same.

[0055] Step S2: Based on the voltage of the battery after each charge, the battery is divided into a low internal resistance battery and a high internal resistance battery; according to the difference between the voltage of the high internal resistance battery after each charge and the voltage of the low internal resistance battery after the photovoltaic charging power is adjusted, the low internal resistance battery and the high internal resistance battery of each charge are matched to obtain a matching battery of the high internal resistance battery.

[0056] Different batteries have inconsistent performance due to differences in battery manufacturing processes. Batteries with poor performance have larger internal resistance than normal batteries. Batteries with poor performance consume more energy during charging, resulting in a smaller voltage for batteries with poor performance within the same charging time. Batteries can be divided into low internal resistance batteries and high internal resistance batteries based on voltage.

[0057] When the PV charging power is high, meaning there's sufficient sunlight, the charging needs of batteries of varying performance can be met, and internal resistance differences have little impact on the charge capacity. When the PV charging power is low, meaning there's insufficient sunlight, batteries with low internal resistance absorb more energy due to lower energy losses, while batteries with high internal resistance experience greater energy losses. Consequently, within the same amount of sunlight and charging time, batteries with low internal resistance receive far more energy than batteries with high internal resistance, exacerbating the imbalance in charge between batteries. Therefore, PV charging power can be used to measure the difference in charge between batteries.

[0058] In order to solve the problem of unbalanced charge between batteries caused by fluctuations in light intensity and differences in battery performance, it is necessary to transfer the excess charge of low-resistance batteries to high-resistance batteries to achieve charge balancing. It is known that the smaller the photovoltaic charging power, the greater the charge difference between batteries. The higher-resistance batteries with poorer performance will generate more internal resistance energy consumption during charge balancing. To ensure the effectiveness of charge balancing, the low-resistance battery should ensure that it can still transfer charge after the internal resistance energy consumption of the high-resistance battery. The voltage of the low-resistance battery after photovoltaic charging power adjustment reflects its voltage after the internal resistance energy consumption of the high-resistance battery. If it is greater than the voltage of the high-resistance battery, it indicates that the high and low-resistance batteries can still balance the charge after considering the internal resistance energy consumption. The low-resistance battery and the high-resistance battery should be matched to ensure the effectiveness of charge balancing and improve the efficiency of charge balancing.

[0059] Step S3: Based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after photovoltaic charging power adjustment, as well as the voltage of the high-resistance battery, a battery to be balanced is selected from the high-resistance batteries charged each time, and power balancing is performed on the battery to be balanced and its matching battery.

[0060] The voltage of a low-resistance battery adjusted by PV charging power reflects its voltage after the energy consumed by the high-resistance battery's internal resistance. The difference between the voltage of a high-resistance battery and its matching battery adjusted by PV charging power reflects the energy distribution imbalance caused by the internal resistance difference. A larger difference indicates a more significant dynamic deviation of the high-resistance battery and a more urgent need for cell balancing. When balancing batteries, there is an ideal balancing voltage, or balancing benchmark. The greater the difference between the voltage of a high-resistance battery and the balancing target voltage, the more severe the deviation of the high-resistance battery's voltage from the balancing benchmark, and the more urgent the need for balancing. Therefore, through a dual-dimensional assessment of dynamic deviation monitoring and benchmark deviation calibration, the degree of balancing need of high-resistance batteries can be accurately analyzed. Cells with the highest balancing need can then be selected from the high-resistance battery pool for cell balancing with their matching cells, improving balancing efficiency, extending battery life, and dynamically adapting to light intensity fluctuations.

[0061] It should be noted that there is a line with a control switch between all two batteries in the photovoltaic storage charging and discharging station. When the battery is undergoing photovoltaic charging, all control switches are turned off; when the battery is undergoing power balancing, the control switch of the line between each battery to be balanced and its matching battery is turned on, and the other control switches are in the off state; after power balancing is completed, all control switches are turned off.

[0062] Step S4: Release the battery after the battery balancing is completed. According to the current change of the battery during the discharge process, the actual discharge power of the photovoltaic storage charging and discharging station after each charging is obtained, and participates in the regulation of the virtual power plant operation and maintenance.

[0063] The area between the curve of the battery's current versus time during discharge and the coordinate axis represents the total charge released by the battery. The total amount of charge released after each solar charge, or actual discharge capacity, can be calculated based on the current changes in the battery during discharge in the PV-storage charging and discharging station. The specific method for controlling the actual discharge capacity in the virtual power plant operation and maintenance is as follows: First, the actual discharge capacity after each charge is packaged into a standardized data packet and uploaded to the virtual power plant platform via the IEC 61850 protocol. Second, the platform calculates the dispatchable power window based on the reported capacity and dynamically allocates power usage based on electricity price signals and grid demand. Finally, after the virtual grid platform issues instructions, the PV-storage charging and discharging station dynamically adjusts via the local controller. This reduces the impact of light intensity fluctuations on actual discharge capacity, reduces virtual power plant scheduling errors, and improves the grid's ability to absorb fluctuating power sources caused by light intensity fluctuations.

[0064] Preferably, in some possible implementations of the embodiments of the present invention, the battery classification method includes: for each battery after charging, calculating the centralized value of the voltage of all batteries, and classifying the batteries corresponding to voltages less than the centralized value as high internal resistance batteries, and the batteries corresponding to voltages greater than or equal to the centralized value as low internal resistance batteries.

[0065] It should be noted that because batteries with larger internal resistance consume more energy during charging, resulting in a smaller voltage generated within the same charging time, batteries with a voltage less than the central value have a larger internal resistance and are recorded as high-internal-resistance batteries. In this embodiment of the present invention, the central value is the mean, and the voltage concentration level is reflected by the mean of the voltage of all batteries after each charge; the mean, median, and mode can all reflect the central tendency of a set of data. Other embodiments can replace the mean with the median or mode. The central values ​​in other locations in this solution have the same meaning as the central value in this embodiment.

[0066] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining a matching battery for a high internal resistance battery can be found in Figure 2 , which shows a flow chart of a method for obtaining a matching battery for a high internal resistance battery provided by one embodiment of the present invention, the method comprising:

[0067] Step S210: Based on the photovoltaic charging power of each charging, the battery power separation degree of each charging is obtained.

[0068] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the battery power separation degree includes: selecting a full-charge charging power from the photovoltaic charging powers of several charges before each charging, and the voltage of the battery after the full-charge charging power corresponding to the first charge is within the full-charge voltage range; normalizing the cumulative sum of the differences between all full-charge charging powers of each charge and the photovoltaic charging power to obtain the battery power separation degree of each charge.

[0069] It should be noted that the full-charge charging power refers to the photovoltaic charging power required to fully charge the batteries in the power station. The smaller the photovoltaic charging power per charge, the greater the difference between the full-charge charging power and the photovoltaic charging power per charge, indicating that the sunlight for that charge was less sufficient and the more accurate the difference, the greater the difference in charge between the batteries resulting from that charge, and the greater the battery charge separation. In this embodiment of the present invention, the Norm function is used for normalization processing, but other normalization methods such as function conversion can also be selected.

[0070] In one implementation of the embodiment of the present invention, the full-power voltage range is set to , where M represents the battery's charge limit voltage, which can be set to 2% based on specific circumstances. It should be noted that the charge limit voltage is the maximum voltage threshold a battery can reach during charging, and is usually clearly indicated on the battery specification sheet or label. When a battery is fully charged, the battery voltage may fluctuate due to environmental conditions and system operating conditions. If the battery voltage fluctuates near the charge limit voltage, the battery is considered fully charged.

[0071] In other embodiments, the maximum value of the photovoltaic charging power from n charging times before each charging may be used as the full-charge charging power, where n is set to 10.

[0072] Step S220: Using the battery charge separation degree, the voltage of the low internal resistance battery after each charge is adjusted to obtain a corrected voltage; the corrected voltage of the low internal resistance battery and the voltage of the high internal resistance battery after each charge are arranged in sequence to obtain a low internal resistance voltage sequence and a high internal resistance voltage sequence; and a target balancing voltage for each charge is obtained, where the elements in the low internal resistance voltage sequence are greater than the target balancing voltage, and the elements in the high internal resistance voltage sequence are less than the target balancing voltage.

[0073] It should be noted that the greater the battery charge separation, the greater the difference in charge between the batteries. The high internal resistance battery generates more internal resistance energy consumption during charge balancing, and the voltage of the low internal resistance battery is greater than the voltage actually used for charge balancing. Therefore, the battery charge separation is negatively correlated with the correction voltage. The method for obtaining the correction voltage is: negatively correlate and normalize the battery charge separation, and use the processing result to weight the voltage of the low internal resistance battery after each charge to obtain the correction voltage. In the embodiment of the present invention, the constant 1 is subtracted from the battery charge separation to achieve negative correlation and normalization. Other methods such as using the battery charge separation as the exponent of an exponential function with a natural constant as the base can also be used to achieve negative correlation and normalization.

[0074] The target balancing voltage is the ideal balancing voltage, or balancing reference, for battery charge balancing. High-resistance batteries with voltages lower than the target balancing voltage are undercharged and require charge balancing. Low-resistance batteries with correction voltages higher than the target balancing voltage can support charge transfer to high-resistance batteries. Matching these batteries can improve balancing effectiveness. When there is sufficient sunlight, the difference in charge between batteries, or the battery charge separation, is small. To reduce ineffective energy transfer, the ideal balancing voltage should be closer to the average voltage of all batteries. When there is insufficient sunlight, the difference in charge between batteries, or the battery charge separation, is large. To compensate for the internal resistance energy loss of high-resistance batteries, the ideal balancing voltage should be greater than the average voltage of all batteries. In an embodiment of the present invention, the product of the sum of the battery charge separation and a constant 1 and the average voltage of all batteries after each charge is used as the target balancing voltage, or balancing reference, which helps improve balancing effectiveness under low-light conditions.

[0075] When a low-resistance battery with a larger correction voltage is balanced with a high-resistance battery with a larger voltage, the high-resistance battery requires less power compensation, but the low-resistance battery will transfer a large amount of power to the high-resistance battery, resulting in overcompensation of the high-resistance battery. To avoid local overcompensation of battery power, the order of elements in the low-resistance voltage sequence and the high-resistance voltage sequence is opposite, so that the balancing current between the high-resistance battery and its matching battery can overcome the high-resistance loss and complete effective power transfer, thus avoiding overcharging of the high-resistance battery and extending battery life.

[0076] Step S230: setting the initial subscript to be tested to 0, and taking the low internal resistance voltage sequence as the initial voltage sequence to be tested; determining whether the element corresponding to the subscript to be tested in the voltage sequence to be tested is smaller than the element corresponding to the subscript to be tested in the high internal resistance voltage sequence; if so, deleting the element corresponding to the subscript to be tested in the voltage sequence to be tested to obtain a new voltage sequence to be tested; if not, determining a new subscript to be tested, and determining whether the element corresponding to the new subscript to be tested in the new voltage sequence to be tested is smaller than the element corresponding to the new subscript to be tested in the high internal resistance voltage sequence; stopping updating the voltage sequence to be tested until the new subscript to be tested is greater than the subscript corresponding to the last element in the high internal resistance voltage sequence, and taking the updated voltage sequence to be tested as the voltage sequence that satisfies equilibrium; determining a matching battery for each high internal resistance battery charged each time, wherein the subscript of the corresponding element of each high internal resistance battery in the high internal resistance voltage sequence is equal to the subscript of the corresponding element of the matching battery in the voltage sequence that satisfies equilibrium.

[0077] As an example, a high internal resistance voltage sequence , low internal resistance voltage sequence , Represents the voltage of a high internal resistance battery, Represents the corrected voltage of the low internal resistance battery. The initial voltage sequence to be measured is C0 = D, and the initial subscript to be measured is X0 = 0. If V3 with subscript 0 in sequence C0 is less than V1 with subscript 0 in sequence G, it means that the power of the low internal resistance battery corresponding to V3 after removing the internal resistance energy consumption is insufficient to support the power balancing of the high internal resistance battery corresponding to V1. Delete V3 to obtain a new voltage sequence to be measured. Continue to determine whether V4 with subscript 0 in sequence C1 is less than V1 with subscript 0 in sequence G. If V4 is greater than or equal to V1, it indicates that the power of the low-resistance battery corresponding to V4 after removing the internal resistance energy consumption can support the high-resistance battery corresponding to V1 for power balancing, and the two batteries are successfully matched. The new subscript X1 to be tested is equal to the sum of the subscript X0 to be tested and the constant 1 before the update, which is 1. If V5 with subscript 1 in sequence C1 is greater than or equal to V2 with subscript 1 in sequence G, it indicates that the batteries corresponding to V5 and V2 are successfully matched, and the new subscript X2 to be tested is equal to the sum of the subscript X1 to be tested and the constant 1 before the update, which is 2. At this time, the subscript X2 to be tested is greater than the subscript 1 of the last element V2 in sequence C, which indicates that all high-resistance batteries have selected low-resistance batteries for power balancing, then the sequence As a balanced voltage sequence, therefore, the matching battery for V1 corresponding to the high internal resistance battery is V4 corresponding to the low internal resistance battery, and the matching battery for V2 corresponding to the high internal resistance battery is V5 corresponding to the low internal resistance battery.

[0078] It should be noted that the subscripts in the sequence start at 0; the new subscript to be tested is equal to the sum of the subscript to be tested before the update and the constant 1; because power stations usually undergo regular maintenance and replace batteries with poor performance, the number of low-resistance batteries is much greater than the number of high-resistance batteries; only batteries with a voltage less than the target balancing voltage have matching batteries corresponding to the high-resistance batteries.

[0079] In other embodiments of the present invention, for a high-resistance battery having a voltage less than the target balancing voltage and a low-resistance battery having a corrected voltage greater than the target balancing voltage, the absolute value of the difference between the voltage of the high-resistance battery and the target balancing voltage is used as the first difference, and the absolute value of the difference between the corrected voltage of the low-resistance battery and the target balancing voltage is used as the second difference. The absolute value of the difference between the first difference of each high-resistance battery and the second difference of all low-resistance batteries is calculated, and the low-resistance battery corresponding to the minimum absolute value of the difference is selected as the matching battery for each high-resistance battery.

[0080] Preferably, in some possible implementations of the embodiments of the present invention, a method for obtaining batteries to be balanced includes: normalizing the difference between the voltage of each high-resistance battery after each charge and the target balancing voltage to obtain a balancing reference deviation; obtaining the matching balancing requirement of the corresponding high-resistance battery based on the difference between the voltage of each high-resistance battery after each charge and the corrected voltage of its matching battery, as well as the balancing reference deviation; and selecting, from the high-resistance batteries charged each time, the high-resistance battery corresponding to the matching balancing requirement less than a preset requirement threshold as the battery to be balanced. The difference refers to the absolute value of the difference.

[0081] It should be noted that the greater the difference between the high-resistance battery's voltage and the target balancing voltage, the greater the deviation of the high-resistance battery's voltage from the balancing benchmark, and the greater the deviation from the balancing benchmark, the more important it is to consider cell balancing for the high-resistance battery. The greater the difference between the high-resistance battery's voltage and the corrected voltage of its matching battery, the more significant its dynamic deviation and the more urgent its need for cell balancing. The greater the deviation from the balancing benchmark, the more urgent the need for cell balancing for the high-resistance battery. Therefore, the difference between the high-resistance battery's voltage and the corrected voltage of its matching battery and the deviation from the balancing benchmark are both positively correlated with the matching balancing requirement. In this embodiment of the present invention, the product of the absolute value of the difference between the voltage of each high-resistance battery and the corrected voltage after each charge and the deviation from the balancing benchmark is normalized to obtain the matching balancing requirement. The cells to be balanced have a greater need for cell balancing. While the Norm function is used for normalization in this embodiment of the present invention, other normalization methods, such as function transformation, maximum-minimum normalization, and other methods may also be used, and are not limited here. Only select the batteries to be balanced from the high internal resistance batteries whose voltage is less than the target balancing voltage.

[0082] In one implementation of the embodiment of the present invention, the preset demand threshold is an empirical value of 0.4.

[0083] Preferably, in some possible implementations of the embodiments of the present invention, the method of power balancing includes: for each battery to be balanced, discharging a matching battery of the battery to be balanced, transferring excess power to the battery to be balanced, obtaining the discharge voltage of the battery to be balanced and its matching battery at each moment during the power transfer process, and continuing power transfer when the discharge voltage difference between the battery to be balanced and its matching battery at the same moment is not within a required balancing range until the discharge voltage difference is within the required balancing range, thereby completing power balancing of the batteries after each charge.

[0084] It should be noted that the voltage sensor collects the battery voltage at each moment during the cell balancing process and records it as the discharge voltage. If the discharge voltage difference between the cell to be balanced and its matching cell at the same moment is not within the balancing requirement, it indicates that the two cells have not yet completed cell balancing. Otherwise, it indicates that cell balancing is complete. The difference refers to the absolute value of the difference.

[0085] In one implementation of the embodiment of the present invention, the balance requirement range is set to , where B represents the target balancing voltage for each charge.

[0086] Preferably, in some possible implementations of the embodiments of the present invention, the method for obtaining the actual discharged power includes: obtaining the discharge current of all batteries at each moment in the power release time period, calculating the average of the discharge current at the same moment, performing curve fitting on the corresponding averages at all moments in the power release time period, and obtaining a discharge current function; integrating the discharge current function in the discharge time period, and taking the product of the integral result and the total number of batteries as the actual discharged power of the solar storage charging and discharging station after each charge.

[0087] It should be noted that a current sensor is used to collect the battery's current at each moment during the charge release period, which is recorded as the discharge current. The battery discharge current varies nonlinearly with time. The discharge current function is a model of the current variation during the battery discharge process. The integral of the discharge current function over the discharge period reflects the amount of charge that can be released by a single battery. The actual discharge amount represents the total amount of charge that can be released by all batteries in the power station after each light-charged cycle. The specific fitting process is: a two-dimensional coordinate system is established with time as the horizontal axis and current as the vertical axis. The least squares method is used to perform a curve fit to the corresponding coordinate points in the two-dimensional coordinate system for the mean discharge current of all batteries at the same moment during the charge release period during each charge.

[0088] In one implementation of the present invention, the end time of the power discharge period is when the battery that first reaches the cutoff voltage reaches the cutoff voltage. The cutoff voltage is the lowest voltage threshold that the battery can reach during discharge and is usually clearly indicated on the battery specification sheet or label.

[0089] So far, the present invention is completed.

[0090] Example 2:

[0091] This invention proposes an intelligent control system for photovoltaic storage charging and discharging stations to participate in the operation and maintenance of virtual power plants. Figure 3 , which shows a system structure diagram of an intelligent control system for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant, provided by one embodiment of the present invention. The system includes:

[0092] The data acquisition module 510 is used to obtain the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charging and the battery voltage after each charging;

[0093] The battery matching module 520 is configured to classify the batteries into low-internal-resistance batteries and high-internal-resistance batteries based on the battery voltage after each charge; and to match the low-internal-resistance batteries with the high-internal-resistance batteries after each charge based on the difference between the voltage of the high-internal-resistance batteries after each charge and the voltage of the low-internal-resistance batteries after adjustment by the photovoltaic charging power, to obtain a matching battery for the high-internal-resistance battery;

[0094] The cell balancing module 530 is configured to select a cell to be balanced from the high-resistance batteries that are charged each time, based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after adjustment by photovoltaic charging power, as well as the voltage of the high-resistance battery, and perform cell balancing on the cell to be balanced and its matching battery.

[0095] The virtual power plant control module 540 is used to release the power of the battery after the power balancing is completed. According to the current change of the battery during the power release process, the actual discharge power of the photovoltaic storage charging and discharging station after each charging is obtained, and it participates in the control of the virtual power plant operation and maintenance.

[0096] It should be noted that the devices provided in the above embodiments are merely exemplified by the division of the above functional modules. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the computer device can be divided into different functional modules to complete all or part of the functions described above. In addition, the intelligent control system for photovoltaic storage charging and discharging stations participating in the operation and maintenance of virtual power plants and the intelligent control method embodiment for photovoltaic storage charging and discharging stations participating in the operation and maintenance of virtual power plants provided in the above embodiments are based on the same concept. The specific implementation process is detailed in the method embodiment and will not be repeated here.

[0097] Example 3:

[0098] The present invention also proposes a computer device schematic diagram of an intelligent control device for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant. Figure 4 The computer device includes a memory 601, a processor 602, and a computer program 603 stored in the memory 601 and running on the processor 602. When the processor 602 executes the computer program 603, the computer device can execute any of the intelligent control methods for the photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant introduced above.

[0099] In addition, an embodiment of the present application also protects a device, which may include a memory and a processor, wherein the memory stores executable program code, and the processor is used to call and execute the executable program code to execute an intelligent control method for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant provided by an embodiment of the present application.

[0100] In this embodiment, the device can be divided into functional modules based on the above-described method examples. For example, each functional module can be mapped to a specific functional module, or two or more functions can be integrated into a single processing module. The integrated module can be implemented in hardware. It should be noted that the module division in this embodiment is illustrative and represents only a logical functional division. In actual implementation, other division methods may be used.

[0101] In the case of dividing the modules into modules corresponding to their functions, the device may further include a communication module, a signal analysis module, a complexity analysis module, a positioning module, etc. It should be noted that all relevant contents of the various steps involved in the above method embodiment can be referred to the functional description of the corresponding functional modules and will not be repeated here.

[0102] It should be understood that the device provided in this embodiment is used to execute the above-mentioned intelligent control method for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant, and thus can achieve the same effect as the above-mentioned implementation method.

[0103] In the case of an integrated unit, the device may include a processing module and a storage module. When the device is applied to a device, the processing module may be used to control and manage the operation of the device. The storage module may be used to support the device in executing mutual program codes, etc.

[0104] The processing module may be a processor or controller that implements or executes the various exemplary logic blocks, modules, and circuits disclosed herein. The processor may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a digital signal processor (DSP) and a microprocessor, and the like. The storage module may be a memory.

[0105] Example 4:

[0106] This embodiment also provides a computer-readable storage medium, which stores computer program code. When the computer program code runs on a computer, the computer executes the above-mentioned related method steps to implement an intelligent control method for a photovoltaic storage charging and discharging station to participate in the operation and maintenance of a virtual power plant provided by the above embodiment.

[0107] Example 5:

[0108] This embodiment also provides a computer program product. When the computer program product runs on a computer, it enables the computer to execute the above-mentioned related steps to implement the intelligent control method for the photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant provided by the above embodiment.

[0109] Among them, the device, computer-readable storage medium or computer program product provided in this embodiment is used to execute the corresponding method provided above. Therefore, the beneficial effects that can be achieved can refer to the beneficial effects in the corresponding method provided above, and will not be repeated here.

[0110] In the embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of modules or units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0111] It should be noted that the order in which the embodiments of the present invention are described above is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0112] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. An intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance, characterized in that: The method includes: Obtaining the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charge and the battery voltage after each charge; the photovoltaic charging power is obtained by collecting the voltage and current output by the combiner box at each moment during each charging cycle of the battery, taking the product of the voltage and current at the same moment as the charging power, and taking the average of the charging power at all moments as the photovoltaic charging power for each charge; Based on the battery voltage after each charge, the batteries are divided into low internal resistance batteries and high internal resistance batteries; based on the difference between the voltage of the high internal resistance battery after each charge and the voltage of the low internal resistance battery after adjustment by the photovoltaic charging power, the low internal resistance battery and the high internal resistance battery of each charge are matched to obtain matching batteries for the high internal resistance battery; Based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after photovoltaic charging power adjustment, as well as the voltage of the high-resistance battery, a battery to be balanced is selected from the high-resistance batteries charged each time, and the battery to be balanced and its matching battery are balanced. After the battery has completed power balancing, the battery is discharged. According to the current change of the battery during the power discharge process, the actual discharge power of the photovoltaic storage charging and discharging station after each charge is obtained, and it participates in the regulation of virtual power plant operation and maintenance; The method of obtaining a matching battery for the high internal resistance battery includes: Based on the photovoltaic charging power of each charge, the battery power separation degree of each charge is obtained; Using the battery charge separation degree to adjust the voltage of the low internal resistance battery after each charge to obtain a corrected voltage; For a high-resistance battery whose voltage is less than the target balancing voltage and a low-resistance battery whose corrected voltage is greater than the target balancing voltage, the absolute value of the difference between the voltage of the high-resistance battery and the target balancing voltage is used as the first difference, and the absolute value of the difference between the corrected voltage of the low-resistance battery and the target balancing voltage is used as the second difference; the absolute value of the difference between the first difference of each high-resistance battery and the second difference of all low-resistance batteries is calculated, and the low-resistance battery corresponding to the minimum absolute value of the difference is selected as the matching battery for each high-resistance battery; The method for obtaining the correction voltage is as follows: negatively correlating and normalizing the battery charge separation degree, and using the processing result to weight the voltage of the low internal resistance battery after each charge to obtain the correction voltage; The obtaining of the battery power separation degree for each charging includes: Selecting a full-charge charging power from the photovoltaic charging powers of several charging times before each charging, wherein the full-charge charging power corresponds to a battery voltage within a full-charge voltage range after the first charging; The cumulative sum of the differences between all full-charge charging powers and the photovoltaic charging power of each charge is normalized to obtain the battery power separation degree of each charge.

2. The intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance according to claim 1 is characterized in that: The step of selecting batteries to be balanced from the high internal resistance batteries charged each time includes: Normalizing the difference between the voltage of each high-resistance battery and the target balancing voltage after each charge to obtain a balancing reference deviation; the balancing reference deviation represents the degree of deviation of the voltage of the high-resistance battery from the balancing reference; Obtaining a matching balancing requirement for the corresponding high-internal-resistance battery based on the difference between the voltage of each high-internal-resistance battery and the corrected voltage of its matching battery after each charge, and the balancing reference deviation; selecting a high-internal-resistance battery corresponding to a matching balancing requirement less than a preset requirement threshold from the high-internal-resistance batteries charged each time as a battery to be balanced; The method for obtaining the matching balance requirement is to normalize the product of the absolute value of the difference between the voltage of each high internal resistance battery and the correction voltage after each charging and the balance reference deviation to obtain the matching balance requirement.

3. The intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance according to claim 1 is characterized in that: The target balancing voltage is equal to the product of the sum of the battery charge separation degree and a constant 1 and the average value of the voltages of all batteries after each charge.

4. The intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance according to claim 1 is characterized in that: The method for obtaining the actual discharged power includes: Obtain the discharge current of all batteries at each moment in the power release time period, calculate the average of the discharge currents at the same moment, perform curve fitting on the average values ​​corresponding to all moments in the power release time period, and obtain a discharge current function; integrate the discharge current function within the discharge time period, and take the product of the integral result and the total number of batteries as the actual discharge capacity of the solar storage charging and discharging station after each charge.

5. The intelligent control method for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant according to claim 1 is characterized in that: Balancing the battery to be balanced and its matching battery includes: For each battery to be balanced, the matching battery of the battery to be balanced is discharged, and the excess power is transferred to the battery to be balanced. The discharge voltage of the battery to be balanced and its matching battery at each moment during the power transfer process is obtained. If the discharge voltage difference between the battery to be balanced and its matching battery at the same moment is not within the balancing requirement range, the power transfer continues until the discharge voltage difference is within the balancing requirement range, and the power transfer is stopped, completing the power balancing of the batteries after each charge.

6. The intelligent control method for a photovoltaic storage charging and discharging station participating in the operation and maintenance of a virtual power plant according to claim 1, characterized in that: The classification of batteries into low internal resistance batteries and high internal resistance batteries includes: For each battery after charging, the mean value of the voltage of all batteries is calculated, and batteries with voltages less than the mean value are classified as high internal resistance batteries, and batteries with voltages greater than or equal to the mean value are classified as low internal resistance batteries.

7. The intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance according to claim 1 is characterized in that: The battery charge separation degree is negatively correlated with the correction voltage.

8. The intelligent control method for photovoltaic storage charging and discharging stations participating in virtual power plant operation and maintenance according to claim 1 is characterized in that: The number of low internal resistance batteries charged each time is greater than the number of high internal resistance batteries.

9. An intelligent control system for photovoltaic and storage charging and discharging stations participating in the operation and maintenance of virtual power plants is characterized by: The system includes: A data acquisition module is used to obtain the photovoltaic charging power of the battery in the photovoltaic storage charging and discharging station during each charge and the battery voltage after each charge; the photovoltaic charging power is obtained by collecting the voltage and current output by the combiner box at each moment during each charging cycle of the battery, taking the product of the voltage and current at the same moment as the charging power, and taking the average of the charging power at all moments as the photovoltaic charging power for each charge; A battery matching module is used to classify batteries into low-internal-resistance batteries and high-internal-resistance batteries based on the voltage of the batteries after each charge; and to match the low-internal-resistance batteries with the high-internal-resistance batteries after each charge based on the difference between the voltage of the high-internal-resistance batteries after each charge and the voltage of the low-internal-resistance batteries after adjustment by the photovoltaic charging power, to obtain matching batteries for the high-internal-resistance batteries; The battery balancing module is used to select a battery to be balanced from the high-resistance batteries charged each time based on the difference between the voltage of the high-resistance battery after each charge and the voltage of its matching battery after adjustment by photovoltaic charging power, as well as the voltage of the high-resistance battery, and perform battery balancing on the battery to be balanced and its matching battery; The virtual power plant control module is used to discharge the battery after the battery has completed power balancing. Based on the current changes of the battery during the power discharge process, it obtains the actual discharge power of the photovoltaic storage charging and discharging station after each charge, and participates in the control of the virtual power plant operation and maintenance; Based on the photovoltaic charging power of each charge, the battery power separation degree of each charge is obtained; Using the battery charge separation degree to adjust the voltage of the low internal resistance battery after each charge to obtain a corrected voltage; For a high-resistance battery whose voltage is less than the target balancing voltage and a low-resistance battery whose corrected voltage is greater than the target balancing voltage, the absolute value of the difference between the voltage of the high-resistance battery and the target balancing voltage is used as the first difference, and the absolute value of the difference between the corrected voltage of the low-resistance battery and the target balancing voltage is used as the second difference; the absolute value of the difference between the first difference of each high-resistance battery and the second difference of all low-resistance batteries is calculated, and the low-resistance battery corresponding to the minimum absolute value of the difference is selected as the matching battery for each high-resistance battery; The method for obtaining the correction voltage is as follows: negatively correlating and normalizing the battery charge separation degree, and using the processing result to weight the voltage of the low internal resistance battery after each charge to obtain the correction voltage; The obtaining of the battery power separation degree for each charging includes: Selecting a full-charge charging power from the photovoltaic charging powers of several charging times before each charging, wherein the full-charge charging power corresponds to a battery voltage within a full-charge voltage range after the first charging; The cumulative sum of the differences between all full-charge charging powers and the photovoltaic charging power of each charge is normalized to obtain the battery power separation degree of each charge.

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