Power balance control method and system based on photovoltaic sodium ion battery energy storage system

Abstract

The present invention discloses a power balance control method and system based on a photovoltaic sodium ion battery energy storage system, which relates to the field of intelligent power balance technology, and includes the following steps: obtaining battery pack state parameters of sodium ion batteries, the battery pack state parameters including battery capacity decay rate, single cell ambient temperature gradient, and voltage balance at single cell ambient temperature; based on the battery pack state parameters, calculating the thermal management efficiency of the battery pack; when the thermal management efficiency of the battery pack is lower than a preset standard threshold, calculating the ionic conductivity and rate value of the single cell in the battery pack; when the ionic conductivity and rate value of the single cell in the battery pack are lower than the preset value, switching the single cell that has lost temperature to a charging mode. The present invention solves the problem that the existing battery power balance control technology cannot accurately control the sodium ion battery to be stable at a suitable temperature and voltage by quantifying the thermal management efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of intelligent power balance control, and in particular to a power balance control method and system based on a photovoltaic sodium ion battery energy storage system. Background Art

[0002] With the rapid development of renewable energy, especially the large-scale application of solar and wind energy, the market demand for energy storage technology has increased significantly. As a lower-cost and more resource-rich alternative, sodium-ion batteries have huge market potential.

[0003] In the sodium-ion battery energy storage system, the core purpose of intelligent balancing control of battery power is to accurately adjust the battery power output, avoid overcharging and discharging or uneven load distribution, and reduce stress accumulation and loss inside the battery. This can effectively extend the battery life, reduce maintenance costs and improve the efficiency of the energy storage system.

[0004] For example, the invention patent with announcement number CN105552963A announces a photovoltaic power generation grid-connected system based on lithium-ion battery energy storage, including: an energy control system and a microgrid system, the energy control system and the microgrid system are control-connected, the microgrid system includes an energy storage control system and a photovoltaic power generation system, and the energy storage control system and the photovoltaic power generation system are both control-connected with the energy control system. Through the above method, the photovoltaic power generation grid-connected system based on lithium-ion battery energy storage provided by the present invention combines the solar power station with the lithium-ion battery energy storage system to form a local microgrid system, and realizes the smooth output of photovoltaic power generation power by controlling the charging and discharging of the bidirectional converter (PCS), effectively reducing the impact on the power grid, improving the quality of electric energy, reducing power grid safety accidents, and can realize peak shaving and valley filling of the power grid and power control, which plays a certain role in the peak regulation of the power grid.

[0005] For example, the invention patent with announcement number: CN114726004B announces a new type of energy storage photovoltaic power station system and its control method, the system includes a photovoltaic power station, at least one flywheel energy storage unit, at least one lithium-ion battery energy storage unit, a hydrogen energy storage unit, an optical power prediction unit, an energy storage monitoring control unit and a first step-up transformer. The present invention combines optical power prediction and load power prediction, collects the grid-connected power generation power in real time, and monitors and controls the flywheel energy storage unit, lithium-ion battery energy storage unit and hydrogen energy storage unit according to the revised next-day scheduling power generation plan curve, which can solve the problem of insufficient active power regulation of photovoltaic power stations on multiple time scales such as millisecond-level inertia response, second-level primary frequency modulation, minute-level secondary frequency modulation, hour-level intraday peak regulation, etc., improve the active power support capacity of photovoltaic power stations, balance the peak and valley state of power supply, and ensure the frequency stability of the power system.

[0006] For example, the invention patent with announcement number CN113691023B discloses a photovoltaic DC composite energy storage system and method based on temperature field control technology, including a high-temperature superconducting electromagnetic energy storage device, a liquid nitrogen tank, a lithium battery energy storage array, and a lithium-ion battery array cooling system; the lithium battery energy storage array is arranged circumferentially outside the high-temperature superconducting electromagnetic energy storage device and the liquid nitrogen tank, and the lithium-ion battery array cooling system is arranged adjacent to the lithium battery energy storage array; the high-temperature superconducting electromagnetic energy storage device includes a bidirectional coil, a high-temperature superconducting electromagnetic energy storage charging coil, a high-temperature superconducting electromagnetic energy storage release coil, and a high-temperature superconducting electromagnetic energy storage measurement and control device, a column core is provided in the liquid nitrogen tank, and grooves are distributed on the side walls of the column core, the bidirectional coil is wound in the grooves, and the high-temperature superconducting electromagnetic energy storage charging coil and the high-temperature superconducting electromagnetic energy storage release coil are respectively connected to the bidirectional coil. Through the design of the temperature field and the composite energy storage system, the energy storage and rapid response to grid frequency modulation of the photovoltaic power station are realized, and the energy conversion efficiency of the energy storage is improved.

[0007] The most important connection between battery power balance and temperature is that when the temperature is too low, the sodium ions in the sodium-ion battery will be non-rich, which will affect the output power of the battery. The existing battery power balance control technology cannot accurately control the sodium-ion battery to be stable at an appropriate temperature and voltage, resulting in certain errors in the existing sodium-ion battery state estimation method, which in turn leads to battery power imbalance. Summary of the invention

[0008] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a power balancing control method and system based on a photovoltaic sodium-ion battery energy storage system to solve the problem that the existing battery power balancing control technology cannot accurately control the sodium-ion battery to be stable at a suitable temperature and voltage.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A power balance control method based on a photovoltaic sodium-ion battery energy storage system comprises the following steps: obtaining battery pack state parameters of the sodium-ion battery, wherein the battery pack state parameters include a battery capacity decay rate, a single cell ambient temperature gradient, and a voltage balance degree at a single cell ambient temperature; calculating the thermal management efficiency of the battery pack based on the battery pack state parameters; when the thermal management efficiency of the battery pack is lower than a preset standard threshold, calculating the ionic conductivity and rate value of the single cell in the battery pack;

[0011] When the ion conductivity and rate value of the single battery in the battery pack are lower than the preset value, the single battery with loss of temperature is switched to the charging mode.

[0012] In a preferred embodiment, the battery capacity decay rate is obtained by the following method: recording the initial rated capacity of the battery, and tracking the number of charge and discharge cycles the battery has gone through through a special counter; measuring the battery capacity at the current moment while ensuring that the battery is in a no-load state; and obtaining the battery capacity decay rate based on the obtained number of charge and discharge cycles and the measured battery capacity in combination with the battery capacity decay rate calculation formula.

[0013] In a preferred embodiment, the voltage balance degree of the single cell at the ambient temperature is obtained by: measuring and recording the voltage of each single cell in the battery pack, and calculating the average voltage of the battery pack according to the voltage data of all the single cells; obtaining the current temperature of each battery cell, and performing temperature compensation on the battery voltage according to the temperature coefficient of the sodium ion battery to obtain the standard battery voltage value at the standard temperature; calculating the deviation between the voltage of each single cell and the average voltage to obtain the voltage balance degree of the single cell at the ambient temperature.

[0014] In a preferred embodiment, the battery environment temperature gradient is obtained by the following method: for each battery cell, a temperature sensor is used to obtain its temperature value at a preset time point; based on the temperature data of all single cells, the average temperature of the entire battery pack within a preset time period is calculated; the data of the single cell with the highest temperature and the data of the single cell with the lowest temperature in the battery pack are marked to calculate the battery environment temperature gradient.

[0015] In a preferred embodiment, the ionic conductivity of the single cells in the battery pack is obtained by: measuring the geometric dimensions of the electrolyte flow channel, the geometric dimensions including the diameter and rectangular dimensions of the pipe through which the electrolyte flows; presetting the test current value, and setting the operating voltage range of the battery at the same time, applying the operating voltage of the battery with the same difference at the preset current value; after applying the voltage, recording the current value flowing through the battery electrolyte to obtain the ionic conductivity.

[0016] In a preferred embodiment, the switching of charging modes of the temperature-depleted single-cell battery is specifically as follows: when the total number of the temperature-depleted single-cell battery is single, the charging mode is directly switched; when the total number of the temperature-depleted single-cell battery is multiple, they are sorted based on ion conductivity, the mode is switched first for the single-cell battery with the smallest ion conductivity, and the other single-cell batteries are put into sleep mode.

[0017] The technical effects and advantages of the power balance control method and system based on the photovoltaic sodium ion battery energy storage system of the present invention are as follows:

[0018] 1. By obtaining multiple battery pack status parameters such as battery capacity decay rate, single cell environmental temperature gradient and voltage balance, the battery pack status can be fully monitored, which effectively solves the problem in the existing technology that the sodium ion battery cannot be accurately controlled to be stable at a suitable temperature and voltage.

[0019] 2. By calculating the ionic conductivity and rate value, it provides a method for automatically switching the charging mode of the single cell that has lost temperature when the performance of the single cell is low, thereby maximizing the charging efficiency and battery safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of a power balance control method based on a photovoltaic sodium-ion battery energy storage system provided in an embodiment of the present application;

[0021] Figure 2 A schematic diagram of the system structure of a power balance control method based on a photovoltaic sodium-ion battery energy storage system provided in an embodiment of the present application; DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "include..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0024] Embodiment 1, Figure 1 The present invention provides a power balance control method based on a photovoltaic sodium ion battery energy storage system, comprising the following steps:

[0025] S1 obtains battery pack state parameters of the sodium ion battery, wherein the battery pack state parameters include battery capacity decay rate, single cell ambient temperature gradient, and voltage balance degree of the single cell ambient temperature;

[0026] S2, calculating the thermal management efficiency of the battery pack based on the battery pack state parameters;

[0027] S3: when the thermal management efficiency of the battery pack is lower than a preset standard threshold, the ionic conductivity and rate value of the single battery in the battery pack are calculated;

[0028] S4: When the ion conductivity and rate value of the single battery in the battery pack are lower than the preset value, the single battery with loss of temperature is switched to a charging mode.

[0029] The battery capacity decay rate refers to the degree to which the maximum energy storage capacity of the battery (i.e. the rated capacity of the battery) gradually decreases as the battery experiences an increase in charge and discharge cycles during use. It reflects the speed and degree of battery capacity decline over time, especially after multiple charge and discharge cycles.

[0030] The maximum capacity of a battery gradually decreases with the number of uses, especially when the battery has undergone multiple charge and discharge cycles and environmental conditions have changed. The rate of battery capacity decay will vary. As the number of charge and discharge cycles increases, the battery capacity will gradually decrease. The effect of the number of charge cycles on battery capacity is usually expressed as exponential decay.

[0031] The battery capacity decay rate is obtained as follows:

[0032] Record the initial rated capacity of the battery and track the number of charge and discharge cycles the battery has gone through using a dedicated counter;

[0033] Make sure the battery is under no load and use a digital multimeter to measure the battery capacity at the current moment.

[0034] The battery capacity decay rate is calculated by the following formula:

[0035]

[0036] Where: f is the battery capacity decay rate, N is the number of charge and discharge cycles, is a constant that represents the effect of each charge and discharge cycle on the battery capacity. S is the initial rated capacity of the battery, which is taken as 100% here. is the battery capacity at the current moment, and k is the battery state factor.

[0037] It should be noted that the battery state factor is a constant that may affect the battery performance, and the present invention takes the chemical properties of the battery electrolyte.

[0038] It should be noted that the battery capacity decay rate reflects the attenuation of the battery capacity during multiple charge and discharge cycles. The lower the battery capacity decay rate, the more serious the battery capacity decay, and the battery output power will also be affected and reduced. The higher the battery capacity decay rate, the more ideal the battery capacity decay, and the less the battery output power is affected by the battery capacity.

[0039] The temperature gradient of a single cell environment refers to the temperature difference between different single cells in a battery pack. Since the battery cells generate heat during the charging and discharging process, and the thermal response of each single cell is different, different temperature distributions may occur inside the battery pack. If the temperature difference is too large, it may affect the performance of the battery, leading to battery overheating, capacity attenuation, and reduced charging and discharging efficiency.

[0040] The battery environment temperature gradient is obtained by the following method:

[0041] For each battery cell, a temperature sensor is used to obtain its temperature value at a preset time point;

[0042] Calculate the average temperature of the entire battery pack within a preset time period based on the temperature data of all single batteries;

[0043] The data of the single cell with the highest temperature and the data of the single cell with the lowest temperature in the battery pack are marked, and the battery environment temperature gradient is calculated.

[0044] The battery environment temperature gradient is calculated as follows:

[0045]

[0046] Where: represents the temperature gradient inside the battery pack, represents the temperature of the ith single cell in the battery pack, represents the lowest average temperature in the battery pack in the unit time series, represents the highest average temperature in the battery pack in the unit time series, is the maximum temperature of all cells in the battery pack, It is the lowest temperature of all cells in the battery pack.

[0047] It should be noted that the battery ambient temperature gradient indicates the temperature difference inside the battery pack. The smaller the value of the battery ambient temperature gradient, the more uniform the temperature distribution inside the battery pack and the better the thermal management effect. The larger the value of the battery ambient temperature gradient, the more performance differences in battery cells may cause some batteries to overheat or have low temperatures, thereby affecting the battery's charge and discharge efficiency and life, and further affecting the power balance of the battery energy storage system.

[0048] Voltage balance measures the degree of voltage difference between each battery cell in the battery pack. Each battery cell in the battery pack may have a voltage difference during the charging and discharging process. The voltage difference will cause the overall performance of the battery pack to decline, especially during high-power discharge or charging. Some battery cells may be over-discharged or over-charged, which may seriously affect the safety and service life of the battery.

[0049] There is a certain relationship between the change in battery voltage and temperature. Voltage usually changes with temperature. If the operating temperatures of multiple battery cells are different, their voltage differences will be affected by the temperature difference. Specifically, changes in ambient temperature will cause the voltage of each single cell to change differently, thereby causing changes in the voltage balance between the single cells in the battery pack. If there are significant differences in the ambient temperatures of different single cells (for example, due to different battery positions and uneven temperatures), the voltage balance will increase. The voltage change of each single cell is directly related to the temperature difference. The higher or lower the temperature, the greater the change in battery voltage.

[0050] The voltage balance degree of the single cell at the ambient temperature is obtained by:

[0051] Measure and record the voltage of each single cell in the battery pack, and calculate the average voltage of the battery pack based on the voltage data of all single cells;

[0052] Obtain the current temperature of each battery cell, and perform temperature compensation on the battery voltage according to the temperature coefficient of the sodium ion battery to obtain the standard battery voltage value at the standard temperature;

[0053] Calculate the deviation of each cell's voltage from the average voltage.

[0054] The voltage balance degree of the single cell at ambient temperature is calculated by the following formula:

[0055]

[0056] Where: is the voltage balance of the battery pack, M is the number of battery cells in the battery pack, is the standard battery voltage at standard temperature, is the standard temperature, is the voltage of the ith battery cell, is the average voltage of all battery cells in the battery pack, which is used as a benchmark for measuring voltage differences. T is the current ambient temperature of the battery cells. is the temperature coefficient of the sodium-ion battery, which is a constant.

[0057] It should be noted that at standard temperature, the battery voltage and other performance parameters are considered to be standard values, that is, at standard temperature, the battery's internal resistance, voltage change, chemical reaction rate, etc. are least affected by temperature.

[0058] It should be noted that, the smaller the value of the voltage balance, the more balanced the voltage of the battery pack at the current temperature, and the larger the value of the voltage balance, the greater the voltage difference between the battery cells of the battery pack at the current temperature.

[0059] The thermal management efficiency of a battery pack refers to the ability of the battery pack to maintain the battery cells within the optimal operating temperature range through effective thermal management measures (such as cooling systems, thermal isolation, heat dissipation design, etc.) during use. The level of this efficiency directly affects the battery's service life, charge and discharge performance, and safety, and thus affects the battery's ion activity and power output. An efficient thermal management system can prevent battery cells from overheating or overcooling, thereby reducing battery temperature imbalance, reducing battery degradation, and improving energy conversion efficiency.

[0060] The thermal management efficiency of a battery pack is an important indicator for measuring the temperature control performance of a battery system. It is directly related to the safety, performance and service life of the battery pack. Through the above formula, the thermal management effect of a battery pack can be evaluated based on the battery capacity decay rate, temperature gradient and voltage balance. Improving thermal management efficiency can effectively extend battery life, improve battery performance and ensure system safety.

[0061] The thermal management efficiency of the battery pack is calculated as follows:

[0062]

[0063] Where: For the thermal management efficiency of the battery pack, is the voltage balance of the battery pack, It represents the temperature gradient inside the battery pack, represents the temperature difference between battery cells, and f is the battery capacity decay rate.

[0064] It should be noted that when the value of the thermal management efficiency of the battery pack is close to 1, it means that the thermal management of the battery pack is very efficient, the battery temperature distribution is uniform, the capacity decay is small, and the battery voltage balance is good. This usually means that the thermal management system can effectively control the operating temperature of the battery cell and reduce performance degradation and safety hazards caused by overheating or overcooling. When the value of the thermal management efficiency of the battery pack is close to 0, it means that the thermal management efficiency of the battery pack is low, the temperature difference inside the battery pack is large, and the temperature imbalance is serious, resulting in rapid battery capacity decay, obvious voltage imbalance, and may even cause problems such as thermal runaway.

[0065] The preset standard thresholds are usually set based on the expected performance and safety requirements when designing the battery pack. The standard thresholds include the minimum requirements for thermal management efficiency and are usually based on factors such as the working environment, charge and discharge rates, and temperature range of the battery pack. These thresholds may be determined through a large amount of experimental data and simulation tests to ensure that the battery pack can operate stably, safely, and efficiently in actual applications.

[0066] Once the thermal management efficiency value is obtained, it can be compared with the preset standard threshold. The comparison process is as follows:

[0067] If the thermal management efficiency is higher than or equal to the threshold, it indicates that the thermal management system of the battery pack can effectively control temperature changes and work within the ideal temperature control range, which can usually ensure the service life, performance and safety of the battery;

[0068] If the thermal management efficiency is lower than the threshold, it means that the thermal management system of the battery pack is not sufficient to cope with the actual operating conditions, and there are potential temperature imbalances, performance degradation and safety risks. Further analysis of the ionic conductivity and rate value of the single cells in the battery pack is required.

[0069] If thermal management efficiency falls below the standard threshold, the following specific consequences may occur:

[0070] Accelerated capacity decay: Due to temperature non-uniformity, some battery cells may overheat or overcool, causing the battery capacity to decay faster, which means that the service life of the battery pack will be significantly shortened and it will not be able to provide continuous power output.

[0071] Voltage imbalance: Temperature difference causes differences in the charging and discharging performance of different battery cells, resulting in voltage imbalance. Battery voltage imbalance will affect the stability of the entire battery pack and may cause overcharging or over-discharging in some cells, increasing safety risks.

[0072] Heat dissipation problem: If the thermal management system fails to dissipate heat effectively, excessively high temperatures will accelerate the chemical reactions inside the battery and may even cause thermal runaway, ultimately leading to catastrophic accidents such as fire or explosion.

[0073] Ionic conductivity refers to the ability of ions in the electrolyte to move under the action of an electric field. It directly affects the speed of ion migration inside the battery, thereby determining the battery's charging and discharging efficiency, power output and energy storage capacity. Under different temperature environments, the viscosity of the electrolyte will change, thereby affecting the ionic conductivity.

[0074] The ionic conductivity of the single cell in the battery pack is obtained by:

[0075] Measuring geometric dimensions of the electrolyte flow channel, the geometric dimensions including the diameter and rectangular dimensions of the channel through which the electrolyte flows;

[0076] Preset the test current value and set the working voltage range of the battery at the same time, and apply the working voltage of the battery with the same difference under the preset current value;

[0077] After applying voltage, the current value flowing through the battery electrolyte is recorded to obtain the ionic conductivity.

[0078] It should be noted that, during the process of obtaining the ion conductivity, if the operating voltage of the battery exceeds the set operating voltage range of the battery, the battery is immediately stopped and shut down.

[0079] The ionic conductivity of the single cell in the battery pack is calculated by the following formula:

[0080]

[0081] Where: is the ionic conductivity of the single cell in the battery pack, I is the charge and discharge current, V is the effective voltage, A is the cross-sectional area of ​​the electrolyte, and L is the length of the ion flow in the battery.

[0082] It should be noted that the higher the ionic conductivity, the smoother the migration of ions in the battery, and the lower the ionic conductivity, the lower the number of ions in the battery, resulting in less smooth migration.

[0083] The C-rate is a measure of the battery charge and discharge rate. The C-rate represents the ratio of the battery charge or discharge current to the battery capacity per unit time, which directly affects the battery's charge time, discharge capacity, temperature rise and life at high rates.

[0084] The multiplier value is calculated by the following formula:

[0085]

[0086] Where: C is the rate value, I is the charge and discharge current, is the battery capacity at the current moment.

[0087] It should be noted that when the multiplier value is greater than 1, it means that the battery's charge and discharge current is greater than the battery capacity at the current moment. When the multiplier value is equal to 1, it means that the battery's charge and discharge current is the battery capacity at the current moment. When the multiplier value is less than 1, it means that the charge and discharge current is lower than the battery capacity at the current moment.

[0088] It should be noted that in low temperature environments, the viscosity of the electrolyte increases, the fluidity deteriorates, and the ion conductivity decreases, which affects the charge and discharge performance of the battery and reduces the power output of the battery. In low temperature environments, the transfer rate of sodium ions is slow, which affects the rate performance of the battery. This will cause the battery to perform poorly when discharging at high currents.

[0089] Ionic conductivity and rate value are closely related. The higher the ionic conductivity, the faster the migration of ions in the battery, and the rate performance will also improve accordingly, because the battery can respond to external load requirements more quickly. When the ionic conductivity is low, the rate value of the battery will be limited, especially when discharging at high currents, the battery may not be able to quickly provide enough current, resulting in a decrease in power output.

[0090] The switching of the charging mode of the temperature-depleted single battery cell is specifically as follows:

[0091] When the total number of single cells that lose temperature is only one, the charging mode is directly switched;

[0092] When there are multiple single cells that have lost temperature, they are sorted based on ion conductivity, and the single cells with the smallest ion conductivity are switched to a mode first, while the other single cells are in sleep mode.

[0093] The system of the power balance control method based on the photovoltaic sodium-ion battery energy storage system is characterized by comprising a battery pack state acquisition module, a thermal management efficiency calculation module, a thermal management efficiency evaluation module, and a charging mode switching judgment module, specifically:

[0094] A battery pack state acquisition module, used to acquire battery pack state parameters of the sodium ion battery, wherein the battery pack state parameters include battery capacity decay rate, single cell ambient temperature gradient, and voltage balance degree at single cell ambient temperature;

[0095] A thermal management efficiency calculation module, used to calculate the thermal management efficiency of the battery pack based on the battery pack state parameters;

[0096] A thermal management efficiency evaluation module is used to calculate the ionic conductivity and rate value of the single cells in the battery pack when the thermal management efficiency of the battery pack is lower than a preset standard threshold;

[0097] The charging mode switching judgment module is used to switch the charging mode of the single battery with loss of temperature when the ion conductivity and the rate value of the single battery in the battery pack are both lower than the preset value.

[0098] The above formulas are all dimensionless and numerical calculations. The formula is a formula for the most recent real situation obtained by collecting a large amount of data and performing software simulation. The preset parameters in the formula are set by technicians in this field according to actual conditions.

[0099] The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination. When implemented by software, the above embodiments may be implemented in whole or in part in the form of a computer program product.

[0100] Those of ordinary skill in the art will appreciate that the modules and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the preset application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each preset application, but such implementation should not be considered to be beyond the scope of this application.

[0101] In addition, each functional module in each embodiment of the present application may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0102] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0103] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A power balance control method based on a photovoltaic sodium-ion battery energy storage system, characterized in that: The following steps are involved: Acquire battery pack state parameters of the sodium ion battery, wherein the battery pack state parameters include battery capacity decay rate, single cell ambient temperature gradient, and voltage balance degree of the single cell ambient temperature; Calculating the thermal management efficiency of the battery pack based on the battery pack state parameters; When the thermal management efficiency of the battery pack is lower than a preset standard threshold, the ionic conductivity and rate value of the single cells in the battery pack are calculated; When the ionic conductivity and rate value of the single battery in the battery pack are both lower than the preset value, the single battery with loss of temperature is switched to a charging mode; The battery capacity decay rate can be obtained as follows: Record the initial rated capacity of the battery and the number of charge and discharge cycles obtained; Measure the battery capacity when the battery is not under load; The battery capacity decay rate is obtained according to the obtained charge and discharge cycle number and the measured battery capacity combined with the battery capacity decay rate calculation formula; The method for obtaining the temperature gradient of the single cell environment is as follows: Obtain the temperature value of each battery cell at a preset time point; Calculate the average temperature of the entire battery pack within a preset time period based on the temperature value data of all single batteries; Mark the data of the single cell with the highest temperature and the data of the single cell with the lowest temperature in the battery pack, and calculate the environmental temperature gradient of the single cell; Combined with the average temperature of the battery pack in a preset time period and the temperature difference of the single battery, the temperature gradient of the single battery environment is calculated; The voltage balance degree of the single cell at the ambient temperature is obtained by: Measure and record the voltage of each single cell in the battery pack, and calculate the average voltage of the battery pack based on the voltage data of all single cells; Obtain the current temperature of each battery cell, and perform temperature compensation on the battery voltage according to the temperature coefficient of the sodium ion battery to obtain the standard battery voltage value at the standard temperature; Calculate the deviation between the voltage of each single cell and the average voltage, and calculate the voltage balance of the single cell at the ambient temperature by combining the standard battery voltage value at the standard temperature; The thermal management efficiency of the battery pack is calculated as follows: Where: For the thermal management efficiency of the battery pack, is the voltage balance of the battery pack, It represents the temperature gradient inside the battery pack, represents the temperature difference between battery cells, and f is the battery capacity decay rate.

2. The power balance control method based on the photovoltaic sodium ion battery energy storage system according to claim 1, characterized in that: The ionic conductivity of the single cell in the battery pack is obtained by: Measuring geometric dimensions of the electrolyte flow channel, the geometric dimensions including the diameter and rectangular dimensions of the channel through which the electrolyte flows; Preset the test current value and set the working voltage range of the battery at the same time, and apply the working voltage of the battery with the same difference under the preset current value; After applying voltage, the current value flowing through the battery electrolyte is recorded to obtain the ionic conductivity.

3. The power balance control method based on the photovoltaic sodium ion battery energy storage system as claimed in claim 2, characterized in that: The switching of the charging mode of the temperature-depleted single battery cell is specifically as follows: When the total number of single cells that lose temperature is only one, the charging mode is directly switched; When there are multiple single cells that have lost temperature, they are sorted based on ion conductivity, and the single cells with the smallest ion conductivity are switched to a mode first, while the other single cells are in sleep mode.

4. The power balance control method based on the photovoltaic sodium ion battery energy storage system as claimed in claim 3, characterized in that: The battery capacity decay rate is calculated by the following formula: Where: f is the battery capacity decay rate, N is the number of charge and discharge cycles, is a constant that represents the effect of each charge and discharge cycle on the battery capacity. S is the initial rated capacity of the battery, which is taken as 100% here. is the battery capacity at the current moment, and k is the battery state factor.

5. The power balance control method based on the photovoltaic sodium ion battery energy storage system as claimed in claim 4, characterized in that: The voltage balance degree of the single cell at ambient temperature is calculated by the following formula: Where: is the voltage balance of the battery pack, M is the number of battery cells in the battery pack, is the standard battery voltage at standard temperature, is the standard temperature, is the voltage of the ith battery cell, is the average voltage of all battery cells in the battery pack, which is used as a benchmark for measuring voltage differences. T is the current ambient temperature of the battery cells. is the temperature coefficient of the sodium-ion battery, which is a constant.

6. A system using the power balance control method based on the photovoltaic sodium ion battery energy storage system according to any one of claims 1 to 5, characterized in that: It includes a battery pack status acquisition module, a thermal management efficiency calculation module, a thermal management efficiency evaluation module, and a charging mode switching judgment module, specifically: A battery pack state acquisition module, used to acquire battery pack state parameters of the sodium ion battery, wherein the battery pack state parameters include battery capacity decay rate, single cell ambient temperature gradient, and voltage balance degree at single cell ambient temperature; A thermal management efficiency calculation module, used to calculate the thermal management efficiency of the battery pack based on the battery pack state parameters; A thermal management efficiency evaluation module is used to calculate the ionic conductivity and rate value of the single cells in the battery pack when the thermal management efficiency of the battery pack is lower than a preset standard threshold; The charging mode switching judgment module is used to switch the charging mode of the single battery with loss of temperature when the ion conductivity and the rate value of the single battery in the battery pack are both lower than the preset value.

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