A battery replacement battery series heating control method and system

Abstract

The present invention relates to a battery heating technology, and specifically to a battery series heating control method and system, comprising obtaining a battery data set, fitting a battery characteristic curve through the battery data set, obtaining a current input variable, and controlling the battery to heat itself through its own charging and discharging according to the output value of the battery characteristic curve; discharging at a first preset time interval, and charging at a second preset time interval through an electric vehicle kinetic energy recovery system to obtain a pulse current to increase the internal resistance of the battery to achieve a battery heating effect; calculating the charging current according to the electric vehicle's recovered kinetic energy and the charging voltage, and maximizing the battery's thermal efficiency by controlling the pulse current frequency; calculating the lithium deposition voltage according to the battery temperature and the charging rate, and controlling the charging voltage within the lithium voltage range to ensure safe operation of the battery and extend the battery life.

Description

Technical Field

[0001] The present invention relates to battery heating technology, and specifically to a battery series heating control method and system for battery replacement. Background Art

[0002] In recent years, the electric vehicle industry has developed rapidly. The single cell of lithium battery is usually 3.7V. In order to meet the power demand of electric vehicles, 80-100 single cells are generally connected in series to form a battery pack. The total voltage can be greatly increased to about 300-400V through series connection. At the same time, four groups of such battery packs are connected in parallel to increase the battery capacity and extend the range of electric vehicles. However, as the energy source and energy storage device of electric vehicles, lithium-ion batteries are easily affected by ambient temperature, especially in low temperature environments, the battery capacity and performance drop sharply, the range of electric vehicles is greatly reduced, and its safe and efficient application in all-weather environments is seriously limited. At the same time, the charging and discharging performance of lithium-ion batteries in low temperature environments is seriously reduced, especially the charging acceptance capacity is significantly reduced, which has become one of the main limiting factors restricting the charging rate of electric vehicles. In order to solve the problem of serious decline in capacity and performance of lithium-ion batteries in low temperature environments, it is currently generally used to conduct heating batteries by heating liquids, heating metal films, etc. This method has problems such as large energy dissipation, low preheating efficiency, uneven heat transfer, and occupying battery space. Therefore, it is considered to generate heat in the battery's internal resistance through pulse current, and to preheat the battery evenly with appropriate control strategies, so as to achieve less heat dissipation in the heat transfer and heat conduction links, higher energy conversion rate, and more uniform heat transfer layout. In addition, the battery heating methods for swappable technologies launched by many car companies also focus on using more centralized and efficient heating methods in swap stations, such as using large heating equipment or special thermal management systems. Therefore, it is considered to generate heat in the battery's internal resistance through pulse current, calculate the battery's internal resistance using the AC frequency in the swap station as a fixed condition, calculate the charging current using the AC voltage as a limiting condition, and achieve efficient and uniform battery heating through appropriate control strategies. Summary of the invention

[0003] (1) Technical issues to be resolved

[0004] The purpose of the present invention is to provide a battery replacement battery series heating control method and system to solve the problem of rapid decline in battery capacity and performance in low temperature environments.

[0005] (2) Technical solution

[0006] To achieve the above objectives, on the one hand, the present invention provides a battery replacement battery series heating control method, the method comprising:

[0007] S1. Obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset conditions are met, heat the battery by self-charging and discharging;

[0008] S2, obtaining a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; obtaining a second characteristic curve by data fitting the second battery data set; when the battery is heated by self-charging and discharging, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating;

[0009] S3. When the battery temperature does not change within the preset time interval or the change amplitude is less than the preset threshold, the battery data set is collected at a third preset time interval, and the most recently collected data set is used as a new data set to re-optimize the first and second characteristic curves.

[0010] Furthermore, the method of calculating the ratio and difference of the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to the preset standard battery temperature according to the first characteristic curve, and heating by self-charging and discharging when the preset conditions are met, includes:

[0011] The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is:

[0012] ;

[0013] in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is:

[0014] S= ;

[0015] in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

[0016] Furthermore, when the battery is heated by charging and discharging itself, the battery is discharged at a first preset time interval, and charged at a second preset time interval by the electric vehicle kinetic energy recovery system, and the method for obtaining a pulse current for battery heating includes:

[0017] Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is:

[0018] ;

[0019] in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is:

[0020] ;

[0021] in is the pulse current frequency, is a first preset time interval, is a second preset time interval;

[0022] The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is:

[0023] ;

[0024] in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is:

[0025] ;

[0026] in is the discharge current, is the charging current.

[0027] Furthermore, the method of obtaining the speed and mass of the electric vehicle, calculating the recovered electric energy at the second preset time interval, and establishing a mapping relationship between the charging current and the recovered electric energy includes:

[0028] The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is:

[0029] ;

[0030] in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is:

[0031] ;

[0032] in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is:

[0033] ;

[0034] in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium plating voltage corresponding to the current temperature and the battery heating power is calculated.

[0035] Furthermore, the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature and calculating the battery heating power includes:

[0036] The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is:

[0037] ;

[0038] in is the lithium deposition voltage of the battery, is the battery temperature, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is:

[0039] ;

[0040] in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ;

[0041] Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain:

[0042] ;

[0043] The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval.

[0044] Based on the same inventive concept, on the other hand, the present invention also provides a battery-swap battery series heating control system, the system comprising: a condition judgment module, a heating control module, and a battery characteristic update module; the heating control module comprises an internal resistance calculation module, a charging current calculation module, and a lithium deposition voltage calculation module; the condition judgment module is connected to the battery characteristic update module, and the internal resistance calculation module, the charging current calculation module, and the lithium deposition voltage calculation module are connected to the heating control module;

[0045] A condition judgment module is used to obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset condition is met, heat the battery by self-charging and discharging;

[0046] A heating control module is used to obtain a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; the second battery data set is fitted to obtain a second characteristic curve; when the battery is heated by charging and discharging itself, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating;

[0047] The battery characteristic updating module is used to collect the battery data set at a third preset time interval when the battery temperature does not change within the preset time interval or the change amplitude is less than the preset threshold, and re-optimize the first and second characteristic curves using the most recently collected data set as a new data set.

[0048] Furthermore, the working steps of the condition judgment module include:

[0049] The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is:

[0050] ;

[0051] in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is:

[0052] S= ;

[0053] in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

[0054] Furthermore, the working steps of the internal resistance calculation module include:

[0055] Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is:

[0056] ;

[0057] in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is:

[0058] ;

[0059] in is the pulse current frequency, is a first preset time interval, is a second preset time interval;

[0060] The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is:

[0061] ;

[0062] in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is:

[0063] ;

[0064] in is the discharge current, is the charging current.

[0065] Furthermore, the working steps of the charging current calculation module include:

[0066] The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is:

[0067] ;

[0068] in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is:

[0069] ;

[0070] in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is:

[0071] ;

[0072] in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium plating voltage corresponding to the current temperature and the battery heating power is calculated.

[0073] Furthermore, the working steps of the lithium deposition voltage calculation module include:

[0074] The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is:

[0075] ;

[0076] in is the lithium deposition voltage of the battery, is the battery temperature, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is:

[0077] ;

[0078] in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ;

[0079] Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain:

[0080] ;

[0081] The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval.

[0082] (3) Beneficial effects

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] 1. Generate pulse current during the driving of electric vehicles and generate heat through the internal resistance of the battery to achieve less heat dissipation, higher energy conversion rate and more uniform heat transfer layout.

[0085] 2. By controlling the charging voltage to be lower than the lithium plating voltage corresponding to the current temperature, the safe operation of the battery is ensured and the battery life is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 This is a flowchart of a method for controlling series heating of battery replacement batteries according to Embodiment 1 of the present invention;

[0087] Figure 2 This is a module block diagram of a battery series heating control system for a battery replacement according to embodiment 2 of the present invention. DETAILED DESCRIPTION

[0088] 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.

[0089] Before giving examples, it is necessary to explain the application scenarios of the present invention. A certain automobile platform tested the endurance of current mainstream electric vehicle brands in a low-temperature environment and found that less than 30% of the brands achieved an endurance rate of more than 60%. This shows that the battery capacity attenuation of lithium batteries in a low-temperature environment is very serious. Many electric vehicle manufacturers currently use different types of external heating methods to heat the battery. For example, BYD, Xiaopeng, Ideal, etc. all use resistance wires or other heating elements, or use heat pump technology to obtain heat from the outside to heat the battery. In recent years, some scholars have experimentally studied the method of heating the battery by pulse current frequency and amplitude, and found that low-frequency, high-amplitude pulse current is conducive to battery temperature rise.

[0090] Example 1: Figure 1 As shown, this embodiment provides a battery replacement battery series heating control method, the method comprising:

[0091] S1. Obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset conditions are met, heat the battery by self-charging and discharging;

[0092] S2, obtaining a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; obtaining a second characteristic curve by data fitting the second battery data set; when the battery is heated by self-charging and discharging, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating;

[0093] S3. When the battery temperature does not change within the preset time interval or the change amplitude is less than the preset threshold, the battery data set is collected at a third preset time interval, and the most recently collected data set is used as a new data set to re-optimize the first and second characteristic curves.

[0094] Exemplarily, when the battery leaves the factory, the data of battery temperature and battery capacity are collected, and a first characteristic curve is obtained by data fitting, and a relationship model between battery capacity and temperature is established. The data of battery internal resistance and pulse current frequency are obtained, and a second characteristic curve is obtained by data fitting, and a relationship model between battery internal resistance and frequency is established. During the use of the battery, by analyzing the relationship between the current battery temperature and the preset standard battery temperature, the ratio and difference of battery capacity and temperature are calculated to determine whether a heating operation is required. When the battery needs to be heated, the battery control system controls the battery to heat by charging and discharging itself, and at the same time, the battery management system controls the battery to discharge at a first preset time interval, and to charge at a second preset time interval through the electric vehicle kinetic energy recovery system, and to use the obtained pulse current for heating.

[0095] Furthermore, the method of calculating the ratio and difference of the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to the preset standard battery temperature according to the first characteristic curve, and heating by self-charging and discharging when the preset conditions are met, includes:

[0096] The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is:

[0097] ;

[0098] in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is:

[0099] S= ;

[0100] in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

[0101] For example, a preset standard battery temperature is set For 25℃, preset proportional threshold The preset difference threshold is 0.8. 5Ah. Get the current battery temperature The battery capacity corresponding to the current battery temperature is calculated by the first characteristic curve. The current battery temperature is 80Ah. Substitute the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature Available , the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is calculated as , calculate the difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to the standard battery temperature , satisfying the logical relationship Under certain conditions, the battery management system will control the battery to heat up through its own charging and discharging.

[0102] Furthermore, when the battery is heated by charging and discharging itself, the battery is discharged at a first preset time interval, and charged at a second preset time interval by the electric vehicle kinetic energy recovery system, and the method of using the pulse current for battery heating includes:

[0103] Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is:

[0104] ;

[0105] in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is:

[0106] ;

[0107] in is the pulse current frequency, is a first preset time interval, is a second preset time interval;

[0108] The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is:

[0109] ;

[0110] in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is:

[0111] ;

[0112] in is the discharge current, is the charging current.

[0113] Exemplarily, the first preset time interval Seconds, second preset time interval seconds, calculate the pulse current frequency , the static resistance is known , calculate the battery internal resistance , get the discharge current , charging current , calculate the average current , calculate the battery heating power .

[0114] Furthermore, the method of obtaining the speed and mass of the electric vehicle, calculating the recovered electric energy at the second preset time interval, and establishing a mapping relationship between the charging current and the recovered electric energy includes:

[0115] The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is:

[0116] ;

[0117] in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is:

[0118] ;

[0119] in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is:

[0120] ;

[0121] in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium plating voltage corresponding to the current temperature and the battery heating power is calculated.

[0122] For example, the current regenerative braking efficiency has a typical deceleration factor of 1-5 m / s, assuming , The value is 2, then ; Assuming the vehicle mass is 1800kg, the efficiency of converting kinetic energy into electrical energy is , calculate the recovered electrical energy , assuming the charging voltage , then the charging current is .

[0123] Furthermore, the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature and calculating the battery heating power includes:

[0124] The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is:

[0125] ;

[0126] in is the lithium deposition voltage of the battery, is the battery temperature, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is:

[0127] ;

[0128] in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ;

[0129] Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain:

[0130] ;

[0131] The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval.

[0132] For example, assuming that the battery temperature is 20 degrees Celsius and the charge ratio is 1, the lithium deposition voltage is 400 volts, and as the temperature and charge ratio decrease, the lithium deposition voltage decreases; assuming that the battery temperature is -10 degrees Celsius and the charge ratio is 0.8, the lithium deposition voltage is 300 volts; the first preset time interval Seconds, second preset time interval seconds, calculate the pulse current frequency , the static resistance is known , calculate the battery internal resistance , get the discharge current ; Control the charging voltage to be less than or equal to the lithium deposition voltage of 300 volts, and calculate the charging current , calculate the average current , calculate the battery heating power .

[0133] Embodiment 2: Based on the same inventive concept, Figure 2 As shown, this embodiment also provides a battery replacement battery series heating control system, the system includes: a condition judgment module, a heating control module, and a battery characteristic update module; the heating control module includes an internal resistance calculation module, a charging current calculation module, and a lithium deposition voltage calculation module; the condition judgment module is connected to the battery characteristic update module, and the internal resistance calculation module, the charging current calculation module, and the lithium deposition voltage calculation module are connected to the heating control module;

[0134] A condition judgment module is used to obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset condition is met, heat the battery by self-charging and discharging;

[0135] A heating control module is used to obtain a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; the second battery data set is fitted to obtain a second characteristic curve; when the battery is heated by charging and discharging itself, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating;

[0136] The battery characteristic updating module is used to collect the battery data set at a third preset time interval when the battery temperature does not change within the preset time interval or the change amplitude is less than the preset threshold, and re-optimize the first and second characteristic curves using the most recently collected data set as a new data set.

[0137] Furthermore, the working steps of the condition judgment module include:

[0138] The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is:

[0139] ;

[0140] in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is:

[0141] S= ;

[0142] in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

[0143] Furthermore, the working steps of the internal resistance calculation module include:

[0144] Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is:

[0145] ;

[0146] in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is:

[0147] ;

[0148] in is the pulse current frequency, is a first preset time interval, is a second preset time interval;

[0149] The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is:

[0150] ;

[0151] in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is:

[0152] ;

[0153] in is the discharge current, is the charging current.

[0154] Furthermore, the working steps of the charging current calculation module include:

[0155] The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is:

[0156] ;

[0157] in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is:

[0158] ;

[0159] in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is:

[0160] ;

[0161] in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium plating voltage corresponding to the current temperature and the battery heating power is calculated.

[0162] Furthermore, the working steps of the lithium deposition voltage calculation module include:

[0163] The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is:

[0164] ;

[0165] in is the lithium deposition voltage of the battery, is the battery temperature, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is:

[0166] ;

[0167] in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ;

[0168] Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain:

[0169] ;

[0170] The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval.

[0171] It should be noted that, regarding the system in the above embodiment, the specific manner in which each module performs operations has been described in detail in the embodiment of the method, and will not be elaborated here.

[0172] Finally, it should be noted that: Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. 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 method for controlling heating of series-connected batteries, characterized in that: The method comprises: S1. Obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset conditions are met, heat the battery by self-charging and discharging; S2, obtaining a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; obtaining a second characteristic curve by data fitting the second battery data set; when the battery is heated by self-charging and discharging, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating; The method of heating the battery by discharging and discharging the battery at a first preset time interval and charging the battery at a second preset time interval by the electric vehicle kinetic energy recovery system includes: Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is: ； in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is: ； in is the pulse current frequency, is a first preset time interval, is a second preset time interval; The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is: ； in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is: ； in is the discharge current, is the charging current; The method of obtaining the speed and mass of the electric vehicle, calculating the recovered electric energy in the second preset time interval, and establishing a mapping relationship between the charging current and the recovered electric energy includes: The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is: ； in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is: ； in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is: ； in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium deposition voltage corresponding to the current temperature and the battery heating power is calculated; The method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature and calculating the battery heating power comprises: The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is: ； in is the lithium deposition voltage of the battery, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is: ； in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ; Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain: ； The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval; S3. When the battery temperature does not change within the preset time interval or the change amplitude is less than the preset threshold, the battery data set is collected at a third preset time interval, and the most recently collected data set is used as a new data set to re-optimize the first and second characteristic curves.

2. A battery replacement battery series heating control method according to claim 1, characterized in that: The method of calculating the ratio and difference of the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to the preset standard battery temperature according to the first characteristic curve, and heating by self-charging and discharging when the preset conditions are met, comprises: The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is: ； in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is: S= ； in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

3. A battery replacement series heating control system, characterized in that: The system comprises: a condition judgment module, a heating control module, and a battery characteristic update module; the heating control module comprises an internal resistance calculation module, a charging current calculation module, and a lithium deposition voltage calculation module; the condition judgment module is connected to the battery characteristic update module, and the internal resistance calculation module, the charging current calculation module, and the lithium deposition voltage calculation module are connected to the heating control module; A condition judgment module is used to obtain a first battery data set of the electric vehicle, wherein the first battery data set includes a battery temperature and a battery capacity; obtain a first characteristic curve by data fitting the first battery data set; obtain the current battery temperature, and calculate the ratio and difference between the battery capacity corresponding to the current battery temperature and the battery capacity corresponding to a preset standard battery temperature according to the first characteristic curve, and when the preset condition is met, heat the battery by self-charging and discharging; A heating control module is used to obtain a second battery data set of the electric vehicle, wherein the second battery data set includes a battery internal resistance and a pulse current frequency; the second battery data set is fitted to obtain a second characteristic curve; when the battery is heated by charging and discharging itself, the battery is discharged at a first preset time interval, and charged at a second preset time interval through a kinetic energy recovery system of the electric vehicle, and the pulse current is obtained for battery heating; A battery characteristic updating module, configured to collect a battery data set at a third preset time interval when the battery temperature does not change within a preset time interval or the change amplitude is less than a preset threshold, and to use the most recently collected data set as a new data set to re-optimize the first and second characteristic curves; The working steps of the internal resistance calculation module include: Obtain the pulse current frequency and the battery internal resistance, the battery internal resistance includes ohmic internal resistance and polarization internal resistance, and establish a mapping relationship between the battery internal resistance and the pulse current frequency through data fitting; the battery internal resistance The calculation formula is: ； in is the static resistance of the battery, is the pulse current frequency, is the coefficient of the battery internal resistance mapping relationship, is the mapping relationship battery characteristic constant; where the pulse current frequency The calculation formula is: ； in is the pulse current frequency, is a first preset time interval, is a second preset time interval; The speed and mass of the electric vehicle are obtained, the recovered electric energy in the second preset time interval is calculated, and a mapping relationship between the charging current and the recovered electric energy is established; the discharge current of the battery is obtained, and the average current of the battery during charging and discharging is calculated through the charging current and the discharging current; the average current and the battery resistance are brought into the battery heating power calculation formula, and the battery heating power is calculated through the battery heating power calculation formula and the constraint conditions, wherein the battery heating power The calculation formula is: ； in The heat generated by the battery, is the average current of the pulse current; the average current The calculation formula is: ； in is the discharge current, is the charging current; The working steps of the charging current calculation module include: The speed and mass of the electric vehicle are obtained, and a mapping relationship between the recovered electric energy and the mass and speed is established based on the characteristics that the kinetic energy is proportional to the square of the speed and that there is energy loss when the kinetic energy is converted into electric energy. The calculation formula is: ； in To recover electrical energy, For the quality of electric vehicles, is the efficiency of converting kinetic energy into electrical energy, is the vehicle speed at the start of the second preset time interval, is the vehicle speed at the end of the second preset time interval, and the vehicle speed at the end of the second preset time interval The calculation formula is: ； in is the deceleration coefficient; according to the proportional relationship between charging current and recovered electric energy, a mapping relationship between charging current and recovered electric energy is established. The calculation formula is: ； in is the power conversion efficiency coefficient, is the charging voltage; the charging current is substituted into the average current calculation formula, and the average current and the battery internal resistance are substituted into the battery heating power calculation formula; the charging voltage is controlled to be less than the lithium deposition voltage corresponding to the current temperature and the battery heating power is calculated; The working steps of the lithium deposition voltage calculation module include: The battery temperature, charging rate, battery charging voltage and whether lithium deposition occurs are obtained through experiments, and the data are fitted through MATLAB to establish a mapping relationship between the lithium deposition voltage and the battery temperature and charging rate; the lithium deposition voltage The calculation formula is: ； in is the lithium deposition voltage of the battery, is the charging rate, To control the coefficient of the mapping relationship, To control the bias of the mapping relationship, The battery temperature affects the bias of the battery lithium deposition voltage. The charging rate affects the bias of the battery lithium deposition voltage; the charging rate The calculation formula is: ； in is the rated capacity of the battery; the method of controlling the charging voltage to be less than the lithium deposition voltage corresponding to the current temperature is: ; Substitute the charging current into the average current calculation formula, and substitute the average current and battery internal resistance into the battery heating power calculation formula to obtain: ； The calculation formula of the battery heating power is used as the objective function, the calculation formula of the lithium deposition voltage is used as the restriction condition, and the maximum value of the battery heating power is obtained by controlling the first preset time interval and the second preset time interval.

4. A battery replacement series heating control system according to claim 3, characterized in that: The working steps of the condition judgment module include: The battery is left to stand for a preset time, the battery temperature and battery capacity are obtained, and the data are fitted through MATLAB to establish a mapping relationship between the battery capacity and the battery temperature; the battery capacity The calculation formula is: ； in is the battery temperature, is the coefficient of the battery capacity mapping relationship, is the bias of the battery capacity mapping relationship; obtain the current battery temperature, bring the current battery temperature into the battery characteristic curve to calculate the battery capacity corresponding to the current battery temperature, if the ratio of the battery capacity corresponding to the current battery temperature to the battery capacity corresponding to the standard battery temperature is less than the preset ratio threshold and the difference is greater than the preset difference threshold, the battery is heated by its own charging and discharging; the logical relationship of the battery being heated by its own charging and discharging The expression relationship is: S= ； in It means that the battery management system controls the battery to heat up through its own charging and discharging. This means that the battery management system does not control the battery to heat up through its own charging and discharging. To preset the standard battery temperature, is the current battery temperature, Indicates the battery capacity corresponding to the current battery temperature. Indicates the battery capacity corresponding to the preset standard battery temperature. Preset proportional threshold for battery degradation, Preset difference threshold for battery degradation.

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