A new energy vehicle low-voltage lithium battery charging control method

Abstract

The application discloses a new energy automobile low-voltage lithium battery charging control method, comprising the following steps: constructing a lithium battery charging control system; performing battery health state estimation calculation; performing residual power estimation calculation; realizing state switching of a DC / DC control module; and regulating the DC / DC output voltage in a proportional regulation mode to avoid overcharging of the battery in the regulation process. The above technical scheme realizes the cooperation among a battery health state estimation module, a residual power estimation module and a DC / DC control module, estimates the battery health state, triggers full charging calibration SOC when the SOC cumulative error is too large, ensures that the SOC estimation error is within a controllable range, regulates the DC / DC output voltage in a proportional regulation mode to avoid the overcharging problem of the battery in the regulation of the DC / DC voltage, and realizes the optimization of the lithium battery charging control.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle technology, and in particular to a charging control method for low-voltage lithium batteries in new energy vehicles. Background Technology

[0002] With the trend of vehicle electrification, intelligence and connectivity, the static power consumption of electric vehicles has increased significantly. When electric vehicles have large static power consumption, low-voltage batteries cannot support standby time of several weeks or longer like traditional fuel vehicles. Especially at low temperatures, the charging and discharging efficiency of low-voltage batteries such as lithium batteries is very low, resulting in very little charging. If the vehicle is left unattended for a long time, the low-voltage battery will inevitably be depleted, which will prevent the vehicle from starting.

[0003] Data shows that existing fixed constant-voltage charging control methods for lead-acid batteries in vehicles do not use lithium batteries. Compared to lead-acid batteries, lithium-ion batteries are more prone to lithium plating due to overcurrent during charging, especially at low temperatures. Direct fixed constant-voltage charging easily leads to overcurrent, affecting battery life. Existing high-voltage lithium battery pack charging control methods are not suitable for low-voltage lithium batteries in new energy vehicles. During driving, low-voltage lithium batteries serve as backup power and cannot be disconnected from the DC / DC converter. Therefore, low-voltage lithium batteries are also passively charged, but at this time, the DC / DC converter cannot operate in constant-current charging mode like a charger for high-voltage lithium battery packs.

[0004] Chinese patent document CN113258624A discloses a "DC charging control system for low-voltage batteries of electric vehicles." It employs an on-board controller, an electronic control switch, a low-voltage battery, a battery management system, and a vehicle charging interface. The on-board controller is connected in series with the low-voltage battery via the electronic control switch, and also in series with the battery management system. The battery management system is communicatively connected to both the electronic control switch and the low-voltage battery. The vehicle charging interface is used for electrical connection to external power supply equipment. The vehicle charging interface includes an A+ interface, an A- interface, an S+ interface, and an S- interface, all electrically connected to the on-board controller. The power supply equipment includes a power supply controller, a first connector terminal matching the A+ interface, a second connector terminal matching the A- interface, a third connector terminal matching the S+ interface, and a fourth connector terminal matching the S- interface. The power supply controller is electrically connected to the first, second, third, and fourth connector terminals. However, this technical solution lacks a practically optimized control algorithm strategy and cannot effectively achieve targeted charging optimization control. Summary of the Invention

[0005] This invention primarily addresses the technical problem that existing technical solutions lack practically optimized control algorithms and strategies, making it impossible to effectively achieve targeted charging optimization control. It provides a charging control method for low-voltage lithium batteries in new energy vehicles. Through the cooperation of three modules—a battery health state estimation module, a remaining capacity estimation module, and a DC / DC control module—the battery health state is estimated. Simultaneously, when the accumulated SOC error is too large, a full-charge calibration of the SOC is triggered to ensure that the SOC estimation error remains within a controllable range. The DC / DC output voltage is adjusted proportionally to avoid overcharging during DC / DC voltage adjustment, thus optimizing lithium battery charging control.

[0006] The above-mentioned technical problems of the present invention are mainly solved by the following technical solution: The present invention includes the following steps:

[0007] S1 constructs a lithium battery charging control system;

[0008] S2 performs battery health status estimation calculations;

[0009] S3 performs remaining power estimation calculations;

[0010] S4 enables the switching of the state of the DC / DC control module;

[0011] The S5 uses proportional adjustment to regulate the DC / DC output voltage, avoiding overcharging of the battery during the adjustment process.

[0012] Given the unique operating conditions of 12V lithium batteries in new energy vehicles, this approach ignores cycle life and equates the calendar life at different temperatures to room temperature to estimate battery health, saving significant cycle testing costs. Addressing the issue of poor remaining capacity estimation accuracy for lithium iron phosphate batteries, a cross-platform SOC error calibration strategy is implemented to prevent large SOC errors. Furthermore, triggering full-charge calibration when the accumulated SOC error becomes too large ensures that the SOC estimation error remains within a controllable range. During charging, the charging map is directly consulted based on measured charging voltage and temperature, avoiding overcharging issues caused by SOC estimation errors, which are common with traditional methods relying on SOC and temperature. During driving, to ensure sufficient power supply, the DC / DC converter must be set to constant voltage mode. The DC / DC output voltage is adjusted proportionally based on whether the charging current is excessive, preventing overcharging during DC / DC voltage adjustment.

[0013] Preferably, the lithium battery charging control system in step S1 includes a battery health status estimation module, a remaining capacity estimation module, and a DC / DC control module, which are connected in sequence. The remaining capacity estimation module is an important input to the DC / DC control module, and the battery health status estimation module is an important input to the remaining capacity estimation module.

[0014] Preferably, the formula for calculating the battery health state estimation (SOH) in step S2 is as follows:

[0015]

[0016] KR i This represents the equivalence factor from the reference temperature of 25°C; t i Indicates that the battery is in KT i The total service time at the specified temperature, BTtime represents the time from battery degradation to end-of-life serviceability at a reference temperature of 25°C; KT i BTtime is a calibration quantity, used for battery calendar life testing and calibration according to different projects.

[0017] Since low-voltage lithium batteries in new energy vehicles operate within a relatively small SOC range for extended periods and are primarily powered by DC / DC converters during driving, the number of cycles required within their lifespan is limited, and the capacity degradation caused by cycling is negligible. Therefore, only calendar life needs to be considered. SOC and temperature are two key factors affecting calendar life. Since low-voltage lithium batteries in new energy vehicles operate within a specific, relatively small SOC range, the SOC can be considered a fixed value. In this patent, this value is set at 80%, and only the influence of different temperatures at this SOC is considered.

[0018] Preferably, the remaining power estimation of the remaining power estimation module in step S3 mainly includes: OCV calibration SOC, ampere-hour integration update SOC and error, and full charge calibration SOC module; the OCV calibration SOC part is used to determine whether the battery is completely in a static state when powered on, and if the condition is met, then enter the OCV calibration SOC.

[0019] Preferably, the conditions for determining that the battery is completely stationary include: the time difference between the current power-on and the previous power-off is greater than a set threshold; the average single-cell voltage between the current power-on and the previous power-off is less than a set threshold; and the absolute value of the current during the current power-on is less than a set threshold.

[0020] 1) The time difference between the current power-on and the previous power-off is greater than a certain threshold (set to 1h in this patent); 2) The average single-cell voltage between the current power-on and the previous power-off is less than a certain threshold (set to 2mV in this patent); 3) The absolute value of the current during the current power-on is less than a certain threshold (set to 2A in this patent).

[0021] Preferably, step S3, the cross-platform SOC calibration method based on OCV, includes the following steps:

[0022] S3.1 When looking up the table and finding that SOC (SocOCV) ≥ LimHiSocThd or SOC (SocOCV) ≤ LoSocThd, accurately calibrate SOC = SocOCV and clear the SOC cumulative error;

[0023] S3.2 If SocOCV >= HiSocThd and SOC < HiSocThd, then perform fuzzy calibration: SOC = HiSocThd;

[0024] S3.3 If SocOCV < HiSocThd and SocOCV > LoSocThd and SOC >= HiSocThd, then perform fuzzy calibration: SOC = HiSocThd;

[0025] S3.4 If SocOCV < HiSocThd and SocOCV > LoSocThd and SOC ≤ LoSocThd, then perform fuzzy calibration: SOC = LoSocThd;

[0026] S3.5 When both SocOCV and SOC are in the plateau region, no SOC calibration is performed;

[0027] Among them, LimHiSocThd = 99%, HiSocThd = 70%, LoSocThd = 30%.

[0028] Preferably, the formulas for updating SOC and error by ampere-hour integration are as follows:

[0029] SOC update formula:

[0030]

[0031] SOC error update formula:

[0032]

[0033] Among them, Cap represents the rated capacity of the battery, Cur represents the battery current, Qin represents the cumulative charge, Qout represents the cumulative discharge, QinAtCalib represents the cumulative charge corresponding to the last accurate calibration of SOC, QoutAtCalib represents the cumulative discharge corresponding to the last accurate calibration of SOC, RTCtime represents the current calendar time, RTCtimeAtCalib represents the calendar time corresponding to the last calibration, K represents the linear error of the current sensor, and b represents the offset error of the current sensor;

[0034] When it is detected that SocErr is greater than the set threshold, then request DC / DC full charge battery calibration of SOC, and the set threshold is taken as 10%.

[0035] Preferably, the DC / DC control module in step S4 includes four states: standby mode, driving mode, normal charging, and calibration charging. When the DC / DC malfunctions or switches from another state to the standby state, it operates in standby mode. When the charging conditions are met and the vehicle responds allowing charging, it enters the charging state, which is divided into normal charging and calibration charging. When the charging conditions are not met but the DC / DC is working normally and the charging MOSFET is closed, it enters the driving mode. In the driving mode, the DC / DC operates in constant voltage mode to ensure sufficient power is provided and the battery is not overcharged.

[0036] The beneficial effects of this invention are:

[0037] 1. Based on the special operating conditions of 12V lithium batteries in new energy vehicles, unnecessary cycle life tests are optimized to reduce development costs;

[0038] 2. Cross-platform large-error SOC fuzzy calibration to avoid large errors; at the same time, combined with calibration charging methods, the SOC error is controlled within a certain controllable range;

[0039] 3. Use the measured voltage value directly instead of estimating the SOC value, and check the charging map table to avoid overcharging due to SOC estimation errors;

[0040] 4. During driving, check if the charging current is too high, and adjust the DC / DC output voltage to avoid overcurrent during battery charging and extend battery life. Attached Figure Description

[0041] Figure 1 This is a flowchart of the present invention.

[0042] Figure 2 This is a schematic diagram of the principle structure of the present invention.

[0043] Figure 3 This is a flowchart of SOC estimation according to the present invention.

[0044] Figure 4 This is a flowchart of a cross-platform SOC calibration process based on OCV according to the present invention.

[0045] Figure 5 This is a DC / DC module state transition diagram according to the present invention.

[0046] Figure 6 This is a flowchart of a normal charging state according to the present invention.

[0047] Figure 7 This is a driving mode state flowchart of the present invention. Detailed Implementation

[0048] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0049] Example: This example describes a charging control method for low-voltage lithium batteries in new energy vehicles, such as... Figure 1 As shown, the following steps are:

[0050] S1 constructs a lithium battery charging control system;

[0051] S2 performs battery health status estimation calculations;

[0052] S3 performs remaining power estimation calculations;

[0053] S4 enables the switching of the state of the DC / DC control module;

[0054] The S5 uses proportional adjustment to regulate the DC / DC output voltage, avoiding overcharging of the battery during the adjustment process.

[0055] The lithium battery charging control system comprises three modules: battery health state estimation, remaining capacity estimation, and DC / DC control. Figure 2 As shown, the remaining power estimation is an important input to the DC / DC control module, and the battery health status estimation is an important input to the remaining power estimation module.

[0056] Battery State of Health (SOH) estimation:

[0057] Since low-voltage lithium batteries in new energy vehicles operate within a relatively small SOC range for extended periods and are primarily powered by DC / DC converters during driving, the number of cycles required within their lifespan is limited, and the capacity degradation caused by cycling is negligible. Therefore, only calendar life needs to be considered. SOC and temperature are two key factors affecting calendar life. Since low-voltage lithium batteries in new energy vehicles operate within a specific, relatively small SOC range, the SOC can be considered a fixed value (set to 80% in this patent). Only the influence of different temperatures at this SOC is considered; therefore, the SOH calculation formula is as follows:

[0058]

[0059] KT i This represents the equivalence factor from the reference temperature of 25°C; t i Indicates that the battery is in KT i The total service time at the specified temperature, BTtime represents the time from battery degradation to end-of-life serviceability at a reference temperature of 25°C; KT i BTtime is a calibration quantity, and battery calendar life test calibration needs to be performed according to different projects.

[0060] Remaining power estimate (SOC) such as Figure 3 As shown

[0061] The remaining power estimation mainly includes three parts: OCV calibration of SOC, Ampere-hour integration for updating SOC and error, and full charge calibration of SOC module.

[0062] In the part of OCV calibration of SOC, when the power is turned on, it is determined whether the battery is completely in a static state. If the conditions are met, then enter the OCV calibration of SOC. The judgment conditions for the battery to be in a completely static state are: 1) The time difference between this power-on and the last power-off is greater than a certain threshold (set to 1h in this patent); 2) The average single-cell voltage between this power-on and the last power-off is less than a certain threshold (set to 2mV in this patent); 3) The absolute value of the current at the time of this power-on is less than a certain threshold (set to 2A in this patent). Based on the static OCV characteristics of lithium iron phosphate batteries, as Figure 3 shown, this patent discloses a cross-platform SOC calibration method based on OCV, and the flowchart is as Figure 4 shown:

[0063] When looking up the table SOC (SocOCV): ≥ LimHiSocThd or ≤ LoSocThd, the accurate calibration SOC = SocOCV, and the SOC cumulative error is cleared;

[0064] Otherwise, if SocOCV >= HiSocThd and SOC < HiSocThd, then the fuzzy calibration SOC = HiSocThd;

[0065] Otherwise, if SocOCV < HiSocThd and SocOCV > LoSocThd and SOC >= HiSocThd, then the fuzzy calibration SOC = HiSocThd;

[0066] Otherwise, if SocOCV < HiSocThd and SocOCV > LoSocThd and SOC ≤ LoSocThd, then the fuzzy calibration SOC = LoSocThd;

[0067] Otherwise, both SocOCV and SOC are in the platform area, and no SOC calibration is performed.

[0068] In this invention patent, LimHiSocThd = 99%, HiSocThd = 70%, LoSocThd = 30%.

[0069] The calculation formulas for Ampere-hour integration to update SOC and error are as follows:

[0070] SOC update formula:

[0071]

[0072] SOC error update formula:

[0073]

[0074] Among them, Cap represents the rated capacity of the battery, Cur represents the battery current, Qin represents the cumulative charge, Qout represents the cumulative discharge, QinAtCalib represents the cumulative charge corresponding to the last accurate calibration of SOC, QoutAtCalib represents the cumulative discharge corresponding to the last accurate calibration of SOC, RTCtime represents the current calendar time, RTCtimeAtCalib represents the calendar time corresponding to the last calibration, K represents the linear error of the current sensor, and b represents the offset error of the current sensor.

[0075] When it is detected that SocErr is greater than a certain threshold, a request for DC / DC full charge battery calibration of SOC is made. In this patent, this threshold is taken as 10%.

[0076] DC / DC control module:

[0077] The DC / DC control module includes four states: standby mode, driving mode, normal charging, and calibration charging; when there is a DC / DC fault or when switching from other states to the waiting state, it works in the standby mode; when the charging conditions are met and the vehicle responds to allow charging, it enters the charging state, and the charging state is divided into two types: normal charging and calibration charging. The purpose of charging is to ensure that the low-voltage lithium battery does not discharge during long-term parking. At the same time, calibration charging can also play a role in calibrating SOC; when the charging conditions are not met, the D / DC works normally, and the charging MOSFET is closed, it enters the driving mode. In this state, the DC / DC works in the constant voltage mode to ensure that sufficient power can be provided, and at the same time, it is necessary to ensure that the battery is not overcharged; the jump conditions between each state are as Figure 5 shown;

[0078] Standby mode: It directly enters the standby mode after initialization; in the standby mode, it is requested that the DC / DC works in the constant voltage mode. In this patent, the requested output voltage is 13.3V and the current is the default maximum value of 200A; in the standby mode, if all the following conditions are met, a charging request is sent:

[0079] 1) SocMin < LoSocChg or Vmin < LoCellVoltChg;

[0080] 2) Overcharge has not been started;

[0081] 3) The charging MOSFET is closed;

[0082] 4) There is no charging response timeout fault.

[0083] Wherein, SocMin represents the minimum SOC in the battery pack, Vmin represents the minimum single-cell voltage, LoSocChg represents the SOC threshold for allowing charging (25% in this patent), and LoCellVoltChg represents the single-cell voltage threshold for allowing charging (3.29V in this patent). If no charging permission response is received within 10 seconds after sending a charging request, a charging response timeout fault is set.

[0084] If the conditions for sending a charging request are met, and the following conditions are also met, the system will enter normal charging mode:

[0085] 1) The DC / DC converter is working normally;

[0086] 2) Received a charging permission response;

[0087] 3) No calibration charging request.

[0088] If the conditions for sending a charging request are met, and the following conditions are also met, the system will enter the calibration charging state:

[0089] 1) The DC / DC converter is working normally;

[0090] 2) Received a charging permission response;

[0091] 3) There is a calibration charging request.

[0092] If the conditions for sending a charging request are not met in standby mode, and the DC / DC converter is working normally, then the system will enter constant voltage mode.

[0093] Normal charging state: The flowchart for the normal charging state is as follows Figure 6 As shown; during normal charging, the DC / DC converter operates in constant current mode, requesting the DC / DC output current Cur2DC = f(Vmax,Tcell) + MovAvg_3s(DC_OupCur - PackChgCur), where f(Vmax,Tcell) is the maximum allowable charging current obtained by looking up the charging map table based on the highest single-cell voltage and temperature of the battery, DC_OupCur is the actual output current of the DC / DC converter, PackChgCur is the battery charging current, and MovAg_3s(DC_OupCur - PackChgCur) is the average current load of the entire vehicle in the last 3 seconds; in this mode, the requested DC / DC output voltage in this patent is the default maximum value of 14.6V. During normal charging, the following fault diagnoses are available:

[0094] If the current value of DC_OupCur–Cur2DC > CurDiagRatioK*Cur2DC+CurDaigOffset is maintained for 10 seconds, then charging ends and an overcurrent fault is set. Here, CurDiagRatioK represents the maximum linearity error of the DC / DC constant current mode output, which is 5% in this patent, and CurDaigOffset represents the maximum offset of the DC / DC constant current mode output, which is 0.5A in this patent.

[0095] Otherwise, if Cur2DC-DC_OupCur > CurDiagRatioK*Cur2DC+CurDaigOffset for 10 seconds, set the undercurrent charging fault and continue charging;

[0096] Otherwise, if Vmax > ChgCutOffCellVolt + VoltDiagOffset for 10 seconds, charging ends and an overvoltage fault is set. Here, ChgCutOffCellVolt represents the normal charging cutoff voltage of the battery, which is 3.5V in this patent, and VoltDiagOffset represents the overvoltage diagnostic offset threshold, which is 10mV in this patent.

[0097] Otherwise, if the charging time exceeds ChgTimeout, charging will be stopped and a charging timeout fault will be set. In this patent, this value is 10h.

[0098] Otherwise, if Vmax ≥ ChgCutOffCellVolt for 3 seconds, then stop charging and set the charging end flag.

[0099] In addition to the above conditions for ending normal or abnormal charging, the conditions for exiting normal charging state also include: DC / DC failure or failure to receive a charging permission response.

[0100] Calibration charging state: The control process for calibration charging state is the same as that for normal charging state. The only difference is that calibration charging will fully charge the battery SOC to 100%, which means that the charging cut-off voltage ChgCutOffCellVolt is different; in this patent, the calibration charging ChgCutOffCellVolt is 3.65V.

[0101] Driving Mode: The driving mode status flowchart is as follows Figure 7 As shown; in driving mode, the DC / DC converter requests constant voltage output, and the requested current is the default maximum value, which is 200A in this patent. In this mode, it is necessary to ensure that the DC / DC converter operates within a certain voltage range, and at the same time ensure that the battery is not overcharged, which would affect battery life and safety.

[0102] In standby mode, the vehicle will enter driving mode if all of the following conditions are met:

[0103] 1) The DC / DC operates normally;

[0104] 2) The charging MOSFET is closed;

[0105] 3) There is no charging request.

[0106] When one of the following conditions is met, it is the driving mode exit condition:

[0107] 1) The DC / DC fails;

[0108] 2) The charging MOSFET is open.

[0109] In the driving mode, the control method for the output voltage Volt2DC of the requested DC / DC is as follows:

[0110] After entering the constant voltage mode, if the battery pack terminal voltage PackVolt > DcDefltSetLoVolt, then Volt2DC steps up by DCvarStep every FilterTim seconds from PackVolt, otherwise if PackVolt ≤ DcDefltSetLoVolt, then Volt2DC steps up by DCvarStep every FilterTim seconds from DcDefltSetLoVolt until Volt2DC = DcDefltSetHiVolt; and during the rising process, if continuous overcurrent charging is detected for FilterTim seconds, then Volt2DC drops by DCvarStep every FilterTim seconds until there is no overcurrent charging or Volt2DC = DcDefltSetHiVolt; at the same time, if it is detected that Vmax > HiCellVoltDec and the charging current > 0.1A continuously for FilterTim seconds, then Volt2DC drops by DCvarStep every FilterTim seconds until Vmax ≤ HiCellVoltDec, and after this condition is triggered, the process of rising Volt2DC to DcDefltSetHiVolt stops until Vmax < LoCellVoltInc and then this process is restarted. [[ID=二十四]] [[ID=二十五]]

[0111] In this patent, DcDefltSetLoVolt = 12.5V, which cannot be lower than the minimum voltage required for normal operation of other low-voltage electrical equipment in the vehicle; FilterTim = 3s, which is calibrated on the vehicle based on the actual operating conditions of the battery, and the calibration criteria are that the battery must have sufficient time to respond to DC / DC voltage changes; DCvarStep = 100mV, which is the minimum step size for DC / DC voltage adjustment; DcDefltSetHiVolt = 13.3V, which needs to take into account both the battery lifespan (the higher the voltage, the shorter the lifespan) and the maximum allowable operating voltage of the low-voltage electrical equipment in the vehicle; DcDefltSetHiVolt = 3.345V, which is set to ensure that the battery is not overcharged; LoCellVoltInc = 3.325V, which is to avoid frequent DC / DC voltage adjustments.

[0112] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0113] Although this paper uses terms such as battery health status estimation and remaining capacity estimation frequently, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention.

Claims

1. A charging control method for low-voltage lithium batteries in new energy vehicles, characterized in that, It includes the following steps: S1 Build a lithium battery charging control system; S2 Perform battery health state estimation calculation; S3 Perform remaining power estimation calculation, including: when powering on, if the battery is completely in a static state, enter OCV calibration SOC; when the looked-up SOC (SocOCV) ≥ 99% or ≤ 30%, accurately calibrate SOC = SocOCV and clear the accumulated error; when SocOCV is in the 30%-70% platform area and SOC deviates from the platform area, fuzzily calibrate SOC to the boundary of the platform area; update SOC and error by ampere-hour integration method; when the SOC error is greater than 10%, request DC / DC full charge calibration of SOC; S4 Implement the state switching of the DC / DC control module; S5 Adjust the DC / DC output voltage in a proportional regulation manner to avoid overcharging the battery during the adjustment process.

2. The charging control method for low-voltage lithium batteries in new energy vehicles according to claim 1, characterized in that, The lithium battery charging control system in step S1 includes a battery health state estimation module, a remaining power estimation module, and a DC / DC control module, and the battery health state estimation module, the remaining power estimation module, and the DC / DC control module are connected in sequence.

3. A charging control method for low-voltage lithium batteries in new energy vehicles according to claim 1 or 2, characterized in that, The calculation formula for the battery health state estimation SOH in step S2 is as follows: KT i This represents the equivalent coefficient of the battery's service temperature at KTi temperature to the reference temperature of 25°C; t i Indicates that the battery is in KT i The total service time at the specified temperature, BTtime represents the time from battery degradation to end-of-life serviceability at a reference temperature of 25°C; KT i BTtime is a calibration quantity, used for battery calendar life testing and calibration according to different projects.

4. A charging control method for low-voltage lithium batteries in new energy vehicles according to claim 1 or 2, characterized in that, The remaining power estimation of the remaining power estimation module in step S3 includes: OCV calibration SOC, ampere-hour integration update of SOC and error, full charge calibration SOC module; the OCV calibration SOC part is used to determine whether the battery is completely in a static state when powering on, and if the condition is met, enter OCV calibration SOC.

5. The charging control method for low-voltage lithium batteries in new energy vehicles according to claim 4, characterized in that, The judgment conditions for the battery to be completely static include: the time difference between this power-on and the last power-off is greater than the set threshold; the average single-cell voltage between this power-on and the last power-off is less than the set threshold; the absolute value of the current at this power-on is less than the set threshold.

6. The charging control method for low-voltage lithium batteries in new energy vehicles according to claim 1, characterized in that, The cross-platform SOC calibration method based on OCV in step S3 includes the following steps: S3.2 If SocOCV >= HiSocThd and SOC < HiSocThd, then fuzzily calibrate SOC = HiSocThd; S3.5 Both SocOCV and SOC are in the platform area, and no SOC calibration is performed; Among them, LimHiSocThd = 99%, HiSocThd = 70%, LoSocThd = 30%.

7. The charging control method for low-voltage lithium batteries in new energy vehicles according to claim 4, characterized in that, The calculation formulas for updating SOC and error by ampere-hour integration are as follows: SOC update formula: SOC error update formula: Among them, Cap represents the battery rated capacity, Cur represents the battery current, Qin represents the cumulative charge, Qout represents the cumulative discharge, QinAtCalib represents the cumulative charge corresponding to the last accurate calibration of SOC, QoutAtCalib represents the cumulative discharge corresponding to the last accurate calibration of SOC, RTCtime represents the current calendar time, RTCtimeAtCalib represents the calendar time corresponding to the last calibration, K represents the linear error of the current sensor, and b represents the offset error of the current sensor; When it is detected that SocErr is greater than the set threshold, then request DC / DC full charge calibration of the battery for SOC, and the set threshold is taken as 10%.

8. The charging control method for low-voltage lithium batteries in new energy vehicles according to claim 1, characterized in that, In step S4, the DC / DC control module includes four states: standby mode, driving mode, normal charging, and calibration charging. When the DC / DC malfunctions or exits the waiting state from another state, it operates in standby mode. When the charging conditions are met and the vehicle responds to allow charging, it enters the charging state, which is divided into normal charging and calibration charging. When the charging conditions are not met but the DC / DC is working normally and the charging MOSFET is closed, it enters driving mode. In driving mode, the DC / DC operates in constant voltage mode to ensure sufficient power is provided and the battery is not overcharged.

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