Sodium-lithium combined battery soc calibration and equalization method using rtc clock management

Abstract

This invention discloses a method for SOC calibration and equalization of sodium-lithium battery packs using RTC clock management. The invention incorporates an onboard independent RTC real-time clock module and is applied to a hybrid battery BMS system combining lithium-ion and sodium-ion cells. The method includes the following steps: S1: Offline parameter calibration within a temperature range of -20℃ to 55℃; S2: Uninterrupted timing control of the RTC clock; S3: Combining real-time loop current with the precise resting time recorded by the RTC; S4: SOC self-discharge compensation based on the RTC power-off time; S5: RTC-timed wake-up dynamic equalization; S6: Timing closed-loop linkage correction. This invention adapts to the differentiated resting calibration requirements of sodium-lithium cells, compensates for SOC self-discharge losses during long-term power-off resting, achieves automatic equalization with low power consumption during resting, and synchronizes and unifies calibration and equalization timing, comprehensively improving the accuracy of battery SOC estimation and the consistency of individual cells.

Description

Technical Field

[0001] This invention relates to the field of battery management, and more specifically, to a method for precise SOC calibration and sleep equalization of sodium-lithium battery packs based on RTC clock timing control. Background Technology

[0002] Lithium-ion batteries boast high energy density and excellent cycle stability, while sodium-ion batteries offer superior low-temperature performance, low raw material costs, and fast-charging capabilities. However, the OCV-SOC curve of lithium iron phosphate batteries exhibits a plateau in the 5%–95% range, meaning the mapping between OCV and SOC is not significant (dV / dQ is extremely small). Sodium batteries are often used to assist in calibrating the SOC of lithium iron phosphate batteries, thereby improving SOC accuracy. However, due to differences in polarization dissipation time, self-discharge rate, and high / low temperature performance between sodium and lithium cells, it is generally impossible to simultaneously achieve optimal performance for both types. Furthermore, common SOC calibration and battery balancing operate as two independent modules. Calibration results cannot guide balancing strategies, and voltage changes resulting from balancing do not provide feedback to correct SOC estimates, creating a control blind spot. Summary of the Invention

[0003] This invention overcomes the shortcomings of existing technologies, solves various calibration and measurement problems caused by the differences in sodium-lithium dual-cell batteries, and improves the measurement accuracy of SOC and the consistency of individual cells by providing a method for accurate SOC calibration and sleep equalization of sodium-lithium battery packs based on RTC clock timing control.

[0004] This invention discloses a method for precise SOC calibration and sleep equalization of sodium-lithium battery packs based on RTC clock timing control. The method is implemented through the following technical solution: it incorporates an onboard independent RTC real-time clock module and is applied to a hybrid battery BMS system that combines lithium-ion and sodium-ion cells. The method includes the following steps: S1: Offline parameter calibration in the temperature range of -20℃ to 55℃, and construct three-dimensional lookup table models of temperature-OCV-SOC for the two types of cells after static depolarization elimination. At the same time, set the voltage equalization threshold, polarization dissipation time, and dormancy pre-equalization interval time for the two types of cells. S2: RTC clock uninterrupted timing control, divided into power-on working timing mode and power-off sleep independent timing mode, which records the total resting time of sodium and lithium battery systems, the average temperature of each stage, the calibration time stamp, and the equalization action time stamp throughout the process. S3: Combining real-time loop current with precise resting time recorded by RTC, matching the specific resting time thresholds for sodium and lithium battery cells and the time thresholds under low current conditions, determining whether cell polarization has completely dissipated, and completing static and dynamic OCV-SOC calibration.

[0005] S4: SOC self-discharge compensation based on RTC power-off duration: During the battery power-off hibernation period, the main control MCU is powered off and hibernates, and only the RTC module runs at low power; at the moment of power-on, the total hibernation duration and segmented temperature data recorded by the RTC are read, and the sodium lithium battery cell self-discharge model is called to compensate for the natural SOC loss during the entire power-off process; S5: RTC timed wake-up and sleep dynamic equalization: a fixed RTC wake-up cycle is preset. When the battery is off, the RTC triggers the BMS to partially wake up and perform low-power passive pre-equalization. After the equalization is completed, it enters sleep mode again. S6: Timing Closed-Loop Linkage Correction: Through the unified timestamp of RTC, the timing of SOC calibration data and equalization data is fully synchronized. During the equalization process, the cell voltage change is fed back to the SOC calibration module in real time, dynamically correcting the OCV lookup table offset, and achieving full life cycle timing collaborative management through iterative loops.

[0006] The differential resting time threshold in step S1 is configured as follows: 50 min for polarization dissipation resting time for lithium-ion batteries and 40 min for polarization dissipation resting time for sodium-ion batteries; the RTC sleep pre-equalization fixed wake-up cycle is set to be adjustable from 2 h to 4 h.

[0007] The specific logic of the dual-mode timing in step S2 is as follows: Power-on operating mode: The RTC synchronously records the battery running time, the duration of static interruption, and the precise time of each SOC calibration, eliminating the cumulative timing error of traditional software timers; Power-down sleep mode: The BMS main control MCU and acquisition circuit are all powered off, and only the RTC button battery is independently powered to continuously keep track of the total sleep time of the battery. At the same time, the ambient temperature of the battery cell is recorded every 1 hour to form a sleep time-temperature timing data table.

[0008] Step S3 specifically includes: S31: Static and low current (loop current ≤ 0.05C) calibration judgment: When the battery loop current is ≤ 0.05C and the continuous static time recorded by RTC reaches the corresponding cell threshold, the static time for lithium batteries is ≥ 50min and for sodium batteries it is ≥ 40min, it is determined that the internal polarization of the cell has been completely dissipated, and the OCV open circuit voltage SOC calibration is immediately performed to prevent premature calibration and invalid calibration caused by inaccurate software timing; S32: High current (loop current > 0.05C) operating condition: Calibration and equalization are prohibited during high current charging and discharging. The RTC only records the running sequence data for subsequent error tracing and model iteration.

[0009] The specific method for self-discharge compensation in step S4 is as follows: Based on the segmented dormancy duration and corresponding average temperature recorded by RTC, the temperature-time-self-discharge rate fitting formulas for lithium-ion batteries and sodium-ion batteries are retrieved respectively. The SOC loss value of each static interval is calculated segment by segment, and the total self-discharge SOC offset is obtained by summing them. After power-on, the initial SOC value is corrected, which solves the problem of seriously inaccurate SOC after the battery has been static for a long time.

[0010] The specific process of RTC timed sleep balancing in step S5 is as follows: S51: After the battery enters power-off sleep mode, the main control MCU and voltage and current acquisition chip are all powered off, and only the RTC module continues to run the timer. S52: After the preset RTC wake-up time is reached, the RTC outputs an interrupt signal to partially wake up the equalization drive circuit without waking up the main control MCU, thus achieving ultra-low power operation. S53: Retrieve the single-cell SOC deviation data stored from the last power-on and perform low-current passive pre-equalization on single cells with deviations exceeding the threshold; S54: Once the equalization duration reaches the preset timing threshold, the equalization circuit is immediately shut down, and the system re-enters deep sleep; no manual intervention is required throughout the process, and consistency repair is automatically completed during the sleep phase.

[0011] This invention also provides a sodium-lithium hybrid battery BMS management system, including a voltage acquisition module, a current acquisition module, a temperature acquisition module, an RTC real-time clock module, an equalization drive module, a main control MCU, and an independent button cell battery power supply unit; the RTC real-time clock module is independently powered by a button cell battery and is not affected by system power-on or power-off; the main control MCU performs the above-mentioned SOC calibration and sleep equalization methods.

[0012] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the above-described SOC calibration and sleep equalization method is implemented.

[0013] Compared with the prior art, the beneficial effects of the present invention are: To address the technical shortcomings of existing sodium-lithium hybrid batteries, such as inaccurate SOC calibration timing, inability to compensate for power-off self-discharge, lack of balancing capability during sleep, misaligned calibration and balancing timing, and software timer failure upon power-off, this invention utilizes an independently powered RTC clock to achieve uninterrupted and accurate timing throughout the entire time period. It adapts to the differentiated static calibration requirements of sodium-lithium battery cells, compensates for SOC self-discharge losses during prolonged static storage after power-off, achieves low-power automatic balancing during sleep, and synchronizes and unifies calibration and balancing timing, thereby comprehensively improving the accuracy of battery SOC estimation and the consistency of individual cells. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the module assembly of the present invention; Figure 2 The charging curves of the lithium battery and sodium battery of this invention are shown. Figure 3 The discharge curves of the lithium battery and sodium battery of this invention are shown. Figure 4 This is a schematic diagram of the overall hardware architecture of the present invention. Detailed Implementation

[0015] To better understand the above-mentioned objects, features, and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention.

[0016] Example 1: Standard operating condition at room temperature (25℃) (I) Offline Dual-Cell Global Parameter Calibration like Figure 1 As shown, this solution uses 8 cells as one module, with a total of 12 modules. The first 11 modules are lithium iron phosphate battery modules, and the 12th module is a sodium-ion battery module. The rated capacity of each individual battery is 100Ah, and the RTC wake-up cycle is 2h.

[0017] like Figure 2 and Figure 3 As shown, independent temperature-OCV-SOC three-dimensional lookup table charge-discharge models for both sodium and lithium batteries were established offline under normal temperature conditions, with parameters that are not interchangeable. Differential polarization dissipation settling thresholds were calibrated: 50 min for lithium battery polarization dissipation settling time; 40 min for sodium battery polarization dissipation settling time. The daily self-discharge rate of sodium battery at normal temperature was 0.034%, and the self-discharge rate of lithium iron phosphate battery was 0.04%.

[0018] (ii) RTC Dual-Mode Uninterrupted Independent Timing Control 1. Power-on working timing mode: The BMS main controller works normally, and the RTC synchronously records the resting time and running time of the battery for each period of time, adding a high-precision timestamp for each voltage sampling, SOC calibration and equalization action to eliminate multi-channel sampling timing offset; 2. Power-off sleep independent timing mode: After the battery pack is powered off, the BMS main control MCU and voltage and current acquisition chip are all powered off and enter deep sleep. Only the RTC relies on the button battery to run at low power, continuously accumulating the total sleep time, and automatically recording the ambient temperature every 1 hour to generate a time-temperature correlation data table.

[0019] (III) Dual-cell differentiated SOC calibration based on RTC's precise duration 1. Static calibration: The battery system is powered off for 72 hours, with only the RTC module continuously timing and recording the ambient temperature every hour; after power-on, the total sleep time and segmented temperature of the RTC are read, and the self-discharge SOC loss of the lithium battery and sodium battery are calculated respectively. At this time, since the battery rest time is long enough to meet the polarization dissipation time of the lithium battery and sodium battery, the dual-cell OCV-SOC calibration is started, completely eliminating the problem of voltage overshoot and SOC calibration deviation caused by premature calibration.

[0020] 2. Low-current dynamic calibration: Low-current float charging with current ≤0.05C utilizes RTC to unify timing reference, aligns the three asynchronous sampling signals of voltage, current, and temperature, and eliminates sampling delay errors to complete dynamic SOC correction; 3. High current operation: During high current charging and discharging, calibration and equalization are turned off, and the RTC only retains timing and temperature logs for subsequent algorithm error review and model parameter iteration.

[0021] (iv) SOC self-discharge compensation driven by RTC power-down duration Prolonged battery shutdown and inactivity are the main causes of State of Charge (SOC) drift. Traditional solutions cannot keep track of SOC after power-off and cannot compensate for errors upon power-on. This invention achieves accurate SOC compensation throughout the entire sleep cycle using an RTC (Real-Time Clock). The moment the system powers on, the main control MCU immediately reads the total sleep time plus hourly segmented temperature data stored in the RTC; Based on the segmented resting time and corresponding temperature, the self-discharge models of sodium and lithium battery cells were called respectively to calculate the natural SOC loss segment by segment. The accumulated self-discharge loss value is superimposed on the initial SOC upon power-on, completing one-click compensation and completely solving the industry problem of severely inaccurate SOC after the battery has been stored for several days or weeks.

[0022] (v) Low-power pre-equalization of sleep mode wake-up via RTC timer interrupt After the system is powered down and enters hibernation, all hardware except the RTC and equalization drive circuit is powered off, and the static power consumption of the whole machine is reduced to the microampere level. Every 2 hours, the RTC actively sends a hardware interrupt signal to partially wake up the equalization drive circuit without waking up the main control MCU, and starts low-power equalization; it retrieves the individual voltage deviation data stored from the last power-on, and performs low-current passive pre-equalization only on the individual cells whose voltage deviation exceeds the standard; when the individual cell voltage returns to the normal range, it immediately shuts down the equalization loop and the system returns to deep sleep. (vi) Calibration-Equalization Closed-Loop Linkage Based on RTC Unified Timestamp All SOC calibration and equalization actions are bound to a unique RTC timestamp to achieve complete data timing synchronization. During the equalization process, the cell voltage changes, and the voltage data with time-marked labels is transmitted back to the SOC calibration module in real time to dynamically fine-tune the OCV lookup curve. The time-series SOC deviation data output by the SOC calibration accurately guides the start time and duration of the next sleep equalization.

[0023] (vii) as follows Figure 4 As shown, a sodium-lithium hybrid battery BMS management system mainly includes a voltage acquisition module, a current acquisition module, a temperature acquisition module, an RTC real-time clock module, an equalization drive module, a main control MCU, and an independent button cell battery power supply unit; the RTC real-time clock module is independently powered by a button cell battery and is not affected by system power-on or power-off.

[0024] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for SOC calibration and equalization of sodium-lithium battery packs using RTC clock management, characterized in that, Equipped with an onboard independent RTC real-time clock module, this system is used in a hybrid battery BMS system that combines lithium-ion and sodium-ion cells, and includes the following steps: S1: Offline parameter calibration in the temperature range of -20℃ to 55℃, construct three-dimensional lookup table models of temperature-OCV-SOC for lithium-ion cells and sodium-ion cells after static depolarization elimination, and set voltage equalization threshold, polarization dissipation time and dormancy pre-equalization interval for the two types of cells. S2: RTC clock uninterrupted timing control, divided into power-on working timing mode and power-off sleep independent timing mode, which records the total resting time of sodium and lithium battery systems, the average temperature of each stage, the calibration time stamp, and the equalization action time stamp throughout the process. S3: Combining real-time loop current with the precise resting time recorded by RTC, matching the specific resting time thresholds for sodium and lithium battery cells and the time thresholds for loop current ≤0.05C, determining whether the cell polarization has been completely dissipated, and completing static and dynamic OCV-SOC calibration; S4: SOC self-discharge compensation based on RTC power-off duration: During the battery power-off hibernation period, the main control MCU is powered off and hibernates, and only the RTC module runs at low power; at the moment of power-on, the total hibernation duration and segmented temperature data recorded by the RTC are read, and the sodium lithium battery cell self-discharge model is called to compensate for the natural SOC loss during the entire power-off process; S5: RTC timed wake-up and sleep dynamic equalization: a fixed RTC wake-up cycle is preset. When the battery is off, the RTC triggers the BMS to wake up locally and perform low-power passive pre-equalization. After the equalization is completed, it enters sleep mode again. S6: Timing Closed-Loop Linkage Correction: Through the unified timestamp of RTC, the timing of SOC calibration data and equalization data is fully synchronized. During the equalization process, the cell voltage change is fed back to the SOC calibration module in real time, dynamically correcting the OCV lookup table offset, and achieving full life cycle timing collaborative management through iterative loops.

2. The method for SOC calibration and equalization of a sodium-lithium battery pack using RTC clock management according to claim 1, characterized in that, In step S1, the threshold for differentiated resting time is configured as follows: 50 min for polarization dissipation resting time for lithium-ion batteries and 40 min for polarization dissipation resting time for sodium-ion batteries; the fixed wake-up cycle of the RTC sleep pre-equalization is set to be adjustable from 2 h to 4 h.

3. The method for SOC calibration and equalization of a sodium-lithium battery pack using RTC clock management according to claim 1, characterized in that, The specific logic for dual-mode timing in step S2: Power-on operating mode: RTC synchronously records battery runtime, idle interval duration, and the precise moment of each SOC calibration; Power-down sleep mode: The BMS main control MCU and acquisition circuit are all powered off, and only the RTC button battery is independently powered to continuously keep track of the total sleep time of the battery. At the same time, the ambient temperature of the battery cell is recorded every 1 hour to form a sleep time-temperature timing data table.

4. The method for SOC calibration and equalization of a sodium-lithium battery pack using RTC clock management according to claim 1, characterized in that, Step S3 specifically includes: S31: Static and loop current ≤0.05C calibration judgment: When the battery loop current is ≤0.05C and the RTC record of continuous static time reaches the corresponding cell threshold, lithium battery static time ≥50min, sodium battery static time ≥40min, it is determined that the internal polarization of the cell is completely dissipated, and OCV open circuit voltage SOC calibration is immediately performed; S32: Circuit current > 0.05C: Calibration and equalization are prohibited during high-current charging and discharging. The RTC only records runtime sequence data for subsequent error tracing and model iteration.

5. A method for SOC calibration and equalization of a sodium-lithium battery pack using RTC clock management according to claim 1, characterized in that, The specific method for self-discharge compensation in step S4 is as follows: Based on the segmented sleep duration and corresponding average temperature recorded by RTC, the temperature-time-self-discharge rate fitting formulas for lithium-ion batteries and sodium-ion batteries are retrieved respectively. The SOC loss value of each rest interval is calculated segment by segment, and the total self-discharge SOC offset is obtained by summing them up. The initial SOC value is then corrected after power-on.

6. A method for SOC calibration and equalization of a sodium-lithium battery pack using RTC clock management according to claim 1, characterized in that, The specific process for RTC timed sleep balancing in step S5 is as follows: S51: After the battery enters power-off sleep mode, the main control MCU and voltage and current acquisition chip are all powered off, and only the RTC module continues to run the timer. S52: After the preset RTC wake-up time is reached, the RTC outputs an interrupt signal to partially wake up the equalization drive circuit without waking up the main control MCU, thus achieving ultra-low power operation. S53: Retrieve the single-cell SOC deviation data stored from the last power-on and perform low-current passive pre-equalization on single cells with deviations exceeding the threshold; S54: After the equalization duration reaches the preset timing threshold, the equalization circuit is immediately turned off, and the system enters deep sleep again. No manual intervention is required throughout the process; consistency repair is automatically completed during the dormant phase.

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