A power battery passive equalization method and system and a new energy vehicle

Abstract

The application relates to the field of battery equalization technology and provides a power battery passive equalization method, a system and a new energy vehicle, the method comprises the following steps: S1, determining whether the current power battery of the vehicle satisfies an equalization starting condition; S2, if the detection result is yes, determining the single battery cell to be equalized at present and the equalization time of the single battery cell under the equalization voltage; S3, equalizing the corresponding single battery cell based on the equalization voltage and the equalization time, executing step S1 until the current power battery does not satisfy the equalization starting condition. The application provides a power battery passive equalization method suitable for a "plateau period" and a "non-plateau period", the passive equalization of the power battery can be carried out when the power battery is in the equalization period, the passive equalization time of the power battery is greatly prolonged, the pressure difference consistency between the battery cells is beneficially ensured, and in addition, the passive equalization of the power battery can be carried out even if the BMS is in a dormant state, the passive equalization time of the power battery is further prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery balancing technology, and provides a passive balancing method, system, and new energy vehicle for power batteries. Background Technology

[0002] Electrification has driven battery development, leading to a range of applications including electric vehicles, ships, electric aircraft, and large-scale energy storage systems. Power battery packs contain numerous individual cells connected in series and parallel. Due to uneven electrochemical reactions within the battery (including initial capacity, internal impedance, physical volume, self-discharge rate, etc.) and various unpredictable abuse behaviors in real-world applications (such as ambient temperature and operating conditions), inconsistencies arise within the battery pack. These changes can induce significant voltage imbalances between series-connected cells, resulting in decreased usable capacity and lifespan, reduced driving range, and other negative impacts. This can lead to aging failures and premature repairs / replacements, ultimately increasing the risk of thermal runaway.

[0003] Therefore, more stringent monitoring and protection of battery packs are required. Developing passive balancing functionality in battery management systems is a widely recognized, efficient, and low-cost approach. This involves adding passive balancing circuits to the battery pack and dissipating excess charge through appropriate resistors or capacitors, thereby maintaining the individual cell voltage within a threshold range set for balanced distribution. This is a key technology for maintaining the balance within the battery system.

[0004] For lithium iron phosphate batteries, due to the physicochemical properties of the material itself, there are significant voltage changes at the end of charging and discharging, and gradual voltage changes during the plateau period. The power battery is in the plateau period for a much longer time than in the non-plateau period. The equalization of the battery pack only occurs in the non-plateau period when the voltage changes significantly at the end of charging and discharging, i.e., the high and low charge periods. This results in a short equalization discharge time, which makes it difficult to meet the requirement of consistent voltage difference between individual cells in the battery pack. Summary of the Invention

[0005] In view of this, this application provides a passive balancing method for power batteries, which aims to improve the above-mentioned problems.

[0006] Specifically, the following technical solutions are included:

[0007] On one hand, embodiments of this application provide a passive balancing method for power batteries, the method comprising the following steps:

[0008] S1. Determine whether the vehicle's power battery currently meets the conditions for equalization activation;

[0009] S2. If the detection result is yes, then determine the single cell to be balanced and its balancing time under the balancing voltage.

[0010] S3. Equalize the corresponding individual cells based on the equalization voltage and equalization time, and execute step S1 until the power battery no longer meets the equalization start conditions.

[0011] In some embodiments, if conditions (1) to (3) are met, the power battery is considered to currently meet the equalization activation condition;

[0012] Condition (1) Other operating conditions besides the vehicle being in a charging state;

[0013] Condition (2) The lowest and highest SOC of the cells in the power battery are both within the SOC range set under driving conditions, and there is a cell voltage difference greater than the voltage difference equalization threshold.

[0014] Condition (3) The overvoltage signal of a single cell is not triggered.

[0015] In some embodiments, the method for determining the differential pressure equalization threshold is as follows:

[0016] The battery cell is controlled to undergo static constant current cyclic testing, and the sampling voltage and its corresponding state of charge are collected.

[0017] Using the sampled voltage as the vertical axis and the corresponding state of charge (SOC) as the horizontal axis, an OCV-SOC table is obtained to acquire a reliable voltage range. The minimum voltage difference within the reliable voltage range is marked as the voltage difference equalization threshold ΔV.

[0018] In some embodiments, the method for determining the reliable voltage range is as follows:

[0019] Determine the maximum deviation of the sampled voltage during the plateau period, detect the difference in the continuous sampled voltage in the OCV-SOC table, and obtain the voltage range where the difference is greater than the maximum deviation. This voltage range is the reliable voltage range.

[0020] In some embodiments, the method for determining the individual battery cell to be balanced is as follows:

[0021] (1) Collect the minimum voltage V in a single battery cell m , will the minimum voltage V m The sum of the voltage difference equalization threshold ΔV and the voltage difference equalization threshold is used as the protection voltage V2;

[0022] (2) Collect the voltage value V1 of each individual cell. If the individual cell voltage V1 is greater than the protection voltage V2, mark the corresponding individual cell as the balancing object, that is, the individual cell to be balanced.

[0023] In some embodiments, the equalization voltage of the cell to be equalized is the difference between the cell voltage V1 and the protection voltage V2.

[0024] In some embodiments, the equalization time T of the current cell to be equalized under the equalization voltage is determined as follows:

[0025] (1) Find the corresponding quantities SOC1 and SOC2 of the individual cell voltage V1 and protection voltage V2 in the OCV-SOC table. The difference between the two is the quantity ΔSOC to be balanced, ΔSOC = SOC1 - SOC2.

[0026] (2) Calculate the balancing time T of the cell to be balanced based on the charge ΔSOC to be balanced.

[0027] In some embodiments, the formula for calculating the equilibrium time T is as follows:

[0028]

[0029] Where Capacity is the single-cell capacity; internal resistance R is the sum of the equalization resistors and the fixed group resistance of the MOSFET; and V is the voltage acquisition value of the single cell to be equalized.

[0030] On the other hand, embodiments of this application provide a passive balancing system for power batteries, the system comprising:

[0031] Power batteries, and balancing circuits for passive balancing of power batteries;

[0032] The power battery, the equalization circuit, and the power battery are all connected via communication with the battery management system (BMS), and the equalization circuit is electrically connected to the power battery.

[0033] The battery management system (BMS) uses the aforementioned passive balancing method for power batteries to control the balancing circuit to perform passive balancing on the individual cells to be balanced.

[0034] On the other hand, this application provides a new energy vehicle that integrates the aforementioned passive balancing system for power batteries.

[0035] This invention proposes a passive equalization method for power batteries applicable to both "plateau period" and "non-plateau period". Passive equalization of power batteries can be performed even when the power battery is in the equilibrium period, which greatly extends the passive equalization time of the power battery and helps to ensure the consistency of voltage difference between cells. In addition, passive equalization of power batteries can be performed even when the BMS is in dormant state, which further extends the passive equalization time of the power battery. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a passive balancing method for power batteries provided in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of the passive balancing system for power batteries provided in an embodiment of the present invention;

[0039] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] Unless otherwise defined, all technical terms used in the embodiments of this application have the same meaning as commonly understood by one of ordinary skill in the art.

[0042] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0043] Figure 1 The flowchart of the passive balancing method for power batteries provided in this embodiment of the invention includes the following steps:

[0044] S1. Determine whether the vehicle's power battery currently meets the conditions for equalization activation;

[0045] In this embodiment of the invention, there are two operating modes: wake-up and hibernation. The balanced activation condition is the same in both wake-up and hibernation modes, and the specific balanced activation condition is as follows:

[0046] Condition (1) Other operating conditions besides the vehicle being in a charging state;

[0047] Condition (2) The lowest and highest SOC of the cells in the power battery are both within the SOC range set under driving conditions, and there is a cell voltage difference greater than the voltage difference equalization threshold. The voltage difference is the difference between the current voltage acquisition value of the cell and the minimum voltage value.

[0048] Condition (3) The overvoltage signal of a single cell is not triggered;

[0049] In this embodiment of the invention, when the above conditions (1) to (3) are met, the equalization activation condition is met, and the equalization confirmation value is output.

[0050] In this embodiment of the invention, the method for determining the differential pressure equalization threshold is as follows:

[0051] The battery cell is controlled to undergo static constant current cyclic testing, and the sampling voltage and its corresponding state of charge are collected.

[0052] Using the sampled voltage as the vertical axis and the corresponding state of charge as the horizontal axis, an OCV-SOC table is obtained to acquire a reliable voltage range. The minimum voltage difference within the reliable voltage range is marked as the voltage difference equalization threshold ΔV.

[0053] In this embodiment of the invention, the method for determining the reliable voltage range is as follows:

[0054] Determine the maximum deviation of the sampled voltage during the plateau period, detect the difference in the continuous sampled voltage in the OCV-SOC table, and obtain the voltage range where the difference is greater than the maximum deviation. This voltage range is the reliable voltage range.

[0055] This invention uses lithium iron phosphate batteries as an example for illustration. Their material characteristics show that the voltage change trend at the end of charging / discharging is obvious, but the plateau period is long and the voltage change is not obvious. Due to the limitation of hardware sampling accuracy, there is generally an error of ±5mV. Therefore, the difference in voltage change of continuous sampling in the OCV-SOC table is judged, and the voltage segment with a difference greater than 5mV is marked and defined as the reliable voltage range.

[0056] S2. If the detection result is yes, then determine the single cell to be balanced and its balancing time under the balancing voltage. If the detection result is no, then there is no need to perform balancing operation on the power battery.

[0057] In this embodiment of the invention, the method for determining the individual battery cell to be balanced is as follows:

[0058] (1) Collect the minimum voltage V in a single battery cell m , will the minimum voltage V m The sum of the voltage difference equalization threshold ΔV and the voltage difference equalization threshold is used as the protection voltage V2;

[0059] (2) Collect the voltage value V1 of each individual cell. If the individual cell voltage V1 is greater than the protection voltage V2, mark the corresponding individual cell as the balancing object, that is, the individual cell to be balanced.

[0060] (3) The equalization voltage of the single cell to be equalized is: the difference between the single cell voltage V1 and the protection voltage V2 is the discharge voltage during equalization, i.e., the equalization voltage.

[0061] In this embodiment of the invention, the method for determining the equalization time T of the current single cell to be equalized under the aforementioned equalization voltage is as follows:

[0062] (1) Find the corresponding quantities SOC1 and SOC2 of the individual cell voltage V1 and protection voltage V2 in the OCV-SOC table. The difference between the two is the quantity ΔSOC to be balanced, ΔSOC = SOC1 - SOC2.

[0063] (2) Calculate the balancing time T of the cell to be balanced based on the SOC of the charge to be balanced. The specific formula for calculating the balancing time T is as follows:

[0064]

[0065] Among them, Capacity is the single-cell capacity, which is related to the state of health (SOH) of the power battery; internal resistance R is the fixed group resistance value of the balancing resistor plus the MOSFET; and V is the voltage acquisition value of the single cell to be balanced.

[0066] In this embodiment of the invention, when the equalization circuit is not open, the voltage acquisition value of the single cell to be equalized is directly adopted as the sampled value. When the equalization circuit is open, the voltage acquisition value of the single cell to be equalized is offset and needs to be compensated. The compensation voltage value is determined based on the type of battery. Because the sampling board circuits of different power batteries are different, the sampling errors that occur are also different. At this time, the voltage acquisition value V involved in the equalization time is the sum of the voltage acquisition value of the single cell to be equalized and the compensation voltage value.

[0067] S3. Equalize the corresponding individual cells based on the equalization voltage and equalization time, and execute step S1.

[0068] In this embodiment of the invention, the equalization time and equalization voltage of each individual cell to be equalized have been determined in step (2), and the equalization operation is performed on the cells to be equalized based on the determined equalization time and equalization voltage.

[0069] Figure 2 This is a schematic diagram of a passive balancing system for power batteries provided in an embodiment of the present invention. For ease of explanation, only the parts relevant to the embodiment of the present invention are shown. The system includes:

[0070] Power batteries, and balancing circuits for passive balancing of power batteries;

[0071] The power battery, the equalization circuit, and the power battery are all connected via communication with the battery management system (BMS), and the equalization circuit is electrically connected to the power battery.

[0072] The battery management system (BMS) uses the aforementioned passive balancing method for power batteries to control the balancing circuit to perform passive balancing on the individual cells to be balanced.

[0073] This invention also provides a new energy vehicle that integrates the aforementioned passive balancing system for power batteries. This system balances the power batteries, maintaining as much voltage and capacity consistency as possible among the individual cells within the battery pack, mitigating severe voltage fluctuations, and improving the overall driving range.

[0074] In this invention, we designed the software to calculate the equalization time once per second (under certain conditions); the single-cell capacity is related to the state of charge (SOH); the single-cell voltage uses the sampled value when the equalization circuit is not open, and the sampled value is used for compensation when the equalization circuit is open; in order to achieve a better equalization effect, equalization is performed by waking up the RTC when the vehicle is not driving or charging; the equalization opening circuit is designed to prevent errors and errors, and to judge the internal equalization fault strategy to avoid accidental opening and constant opening, which would lead to abnormal undervoltage of the cell.

[0075] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A passive balancing method for power batteries, characterized in that, The method includes the following steps: S1. Determine whether the vehicle's power battery currently meets the conditions for equalization activation; S2. If the detection result is yes, then determine the single cell to be balanced and its balancing time under the balancing voltage. S3. Equalize the corresponding individual cells based on the equalization voltage and equalization time, and execute step S1 until the power battery does not currently meet the equalization start condition. If conditions (1) to (3) are met, then the power battery is considered to currently meet the equalization activation conditions; Condition (1) Other operating conditions besides the vehicle being in a charging state; Condition (2) The lowest and highest SOC of the cells in the power battery are both within the SOC range set under driving conditions, and there is a cell voltage difference greater than the voltage difference equalization threshold. Condition (3) The overvoltage signal of a single cell is not triggered; The method for determining the differential pressure equalization threshold is as follows: The battery cell is controlled to undergo static constant current cyclic testing, and the sampling voltage and its corresponding state of charge are collected. Using the sampled voltage as the vertical axis and the corresponding state of charge as the horizontal axis, an OCV-SOC table is obtained to acquire a reliable voltage range. The minimum voltage difference within the reliable voltage range is marked as the voltage difference equalization threshold ΔV. The specific method for determining the individual battery cells to be balanced is as follows: (1) Collect the minimum voltage V in a single battery cell m , will the minimum voltage V m The sum of the voltage difference equalization threshold ΔV and the voltage difference equalization threshold is used as the protection voltage V2; (2) Collect the voltage value V1 of each individual cell. If the individual cell voltage V1 is greater than the protection voltage V2, then mark the corresponding individual cell as the balancing object, that is, the individual cell to be balanced.

2. The passive balancing method for power batteries as described in claim 1, characterized in that, The specific method for determining the reliable voltage range is as follows: Determine the maximum deviation of the sampled voltage during the plateau period, detect the difference in the continuous sampled voltage in the OCV-SOC table, and obtain the voltage range where the difference is greater than the maximum deviation. This voltage range is the reliable voltage range.

3. The passive balancing method for power batteries as described in claim 1, characterized in that, The equalization voltage of the cell to be equalized is the difference between the cell voltage V1 and the protection voltage V2.

4. The passive balancing method for power batteries as described in claim 3, characterized in that, The method for determining the equalization time T of the single cell to be equalized under the equalization voltage is as follows: (1) Find the corresponding quantities SOC1 and SOC2 of the individual cell voltage V1 and protection voltage V2 in the OCV-SOC table. The difference between the two is the quantity ΔSOC to be balanced, ΔSOC = SOC1 - SOC2. (2) Calculate the balancing time T of the cell to be balanced based on the balancing charge ΔSOC.

5. The passive balancing method for power batteries as described in claim 4, characterized in that, The formula for calculating the equilibrium time T is as follows: ； Where Capacity is the single-cell capacity, R is the equalization resistor plus the fixed group resistance of the MOSFET, and V is the voltage acquisition value of the single cell to be equalized.

6. A passive balancing system for power batteries, characterized in that, The system includes: Power batteries, and balancing circuits for passive balancing of power batteries; The power battery, the equalization circuit, and the power battery are all connected via communication with the battery management system (BMS), and the equalization circuit is electrically connected to the power battery. The battery management system (BMS) controls the balancing circuit to passively balance the individual cells to be balanced based on the passive balancing method of any one of claims 1 to 5.

7. A new energy vehicle, characterized in that, The new energy vehicle integrates the power battery passive balancing system as described in claim 6.

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