Optimization method for cut-off voltage of battery system

Abstract

The invention relates to a method for optimizing cut-off voltage of a battery system, which comprises the following steps of: S1, measuring alternating-current impedance by adopting alternating-current impedance frequency A or B in a charging and discharging process, and acquiring voltage, temperature, current and alternating-current impedance of each single battery in the battery system in real time; s2, judging the current voltage and charging and discharging states of the battery; when the charging voltage value of the battery reaches Vchg, recording a charging benchmark reference value under the condition that the first alternating current impedance frequency is A or B; when the battery discharge voltage value reaches Vdis, recording a discharge benchmark reference value when the first AC impedance frequency is A or B; s3, judging whether a charging benchmark reference value or a discharging benchmark reference value exists or not, and if yes, calculating an impedance outlier factor w; if not, exiting; and S4, optimizing the cut-off voltage of the battery according to the impedance outlier factor w, and updating the cut-off voltage of the battery. Optimization of the cut-off voltage of the battery is achieved through the impedance outlier factor w, the method is convenient and easy to implement, and the use efficiency of the battery is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a method for optimizing the cut-off voltage of a battery system. Background Art

[0002] In the field of electrochemistry, the battery cut-off voltage plays a vital role. It is not only the termination signal of battery charging and discharging, but also an important guarantee for the economy and safety of the battery system. The battery cut-off voltage is divided into charging cut-off voltage and discharging cut-off voltage, both of which need to be precisely controlled to ensure the stable operation of the battery.

[0003] When the battery is charging, the voltage will gradually increase as the amount of charge increases. However, excessive voltage will trigger a series of changes in electrochemical reactions, affecting the life of the battery's internal structure and materials. Therefore, in order to maintain the long-term stability of battery performance and prevent possible damage, a suitable charging cut-off voltage must be set. The determination of this voltage depends not only on the type and capacity of the battery, but also on the ambient temperature and the actual needs of the user. During the battery discharge process, as the power is consumed, the voltage will gradually decrease. If the voltage is too low, it may cause the battery to over-discharge, thereby affecting its internal chemical balance and structural stability, leading to irreversible damage. Therefore, it is particularly important to determine a reasonable discharge cut-off voltage. This process also needs to take into account the influence of electrical performance indicators and various factors, such as working conditions under different loads, temperature changes, etc.

[0004] However, the complexity of the chemical changes inside the battery makes it very difficult to build an accurate model to estimate the optimal cut-off voltage. It requires us to collect a lot of data on battery usage status, environmental conditions, etc., and then calculate and analyze through algorithms and models to finally derive the optimal cut-off voltage value.

[0005] Chinese patent CN117713312A discloses a charging cut-off voltage control method, device, equipment and medium, the method comprising: obtaining the number of charging times of a battery to be charged this time; according to the number of charging times of this time, querying the charging cut-off voltage corresponding to each charging number interval, and determining the charging cut-off voltage corresponding to the current charging number interval where the number of charging times of this time is located; using the charging cut-off voltage corresponding to the current charging number interval as the charging cut-off voltage of this charging, and charging the battery to be charged. Based on the method provided by it, it can ensure that the battery is always charged and discharged within a healthy voltage range, but it can only control the cut-off voltage during charging, and cannot optimize the cut-off voltage during discharging, and cannot realize real-time optimization of the cut-off voltage during battery charging and discharging. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for optimizing the cut-off voltage of a battery system, which combines voltage, temperature and current to analyze the AC impedance of the battery at a specific frequency, and can optimize the current cut-off voltage of the battery in real time during the charging and discharging state.

[0007] The present invention provides a method for optimizing the cut-off voltage of a battery system, comprising the following steps: S1: During the charging and discharging process, the AC impedance is measured using the AC impedance frequency A or B, and the voltage, temperature, current, and AC impedance of each single cell in the battery system are obtained in real time; S2: Determine the current battery voltage and charge and discharge status; During the charging process, when the battery voltage reaches the charging limit voltage V chg When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the charging impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during charging are used as charging reference values; During the discharge process, when the battery voltage reaches the discharge limit voltage V dis When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the discharge impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during discharge are used as the discharge benchmark reference value; S3: Determine whether there is a charging reference value or a discharging reference value. If so, perform AC impedance analysis and calculate the impedance outlier factor w. If not, exit. S4: Optimize the battery cutoff voltage according to the impedance outlier factor w, and update the battery cutoff voltage.

[0008] Preferably, the step S3 further comprises compensating the battery system according to the temperature difference compensation coefficient and the current compensation coefficient, wherein the temperature difference compensation coefficient k T As shown in formula (1), (1) Among them, C is the temperature difference compensation coefficient when the temperature is less than 25℃, which is 0.02 mΩ / ℃, D is the temperature difference compensation coefficient when the temperature is greater than or equal to 25℃, which is 0.003 mΩ / ℃, and the current compensation coefficient k I 0.0005 mΩ / A.

[0009] Preferably, when there is a charging benchmark reference value in step S3, the impedance outlier factor w is calculated as shown in formula (2): (2) Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k Iis the current compensation coefficient, Z chgA0 is the real part of the charging impedance at the first recorded AC impedance frequency A, Z chgB0 is the real part of the charging impedance at the first recorded AC impedance frequency B, T chg0 The initial voltage reaches the charging limit voltage V chg The battery temperature, I chg0 The initial voltage reaches the charging limit voltage V chg of current.

[0010] Preferably, when there is a discharge benchmark reference value in step S3, the impedance outlier factor w is calculated as shown in formula (3): (3) Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k I is the current compensation coefficient, Z disA0 is the real part of the discharge impedance at the first recorded AC impedance frequency A, Z disB0 is the real part of the discharge impedance at the first recorded AC impedance frequency B, T dis0 The initial voltage reaches the discharge limit voltage V dis The battery temperature, I dis0 The initial voltage reaches the discharge limit voltage V dis of current.

[0011] Preferably, in step S4, during charging, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (4): (4) Among them, V chgend0 is the initial charge cut-off voltage, V chgend is the current charging cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

[0012] Preferably, in step S4, during discharge, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (5): (5) Among them, V disend0 is the initial discharge cut-off voltage, V disend is the current discharge cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

[0013] The present invention has the following technical effects: By combining voltage, temperature and current to analyze the data of the AC impedance of the battery at a specific frequency, the battery cut-off voltage is optimized according to the impedance outlier factor w, thereby achieving real-time optimization of the battery cut-off voltage. The method is convenient and easy to use, and can effectively improve the battery utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The figure is a flow chart of a method for optimizing the cut-off voltage of a battery system according to the present invention. DETAILED DESCRIPTION

[0015] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings.

[0016] like Figure 1 As shown, a method for optimizing the cut-off voltage of a battery system comprises the following steps: S1: During the charging and discharging process, the AC impedance is measured using the AC impedance frequency A or B, and the voltage, temperature, current, and AC impedance of each single cell in the battery system are obtained in real time; S2: Determine the current battery voltage and charge and discharge status; During the charging process, when the battery voltage reaches the charging limit voltage V chg When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the charging impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during charging are used as charging reference values; During the discharge process, when the battery voltage reaches the discharge limit voltage V dis When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the discharge impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during discharge are used as the discharge benchmark reference value; S3: Determine whether there is a charging reference value or a discharging reference value. If so, perform AC impedance analysis and calculate the impedance outlier factor w. If not, exit. S4: Optimize the battery cutoff voltage according to the impedance outlier factor w, and update the battery cutoff voltage.

[0017] The step S3 also includes compensating the battery system according to the temperature difference compensation coefficient and the current compensation coefficient, wherein the temperature difference compensation coefficient k T As shown in formula (1), (1) Among them, C is the temperature difference compensation coefficient when the temperature is less than 25℃, which is 0.02 mΩ / ℃, D is the temperature difference compensation coefficient when the temperature is greater than or equal to 25℃, which is 0.003 mΩ / ℃, and the current compensation coefficient k I0.0005 mΩ / A.

[0018] When the charging reference value exists in step S3, the impedance outlier factor w is calculated as shown in formula (2): (2) Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k I is the current compensation coefficient, Z chgA0 is the real part of the charging impedance at the first recorded AC impedance frequency A, Z chgB0 is the real part of the charging impedance at the first recorded AC impedance frequency B, T chg0 The initial voltage reaches the charging limit voltage V chg The battery temperature, I chg0 The initial voltage reaches the charging limit voltage V chg of current.

[0019] When the discharge reference value exists in step S3, the impedance outlier factor w is calculated as shown in formula (3): (3) Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k I is the current compensation coefficient, Z disA0 is the real part of the discharge impedance at the first recorded AC impedance frequency A, Z disB0 is the real part of the discharge impedance at the first recorded AC impedance frequency B, T dis0 The initial voltage reaches the discharge limit voltage V dis The battery temperature, I dis0 The initial voltage reaches the discharge limit voltage V dis of current.

[0020] In step S4, during charging, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (4): (4) Among them, V chgend0 is the initial charge cut-off voltage, V chgend is the current charging cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

[0021] In step S4, during discharge, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (5): (5) Among them, V disend0 is the initial discharge cut-off voltage, Vdisend is the current discharge cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

[0022] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for optimizing the cut-off voltage of a battery system, characterized in that: The steps include: S1: During the charging and discharging process, the AC impedance is measured using the AC impedance frequency A or B, and the voltage, temperature, current, and AC impedance of each single cell in the battery system are obtained in real time; S2: Determine the current battery voltage and charge and discharge status; During the charging process, when the battery voltage reaches the charging limit voltage V chg When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the charging impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during charging are used as charging reference values; During the discharge process, when the battery voltage reaches the discharge limit voltage V dis When the current real-time AC impedance and its corresponding temperature and current are recorded, the real part of the discharge impedance and its corresponding temperature and current data at the AC impedance frequency A or B recorded for the first time during discharge are used as the discharge benchmark reference value; S3: Determine whether there is a charging reference value or a discharging reference value. If so, perform AC impedance analysis and calculate the impedance outlier factor w. If it does not exist, exit; S4: Optimize the battery cutoff voltage according to the impedance outlier factor w, and update the battery cutoff voltage.

2. The method for optimizing the cut-off voltage of a battery system according to claim 1, characterized in that: The step S3 also includes compensating the battery system according to the temperature difference compensation coefficient and the current compensation coefficient, wherein the temperature difference compensation coefficient k T As shown in formula (1), (1)， Among them, C is the temperature difference compensation coefficient when the temperature is less than 25℃, which is 0.02 mΩ / ℃, D is the temperature difference compensation coefficient when the temperature is greater than or equal to 25℃, which is 0.003 mΩ / ℃, and the current compensation coefficient k I 0.0005 mΩ / A.

3. The method for optimizing the cut-off voltage of a battery system according to claim 2, characterized in that: When the charging reference value exists in step S3, the impedance outlier factor w is calculated as shown in formula (2): (2)， Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k I is the current compensation coefficient, Z chgA0 is the real part of the charging impedance at the first recorded AC impedance frequency A, Z chgB0 is the real part of the charging impedance at the first recorded AC impedance frequency B, T chg0 The initial voltage reaches the charging limit voltage V chg The battery temperature, I chg0 The initial voltage reaches the charging limit voltage V chg of current.

4. The method for optimizing the cut-off voltage of a battery system according to claim 2, characterized in that: When the discharge reference value exists in step S3, the impedance outlier factor w is calculated as shown in formula (3): (3)， Where w is the impedance outlier factor, k T is the temperature difference compensation coefficient, k I is the current compensation coefficient, Z disA0 is the real part of the discharge impedance at the first recorded AC impedance frequency A, Z disB0 is the real part of the discharge impedance at the first recorded AC impedance frequency B, T dis0 The initial voltage reaches the discharge limit voltage V dis The battery temperature, I dis0 The initial voltage reaches the discharge limit voltage V dis of current.

5. The method for optimizing the cut-off voltage of a battery system according to claim 2, characterized in that: In step S4, during charging, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (4): (4)， Among them, V chgend0 is the initial charge cut-off voltage, V chgend is the current charging cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

6. The method for optimizing the cut-off voltage of a battery system according to claim 3, characterized in that: In step S4, during discharge, the battery cut-off voltage calculation formula is optimized according to the impedance outlier factor w as shown in formula (5): (5)， Among them, V disend0 is the initial discharge cut-off voltage, V disend is the current discharge cut-off voltage, △V is the voltage compensation amplitude of 100 mV.

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