Battery SOH evaluation method

Abstract

The invention discloses a battery SOH evaluation method. The method comprises the following steps: determining a battery capacity coefficient based on a battery charging temperature; estimating the basic SOH in the battery charging process according to the battery capacity coefficient; determining a battery consistency parameter based on the battery monomer SOC consistency parameter and the battery monomer voltage consistency parameter; and determining the final SOH of the battery according to the basic SOH and the battery consistency parameter in the battery charging process. According to the method, the influence of the battery temperature on the capacity is considered, the SOH estimation precision of the battery is improved, meanwhile, the battery consistency parameters are introduced, the health state of a power battery system can be better reflected, the evaluation precision of the health state of the battery is improved, and estimation errors are reduced.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and particularly relates to a battery SOH evaluation method. Background Art

[0002] With increasing environmental pollution and the deepening fossil energy crisis, energy-saving, environmentally friendly new energy electric vehicles have been developed and popularized. The demand and requirements for power batteries, the power source of electric vehicles, are growing and becoming increasingly demanding. Lithium-ion batteries have become the mainstream automotive power battery due to their advantages such as high energy density, high power, high voltage platform, low self-discharge rate, and lack of memory effect. Power battery cells are made of chemical materials. Over time, power batteries will naturally age, their performance will deteriorate, and their health will decline. Batteries with poor health levels experience accelerated aging and poor safety, posing safety risks to vehicles and users. Therefore, methods for assessing the health of power batteries are necessary and important. Accurately assessing the health of retired batteries is also necessary to facilitate their reuse.

[0003] At present, the health status of power batteries in the industry is evaluated by estimating SOH. The battery SOH (health status) is estimated based on the capacity change during the battery charging and discharging process. The calculation principle formula is SOH=C R / C B ×100%, where C R is the available capacity, C B The rated capacity is the capacity of the battery. By monitoring the capacity change during the charging or discharging process and combining it with the principle formula, the power battery SOH can be obtained. The battery health status is directly expressed based on the battery SOH, that is, 90% SOH means 90% health status.

[0004] The existing battery health status assessment has the following two shortcomings: 1 Existing solutions do not consider the impact between battery temperature and capacity.

[0005] 2 The existing solution estimates the average SOH of the entire power battery system, which is composed of dozens or hundreds of cells connected in series. It does not consider the impact of cell consistency on battery health status.

[0006] These two shortcomings will lead to large errors in battery SOH estimation, making it impossible to accurately assess the health status of the power battery system. Summary of the Invention

[0007] The purpose of the present invention is to address the deficiencies in the above-mentioned background technology and to provide a simple and highly accurate battery SOH evaluation method.

[0008] The technical solution adopted by the present invention is: a battery SOH evaluation method, determining a battery capacity factor based on the temperature of the battery while charging; Estimate the basic SOH of the battery during charging based on the battery capacity coefficient; Determining a battery consistency parameter based on a battery cell SOC consistency parameter and a battery cell voltage consistency parameter; The final SOH of the battery is determined based on the basic SOH and battery consistency parameters during the battery charging process.

[0009] Furthermore, the process of determining the battery capacity coefficient is as follows: The T-σ relationship curve of the battery is established through experiments in a laboratory environment; T is the battery temperature; σ is the capacity coefficient at temperature T, which is the charge capacity C T With rated capacity C B The ratio of Substitute the lowest temperature of the battery cell at the start of charging into the T-σ relationship curve to obtain the battery capacity coefficient.

[0010] Furthermore, the basic SOH during the battery charging process is determined by the following formula: SOH0=C R / (σ m × C B ) Among them, SOH0 is the basic SOH during battery charging; C R is the available capacity of the battery; σ m is the battery capacity coefficient; C B is the rated capacity of the battery.

[0011] Furthermore, the available capacity of the battery is determined by the following formula: C R =ΔC / ΔSOC Among them, C R is the available capacity of the battery; ΔC is the capacity change during charging; ΔSOC is the SOC difference between the end and start times of charging.

[0012] Furthermore, the battery consistency parameter is determined by the following formula: ξ=ξ soc ×ξ vol Among them, ξ is the battery consistency parameter; soc is the battery cell SOC consistency parameter; ξ vol It is the battery cell voltage consistency parameter.

[0013] Furthermore, the battery cell SOC consistency parameter is determined by the following formula: ξsoc =(SOC ema -SOC emi ) / SOC0 Among them, ξ soc is the battery cell SOC consistency parameter; SOC ema The maximum SOC value of the battery cell at the end of charging; SOC emi It is the minimum SOC value of the battery cell at the end of charging; SOC0 is the actual battery cell SOC extreme value threshold.

[0014] Furthermore, the actual battery cell SOC extreme difference threshold is determined as follows: Set two SOC thresholds, divide the SOC intervals into three according to the two SOC thresholds, and set the theoretical battery cell SOC extreme value threshold for each SOC interval. Calculate the average SOC value of the battery cells at the end of charging avg , according to SOC avg The theoretical battery cell SOC extreme value in the SOC range determines SOC0.

[0015] Furthermore, the battery cell voltage consistency parameter is determined by the following formula: ξ vol =(V ema -V emi ) / V0 Among them, ξ vol is the battery cell voltage consistency parameter; V ema V is the maximum voltage of the battery cell at the end of charging; emi It is the lowest voltage of the battery cell at the end of charging; V0 is the actual battery cell voltage extreme difference threshold.

[0016] Furthermore, the actual battery cell voltage range difference threshold is determined as follows: Set two SOC thresholds, divide the SOC intervals into three according to the two SOC thresholds, and set the theoretical battery cell voltage extreme difference threshold for each SOC interval. Calculate the average SOC value of the battery cells at the end of charging avg , according to SOC avg The theoretical battery cell voltage extreme difference threshold value V0 of the SOC interval is determined.

[0017] Furthermore, the final SOH of the battery is determined by the following formula: SOH f =SOH0×ξ Among them, SOH f is the final SOH of the battery; SOH0 is the basic SOH during the battery charging process; ξ is the battery consistency parameter.

[0018] The beneficial effects of the present invention are: The present invention takes into account the impact of battery temperature on capacity, improves the accuracy of battery SOH estimation, and introduces battery consistency parameters to better reflect the health status of the power battery system, improves the accuracy of battery health status assessment (including in-service and retired batteries), and reduces estimation errors.

[0019] The present invention establishes a T-σ relationship curve of the battery through experiments. Since low temperature has a greater impact on battery capacity than high temperature, the battery capacity coefficient is determined according to the lowest temperature of the battery cell at the start of charging, making the estimation of the basic SOH more accurate, taking into account the impact of temperature on battery capacity, and improving the accuracy of SOH estimation.

[0020] The present invention introduces the battery capacity coefficient into the basic SOH, so that the estimation of the basic SOH can more truly reflect the health status of the battery at a specific temperature, thereby improving the reliability of the estimation.

[0021] The present invention calculates the battery available capacity by a clear formula, making the calculation of the available capacity more intuitive and accurate, and providing a reliable data basis for subsequent basic SOH estimation.

[0022] The present invention comprehensively considers the impact of battery cell SOC consistency and battery cell voltage consistency on the battery health state, making the final SOH estimation more comprehensive and accurate.

[0023] The present invention determines the battery cell SOC and battery cell voltage consistency parameters through a specific formula, can quantify the difference between the battery cell SOC and the battery cell voltage, provides an effective indicator for evaluating battery cell consistency, and improves the accuracy of SOH estimation.

[0024] The present invention sets an SOC threshold and divides the SOC intervals, and sets a theoretical battery cell SOC and a theoretical battery cell voltage extreme difference threshold for each interval, so that the determination of the battery cell SOC and battery cell voltage consistency parameters is more reasonable and accurate, which can more comprehensively reflect the health status of the battery cell and improve the flexibility of the estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0026] The following is a further description of specific embodiments of the present invention in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0027] like Figure 1 As shown, the present invention provides a battery SOH evaluation method, comprising the following steps: determining a battery capacity factor based on the temperature of the battery while charging; Estimate the basic SOH of the battery during charging based on the battery capacity coefficient; Determining a battery consistency parameter based on a battery cell SOC consistency parameter and a battery cell voltage consistency parameter; The final SOH of the battery is determined based on the basic SOH and battery consistency parameters during the battery charging process.

[0028] The present invention takes into account the impact of battery temperature on capacity, improves the accuracy of battery SOH estimation, and introduces battery consistency parameters to better reflect the health status of the power battery system, improves the accuracy of battery health status assessment (including in-service and retired batteries), and reduces estimation errors.

[0029] In some embodiments, the battery SOH0 estimation method during charging is as follows: The battery contains several battery cells. When charging, the SOC value and temperature value of all battery cells at the start of charging, as well as the current during the charging process, are recorded. After charging is completed, the SOC value, voltage value and temperature value of all battery cells at the end of charging are recorded, thereby obtaining the maximum SOC value SOC of the battery cell at the start of charging. bma , minimum SOC value of battery cell SOC bmi , the maximum temperature value of the battery cell T bma , the lowest temperature value of the battery cell T bmi , and the maximum SOC value of the battery cell at the end of charging SOC ema , minimum SOC value of battery cell SOC emi , the maximum temperature value of the battery cell T ema , the lowest temperature value of the battery cell T emi .

[0030] It should be noted that the extreme values ​​of the above battery cells (maximum, minimum, highest, and lowest parameters) refer to the comparison of the corresponding parameters of all battery cells, such as the maximum SOC value SOC of the battery cell at the start of charging. bma It is the maximum SOC value of all battery cells at the start of charging.

[0031] The T-σ relationship curve is established through experiments in the laboratory environment. T is the battery temperature, σ is the capacity coefficient at T temperature, and is the charging capacity C T With rated capacity C B The ratio of σ = C T / C B , that is, different σ are obtained by conducting experiments at different temperatures T, and then the T-σ relationship curve is obtained. Since low temperature has a greater impact on battery capacity than high temperature, the lowest temperature of the battery cell at the start of charging, T bmi As the reference temperature of capacity, T bmi Substituting into the T-σ relationship curve, the battery capacity coefficient σ can be obtained m .

[0032] It is understood that the basic SOH during battery charging can be determined based on the above-mentioned recorded and calculated parameters using the following formula: SOH0=C R / (σ m ×C B ) Among them, SOH0 is the basic SOH during battery charging; C R is the available capacity of the battery; σ m is the battery capacity coefficient; C B is the rated capacity of the battery.

[0033] The battery's usable capacity is determined by the following formula: C R =ΔC / ΔSOC Among them, C R is the available capacity of the battery; ΔC is the capacity change during the charging process, which is calculated by integrating the charging current over time, that is, ΔC= , I is the charging current, t is the charging time; ΔSOC is the SOC difference between the end and start time of charging, that is, ΔSOC=(SOC ema +SOC emi ) / 2-(SOC bma +SOC bmi ) / 2.

[0034] In some embodiments, the battery consistency parameter measurement method is as follows: Two SOC thresholds are set, and three SOC intervals are divided according to the two SOC thresholds. Each SOC interval is set with a battery cell SOC extreme difference threshold and a battery cell voltage extreme difference threshold.

[0035] It should be noted that the two SOC thresholds are the first SOC threshold and the second SOC threshold, both of which are calibrated values. The first SOC threshold can be set to 30%-40%, and the second SOC threshold can be set to 70%-80%. For example, if the first SOC threshold is set to 40% and the second SOC threshold is set to 70%, the divided SOC intervals are: the first SOC interval is SOC<40%, the second SOC interval is 40%≤SOC<70%, and the third SOC interval is SOC≥70%.

[0036] Each SOC interval sets the corresponding theoretical battery cell SOC extreme difference threshold SOC i and the theoretical battery cell voltage extreme difference threshold and V i , that is, the theoretical battery cell SOC extreme difference threshold and the theoretical battery cell voltage extreme difference threshold corresponding to the first SOC interval are SOC1 and V1 respectively, the theoretical battery cell SOC extreme difference threshold and the theoretical battery cell voltage extreme difference threshold corresponding to the second SOC interval are SOC2 and V2 respectively, and the theoretical battery cell SOC extreme difference threshold and the theoretical battery cell voltage extreme difference threshold corresponding to the third SOC interval are SOC3 and V3 respectively.

[0037] After SOC interval division and determination of extreme difference threshold, calculate the average SOC value of battery cells at the end of charging. avg , according to SOC avg The theoretical battery cell SOC range threshold in the SOC interval determines the actual battery cell SOC range threshold SOC0 and the actual battery cell voltage range threshold V0, that is, SOC0 = SOC i , V0 = V i , i takes the value of 1, 2 or 3. Among them, SOC avg =(SOC ema +SOC emi ) / 2, when SOC avg When <40%, it means it is in the first SOC range, then SOC0= SOC1, V0= V1; when 40%≤SOC avg When it is less than 70%, it means it is in the second SOC range, then SOC0= SOC2, V0= V2; when SOC avg When ≥70%, it means it is in the third SOC range, then SOC0= SOC3, V0= V3.

[0038] The battery consistency parameters are calculated based on the determined SOC0 and V0 using the following formula: ξ=ξ soc ×ξ vol ξ soc =(SOC ema -SOC emi) / SOC0 ξ vol =(V ema -V emi ) / V0 Among them, ξ is the battery consistency parameter; soc is the battery cell SOC consistency parameter; ξ vol is the battery cell voltage consistency parameter; SOC ema The maximum SOC value of the battery cell at the end of charging; SOC emi is the minimum SOC value of the battery cell at the end of charging; SOC0 is the actual battery cell SOC extreme value threshold; V ema V is the maximum voltage of the battery cell at the end of charging; emi It is the lowest voltage of the battery cell at the end of charging; V0 is the actual battery cell voltage extreme difference threshold.

[0039] It is understandable that the health status of the power battery is measured through SOH f Parameter evaluation, SOH f It is a comprehensive calculation of the basic SOH and battery consistency parameters during battery charging, namely SOH f =SOH0×ξ. This method comprehensively considers the influence of basic SOH and battery consistency parameters, making the final SOH estimation more comprehensive and accurate, and can more truly reflect the health status of the power battery system, providing a reliable basis for battery maintenance and management.

[0040] The above are only specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be covered by the scope of protection of the present invention. Matters not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A battery SOH evaluation method, characterized by: determining a battery capacity factor based on the temperature of the battery while charging; Estimate the basic SOH of the battery during charging based on the battery capacity coefficient; Determining a battery consistency parameter based on a battery cell SOC consistency parameter and a battery cell voltage consistency parameter; The final SOH of the battery is determined based on the basic SOH and battery consistency parameters during the battery charging process.

2. The battery SOH evaluation method according to claim 1, characterized in that: The process of determining the battery capacity coefficient is as follows: The T-σ relationship curve of the battery is established through experiments in a laboratory environment; T is the battery temperature; σ is the capacity coefficient at temperature T, which is the charge capacity C T With rated capacity C B The ratio of Substitute the lowest temperature of the battery cell at the start of charging into the T-σ relationship curve to obtain the battery capacity coefficient.

3. The battery SOH evaluation method according to claim 1, characterized in that: The basic SOH during the battery charging process is determined by the following formula: SOH0=C R / (σ m ×C B ) Among them, SOH0 is the basic SOH during battery charging; C R is the available capacity of the battery; σ m is the battery capacity coefficient; C B is the rated capacity of the battery.

4. The battery SOH evaluation method according to claim 3, characterized in that: The battery usable capacity is determined by the following formula: C R =ΔC / ΔSOC Among them, C R is the available capacity of the battery; ΔC is the capacity change during charging; ΔSOC is the SOC difference between the end and start times of charging.

5. The battery SOH evaluation method according to claim 1, characterized in that: The battery consistency parameter is determined by the following formula: ξ=ξ soc ×ξ vol Among them, ξ is the battery consistency parameter; soc is the battery cell SOC consistency parameter; ξ vol It is the battery cell voltage consistency parameter.

6. The battery SOH evaluation method according to claim 1, characterized in that: The battery cell SOC consistency parameter is determined by the following formula: ξ soc =(SOC ema -DIRTY emi ) / SOC0 Among them, ξ soc is the battery cell SOC consistency parameter; SOC ema The maximum SOC value of the battery cell at the end of charging; SOC emi It is the minimum SOC value of the battery cell at the end of charging; SOC0 is the actual battery cell SOC extreme value threshold.

7. The battery SOH evaluation method according to claim 6, characterized in that: The process of determining the actual battery cell SOC extreme difference threshold is as follows: Set two SOC thresholds, divide the SOC intervals into three according to the two SOC thresholds, and set the theoretical battery cell SOC extreme value threshold for each SOC interval. Calculate the average SOC value of the battery cells at the end of charging avg , according to SOC avg The theoretical battery cell SOC extreme value in the SOC range determines SOC0.

8. The battery SOH evaluation method according to claim 1, characterized in that: The battery cell voltage consistency parameter is determined by the following formula: ξ vol =(V ema -V emi ) / V0 Among them, ξ vol is the battery cell voltage consistency parameter; V ema V is the maximum voltage of the battery cell at the end of charging; emi It is the lowest voltage of the battery cell at the end of charging; V0 is the actual battery cell voltage extreme difference threshold.

9. The battery SOH evaluation method according to claim 8, characterized in that: The process of determining the actual battery cell voltage extreme difference threshold is as follows: Set two SOC thresholds, divide the SOC intervals into three according to the two SOC thresholds, and set the theoretical battery cell voltage extreme difference threshold for each SOC interval. Calculate the average SOC value of the battery cells at the end of charging avg , according to SOC avg The theoretical battery cell voltage extreme difference threshold value V0 of the SOC interval is determined.

10. The battery SOH evaluation method according to claim 1, wherein: The final SOH of the battery is determined by the following formula: SOH f =SOH0×ξ Among them, SOH f is the final SOH of the battery; SOH0 is the basic SOH during the battery charging process; ξ is the battery consistency parameter.

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