Method for preventing recharge after full charging of large-capacity lithium-ion battery pack

Abstract

The present invention relates to a method for preventing recharging of a fully charged lithium-ion battery pack. More specifically, the invention relates to a method in which a Battery Management System (BMS) included in an Energy Storage System (ESS) prevents unnecessary recharging after fully charging a large-capacity lithium-ion battery pack. To this end, the present invention calculates the Open Circuit Voltage (OCV) State of Charge (SOC) of the battery pack at regular time intervals and compares it with the output SOC of the battery pack; if the difference exceeds a certain range, the output SOC value is changed to the OCV SOC value, thereby enabling recharging.

Description

Technology Field

[0001] The present invention relates to a method for preventing recharging of a fully charged lithium-ion battery pack. More specifically, the invention relates to a method in which a Battery Management System (BMS) included in an Energy Storage System (ESS) prevents unnecessary recharging after fully charging a large-capacity lithium-ion battery pack. To this end, the present invention calculates the Open Circuit Voltage (OCV) State of Charge (SOC) of the battery pack at regular time intervals and compares it with the output SOC of the battery pack; if the difference exceeds a certain range, the output SOC value is changed to the OCV SOC value, thereby preventing recharging. Background Technology

[0002] Lithium-ion batteries are widely used as an eco-friendly energy source for everything from electric vehicles to household appliances, and have recently been attracting a lot of attention. In particular, large-capacity lithium-ion batteries used in Energy Storage Systems (ESS) are connected in series or parallel and are used in homes, industries, and power plants.

[0003] The Battery Management System (BMS) of lithium-ion batteries used in ESS is a battery management device that detects and protects against overcharging or over-discharging. The BMS has a fault diagnosis function that protects the battery and performs the function of blocking charging or discharging by turning off the relay on the high-power line when a fault occurs. The BMS also has the function of estimating the State of Charge (SOC) and State of Health (SOH). Since the higher the precision of the SOC, the greater the utilization of the ESS's maximum capacity, much research is being conducted.

[0004] When charging an ESS, if the State of Charge (SOC) calculated by the BMS does not match the actual charge state, overcharging may occur or the unit may not be fully charged. If the actual charge state is higher than the BMS's calculated SOC, the system checks for overvoltage. If overvoltage is detected, the BMS can prevent overcharging by performing a Relay Off based on fault diagnosis. However, if the actual charge state is lower than the BMS's calculated SOC, charging is often completed based on the output SOC of 100%, depending on the product.

[0005] However, even though the output SOC of the BMS is 100%, the actual SOC may differ depending on the precision. If we assume that the BMS output SOC is 100% but there is an error of about 3%, the actual charge state is 97%, and if the SOC is corrected to the stable battery voltage after charging is complete, the output SOC becomes 97%. If connected to a charger at 97% SOC, the ESS will attempt to recharge to achieve a full 100% charge.

[0006] Therefore, assuming the device remains continuously connected to the charger, charging and stopping at regular intervals will repeat continuously. In this situation, the user may conclude that the product is defective upon realizing that the SOC has reached 100% and the device is fully charged, only to discover that the SOC has subsequently dropped and charging has resumed. Furthermore, as the ESS undergoes repeated recharging, some cells of the multiple series-parallel lithium-ion batteries may exceed the safety upper voltage limit; in such cases, performance degradation issues, such as a shortened lifespan of the lithium-ion batteries, may occur. Prior art literature

[0007] Song, Hyun-chul, & Ha, Mi-rim, “A Study on SOC and Balancing Operation Methods for Multi-Parallel Lithium Battery Systems for Electric Ships,” Proceedings of the 2017 General Conference of the Korean Society for Military Science and Technology, 957-958, 2017. Wang, C. Zhang, Z. Chen, “A method for joint estimation of state-of-charge and available energy of LiFePO4 batteries,” Applied Energy, vol 135, pp 81–87, Dec. 2014. Soo Seok Choi, Hong S Lim, “Factors that affect cycle-life and possible degradation mechanisms of a Li-ion cell based on LiCoO2”, Journal of Power Sources, Vol. 111, Issue 1, pp. 130-136, 18 September 2002Seongjun Lee, Jonghoon Kim, and BHCho, “Maximum pulse current estimation for high accuracy power capability prediction of a Li-Ion battery”, Microelectronics Reliability, Vol. 55, no. 3-4, pp. 572-581, 2005, Feb. S. Sato and A. Kawamura, “A New Estimation Method of State of Charge Using Terminal Voltage and Internal Resistance for Lead Acid Battery,” Proceedings of IEEE PCC, Vol. 2, pp. 565-570. Osaka, Japan, 2002Ng, KS; Moo, C.-S.; Chen, Y.-P.; Hsieh, Y.-C.Enhanced coulomb counting method for estimating state-of-charge and state-of-health of lithium-ion batteries. Appl. Energy 2009,86, 1506-1511. The problem to be solved

[0008] The present invention, devised to solve the aforementioned problems, aims to provide a method in which a Battery Management System (BMS) in an Energy Storage System (ESS) can prevent unnecessary recharging after a large-capacity lithium-ion battery pack is fully charged.

[0009] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0010] To achieve the above objective, the present invention provides a method for preventing unnecessary recharging after a lithium-ion battery pack is fully charged by a Battery Management System (BMS), comprising: a first step of measuring an elapsed time after the BMS has completed charging the battery pack; a second step of waiting until the elapsed time reaches a certain time, and when the certain time is reached, calculating an Open Circuit Voltage (OCV) State of Charge (SOC) using an average cell voltage table for the battery pack; a third step of measuring an output SOC for the battery pack; a fourth step of comparing the output SOC with the OCV SOC; and a fifth step of replacing the output SOC value with the OCV SOC value and terminating if the difference between the output SOC and the OCV SOC exceeds a certain range. It is preferable to have a method for preventing recharging of a fully charged lithium-ion battery pack, characterized by including: a sixth step of resetting the elapsed time to 0 and repeating from the first step again when the difference between the output SOC and the OCV SOC does not exceed the predetermined range.

[0011] In addition to the features described above, the present invention is also preferably a method for preventing recharging of a fully charged lithium-ion battery pack, characterized in that, in the third step, if the output SOC is not 100%, the BMS replaces the output SOC value with the OCV SOC value and terminates.

[0012] In addition to the features described above, the present invention is also preferably a method for preventing recharging of a fully charged lithium-ion battery pack, characterized in that the certain time is 2 hours and the certain range is 5%. Effects of the invention

[0013] Generally, if an ESS attempts to recharge continuously after a full charge, customers may assume that the recharging is occurring due to a defect in the SOC or battery. Consequently, this creates a problem that undermines product reliability for users. Furthermore, the lithium-ion battery may continue to charge beyond its upper charging voltage limit, which could lead to performance degradation, such as reduced battery life.

[0014] However, as seen above, the present invention provides a method in which a Battery Management System (BMS) in an Energy Storage System (ESS) can prevent unnecessary recharging after fully charging a large-capacity lithium-ion battery pack, thereby not only enhancing customer reliability but also preventing degradation of battery performance due to frequent charging or shortening of lifespan caused by such factors. Brief explanation of the drawing

[0015] Figure 1 is a configuration diagram of a typical ESS system. Figure 2 illustrates a flowchart of the procedure in which the present invention is performed. Figure 3 shows the results of a cell simulation experiment conducted in an ESS to which the present invention is applied. Specific details for implementing the invention

[0016] The present invention will be described in detail below so that the aforementioned objectives and features may be clearly understood, and accordingly, a person skilled in the art to which the present invention pertains will be able to easily implement the technical concept of the present invention. Furthermore, in describing the present invention, regarding known technologies related to the present invention that are already well known in the technical field, if it is determined that a detailed description of such known technology might unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0017] Furthermore, while the terms used in this invention have been selected to be as widely used as possible, there are also terms arbitrarily chosen by the applicant in specific cases; since the meanings of such terms are described in detail in the relevant description of the invention, it should be noted that the invention should be understood based on the meaning of the terms rather than their mere names. The terms used in the description of the embodiments are used merely to explain specific embodiments and are not intended to limit the embodiments. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0018] Embodiments may be modified in various forms and may have various additional embodiments, and specific embodiments are shown in the drawings and described in detail. However, this is not intended to limit the embodiments to specific forms, and it should be understood that they include all modifications, equivalents, or substitutions that fall within the spirit and scope of the embodiments.

[0019] In the description of various embodiments, expressions such as “first,” “second,” “first,” or “second” may modify various components of the embodiments, but do not limit said components. For example, said expressions do not limit the order and / or importance of said components. Such expressions may be used to distinguish one component from another.

[0020] The present invention will be described below with reference to the attached drawings. Figure 1 is a configuration diagram of a general Energy Storage System (ESS, 10). The ESS (10) receives power from a power line (100), and if necessary, passes through a transformer (200) and is converted into direct current by a power conversion device (300) called a Power Conversion System (PCS), and then supplies the converted power to a battery (500) for charging. In this process, a Battery Management System (BMS, 400) controls the charging of the battery (500).

[0021] In the above ESS (10), there are methods for completing full charging based on the voltage of the battery (500) or based on the SOC (State Of Charge) of the battery (500). Here, methods for calculating the SOC include electrical equivalent circuit modeling, internal resistance modeling, and current calculation methods.

[0022] Since the industry often operates based on SOC, the above ESS (10) completes full charging in a normal state, that is, when the SOC reaches 100%, charging is completed. After charging is completed, the lithium-ion battery pack does not perform charging, so the cell gradually becomes stable. At this time, the above BMS (400) generally determines that the lithium-ion battery (500) is in a stable state after 2 hours and calculates the SOC using the average cell voltage of the stable battery, which is called OCV (Open Circuit Voltage) SOC correction.

[0023] The above BMS (400) performs a comparison between the output SOC and the current OCV SOC, and if it does not match the OCV SOC, it changes the output SOC. Therefore, even if the SOC error is not large, SOC correction is performed, and the output SOC is changed frequently, and accordingly, recharging is performed frequently even after full charge. Therefore, if recharging occurs frequently even after full charge, the user may judge it as an error in the SOC or the product of the ESS (10), so in order to reduce such errors, a method is needed not to perform correction unless it deviates from the guaranteed standard.

[0024] The standard for guarantee is the precision of the SOC guaranteed by the product. When performing OCV SOC correction after a certain period has elapsed since the output SOC reached 100%, it is advisable to perform the correction only when the difference between the output SOC of 100% and the OCV SOC exceeds the product's SOC precision. For example, if the product's SOC precision is a maximum of 5%, and the output SOC is 100% while the current OCV SOC is 97%, the SOC error is within 3%; therefore, there is no problem as the result falls within the product's precision without needing to perform correction.

[0025] However, when the OCV SOC is 94%, the SOC error is 6% when compared to the output SOC, so it is desirable to change the output SOC to the OCV SOC because it is outside the precision. With the output SOC changed in this way, the ESS (10) recognizes that it is not yet fully charged and recharges. However, generally, the SOC precision listed in the specifications for product warranty is guaranteed through numerous tests. Therefore, since the error between the output SOC and the OCV SOC after a certain period of time after full charge rarely exceeds the error of the SOC precision guaranteed by the product, it is desirable to prevent recharging after full charge.

[0026] To this end, the present invention provides logic that prevents recharging after full charging. Accordingly, it is desirable for the present invention to include logic for calculating OCV SOC. OCV SOC is a table representing the SOC based on the average cell voltage, which is basically provided by the manufacturer through specifications, and the BMS calculates the SOC using the average cell voltage from the OCV SOC table.

[0027] Generally, the BMS has a resting period (0A) during which there is no charging or discharging when it does not discharge to the grid after charging is complete. Therefore, in the present invention, it is desirable to calculate the OCV SOC to correct the SOC to a stable average cell voltage after 2 hours with a current of 0A during which there is no charging or discharging. In addition, in the present invention, it is desirable to check whether the difference between the OCV SOC and the output SOC exceeds a predetermined precision (e.g., 5%) when the output SOC is 100%. If it exceeds the predetermined precision, it is desirable to replace the output SOC value with the OCV SOC value. However, if it does not exceed the predetermined precision, it is desirable to maintain the output SOC as the previous output SOC. Furthermore, if the previous output SOC is not 100%, it is desirable to update the output SOC to the OCV SOC every 2 hours because the user has not fully charged to 100%. If current is supplied during a rest period without charging or discharging after charging is complete, the time counter is reset, and it is desirable to start counting again for 2 hours with a current of 0A.

[0028] FIG. 2 illustrates a flowchart of a logic for preventing recharging after full charging. The present invention will be described below with reference to FIG. 2. As described above, the present invention is a method for preventing unnecessary recharging after the BMS (400) of the ESS (10) has fully charged a lithium-ion battery (500) pack. When the charging current for the battery (500) becomes 0A (s110), this means that the charging of the battery (500) is completed. Therefore, it is preferable for the BMS (400) to perform a first step of measuring the elapsed time after the charging of the battery (500) is completed (s120).

[0029] And it is preferable to wait until the above elapsed time reaches a certain time (s130), and when the above certain time is reached, to perform a second step of calculating the Open Circuit Voltage (OCV) and State Of Charge (SOC) using an average cell voltage table for the battery pack (s140).

[0030] And, it is preferable to perform a third step (s150) of measuring the output SOC for the battery (500), and if the output SOC is not 100%, replace the output SOC value with the OCV SOC value and terminate. However, if the output SOC is 100%, it is preferable to perform the next step.

[0031] And, after performing the fourth step of comparing the output SOC and the OCV SOC, if the difference between the output SOC and the OCV SOC exceeds a certain range, it is preferable to perform the fifth step of replacing the output SOC value with the OCV SOC value (s170) and terminating (s160).

[0032] However, if the difference between the output SOC and the OCV SOC does not exceed the above-mentioned range, it is more preferable to reset the elapsed time to 0 (s180) and perform the 6th step, which repeats from the 1st step again. Here, it is most preferable to set the above-mentioned time to 2 hours and the above-mentioned range to 5%.

[0033] Meanwhile, Figure 3 shows the results of a cell simulation with a logic applied to prevent recharging after full charging. As seen in Figure 3, charging stops and the cell voltage decreases after full charging to 100% SOC, and the SOC correction value based on the average cell voltage after 2 hours is 99.5%, which is within 5% precision. It can be confirmed that the New SOC with the recharging prevention logic applied maintains the SOC at 100% compared to the Old SOC without the recharging prevention logic applied.

[0034] In this way, using a logic to prevent recharging after full charge can resolve the problem of frequent recharging caused by changes in the output SOC. Additionally, values ​​can be appropriately modified for each application. For example, the idle time can be set to less than 2A instead of 0A, and the precision can be changed to 3% instead of 5%.

[0035] The present invention proposes a method to prevent recharging after a full charge of a large-capacity lithium-ion battery pack. Generally, if an ESS continues to attempt recharging after a full charge, the customer may assume that the recharging is occurring due to a defect in the SOC or battery. Consequently, this causes a problem that reduces the reliability of the product for the user.

[0036] In addition, lithium-ion batteries may continue to charge beyond their upper voltage limit, which can lead to performance degradation such as reduced battery life. However, by using the proposed logic, recharging is prevented within the product's SOC guarantee range, thereby resolving the issue of frequent recharging after a full charge. This provides a method and standard for trouble-free use without the need for recharging, allowing customers to perceive the product as reliable.

[0037] Although the present invention has been described with various examples as stated above, the present invention is not necessarily limited to these examples and may be implemented with various modifications within the scope of the technical concept of the present invention. Accordingly, the examples disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these examples. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention. Explanation of the symbols

[0038] 10 ESS(Energy Storage System) 100 power lines 200 transformer 300 power converter 400 BMS 500 battery

Claims

Claim 1 A Battery Management System (BMS) performs a method for preventing unnecessary recharging after fully charging a lithium-ion battery pack, which is performed after confirming that the output State of Charge (SOC) of the battery pack has reached 100% and is in a fully charged state, comprising: a first step of measuring the elapsed time during which an idle state in which the charging current and discharging current of the battery pack are continuously maintained at 0A after the BMS has completed charging the battery pack; a second step of waiting until the elapsed time reaches a certain time, and when the certain time is reached, calculating the Open Circuit Voltage (OCV) State of Charge (SOC) using an average cell voltage table for the battery pack; a third step of measuring the output SOC of the battery pack; a fourth step of comparing the output SOC with the OCV SOC; and a fifth step of replacing the output SOC value with the OCV SOC value and terminating only if the difference between the output SOC and the OCV SOC exceeds a preset SOC precision range for the battery pack. A method for preventing recharging of a fully charged lithium-ion battery pack, comprising: a sixth step in which, if the difference between the output SOC and the OCV SOC does not exceed the SOC precision range, charging control that induces recharging while maintaining the output SOC is not performed, and the elapsed time is reset to 0 and repeated from the first step; wherein in the third step, if the output SOC is not 100%, the BMS replaces the output SOC value with the OCV SOC value and terminates; the certain time is 2 hours as the time until the voltage stabilizes in the idle state where the battery pack is not charged or discharged; and the SOC precision range is the SOC error range guaranteed by the product specifications of the battery pack. Claim 2 delete Claim 3 delete

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