KR20250028579A - Initial state-of-charge correction method by estimating the state of the li-ion battery before - Google Patents

Abstract

The present invention relates to an initial SOC correction method through estimation of the previous state of a lithium battery. A lithium-ion battery is managed using SOC (State of Charge) indicating its state of charge, and by setting an initial SOC in a BMS (Battery Management System), which is a device that manages a lithium-ion battery, the BMS manages charging and discharging of the battery with the SOC. However, in a product development company that manufactures electronic products using lithium-ion batteries, abnormal cases occur in which the BMS power is reset while performing tests, settings, or inspections during the manufacturing process of related products. In such cases, there is a problem in that it is difficult to accurately set the initial SOC of the lithium-ion battery. The present invention provides an initial SOC correction method through estimation of the previous state of the battery in order to accurately set the initial SOC even when the BMS is abnormally reset.

Description

{Initial state-of-charge correction method by estimating the state of the li-ion battery before}

The present invention relates to an initial SOC correction method through estimation of the previous state of a lithium battery. A lithium-ion battery is managed using SOC (State of Charge) indicating its state of charge, and by setting an initial SOC in a BMS (Battery Management System), which is a device that manages a lithium-ion battery, the BMS manages charging and discharging of the battery with the SOC. However, in a product development company that manufactures electronic products using lithium-ion batteries, abnormal cases occur in which the BMS power is reset while performing tests, settings, or inspections during the manufacturing process of related products. In such cases, there is a problem in that it is difficult to accurately set the initial SOC of the lithium-ion battery. The present invention provides an initial SOC correction method through estimation of the previous state of the battery in order to accurately set the initial SOC even when the BMS is abnormally reset.

Lithium-ion batteries are widely used as a power source for home appliances such as laptops, mobile phones, and drones, and research is being conducted recently to use them as a power source for electric ships. Lithium-ion battery products are configured in series or parallel with single cells to meet requirements such as voltage range, discharge capacity, and energy capacity according to the characteristics of the load.

In general, lithium-ion batteries are managed by battery management devices such as a BMS (Battery Management System) or BMD (Battery Management Device). These battery management devices not only control charging and discharging while monitoring the state-of-charge (SOC) of lithium-ion batteries, but also protect the batteries from overcharge, over-discharge, over-current, etc., and manage the state-of-charge as well as the state-of-health (SOH).

Meanwhile, in order for BMS, etc. to control charging and discharging according to the capacity of the battery, the BMS must accurately know the state of charge (SOC) of the lithium battery. Usually, the SOC is estimated by measuring the battery voltage. However, due to the characteristics of lithium-ion batteries, when charging and discharging, the voltage rises due to the internal resistance of the battery, and when discharging, the voltage is unstable, such as when charging. The voltage of the battery when it is not stable is called a spurious voltage, and it is difficult to accurately estimate the SOC in this spurious voltage state. Generally, the internal characteristics of lithium-ion batteries must stabilize after a certain period of time after charging and discharging for the spurious voltage to disappear and the normal voltage to appear. This takes about 2 hours.

In order to measure the accurate SOC of a lithium-ion battery, the voltage is measured when the battery is not connected to a load and is in an open state. The SOC in this state is called OCV (Open Circuit Voltage) SOC. The general standard for measuring OCV SOC is to measure it when the battery is in a stable state about 2 hours after charging and discharging. Battery manufacturers provide customers with an OCV SOC table so that they can check the charge capacity of the battery. The OCV SOC table lists the SOC according to the average voltage of the battery. Therefore, after measuring the OCV SOC, the measured value is found in the OCV SOC table and the corresponding SOC is set as the initial SOC. This is set when the battery is in a stable state 2 hours after charging and discharging.

However, in the case where a product development company that manufactures a product using lithium-ion batteries resets the BMS power (Power Off and then Power On) immediately after charging and discharging before setting the initial SOC using the OCV SOC provided by the battery manufacturer, it is difficult to apply the OCV SOC due to the spurious voltage because the battery is not in a stable state. On the other hand, there are frequent cases where the BMS power is reset during testing, setting, or inspection immediately after manufacturing a battery product. In such cases where the BMS is abnormally reset, it is difficult to accurately calibrate the initial SOC because the status information on the battery charge and discharge is not known.

Ku, H. K., Seo, H. R., & Kim, J. M. (2015). Lithiumion Battery Energy Storage System for Power Quality Improvement in Electrical Propulsion Ships. The Transactions of the Korean Institute of Power Electronics, 20(4), 351-355. Misyris, George S., et al. “On battery state estimation algorithms for electric ship applications.” Electric Power Systems Research 151 (2017): 115-124 Song Hyun-cheol, Ha Mi-rim, “Study on the SOC and balancing operation method of the multi-parallel lithium battery system for electric ships” Military Science and Technology Society 2017 General Academic Conference, 957-958, 2017 Mirim Ha, Hyun-Chul Song and Jin-Ju Lee, “A diagnostic function preventing over charging and discharging for a lithium-ion battery management system of electric vehicles”, Control, Automation and Systems (ICCAS) 2017 17th International Conference on, 1309-1212, 2017 Lu, Languang, et al. “A review on the key issues for lithium-ion battery management in electric vehicles.” Journal of power sources 226 (2013): 272-288.

In order to solve the above-described problem, the present invention aims to propose a method of correcting the initial SOC by estimating the previous state of the battery even in cases where abnormal cases occur in which the BMS power is reset when operating or testing a battery product.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

In order to achieve the above object, the present invention is preferably a method for correcting the initial SOC by estimating the previous state of a lithium battery by a BMS when the BMS power is abnormally reset in a state where the initial SOC is not set, the method comprising: a step of calculating an OCV SOC value using an OCV SOC table; a step of reading an OLD SOC, which is an SOC stored immediately before the reset, from a storage means included in the BMS; a step of reading the previous state of the BMS stored immediately before the reset from the storage means; a step of using a value obtained by subtracting the OLD SOC from the OCV SOC as a SOC deviation; and a step of storing the OCV SOC value as a SOC value when the previous state is charging and the SOC deviation is a positive number and less than 5%, and storing the OLD SOC value as a SOC value when the SOC deviation is not a positive number or is 5% or more.

The present invention is also preferably characterized by a method for initial SOC correction through estimation of a previous state of a lithium battery, characterized in that, in addition to the above-described features, it further includes a step of storing the OCV SOC value as a SOC value when the previous state is discharging and the SOC deviation is a negative number and less than 5%, and storing the OLD SOC value as a SOC value when the SOC deviation is not a negative number or is 5% or more.

The present invention also preferably comprises, in addition to the above-described features, a step of storing the OCV SOC value as the SOC value when the previous state is Idle and the absolute value of the SOC deviation is 5% or more or the OLD SOC value is 0, and storing the OLD SOC value as the SOC value when the OLD SOC value is not 0 and the absolute value of the SOC deviation is less than 5%; It is also preferable to use a method for initial SOC correction through estimation of the previous state of a lithium battery.

As described above, the present invention provides a method for the BMS to estimate the previous state of the lithium battery and correct the initial SOC when the BMS power is abnormally reset in a state where the initial SOC is not set, so that even in a situation where the BMS is abnormally reset, the battery can be prevented from being overcharged and overdischarged, enabling stable charge and discharge operation and allowing for the expected improvement of the precision of the SOC.

Figure 1 is a flow chart of the procedure for performing the SOC correction method according to the present invention.
Figure 2 illustrates an example of implementing the judgment logic for performing the SOC correction method according to the present invention as a program source code.

Hereinafter, the present invention will be described in detail so that the purpose and features described above become clear, so that a person having ordinary skill in the art to which the present invention pertains can easily practice the technical idea of the present invention. In addition, in describing the present invention, if it is determined that a detailed description of a known technology related to the present invention, which is already well known in the art, may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

In addition, the terms used in the present invention are selected from general terms that are widely used at present as much as possible, but in certain cases, there are terms arbitrarily selected by the applicant, and in such cases, the meanings thereof are described in detail in the description of the relevant invention. Therefore, it should be noted that the present invention should be understood based on the meanings of the terms and not simply the names of the terms. The terms used in the description of the embodiments are only used to describe specific embodiments and are not intended to limit the embodiments. Singular expressions include plural expressions unless the context clearly indicates otherwise.

The embodiments may be modified in many ways and may have various additional embodiments, and specific embodiments are shown in the drawings and detailed descriptions related thereto are described herein. However, this is not intended to limit the embodiments to specific forms, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the embodiments.

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 the components. For example, the expressions do not limit the order and/or importance of the components. The expressions may be used to distinguish one component from another.

Hereinafter, the present invention will be described with reference to the attached drawings. For maintenance purposes, the BMS generally periodically stores information on SOC and operating status (charging, discharging, idle, etc.), and records the information in a storage means (memory, EEPROM) included in the BMS every few seconds to every few hours. This is used for debugging purposes when a problem occurs in the future.

However, in the case of embedded systems, if memory is accessed frequently, the MCU's load increases and it is difficult to do other things, so it is designed to record periodically rather than in real time. Therefore, if the BMS power is abnormally reset, the last current status and SOC information are not accurately stored.

In cases where the BMS power is abnormally reset, it is uncertain whether the battery has calculated the OCV SOC in a stable state and stored the initial SOC. Therefore, information about the stored SOC and the operating state (charging, discharging, and idle) before the BMS is reset can be utilized. By comparing the deviation between the previously applied SOC and the current OCV SOC, it is possible to estimate whether the battery was in a charging or discharging state before the BMS was reset.

The BMS needs to determine whether there is a problem in unconditionally changing the current SOC to OCV SOC using only the current state before being reset, the previous SOC, and the current OCV SOC. The judgment criterion can be checked to see if the current SOC is increasing because it is being charged normally, or decreasing because it is being discharged.

Figures 1 and 2 show the initial SOC judgment logic flowchart and code implementation for determining the current OCV SOC application using the previous SOC and current status.

Since the BMS is always in the Off state after a power reset (Power On), it is assumed that the battery is initially in an Idle state where no current flows. The BMS divides into three states according to the current flow, and the states stored before the BMS is reset are also divided into three: charging, discharging, and Idle. In addition, the Depth-Of-Discharge (DOD) uses 80% (SOC operating range: 10% to 90%), and the SOC accuracy is designed based on 5%.

In the present invention, the previous state of the battery is estimated by using the ‘BMS state and SOC saved before BMS reset’ stored in the storage means (EEPROM) of the BMS, and an initial SOC correction method is proposed through this.

To this end, in the present invention, if the previous state is charging, if the OCV SOC and the previous SOC deviation are positive values and the absolute value is less than 5%, it is preferable to determine that the current OCV SOC is normally increased in the charging state and calculated correctly within the 5% accuracy deviation, and to apply the OCV SOC as the SOC of the BMS.

If the previous state is discharging, and the OCV SOC and the previous SOC deviation is a negative value and the absolute value is less than 5%, it is desirable to determine that the current OCV SOC is normally calculated as the SOC decreased in the discharging state and within the 5% accuracy deviation, and to apply the OCV SOC as the SOC of the BMS.

If the previous state is Idle and the deviation is greater than 5% in absolute value, it is judged that there is an error in the previous SOC or that the initial SOC is being calculated, and it is desirable to apply the OCV SOC to the BMS SOC.

Also, if the previous SOC is 0, it is judged that the initial SOC is calculated because there is no stored SOC at the beginning, and the OCV SOC is applied. If none of the above cases are present, it is judged that the current battery is not stable, and it is desirable to apply the previous SOC as the SOC of the BMS.

If the calculated OCV SOC is unconditionally applied when the battery is in a non-steady state, the initial SOC error will be large. Using the initial SOC judgment logic, the SOC can be applied as the OCV SOC or the previous SOC within 5% accuracy. This initial SOC judgment logic solves the limitation of the SOC logic that unconditionally compensates for the OCV SOC at the beginning.

Hereinafter, the execution process of the present invention will be described in more detail with reference to FIG. 1. As described above, the present invention is a method in which, when the BMS power is abnormally reset in a state in which the initial SOC is not set, the BMS estimates the previous state of the lithium battery and corrects the initial SOC.

Therefore, if it is determined that the initial OCV is not stored while power is supplied to the BMS (s110), it is desirable for the BMS to first perform a step of calculating the OCV SOC value using the OCV SOC table provided by the battery manufacturer (s120).

Then, it is preferable to perform a step of reading OLD SOC, which is SOC stored immediately before the reset, from the storage means (EEPROM) included in the BMS, and a step (s130) of reading a previous state (Old State) of the BMS stored immediately before the reset from the storage means (EEPROM). In addition, it is preferable to perform a step (s140) of making a value obtained by subtracting the OLD SOC from the OCV SOC into the SOC deviation.

And, if the result of determining the previous state (Old State) is that the previous state (Old State) is charging (s150), it is preferable to perform the step of checking the SOC deviation (s151), and if the SOC deviation (SOC Deviation) is positive and less than 5%, storing the OCV SOC value as the SOC value (s152), and if the SOC deviation is not positive or is 5% or more, storing the OLD SOC value as the SOC value (s153).

However, if the result of determining the previous state (Old State) is that the previous state (Old State) is discharging (s160), it is preferable to perform the step of checking the SOC deviation (s161), storing the OCV SOC value as the SOC value if the SOC deviation (SOC Deviation) is negative and less than 5% (s162), and storing the OLD SOC value as the SOC value if the SOC deviation is not negative or greater than 5% (s163).

And, if the result of determining the above-mentioned previous state (Old State) is that the above-mentioned previous state (Old State) is neither charging nor discharging but is an Idle state (s170), it is preferable to perform a step (s171) of checking the SOC deviation (SOC Deviation), and if the absolute value of the SOC deviation (SOC Deviation) is 5% or more or the OLD SOC value is 0, storing the OCV SOC value as the SOC value (s171), and if the OLD SOC value is not 0 and the absolute value of the SOC deviation (SOC Deviation) is less than 5%, storing the OLD SOC value as the SOC value (s172).

In this way, the present invention proposes a method of estimating the previous state of the battery through the information stored at the end of the memory in an operating state where the BMS power is abnormally reset, and thereby correcting the initial SOC. If the proposed method is applied to calculate the initial SOC when the BMS is abnormally reset, stable charging and discharging operations are possible so that the battery is not overcharged or overdischarged, and improved SOC accuracy can also be expected.

Although the present invention has been described with various examples as described above, the present invention is not necessarily limited to these examples, and various modifications can be implemented without departing from the technical idea of the present invention. Therefore, the examples disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain it, and the scope of the technical idea of the present invention is not limited by these examples. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the rights of the present invention.

Claims (3)

A method for compensating the initial SOC by estimating the previous state of the lithium battery by the BMS when the BMS power is abnormally reset without setting the initial SOC.
Step of calculating OCV SOC value using OCV SOC table;
A step of reading OLD SOC, which is a SOC stored immediately before the reset, from a storage means included in the BMS;
A step of reading the previous state of the BMS stored immediately before the reset from the above storage means;
A step of making the value obtained by subtracting the OLD SOC from the OCV SOC as the SOC deviation; and
A method for initial SOC correction through estimation of a previous state of a lithium battery, characterized in that it comprises the steps of: storing the OCV SOC value as a SOC value when the previous state is charging and the SOC deviation is a positive number and less than 5%, and storing the OLD SOC value as a SOC value when the SOC deviation is not positive or is 5% or more. In the first paragraph,
A method for initial SOC correction through estimation of a previous state of a lithium battery, characterized in that it further includes a step of storing the OCV SOC value as a SOC value when the previous state is discharging and the SOC deviation is negative and less than 5%, and storing the OLD SOC value as a SOC value when the SOC deviation is not negative or is 5% or more. In the first paragraph,
A method for initial SOC correction through estimation of a previous state of a lithium battery, characterized in that it further includes a step of storing the OCV SOC value as a SOC value when the previous state is Idle and the absolute value of the SOC deviation is 5% or more or the OLD SOC value is 0, and storing the OLD SOC value as a SOC value when the OLD SOC value is not 0 and the absolute value of the SOC deviation is less than 5%.