STATE OF CHARGE CALIBRATION FOR BATTERY CELLS

Abstract

A battery system includes a pressure sensor configured to detect pressure changes corresponding to thickness changes of at least one of a plurality of battery cells of a battery. A battery management module includes a state of charge (SOC) estimator configured to estimate the SOC of the battery. Based on measured pressure, the SOC estimator detects at least a first inflection point and a second inflection point during one of charging and discharging the battery and calibrates the SOC of the battery based on one of a first SOC value and a second SOC value corresponding to at least one of the first inflection point and the second inflection point, respectively.

Description

INTRODUCTION

[0001] The information provided in this section is intended to provide a general context for the disclosure. Work by the presently named inventors, to the extent described in this section, as well as aspects of the description that may not be prior art at the time of filing, are neither expressly nor impliedly acknowledged as prior art to the present disclosure.

[0002] The present disclosure relates to battery systems and, more particularly, to calibrating state of charge estimates for battery systems.

[0003] Electric vehicles (EVs), such as battery electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, comprise one or more electric machines and a battery system comprising one or more battery cells, modules, and / or packs. A power control system is used to control the charging and / or discharging of the battery system during charging and / or driving. A battery management system monitors various battery parameters and estimates the battery system's state-of-charge (SOC). SUMMARY

[0004] A battery system includes a pressure sensor configured to detect pressure changes corresponding to thickness changes of at least one of a plurality of battery cells of a battery. A battery management module includes a state of charge (SOC) estimator configured to estimate the SOC of the battery. Based on measured pressure, the SOC estimator detects at least a first inflection point and a second inflection point during one of charging and discharging the battery and calibrates the SOC of the battery based on one of a first SOC value and a second SOC value corresponding to at least one of the first inflection point and the second inflection point, respectively.

[0005] In other features, the battery system includes the battery comprising the plurality of battery cells. The plurality of battery cells includes cathode electrodes comprising LFP cathode active material.

[0006] In other features, the battery comprises a plurality of battery cells. The plurality of battery cells include anode electrodes comprising active graphite anode material.

[0007] In other features, the battery comprises a plurality of battery cells. The majority of the battery's battery cells comprise capacitor-assisted batteries (CABs).

[0008] In other features, the pressure sensor is arranged between at least two adjacent ones of the plurality of battery cells. The pressure sensor comprises a 2D pressure sensor.

[0009] In other features, the SOC estimator does not calibrate the SOC in response to inflection points within a predetermined period of current polarity change. The battery management module is configured to calculate capacity maintenance and to adjust at least one of the first SOC value and the second SOC value based on capacity maintenance. The SOC estimator is configured to calibrate the SOC of the battery based on the first SOC value and the second SOC value.

[0010] In other features, the SOC estimator is configured to detect a third inflection point and a fourth inflection point based on measured pressure during the other charging and discharging process of the battery, and to calibrate the SOC of the battery based on one of a third SOC value and a fourth SOC value corresponding to at least one of the third inflection point and the fourth inflection point, respectively.

[0011] A method for estimating the state of charge (SOC) of a battery system includes sensing pressure changes corresponding to thickness changes of at least one of a plurality of battery cells; estimating the SOC of a battery; based on the measured pressure, detecting at least one of a first inflection point and a second inflection point during one of charging and discharging the battery; and calibrating the SOC of the battery based on one of a first SOC value and a second SOC value corresponding to at least one of the first inflection point and the second inflection point, respectively.

[0012] In other features, the plurality of battery cells comprise cathode electrodes comprising LFP cathode active material. The plurality of battery cells comprise anode electrodes comprising graphite anode active material. The plurality of battery cells of the battery comprise capacitor-assisted battery (CAB) cells.

[0013] In other features, the method includes disposing a pressure sensor between at least two adjacent battery cells of the plurality of battery cells. The pressure sensor includes a 2D pressure sensor. The method includes not calibrating the SOC in response to inflection points within a predetermined period of current polarity change. The method includes calculating capacity retention and adjusting at least one of the first SOC value and the second SOC value based on the capacity retention.

[0014] In other features, the method includes calibrating the SOC of the battery based on the first SOC value and the second SOC value.

[0015] In other features, the method includes, based on the sensed pressure, detecting a third inflection point and a fourth inflection point during the other of charging and discharging the battery; and calibrating the SOC of the battery based on one of a third SOC value and a fourth SOC value corresponding to at least one of the third inflection point and the fourth inflection point, respectively.

[0016] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are provided for purposes of illustration only and are not intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present disclosure will be more fully understood from the detailed description and the accompanying drawings, in which: Fig. 1 is a functional block diagram of a vehicle including a battery system according to the present disclosure; Fig. 2 is a functional block diagram of an example state of charge estimator; Fig. 3 is a graph illustrating an example of voltage versus state of charge for a battery cell having cathode electrodes using lithium iron phosphate (LFP) and anode electrodes using graphite; Fig. Figure 4 is a graph illustrating an example of thickness change as a function of time during charging and discharging; Fig. 5 is a graph illustrating an example of a swelling curve (thickness as a function of state of charge and capacity) for an anode electrode using graphite active material; Fig. Figure 6 is a graph illustrating an example of a swelling curve (thickness as a function of voltage) for a cathode electrode using LFP active material; Fig. 7 is a side cross-sectional view of an example of a battery module including battery cells with a pressure sensor disposed between the battery cells, according to the present disclosure; Fig. 8 is a top view of an example of a 2D pressure sensor according to the present disclosure; Fig. 9 is a graph illustrating an example of voltage, current, SOC, and thickness during charging and discharging according to the present disclosure; Fig. 10 is a flowchart of an example method for calibrating the SOC according to the present disclosure; and Fig. 11 is a flowchart of a method for adjusting SOC values ​​at the inflection points based on changes in capacity retention according to the present disclosure.

[0018] Reference numerals may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0019] The systems and methods for calibrating the state-of-charge (SOC) are described below in the context of electric and hybrid vehicles, but can also be used to calibrate the SOC of battery systems in other applications.

[0020] It is difficult to estimate the state-of-charge (SOC) of battery cells that contain lithium iron phosphate (LFP) as the active cathode material and graphite as the active anode material. LFP / graphite-based battery cells exhibit an extremely flat voltage profile, making it difficult to estimate SOC based on voltage changes. Currently, LFP / graphite battery cells estimate SOC using a coulomb counter, which tracks current consumption over time.

[0021] However, the coulomb counter has an accumulated error and requires periodic recalibration. The current procedure for calibrating the SOC estimate for LFP-based battery cells involves slowly charging the LFP-based cell from a low SOC to verify capacity.

[0022] This calibration procedure requires a significant amount of time. Furthermore, the vehicle's SOC may not be low enough often to effectively calibrate the SOC estimates.

[0023] During charging, the thickness of the LFP-based battery cells increases, decreases, and then increases again (corresponding to two charging inflection points). During discharging, the thickness of the battery cells decreases, increases, and then decreases again (corresponding to two discharging inflection points). The SOCs at the inflection points are not affected by the current charge rate (C) and / or other dynamic inputs (but change slowly over time in response to reducing capacity retention).

[0024] The SOC estimation systems and methods according to the present disclosure are calibrated by detecting inflection points corresponding to thickness changes during charging and discharging. The inflection points correspond to known SOC values. When the inflection points occur, the known SOC values ​​are used to calibrate or correct the SOC values ​​calculated by the SOC estimator. The SOC calibration method is more accurate and faster than previous calibration methods.

[0025] With reference now to Fig. 1, a vehicle 100 includes an electric motor 110 that drives one or more wheels 112 of the vehicle 100. A battery 120 provides motive power to the electric motor 110 and / or receives regenerative power therefrom via an inverter 126. In some examples, the battery 120 includes LFP / graphite battery cells. In some examples, the battery 120 includes capacitor-assisted LFP / graphite battery cells. In some examples, the battery 120 includes pouch-shaped or prismatic battery cells. Although a battery-electric vehicle is illustrated, the vehicle 100 may also be a hybrid vehicle including an internal combustion engine (ICE).

[0026] A propulsion controller 136 receives the throttle position from an accelerator pedal 138 (or an autonomous driving system or adaptive cruise control). A battery management module 124 receives the parameters sensed by the sensors 130 and estimates the SOC of the battery 120. The propulsion controller 136 controls the inverter 126 based on the SOC of the battery 120, the throttle position (or other propulsion demand), and the sensed parameters. The battery management module 124 includes a state of charge (SOC) estimator 128 configured to estimate the SOC of the battery 120. As described further below, the battery 120 includes a plurality of battery cells and one or more pressure sensors 122 disposed between the battery cells. The pressure sensors 122 are used to monitor thickness changes of the battery cells to identify thickness inflection points corresponding to known SOC values.

[0027] With reference now to Fig. 2, the SOC estimator 128 estimates the SOC using any suitable SOC estimation method. For example, an SOC estimator 200 includes a coulomb counter 210 that receives and accumulates the current output to the inverter 126 (or received from the inverter 126). The SOC estimator 200 estimates the SOC of the battery system based on the current consumed (and / or restored by regeneration) since the last charge cycle. For example, the coulomb counter 210 may i = I*Δt / Q0 + SOC i-1Calculate. Due to current measurement errors, I*Δt is not always accurate. As a result, the errors can accumulate and cause the estimated SOC value to differ from the actual value. If the vehicle is not driven for an extended period of time, the battery management system does not know the degree of self-discharge that occurred during storage, and the SOC estimate requires recalibration to be accurate.

[0028] With reference now to Fig. Figure 3 shows the voltage as a function of state of charge for a battery comprising cathode electrodes using lithium iron phosphate (LFP) as the active cathode material and anode electrodes using graphite as the active anode material. The voltage slope is relatively small between low SOC and high SOC values ​​(e.g., positive during charging and negative during discharging), making SOC estimation based on voltage difficult.

[0029] With reference now to Fig. Figure 4 illustrates thickness changes as a function of time during charging and discharging for a battery cell comprising LFP / graphite. During charging at 306, the thickness increases, then decreases (creating a first inflection point 310), and then increases again (creating a second inflection point 312). During discharging at 308, the thickness decreases, then increases (creating a first inflection point 320), and then decreases again (creating a second inflection point 322). In other words, there are two inflection points during both charging and discharging. The transitions between charging and discharging (where the current polarity changes) are not used at 324.

[0030] With reference now to Fig. 5 and Fig. 6 the anode and cathode electrodes swell and shrink during charging and discharging. In Fig. Figure 5 shows an example of a swelling curve (volume fraction as a function of state of charge and capacity) for an anode electrode using active graphite material during charging. Fig. Figure 6 shows an example of a swelling curve (thickness change as a function of voltage) for a cathode electrode using LFP active material. As can be seen, the thickness inflection points during charging and discharging are related to the swelling / shrinkage of the active graphite anode material.

[0031] With reference now to Fig. 7 illustrates an example of a battery module 372 including a plurality of battery cells 374. One or more pressure sensors 378 are disposed between adjacent ones of the plurality of battery cells 374. The pressure sensors 378 may include a pressure sensor that measures pressure at a point location and / or a 2D pressure sensor that measures pressure over a two-dimensional (2D) area. In some examples, the pressure sensors 378 may be disposed inside or outside the housing of the battery cells. In some examples, the pressure sensors 378 are disposed between the housings of one or more adjacent pairs of battery cells.

[0032] With reference now to Fig. Figure 8 shows an example of pressure sensor 378 operating as a 2D pressure sensor. Pressure sensor 378 includes a substrate 379 (such as an insulating layer) and a pattern of conductive traces 380.

[0033] With reference now to Fig. Figure 9 shows an example of voltage, current, SOC, and thickness during charging and discharging. As can be seen, the thickness inflection points during charging and discharging correspond to the predetermined SOC values ​​at 420 and 424. The battery management module determines when the inflection points occur and calibrates the SOC estimate using the predetermined SOC values ​​at the thickness inflection points.

[0034] With reference now to Fig. Figure 10 illustrates a method for calibrating the SOC estimate. At 450, pressure data for one or more battery cells is measured during cycling. At 454, the thickness inflection points are identified in the pressure data. At 458, the method determines whether the current has reversed (polarity change) simultaneously with the inflection point or within a predetermined period of time after the inflection point.

[0035] If 458 is true, the inflection point at 462 is not used because it corresponds to a transition between charging and discharging (or vice versa). If 458 is false, the SOC estimate is calibrated based on a SOC value from an inflection point table at 466. At 468, the calibrated SOC estimate is output to other vehicle systems.

[0036] With reference now to Fig.11 illustrates a method for adjusting the SOC values ​​at the inflection points based on changes in capacity retention. At 510, the method determines whether the SOC values ​​at the inflection points need to be updated. In some examples, the updates are performed in response to an event, such as the elapse of a predetermined period of time, a predetermined number of cycles, button activation, and / or any other event. If 510 is true, the method continues to 520 and calculates capacity retention a. At 530, the SOC values ​​for the inflection points are updated by SOC' = SOC / a.

[0037] The foregoing description is merely illustrative and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be embodied in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be limited thereto, since other changes will become apparent after studying the drawings, the patent specification, and the following claims. It is understood that one or more steps within a method may be performed in a different order (or simultaneously) without altering the principles of the present disclosure.Furthermore, although the embodiments are each described above as having specific features, any one or more of these features described with respect to one embodiment of the disclosure may be implemented and / or combined with features of any of the other embodiments, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and an exchange of one or more embodiments for one another remains within the scope of this disclosure.

[0038] Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including "connected," "engaging," "coupled," "adjacent," "beside," "on top of," "over," "below," and "disposed." Where a relationship between first and second elements is not explicitly described as "direct" in the above disclosure, that relationship may be a direct relationship, with no other intervening elements between the first and second elements, or an indirect relationship, with one or more intervening elements (either spatial or functional) between the first and second elements.As used herein, the term “A, B and / or C” should be construed as logical (A ORed with B ORed with C) using a non-exclusive logical OR and should not be understood as “at least one of A, at least one of B and at least one of C”.

[0039] In the figures, the direction of an arrow, as indicated by the arrowhead, generally illustrates the flow of information (such as data or instructions) of interest to the illustration. For example, if element A and element B exchange a plurality of pieces of information, but the information sent from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is sent from element B to element A. Further, for information sent from element A to element B, element B may send requests or acknowledgments for the information to element A.

[0040] In this application, which includes the definitions below, the term "module" or the term "controller" may be replaced by the term "circuit". The term "module" may refer to, be a portion of, or include: an application-specific integrated circuit (ASIC), a digital, analog, or mixed analog / digital discrete circuit, a digital, analog, or mixed analog / digital integrated circuit, a combinational logic circuit, a field-programmable gate array (FPGA), processor circuitry (common, dedicated, or group) that executes code, memory circuitry (common, dedicated, or group) that stores code executed by the processor circuitry, other suitable hardware components that provide the described functionality, or a combination of some or all of the foregoing components, such as in a system on a chip.

[0041] The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules connected via interface circuits. For example, multiple modules may enable load balancing. In another example, a server module (also referred to as a remote or cloud module) may perform some functions on behalf of a client module.

[0042] The term "code," as used above, may include software, firmware, and / or microcode and may refer to programs, routines, functions, classes, data structures, and / or objects. The term "common processor circuit" includes a single processor circuit that executes code from multiple modules, in part or in whole. The term "group processor circuit" includes a processor circuit that, in combination with additional processor circuits, executes code from one or more modules, in part or in whole. References to multiple processor circuits include multiple processor circuits on discrete chips, multiple processor circuits on a single chip, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination thereof.The term "shared memory circuit" encompasses a single memory circuit that stores code from multiple modules, either individually or collectively. The term "group memory circuit" encompasses a memory circuit that, in combination with additional memories, stores code from one or more modules, either individually or collectively.

[0043] The term "memory circuit" is a subset of the term computer-readable medium. As used herein, the term "computer-readable medium" does not include transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); therefore, the term "computer-readable medium" can be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible, computer-readable medium include non-volatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

[0044] The devices and methods described in this application may be implemented, in part or in whole, by a special-purpose computer created by configuring a general-purpose computer to perform one or more specific functions contained in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications that can be translated into computer programs through the routine work of a skilled technician or programmer.

[0045] The computer programs comprise processor-executable instructions stored on at least one non-transitory, tangible, computer-readable medium. The computer programs may also include or be based on stored data. The computer programs may include a basic input / output system (BIOS) that interacts with the hardware of the special-purpose computer, device drivers that interact with specific devices of the special-purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0046] The computer programs may comprise: (i) descriptive text to be parsed, such as HTML (Hypertext Markup Language), XML (Extensible Markup Language) or JSON (JavaScript Object Notation), (ii) assembly code, (iii) object code generated from the source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. By way of example only, source code may be written using the syntax of languages ​​including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th Revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK and Python®. legend

[0047] In the drawings, N stands for No and Y stands for Yes.

Claims

[1] Battery system comprising: a pressure sensor configured to detect pressure changes corresponding to thickness changes of at least one of a plurality of battery cells of a battery; and a battery management module including a state of charge (SOC) estimator configured to: estimate the SOC of the battery; detecting at least one of a first inflection point and a second inflection point based on the measured pressure during one of charging and discharging the battery; and calibrate the SOC of the battery based on one of a first SOC value and a second SOC value corresponding to at least one of the first inflection point and the second inflection point. [2] The battery system of claim 1, further comprising the battery comprising the plurality of battery cells, wherein the plurality of battery cells comprise cathode electrodes comprising LFP cathode active material. [3] The battery system of claim 1, further comprising the battery comprising the plurality of battery cells, wherein the plurality of battery cells comprise anode electrodes comprising graphite anode active material. [4] The battery system of claim 1, further comprising the battery comprising the plurality of battery cells, wherein the plurality of battery cells of the battery comprise capacitor assisted battery (CAB) battery cells. [5] The battery system of claim 1, wherein the pressure sensor is arranged between at least two adjacent ones of the plurality of battery cells. [6] The battery system of claim 1, wherein the pressure sensor comprises a 2D pressure sensor. [7] The battery system of claim 1, wherein the SOC estimator does not calibrate the SOC in response to inflection points within a predetermined period of current polarity change. [8] The battery system of claim 1, wherein the battery management module is configured to calculate the capacity maintenance and to adjust at least one of the first SOC value and the second SOC value based on the capacity maintenance. [9] The battery system of claim 1, wherein the SOC estimator is configured to calibrate the SOC of the battery based on the first SOC value and the second SOC value. [10] The battery system of claim 1, wherein the SOC estimator is configured to: to detect a third inflection point and a fourth inflection point based on sensed pressure during the other of the battery charging and discharging processes; and calibrate the SOC of the battery based on one of a third SOC value and a fourth SOC value that corresponds to at least one of the third inflection point and the fourth inflection point, respectively.

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