WO2015056962A1 - Apparatus for estimating voltage of hybrid secondary battery and method therefor - Google Patents

Abstract

Disclosed are an apparatus and a method for estimating the voltage of a hybrid secondary battery including a first secondary battery and a second secondary battery which have different electrochemical characteristics and which are connected in parallel with each other. The apparatus according to the present invention comprises: a sensor unit for measuring the operation current of the hybrid secondary battery; and a control unit for estimating the voltage of the hybrid secondary battery using the operation current and a voltage equation derived from a circuit model comprising a first circuit unit for simulating a change in the voltage of the first secondary battery by means of a first open circuit voltage element and optionally a first impedance element, and a second circuit unit for simulating a change in the voltage of the second secondary battery by means of a second open circuit voltage element and optionally a second impedance element, the second circuit unit being connected in parallel with the first circuit unit.

Description

Apparatus and method for estimating voltage of hybrid secondary battery

The present invention relates to an apparatus and method capable of estimating the voltage of a hybrid secondary battery.

This application claims the priority based on Korea Patent Application No. 10-2013-0122272 filed on October 14, 2013, all the contents disclosed in the specification and drawings of the application are incorporated in this application. In addition, the present application claims priority based on Korean Patent Application No. 10-2014-0137724 filed on October 13, 2014, all the contents disclosed in the specification and drawings of the application are incorporated in this application.

Batteries generate electrical energy through electrochemical oxidation and reduction reactions, and are widely used for various purposes. For example, a battery may be a device that can be carried in a human hand such as a mobile phone, a laptop computer, a digital camera, a video camera, a tablet computer, a power tool, or the like; Various electric drive power devices such as electric bicycles, electric motorcycles, electric vehicles, hybrid vehicles, electric boats, electric airplanes, and the like; A power storage device used to store power generated by renewable energy or surplus generated power; Increasingly, the field of use extends to an uninterruptible power supply for stably supplying power to various information communication devices including server computers and communication base stations.

The cell comprises three basic components: an anode comprising a material that is oxidized while releasing electrons during discharge, and a cathode comprising a material that is reduced while receiving electrons during discharge. And an electrolyte that allows the movement of working ions between the cathode and the anode.

The battery may be classified into a primary battery that cannot be reused after being discharged and a secondary battery capable of repetitive charging and discharging because the electrochemical reaction is at least partially reversible.

Examples of secondary batteries include lead-acid batteries, nickel-cadmium batteries, nickel-zinc batteries, nickel-iron batteries, silver oxide batteries, nickel metal hydride batteries, zinc-manganese oxide batteries, zinc-bromide batteries, and metal- Air batteries, lithium secondary batteries and the like are known.

Among them, lithium secondary batteries have attracted the greatest commercial interest because of their higher energy density, higher battery voltage, and longer shelf life than other secondary batteries.

In the secondary battery, materials used as the positive electrode material and the negative electrode material have an important effect on the performance of the secondary battery. Therefore, various attempts have been made to provide a cathode material and a cathode material that are stable at high temperatures, can provide a high energy capacity, and have low manufacturing costs.

However, it is not easy to develop a positive electrode material and a negative electrode material having excellent performance in all aspects, and in recent years, each secondary battery has been connected by connecting secondary batteries including different kinds of positive electrode materials and negative electrode materials in parallel. Attempts have been made to make up for the shortcomings.

Hereinafter, the secondary battery of the form which connected the different types of secondary batteries in parallel is called a hybrid secondary battery.

On the other hand, a hybrid secondary battery often has a voltage profile including an inflection point when the component batteries have different operating voltage ranges. If the operating voltage range of the constituent cells is different, the dominant reaction kinetics are different while the hybrid secondary battery is being charged or discharged.

However, when an inflection point exists in the voltage profile of the hybrid secondary battery, the amount of voltage change relative to the state of charge is relatively small near the inflection point. That is, even if the state of charge varies greatly, the voltage hardly changes. By the way, the voltage measured by the sensor has an error due to the error of the sensor or the polarization voltage that is dynamically changed. Therefore, if the hybrid secondary battery is controlled using the measured voltage as it is near the inflection point, it is difficult to guarantee the accuracy. This is because the conventional battery control system assumes that the electrochemical state of the battery has changed significantly even when the measured voltage slightly changes near the inflection point.

Accordingly, there is a demand for a method of indirectly estimating a voltage using a different measurable parameter without directly measuring the voltage of a hybrid secondary battery.

The present invention provides an apparatus and method for indirect estimation using a iterative algorithm without directly measuring a voltage of a hybrid secondary battery in which secondary batteries having different electrochemical characteristics are connected in parallel.

According to an aspect of the present invention, there is provided a voltage estimating apparatus for a hybrid secondary battery according to an embodiment of the present invention, which estimates a voltage of a hybrid secondary battery including a first secondary battery and a second secondary battery which have different electrochemical characteristics and are connected in parallel to each other. An apparatus includes a sensor unit measuring an operating current of a hybrid secondary battery, and a control unit estimating a voltage of the hybrid secondary battery using the operating current and a voltage equation derived from a predefined circuit model.

According to one aspect, the first secondary battery and the second secondary battery may be packaged in different packaging materials as independent batteries, or may be packaged together in one packaging material.

In the latter case, the first secondary battery and the second secondary battery are composed of a unit cell including a positive electrode plate and a negative electrode plate and a separator interposed therebetween. The first secondary battery and the second secondary battery may include a coating layer of an active material having different electrochemical properties on the positive electrode plate and / or the negative electrode plate.

According to another aspect, the first secondary battery and the second secondary battery may each include a plurality of unit cells or a plurality of battery modules connected in series and / or in parallel.

Preferably, the circuit model includes a first circuit unit that simulates a voltage change of the first secondary battery by a first open voltage element and optionally a first impedance element of the first secondary battery, and the first circuit unit And a second circuit unit connected in parallel with the second open circuit of the second secondary battery and selectively simulating a voltage change of the second secondary battery by a second impedance element.

Preferably, the first open voltage formed by the first open voltage element may be determined from a predefined correlation between the first charged state and the first open voltage of the first secondary battery.

Similarly, the second open voltage formed by the second open voltage element may be determined from a predefined correlation between the second charged state and the second open voltage of the second secondary battery.

For reference, the state of charge is known in the art as a parameter called state of charge (SOC). The state of charge can be quantitatively indicated by the SOC and z parameters. The SOC parameter is used to indicate the state of charge as a percentage of 0-100%, and the z parameter is used to indicate the state of charge as a number from 0-1. The state of charge may be measured by an ampere counting method as a non-limiting example.

Preferably, the predefined correlation may be obtained from an open voltage profile measured according to a change in state of charge.

According to an aspect, the predefined correlation may be a lookup table capable of mapping an open voltage corresponding to each state of charge.

The lookup table may be obtained by using open voltage data measured for each of the first and second secondary batteries according to the state of charge. The open voltage data can be obtained through experiments.

According to another aspect, the predefined correlation may be a lookup function that includes a state of charge and an open voltage as input variables and output variables, respectively.

The lookup function may be obtained by numerical analysis of coordinate data constituting an open voltage profile measured for each state of charge of the first and second secondary batteries.

Preferably, the first impedance element and the second impedance element, respectively, at least one circuit for simulating the IR voltage and / or polarization voltage generated when the first secondary battery and the second secondary battery operating, etc. It can contain elements.

Here, the IR voltage means a voltage generated by the internal resistance of the secondary battery when the secondary battery is charged or discharged.

The voltage of the secondary battery is higher than the open voltage while the secondary battery is charged due to the IR voltage, and vice versa while the secondary battery is discharged.

According to one aspect, the first and / or second impedance element may include at least one resistor, at least one capacitor, at least one inductor, and combinations thereof.

According to another aspect, the first and / or second impedance element may include an RC circuit in which a resistor and a capacitor are connected in parallel, and a resistor in series with the same.

According to another aspect, the first and / or second impedance element includes a plurality of RC circuits in which a resistor and a capacitor are connected in parallel, and the plurality of RC circuits may be connected in series and / or in parallel.

Preferably, the first open voltage component and the first impedance element may be connected in series. Similarly, the second open voltage component and the second impedance element may be connected in series.

Preferably, the control unit is configured to obtain a first impedance voltage formed by the first impedance element by using a first impedance voltage calculation equation derived from a connection characteristic and an electrical characteristic value of a circuit element included in the first impedance element. You can decide.

Similarly, the control unit is configured to obtain a second impedance voltage formed by the second impedance element using a second impedance voltage calculation formula derived from a connection characteristic and an electrical characteristic value of a circuit element included in the second impedance element. You can decide.

The electrical characteristic value of each circuit element is determined by the type of the circuit element, and may be any one of a resistance value, a capacitance value, and an inductance value.

In the present invention, the operating current is equal to the sum of the first current flowing through the first circuit unit and the second current flowing through the second circuit unit.

Preferably, the control unit may determine the first current and the second current, respectively, by using a first current distribution equation and a second current distribution equation derived from the circuit model.

Preferably, the first current equation may include, as an input variable, the first and second open voltages, the first and impedance voltages, and the operating current. Similarly, the second current equation may include, as an input variable, the first and second open voltages, the first and impedance voltages, and the operating current.

According to one aspect, when the first impedance element includes a series resistance, the first impedance voltage may be determined by the voltage formed by the circuit elements other than the series resistance.

Similarly, when the second impedance element includes a series resistance, the second impedance voltage may be determined by the voltage formed by the circuit elements other than the series resistance.

Preferably, the control unit may update the first charging state by integrating the first current over time. Similarly, the control unit may time update the second charging state by integrating the second current over time.

The control unit may be a battery management system (BMS) that may be electrically coupled with a secondary battery or may be a control element included in the battery management system.

The battery management system may mean a system called BMS in the technical field to which the present invention belongs, but any system that performs at least one function described in the present invention from a functional point of view may be a category of the battery management system. Can be included.

The battery management system may include the circuit model as a software algorithm executable by a processor. As an example, the circuit model may be written as program code, stored in a memory device, and executed by the processor.

The above technical problem of the present invention can also be achieved by a voltage estimation method of a hybrid secondary battery.

According to one aspect, the method of estimating the voltage of the hybrid secondary battery, a method of estimating the voltage of the hybrid secondary battery comprising a first secondary battery and a second secondary battery having different electrochemical characteristics and connected in parallel to each other,

Measuring an operating current of the hybrid secondary battery and determining first and second currents flowing through the first circuit unit and the second circuit unit, respectively, from first and second current distribution equations derived from the circuit model. And updating the first charge state of the first secondary battery and the second charge state of the secondary battery by integrating the first current and the second current; Determining a first open voltage and a second open voltage respectively corresponding to the second charged state; and converting the first current into a first impedance voltage formed by a first impedance element included in the first circuit unit. Time updating using the second current, and updating the second impedance voltage formed by the second impedance element included in the second circuit unit using the second current. Using a second open-circuit voltage and the time that the updated first and second impedance voltage and the operating current, and a step of estimating the voltage of the secondary cell hybrid.

The technical problem of the present invention can also be achieved by a computer-readable recording medium in which a method for estimating the voltage of a hybrid secondary battery according to the present invention is programmed.

According to an aspect of the present invention, the voltage of the hybrid secondary battery can be estimated simply by using the voltage equation derived from the operating current and the circuit model.

According to another aspect of the present invention, the voltage of the hybrid secondary battery having the voltage profile including the inflection point can be estimated accurately, especially in the state of charge near the inflection point.

According to another aspect of the present invention, since the voltage of the hybrid secondary battery can be reliably estimated, it is possible to provide a hybrid secondary battery whose combination is optimized for the purpose of using the secondary battery.

According to another aspect of the present invention, it is possible to provide a secondary battery that can meet various specifications required for new applications, such as electric vehicles or power storage devices.

The following drawings appended hereto illustrate one embodiment of the present invention, and together with the following description serve to further understand the spirit of the present invention, the present invention is limited only to those described in such drawings. It should not be interpreted.

1 is a block diagram schematically illustrating a configuration of an apparatus for estimating a voltage of a hybrid secondary battery according to an exemplary embodiment of the present invention.

2 is a conceptual diagram illustrating a case where the first secondary battery and the second secondary battery are packaged in different packaging materials and connected in parallel.

3 is a conceptual diagram illustrating a case where the first secondary battery and the second secondary battery are packaged together in the same packaging material and connected in parallel in the packaging material.

4 is a circuit diagram illustrating a circuit model according to an embodiment of the present invention.

5 is a flowchart sequentially illustrating a voltage estimating method of a hybrid secondary battery according to an exemplary embodiment of the present invention.

6 is a graph showing the results of the voltage estimation experiment conducted to verify the effect of the voltage estimation method of the hybrid secondary battery according to the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own applications. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one embodiment of the present invention and do not represent all of the technical idea of the present invention, various equivalents that may be substituted for them in the present invention point of view. It should be understood that there may be variations and examples.

1 is a block diagram schematically illustrating a configuration of a voltage estimating apparatus 100 of a hybrid secondary battery according to an exemplary embodiment of the present disclosure.

As shown in the drawing, the voltage estimating apparatus 100 includes a sensor unit 120 and a control unit 130, and is electrically connected to the hybrid secondary battery 110 to provide a voltage of the hybrid secondary battery 110. Estimate

The hybrid secondary battery 110 includes at least first and second secondary batteries connected in parallel to each other and having different electrochemical characteristics.

The electrochemical characteristics, the maximum / minimum charge rate or maximum / minimum discharge rate of the battery, the low rate discharge characteristics, high rate discharge characteristics, the maximum / minimum charging rate or maximum / At least one selected from among a minimum discharge rate, a charge or discharge profile, a resistance profile according to a state of charge change, an open voltage profile according to a state of charge change, and a dQ / dV distribution indicating a capacity characteristic of the battery with respect to the voltage.

Preferably, the first and second secondary batteries may be lithium secondary batteries in which an electrochemical reaction is caused by lithium ions. In this case, at least one selected from the type of the positive electrode material, the type of the negative electrode material, and the type of the electrolyte may be different in the first and second secondary batteries.

In one embodiment, the first secondary battery, as a positive electrode material, a general formula A [A _x M _y ] O _{2 + z} (A includes at least one element of Li, Na and K; M is Ni, Co At least one element selected from Mn, Ca, Mg, Al, Ti, Si, Fe, Mo, V, Zr, Zn, Cu, Al, Mo, Sc, Zr, Ru, and Cr; x ≥ 0, 1 ≦ x + y ≦ 2, −0.1 ≦ z ≦ 2; the stoichiometric coefficients of the components included in x, y, z, and M may be selected from the following formulas. have.

Alternatively, the first secondary battery, as a cathode material, an alkali metal compound xLiM ¹ O _2- (1-x) Li ₂ M ² O ₃ disclosed in US 6,677,082, US 6,680,143, etc. (M ¹ is an average oxidation state. At least one element having 3; M ² comprises at least one element having an average oxidation state of 4; 0 ≦ x ≦ 1).

In addition, the second secondary battery, as a positive electrode material, a general formula Li _a M ¹ _x Fe _1-x M ² _y P _1-y M ³ _z O _4- z (M ¹ is Ti, Si, Mn, Co, At least one element selected from Fe, V, Cr, Mo, Ni, Nd, Mg and Al; M ² is Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Mg, Al At least one element selected from As, Sb, Si, Ge, V and S; M ³ comprises a halogenated element optionally comprising F; 0 <a ≤ 2, 0 ≤ x ≤ 1, 0 ≤ y <1, 0 <z <1; the stoichiometric coefficients of the components contained in a, x, y, z, M ¹ , M ² , and M ³ are chosen so that the compound maintains electrical neutrality, or Li ₃ M ₂ Lithium metal phosphate represented by (PO ₄ ) ₃ [M includes at least one element selected from Ti, Si, Mn, Fe, Co, V, Cr, Mo, Ni, Mg and Al].

Optionally, the positive electrode material included in the first and / or second secondary battery may include a coating layer. The coating layer includes a carbon layer or at least selected from the group consisting of Ti, Si, Mn, Co, Fe, V, Cr, Mo, Ni, Nd, Mg, Al, As, Sb, Si, Ge, V and S It may include an oxide layer or fluoride layer containing one or more elements.

In addition, the first and second secondary batteries may include different kinds of negative electrode materials in the negative electrode in order to have different electrochemical characteristics. The negative electrode material may include a carbon material, lithium metal, silicon, tin, or the like, or may also include a metal oxide such as TiO ₂ and SnO ₂ having a potential of less than 2V. As the carbon material, both low crystalline carbon and high crystalline carbon may be used. Soft crystalline carbon and hard carbon are typical low crystalline carbon, and high crystalline carbon is natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch High temperature firing such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum derived cokes, and tar pitch derived cokes Carbon is representative.

In addition, the first and / or second secondary battery may include different kinds of electrolytes to have different electrochemical characteristics, and the electrolytes may include salts having a structure such as A ⁺ B ^−. can do. Here, A ⁺ includes an ion composed of an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ or a combination thereof. And B ^- is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 - _{^{, AsF 6 -, BF 2 C}} 2 O 4 -, BC 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) _{^{5 PF -, (CF 3)}} 6 P -, CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N _{^{-, CF 3 CF 2 (CF}} 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO _{^{3 -, CF 3 CO 2 -}} , CH 3 CO 2 -, SCN ^- comprises one or more anions selected from the group consisting of ^- and _{(CF 3 CF 2 SO 2)} 2 N.

In addition, the electrolyte may include an organic solvent. As the organic solvent, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) ), Dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (N-methyl 2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone or mixtures thereof may be used.

In the present invention, if the first secondary battery and the second secondary battery is different in the electrochemical characteristics and connected in parallel with each other, the configuration is determined by the package form of each secondary battery and the number of unit cells constituting each secondary battery It is not limited.

In addition, the first secondary battery and the second secondary battery are understood to include a plurality of battery elements, such as a unit cell, a module including a plurality of unit cells, a pack including a plurality of modules, and the like. shall.

According to one aspect, the first secondary battery and the second secondary battery, as shown in FIG. 2 may be an independent battery packaged in different packaging materials, as shown in Figure 3 in one packaging material It may be packaged together.

As an example, the first and second secondary batteries may be different types of lithium secondary batteries individually packaged in flexible pouch packaging materials. Alternatively, the first and second secondary batteries may be different types of lithium secondary batteries packaged together in one pouch packaging material.

In addition, when different types of first and second unit cells are alternately stacked and connected in parallel in one packaging material, the groups of the first and second unit cells alternately stacked and the groups of the second unit cells may also be the first secondary battery and the first battery. It can be regarded as a secondary battery.

The first unit cell and the second unit cell include at least a positive electrode plate and a negative electrode plate, and a separator interposed therebetween. The first unit cell and the second unit cell have different electrochemical characteristics. To this end, the positive electrode plates and / or negative electrode plates of the first unit cell and the second unit cell may include different active material coating layers.

According to another aspect, the first secondary battery and the second secondary battery, at least one unit cell having a negative electrode / separator / anode as a minimum unit, or at least two or more unit cells are connected in series and / or parallel And an assembly of stacked unit cells.

According to another aspect, the first secondary battery may include a secondary battery module in which a plurality of secondary batteries having first electrochemical characteristics individually packaged are connected in series and / or in parallel. Similarly, the second secondary battery may include a secondary battery module in which a plurality of secondary batteries having individually packaged second electrochemical characteristics are connected in series and / or in parallel.

The secondary battery 110 may be electrically connected to the load 140. The load 140 is included in various electric driving apparatuses, and means an energy consuming apparatus included in the electric driving apparatus operated by electric energy supplied when the secondary battery 110 is discharged.

The electric drive device may include, but are not limited to, an electric drive mobile device such as an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), or an electric bicycle (E-bike); Hand held devices such as mobile phones, smartphones or smart pads; Mobile computers such as laptop computers; Mobile imaging devices such as camcorders or digital cameras; It may be a large capacity power storage device (ESS) used in a power grid or an uninterruptible power supply.

The load may be a rotary power device such as a motor, a power converter such as an inverter, or the like as a non-limiting example, but the present invention is not limited by the type of load.

The voltage estimating apparatus 100 may further include a storage unit 160 selectively. The storage unit 160 is not particularly limited as long as it is a storage medium capable of recording and erasing information. As an example, the storage unit 160 may be a RAM, a ROM, a register, a hard disk, an optical recording medium, or a magnetic recording medium. The storage unit 160 may also be connected with the control unit 130 via, for example, a data bus so as to be accessible by the control unit 130. The storage unit 160 also stores and / or updates and / or erases and / or programs containing various control logics performed by the control unit 130 and / or data generated when the control logic is executed. send. The storage unit 160 may be logically divided into two or more, and is not limited to being included in the control unit 130.

The voltage estimating apparatus 100 may further optionally further include a display unit 150. The display unit 150 is not particularly limited as long as it can display the information generated by the control unit 130 in a graphic interface. As an example, the display unit 150 may be a liquid crystal display, an LED display, an OLED display, an E-INK display, a flexible display, or the like. The display unit 150 may be directly or indirectly connected to the control unit 130. When the latter method is adopted, the display unit 150 may be located in an area physically separated from the area in which the control unit 130 is located. A third control unit (not shown) is interposed between the display unit 150 and the control unit 130 so that the third control unit can express the display unit 150 from the control unit 130. The information may be provided and displayed on the display unit 150. To this end, the third control unit and the control unit 130 may be connected through a communication interface.

The sensor unit 120, under the control of the control unit 130, repeatedly measures the operating current I of the hybrid secondary battery 110 at a time interval and controls the measured operating current I. And output to 130. Here, the operating current I means the charging current or the discharge current of the hybrid secondary battery 110.

Optionally, the sensor unit 120 may measure the voltage of the hybrid secondary battery 110 under the control of the control unit 130, and output the measured voltage to the control unit 130. This voltage measurement is intended to set initial conditions of some variables used in the circuit model, which will be described later.

The sensor unit 120 may include a voltage measuring unit and a current measuring unit. The voltage measuring unit may be configured as a circuit for measuring the voltage of the hybrid secondary battery 110 based on a reference potential. The current measuring unit may be formed of a sense resistor installed in a line through which a charging current or a discharge current flows. However, the present invention is not limited by the specific configurations of the voltage measuring unit and the current measuring unit.

The voltage measuring unit and the current measuring unit may be included in one sensor unit 120, but may be physically separated from each other. In this case, the sensor unit 120 should be understood as a concept including a voltage measuring unit and a current measuring unit separated from each other.

The control unit 130 is a component capable of executing at least one or more control logics necessary for estimating the voltage of the hybrid secondary battery 110. As a non-limiting example, the control unit 130 may use a hybrid secondary battery (eg, a pre-defined circuit model). The voltage of 110 may be estimated.

In a preferred embodiment, the circuit model may include at least one circuit unit connected in series and / or in parallel to simulate a voltage change of the hybrid secondary battery 110.

4 is a circuit diagram illustrating a circuit model 200 according to an embodiment of the present invention.

Referring to FIG. 4, the circuit model 200 includes a first circuit unit 210 and a second circuit unit 220 connected in parallel to model a voltage change of the hybrid secondary battery 110.

The first circuit unit 210 is for simulating the voltage change of the first secondary battery, and includes a first open voltage element 210a and a first impedance element 210b, which are connected in series.

Similarly, the second circuit unit 22, for simulating the voltage change of the second secondary battery, includes a second open voltage element 220a and an optional second impedance element 220b connected in series. do.

When the hybrid secondary battery 110 is charged or discharged, a first open voltage whose magnitude varies depending on a first charged state z _c1 of the first secondary battery at both ends of the first open voltage element 210a. (OCV _c1 (z _c1 )) is formed, and at both ends of the second open voltage element 220a, a second open voltage (OCV _c2 ) whose size is changed by a second charged state z _c2 of the second secondary battery. (z _c2 )) is formed.

Preferably, the first open voltage OCV _c1 (z _c1 ) may be determined from a predefined correlation between the first charged state z _c1 and the open voltage of the first secondary battery corresponding thereto. .

Similarly, the second open voltage OCV _c2 (z _c2 ) may be determined from a predefined correlation between the second charged state z _c2 and the open voltage of the second secondary battery corresponding thereto. .

Preferably, the predefined correlation may be obtained from an open voltage profile measured according to a change in state of charge.

In one embodiment, the predefined correlation may be a lookup table capable of mapping an open voltage corresponding to each state of charge. Such a lookup table may be obtained by using open voltage data measured for each state of charge of the first and second secondary batteries. Here, the open voltage data can be obtained through an experiment.

In another embodiment, the predefined correlation may be a lookup function that includes a state of charge and an open voltage as input and output variables, respectively. Such a lookup function may be obtained by numerically analyzing coordinate data included in an open voltage profile measured for each state of charge of the first and second secondary batteries.

Preferably, the first impedance element 210b and the second impedance element 220b each simulate an IR voltage and / or a polarization voltage generated when the first secondary battery and the second secondary battery operate. To include at least one circuit element.

Here, the IR voltage means a voltage generated by the internal resistance of the secondary battery when the secondary battery is charged or discharged.

The voltage of the secondary battery is higher than the open voltage while the secondary battery is charged due to the IR voltage, and vice versa while the secondary battery is discharged.

The number and type of circuit elements included in the first impedance element 210b and the second impedance element 220b, and the connection relationship between the circuit elements are determined by the electrochemical properties of the first secondary battery and the second secondary battery. It can be determined according to, preferably through trial and error (trial & error) through the AC impedance measurement experiment. In addition, the electrical characteristic value of each circuit element may be adjusted to an optimal value by determining an approximation value through an AC impedance measurement experiment and then tuning to minimize the error between the voltage estimated by the present invention and the voltage measured under precise experimental conditions. Can be.

According to an aspect, the first impedance element 210b and / or the second impedance element 220b may include at least one resistor, at least one capacitor, at least one inductor, and a selective combination thereof. . When the first impedance element 210b and / or the second impedance element 220b includes a plurality of circuit elements, each circuit element may be connected in series and / or in parallel with another circuit element.

In a specific embodiment, the first impedance element 210b may include at least one RC circuit RC _{n, c1} connected in parallel with a resistor and a capacitor, and a resistor R _{0, c1} connected in series with the resistor. Here, n is an index indicating the nth RC circuit.

Similarly, the second impedance element 220b may include at least one RC circuit RC _{m, c2} connected in parallel with a resistor and a capacitor, and a resistor R _{0, c2} connected in series with the second impedance element 220b. Here, m is an index indicating the m-th RC circuit.

The RC circuits RC _{n, c1} , RC _{m, and c2} correspond to circuit elements for simulating polarization voltages generated when the first secondary battery and the second secondary battery operate. The number of the RC circuit (RC _{n, c1,} RC _{m ,, c2)} a number of electric characteristic value of the device resistance and the capacitor, and the RC circuit (RC _{n, c1,} RC _{m ,, c2)} is included in the It may vary depending on the polarization voltage characteristics of the first secondary battery and the second secondary battery. In addition, if the polarization voltages of the first secondary battery and the second secondary battery are negligibly small, the RC circuits RC _{n, c1} , RC _{m, and c2} may be omitted.

The series resistors R _{0, c 1} , R _{0, c} 2 correspond to circuit elements for simulating IR voltages generated when the first secondary battery and the second secondary battery operate. The electrical characteristic values of the series resistors R _{0, c 1} , R _{0, c 2} may vary according to IR voltage characteristics. In addition, the number of series resistors R _{0, c 1} , R _{0, c} 2 may be two or more as necessary. If the IR voltages of the first and second secondary batteries are negligibly small, the series resistors R _{0, c 1} , R _{0, c} 2 may be omitted.

Preferably, the control unit 130 is formed by the first impedance element using a first impedance voltage calculation formula derived from the connection characteristic and electrical characteristic values of the circuit elements included in the first impedance element 210b. The first impedance voltage _{Vi, c1} may be determined. Similarly, the control unit 130 may use the second impedance element 220b by using a second impedance voltage equation derived from a connection characteristic and an electrical characteristic value of a circuit element included in the second impedance element 220b. It is possible to determine the second impedance voltage (V _{i, c2} ) formed by. The electrical characteristic value of each circuit element is determined by the type of the circuit element, and may be any one of a resistance value, a capacitance value, and an inductance value.

The first impedance voltage _{Vi, c1} may be determined as a sum of voltages formed by series circuit elements included in the first impedance element 210b, and the second impedance voltage _{Vi, c2} may be determined. Is determined by the sum of the voltages formed by the series circuit elements included in the second impedance element 220b.

Preferably, when the first impedance element 210b and the second impedance element 220b include a series resistance, the first impedance voltage _Vi and _c1 and the second impedance voltage _{Vi and c2 are provided.} ) May not consider the voltage formed by the series resistance.

When the first impedance element 210b and / or the second impedance element 220b includes at least one RC circuit, the voltage formed by each RC circuit is a discrete time equation such as Equation (1) below. Can be determined by. The following discrete time equations are known in the art, so specific derivation steps are omitted.

In Equation (1), k denotes a time index, Δt denotes a time interval between a time index k and a time index k + 1, and R and C respectively represent a resistance value of a resistor included in an RC circuit and a capacitance of a capacitor. Value, and I _RC [k] represents the current flowing in the RC circuit.

The operating current I is equal to the sum of the first current I _c1 flowing through the first circuit unit 210 and the second current I _c2 flowing through the second circuit unit 220. Therefore, the relationship between the operating current I, the first current I _c1 , and the second current I _c2 may be represented by a discrete time equation such as the following Equation (2).

In Equation (2), when the hybrid secondary battery 110 is being charged, I [k], I _c1 [k] and I _c2 [k] have positive values. Conversely, when the hybrid secondary battery 110 is being discharged, I [k], I _c1 [k] and I _c2 [k] have negative values.

The control unit 130 may use the first current I _c1 [k] and the second current I _c2 using a first current distribution equation and a second current distribution equation derived from the circuit model 200. [k]) can be determined respectively.

The process of deriving the first current distribution equation and the second current distribution equation in the form of a discrete time equation is as follows.

First, at the time index k, the first current and the second current can be expressed by the following equations (3) and (4).

In the above formula, V [k] represents the voltage of the hybrid secondary battery.

Is a sum of voltages formed by at least one RC circuit RC _{n, c1} included in the first circuit unit 210, and V ⁿ _{RC, c1} represents a voltage formed in the nth RC circuit. n is a natural number between 1 and p, and the minimum value of p is 1. Similarly,

Is a sum of voltages formed by at least one RC circuit RC _{m, c2} included in the second circuit unit 220, and V ^m _{RC, c2} represents a voltage formed in the m-th RC circuit. m is a natural number between 1 and q, and the minimum value of q is 1. z _c1 [k] and z _c2 [k] indicate the state of charge of the first secondary battery and the second secondary battery, respectively. R _{0, c 1} and R _{0, c} 2 represent resistance values of series resistors included in the first circuit unit 210 and the second circuit unit 220, respectively.

Substituting Equations (3) and (4) into Equation (2) and arranging the voltage V [k] of the hybrid secondary battery, a voltage equation as in Equation (5) can be obtained.

Then, by substituting Equation (5) into Equations (3) and (4), respectively, the first current distribution equation (6) and the second current distribution equation (7) can be obtained as follows.

Equations (6) and (7) can be used to quantitatively determine the magnitude of the current when the operating current I of the hybrid secondary battery flows separately into the first secondary battery and the second secondary battery.

In addition, Equations (6) and (7) calculate the state of charge of the first secondary battery (z _c1 [k]) and the state of charge of the second secondary battery (z _c2 [k]) by the following formulas (8) and (9). ) Can be used to update the time according to the ampere counting method.

In the above formulas (8) and (9), Q _c1 and Q _c2 represent the capacity of the first secondary battery and the second secondary battery, respectively. Δt represents the time interval between time indices k and k + 1.

In the above formulas (6) and (7),

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May be determined using the open voltage profiles of the first secondary battery and the second secondary battery,

and

May be determined using Equation (1), the first current (I _c1 [k]) and the second current (I _c2 [k]).

On the other hand, in order for the control unit 130 to estimate the voltage of the hybrid secondary battery using the above-described equations represented by the discrete time equation, the state of charge (z _c1 [k]) of the first secondary battery, the second secondary battery State of charge (z _c2 [k]), the voltage formed by the at least one RC circuit included in the first circuit unit 210

And a voltage formed by at least one RC circuit included in the second circuit unit 220.

It is desirable to set initial conditions for.

In one embodiment, the control unit 130 may set an initial condition as shown in Equation 10, but the present invention is not necessarily limited thereto.

In the initial condition, V [0] is an operation start voltage of the secondary battery first measured by the sensor unit 120 when charging or discharging of the hybrid secondary battery is started, and approximately, charging or discharging of the secondary battery is approximately. Corresponds to the open voltage at the start. The operator OCV _c1 ^-1 is an inverse conversion operator of OCV _c1 (z _c1 [k]), which is an operator that converts the state of charge of the first secondary battery to an open voltage, and the operator OCV _c2 ^-1 opens the state of charge of the second secondary battery. This is the inverse conversion operator of OCV _c2 (z _c2 [k]), an operator that converts to voltage. The calculation results of the operator OCV _c1 ^-1 and the operator OCV _c2 ^-1 can be determined using the open voltage profile of the first secondary battery and the open voltage profile of the second secondary battery obtained through experiments.

Hereinafter, referring to FIG. 5, a method of estimating the voltage of the secondary battery whenever the time Δt elapses from immediately after the charging or discharging of the hybrid secondary battery is started will be described in more detail. do.

First, in step S10, the control unit 130 monitors the direction and magnitude of the operating current flowing through the hybrid secondary battery 110 using the sensor unit 120 to operate the secondary battery (charge or discharge). Determine if it is started.

If it is determined that the operation of the secondary battery 110 is started, the control unit 130 initializes the time index k to 0 in step S20.

Then, the control unit 130, at step S30, through the sensor 120, V [0] corresponding to the operation start voltage of the secondary battery 110 and I [0] corresponding to the operation start current. Measure and store in the storage unit 160 (S30).

The control unit 130, after measuring and storing V [0] and I [0], initializes the voltage of the hybrid secondary battery using the equations derived from the circuit model at step S40 as follows. Set the condition.

The control unit 130 may refer to electrical characteristic values of various circuit elements included in the first circuit unit 210 and the second circuit unit 210 when the initial condition is set. For this purpose, the electrical characteristic values are preferably stored in the storage unit 160 in advance. The electrical characteristic values of each circuit element can be stored as fixed values or as values that can be varied. When the electrical characteristic value is stored as a variable value, the electrical characteristic value may vary according to the state of charge, temperature, capacity deterioration, etc. of the hybrid secondary battery.

Subsequently, the control unit 130 uses the first current distribution equation (6) and the second current distribution equation (7) in step S50 as follows to describe the first current I _c1 [0] and the second current I _c2. Determine [0]. At this time, the initial conditions set in the step S40, the predefined open voltage profile for the first secondary battery and the second secondary battery OCV _c1 [z _c1 ] and OCV _c2 [z _c2 ], and the first Electrical characteristic values of each circuit element included in the circuit unit 210 and the second circuit unit 220 are used.

Then, the control unit 130 increases the time index k by one in step S60. Then, the control unit 130, in step S70, the first current I _c1 [0] and the second current I _c2 [0] determined in the step S50, equation (1), equation (8) and equation (9) is formed by each RC circuit included in the state of charge z _c1 of the first secondary battery, the state of charge z _c2 of the second secondary battery, the first circuit unit and the second circuit unit as follows. Perform a time update on the voltage. Hereinafter, four variables that are time updated will be referred to as input variables.

(n = 1,2,…, p)

(m = 1,2,…, q)

In the above formula, R _{n, c1} and C _{n, c1} represent the resistance value and capacitance value of the nth RC circuit included in the first circuit unit, respectively. Similarly, R _{m, c 2} and C _{m, c} 2 represent the resistance value and capacitance value of the m-th RC circuit included in the second circuit unit, respectively. n and m may be one or more natural numbers, and if the RC circuit is not included in the first circuit unit and / or the second circuit unit, the time update of the voltage formed by the RC circuit may be omitted.

Subsequently, the control unit 130 performs a measurement update on the operating current by measuring the operating current of the hybrid secondary battery through the sensor unit 120 in step S80.

Then, in step S90, the control unit 130 substitutes the time updated input variable and the measured updated operating current into equation (5) corresponding to the voltage equation to estimate the voltage of the hybrid secondary battery as follows. .

In the above formula,

And

May be determined using a predefined open voltage profile for the first secondary battery and the second secondary battery. Also,

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Can be determined using the time updated RC circuit voltage. I [1] is the operating current measured and updated by the sensor unit 120. The series resistance values R _{0, c1} , R _{0, c2 of} the first and second circuit units are predetermined through experiments and are fixed or variable values.

When the voltage estimation using Equation (5) is completed, the control unit 130 determines whether Δt corresponding to the time update period for the input variable has elapsed in step S100.

If it is determined that the time Δt has elapsed, the control unit 130 monitors the operating current of the secondary battery through the sensor unit 120 in step S110 to determine whether the secondary battery is being charged or discharged.

If it is determined that the charging or discharging of the secondary battery continues, the control unit 130 shifts the process to step S50 so as to extend from the time update step of the first current and the second current to the voltage estimation step of the hybrid secondary battery. Repeat once again.

Such a recursive algorithm is repeated whenever the time update period Δt of the input variable elapses while the secondary battery is being charged or discharged.

On the other hand, if it is determined in step S110 that the charging or discharging is substantially terminated, the control unit 130 determines whether sufficient time has elapsed after the charging or discharging is finished.

Here, sufficient time means the time required until the voltage of the hybrid secondary battery stabilizes to a voltage level corresponding to the open voltage.

If it is determined that sufficient time has elapsed after the charging or discharging ends, the control unit 130 ends the voltage estimation process of the hybrid secondary battery using the circuit model.

The control unit 130 may store the result determined in each step in the storage unit 160, transmit it to another external control unit, or display the result via the display unit 150 in a graphic interface. Here, the graphic interface includes a character, a picture, a graphic, or a combination thereof.

In addition, the control unit 130 may use the voltage of the hybrid secondary battery estimated using the circuit model to control charging or discharging of the secondary battery. In addition, the control unit 130 may refer to determining the state of charge or capacity decay of the secondary battery using the estimated voltage of the hybrid secondary battery. In this case, the control unit 130 may be included as part of a battery management system that generally controls the operation of the secondary battery.

Alternatively, the control unit 130 may transmit the estimated voltage of the hybrid secondary battery to a control unit in charge of controlling the secondary battery. For example, when the hybrid secondary battery is mounted in the electric vehicle or the hybrid vehicle, the control unit 130 may transmit the estimated voltage of the hybrid secondary battery to the central control device of the vehicle.

The control unit 130 selectively selects a processor, an application-specific integrated circuit (ASIC), another chipset, a logic circuit, a register, a communication modem, a data processing device, or the like, which are known in the art, to execute the various control logics described above. It may include. In addition, when the control logic is implemented in software, the control unit 130 may be implemented as a set of program modules. In this case, the program module may be stored in a memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor through various well known computer components. In addition, the memory may be included in the storage unit 160 of the present invention. In addition, the memory refers to a device that stores information regardless of the type of device, and does not refer to a specific memory device.

In addition, it is apparent that the control logics of the control unit 130 may configure a process of the method for estimating the voltage of the hybrid secondary battery according to the exemplary embodiment of the present invention.

In addition, at least one of various control logics of the control unit 130 may be combined, and the combined control logics may be written in a computer readable code system and stored in a computer readable recording medium. The recording medium is not particularly limited as long as it is accessible by a processor included in the computer. In one example, the recording medium includes at least one selected from the group consisting of a ROM, a RAM, a register, a CD-ROM, a magnetic tape, a hard disk, a floppy disk, and an optical data recording device. In addition, the code system may be modulated into a carrier signal to be included in a communication carrier at a specific point in time, and may be distributed and stored and executed in a networked computer. In addition, functional programs, code and code segments for implementing the combined control logics can be easily inferred by programmers in the art to which the present invention pertains.

Experimental Example

First, a 30-Ah capacity and pouch-type first lithium secondary battery including Li [Ni _x Mn _y Co _z ] O ₂ and a carbon material in a positive electrode and a negative electrode, and a LiFePO ₄ and a carbon material in a positive electrode and a negative electrode, respectively A 5 Lih capacity and a pouch type secondary lithium secondary battery were produced.

Then, the first lithium secondary battery and the second lithium secondary battery were connected in parallel to produce a hybrid secondary battery, and then loaded in the constant temperature chamber of the charge / discharge tester. Thereafter, while maintaining the temperature of the hybrid secondary battery at 25 degrees, the battery was discharged until the open voltage became 3.7 V and allowed to rest for a sufficient time. Thereafter, a pulse discharge experiment was conducted in which a short discharge was performed for several tens of seconds under a high rate discharge condition of 200 A.

6 is a graph showing the voltage of the hybrid secondary battery estimated according to the present invention according to the time change during the pulse discharge experiment.

Referring to FIG. 6, during the pulse discharge of the hybrid secondary battery, it may be confirmed that the waveform of the estimated voltage is substantially the same as the voltage waveform observed in the pulse discharge. In addition, it can be seen that the change pattern of the voltage estimated immediately after the end of the pulse discharge converges toward the open voltage substantially the same as the change pattern indicated by the actual voltage of the hybrid secondary battery. In addition, in the hybrid secondary battery manufactured in the experimental example, when the actual voltage change is observed, the inflection point occurs immediately after the end of the pulse discharge, it can be seen that the inflection point also appeared in the profile of the estimated voltage. Through these experimental results, the circuit model according to the present invention can reliably simulate the voltage of the hybrid secondary battery, and especially can effectively reliably simulate the voltage of the hybrid secondary battery even if the inflection point appears in the voltage change profile. It can be seen.

Although the present invention has been described above by means of limited embodiments and drawings, the present invention is not limited thereto and will be described below by the person skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible within the scope of the claims.

Explanation of the sign

100: hybrid secondary battery voltage estimation device

110: hybrid secondary battery 120: sensor unit

130: control unit 140: load

150: display unit 160: storage unit

Claims (16)

1. An apparatus for estimating the voltage of a hybrid secondary battery including a first secondary battery and a second secondary battery having different electrochemical characteristics and connected in parallel to each other,

   A sensor unit measuring an operating current of the hybrid secondary battery; And

   A first circuit unit that simulates a voltage change of the first secondary battery by a first open voltage element and optionally a first impedance element, and a second battery by a second open voltage element and optionally a second impedance element And a control unit for estimating the voltage of the hybrid secondary battery using the operating current and a voltage equation derived from a circuit model including a second circuit unit connected in parallel with the first circuit unit. A voltage estimating device for a hybrid secondary battery, characterized in that.
2. The method of claim 1,

   The first secondary battery and the second secondary battery is an independent battery, the voltage estimation device of the hybrid secondary battery, characterized in that packaged in different packaging materials or packaged together in one packaging material.
3. The method according to claim 1 or 2,

   At least one of the first secondary battery and the second secondary battery voltage estimation apparatus of the hybrid secondary battery, characterized in that it comprises a plurality of unit cells or a plurality of battery modules.
4. The method of claim 1, wherein the control unit,

   Determine a first open voltage formed by the first open voltage element from a first predefined correlation between the first charged state of the first secondary battery and the first open voltage,

   And a second open voltage formed by the second open voltage element is determined from a predefined second correlation between the second charged state of the second secondary battery and the second open voltage. Battery voltage estimation device.
5. The method of claim 4, wherein

   The first correlation may be a lookup table or a lookup function obtained from an open voltage profile according to a change in state of charge of the first secondary battery.

   The second correlation may be a look-up table or a look-up function obtained from an open voltage profile according to a change in state of charge of the second secondary battery.
6. The method of claim 1,

   And the first impedance element and the second impedance element include at least one resistor, at least one capacitor, at least one inductor, and a combination thereof.
7. The method of claim 6,

   And the first impedance element and the second impedance element include at least one RC circuit connected in parallel with a resistor and a capacitor, and a resistor connected in series with the resistor.
8. The method of claim 1,

   And the first open voltage element and the first impedance element, and the second open voltage element and the second impedance element are connected in series with each other.
9. The method of claim 1, wherein the control unit,

   A first impedance voltage formed by the first impedance element is determined by using a first impedance voltage calculation formula derived from a connection relationship of a circuit element included in the first impedance element and an electrical characteristic value.

   And a second impedance voltage formed by the second impedance element is determined using a second impedance voltage calculation formula derived from a connection relationship between a circuit element included in the second impedance element and an electrical characteristic value. Battery voltage estimation device.
10. The method of claim 1, wherein the control unit,

    Determine a first current and a second current flowing through the first circuit unit and the second circuit unit from the circuit model,

    Accumulate the first current and the second current, respectively, to time update the first charge state of the first secondary battery and the second charge state of the second secondary battery;

    A first impedance voltage formed by the first impedance element and a second formed by the second impedance element using the time-updated first and second charged states and the first and second currents; Time-impedance the impedance voltage,

    Determine a first open voltage of the first secondary battery and a second open voltage of the second secondary battery corresponding to the time-updated first charged state and the second charged state;

    Estimating a voltage of the hybrid secondary battery by substituting the determined first open voltage and the second open voltage, the time updated first impedance voltage and the second impedance voltage, and the measured operating current into the voltage equation. Voltage estimation device of a hybrid secondary battery, characterized in that.
11. The voltage of the hybrid secondary battery including the first secondary battery and the second secondary battery having different electrochemical characteristics and connected in parallel to each other is determined by a first open voltage element and optionally a first impedance element. A first circuit unit that simulates a change, and a second circuit unit that simulates a voltage change of the secondary battery by a second open voltage element and optionally a second impedance element and is connected in parallel with the first circuit unit. In the method for estimating using a circuit model,

    Measuring an operating current of the hybrid secondary battery;

    Determining a first current and a second current flowing through the first circuit unit and the second circuit unit, respectively, from the circuit model;

    Integrating the determined first current and second current, respectively, to time update the first charge state of the first secondary battery and the second charge state of the second secondary battery;

    A first impedance voltage formed by the first impedance element and a second formed by the second impedance element using the time-updated first and second charged states and the first and second currents; Time updating the impedance voltage;

    Determining a first open voltage of the first secondary battery and a second open voltage of the second secondary battery corresponding to the time updated first charge state and the second charge state; And

    The hybrid secondary battery is substituted with the determined first open voltage and the second open voltage, the time updated first impedance voltage and the second impedance voltage, and the measured operating current into a voltage equation derived from the circuit model. And estimating a voltage of the hybrid secondary battery.
12. The method of claim 11,

    Measuring an operation start voltage of the hybrid secondary battery; And

    And determining, as initial conditions, a state of charge of the first secondary battery and a state of charge of the second secondary battery corresponding to the operation start voltage.
13. The method of claim 11,

    And determining an initial condition for the first impedance voltage and the second impedance voltage.
14. The method of claim 11,

    Each of the first current and the second current includes the first opening voltage and the second opening voltage, the first impedance voltage and the second impedance voltage, and the operating current as input variables, respectively. The voltage estimation method of the hybrid secondary battery, characterized in that determined from the current distribution equation and the second current distribution equation.
15. An electric drive device comprising a voltage estimating device of a hybrid secondary battery according to claim 1.
16. A computer-readable recording medium having programmed therein a voltage estimation method of a hybrid secondary battery according to claim 11.

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