KR20200102891A - Battery management system, battery management method and battery pack - Google Patents

Abstract

Provided are a battery management system, a battery management method, and a battery pack. The battery management system separately sets a first process noise and a second process noise so that the ratio of the second process noise to the first process noise is greater than the reference ratio when estimated that a state of charge of a battery is within a nonlinear characteristic range. The first process noise is a value representing the reliability of a current integration model included in an extended Kalman filter. The second process noise is a value representing the reliability of an equivalent circuit model included in the extended Kalman filter.

Description

Battery management system, battery management method and battery pack {BATTERY MANAGEMENT SYSTEM, BATTERY MANAGEMENT METHOD AND BATTERY PACK}

The present invention relates to a battery management system, a battery management method, and a battery pack for estimating a state of charge of a battery by using an extended Kalmann filter.

This application is an application for claiming priority for Korean Patent Application No. 10-2019-0021449 filed on February 22, 2019, and all contents disclosed in the specification and drawings of the application are incorporated herein by reference.

Recently, as the demand for portable electronic products such as notebook computers, video cameras, and portable telephones has increased rapidly, and development of electric vehicles, energy storage batteries, robots, satellites, etc. is in full swing, high-performance batteries capable of repetitive charging and discharging have been developed. There is an active research on the Korean market.

Currently commercialized batteries include nickel cadmium batteries, nickel hydride batteries, nickel zinc batteries, and lithium batteries, among which lithium batteries have little memory effect compared to nickel-based batteries, so charging and discharging are free and self-discharge rate is very high. It is in the spotlight for its low energy density and high energy density.

The state of charge (SOC) of the battery represents the relative ratio of the current remaining capacity to the maximum capacity of the battery (i.e., the amount of charge when the battery is fully charged), and 0 to 1 or 0 to 100% It is usually expressed as a number in a range.

The state of charge is essential for the safe use of the battery. Ampere counting, which can be used for estimating the state of charge, is to periodically determine the state of charge of the battery by integrating the current value indicating the magnitude and direction of the current flowing through the battery every unit time (e.g., 0.01 seconds). This is the way. However, while current flows through the battery, the current measured by the current sensor is not completely the same as the actual current. For this reason, when estimating the state of charge of a battery using only amperage counting, the accuracy gradually decreases as time passes.

In addition to amperage counting, an extended Kalman filter using an Equivalent Circuit Model (ECM) designed to simulate the electrochemical characteristics of a battery is being used to estimate the state of charge of the battery. The extended Kalman filter can be said to be a probabilistic statistical algorithm that estimates the state of a specific system using measurable parameters.

The battery has linear characteristics or non-linear characteristics according to the state of charge of the battery. The linear characteristic refers to a characteristic in which the amount of change in voltage of the battery with respect to the unit change amount (eg, 0.1%) of the state of charge of the battery becomes less than a threshold value while the battery is being charged or discharged. On the other hand, the nonlinear characteristic refers to a characteristic in which a change in a voltage of a battery with respect to a unit change in a state of charge of a battery becomes greater than or equal to a threshold associated with the magnitude of the constant current while the battery is being charged or discharged. The inventors of the present invention have confirmed that in a state in which the state of charge of the battery is lowered to some extent, the nonlinear characteristic of the battery tends to be stronger as the state of charge of the battery approaches 0%.

By the way, in order to simplify the equivalent circuit model, the equivalent circuit model is generally designed to better simulate the linear characteristics rather than the nonlinear characteristics of the battery. Accordingly, when the state of charge of the battery is within a range in which the nonlinear characteristic is strongly exhibited, there is a disadvantage in that the difference between the state of charge of the battery estimated using the extended Kalman filter and the state of actual charge may not be ignored.

The present invention provides a battery management system and a battery management method capable of accurately estimating the state of charge of a battery even while the state of charge of the battery is within a range indicated by the nonlinear characteristics of the battery, and a battery pack including the battery management system. There is a purpose.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by examples of the present invention. In addition, it will be easily understood that the objects and advantages of the present invention can be realized by the means shown in the claims and combinations thereof.

A battery management system according to an aspect of the present invention includes: a sensing unit configured to output a sensing signal representing voltage and current of a battery per unit time; And a control unit operatively coupled to the sensing unit. The control unit estimates a state of charge of the battery based on the sensing signal for each unit time output by the sensing unit using an extended Kalman filter. The control unit may individually separate the first process noise and the second process noise so that a ratio of the second process noise to the first process noise is equal to a reference ratio when the estimated state of charge is out of a nonlinear characteristic range. Set. The control unit, when the estimated state of charge is within a nonlinear characteristic range, the first process noise and the second process noise so that a ratio of the second process noise to the first process noise is greater than the reference ratio. Set individually. The first process noise is a value representing the reliability of the current integration model included in the extended Kalman filter. The second process noise is a value representing the reliability of an equivalent circuit model included in the extended Kalman filter.

The nonlinear characteristic range may be between a predetermined lower limit and a predetermined upper limit.

When the estimated state of charge is out of the nonlinear characteristic range, the control unit sets the first process noise equal to a first predetermined reference value, and sets the second process noise equal to a second predetermined reference value. I can. A ratio of the second predetermined reference value to the first predetermined reference value may be the same as the reference ratio.

When the estimated state of charge is within the nonlinear characteristic range, the control unit sets the first process noise to a first value smaller than a first predetermined reference value, and sets the second process noise equal to a second predetermined reference value. Can be set. A ratio of the second predetermined reference value to the first predetermined reference value may be the same as the reference ratio.

When the estimated state of charge is within the nonlinear characteristic range, the control unit sets the first process noise equal to a first predetermined reference value, and sets the second process noise to a second value greater than a second predetermined reference value. Can be set to A ratio of the second predetermined reference value to the first predetermined reference value may be the same as the reference ratio.

When the estimated state of charge is within the non-linear characteristic range, the control unit sets the first process noise to a third value smaller than a first predetermined reference value, and sets the second process noise to be greater than a second predetermined reference value. It can be set to the fourth value. A ratio of the second predetermined reference value to the first predetermined reference value may be the same as the reference ratio.

The controller may obtain an upper limit value related to the maximum capacity of the battery from a lookup table in which a correspondence relationship between the maximum capacity and an upper limit value is recorded, using the maximum capacity of the battery as an index. The nonlinear characteristic range may be between a predetermined lower limit value and the obtained upper limit value.

When the estimated state of charge is within the nonlinear characteristic range, the control unit may determine a correction value based on a lookup table in which a correspondence relationship between the state of charge and a correction factor is recorded and a state of charge history of an interest period. The controller may determine the second value by summing the second predetermined reference value and the correction value. The interest period may be the most recent period in which the state of charge of the battery is continuously estimated to be within the nonlinear characteristic range.

A battery pack according to another aspect of the present invention includes the battery management system.

A battery management method according to another aspect of the present invention includes: estimating a state of charge of the battery based on a sensing signal for each unit time representing a voltage and a current of a battery, using an extended Kalman filter; Determining whether the estimated state of charge is within a nonlinear characteristic range; When the estimated state of charge is out of the nonlinear characteristic range, individually setting the first process noise and the second process noise such that a ratio of the second process noise to the first process noise is the same as a reference ratio. ; And when the estimated state of charge is within a nonlinear characteristic range, the first process noise and the second process noise are individually set so that a ratio of the second process noise to the first process noise is greater than the reference ratio. It includes the step of. The first process noise is a value representing the reliability of the current integration model included in the extended Kalman filter. The second process noise is a value representing the reliability of an equivalent circuit model included in the extended Kalman filter.

The method may further include obtaining an upper limit value associated with the maximum capacity of the battery from a lookup table in which a correspondence relationship between the maximum capacity and an upper limit value is recorded by using the maximum capacity of the battery as an index. The nonlinear characteristic range may be between a predetermined lower limit value and the obtained upper limit value.

According to at least one of the embodiments of the present invention, it is possible to accurately estimate the state of charge of the battery even while the state of charge of the battery is within the nonlinear characteristic range.

In addition, by adjusting the nonlinear characteristic range based on the maximum capacity of the battery that gradually decreases as the battery deteriorates, the state of charge of the battery can be more accurately estimated.

The effects of the present invention are not limited to the effects mentioned above, and other effects that are not mentioned will be clearly understood by those skilled in the art from the description of the claims.

The following drawings attached to the present specification illustrate one embodiment of the present invention, and serve to further understand the technical idea of the present invention together with the detailed description to be described later, so the present invention is limited to the matters described in such drawings. And should not be interpreted.
1 is a diagram showing an exemplary configuration of a battery pack according to an embodiment of the present invention.
2 is a diagram illustrating an exemplary circuit configuration visualizing an equivalent circuit model for a battery.
3 is a graph exemplarily showing a SOC-OCV curve related to a battery.
4 exemplarily shows a lookup table referred to in determining the range of nonlinear characteristics of a battery.
5 exemplarily shows a look-up table referenced to determine the first process noise and the second process noise.
6 is a flowchart illustrating a battery management method according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventors appropriately explain the concept of terms in order to explain their own invention in the best way. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all the technical spirit of the present invention, and thus various alternatives that can be substituted for them at the time of application It should be understood that there may be equivalents and variations.

Terms including an ordinal number, such as first and second, are used for the purpose of distinguishing one of various elements from the others, and are not used to limit the elements by such terms.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components unless specifically stated to the contrary. In addition, terms such as <control unit> described in the specification mean a unit that processes at least one function or operation, and may be implemented by hardware, software, or a combination of hardware and software.

In addition, throughout the specification, when a part is said to be "connected" to another part, it is not only "directly connected", but also "indirectly connected" with another element interposed therebetween. Include.

1 is a diagram illustrating an exemplary configuration of a battery pack according to an embodiment of the present invention, FIG. 2 exemplarily shows a circuit configuration visualizing an equivalent circuit model for a battery, and FIG. 3 is a battery 20 ) Is a graph showing an example SOC-OCV curve associated with.

Referring to FIG. 1, the battery pack 10 is for providing electric energy required for a power system 1 such as an electric vehicle, and includes a battery 20, a switch 30, and a battery management system 100. Include.

The battery 20 includes at least one battery cell. Each battery cell may be, for example, a lithium ion battery. Of course, the type of battery cell is not limited to the lithium ion battery, and is not particularly limited as long as it can be repeatedly charged and discharged. Each battery cell included in the battery 20 is electrically connected to other battery cells in series or parallel.

The switch 30 is installed in a current path for charging and discharging the battery 20. The control terminal of the switch 30 is provided to be electrically connected to the control unit 120. The switch 30 is turned on and off according to the duty ratio of the switching signal SS in response to the switching signal SS output by the controller 120.

The battery management system 100 is provided for management of the battery 20. The battery management system 100 is provided to be electrically connected to the positive terminal and the negative terminal of the battery 20 in order to periodically determine the SOC of the battery 20. The battery management system 100 includes a sensing unit 110, a control unit 120, a memory unit 130, and a communication unit 140.

The sensing unit 110 is configured to detect various parameters related to the SOC of the battery 20 (eg, voltage, current, temperature of the battery 20) per unit time. The sensing unit 110 includes a current sensor 111 and a voltage sensor 112. Hereinafter, it is assumed that the sensing unit 110 also includes a temperature sensor 113.

The current sensor 111 is provided to be electrically connected to the charge/discharge path of the battery 20. The current sensor 111 is configured to detect a current flowing through the battery 20 and to output a first sensing signal SI representing the detected current to the controller 120. A Hall effect sensor or a shunt resistor or the like may be used as the current sensor 111.

The voltage sensor 112 is provided to be electrically connected to the positive terminal and the negative terminal of the battery 20. The voltage sensor 112 detects a voltage across the battery 20 (that is, a potential difference between the positive terminal and the negative terminal of the battery 20), and controls a second sensing signal SV representing the detected voltage ( 120).

The temperature sensor 113 is configured to detect a temperature of an area within a predetermined distance from the battery 20 as the temperature of the battery 20 and output a third sensing signal ST indicating the detected temperature to the controller 120 do.

The control unit 120 is operatively coupled to the sensing unit 110, the memory unit 130, the communication unit 140, and the switch 30. In hardware, the control unit 120 includes application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), and microprocessors. It may be implemented using at least one of (microprocessors) and electrical units for performing other functions.

The controller 120 is configured to periodically receive a first sensing signal SI, a second sensing signal SV, and a third sensing signal ST output by the sensing unit 110. The control unit 120 uses an analog-to-digital converter (ADC) included in the control unit 120 to provide a first sensing signal SI, a second sensing signal SV, and Each of the third sensing signals ST may be converted into a digital current value, a voltage value, and a temperature value, and then stored in the memory unit 130. That is, at least one of current history, voltage history, temperature history, and SOC history of the battery 20 may be stored in the memory unit 130 for each unit market price.

The memory unit 130 is operatively coupled to the control unit 120. In the memory unit 130, programs and various data necessary for executing steps to be described later may be stored. The memory unit 130 is, for example, a flash memory type, a hard disk type, a solid state disk type, an SDD type, a multimedia card micro type (multimedia card micro type), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM) ) May include at least one type of storage medium.

The communication unit 140 may be communicatively coupled to an external device 2 included in the power system 1. The external device 2 may be, for example, an Electronic Control Unit (ECU). The communication unit 140 may receive a command message from the external device 2 and provide the received command message to the controller 130. The command message may be a message requesting activation of a specific function of the battery management system 100 (eg, SOC estimation, on/off control of the switch 30). The communication unit 140 may transmit a notification message from the control unit 130 to the external device 2. The notification message may be a message for informing the external device 2 of the result of a function executed by the controller 130 (eg, an estimated SOC). For example, the communication unit 140 may connect an external device 2 and a wired network such as a local area network (LAN), a controller area network (CAN), and a daisy chain, and/or a short-range wireless network such as Bluetooth, ZigBee, and Wi-Fi. Can communicate through.

The control unit 120 is configured to determine the maximum capacity of the battery 20. The maximum capacity represents the amount of electric charge that can currently be stored in the battery 20. That is, the maximum capacity is equal to the accumulated value of the current flowing while discharging the battery 20 until the SOC of which the SOC is 1 (=100%) becomes 0 (=0%). As the battery 20 deteriorates, the maximum capacity of the battery 20 gradually decreases. The capacity retention ratio is a term that can also be referred to as SOH (State Of Health), and the maximum capacity (that is, the initial maximum capacity) when the battery 2 is in its initial state (BOL: Beginning Of Life) is 100 When set to, indicates the ratio of the current maximum capacity of the battery 20.

For example, the controller 120 calculates the internal resistance of the battery 20, and then calculates the maximum capacity (or capacity retention rate) of the battery 20 based on the difference between the calculated internal resistance and the reference resistance. You can decide.

As another example, the controller 120 uses the following Equation 1, based on the SOC at each of two different times when the battery 20 is charged and discharged, and the accumulated current value for a period between the two times, The maximum capacity (or capacity retention rate) of the battery 20 may be determined. Let's say that the _first of the two viewpoints is t ₁ and the latter is t ₂ .

<Equation 1>

In Equation 1, Q _{max_BOL} is the initial maximum capacity, SOC ₁ is the SOC estimated at time t ₁ , SOC ₂ is the SOC estimated at time t ₂ , ΔSOC is the difference between SOC ₁ and SOC ₂ , i _t is the time t Current value representing the current detected at time t between ₁ and t ₂ , ΔC is the accumulated current value for the period between time t ₁ and time t ₂ , and Q _{max_deg} is the maximum of the battery 20 at time t ₂ The capacity, CRR _deg , represents the capacity maintenance rate of the battery 20 at the time point t ₂ . Q _{max_BOL} is a predetermined value and may be stored in advance in the memory unit 130.

Regarding Equation 1, when ΔSOC is too small, Q _{max_deg} may show a large difference from the actual value. Accordingly, the controller 120 may be configured to determine the maximum capacity (or capacity retention rate) of the battery 20 using Equation 1 only when ΔSOC is equal to or greater than a predetermined value (eg, 0.5). While ΔSOC is less than a predetermined value (eg, 0.5), the control unit 120 may utilize the last estimated maximum capacity (or capacity retention rate) as the current maximum capacity (or capacity retention rate).

From now on, an operation for estimating the SOC of the battery 20, which is executed by the control unit 120, will be described in detail.

First, a current integration model based on amperage counting may be expressed as Equation 2 below.

<Equation 2>

The symbols used in Equation 2 will be described as follows. Δt represents the length of time per cycle (ie, the unit time). k is a time index that increases by 1 each time the unit time elapses, and represents the number of periods that have elapsed from the time when a predetermined event occurs to the present. For example, the event may be that charging and discharging of the battery 20 is started while the voltage of the battery 20 is stabilized. The state in which the voltage of the battery 20 is stabilized may be a state in which the voltage of the battery 20 is kept constant as a result of no current flowing through the battery 20 for a long period of time. In this case, SOC _e [0] is determined from the SOC-OCV curve for the battery 20 using the open circuit voltage (OCV) of the battery 20 at the time the event occurs as an index. I can. The SOC-OCV curve is a data set representing a correspondence relationship between OCV and SOC of the battery 20 and may be previously stored in the memory unit 130.

In Equation 2, i[k+1] represents the current detected in the current period, and SOC _e [k] represents the previous SOC. The previous SOC means an SOC determined using a current integration model or an extended Kalman filter in the previous period (corresponding to the time index k) when the time index k+1 corresponds to the current period. SOC[k+1] is the current SOC determined from the current integration model. In Equation 2, i[k+1] may be replaced with i[k].

The extended Kalman filter is an algorithm for periodically updating the SOC of the battery 20 by additionally utilizing the equivalent circuit model 200 for the battery 20 in addition to the current integration model represented by Equation 2.

From now on, the equivalent circuit model 200 will be described. Referring to FIG. 2, the equivalent circuit model 200 includes an open circuit voltage source 210, an ohmic resistor R ₁ , and an RC pair 220.

The open-circuit voltage source 210 simulates an open-circuit voltage that is a potential difference between the positive electrode and the negative electrode of the battery 20 electrochemically stabilized over a long period of time. The open-circuit voltage output by the open-circuit voltage source 210 has a nonlinear functional relationship with the SOC of the battery 20. That is, OCV = f ₁ (SOC) and SOC = f ₂ (OCV), where f ₁ and f ₂ are inverse functions of each other. For example, referring to FIG. 3, 3.3 V = f ₁ (0.5) and 0.7 = f ₂ (3.47).

The open-circuit voltage (OCV) output by the open-circuit voltage source 210 may be predetermined for various SOCs and temperatures through a preliminary experiment.

The ohmic resistance R ₁ is related to the IR drop V ₁ of the battery 20. The IR drop refers to an instantaneous change in voltage across both ends of the battery 20 during charging and discharging of the battery 20. For example, the voltage of the battery 20 measured when charging the battery 20 in the no-load state is started is greater than the open-circuit voltage. As another example, the voltage of the battery 20 measured when discharging the battery 20 in the no-load state starts is less than the open-circuit voltage. The ohmic resistance (R ₁ ) may also be predetermined for various SOCs and temperatures through a pre-experiment.

The RC pair 220 outputs an over potential (may also be referred to as'polarization voltage') V ₂ induced by an electric double layer of the battery 20 and the like, and a resistance R ₂ ) and capacitance (C ₂ ). The over potential (V ₂ ) may also be referred to as a'polarization voltage'. The time constant of the RC pair 220 is a product of resistance (R ₂ ) and capacitance (C ₂ ), and may be predetermined for various charging states and temperatures through prior experiments. V _ecm represents the output voltage of the equivalent circuit model 200. V _ecm is equal to the sum of the open-circuit voltage (OCV) by the open-circuit voltage source 210, the IR drop (V ₁ ) by the ohmic resistance (R ₁ ), and the over potential (V ₂ ) by the RC pair 220 .

In the equivalent circuit model 200, the over potential of the current period may be expressed as Equation 3 below.

<Equation 3>

In Equation 3, R ₂ [k+1] is the resistance value of the second resistance R ₂ of the current period, τ[k+1] is the time constant of the RC pair 220, and V ₂ [k] is the previous period The over potential of, V ₂ [k+1] represents the over potential of the current period. In Equation 3, i[k+1] may be replaced with i[k]. The over potential V ₂ [0] at the time when the event occurs may be 0 V.

In the memory unit 130, a first lookup table in which a correspondence relationship between SOC, temperature value, and resistance R ₂ is recorded may be previously stored. The controller 120 may obtain R ₂ [k+1] from the first lookup table by using the temperature value of the current period and the SOC determined in the previous period as an index.

In the memory unit 130, a second lookup table in which a correspondence relationship between SOC, temperature value, and time constant is recorded may be stored in advance. The controller 120 may obtain τ[k+1] from the second lookup table by using the temperature value of the current period and the SOC determined in the previous period as an index.

The following Equation 4 is a first state equation related to the temporal update process of the extended Kalman filter, and is derived from a combination of Equations 2 and 3.

<Equation 4>

In Equation 4 and Equations 5 to 8 below, a symbol ^ indicated by a superscript is a symbol indicating a value predicted by a time update process. In addition, the symbol ^- indicated by a superscript is a symbol indicating that the value has been corrected by the measurement update process.

Equation 5 below is a second equation of state related to the temporal update process of the extended Kalman filter.

<Equation 5>

In Equation 5, P _k is the error corvariance matrix corrected in the previous period, Q _k is the process noise covariance matrix in the previous period, T is the transpose matrix operator, P ^- _{k+ 1} represents the error covariance matrix for the current period. At k=0, P ₀ =[ 1 0; It can be 0 1 ].

W1 _k is the first process noise of the previous period and is a positive number indicating the reliability of the current integration model. As the first process noise increases, the reliability of the current integration model decreases. As a result, the influence of the integrated current value (refer to Equation 2) on determining the SOC of the battery 20 is reduced. Conversely, as the first process noise decreases, the reliability of the integrated current value by amperage counting increases.

W2 _k is the second process noise of the previous period and is a positive number representing the reliability of the equivalent circuit model 200. As the second process noise increases, the reliability of the equivalent circuit model 200 decreases. As a result, the influence of the over potential (refer to Equation 3) on determining the SOC of the battery 20 is reduced. Conversely, as the second process noise decreases, the reliability of the equivalent circuit model 200 increases.

When the time update process using Equations 4 and 5 is completed, the controller 120 executes a measurement update process related to the extended Kalman filter.

Equation 6 below is a first observation equation associated with the measurement update process.

<Equation 6>

In Equation 6, K _k+1 represents the Kalman gain. R is a measurement noise covariance matrix and has predetermined components. H _k+1 is a system matrix, and is for reflecting a change trend of the open circuit voltage of the battery 20 according to the SOC-OCV curve when estimating the SOC of the battery 20. n is a predetermined positive integer (eg, 1).

Equation 7 below is a second observation equation related to the measurement update process.

<Equation 7>

In Equation 7, z _k+1 is the voltage of the battery 20 measured in the current period, and V _ecm [k+1] indicates the output voltage of the equivalent circuit model 200 in the current period. f ₁ (SOC[k+1]) represents the open-circuit voltage of the current period (refer to the description of Fig. 2). V ₁ [k+1] represents the voltage across the ohmic resistance (R ₁ ) in the current period, and the product of i[k+1] (or i[k]) and R ₁ [k+1] It can be the same.

R ₁ [k+1] is the resistance value of the ohmic resistance R ₁ of the current period. The controller 120 may determine R ₁ [k+1] based on the temperature value. In the memory unit 130, a third lookup table in which a correspondence relationship between SOC, temperature value, and ohmic resistance R ₁ is recorded may be previously stored. The controller 120 may obtain R ₁ [k+1] from the third lookup table by using the temperature value of the current period as an index. SOC[k+1] and V ₂ [k+1] obtained from Equation 4 are each corrected by Equation 7.

The following Equation 8 is a third observation equation related to the measurement update process.

<Equation 8>

In Equation 8, E represents an identity matrix. P _k+1 is obtained by correcting P ^- _k+1 calculated from Equation 5 by Equation 8.

Whenever the time index k increases by 1, the controller 120 periodically updates the SOC of the battery 20 by executing each process according to Equations 4 to 8 at least once.

The control unit 120 determines whether the SOC of the current cycle of the battery 20 is within a nonlinear characteristic range. The nonlinear characteristic range is a range in which the nonlinear characteristic of the battery 20 appears, and may be, for example, between a predetermined lower limit value (eg, 0%) and a predetermined upper limit value (eg, 10%).

Alternatively, the upper limit of the nonlinear characteristic range may be determined by the controller 120. Based on the maximum capacity of the current battery 20 (refer _{to'Q max_deg} ' in Equation 1) or capacity retention rate (refer _{to'CRR deg} ' in Equation 1), the control unit 120 _sets the upper limit of the nonlinear characteristic range. You can decide.

As illustrated in FIG. 4, in the memory unit 130, a fourth lookup table 400 in which a correspondence relationship between a maximum capacity (or capacity retention rate) and an upper limit value is recorded may be previously stored.

It is _{assumed that} the first to n maximum capacity values Q _{max_1} to Q _{max_n} and the first to n upper limit values U ₁ to U _n recorded in the fourth lookup table 400 are sequentially related to each other. When 1 ≤ i <j ≤ n, the i-th maximum capacity value (Q _{max_i} ) is related to the _i- th upper limit value (U _i ), and the j-th maximum capacity value (Q _{max_j} ) is related to the j-th upper limit value (U _j ). Related.

In the fourth lookup table 400, a relatively small maximum capacity (or capacity maintenance rate) may be associated with a relatively large upper limit value. For example, if the maximum capacity value i (Q _{max_i)} is the j it is larger than the maximum capacitance value (Q _{max_j),} the i-th maximum value (U _i) may be less than the j-th upper limit value (U _j).

The control unit 120 uses the current maximum capacity (or capacity retention rate) of the battery 20 as an index, and uses the current maximum capacity (or capacity retention rate) as an index, and the maximum capacity value (e.g. An upper limit value (eg, U _j ) associated with, Q _{max_j} ) may be obtained from the fourth lookup table 400.

Alternatively, the upper limit of the nonlinear characteristic range is affected by the temperature of the battery 20. For example, as the temperature of the battery 20 increases, the transport, diffusion, insertion, and desorption of chemical species involved in the electrochemical reaction of the battery 20 proceed smoothly, so that the range of nonlinear characteristics may be reduced. I can. Accordingly, it is possible to increase or decrease the upper limit value of the nonlinear characteristic range according to the rate of temperature change of the battery 20 for a predetermined time based on the current point in time. For example, if the temperature change rate is positive, the upper limit value is decreased (ie, the nonlinear characteristic range is reduced), and if the temperature change rate is negative, the upper limit value is increased (ie, the nonlinear characteristic range is expanded). The increase/decrease width of the upper limit value can be determined in advance through an experiment according to the temperature change rate of the battery 20, and a predefined increase/decrease factor according to the temperature change rate will be multiplied by the upper limit value obtained from the fourth lookup table 400 of FIG. I can.

When the SOC of the current cycle of the battery 20 is out of the nonlinear characteristic range, the control unit 120 includes the first process noise and the second process noise so that the ratio of the second process noise to the first process noise is the same as the reference ratio. You can set the noise. The reference ratio may be predetermined, such as 0.1. For example, the control unit 20 may set the first process noise to a first predetermined reference value (eg, 1.0) and the second process noise to a second predetermined reference value (eg, 0.1).

When the SOC of the current cycle of the battery 20 is within the nonlinear characteristic range, the control unit 120 includes the first process noise and the second process noise so that the ratio of the second process noise to the first process noise is greater than the reference ratio. Can be set. For example, the control unit 20 may set the first process noise to a first predetermined reference value and the second process noise to a first value (eg, 2.0) greater than the second predetermined reference value. As another example, the control unit 20 may set the first process noise to a second value smaller than the first predetermined reference value (Example 0.9) and the second process noise to be the same as the second predetermined reference value. As another example, the control unit 20 may set the first process noise to a third value (eg, 0.8) less than a first predetermined reference value, and set the second process noise to a fourth value (eg, It can be set to 0.2).

At least one of the first to fourth values may be a predetermined constant. Alternatively, the controller 120 may determine at least one of the first to fourth values whenever the SOC of the battery 20 is estimated to be within the nonlinear characteristic range.

The controller 120 may obtain the SOC history of the battery 20 for the period of interest from the memory unit 130. The period of interest may be the most recent period in which the SOC of the battery 20 is continuously estimated to be within the nonlinear characteristic range.

For example, suppose that the SOC of the battery 20 is estimated to be out of the nonlinear characteristic range in the x-1th cycle, but the SOC of the battery 20 continues to be within the nonlinear characteristic range from the xth cycle to the current cycle. In this case, the interest period is from the x-th period to the current period, and the SOC history may include information indicating in time series each SOC estimated for each unit time during the interest period.

Referring to FIG. 5, the fifth lookup table 500 may be previously stored in the memory unit 130. In the fifth lookup table 500, a correspondence relationship between the SOC and the correction coefficient is recorded.

In the fifth lookup table 500, suppose that the first to m SOCs (SOC ₁ to SOC _m ) and the first to m correction coefficients (K ₁ to K _m ) are sequentially related to each other. When 1 ≤ i <j ≤ m, the i-th SOC (SOC _i ) is related to the i-th correction coefficient (K _i ), and the j-th SOC (SOC _j ) is related to the _j- th correction factor (K _j ). .

In the fifth lookup table 500, a relatively small SOC may be associated with a relatively large correction factor. For example, when SOC _i is smaller than SOC _j , K _i may be larger than K _j .

When it is estimated that the SOC of the current cycle of the battery 20 is within the nonlinear characteristic range, the controller 120 determines a correction value related to the SOC history of the period of interest based on the SOC history and the fifth lookup table 500 do. The correction value may be used to determine at least one of the first to fourth values.

Specifically, the controller 120 may determine the correction value by sequentially summing the correction coefficients associated with each of at least one SOC included in the SOC history for the period of interest with reference to the fifth lookup table 500. have. In this case, the following Equation 9 may be used.

<Equation 9>

In Equation 9, x is the time index of the start period of the period of interest, and k+1 is the time index of the current period. x is less than or equal to k+1. k _co [q] is a correction coefficient related to the SOC of the q-th period, and Kc is a correction value. For example, when the q-th period SOC is the same as SOC ₁ , k _co [q] is the same as K ₁ .

The controller 120 may determine a first value or a third value by subtracting the correction value Kc from the first predetermined reference value. In order to prevent the first process noise from becoming too small or negative, the correction value Kc may be limited to a predetermined maximum correction value. The predetermined maximum correction value may be less than or equal to the first predetermined reference value. For example, when the correction value Kc from Equation 9 is equal to or greater than a predetermined maximum correction value, the controller 120 subtracts a predetermined maximum correction value from the first predetermined reference value instead of the correction value Kc, 3 values can be determined.

The controller 120 may determine a second value or a fourth value by summing the second predetermined reference value and the correction value Kc.

When it is estimated that the SOC of the current period is out of the nonlinear characteristic range, the controller 120 may initialize the correction value to a predetermined initial value (eg, 0).

The first and second process noises set in the current period are stored in the memory unit 130 and may be used by the controller 120 when estimating the SOC of the battery 20 in the next period. The controller 120 selectively outputs a switching signal SS to control the switch 30, but when the correction value (refer to Equation 9) is greater than or equal to a predetermined maximum correction value, the switching signal SS The duty ratio can be limited to a predetermined reference duty ratio (eg, 0.2) or less.

6 is a flowchart illustrating a battery management method according to another embodiment of the present invention. The method of FIG. 6 may be repeatedly executed every unit time while the battery 20 is being charged or discharged.

Referring to FIG. 6, in step S610, the controller 120 estimates a state of charge of the battery 20 based on the sensing signal.

In step S620, the controller 120 determines a nonlinear characteristic range. Alternatively, the lower limit value and the upper limit value of the nonlinear characteristic range may each be predetermined, and in this case, step S620 may be omitted.

In step S630, the control unit 120 determines whether the state of charge of the battery 20 is estimated to be within the nonlinear characteristic range. If the value of step S630 is "Yes", step S640 (or step S650) proceeds. If the value of step S630 is "No", step S660 proceeds.

In step S640, the controller 120 determines a correction value (see'K _c 'in Equation 9) based on the SOC history of the battery 20 over the period of interest and the fifth lookup table 500. . Step S640 may be omitted if necessary.

In step S650, the control unit 120 individually sets the first process noise and the second process noise so that the ratio of the second process noise to the first process noise is greater than the reference ratio.

In step S660, the control unit 120 individually sets the first process noise and the second process noise so that the ratio of the second process noise to the first process noise is the same as the reference ratio.

The embodiments of the present invention described above are not implemented only through an apparatus and a method, but may be implemented through a program that realizes a function corresponding to the configuration of the embodiment of the present invention or a recording medium in which the program is recorded. Implementation can be easily implemented by an expert in the technical field to which the present invention belongs from the description of the above-described embodiment.

In the above, although the present invention has been described by a limited embodiment and drawings, the present invention is not limited thereto, and the technical idea of the present invention and the following will be described by those of ordinary skill in the art to which the present invention pertains. It goes without saying that various modifications and variations are possible within the equal scope of the claims.

In addition, the present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention to those of ordinary skill in the technical field to which the present invention belongs. It is not limited by the drawings, but may be configured by selectively combining all or part of each embodiment so that various modifications may be made.

1: power system
2: external device
10: battery pack
20: battery
30: switch
100: battery management system
110: sensing unit
111: current sensor
112: voltage sensor
113: temperature sensor
120: control unit
130: memory unit
140: communication department

Claims (11)

In the battery management system,
A sensing unit configured to output a sensing signal representing a voltage of a battery and a current of the battery for each unit time; And
Including a control unit operably coupled to the sensing unit,
The control unit,
Using an extended Kalman filter, based on the sensing signal for each unit time output by the sensing unit, the state of charge of the battery is estimated,
When the estimated state of charge is out of the nonlinear characteristic range, the first process noise and the second process noise are individually set so that the ratio of the second process noise to the first process noise is the same as the reference ratio,
When the estimated state of charge is within a non-linear characteristic range, the first process noise and the second process noise are individually set so that a ratio of the second process noise to the first process noise is greater than the reference ratio. Is composed,
The first process noise is a value representing the reliability of a current integration model included in the extended Kalman filter,
The second process noise is a value indicating reliability of an equivalent circuit model included in the extended Kalman filter.
The method of claim 1,
The nonlinear characteristic range is between a predetermined lower limit and a predetermined upper limit.
The method of claim 1,
The control unit,
When the estimated state of charge is out of the nonlinear characteristic range,
The first process noise is set equal to a first predetermined reference value,
It is configured to set the second process noise equal to a second predetermined reference value,
The battery management system, wherein a ratio of the second predetermined reference value to the first predetermined reference value is the same as the reference ratio.
The method of claim 1,
The control unit,
When the estimated state of charge is within the non-linear characteristic range,
Setting the first process noise to a first value smaller than a first predetermined reference value,
It is configured to set the second process noise equal to a second predetermined reference value,
The battery management system, wherein a ratio of the second predetermined reference value to the first predetermined reference value is the same as the reference ratio.
The method of claim 1,
The control unit,
When the estimated state of charge is within the non-linear characteristic range,
The first process noise is set equal to a first predetermined reference value,
Configured to set the second process noise to a second value greater than a second predetermined reference value,
The battery management system, wherein a ratio of the second predetermined reference value to the first predetermined reference value is the same as the reference ratio.
The method of claim 1,
The control unit,
When the estimated state of charge is within the non-linear characteristic range,
Setting the first process noise to a third value smaller than a first predetermined reference value,
Configured to set the second process noise to a fourth value greater than a second predetermined reference value,
The battery management system, wherein a ratio of the second predetermined reference value to the first predetermined reference value is the same as the reference ratio.
The method of claim 5,
The control unit,
When the estimated state of charge is within the non-linear characteristic range,
A correction value is determined based on a lookup table in which the correspondence between the state of charge and the correction factor is recorded and the state of charge history of the period of interest
Configured to determine the second value by summing the second predetermined reference value and the correction value,
The interest period is the most recent period in which the state of charge of the battery is continuously estimated to be within the nonlinear characteristic range.
The method of claim 1,
The control unit,
Using the maximum capacity of the battery as an index, obtaining an upper limit value related to the maximum capacity of the battery from a lookup table in which a correspondence relationship between the maximum capacity and the upper limit value is recorded,
The nonlinear characteristic range is between a predetermined lower limit value and the obtained upper limit value.
A battery pack comprising the battery management system according to any one of claims 1 to 8.
In the battery management method,
Estimating a state of charge of the battery based on a sensing signal for each unit time representing voltage and current of the battery using an extended Kalman filter;
Determining whether the estimated state of charge is within a nonlinear characteristic range;
When the estimated state of charge is out of the nonlinear characteristic range, individually setting the first process noise and the second process noise such that a ratio of the second process noise to the first process noise is the same as a reference ratio. ; And
When the estimated state of charge is within a nonlinear characteristic range, separately setting the first process noise and the second process noise so that a ratio of the second process noise to the first process noise is greater than the reference ratio. Including steps,
The first process noise is a value representing the reliability of a current integration model included in the extended Kalman filter,
The second process noise is a value indicating reliability of an equivalent circuit model included in the extended Kalman filter.
The method of claim 10,
Using the maximum capacity of the battery as an index, obtaining an upper limit value related to the maximum capacity of the battery from a lookup table in which a correspondence relationship between the maximum capacity and the upper limit value is recorded,
The nonlinear characteristic range is between a predetermined lower limit and the obtained upper limit.

Images