WO2023238426A1

WO2023238426A1 - Battery impedance estimating device, and battery impedance estimating method

Info

Publication number: WO2023238426A1
Application number: PCT/JP2022/047141
Authority: WO
Inventors: 和生松川; 功石部; 幸拓朝長
Original assignee: 株式会社デンソー
Priority date: 2022-06-08
Filing date: 2022-12-21
Publication date: 2023-12-14
Also published as: JPWO2023238426A1

Abstract

In a battery impedance estimating device 21, a current excitation unit 16 causes an excitation current to be conducted to a battery 1, and a voltage measuring unit 4 performs A/D conversion of a terminal voltage V(t) of the battery 1 to measure the same. When a control unit 20 of an overall control unit 17 sends an instruction to the current excitation unit 16 to energize the battery 1, and causes a voltage measuring unit 7 to start measuring the terminal voltage V(t), a voltage measurement control unit 7 calculates a time constant τ from voltage waveform data of a fixed segment from a time point at which excitation of the battery 1 was performed, until a prescribed length of time has elapsed, and estimates a capacitive component C1 of an impedance of the battery 1 from the time constant τ.

Description

Battery impedance estimation device and battery impedance estimation method

Cross-reference of related applications

This application is based on Japanese Application No. 2022-93011 filed on June 8, 2022, and the contents thereof are incorporated herein.

The present disclosure relates to an apparatus and method for estimating impedance of a secondary battery.

For example, various techniques have been proposed for estimating the impedance of a secondary battery such as a lithium ion battery. For example, in Patent Document 1, when a step current is applied to a battery, curve fitting is performed by sweeping impedance parameters for a time response equation established from an assumed battery model for measured voltage response waveform data. The parameters are estimated by doing this. Further, in Patent Document 2, an alternating current excitation current is generated, the current flowing through the battery and the terminal voltage of the battery are measured, and the impedance is estimated by calculation.

Patent No. 7041848 International Publication No. 2020/003841

Although the technique of Patent Document 1 can easily perform the measurement itself, it requires sampling of the measurement data at high speed, and the amount of data to be handled becomes enormous. Curve fitting also requires a huge amount of computing power because it involves repeated trial and error. Furthermore, although the technique disclosed in Patent Document 2 can obtain impedance at any frequency, it is necessary to measure a large number of frequencies in order to estimate the parameters, and the measurement takes a long time. Furthermore, it is necessary to add a circuit for generating an excitation current in order to obtain impedance, which increases costs.

The present disclosure has been made in view of the above circumstances, and its purpose is to provide a battery impedance estimating device and method that can estimate battery impedance without requiring enormous computing power or dedicated circuitry. .

According to the battery impedance estimating device according to the first aspect, the current excitation section applies an excitation current to the battery, and the voltage measurement section measures the terminal voltage of the battery by A/D converting it. When the control unit instructs the current excitation unit to energize the battery and causes the voltage measurement unit to start measuring the terminal voltage, the impedance estimating unit calculates a predetermined value from the time when the battery is energized. A time constant is calculated from the voltage waveform data in a certain section after the elapse of time, and the impedance of the battery is estimated from the time constant.

In the waveform of the terminal voltage that changes in response to energization of the battery, there is a time region in which resistive, inductive, and capacitive components of the battery impedance are dominant. Therefore, the time constant can be determined by analyzing the waveform of the terminal voltage and performing calculations on the time domain in which the capacitive component is dominant. Then, by finding the time constant, the capacitive component of the impedance can be found. This makes it possible to estimate the impedance of a battery without requiring huge amounts of computing power or dedicated circuitry.

Specifically, as in the battery impedance estimating device according to claim 4, in the impedance estimating section, the integral value calculating section calculates the first integral period after a predetermined time has elapsed from the time when the battery is energized. When the first integral value is obtained by integrating the voltage value within the first integral period, the second integral value is obtained by integrating the voltage value within the second integral period which is the same length as the first integral period following the first integral period. Find the value. The time constant calculation unit measures the voltage value Ve after a predetermined time has elapsed from the second integration period, and if the lengths of the first and second integration periods are a period Tint, the voltage value Ve is calculated from the first integration value. The time constant τ is determined from the ratio of the product of the voltage value Ve and the period Tint equal to the length of each integration period minus the product of the voltage value Ve and the period Tint from the second integral value.

According to the battery impedance estimating device according to claim 5, the impedance estimating section measures the terminal voltage V0 and current I0 of the battery before the initial measuring section energizes the battery. The extreme value measurement unit calculates the maximum value or minimum value Vm of the terminal voltage of the battery within a certain period from the time when the battery is energized, and measures the voltage of the battery that has flowed at the time when the terminal voltage of the battery shows the maximum value or the minimum value Vm. Measure the current Im.

When measuring the voltage value Ve, the impedance calculation unit measures the current Ie of the battery at that time, calculates the resistive resistance component R0 of the battery impedance using the following formula,
R0=(Vm-V0)/(Im-I0)
Find the capacitive resistance component R1 of the battery impedance using the following formula,
R1=(Ve-V0)/(Ie-I0)-R0
The capacitance value C1 of the capacitive part of the battery impedance is expressed as follows: C1=τ/R1
Find it with

The above objects and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is a functional block diagram showing the configuration of a battery impedance estimating device in a first embodiment, FIG. 2 is a diagram showing a battery impedance model, FIG. 3 is a diagram showing a Cole-Cole plot of a battery, FIG. 4 is a diagram showing the response voltage waveform when a step-like excitation current is applied to the battery. FIG. 5 is a flowchart showing the contents of the impedance estimation process, FIG. 6 is a timing chart corresponding to the process shown in FIG. FIG. 7 is a functional block diagram showing the configuration of a battery impedance estimating device in the second embodiment, FIG. 8 is a timing chart corresponding to impedance estimation processing, FIG. 9 is a functional block diagram showing the configuration of a battery impedance estimating device in the third embodiment, FIG. 10 is a timing chart corresponding to impedance estimation processing, FIG. 11 is a functional block diagram showing the configuration of a battery impedance estimating device in the fourth embodiment, FIG. 12 is a functional block diagram showing the configuration of a battery impedance estimating device in the fifth embodiment, FIG. 13 is a flowchart showing the contents of the impedance estimation process, FIG. 14 is a timing chart corresponding to the process shown in FIG. FIG. 15 is a timing chart showing excitation current waveforms in the sixth embodiment.

(First embodiment)
As shown in FIG. 1, the battery impedance estimating device of this embodiment is connected to a battery pack 2 formed by connecting a plurality of unit batteries 1 in series, for example, lithium ion secondary voltage. Analog filters 3 are connected to both ends of each unit battery 1. One voltage measuring section 4 is arranged for each number of unit batteries 1 connected in series, for example, about 8 to 40. In the voltage measuring section 4, a ΔΣ type A/D converter 5 and a digital filter 6 are connected in series to each analog filter 3. The voltage measurement section 4 also includes a voltage measurement control section 7 and a communication section 8. The output terminal of each digital filter 6 is connected to the input terminal of the voltage measurement control section 7, respectively. The voltage measurement control unit 7, which corresponds to an impedance estimation unit, analyzes the voltage response waveform data and estimates the impedance of the battery 1.

A current detection resistor 9 is connected to the lowest potential side of the assembled battery 2. Analog filter 3 is also connected to both ends of current detection resistor 9 . A current measuring section 11 is connected to the analog filter 3. The current measurement section 11 includes a ΔΣ type A/D converter 12, a digital filter 13, a current measurement control section 14, and a communication section 15 connected in series. A current excitation section 16 is connected in parallel to the series circuit of the assembled battery 2 and the current detection resistor 9. The current excitation unit 16 applies a charging current to the battery pack 2 or causes a discharge current to flow out from the battery pack 2 . Note that the current applied to the assembled battery 2 to perform impedance estimation is referred to as an "excitation current."

The voltage measurement section 4, the current measurement section 11, and the current excitation section 16 are controlled by the overall control section 17. The overall control section 17 includes a communication section 18, a calculation section 19, and a control section 20. The communication section 18 is connected in a daisy chain with the communication sections 8 of the voltage measurement sections 4(1) and 4(2) and the communication section 15 of the current measurement section 11. The control unit 20 outputs a current excitation command directly to the current excitation unit 16. The above constitutes the battery impedance estimating device 21.

FIG. 2 is an equivalent circuit model of the internal impedance of a general secondary voltage, in which inductive, resistive, capacitive, and diffusive components are connected in series. Further, FIG. 3 is a Cole-Cole plot in which the locus of battery impedance according to frequency is plotted on a complex plane. Furthermore, as shown in Figure 4, when the current flowing through the battery is changed approximately stepwise, the terminal voltage of the battery that can be observed from the outside is the sum of the internal voltage waveforms corresponding to each impedance component. Appears as.

That is, in the waveform of the terminal voltage that changes in response to energization of the battery, there is a time region in which the resistive, inductive, and capacitive components of the battery impedance are dominant. Therefore, the time constant τ can be determined by analyzing the waveform of the terminal voltage and performing calculations on the time domain in which the capacitive component is dominant.

Next, the operation of this embodiment will be explained. Note that, similarly to the case shown in FIG. 4, the response voltage waveform when the current flowing through the battery 1 is changed substantially stepwise will be analyzed. As shown in FIGS. 5 and 6, when the control unit 20 of the overall control unit 17 transmits a waveform analysis instruction to the voltage measurement unit 4 and the current measurement unit 11 (S1), the control unit 20 of the overall control unit 17 11 measures the voltage V0 and current I0 of the battery 1 at that time (S2). Step S2 corresponds to an initial measurement section.

Further, the control unit 20 gives an instruction to the current excitation unit 16 to apply an excitation current to the assembled battery 2 (S3). Application of the excitation current here means changing the current flowing through the assembled battery 2 from I0 to I1 in a substantially stepwise manner, as shown in FIG. The apparent current waveform is the waveform when the battery 1 starts discharging or stops charging.

The voltage measuring unit 4 measures the terminal voltage V(t) of the battery 1 in the period from time t0 to t3 when the excitation current is applied (S4). Here, the period from time t0 to t1 is a time region in which inductive impedance is dominant. At time t2, the response period corresponding to inductive properties ends and resistive impedance becomes dominant and changes. The period from time t2 to t6 is a time domain in which capacitive impedance is dominant. Incidentally, since the response corresponding to the diffusive impedance is extremely slow, it can be assumed that the voltage reaches approximately 0V in a short period of time.

Additionally, for measurement, it is desirable to increase the amplitude of the response voltage to some extent. Therefore, it is desirable that the step excitation current value (I0-I1) be a somewhat large value, such as 0.1 A to 100 A or more. Since the impedance of the battery is, for example, about 1 mΩ, if the step excitation current value is 100 A, the response voltage amplitude will be about 100 mV.

In the subsequent step S5, the maximum value of the voltage V(t) is determined from the measurement result in step S4, and it is set as V2, and the current value measured at the time when the voltage V2 is measured is set as I2. Then, the resistive component R0 of the impedance is calculated using equation (1). Step S5 corresponds to an extreme value measuring section. Note that the voltage V2 corresponds to the voltage Vm, and the current I2 corresponds to the current Im.
R0=(V2-V0)/(I2-I0)...(1)

In subsequent steps S6 and S7, the voltage V(t) is integrated with time t3 to t4 as a first integration period and time t4 to t5 as a second integration period, and a first integral value INT1 and a second integral value INT2 are obtained. . Note that the first integration period and the second integration period are set to the same length Tint. Steps S6 and S7 correspond to an integral value calculation section. Note that the actual first integral value INT1 and second integral value INT2 are obtained by subtracting (V6×Tint) from the integral result.

In step S8, the voltage V6 at time t6, at which the change in voltage value is estimated to have converged, is measured. Furthermore, the current value I6 at time t6 is also measured. Then, the parallel resistance component R1 in the capacitive component of the impedance is calculated using equation (2) (S9). Note that the voltage V6 corresponds to the voltage Ve, and the current I6 corresponds to the current Ie.
R1=(V6-V0)/(I6-I0)-R0...(2)

In the subsequent step S10, the time constant τ of the capacitive component is calculated as follows. Step S10 corresponds to a time constant calculation section. In order to simplify the calculation, the voltage V6 at the end of the capacitive response is assumed to be 0 V, and the changing voltage value in the capacitive response is Vc,
Let time constant τ=R1·C1. V(t), which is the change in the terminal voltage of battery 1 due to the capacitive component, is

The integral value is

becomes. The integral values INT1 and INT2 are

When the integral value INT2 is divided by INT1,

Taking the logarithm of both sides of equation (7), we get

Therefore, the time constant τ becomes (9).

In the following step S11, the capacitive component C1 is calculated by dividing the time constant τ by the parallel resistance component R1 obtained in step S9. Here, it is better to set the start time t3 of the first integration period early from the viewpoint of calculation accuracy, that is, to obtain the ratio between the integral values INT1 and INT2 with high precision. Therefore, it is desirable to match time points t2 and t3.

As described above, according to the present embodiment, in the battery impedance estimating device 21, the current excitation unit 16 supplies an excitation current to the battery 1, and the voltage measurement unit 4 measures the terminal voltage V(t) of the battery 1 at A /D conversion and measurement. In the voltage measurement control unit 7, the control unit 20 of the overall control unit 17 instructs the current excitation unit 16 to energize the battery 1, and causes the voltage measurement unit 7 to start measuring the terminal voltage V(t). Then, the time constant τ is determined from the voltage waveform data in a certain period after a predetermined period of time, usually about 1 msec to 100 msec, when the response due to the series resistance component and the inductive component ends, from the time when the battery 1 is energized. is calculated, and the capacitance component C1 of the impedance of the battery 1 is estimated from the time constant τ. Thereby, the impedance of the battery 1 can be estimated without requiring enormous computing power or a dedicated circuit.

More specifically, the voltage measurement control unit 7 integrates the voltage value within a first integration period after a predetermined time has elapsed from the time when the battery 1 is energized to obtain the first integral value INT1. Then, the voltage value within a second integration period following the first integration period is integrated to obtain a second integral value INT2. Then, the voltage value V6 after a predetermined time has elapsed from the second integral period is measured, and from the first integral value INT1 minus the product of the voltage value V6 and the integral period Tint, and from the second integral value INT2, The time constant τ is calculated from the ratio of the above product minus the product.

Furthermore, before energizing the battery 1, the voltage measurement control unit 7 measures the terminal voltage V0 and current I0 of the battery 1, and from the time when the energization is performed, the response due to the series resistance component or the inductive component is normally measured. Within a certain period of about 1 msec to 100 msec when the voltage ends, the maximum value V2 of the terminal voltage V(t) of the battery 1 is determined, and the current I2 of the battery that flows at the time when the maximum value V2 is shown is measured. . Then, measure the current I6 passed through the battery 1 when measuring the voltage value V6, find the resistive resistance component R0 of the battery impedance using equation (1), and find the capacitive resistance component R1 using equation (2). , the capacitance value C1 of the capacitive portion is determined by equation (9). In this way, the resistance components R0 and R1 of the battery impedance and the capacitance value C1 of the capacitive portion can be specifically determined.

(Second embodiment)
Hereinafter, parts that are the same as those in the first embodiment are given the same reference numerals and explanations will be omitted, and different parts will be explained. A battery impedance estimating device 21A according to the second embodiment shown in FIG. 7 includes a current measuring section 11A and an overall control section 17A instead of the current measuring section 11 and the overall control section 17. What is different from the battery impedance estimating device 21 of the first embodiment is that, as shown in FIG. The waveform analysis instruction to the section 4 is performed by the current measurement control section 14A of the current measurement section 11A.

That is, the current measurement control unit 14A detects that the current excitation unit 16 has applied a step-like excitation current by analyzing the current waveform data. When the application of the excitation current is detected, a waveform analysis instruction is given to the voltage measurement section 4 via the communication section 15.

(Third embodiment)
A battery impedance estimating device 21B according to the third embodiment shown in FIG. This is a replacement for the control section 17B. The difference from the battery impedance estimating device 21A of the second embodiment is that, as shown in FIG. 10, the control section 20B of the overall control section 17B does not issue an excitation instruction to the current excitation section 16B. The current excitation unit 16B spontaneously applies an excitation current to the assembled battery 2. The subsequent process is similar to the second embodiment.

(Fourth embodiment)
The battery impedance estimating device 22 of the fourth embodiment shown in FIG. 1) and 23(2). The voltage measuring section 23 includes a multiplexer 24 , and the analog filter 3 corresponding to each battery 1 is connected to the multiplexer 24 . The A/D converter 5 and the digital filter 6 are integrated into one set, and the voltage measurement control section 7A is connected to the one digital filter 6. According to the fourth embodiment configured as described above, the number of A/D converters 5 and digital filters 6 can be reduced, and the battery impedance estimating device 22 can be configured to be compact.

(Fifth embodiment)
A battery impedance estimating device 25 according to the fifth embodiment shown in FIG. 12 includes a voltage-current measuring section 26 in place of the voltage measuring section 4 and current measuring section 11A in the battery impedance estimating device 21B according to the third embodiment. , n batteries 1 are connected in correspondence with each other. The voltage and current measurement section 26 includes a voltage detection section 27, a voltage measurement control section 7A, a current detection section 28, a voltage measurement control section 14A, and a communication section 8. The voltage detection section 27 is a combination of an analog filter 3, an A/D converter 5, and a digital filter 6. Further, the current detection section 28 is a combination of the A/D converter 12 and the digital filter 13.

(Sixth embodiment)
In the sixth embodiment, as shown in FIG. 13, steps S1 to S5 in the flowchart of the first embodiment are replaced with steps S12 to S14. Since step S1 is not provided, the configuration of the battery impedance estimating device corresponds to that of the third embodiment and subsequent embodiments. In step S12, the current measurement control section 14A detects the application of the excitation current and gives a waveform analysis instruction to the voltage measurement section 4 via the communication section 15. Then, the voltage measurement unit 4 measures the voltage value V0 (S13).

In the subsequent step S14, the voltage at time t2 after a certain period of time has passed from time t0 is measured as V2, as shown in FIG. Find the resistive resistance component R0 of the battery impedance. That is, the excitation current may ring due to the inductance component of the current path, but once the structure, shape, etc. of the battery 1 and wiring are determined, the ringing will converge within a known time. Therefore, as in the sixth embodiment, even if the voltage V2 is measured by setting the time t2 after a certain period of time has elapsed from the time t0, the measurement can be performed with sufficient accuracy.

(Seventh embodiment)
The seventh embodiment shown in FIG. 15 shows a case where the excitation current applied to the battery 1 is increased in a substantially stepwise manner from a current value I0 to a current value I1. The apparent current waveform is equal to the waveform when charging of the battery 1 is started or when discharging is stopped. Basically, each embodiment can be applied, but in the first embodiment, in step S5, the minimum value of the voltage is measured as the voltage V2 instead of the maximum value.

(Other embodiments)
The function of the impedance estimation section does not necessarily need to be provided in the voltage measurement section.
It may also be applied to secondary batteries other than lithium ion batteries.
Although the present disclosure has been described based on examples, it is understood that the present disclosure is not limited to the examples or structures. The present disclosure also includes various modifications and equivalent modifications. In addition, various combinations and configurations, as well as other combinations and configurations that include only one, more, or fewer elements, are within the scope and scope of the present disclosure.

Claims

a current excitation unit (16) that causes an excitation current to flow through the battery (1);
a voltage measuring unit (4, 23, 27) that measures the terminal voltage of the battery by A/D converting it;
a control unit (20) that controls the current excitation unit and the voltage measurement unit;
When the control unit instructs the current excitation unit to energize the battery and causes the voltage measurement unit to start measuring the terminal voltage, a predetermined amount of power starts from the time when the battery is energized. A battery impedance estimating device comprising: an impedance estimating unit (7, 7A) that calculates a time constant from voltage waveform data in a certain section after a lapse of time and estimates the impedance of the battery from the time constant.
a current excitation unit (16) that flows an excitation current to the battery;
a voltage measuring unit (4, 23, 27) that measures the terminal voltage of the battery by A/D converting it;
a current measurement unit (11A) that analyzes current waveform data measured by A/D converting the current applied to the battery;
a control unit (20A) that controls the current excitation unit;
The control unit instructs the current excitation unit to energize the battery,
When the current measurement unit detects that energization of the battery has started based on the analysis result of the current waveform data and inputs an instruction to analyze the voltage waveform data,
an impedance estimation unit (7, 7A) that calculates a time constant from voltage waveform data in a certain section after a predetermined period of time has elapsed from the time when the battery is energized, and estimates the impedance of the battery from the time constant; A battery impedance estimating device.
a current excitation unit (16B) that causes excitation current to flow through the battery;
a voltage measuring unit (4, 23, 27) that measures the terminal voltage of the battery by A/D converting it;
a current measurement unit (11A) that analyzes current waveform data measured by A/D converting the excitation current applied to the battery;
When the current measurement unit detects that energization of the battery has started based on the analysis result of the current waveform data and inputs an instruction to analyze the waveform data,
an impedance estimation unit (7, 7A) that calculates a time constant from voltage waveform data in a certain section after a predetermined period of time has elapsed from the time when the battery is energized, and estimates the impedance of the battery from the time constant; A battery impedance estimating device.
The impedance estimator includes:
When a first integral value is obtained by integrating the voltage value within a first integral period after a predetermined time has elapsed from the time when the battery was energized,
an integral value calculation unit that calculates a second integral value by integrating a voltage value within a second integral period that is the same length as the first integral period following the first integral period;
Measuring the voltage value Ve after a predetermined time has elapsed from the second integration period,
Letting the length of the first and second integration periods be a period Tint,
a value obtained by subtracting the product of the voltage value Ve and the period Tint from the first integral value;
4 . The method according to claim 1 , further comprising a time constant calculation unit that calculates a time constant τ from a ratio of the second integral value minus the product of the voltage value Ve and the period Tint. The battery impedance estimation device described.
The impedance estimator includes:
an initial measurement unit that measures the terminal voltage V0 and current I0 of the battery before energizing the battery;
measuring the current of the battery along with the terminal voltage of the battery;
Within a certain period of time from the time when the battery is energized, determine the maximum value or minimum value Vm of the terminal voltage of the battery, and measure the current Im of the battery at the time when the maximum value or minimum value Vm is shown. an extreme value measuring section,
When measuring the voltage value Ve, measure the current Ie of the battery at that time,
The resistive resistance component R0 of the impedance of the battery is determined by the following formula,
R0=(Vm-V0)/(Im-I0)
The capacitive resistance component R1 of the impedance of the battery is determined by the following formula,
R1=(Ve-V0)/(Ie-I0)-R0
The capacitance value C1 of the capacitive part of the impedance of the battery is expressed as follows: C1=τ/R1
5. The battery impedance estimating device according to claim 4, further comprising an impedance calculating section that calculates the impedance by calculating the impedance.
The battery impedance estimating device according to claim 5, wherein the certain period is from 1 millisecond to 100 milliseconds.
The battery impedance estimating device according to any one of claims 1 to 6, wherein the predetermined time is from 1 millisecond to 100 milliseconds.
energizing the battery and measuring the terminal voltage of the battery;
Integrating the voltage value within a first integration period after a predetermined time has elapsed from the time when the battery was energized to obtain a first integral value;
Integrating the voltage value within a second integration period that follows the first integration period and having the same length as the first integration period to obtain a second integral value;
Measuring the voltage value Ve after a predetermined time has elapsed from the second integration period,
Letting the length of the first and second integration periods be a period Tint,
a value obtained by subtracting the product of the voltage value Ve and the period Tint from the first integral value;
A battery impedance estimation method that calculates a time constant τ from a ratio of the second integral value minus the product of the voltage value Ve and the period Tint.
The battery impedance estimation method according to claim 8, wherein the predetermined time is from 1 millisecond to 100 milliseconds.
Before energizing the battery, measure the terminal voltage V0 and current I0 of the battery,
measuring the current of the battery along with the terminal voltage of the battery;
Within a certain period of time from the time when the battery is energized, determine the maximum value or minimum value Vm of the terminal voltage of the battery, and measure the current Im of the battery at the time when the maximum value or minimum value Vm is shown. death,
When measuring the voltage value Ve, measure the current Ie of the battery at that time,
The resistive resistance component R0 of the impedance of the battery is determined by the following formula,
R0=(Vm-V0)/(Im-I0)
The capacitive resistance component R1 of the impedance of the battery is determined by the following formula,
R1=(Ve-V0)/(Ie-I0)-R0
The capacitance value C1 of the capacitive part of the impedance of the battery is determined by the following formula: C1=τ/R1
The battery impedance estimation method according to claim 8 or 9.
The battery impedance estimation method according to claim 10, wherein the certain period is from 1 millisecond to 100 milliseconds.