KR20130119871A - Cell direct-current resistance evaluation system - Google Patents

Abstract

A cell DC resistance evaluation system includes an impedance measurement means for measuring the AC impedance of a secondary cell and a DC resistance value analysis means. The DC resistance value analysis means calculates a response voltage of the secondary cell on the basis of a calculated circuit integer based on an equivalent circuit of the secondary cell, a current value included in a cell DC resistance measurement condition, and an OCV as a circuit voltage value; and calculates an inner DC resistance value of the secondary cell on the basis of the response voltage and the cell DC resistance measurement condition. The system efficiently measures the DC resistance of the cell in a short time without using high-capacity power. [Reference numerals] (1) Public battery;(4) DCR translation device;(5) Alternating current power source;(6) Impedance measuring device;(AA) Control signal;(BB) Impedance data;(CC) Alternating current signal;(DD) Voltage��urrent wave

Description

Battery DC Resistance Rating System {CELL DIRECT-CURRENT RESISTANCE EVALUATION SYSTEM}

The present invention relates to a battery direct current resistance evaluation system.

For example, one of performance indicators of a secondary battery used in a hybrid electric vehicle is a direct current resistance (DCR) inside the battery. The specific test method of this DCR is prescribed | regulated and published, for example by "The method of calculating the DC resistance of the sealed nickel-hydrogen battery for Japan Electric Vehicle Association standard JEVS D714 hybrid vehicle" (nonpatent literature 1).

12 is a block diagram showing an example of a conventional DCR measurement system. As shown in FIG. 12, the charging / discharging device 2 and the voltage / current measuring device 3 are connected to the battery 1 as the measurement target.

The charging / discharging device 2 applies a charging / discharging pulse to the battery 1. The voltage and current measuring device 3 drives and controls the charging and discharging device 2. In addition, the voltage and current measuring device 3 measures the voltage and current of the battery 1 at the time of application of a charge and discharge pulse. The DCR analyzer 4 is connected to the voltage and current measuring device 3.

When measuring the DCR of the battery 1 having such a configuration, the charge / discharge device 2 applies a charge / discharge current pulse of a predetermined level to the battery 1. For example, when the rated capacity of the battery 1 is 20 Ah, a charge / discharge current pulse having a sequence waveform as shown in FIG. 13 is applied to the battery 1. For example, as shown in FIG. 14, the voltage and current measuring device 3 measures the response voltage ΔV of the battery 1 to the discharge current ΔI corresponding to the applied current pulse. And DCR analyzer 4 calculates DCR (= ΔV / ΔI) by calculating the quotient of these response voltages ΔV and discharge current ΔI.

15 is a block diagram illustrating a specific configuration example of the DCR analyzer 4. As shown in FIG. 15, the DCR measurement condition and response voltage including the measurement time point are input to the DCR calculator 42 via the input unit 41. The DCR calculator 42 calculates the DCR at each measurement time point specified in the DCR measurement conditions based on the above-described expression DCR (= ΔV / ΔI). ΔV is the drop width of the response voltage, and ΔI is the level of the current pulse.

In the conventional DCR measurement system as described above, a relatively large charge / discharge pulse is applied to the battery 1. For this reason, the perturbation which appears at the output of the battery 1 also becomes large. As a result, the following problem may arise.

1) After a charge / discharge pulse is applied to the battery 1, a long rest time is provided to restore the battery 1 to a stable state. If no rest time is provided, it is difficult to ensure reproducibility of the measurement. Therefore, when DCR test | inspection is performed using the conventional DCR measuring system, for example in the manufacturing line of a battery, a test time becomes quite long. For this reason, productivity worsens.

2) A large capacity power supply is used depending on the capacity of the battery 1 to be measured. In the case of using a large power supply, measurement results are likely to be affected by noise generated from these devices, for example. For this reason, in order to perform stable measurement, the noise countermeasure is taken, for example.

Japanese Electric Vehicle Association Standard JEVS D714 Method for calculating DC resistance of sealed nickel-hydrogen battery for hybrid vehicle

One object of the present invention is to provide a battery direct current resistance evaluation system capable of measuring efficiently in a short time without using a large capacity power supply.

The battery DC resistance evaluation system for measuring the internal DC resistance of the secondary battery of the present invention includes an impedance measuring means for measuring the AC impedance of the secondary battery, and a DC resistance value analyzing means. Is the secondary based on the measurement result of the impedance measuring means, the circuit constant calculated based on the equivalent circuit of the secondary battery, the current value included in the battery DC resistance measurement condition, and the OCV which is the open circuit voltage value. The response voltage of the battery is calculated, and the internal DC resistance value of the secondary battery is calculated based on the response voltage and the battery DC resistance measurement condition.

The DC resistance value analyzing means may correct the response voltage using the SOC-OCV table created by measuring the OCV while changing the SOC that is the state of charge of the secondary battery.

The DC resistance value analyzing means may correct the response voltage using the OCV measured while changing temperature.

The equivalent circuit may have a plurality of CPEs connected in series.

The said DC resistance value analysis means may correct the said circuit constant using the AC impedance of the said secondary battery measured while changing temperature.

According to the battery DC resistance evaluation system of the present invention, the DC resistance of the battery can be measured efficiently in a short time without using a large capacity power supply.

1 is a block diagram showing a battery DC resistance evaluation system according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the operation of the evaluation system shown in FIG. 1.
3 is a view for explaining the operation of the evaluation system shown in FIG. 1.
4A and 4B are diagrams for explaining the operation of the evaluation system shown in FIG. 1.
FIG. 5 is a diagram for explaining the operation of the evaluation system shown in FIG. 1.
6 is a block diagram showing a battery DC resistance evaluation system according to another embodiment of the present invention.
FIG. 7 is a diagram for explaining the operation of the evaluation system shown in FIG. 6.
8A to 8E are diagrams for explaining the operation of the evaluation system shown in FIG. 6.
FIG. 9 is a diagram for explaining the operation of the evaluation system shown in FIG. 6.
FIG. 10 is a diagram for explaining the operation of the evaluation system shown in FIG. 6.
11A and 11B are block diagrams illustrating a battery direct current resistance evaluation system according to still another embodiment of the present invention.
12 is a block diagram showing an example of a conventional DCR measurement system.
13 is an example of sequence waveforms of charge and discharge current pulses at the time of DCR measurement.
14 is an example of voltage and current waveforms at the time of DCR measurement.
15 is a block diagram showing a specific configuration example of a conventional DCR analyzer.

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. However, one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown for simplicity of the drawings.

EMBODIMENT OF THE INVENTION Hereinafter, one Embodiment of this invention is described in detail using drawing. 1 is a block diagram showing the configuration of a battery DC resistance evaluation system (this system) according to an embodiment of the present invention.

As shown in FIG. 1, this system evaluates the electrical characteristics of the battery 1. This system has a DCR analyzer 4, an AC power supply 5, and an impedance measuring device 6. The AC power source 5 and the impedance measuring apparatus 6 are connected to the battery 1 which is a measurement object.

One of the differences between the present system in FIG. 1 and the evaluation system in FIG. 12 is that the system has an impedance measuring device 6 instead of the voltage / current measuring device 3 of the evaluation system in FIG. 12. This impedance measuring apparatus 6 measures the impedance as an electrical characteristic of the battery 1. The measurement data (impedance data) is input to the DCR analyzer 4.

FIG. 2 is a block diagram illustrating a specific configuration example of the DCR analyzer 4 used in FIG. 1. As shown in FIG. 2, the DCR analyzing apparatus 4 includes an input unit 44, an SOC calculating unit 45, a circuit constant calculating unit 46, an SOC-OCV calculating unit 47, a response voltage calculating unit 48, and a DCR calculating unit. It has a 42 and the output part 43. In the DCR analyzer 4, impedance data, an equivalent circuit, data of the SOC-OCV table, and data of the DCR measurement condition are output to each unit through the input unit 44.

The battery DC resistance measurement condition (DCR measurement condition) includes the current value (pulse height) of the charge / discharge pulses applied to the battery 1 and the generation time of the charge / discharge pulses. The SOC calculating part 45 calculates the charge / discharge amount of the battery 1 from the charge / discharge pulse height and pulse generation time prescribed | regulated as DCR measurement conditions. As a result, the state of charge (SOC) value of the battery 1 is calculated. The calculation result is output to the SOC-OCV calculation unit 47. The detailed calculation method of SOC value is demonstrated separately.

The circuit constant calculating unit 46 calculates the optimal circuit constant as an equivalent circuit using the impedance data measured by the impedance measuring apparatus 6. The detailed calculation method of a circuit constant is demonstrated separately.

The SOC-OCV calculation unit 47 calculates an open circuit voltage OCV (Open circuit voltage) value according to the SOC value based on the SOC-OCV table. The detailed calculation method of an OCV value is demonstrated separately.

The response voltage calculator 48 calculates a response voltage obtained by applying a current pulse to the battery 1. Specifically, the response voltage is a value corresponding to an equivalent circuit, a circuit constant, a DCR measurement condition, and an OCV value. The response voltage is calculated as the sum of the voltage change generated when the current pulse is applied to the internal impedance of the battery 1 and the internal electromotive force. The detailed calculation method of a response voltage is demonstrated separately.

The DCR calculation unit 42 receives a DCR measurement condition and response voltage including a measurement time point. The DCR calculation unit 42 calculates the DCR at each measurement time point specified in the DCR measurement conditions based on the calculation DCR (= ΔV / ΔI). ΔV is the drop width of the response voltage, and ΔI is the level of the current pulse.

Before demonstrating the detail of the calculation method mentioned above, each data is demonstrated.

3 is a diagram illustrating an example of impedance data of the battery 1 measured by the impedance measuring apparatus 6. The characteristic curve CHa has shown the measurement result of impedance. The characteristic curve CHb has shown the measurement result of the phase.

4A and 4B are explanatory diagrams of an equivalent circuit. 4A is a diagram illustrating a specific equivalent circuit example. 4B is a list showing an example of specific circuit constants of each element in the circuit shown in FIG. 4A.

5 is a diagram illustrating a specific example of the SOC-OCV table. This table is created by measuring the OCV value while changing the SOC value of the battery 1 by 10% in the range of 0 to 100%.

The SOC value is calculated by the SOC calculator 45 based on the predetermined DCR measurement condition. The SOC value is a value calculated for each measurement time.

The OCV value is calculated by the SOC-OCV calculation unit 47. The OCV value is an open circuit voltage value at each measurement time.

The response voltage is calculated by the response voltage calculator 48.

The electrical characteristic of the battery 1 is demonstrated.

The electromotive force of the battery 1 is calculated as an OCV value.

The internal impedance of the battery 1 corresponds to the circuit constant of one or a plurality of circuit elements. The circuit constant of each element is calculated by the circuit constant calculating unit 46.

[Calculation of Response Voltage]

Response voltage E0 which generate | occur | produces in the battery 1 is represented by the sum of following E1 and E2, as shown to the equivalent circuit of FIG.

a) internal electromotive force; E1

b) voltage change due to internal impedance; E2

The voltage E1 of the electromotive force is a voltage irrespective of the applied state of the current. However, voltage E1 changes with SOC. In general, it is known that the voltage between terminals of a battery decreases during discharge. The cause of such a voltage drop is an internal impedance and is not an application state of an electric current. For this reason, the voltage E1 of electromotive force can be determined by measuring the OCV of the battery 1.

The internal impedance is determined by the material and the structure of the battery 1. When the current is applied to the battery 1, a voltage (voltage in the same direction as the electromotive force) is generated, and when the battery 1 is discharged, a voltage in the opposite direction to the voltage of the electromotive force is generated. Even with the same standard, there is individual difference in internal impedance. This individual difference appears as a difference of the DCR test result.

In this system, the sum of the electromotive force of the battery 1 (E1 in FIG. 6) and the voltage change (E2 in FIG. 6) generated when a current is applied to the internal impedance of the battery 1 is defined as the response voltage E0.

[Voltage change due to internal impedance]

The response voltage e (t) corresponding to the current (current pulse) X (t) at time t is calculated.

In this system, the internal impedance of the battery 1 is approximated using a circuit including a resistor connected in series and a plurality of RC parallel circuits. That is, the internal impedance of the battery 1 is the sum of the resistance and the impedance of each RC parallel circuit.

On the other hand, the voltage e (t) applied to the internal impedance is the sum of the voltages applied to each impedance.

For example, the sum of the voltages applied to the series circuit as shown in FIG. 7 is obtained by the following equation.

e (t) = e _A (t) + e _B (t) + e _C (t)

For example, e _A (t) is obtained by inverse Laplace transform of the voltage E _A (s) in the complex region s.

Where s = jω (ω is the angular frequency).

For example, E _A (s) is obtained by the following formula.

E _A (s) = Z _A (s) × I (s)

Z _A (s): Impedance in s region

I (s): current in the s region

[Calculation of Circuit Constants]

The circuit used to approximate the internal impedance is obtained by measuring the impedance of the battery 1 and optimizing the circuit constant in the circuit using the data.

The optimal circuit constant is the circuit constant x which minimizes the sum of squares of y-f (x). Circuit constant x is calculated | required by the least square method. Here, the impedance data is y, and the impedance calculation formula is a function f (x). As the algorithm of the solution, for example, the Gaussian Newton method or the Levenberg-Marquardt method can be used.

[current in s region]

In the DCR evaluation, the current X (t) applied to the battery 1 is the sum of the step functions X _k (t) of charge / discharge currents whose time is a variable as shown in FIGS. 8A to 8E.

The voltage e (t) applied to the internal impedance is the sum of the response voltages e _k (t) generated by each step function.

The Laplace transform has linearity. Therefore, the voltage e (t) can be obtained by obtaining and integrating the response voltage generated by each step function in the s region.

I _k (s) is obtained by laplace transforming the current in the time domain. For example, the current which changes by ΔI _k in the case of t = 0 is expressed as follows using a step function.

0: t <0

ΔI _k : t≥0

This is represented as follows by using the unit step function u (t).

ΔI _k × u (t)

That is, the following equation holds.

I _k (s) = L [ΔI _k × u (t)] = ΔI _k / s

9 is a diagram showing an example of the relationship between the charge and discharge current and the change in the SOC in the DCR measurement. In FIG. 9, the solid line represents the current pulse, and the broken line represents the SOC.

[Voltage applied to resistance]

When the resistance value of the resistance is r, the voltage e _r (t) applied to the resistance is obtained by the following equation.

e _r (t) = r × X (t)

[Voltage across RC circuit]

When the impedance of the RC circuit is Z _rc (s), the voltage e _rc (t) applied to the RC circuit is as follows.

I _k (s) it is, in the case of the step function of the current to change △ I _k according to t = t _k, the response voltage Y _rck (T) is obtained as follows. However, let T = tt _k .

Since the impedance Z _rc (s) of the RC circuit is the impedance of the resistor R and the RC parallel circuit having the capacitance C, it can be obtained as follows.

At this time, if α = 1 / C and β = -1 / RC, Z (s) = α / (s-β). From this, E _rck (s) is represented as follows.

This, by inverse Laplace transform,

. From this, Y _rck (T) is represented as follows.

[Internal electromotive force]

The internal electromotive force (voltage E1) of the battery 1 shown in FIG. 6 is determined by the OCV value. This OCV value is calculated according to the following procedure.

1) Calculate the change of SOC by DCR charge / discharge pulse.

2) OCV value due to SOC change is calculated.

[SOC output]

In the DCR measurement, a charge pulse or a discharge pulse is applied to the battery 1. For this reason, as shown in FIG. 5, SOC of the battery 1 changes with progress of a measurement. The SOC value at time t can be calculated by the following equation.

Here, S ₀ is an initial value of SOC, and C _max is a maximum capacity of the battery 1. In addition, I (x) is a charge / discharge current.

The calculation example of SOC is demonstrated.

Assume that the battery 1 has a maximum capacity of 2400 mAh, for example, and its SOC is 50% (1200 mAh). When 30 sec of charge pulses are applied to this battery 1 at 2400 mA, SOC is computed with the following formula | equation.

{1200mAh + (2400mA * 0.0083)} / 2400mAh = 0.5083

That is, SOC after charging pulse application is 50.83%.

Similarly, assume that the battery 1 has a maximum capacity of 2400 mAh and its SOC is 50% (1200 mAh). When the discharge pulse for 30 seconds is applied to this battery 1 at 2400 mA, SOC is calculated by the following formula.

{1200mAh + (-2400mA * 0.0083)} / 2400mAh = 0.4917

That is, SOC after discharge pulse application is 49.17%.

[OCV value calculation]

OCV changes with SOC. Therefore, in order to calculate OCV in S (t), first, OCV is measured, changing the state of charge of the battery 1. In this way, the OCV table extracted from the table in the SOC is created. And this OCV table is referred to according to S (t). The median value is calculated by using a calculation method such as linear interpolation, for example.

The calculation example of OCV is demonstrated below.

The OCV value e (t _k ) at time t = t _k is calculated by using the following equation. However, SOC value S (t _k ) = 50.83% and OCV ₁ is an OCV value when SOC is 50%. OCV ₂ is an OCV value when SOC is 60%.

The calculation result of the OCV value by this formula is 3.727V. And according to the same formula, the OCV value in case SOC is 49.17% is 3.706V.

In this system, the DCR measurement result of the battery is estimated based on the AC impedance measurement result. From this, the present system exhibits the following effects.

1) In AC impedance measurement, even if the amplitude of the AC signal applied for measurement is small, it can measure stably. From this, the perturbation which appears at the output of the battery 1 can be suppressed small.

2) Thereby, it is not necessary to provide the waiting time for returning the battery 1 to an original state. For this reason, a measurement time can be shortened. For this reason, the efficiency of the test | inspection in a manufacturing line can be raised, for example.

3) Good reproducibility can be measured.

4) Even if the power supply capacity is small, stable measurement can be performed.

5) In AC impedance measurement, the measurement result is FFT processed. As a result, only the frequency to be analyzed is used. For this reason, influences such as noise are suppressed.

In the above embodiment, SOC is used as a parameter used for calculating OCV. However, this parameter is not limited to SOC. As this parameter, temperature (cell temperature or environmental temperature) may be used. In this case, OCV data is measured while changing the temperature of the battery 1 in advance. From this OCV data, OCV according to temperature is calculated. As a result, the response voltage can be corrected.

In calculating the OCV, the temperature table may be corrected in consideration of the material and / or structure of the battery.

In addition, the parameter used for calculation of OCV may be a combination of SOC and temperature and / or other conditions.

As an equivalent circuit, a circuit having a plurality of CPEs (Constant Phase Element) connected in series may be used. CPE is an element capable of exhibiting impedance due to material diffusion in a battery. The impedance Z of the CPE is generally defined as follows using the integers P and T.

When P = 0.5, the impedance of the CPE is the same as the Warburg impedance represented by the following formula.

Similar to the resistor or RC parallel circuit, the voltage applied to the CPE in the equivalent circuit is obtained. By adding this voltage with the voltage applied to other parts of the equivalent circuit, the response voltage of the entire internal resistance is obtained.

[Voltage across CPE]

When the impedance of the CPE is Z _cpe (s), the voltage E _cpe (t) applied to the CPE is as follows.

When I _k (s) is a step function of a current that changes by _{ΔI k} when t = t _k , the response voltage E _cpek (T) is obtained as follows. However, let T = tt _k .

The impedance of CPE is defined as follows using the constants P and Q. Here, P and Q are characteristics inherent to the battery and are treated as circuit constants.

therefore,

Here, the following inverse Laplace transform is used.

However, n> 0 and Γ (n) is a gamma function. Thereby, E _cpe (T) can be represented as follows.

In determining the circuit constant, impedance measurement results (SOC-impedance data) for each SOC may be used. FIG. 10 is a block diagram showing a specific configuration example of a DCR analyzer 4 using SOC-impedance data. In FIG. 10, the same code | symbol is attached | subjected to the part common to FIG. The SOC-circuit constant table calculator 49a obtains a circuit constant corresponding to the equivalent circuit of each SOC based on the SOC-impedance data table and equivalent circuit data input from the input unit 44.

Specifically, as shown in FIG. 11, the SOC-circuit constant table is created by extracting each circuit constant from the SOC by the table.

The SOC-circuit constant calculating unit 49b calculates a circuit constant corresponding to the SOC value based on the SOC-circuit constant table and the SOC value calculated from the SOC calculating unit 45.

In the calculation of the circuit constant, for example, the circuit constant is optimized based on the measurement data of each SOC so that the parameter falls within the limited range. However, the condition which changes a characteristic is not limited to SOC. For example, you may change a characteristic on condition of temperature.

As described above, in this system, resistance measurement can be efficiently performed in a short time without using a large power supply. This system is suitable for DCR test | inspection in the manufacturing line of a battery, for example.

In addition, the battery DC resistance evaluation system of this invention may be the following 1st-5th battery DC resistance evaluation systems (battery DC resistance evaluation apparatus). The first battery DC resistance evaluation system is a battery DC resistance evaluation system for measuring the internal DC resistance of a secondary battery, the impedance measuring means for measuring the AC impedance of the battery to be measured, and the selected equivalent of the measurement result of the impedance measuring means. DC resistance value analysis that calculates the internal DC resistance value while calculating the response voltage of the battery to be measured based on the circuit constant calculated based on the circuit, the current value of the battery DC resistance measurement condition, and the open circuit voltage value (OCV). A means is provided.

The second battery DC resistance evaluation system is a first battery DC resistance evaluation system, wherein the DC resistance value analyzing means corrects the response voltage using an SOC-OCV table created by measuring OCV data while changing the SOC. It is characterized by. In the third battery DC resistance evaluation system, in the first battery DC resistance evaluation system, the DC resistance value analyzing means corrects the response voltage using the OCV data measured while changing temperature.

The 4th battery DC resistance evaluation system is a battery DC resistance evaluation system in any one of the 1st-3rd, The said equivalent circuit uses the circuit in which CPE was connected in series. The 5th battery DC resistance evaluation system is a battery DC resistance evaluation system in any one of 1st-4th, The circuit constant of the said equivalent circuit correct | amends the said circuit constant using the impedance data measured while changing temperature. It is characterized by.

According to the 1st-4th battery DC resistance evaluation system, the DC resistance of a battery can be measured efficiently in a short time, without using a large capacity power supply.

The above detailed description has been presented for the purpose of illustrating the example and describing it in detail. Many modifications and variations are possible in light of the above teaching. The subject matter described herein is not intended to be exhaustive or to be limited to the precise form disclosed. Although the subject matter has been described in specific language in terms of structural features and / or methodological acts, the subject matter defined in the appended claims is not necessarily limited to the specific construct or act described above. Rather, the specific structures and acts described above are disclosed as example forms of implementing the appended claims.

Claims (7)

A battery DC resistance evaluation system for measuring the internal DC resistance of a secondary battery,
An impedance measuring means for measuring the AC impedance of the secondary battery;
A direct current resistance value analysis means,
The DC resistance value analysis means,
Based on the measurement result of the said impedance measuring means, the circuit constant computed based on the equivalent circuit of the said secondary battery, the electric current value contained in a battery DC resistance measurement condition, and OCV which is an open circuit voltage value, Calculate the response voltage,
The battery DC resistance evaluation system is calculated based on the response voltage and the battery DC resistance measurement conditions. The method of claim 1,
And said DC resistance value analyzing means corrects said response voltage using SOC-OCV table created by measuring said OCV while changing SOC which is a state of charge of said secondary battery. The method of claim 1,
And said DC resistance value analyzing means corrects said response voltage using said OCV measured while changing temperature. The method of claim 1,
The said equivalent circuit has a some CPE connected in series, The battery direct current resistance evaluation system characterized by the above-mentioned. 3. The method of claim 2,
The said equivalent circuit has a some CPE connected in series, The battery direct current resistance evaluation system characterized by the above-mentioned. The method of claim 3,
The said equivalent circuit has a some CPE connected in series, The battery direct current resistance evaluation system characterized by the above-mentioned. 7. The method according to any one of claims 1 to 6,
And said DC resistance value analyzing means corrects said circuit constant using the AC impedance of said secondary battery measured while changing temperature.

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