JP2005221487A - Method and instrument for measuring internal impedance of secondary battery, device for determining deterioration of secondary battery, and power source system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring an internal impedance of a secondary battery capable of avoiding complicated constitution and cost-increase, by conducting Fourier-transformation using charge and discharge currents of various waveforms not having periodicity. <P>SOLUTION: In this method of measuring the internal impedance of the secondary battery in the present invention, the charge current or the discharge current serves as an input current of the secondary battery (step S102), the input current and a response voltage of the secondary battery are measured (steps S103, S104), a plurality of current measured values and voltage measured values are acquired on a time axis, the plurality of acquired current measured values and the plurality of acquired voltage measured values are Fourier-transformed respectively to find respective frequency components of the input current and the response voltage in a prescribed frequency (steps S105, S106), and a ratio of the frequency component of the input current to the frequency component of the response voltage is found to calculate the internal impedance of the secondary battery in the prescribed frequency (step S107). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a technical field such as a method and apparatus for measuring the internal impedance of a secondary battery that supplies power to a load.

  Conventionally, a technique for measuring the internal impedance of a secondary battery such as a lead storage battery mounted in an automobile or the like has been proposed (see, for example, Patent Document 1). In general, the degradation state of the secondary battery can be determined by measuring the internal impedance of the secondary battery, which is a highly important technique. The internal impedance of the secondary battery can be obtained by detecting the current flowing through the secondary battery and the response voltage in a state where charging or discharging is not performed, and performing a predetermined calculation using both.

In Patent Document 1, as a method of measuring the internal impedance of a secondary battery, a method of obtaining internal impedance by applying a discharge current of a constant frequency to the secondary battery and Fourier transforming the discharge current waveform and the response voltage waveform. Has been proposed. By this method, the internal impedance of the secondary battery can be obtained with relatively high accuracy, and the deterioration state of the secondary battery can be accurately determined.
JP-A-10-56744

  However, the method disclosed in Patent Document 1 applies a pulse current having a constant frequency to the secondary battery. For this reason, it is necessary to provide a circuit for generating a pulse current having a constant frequency, resulting in a complicated configuration and an increase in cost. In addition, when the internal impedance of the secondary battery is determined, flowing a periodic pulse current through the secondary battery may cause unnecessary repeated charge and discharge, which may increase the consumption of the secondary battery. .

  Therefore, the present invention has been made to solve these problems. When measuring the internal impedance of a secondary battery, charging and discharging currents having various waveforms having no periodicity were passed through the secondary battery. Since the internal impedance is measured by performing Fourier transform of the input current and response voltage in the state, the inside of the secondary battery that can avoid the complicated configuration and cost increase and suppress the consumption of the secondary battery The object is to provide an impedance measurement method and the like.

  In order to solve the above problem, the internal impedance measuring method of the secondary battery according to claim 1, wherein the charging current or discharging current is used as the input current of the secondary battery, and the input current and response voltage of the secondary battery are measured. And acquiring a plurality of current measurement values and voltage measurement values on a time axis, and performing a Fourier transform on the acquired plurality of current measurement values and voltage measurement values, respectively, and Each frequency component of the response voltage is obtained, and an internal impedance of the secondary battery at the predetermined frequency is calculated by taking a ratio between the frequency component of the input current and the frequency component of the response voltage.

  According to the present invention, when charging / discharging the secondary battery, the frequency components of the input current and the response voltage are obtained by Fourier transform while flowing the charging / discharging current to the secondary battery, thereby the secondary battery. Since the internal impedance is calculated, a current generator other than the charge / discharge circuit and complicated control are not required, and the overall configuration can be simplified and the cost can be reduced. In addition, since the Fourier transform is used, it is not necessary to use a pulse current with a constant frequency, and the internal impedance can be measured while flowing a normal charge / discharge current to the secondary battery. The consumption of the secondary battery due to the application can be prevented.

  The internal impedance measuring method of the secondary battery according to claim 2 is the invention according to claim 1, wherein the plurality of current measurement values and the plurality of voltage measurement values are each sampled at a predetermined time interval Δt. It consists of N measurement values, and each frequency component of the input current and the response voltage at the predetermined frequency is obtained by a discrete Fourier transform.

  According to the present invention, in addition to the operation of the above-described invention, the input current and the response voltage of the secondary battery are sampled, the current measurement values and the voltage measurement values are respectively acquired, and the discrete Fourier transform is applied. The internal impedance of the secondary battery can be calculated by relatively simple arithmetic processing, and the overall configuration and control can be simplified.

  The internal impedance measuring method of the secondary battery according to claim 3 is the invention according to claim 2, wherein the frequency component I (ω) of the input current and the frequency component V (ω) of the response voltage are the predetermined values. Let the frequency be F, and for the integer n (n = 0, 2,..., N−1), the N measured current values are i (n · Δt) and the N measured voltage values are v (n · Δt). When

(However, ω = 2πF)
Respectively, and the internal impedance Z (ω) is

It is calculated by these.

  According to the present invention, in addition to the operation of the above-described invention, the internal impedance Z (ω) can be calculated by a clear and simple calculation process, and the calculation process can be freely optimized by setting the predetermined frequency F and sampling conditions. Can be planned.

  The internal impedance measurement method for a secondary battery according to claim 4 is the invention according to any one of claims 1 to 3, wherein the internal impedance includes a plurality of components corresponding to at least M different frequencies. The M circuit constants are calculated by calculating and solving simultaneous equations having M circuit constants included in the equivalent circuit of the secondary battery as unknowns based on a plurality of components of the internal impedance. And

  According to the present invention, in addition to the operation of the above-described invention, the constants constituting the equivalent circuit of the secondary battery can be determined by solving simultaneous equations with a plurality of frequency components of the internal impedance, and can be applied to more complicated analysis. can do.

  The internal impedance measuring device for a secondary battery according to claim 5 is a charging circuit that supplies a charging current when the secondary battery is charged, a discharging circuit that supplies a discharging current when the secondary battery is discharged, and the charging current. Alternatively, sensor means for measuring the input current and response voltage of the secondary battery using the discharge current as the input current of the secondary battery, and a plurality of current measurement values and voltages on the time axis based on the measurement results of the sensor means A measurement value is obtained, and each of the obtained current measurement value and the plurality of voltage measurement values is Fourier transformed to obtain respective frequency components of the input current and the response voltage at a predetermined frequency, and the input current Control means for calculating the internal impedance of the secondary battery at the predetermined frequency by taking a ratio of the frequency component of the response voltage and the frequency component of the response voltage. And butterflies.

  The internal impedance measuring device for a secondary battery according to claim 6 is the invention according to claim 5, wherein the control means is configured to each of the plurality of current measurement values and the plurality of voltage measurement values as predetermined time intervals. N measurement values sampled at Δt are acquired, and respective frequency components of the input current and the response voltage at the predetermined frequency are obtained by discrete Fourier transform.

  The secondary battery deterioration determination device according to claim 7 determines the deterioration state of the secondary battery based on the internal impedance calculated by the internal impedance measurement device of the secondary battery according to claim 5 or 6. It is characterized by that.

  The power supply system of Claim 8 is provided with the internal impedance measuring apparatus of the secondary battery of Claim 5 or Claim 6.

  According to the present invention, when measuring the internal impedance of the secondary battery, the input current and the response voltage are measured during charging or discharging, and the internal impedance of the secondary battery at a predetermined frequency is calculated by performing Fourier transform. Thus, it is not necessary to provide a special current generator or use a current having a periodic waveform. Therefore, it is possible to realize a secondary battery internal impedance measuring device or the like that is beneficial in terms of simplification of configuration and cost reduction and that can suppress the consumption of the secondary battery.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. Here, the case where this invention is applied with respect to the power supply system provided with the function to measure the internal impedance of a secondary battery is demonstrated.

  FIG. 1 is a block diagram illustrating a schematic configuration of a power supply system according to the present embodiment. In FIG. 1, a power supply system is configured including a secondary battery 10, a current sensor 11, a voltage sensor 12, a control unit 13, a storage unit 14, a charging circuit 15, and a discharging circuit 16. Electric power is supplied from the battery 10 to various loads 20.

  In the configuration of FIG. 1, for example, a lead storage battery for a vehicle is known as the secondary battery 10 for supplying power to the load 20. Here, an equivalent circuit of the secondary battery 10 is shown in FIG. As shown in FIG. 2, the secondary battery 10 may be represented by an equivalent circuit in which resistors RΩ, Rct1, Rct2, and Rct3 are combined with capacitors Cd1, Cd2, and Cd3, and a positive electrode, an electrolyte, and a negative electrode are sequentially connected. it can. In this case, the internal impedance of the secondary battery 10 is represented by a complex impedance that matches the configuration of the series-parallel circuit of each resistor and capacitor in FIG. As will be described later, in the secondary battery 10 represented by the equivalent circuit of FIG. 2, the input current and the response voltage are each subjected to Fourier transform, and each frequency component at a predetermined frequency obtained as a result is used. The internal impedance can be calculated.

  Next, in FIG. 1, the current sensor 11 detects a current flowing through the secondary battery 10 and sends a current value to the control unit 13. The voltage sensor 12 detects the voltage across the secondary battery 10 and sends the voltage value to the control unit 13. These current sensor 11 and voltage sensor 12 function as sensor means of the present invention.

  The control unit 13 that functions as a control unit of the present invention is configured by a CPU, controls the operation of the entire power supply system, and executes calculation processing necessary for calculating internal impedance described later at a predetermined timing. The internal impedance is sent to the vehicle control device. The storage unit 14 connected to the control unit 13 includes a ROM that stores various programs such as a control program in advance, a RAM that temporarily stores data necessary for processing by the control unit 13, and the like.

  The charging circuit 15 is a circuit that supplies a charging current when the secondary battery 10 is charged. The discharge circuit 16 is a circuit that supplies a discharge current that flows from the secondary battery 10 to the load 20 when the secondary battery 10 is discharged. The charging circuit 15 and the discharging circuit 16 are controlled by the control unit 15, and the charging circuit 15 is turned on during the charging operation, and the discharging circuit 16 is turned on during the discharging operation.

  In the present embodiment, the charging current supplied from the charging circuit 15 and the discharging current supplied to the load 20 via the discharging circuit 16 can use various waveforms. That is, since Fourier transform is performed instead of Fourier expansion in the arithmetic processing described later, the Fourier transform can be calculated using various waveforms having no periodicity without being restricted by a pulse waveform having a constant frequency. However, in order to increase the calculation accuracy of the Fourier transform for the discharge current or the charge current, it is preferable to use a waveform pattern that sufficiently includes the required frequency component. Since the frequency is set to about 20 Hz as will be described later, the calculation accuracy can be improved by using a charging current or a discharging current whose waveform changes with time.

  Next, specific processing when measuring the internal impedance of the secondary battery 10 in the power supply system according to the present embodiment will be described. FIG. 3 is a flowchart showing a flow of processing mainly executed by the control unit 13 based on a control program held in the storage unit 14. The arithmetic processing shown in FIG. 3 is started at a predetermined timing when the secondary battery 10 is being charged or discharged in the power supply system.

  In FIG. 3, when processing in the power supply system is started, parameters necessary for calculation by the control unit 13 are initialized (step S101). Parameters to be initially set in step S101 include sampling interval Δt and sampling number N when acquiring a plurality of current measurement values and voltage measurement values, a predetermined reference frequency F in internal impedance measurement, and the like.

  In step S101, for example, initial setting values such as Δt = 0.001 (seconds), N = 100 (pieces), F = 20 (Hz) may be used. Note that an appropriate fixed initial setting value according to the characteristics of the secondary battery 10 can be determined in advance, but the initial setting value may be changed as appropriate according to the operation state or the like.

  Next, it is determined whether or not the secondary battery 10 is started to be charged or discharged (step S102). Depending on the power supply system, the measurement is different during the charging operation or during the discharging operation. In the case of a power supply system that always supplies a certain amount of power to a load during use of a device or apparatus, it is often desirable to measure during a charging operation. Depending on the power supply system, the charging and discharging timings may be set in advance. In that case, it is determined in S102 whether the timing of charging or discharging has been reached.

  If it is determined in step S102 that the charging operation or discharging operation is started, then measurement of the input current and response voltage of the secondary battery 10 is started (step S103). Measurement is performed under the conditions set in step S101. Is performed (step S104). Specifically, the input current of the secondary battery 10 is detected by the current sensor 11 and N current measurement values are sequentially acquired at the sampling interval Δt, and at the same time, the response voltage of the secondary battery 20 is detected by the voltage sensor 12. The N voltage detection values are sequentially acquired at the sampling interval Δt. As a result, N current measurement values corresponding to the input current of the secondary battery 10 and N voltage measurement values corresponding to the response voltage of the secondary battery 10 are obtained on the time axis.

  Here, when the time function of the input current is represented by i (t) and the time function of the response voltage is represented by v (t), an integer n that varies in the range of 0, 2, 3, to N−1 is used. The measured current value obtained in step S104 can be expressed as i (n · Δt), and the measured voltage value can be expressed as v (n · Δt).

  Next, the frequency component of the input current at the reference frequency F is calculated using the N current measurement values obtained in step S104 (step S105). Similarly, the frequency component of the response voltage at the reference frequency F is calculated using the N voltage measurement values obtained in step S104 (step S106).

  In general, the frequency component Y (ω) represented by the following equation (1) can be obtained by Fourier transforming an arbitrary time function y (t).

However, ω = 2πf (f: frequency)
Therefore, the frequency component I (ω) when the input current of the secondary battery 10 is Fourier transformed can be expressed as the following equation (2) using the time function i (t).

Further, the frequency component V (ω) when the response voltage of the secondary battery 10 is Fourier-transformed can be expressed as the following equation (3) using the time function v (t).

When the calculation in step S104 is actually performed, a discrete Fourier transform is performed using N current measurement values i (n · Δt) corresponding to the time function i (t) in equation (2), and As shown in the equation (4), the frequency component I (ω) of the input current at the reference frequency F is calculated.

However, ω = 2πF (F: reference frequency)
Similarly, when the calculation of step S105 is actually performed, a discrete Fourier transform is performed using N current measurement values v (n · Δt) corresponding to the time function v (t) in equation (3), and As shown in equation (5), the frequency component V (ω) of the response voltage at the reference frequency F is calculated.

However, ω = 2πF (F: reference frequency)
Then, the internal impedance Z (ω) of the secondary battery 10 at the reference frequency F is calculated based on the calculation results of the above expressions (4) and (5) (step S107). That is, the ratio of the frequency component I (ω) of the input current and the frequency component V (ω) of the response voltage is taken, and the internal impedance Z (ω) at the reference frequency F may be obtained according to the following equation (6).

However, ω = 2πF (F: reference frequency)
Note that the internal impedance Z (ω) obtained by equation (6) may be calculated as a real part, but it is also possible to calculate an imaginary part or an absolute value.

  For the internal impedance Z (ω) calculated according to the above equation (6), for example, only one component corresponding to F = 20 (Hz) may be obtained, or a plurality of components corresponding to a plurality of frequencies may be obtained. Good. That is, M frequencies F1, F2,... FM may be set in advance, and calculation of equation (6) may be performed for each of them to obtain M internal impedances Z1, Z2,. In this case, simultaneous equations including M unknowns can be solved by using the calculation results of M internal impedances. For example, in the equivalent circuit of the secondary battery 10 shown in FIG. 2, it is possible to establish a simultaneous equation with M circuit constants as unknowns and substitute the calculation results of M internal impedances to determine the circuit constants.

  The internal impedance obtained based on the processing shown in FIG. 3 is used, for example, when detecting the deterioration state of the secondary battery 10 in the power supply system. In general, since the internal impedance of the secondary battery 10 is strongly correlated with the deterioration state of the secondary battery 10, the degree of deterioration of the secondary battery 10 can be determined based on the measurement result of the internal impedance.

  FIG. 4 is a diagram for explaining the relationship between the internal impedance of the secondary battery 10 and the deterioration state. FIG. 4 shows changes in the internal impedance of the secondary battery 10 and changes in the discharge voltage of the secondary battery 10 when a long-term deterioration test of the secondary battery 10 is performed. In the deterioration test of FIG. 4, the internal impedance was measured at 25 ° C., and the discharge voltage was measured at −30 ° for two types of input currents (10A and 25A) at 10 seconds after the start of discharge.

  As shown in FIG. 4, the internal impedance of the secondary battery 10 is stable in the initial state, but the elapsed time has increased from around 30 to 35 weeks. On the other hand, it can be seen that the discharge voltage of the secondary battery 10 has been drastically reduced since the passage of time has passed 35 weeks, and is greatly deteriorated. Further, the degree of deterioration of the secondary battery 10 increases as the input current increases. From such a test result, the usage time of the secondary battery 10 reaches a limit when it reaches 35 to 40 weeks.

  Based on the change in the deterioration state as shown in FIG. 4, it is possible to monitor the increase in the internal impedance calculated as described above and grasp the deterioration state of the secondary battery 10. For example, when the calculated internal impedance exceeds a predetermined set value, it may be determined that the secondary battery 10 is in a deteriorated state, and a display that prompts the user to replace the secondary battery 10 may be performed.

  As described above, according to the present invention, when the internal impedance of the secondary battery 10 is measured, the charging current supplied from the charging circuit 15 or the discharging current supplied from the discharging circuit 16 is used as it is. This eliminates the need for a special current generator and processing associated with operation control, and is advantageous in terms of simplifying the configuration and control of the entire power supply system and reducing costs. In this case, since the Fourier transform method is used to calculate the internal impedance, it is not necessary to use a periodic pulse waveform for the charging current or the discharging current, increasing the degree of freedom in measurement and eliminating the need for an additional circuit configuration. Further, since the internal impedance is measured during the normal charging operation or discharging operation of the secondary battery 10, it is not necessary to repeatedly apply unnecessary current to the secondary battery 10, and the secondary battery 10 can be prevented from being consumed. it can.

It is a block diagram which shows the structure of the outline of the power supply system which concerns on this embodiment. It is a figure which shows the equivalent circuit of a secondary battery. It is a flowchart explaining the specific process at the time of measuring the internal impedance of a secondary battery in the power supply system which concerns on this embodiment. It is a figure explaining the relationship between the internal impedance of a secondary battery, and a deterioration state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Secondary battery 11 ... Current sensor 12 ... Voltage sensor 13 ... Control part 14 ... Memory | storage part 15 ... Charge circuit 16 ... Discharge circuit 20 ... Load

Claims (8)

The charging current or discharging current is set as the input current of the secondary battery, the input current and the response voltage of the secondary battery are measured, and a plurality of current measurement values and voltage measurement values are obtained on the time axis,
Each of the obtained current measurement values and the plurality of voltage measurement values is subjected to Fourier transform to obtain respective frequency components of the input current and the response voltage at a predetermined frequency,
A method for measuring internal impedance of a secondary battery, wherein an internal impedance of the secondary battery at the predetermined frequency is calculated by taking a ratio of a frequency component of the input current and a frequency component of the response voltage. The plurality of current measurement values and the plurality of voltage measurement values are each composed of N measurement values sampled at a predetermined time interval Δt,
The method for measuring internal impedance of a secondary battery according to claim 1, wherein frequency components of the input current and the response voltage at the predetermined frequency are obtained by discrete Fourier transform. The frequency component I (ω) of the input current and the frequency component V (ω) of the response voltage have the predetermined frequency F, and the N currents for an integer n (n = 0, 2,... N−1). When the measured value is i (n · Δt) and the N voltage measured values are v (n · Δt),
(However, ω = 2πF)
Respectively, and the internal impedance Z (ω) is
The internal impedance measurement method for a secondary battery according to claim 2, wherein   As the internal impedance, a plurality of components corresponding to at least M different frequencies are calculated, and simultaneous equations having M circuit constants included in the equivalent circuit of the secondary battery as unknowns are expressed as a plurality of components of the internal impedance. The method of measuring the internal impedance of the secondary battery according to claim 1, wherein the M circuit constants are calculated by solving based on: A charging circuit for supplying a charging current when charging the secondary battery;
A discharge circuit for supplying a discharge current when the secondary battery is discharged;
Sensor means for measuring the input current and response voltage of the secondary battery using the charge current or the discharge current as the input current of the secondary battery,
A plurality of current measurement values and voltage measurement values are acquired on a time axis based on the measurement result of the sensor means, and the acquired plurality of current measurement values and voltage measurement values are respectively Fourier transformed to obtain a predetermined frequency. Control means for calculating the internal impedance of the secondary battery at the predetermined frequency by obtaining the frequency components of the input current and the response voltage of the input current and taking the ratio of the frequency component of the input current and the frequency component of the response voltage When,
A device for measuring internal impedance of a secondary battery, comprising:   The control means acquires N measurement values sampled at a predetermined time interval Δt as the plurality of current measurement values and the plurality of voltage measurement values, respectively, and the input current and the response voltage at the predetermined frequency 6. The internal impedance measuring device for a secondary battery according to claim 5, wherein each of the frequency components is obtained by discrete Fourier transform.   7. A secondary battery deterioration determination device, wherein the deterioration state of the secondary battery is determined based on the internal impedance calculated by the internal impedance measurement device of the secondary battery according to claim 5. The power supply system provided with the internal impedance measuring apparatus of the secondary battery of Claim 5 or Claim 6.