JP2005083798A - Method of detecting battery condition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery condition detecting method for detecting a battery condition accurately. <P>SOLUTION: A resistance R1 of a lead-acid battery is found on the basis of a direct current pulse current and a battery voltage (S104), substitution by two sets of data (I, dE/dt, dI/dt) and the resistance R1 is carried out in Expression I=f(E-IR)+C(dE/dt)-RC(dI/dt) to find a double layer capacity C1, where R represents an internal resistance, I represents the current, E represents the voltage, f is a function of known (E-RI) expressing a Faraday current, C represents the double layer capacity, and t is a time, the electric double layer capacity C1 is determined as the double layer capacity C when an absolute value of a difference between the double layer capacities C1, C2 is less than a prescribed value (S110), and the found double layer capacity is applied to a preliminarily found SOH-C map to detect an SOH of the lead-acid battery (S118). A large current characteristic in engine start is reflected onto the SOH detection. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery state detection method, and more particularly, to a battery state detection method for detecting a battery state from a relationship between a battery double layer capacity and a battery state.

  Conventionally, the internal resistance, discharge voltage, open circuit voltage, etc. of a battery are used as materials for judging the battery state such as a deteriorated state or a charged state, and the battery used for the performance improvement of automobiles, portable devices, etc. In recent years, the importance of battery state monitoring and battery state control has been increasing as the load on the battery increases.

  In the case of automobile batteries, in order to cope with idling stop / start, which is performed to reduce exhaust gas, and regenerative charging, which is performed to increase energy efficiency, the battery is put into a battery state suitable for these applications. The technology to keep is desired. Since the electric double layer capacity depends on the state of charge (SOC) or deterioration (SOH) of the battery, SOC or SOH is used as an indicator of the battery state. Lead batteries are one of the typical batteries that can be applied to these applications.

  When the electric double layer capacity is used for battery state detection, a method of measuring the electric double layer capacity by an alternating current method is common (see, for example, Patent Document 1). In such an AC method, a regular waveform such as a sine wave is superimposed on the current, and the response is analyzed.

JP 2001-235525 A

  However, when the AC method is applied to the battery to determine the electric double layer capacity, it can be seen that the current dependency is large. This is due to the fact that the effective electrode area where the electrode reaction occurs becomes narrower as the current increases. In particular, as the battery deteriorates, the current dependency of the effective electrode area increases. In addition, in an AC method apparatus used for battery state detection, the amplitude of a superimposed current wave is usually a small current of 10 A or less due to cost and other restrictions. Actually, for example, the problem with a vehicle is the output characteristics of the battery at a large current (for example, 500 A) as when the engine is started. Even if the electric double layer capacity is measured at a small current, an accurate battery The state cannot be detected (estimated).

  In view of the above-described case, an object of the present invention is to provide a battery state detection method capable of accurately detecting a battery state.

  In order to solve the above-mentioned problem, the present invention obtains the double layer capacity of the battery from the DC pulse current and the battery voltage supplied from the battery, and determines the battery from the relationship between the double layer capacity obtained in advance and the battery state. A battery state is detected.

  In the present invention, the DC pulse current and the battery voltage supplied from the battery are used to measure the double layer capacity. Therefore, when determining the double layer capacity of the battery, for example, a large current characteristic such as when the engine is started is Since it is reflected in the calculation of the multi-layer capacity, the double-layer capacity of the battery can be accurately obtained regardless of the battery state, and an AC power source is not required, so that a reduction in size and cost can be achieved.

  In the present invention, the internal resistance of the battery is obtained from the direct current pulse current and the battery voltage, the internal resistance is R, the direct current pulse current is I, the battery voltage is E, the function of (E-IR) representing the Faraday current is f, and the double layer When the capacity is C and the time is t, the double layer capacity is obtained by substituting a plurality of sets of data (I, dE / dt, dI / dt) and the internal resistance R into the following equation (1). Also good.

  In this case, when the function f is known, two sets of data (I, dE / dt, dI / dt) having the same value of (E-IR) and the internal resistance R are substituted into the equation (1) and 1 Double layer capacitance is obtained, and another two sets of data (I, dE / dt, dI / dt) having the same value of (E-IR) and the internal resistance R are substituted into the equation (1) to obtain the second second When the absolute value of the difference between the first and second double layer capacitances is less than a predetermined value, the first double layer capacitance, the second double layer capacitance, or any of the first and second double layer capacitances is obtained. The value may be obtained as the double layer capacity of the battery. As an example of such an arbitrary value, an intermediate value obtained by (first double layer capacity + second double layer capacity) / 2 can be given.

  In the present invention, the voltage change amount of the battery is obtained from the difference between two battery voltages measured at different times, and the voltage change occurs when the absolute value of the voltage change amount is longer than a predetermined value and longer than a predetermined time. By dividing the amount by the amount of current change at a predetermined time, the internal resistance of the battery is obtained and integration of DC pulse current is started, and the battery is calculated from the difference between two battery voltages measured at different times after the predetermined time has elapsed. When the absolute value of the voltage change is less than a predetermined value and continues for a predetermined time or longer, the integration of the DC pulse current is terminated, and the integrated integrated current value is divided by the voltage change over the integration time. Thus, the double layer capacity of the battery may be obtained. It should be noted that the voltage drop rate (= voltage change amount / time between different times) may be used when obtaining the voltage change amount of the battery from the difference between the two battery voltages.

  According to the present invention, since the DC pulse current and the battery voltage supplied from the battery are used to measure the double layer capacity, when determining the double layer capacity of the battery, for example, a large current characteristic such as when starting an engine. Is reflected in the calculation of the double layer capacity, so that the double layer capacity of the battery can be accurately obtained regardless of the battery state, and since no AC power supply is required, the size and cost can be reduced. The effect that can be obtained.

  In the present invention, (1) an electric double layer capacity (hereinafter referred to as a double layer capacity) of a battery is measured from a DC pulse current and a battery voltage supplied from the battery, and (2) a double layer capacity and a battery obtained in advance. The battery state of the battery is detected from the relationship with the state.

(1) Measurement of double layer capacity Since the voltage tends to be delayed from the current by the time charged in the electric double layer, the double layer capacity of the battery is calculated from this delay time. Assuming an equivalent circuit of a non-linear resistance and a double layer capacity, the relationship of the following formula (1) is established between the direct current I flowing through the battery and the battery voltage E. Here, R is the internal resistance of the battery, f is a function of (E-IR) representing the Faraday current, C is the electric double layer capacity observed as a battery with the positive and negative electrodes combined, and t is time. Current I represents charging current as positive and discharging current as negative. Note that equation (1) holds even if the voltage E is replaced with the battery polarization ΔE.

  The actual measurement parameters are I, dE / dt, and dI / dt, and the function f, the internal resistance R, and the double layer capacitance C are calculated based on these parameters. Since the function f can be obtained in advance by another method such as IV measurement, the function f may be prepared in advance. In the formula (1), for example, three sets of data having the same voltage E need to be prepared. However, when the function f is given in advance, the number of parameters to be obtained is reduced. Just prepare the data.

  In order to accurately determine the delay time, a pulse current waveform having a large peak current value and a large absolute value of the current change rate is suitable (see FIG. 3). Therefore, it is one of the timings suitable for obtaining the double layer capacity when starting the engine. Suitable timing other than when the engine is started can be considered.For example, in a vehicle with a motor assist function, the data constituting the waveform of the rising and falling timings of the motor load current at the start is used to calculate the double layer capacity You may make it do.

  Further, the measurement timing of the current I and the voltage E may be limited, and the internal resistance R may be measured independently from other parameters. When the amount of electricity after the start of the pulse discharge is sufficiently smaller than the double layer capacitance C, that is, at the timing when the pulse discharge voltage starts to fall, the internal resistance R can be calculated by the following equation (2).

  When the current I is almost the charge / discharge current of the electric double layer, the double layer capacity C can be calculated by the following equation (3). Although strict judgment of such conditions is not easy, from the normally observed double layer capacity C and the data constituting the engine start waveform to the time before the peak of the observed voltage pulse, the expression (3) Is established.

(2) Battery status detection The correspondence between the battery status of the battery of the same specification and model as the battery status detection target and the double layer capacity C is obtained in advance as shown in FIGS. 5 and 7, for example. I can keep it. The correspondence shown in FIG. 5 shows the relationship between the deterioration state (SOH) and the double layer capacitance C (Cd), and the correspondence shown in FIG. 7 shows the relationship between the state of charge (SOC) and the double layer capacitance C (Cd). It is shown. Actually, in order to obtain such a measure, the battery state (SOH, SOC, etc.) of the battery that transitions from a new state to a deteriorated state is measured by a known method, and the double layer capacity C in that battery state is started by the engine. It may be calculated from DC current and voltage data such as time (see step 112 in FIG. 2 and step 166 in FIG. 4 to be described later) to cope with SOH-C or SOC-C. Here, SOH is a ratio of the full charge capacity in the deteriorated state to the initial full charge capacity.

  In addition to the correspondence relationship of SOH-C, FIG. 5 also shows the measurement (calculation) results for the internal resistance R corresponding to SOH when the double layer capacitance C is measured. While the SOH dependency of the internal resistance R is low in a region where the SOH is high, it is difficult to use it for SOH detection (calculation) of the battery, whereas the double layer capacitance C calculated from the current / voltage data in the DC pulse has a wide range. It is highly dependent and suitable for SOH detection. In addition to the SOC-C correspondence relationship, FIG. 7 also shows the measurement results for the internal resistance R corresponding to the SOC when the double layer capacitance C is measured. In this method, the internal resistance R can be obtained from the first part where the voltage falls, and the internal resistance R thus obtained is highly SOC-dependent and can be used for detecting the SOC of the battery. In FIG. 7, there can be two SOC states with the same double layer capacity C value. For example, the open circuit voltage of the battery is separately measured to limit whether the state of charge is in a high region or a low region. For example, the double layer capacitance C can also be used for SOC detection. The size and SOC dependency of the double layer capacity C varies depending on the measurement time scale, current, and battery design, and the double layer capacity C tends to monotonically increase or decrease with respect to the SOC depending on the battery and the type of vehicle. There is. In that case, it is not necessary to limit whether the state of charge is high or low depending on the open circuit voltage.

  Such a correspondence relationship is represented, for example, as a map (table) or a relational expression by a battery (for example, a memory circuit including a plurality of resistors and a Zener diode) in a battery that is a battery state detection target or a control system that controls the battery. ) Or software (eg, writing to ROM).

  To detect the battery state, the calculated value of the double layer capacity C described above is applied to the correspondence between the battery state of the battery and the double layer capacity C by a microcomputer or the like, and the SOH, SOC, etc. of the battery to be detected Detect battery status.

  Note that the battery state detection method of the present embodiment is a versatile double layer capacity measurement method that can be used for battery state detection of various batteries such as a lithium battery in addition to a lead battery, or an electrical electrode such as an electrode for industrial electrolysis. It can also be used for evaluation of chemical equipment.

  Hereinafter, an embodiment in which the present invention is applied to an ISS control system for controlling idle stop / start (ISS) of a vehicle will be described in accordance with the above embodiment. The starting current of the vehicle of the embodiment is about 500A. For comparison, a comparative example is also shown.

(Example 1)
As shown in FIG. 1, the ISS control system 11 according to the present embodiment is configured to determine the deterioration state (SOH) of the current sensor 7 such as a Hall element that detects the current flowing through the bent lead battery 1 in series with six cells and the lead battery 1. A battery state detection unit 6 having a microcomputer (hereinafter simply referred to as a microcomputer) 8 for calculation is provided.

  A lead battery 1 having a nominal value of 12V55Ah was used. A rod-shaped positive terminal and a negative terminal for supplying electric power to the outside of the battery are erected on the upper cover of the lead battery 1. The battery state detection unit 6 is fixed to the side surface of the lead battery 1 on the side away from the vent plug.

  A positive terminal of the lead battery 1 is connected to a central terminal of an ignition switch (hereinafter referred to as IGN switch) 9 through a current sensor 7. The IGN switch 9 has an OFF terminal, an ON / ACC terminal, and a START terminal in addition to the center terminal, and can be switched and connected in a rotary manner.

  The microcomputer 8 functions as a CPU that functions as a central processing unit, a basic control program for the battery state detection unit 6, a ROM that stores a relationship map between the SOC and the double layer capacity C shown in FIG. It includes a RAM and the like. Note that the microcomputer 8 can communicate with the host vehicle-side microcomputer 10 via the I / O.

  The output terminal of the current sensor 7 is connected to an A / D converter built in the microcomputer 8, and the Hall voltage output from the current sensor 7 is converted into a digital value by the A / D converter. The current I flowing through can be captured as a digital value. Also, the positive and negative terminals of the lead battery 1 are connected to another A / D converter built in the microcomputer 8, and the microcomputer 8 can take in the voltage of the lead battery 1 as a digital value. The battery state detection unit 6 includes such wiring.

  On the other hand, a starter 3 for starting the engine 4 by transmitting the rotational driving force to the rotating shaft of the engine 4 via a clutch mechanism (not shown) is disposed on the vehicle side. Further, the rotation shaft of the engine 4 can transmit power to the generator 2 via a clutch mechanism (not shown). When the engine 4 is in a rotating state, the generator 2 is operated via this clutch mechanism. Then, the electric power from the generator 2 is supplied (charged) to the auxiliary machine 5 such as an air conditioner and a radio or the lead battery 1. Such engine control is executed by the vehicle-side microcomputer 10.

  The ON / ACC terminal of the IGN switch 9 is connected to one end of the generator 2 through the auxiliary machine 5 and a rectifying element that allows current flow in one direction. The START terminal is connected to one end of the starter 3. Furthermore, the other end of the generator 2, the starter 3 and the auxiliary machine 5, the negative terminal of the lead battery 1, and the microcomputer 8 are connected to the ground, respectively.

  Next, the operation of the ISS control system 11 will be described focusing on the operation of the CPU (hereinafter simply referred to as CPU) of the microcomputer 8 constituting the battery state detection unit 6.

  The CPU first determines whether or not the IGN switch 9 is located at the START position by determining whether or not the current I flowing through the current sensor 7 is greater than or equal to a predetermined value (for example, 0.1 A). When a negative determination is made, the process waits until the current I flowing through the current sensor 7 becomes 0.1 A or more. When an affirmative determination is made, a battery state detection routine shown in FIG. 2 is executed.

  FIG. 3 schematically shows a measurement result of the current I at the time of engine start. The current waveform of the lead battery 1 at the start of the engine is such that after the start of energization of the engine start current when the IGN switch 9 is located at the START position (time ts), a rapid first-stage pulse discharge to the starter 3 is performed. The current waveform falls sharply and a peak appears after about 50 ms (time tp). After that, the engine start is completed after a few attenuations. Although the current waveform is affected by the structure of the engine 4, the friction of the clutch connecting the engine 4 and the starter 3, etc., the waveform is generally as shown in FIG.

  As shown in FIG. 2, in the battery state detection routine, in step 102, the Hall voltage output from the current sensor 7 and the voltage between both ends of the lead battery 1 are captured as digital values and stored in the RAM. The change over time of the entire current I and voltage E is measured.

  In the next step 104, the resistance R1 and the maximum resistance Rmax are calculated by R1 = Rmax = (voltage before pulse−peak voltage) / (current before pulse−peak current). Next, in step 106, two sets of data having the same value (E-IR1) are substituted into the following equation (1a) to calculate the double layer capacitance C1, and in step 108, another value having the same value (E-IR1) is calculated. Two sets of data are substituted into the following equation (1b) to calculate the double layer capacitance C2.

  Next, in step 110, it is determined whether or not the absolute value of (double layer capacitance C1−double layer capacitance C2) is smaller than a predetermined value ΔC (for example, 0.1 (F)). When a negative determination is made, the process proceeds to step 114, and when an affirmative determination is made, in the next step 112, the internal resistance R of the lead battery 1 is the resistance R1, the electric double layer capacity C is the double layer capacity C1, and the predetermined value ΔC is (double layer). Store as capacitance C1-double layer capacitance C2) and go to step 114.

  In step 114, the resistance R1 = {resistance R1- (maximum resistance Rmax) / 1000} is calculated, and in the next step 116, it is determined whether or not the resistance R1 is smaller than zero. If a negative determination is made, the process returns to step 104. If an affirmative determination is made, the double layer capacity C stored (measured) in step 112 is obtained in advance in step 118 as shown in FIG. The deterioration state (SOH) of the lead battery 1 corresponding to the measured double layer capacity C was calculated by applying the correspondence relationship of SOH-C (stored and expanded in the RAM in the initial setting process), and calculated in the next step 120 The SOH value is notified to the vehicle-side microcomputer 10.

  The vehicle-side microcomputer 10 that has been notified of the value of the SOH of the lead battery 1 from the CPU is capable of supplying the minimum required output for the lead battery 1 to restart the engine 4 even when the engine 4 is stopped. Judge whether it is larger. If the determination is negative, the engine 4 is stopped (idle-stopped) and cannot be restarted (ISS). Therefore, while the engine 4 is maintained, the instrument panel is informed that the deterioration of the lead battery 1 has progressed. When the determination is affirmative, since the engine 4 can be restarted even if it is stopped, the driving of the engine 4 is stopped. Note that the minimum deterioration state SOHmin is preferably acquired by the vehicle-side microcomputer 10 from the microcomputer 8 by communication when the lead battery 1 is replaced, for example, when the microcomputer 8 is initially set.

(Example 2)
The ISS control system 11 according to the second embodiment includes the battery state detection unit 6 as in the first embodiment. In the present embodiment, the correspondence relationship of SOC-C is written in the ROM of the microcomputer 8 instead of the correspondence relationship of SOH-C of the first embodiment, and is expanded in the RAM at the initial setting. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted, and only different points will be described below.

  FIG. 4 shows a battery state detection routine executed by the microcomputer 8 of the second embodiment. In the battery state detection routine, first, in step 152, the current I and voltage E of the lead battery 1 are measured, and in step 154, when the voltage drop rate is lower than −100 V / s, the IGN switch 9 is switched from the lead battery 1 to the battery state detection routine. Therefore, it is assumed that power is supplied to the starter 3, and it is determined whether or not the voltage drop rate smaller than −100 V / s has continued for 1 ms or more.

  If the determination in step 154 is negative, the process returns to step 152. If the determination is positive, in step 156, the value of the internal resistance R for the first 1 ms of the voltage fall is calculated by the above-described equation (2). In step 158, integration of the current I flowing out from the lead battery 1 is started, and (E-IR) at this time is calculated and stored in the RAM.

  Next, in step 160, the current I and voltage E of the lead battery 1 are measured, and in step 162, it is determined whether or not the voltage drop rate greater than −100 V / s has continued for 1 ms or more. If the determination is negative, the process returns to step 160. If the determination is affirmative, the current integration is terminated in the next step 164, and (E-IR) at this time is calculated and stored in the RAM. Next, in step 166, the double layer capacitance C is calculated by the equation (3). In equation (3), the integrated value of current I is used as the amount of electricity that has flowed.

  In the next step 168, as shown in FIG. 7, it is applied to the SOC-C correspondence relationship (stored in the ROM and expanded in the RAM in the initial setting process) obtained in advance, and corresponds to the double layer capacity C. The state of charge (SOC) of the lead battery 1 is calculated, and the SOC value calculated in the next step 170 is notified to the vehicle-side microcomputer 10.

  Receiving the notification, the vehicle-side microcomputer 10 determines whether or not the lead-acid battery 1 is larger than the minimum deterioration state SOCmin that can supply the minimum necessary output for restarting the engine 4 even when the engine 4 is stopped. When the determination is negative, the engine 4 is stopped and cannot be restarted. Therefore, the drive of the engine 4 is maintained, and the instrument panel displays that the deterioration of the lead battery 1 has progressed. Since the engine 4 can be restarted even if it is stopped, the driving of the engine 4 is stopped.

(Comparative Example 1)
In Comparative Example 1, instead of the battery state detection unit 6 of Example 1, an alternating current impedance method using a normal impedance analyzer was used to superimpose a sine wave with an amplitude of 5 A during discharge at a frequency of 1 Hz to 1 kHz and 10 A. The internal resistance R and the double layer capacity C of the full charge with various SOH were obtained by the fitting method to the Cole-Cole plot. The result is shown in FIG. As is clear from comparison with FIG. 5, the double layer capacitance C was less changed by SOH than in Example 1. Therefore, it can be seen that SOH can be detected more accurately in Example 1 than in Comparative Example 1.

(Comparative Example 2)
In Comparative Example 2, instead of the battery state detection unit 6 of Example 2, the internal resistance R and the double layer capacity C at various SOCs were obtained by the same method as in Comparative Example 1. The result is shown in FIG. Compared to Example 2 (see FIG. 7), the variation with respect to the SOC was small. Therefore, it can be seen that the SOC can be detected more accurately in the second embodiment than in the second comparative example.

  Therefore, it turned out that Examples 1 and 2 are advantageous for battery state detection. Moreover, in Example 1, 2, since an alternating current power supply is unnecessary, size reduction and cost reduction of the battery state detection unit 6 can be achieved compared with the case where the alternating current method is used.

  According to the battery state detection method of the present invention, the battery state can be detected accurately, and contributes to the manufacture and sale of a device to which the present invention is embodied or applied, and thus has industrial applicability.

It is a block block diagram of the ISS control system of Example 1 which can apply this invention. It is a flowchart of the battery state detection routine which CPU of the microcomputer of the battery state detection unit of Example 1 performs. It is explanatory drawing which shows typically the waveform of the electric current which flows into the lead battery at the time of engine starting. It is a flowchart of the battery state detection routine which CPU of the microcomputer of the battery state detection unit of Example 2 performs. It is explanatory drawing which shows typically the correspondence map of SOH-C stored in ROM of the microcomputer of the battery state detection unit of Example 1, and also the SOH dependence of internal resistance. It is explanatory drawing which shows the SOH dependence of the internal resistance measured by the comparative example 1, and a double layer capacity | capacitance. It is explanatory drawing which shows typically the SOC dependence of internal resistance while showing typically the correspondence map of SOC-C stored in ROM of the microcomputer of the battery state detection unit of Example 2. FIG. It is explanatory drawing which shows the SOC dependence of the internal resistance measured by the comparative example 2, and a double layer capacity | capacitance.

Explanation of symbols

1 Lead battery (battery)
6 Battery status detection unit 7 Current sensor 8 Microcomputer

Claims (4)

  A battery state characterized in that a double layer capacity of the battery is obtained from a DC pulse current and a battery voltage supplied from the battery, and a battery state of the battery is detected from a relationship between the double layer capacity and the battery state obtained in advance. Detection method. The internal resistance of the battery is obtained from the direct current pulse current and the battery voltage, the internal resistance is R, the direct current pulse current is I, the battery voltage is E, and the function of (E-IR) representing the Faraday current is f, When the double layer capacitance is C and the time is t, the double layer capacitance is calculated by substituting a plurality of sets of data (I, dE / dt, dI / dt) and the internal resistance R into the following equation (1). The battery state detection method according to claim 1, wherein the battery state detection method is obtained.
  When the function f is known, two sets of data (I, dE / dt, dI / dt) having the same value of (E-IR) and the internal resistance R are substituted into the equation (1). The first double layer capacitance is obtained, and another two sets of data (I, dE / dt, dI / dt) having the same value of (E-IR) and the internal resistance R are substituted into the equation (1). The second double layer capacitance is obtained, and when the absolute value of the difference between the first and second double layer capacitances is less than a predetermined value, the first double layer capacitance, the second double layer capacitance, or the first, first The battery state detection method according to claim 2, wherein an arbitrary value between two double layer capacities is obtained as the double layer capacity of the battery.   A voltage change amount of the battery is obtained from a difference between two battery voltages measured at different times, and the voltage change amount is determined when an absolute value of the voltage change amount is longer than a predetermined value and longer than a predetermined time. The two battery voltages measured at another different time after the predetermined time elapses after the internal resistance of the battery is obtained by dividing by the amount of current change at the predetermined time and the integration of the DC pulse current is started. The voltage change amount of the battery is obtained from the difference between the DC pulse currents when the absolute value of the voltage change amount is less than the predetermined value and continues for the predetermined time or more, and the integrated current value is calculated. 2. The battery state detection method according to claim 1, wherein a double layer capacity of the battery is obtained by dividing by a voltage change amount in the integration time.