JP2012189380A - Secondary battery system and method for determining state of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for determining the state of a secondary battery.SOLUTION: A secondary battery system 10 comprises a plurality of secondary batteries 50 connected in series and a voltmeter for sequentially measuring a voltage value of the plurality of secondary batteries 50. In determining the state of the secondary batteries 50, the secondary battery system 10 measures a voltage value V of each secondary battery 50 to calculate a differential voltage value ΔV. In addition, the differential voltage value ΔV is divided by a period ΔT used for calculating the differential voltage value ΔV to calculate a determination value H and the state of the secondary batteries 50 is determined using the determination value H. Since the differential voltage value ΔV is proportional to the internal resistance of the secondary batteries 50, the state of the secondary batteries 50 may be determined using the determination value H.

Description

  The present invention relates to a technique for determining a state such as deterioration of a secondary battery system.

  Conventionally, a system including a rechargeable secondary battery is known. Secondary batteries can be used many times by repeating charging and discharging, are more environmentally friendly than non-chargeable batteries, and are currently expanding their fields of use such as electric vehicles.

  In such a system, as the number of uses increases, the internal resistance of the secondary battery increases due to deterioration, and the capacity decreases. When the internal resistance of the secondary battery increases or the capacity decreases, the performance required for the battery such as maximum voltage and maximum power cannot be realized, and for example, malfunction due to voltage drop may occur. Therefore, conventionally, a technique for determining a state such as deterioration of a secondary battery is known (for example, cited document 1). In this technique, the voltage of the charged and discharged secondary battery and the current discharged from the secondary battery are measured, and the internal resistance is calculated using Ohm's law. Thus, it is possible to calculate the amount of increase in internal resistance from a known state such as the initial state, and to detect a state such as deterioration of the secondary battery.

JP 2005-195604 A

  As a result of repeated evaluation of other methods for determining the state of the secondary battery, the inventors have created a new method for determining the state of the secondary battery based on the amount of change in the battery voltage in the charge / discharge state. It came to.

  The present invention provides a technique for determining the state of a secondary battery.

  The present invention relates to a state determination method for a secondary battery system including a plurality of secondary batteries connected in series and a voltage measurement unit that sequentially measures the voltages of the plurality of secondary batteries. The secondary battery includes a first secondary battery and a second secondary battery, and the first voltage value measured at a first timing with respect to the first secondary battery and the second secondary battery. The plurality of secondary batteries using a determination value obtained by dividing a voltage difference value from a second voltage value measured at a second timing by a time difference between the first timing and the second timing. The state of is determined.

  In this secondary battery system state determination method, a function of sequentially measuring the battery voltages of a plurality of secondary batteries is used, and the difference between the battery voltages of the two secondary batteries when the battery voltages are sequentially measured is calculated using these two battery voltages. A value obtained by dividing the battery voltage of the secondary battery by the time difference of the measured timing is calculated as a determination value. According to this state determination method, the internal resistance of the secondary battery can be evaluated from the determination value, whereby the state of the secondary battery can be easily determined.

  The state determination method of the secondary battery system may include a configuration in which the state of the plurality of secondary batteries is determined by comparing the determination value with a predetermined reference value. According to the state determination method of the secondary battery system, the determination value is compared with the reference value stored in the secondary battery system, so that the state of the secondary battery assumed in advance corresponding to the reference value is obtained. Based on this, the state of the secondary battery can be determined.

  The present invention is also embodied in a secondary battery system capable of executing the above-described secondary battery system state determination method. A secondary battery system according to the present invention is a secondary battery system including a plurality of secondary batteries connected in series and a voltage measurement unit that sequentially measures the voltages of the plurality of secondary batteries. The secondary battery includes a first secondary battery and a second secondary battery, and the first voltage value measured at a first timing with respect to the first secondary battery and the second secondary battery. The plurality of secondary batteries using a determination value obtained by dividing a voltage difference value from a second voltage value measured at a second timing by a time difference between the first timing and the second timing. The determination part which determines the state of is provided. According to this state determination method, the state determination method of the secondary battery system can be executed, and thereby the state of the secondary battery can be determined.

  According to the present invention, the state of the secondary battery can be determined.

Block diagram of the secondary battery system of the present embodiment The flowchart which shows the state determination process of this embodiment Graph showing voltage value V and integrated current amount ΣI Graph showing voltage value V and integrated current amount ΣI Graph explaining the deterioration determination of this embodiment

<Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.
1. Configuration of Secondary Battery System FIG. 1 is a diagram illustrating a configuration of a secondary battery system 10 in the present embodiment. The secondary battery system 10 includes a battery group 26 including a plurality of secondary batteries 50 and has a function of determining a state such as deterioration of the secondary battery 50. The secondary battery system 10 can determine the state of the secondary battery 50 and the battery group 26 in the discharged state by being connected to the load 14, and can be connected to the charger to The states of the secondary battery 50 and the battery group 26 can be determined. In this embodiment, the example at the time of connecting the secondary battery system 10 to the load 14 is shown.

As shown in FIG. 1, the secondary battery system 10 includes an ammeter 22, a battery management device (hereinafter referred to as “BMS”) 20 including a voltmeter 24, a battery group 26, and a wiring 28.
The battery group 26 includes N secondary batteries 50 of the same type (N: a natural number of 2 or more), and these secondary batteries 50 are connected in series. The battery group 26 is connected to the load 14 via the wiring 28 and the output terminal 12, and supplies the power stored in the battery group 26 to the load 14. An ammeter 22 is connected to the wiring 28, and the current flowing through each secondary battery 50 of the battery group 26 is measured in accordance with a command from a central processing unit (hereinafter referred to as CPU) 30 described later.

  The voltmeter 24 is connected to the bipolar terminals of each secondary battery 50 of the battery group 26 and measures the voltage of each secondary battery 50. The voltmeter 24 measures the voltage of one secondary battery 50 at a time. Therefore, the voltmeter 24 switches the secondary battery 50 to be measured according to a command from the CPU 30 and sequentially measures the voltage of each secondary battery 50. The battery voltage of the secondary battery 50 is continuously measured by periodically repeating the battery voltage of the N secondary batteries 50 connected in series.

  The BMS 20 includes a CPU 30, a memory 32 such as a ROM or a RAM, and an analog / digital converter (hereinafter referred to as “ADC”) 34.

  Various programs for controlling the operation of the secondary battery system 10 are stored in the memory 32, and the CPU 30 functions as a determination unit 42, a calculation unit 44, and the like according to the program read from the memory 32. Each unit such as the total 22 and the voltmeter 24 is controlled. The memory 32 also stores a map M in which the reference current value IK and the reference value K are associated as will be described later.

  The ADC 34 is connected to the ammeter 22 and the voltmeter 24, converts the current value I and the voltage value V, which are analog data transmitted from the ammeter 22 and the voltmeter 24, into digital data, and stores them in the memory 32. To do. As will be described later, the CPU 30 functioning as the calculation unit 44 calculates the determination value H using the voltage value V or the like stored in the memory 32.

2. State Determination Processing State determination processing such as deterioration of the secondary battery 50 in the secondary battery system 10 will be described with reference to FIGS. FIG. 2 shows a flowchart of the state determination process executed by the CPU 30.

  When the secondary battery system 10 is connected to the load 14 by the user and the supply of power to the load 14 is started by the user, the CPU 30 executes a state determination process at a certain measurement cycle F described later according to a program stored in the memory 32. To do. When starting the state determination process, the CPU 30 measures the voltage value V of the secondary battery 50 and the current value I of the discharge current (S2).

  When the measurement is started, the CPU 30 outputs a command for measuring the voltage value V of the secondary battery 50 to the voltmeter 24. The CPU 30 stores a measurement interval ΔX in advance. When receiving a command from the CPU 30, the voltmeter 24 switches the secondary battery 50 connected at every measurement interval ΔX and measures the voltage value V of the secondary battery 50. The voltmeter 24 switches and measures the secondary batteries 50 included in the battery group 26 in the order of the secondary batteries 50A, 50B,... 50M, 50N. The measured voltage values VA, VB,..., VM, VN are stored in the memory 32 via the ADC 34.

  The battery voltage of the secondary batteries 50A to 50N is continuously measured by periodically repeating the measurement of the battery voltage of the secondary batteries 50A to 50N. When the battery voltage of any of the secondary batteries 50 reaches the discharge end voltage in the continuous battery voltage measurement, the discharge of the secondary battery system 10 is stopped.

  Further, the CPU 30 outputs a command for measuring the current value I of the discharge current flowing through the secondary battery 50 to the ammeter 22. When the voltmeter 24 receives a command from the CPU 30, the voltmeter 24 measures a current value over a measurement period T during which the voltage value V of the secondary battery 50 is measured by the voltmeter 24. Similarly to the voltage value V, the measured current value I is stored in the memory 32 via the ADC 34.

  FIG. 3 shows the voltage value V of the secondary battery 50 measured in S4. In FIG. 3, the left vertical axis indicates the value of each voltage value V, and the horizontal axis indicates the time tA, tB,... TM, tN when the voltage value V is measured. As described above, each time tA, tB,... TM, tN is set to the measurement interval ΔX, and (N−1) × ΔX including these measurement intervals ΔX is the measurement period T. It becomes. FIG. 3 also shows the current value I measured in S4 (see the right vertical axis).

  In the present embodiment, the current value I is kept substantially constant during the measurement period T of the secondary battery 50. On the other hand, when the discharge current flows, the voltage value V of the secondary battery 50 decreases. As shown in FIG. 3, the voltage values VA, VB,..., VM, VN of the secondary batteries 50A, 50B,... 50M, 50N decrease in this order, and as a result, from the time tA to the time tN. Due to the discharge current up to, a differential voltage value ΔV (ΔVAN) is generated between the voltage value VA of the secondary battery 50A and the voltage value VN of the secondary battery 50N.

  On the other hand, depending on the load 14 to which the secondary battery system 10 is connected, the discharge current may begin to flow behind the start of the measurement period T of the secondary battery 50 as shown in FIG. For example, the current may flow from the measurement time tC of the voltage value VC of the secondary battery 50C. In this case, the voltage value V of each secondary battery 50 does not change from time tA to time tC when no discharge current flows, and the differential voltage value ΔV (ΔVCN) corresponding to the period from time tC to time tN is Has occurred.

  Next, the CPU 30 evaluates the variation in the voltage value V0 measured in the previous cycle (S4). The CPU 20 repeats the state determination process every predetermined time, and stores the voltage value V and the current value I measured in each process in the memory 32. The CPU 30 functions as the determination unit 42, reads the voltage value V0 and the current value I0 measured in the previous cycle from the memory 32, and performs evaluation. For example, when the voltage value V0 measured in the previous cycle varies from a specified value, or the discharge current flows through the secondary battery 50, the voltage value V of the secondary battery 50 is equal to the previous cycle. When the voltage value V0 is increased at time t (S4: NO), it is determined that the variation in the voltage value V is large, and the process is terminated.

  When it is determined that the variation in the voltage value V0 is small (S4: YES), the CPU 20 evaluates the current value I measured this time (S6). At this time, the CPU 20 functions as the calculation unit 44 and calculates a difference current value ΔI between the current value I measured this time and the current value I0 measured last time. At this time, when the current values I and I0 fluctuate in the corresponding measurement period T, an average value of the current values I and I0 is calculated, and a difference current value ΔI between the average values is calculated. The memory 32 stores a limit difference current value ΔIG in advance. The CPU 30 functions as the determination unit 42 and compares the calculated difference current value ΔI with the limit difference current value ΔIG.

  When the calculated difference current value ΔI is larger than the limit difference current value ΔIG (S6: NO), it is confirmed that the current value I measured this time is greatly changed compared to the current value I0 measured last time. I mean. In this case, even when the differential voltage value ΔV of the voltage value V measured this time is different from the differential voltage value ΔV0 of the voltage value V0 measured last time, the difference is due to the deterioration of the secondary battery 50. It is determined that it cannot be distinguished whether there is a difference in the current value I flowing through the secondary battery 50, and the process is terminated.

  On the other hand, when the differential current value ΔI is equal to or smaller than the limit differential current value ΔIG (S6: YES), the CPU 30 functions as the calculation unit 44, and the maximum voltage value Vmax and the minimum voltage among the measured voltage values V are determined. A value Vmin is selected, and a differential voltage value ΔV between the maximum voltage value Vmax and the minimum voltage value Vmin is calculated (S8). As shown in FIG. 3, when the discharge current is flowing over the measurement period T of the secondary battery 50, the maximum voltage value Vmax is VA, the minimum voltage value Vmin is VN, and the differential voltage value ΔV is ΔVAN. . As shown in FIG. 4, when the current flows from the measurement time tC of the measurement period T of the secondary battery 50, the maximum voltage value Vmax is VC, the minimum voltage value Vmin is VN, and the differential voltage value ΔV is ΔVCN.

  Next, the CPU 30 evaluates the differential voltage value ΔV of the calculated voltage value V (S10). The memory 32 stores a limit difference voltage value ΔVG in advance. The CPU 30 functions as the determination unit 42 and compares the calculated differential voltage value ΔV with the limit differential voltage value ΔVG. When the calculated differential voltage value ΔV is smaller than the limit differential voltage value ΔVG (S10: NO), the CPU 30 ends the process. On the other hand, when the calculated differential voltage value ΔV is equal to or greater than the limit differential voltage value ΔVG (S10: YES), the processing is continued.

  When the differential voltage value ΔV is equal to or greater than the limit differential voltage value ΔVG, the period used for calculating the differential voltage value ΔV, that is, the period during which the discharge current flows in the measurement period T of the secondary battery 50 is the limit differential voltage value. It is longer than the reference period assumed from ΔVG. Therefore, as will be described later, when the determination value H is calculated from the differential voltage value ΔV and the determination is made, the determination can be made using the differential voltage value ΔV calculated from a relatively long period. Thus, the determination value H is set based on the difference voltage value ΔV at the adjacent time t, for example, the difference voltage value ΔVAB between the voltage value VA of the secondary battery 50 at the time tA and the voltage value VB of the secondary battery 50 at the time tB. Compared to the case of calculation, the determination value H can be calculated using the average differential voltage value ΔV in the measurement period T of the secondary battery 50, and the secondary battery 50 can be accurately determined using the determination value H. can do.

  Next, the CPU 30 calculates a determination value H (= ΔV / ΔT) (S12). The CPU 30 functions as the calculation unit 44, and calculates the determination value H by dividing the differential voltage value ΔV calculated in S8 by the period ΔT used for calculating the differential voltage value ΔV in S8. As shown in FIG. 3, when the differential voltage value ΔV is ΔVAN, the determination value H = ΔVAN / ΔTAN is calculated by dividing ΔVAN by a period ΔT (ΔTAN) from time tA to time tN. As shown in FIG. 4, when the differential voltage value ΔV is ΔVCN, the determination value H = ΔVCN / ΔTCN is calculated by dividing the ΔVCN by a period ΔT (ΔTCN) from time tC to time tN.

  Next, the CPU 30 stores the selected maximum voltage value Vmax and minimum voltage value Vmin and the calculated determination value H in the memory 32 (S14). The memory 32 stores a map M in which the reference current value IK and the reference value K are associated with each other. The CPU 30 selects the current value measured this time among the plurality of reference current values IK stored in the map M. A reference current value IK closest to I is selected, and a reference value K stored in association with the selected reference current value IK is selected (S16). In the present embodiment, since the reference value K is selected based on the current value I measured this time, the current value is determined when determining the state of the secondary battery 50 using the determination value H, as will be described later. The exact situation of the secondary battery 50 can be determined by suppressing the influence of I. In the present embodiment, the reference value K = ΔV ′ / ΔTAN obtained by dividing the reference differential voltage value ΔV ′ by the period ΔTAN from time tA to time tN is selected as the reference value K.

  Next, the CPU 30 determines a determination value H (S18). The CPU 20 functions as the calculation unit 44 and calculates a difference value ΔH = (ΔV−ΔV ′) / ΔTAN between the determination value H calculated in S12 and the reference value K selected in S16. The memory 32 stores a limit determination value ΔHG in advance. The CPU 30 functions as the determination unit 42 and compares the calculated difference value ΔH with the limit determination value ΔHG.

  When the calculated difference value ΔH is larger than the limit determination value ΔHG (S18: NO), as shown by the arrow 52 in FIG. This means that the limit difference value ΔHG has changed beyond the assumed allowable range compared to the assumed reference differential voltage value ΔV ′. In other words, it means that the internal resistance R of the secondary battery 50 has increased beyond the allowable range of the internal resistance R that is assumed to cause the secondary battery 50 to operate normally. In this case, the CPU 30 determines that the secondary battery 50 has deteriorated (S20), and ends the process.

  On the other hand, when the difference value ΔH is equal to or smaller than the limit determination value ΔHG (S18: YES), the internal resistance R of the secondary battery 50 is within the allowable range of the internal resistance R that is assumed to cause the secondary battery 50 to operate normally. Means that. In this case, the CPU 30 determines that the secondary battery 50 has not deteriorated (S22), and ends the process.

3. Advantages of the present embodiment (1) In the secondary battery system 10 of the present embodiment, the function of sequentially measuring the battery voltages of a plurality of secondary batteries is used, and two secondary batteries when the battery voltages are sequentially measured are used. A value obtained by dividing the difference between the battery voltages by the time difference between the timings when the battery voltages of the secondary batteries are measured is calculated as a determination value. From this determination value, the internal resistance of the secondary battery can be evaluated, whereby the state of the secondary battery can be easily determined. Thereby, the state of the battery group 26 including the secondary battery 50 can be determined, and finally an abnormality of the secondary battery system 10 can be determined.

(2) In the secondary battery system 10 of the present embodiment, the determination value H is determined based on the reference value K selected based on the measured current value I, so that it is assumed in advance corresponding to the reference value K. The state of the secondary battery 50 can be determined based on the state of the secondary battery 50 that is being operated, that is, the allowable range of the internal resistance R of the secondary battery 50.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and the drawings, and for example, the following various aspects are also included in the technical scope of the present invention.
(1) In the above embodiment, the description has been given using the example in which the memory 32 stores the map M in which the reference current value IK and the reference value K are associated. However, in the map M, the reference value K What is stored in association with is not limited to the reference current value IK. For example, in the secondary battery system 10, the CPU 30 continuously measures the charging or discharging current of the secondary battery 50, and calculates the charging (discharging) depth that is an integrated value of the measured charging or discharging current. May have. In this case, the charge (discharge) depth and the reference value K may be associated with the map M.

  In a normal secondary battery, even when the same amount of current flows, the difference voltage value ΔV slightly varies depending on the charge (discharge) depth of the secondary battery. For example, the differential voltage value ΔV decreases at a charge (discharge) depth where the discharge curve is flat, and the differential voltage value ΔV increases at a charge (discharge) depth where the change of the discharge curve is large. In the map M, since both the reference current value IK and the charge (discharge) depth are associated with the reference value K, the state of the battery group 26 including the secondary battery 50 can be determined with higher accuracy.

(2) In the above embodiment, the state of the secondary battery 50 is determined using the limit value such as the limit differential voltage value ΔVG and the reference value K. These values may be determined from the results measured or the like in the initial state of the secondary battery system 10, or may be determined in advance from the results measured or simulated using the same type of secondary battery system 10. Also good.

(3) Although the above embodiment has been described using an example in which the current value I is kept substantially constant during the measurement period T, the current value I during the measurement period T is not necessarily constant. If it is almost included in the range determined from the specific reference current value IK over the measurement period T, the reference value K can be selected and there is no problem.

(4) In the above embodiment, the determination value H is calculated based on the differential voltage value ΔV between the secondary battery 50A and the secondary battery 50N at both ends of the battery group 26 connected in series and the measurement time T. The secondary battery 50 that is the measurement target of the differential voltage value ΔV and the measurement time T is not limited to the secondary battery 50 at both ends of the battery group 26, but the secondary battery 50 other than both ends of the battery group 26 is measured. A battery may be used.

(5) In the above embodiment, the variation of the voltage value V0 measured last time is evaluated in this measurement. However, the variation in the voltage value V0 measured last time may be evaluated in the previous measurement. .

10: secondary battery system, 22: ammeter, 24: voltmeter, 26: battery group, 32: memory, 42: determination unit, 44: calculation unit, 50: secondary battery, H: determination value, IK: reference Current value, K: reference value, M: map, T: measurement period, ΔT: period, ΔV: differential voltage value, ΔX: measurement interval

Claims (3)

A state determination method for a secondary battery system including a plurality of secondary batteries connected in series and a voltage measurement unit that sequentially measures the voltages of the plurality of secondary batteries,
The plurality of secondary batteries include a first secondary battery and a second secondary battery, and the first voltage value measured at a first timing with respect to the first secondary battery and the second secondary battery. The plurality of the secondary batteries using the determination value obtained by dividing the voltage difference value from the second voltage value measured at the second timing by the time difference between the first timing and the second timing. Of determining the state of the secondary battery of the secondary battery system.   The state determination method for a secondary battery system according to claim 1, wherein the state of the plurality of secondary batteries is determined by comparing the determination value with a predetermined reference value. A secondary battery system comprising a plurality of secondary batteries connected in series and a voltage measuring unit for sequentially measuring the voltages of the plurality of secondary batteries,
The plurality of secondary batteries include a first secondary battery and a second secondary battery, and the first voltage value measured at a first timing with respect to the first secondary battery and the second secondary battery. The plurality of the secondary batteries using the determination value obtained by dividing the voltage difference value from the second voltage value measured at the second timing by the time difference between the first timing and the second timing. A secondary battery system comprising a determination unit that determines the state of the secondary battery.

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