JP2019021407A - Secondary battery system - Google Patents

Abstract

To provide a secondary battery system including a nickel-hydrogen battery, in which estimation accuracy of inner pressure of the nickel-hydrogen battery is improved without providing a plurality of sensors at the inside of the nickel-hydrogen battery.SOLUTION: A secondary battery system 2 includes: a battery pack 100 of a nickel-hydrogen battery; a voltage sensor 110 to detect the voltage TB of the battery pack 100; a current sensor 120 to detect the current IB input to and output from the battery pack 100; and a temperature sensor TB to detect the temperature TB of the battery pack 100. An ECU 300 calculates the hydrogen partial pressure Pof the battery pack 100 using detected values of the voltage VB, the current IB and the temperature TB of the battery pack 100. The ECU 300 estimates the inner pressure P of the battery pack 100 by calculating the sum of nitrogen partial pressure P, oxygen partial pressure Pand the hydrogen partial pressure P.SELECTED DRAWING: Figure 6

Description

  The present disclosure relates to a secondary battery system, and more particularly to a secondary battery system including a nickel metal hydride battery.

  In recent years, vehicles such as a hybrid vehicle (HV) or an electric vehicle (EV) equipped with a secondary battery system have been widely used. In secondary battery systems mounted on such vehicles, nickel metal hydride batteries are widely used as secondary batteries.

  In general, it is known that when a nickel hydride battery is charged at a high voltage or high temperature, gas is generated inside the battery by a side reaction different from the charging reaction. If the internal pressure of the nickel-metal hydride battery rises excessively with the generation of this gas, the nickel-metal hydride battery may be deteriorated quickly, or a safety valve provided in the nickel-metal hydride battery may be activated. Therefore, a technique for controlling the charging power of the nickel metal hydride battery according to the internal pressure of the nickel metal hydride battery has been proposed.

  For example, according to the charging control method for a secondary battery disclosed in Japanese Patent Application Laid-Open No. 2011-239573 (Patent Document 1), the voltage of the secondary battery is increased to the potential at which gas is generated in the secondary battery (gas generation potential). The control upper limit value of the charging power is set such that the internal pressure of the secondary battery does not increase and the internal pressure of the secondary battery increases to the pressure at which the safety valve of the secondary battery operates.

JP 2011-239573 A

  The inside of the nickel metal hydride battery contains oxygen gas, hydrogen gas, nitrogen gas, and water vapor. Since the water vapor amount is negligibly small compared to other gas amounts, oxygen gas, hydrogen gas, and nitrogen gas will be considered below. In this case, the internal pressure of the nickel metal hydride battery is represented by the sum of the oxygen partial pressure, the hydrogen partial pressure, and the nitrogen partial pressure.

  In order to calculate the partial pressure of each gas, installing a large number of sensors (for example, a pressure sensor, an oxygen concentration sensor, a hydrogen concentration sensor, a humidity sensor, etc.) inside the nickel metal hydride battery is, for example, installed in a vehicle. In the secondary battery system, it may be difficult from the technical viewpoint or the cost.

  On the other hand, a method is also conceivable in which the temperature dependence of the partial pressure of each gas is obtained in advance and the partial pressure is calculated from the temperature detected by the temperature sensor (see, for example, Patent Document 1). However, although details will be described later (see FIG. 4), according to the measurement results (actual measurement results) of the present inventors, when the charge and discharge of the nickel-metal hydride battery is repeated, the hydrogen partial pressure increases with time. Or, it can rise as the current value increases. Therefore, for example, in a simple method of calculating the hydrogen partial pressure using temperature dependence as in Patent Document 1, a change in the hydrogen partial pressure with the passage of time or current value is not calculated. In other words, the change in the hydrogen partial pressure accompanying the charge / discharge history of the nickel metal hydride battery is not reflected. Therefore, there is a possibility that the hydrogen partial pressure cannot be calculated accurately. In this regard, the estimation method of the internal pressure (particularly hydrogen partial pressure) disclosed in Patent Document 1 has room for improvement in the estimation accuracy.

  The present disclosure has been made in order to solve the above-described problems. The purpose of the present disclosure is to provide a secondary battery system including a nickel-metal hydride battery, such as a pressure sensor, an oxygen concentration sensor, a hydrogen concentration sensor, and a humidity sensor. It is to improve the estimation accuracy of the internal pressure of the nickel metal hydride battery without providing a sensor inside the nickel metal hydride battery.

  (1) A secondary battery system according to an aspect of the present disclosure includes a secondary battery that is a nickel metal hydride battery, a voltage sensor that detects a voltage of the secondary battery, and a current that detects a current input to and output from the secondary battery. A sensor, a temperature sensor that detects the temperature of the secondary battery, and an estimation device that estimates the internal pressure of the secondary battery using detected values of the voltage, current, and temperature of the secondary battery. The estimation device calculates the nitrogen partial pressure of the secondary battery using the detected value of the temperature of the secondary battery. The estimation device calculates the oxygen partial pressure of the secondary battery using the detected values of the voltage, current, and temperature of the secondary battery. The estimation device calculates the hydrogen partial pressure of the secondary battery using the detected values of the voltage, current, and temperature of the secondary battery. The estimation device estimates the internal pressure of the secondary battery by calculating the sum of the nitrogen partial pressure, the oxygen partial pressure, and the hydrogen partial pressure.

  (2) The estimation device calculates the hydrogen gas generation rate and hydrogen gas absorption rate in the secondary battery using the detected values of the voltage, current and temperature of the secondary battery, and calculates the calculated hydrogen gas generation rate and hydrogen gas absorption. The hydrogen partial pressure of the secondary battery is calculated from the speed.

  (3) Preferably, the estimation device includes a parameter indicating a ratio of a current flowing in the negative electrode active material out of a total current of the secondary battery calculated from the detected values of the voltage and current of the secondary battery, and the secondary battery The hydrogen gas generation rate is calculated using the detected current value. The estimation device uses the difference between the hydrogen partial pressure of the secondary battery calculated a predetermined time ago and the equilibrium hydrogen pressure calculated from the temperature of the secondary battery, and the detected value of the temperature of the secondary battery, Calculate the hydrogen gas absorption rate.

  (4) More preferably, the estimation device calculates a change amount of hydrogen gas in the secondary battery by multiplying a difference between the hydrogen gas generation rate and the hydrogen gas absorption rate by a predetermined time. The estimation device calculates the change amount of the hydrogen partial pressure during a predetermined time by multiplying the calculated change amount of the hydrogen gas by a predetermined constant. The estimation device calculates the hydrogen partial pressure after a predetermined time has elapsed by adding the calculated change amount of the hydrogen partial pressure to the hydrogen partial pressure calculated before the predetermined time.

  According to the above configuration, the hydrogen partial pressure is calculated using the voltage and current of the secondary battery in addition to the temperature of the secondary battery in consideration of the temporal change of hydrogen gas. Thus, a large number of sensors (pressure sensor, oxygen concentration sensor, hydrogen concentration sensor, humidity sensor, etc.) need not be provided inside the nickel metal hydride battery. In addition, the estimation accuracy of the hydrogen partial pressure can be improved as compared with the configuration in which the hydrogen partial pressure is calculated from the temperature of the secondary battery using the temperature dependency of the hydrogen partial pressure. Therefore, the estimation accuracy of the internal pressure of the secondary battery can be improved.

  According to the present disclosure, in a secondary battery system including a nickel metal hydride battery, it is possible to improve the estimation accuracy of the internal pressure of the nickel metal hydride battery without providing a large number of sensors inside the nickel metal hydride battery.

It is a block diagram which shows roughly the whole structure of the hybrid vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a figure which shows the structure of the cell contained in an assembled battery. It is a flowchart for demonstrating charge control of the assembled battery in this Embodiment. It is a figure which shows an example of the result of having attached various sensors to the assembled battery and measuring the time change of parameters (voltage, current, and internal pressure). It is a figure which shows an example of the map for calculating a hydrogen gas absorption rate. FIG. 4 is a flowchart for explaining in detail an internal pressure estimation process shown in FIG. 3. FIG. It is a figure which shows an example of the map which shows the relationship between the voltage between electrode plates of an assembled battery, and a current ratio. It is a figure which shows an example of the map for calculating oxygen gas absorption speed. It is a figure which shows the estimation result of the internal pressure by the internal pressure estimation process in this Embodiment.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment]
<Configuration of secondary battery system>
Hereinafter, a configuration in which the secondary battery system according to the present embodiment is mounted on a hybrid vehicle will be described as an example. However, the secondary battery system according to the present embodiment may be mounted on another vehicle such as an electric vehicle or a fuel cell vehicle. Moreover, the use of the secondary battery system according to the present embodiment is not limited to a vehicle, and may be a stationary one, for example.

  FIG. 1 is a block diagram schematically showing an overall configuration of a hybrid vehicle equipped with a secondary battery system according to the present embodiment. The vehicle 1 includes a secondary battery system 2, motor generators (MG) 10 and 20, a power split mechanism 30, an engine 40, and drive wheels 50. The secondary battery system 2 includes an assembled battery 100, a system main relay (SMR) 150, a power control unit (PCU) 200, an electronic control unit (ECU) 300, Is provided.

  Each of motor generators 10 and 20 is a three-phase AC rotating electric machine. Motor generator 10 is coupled to the crankshaft of engine 40 via power split mechanism 30. When starting the engine 40, the motor generator 10 uses the power of the assembled battery 100 to rotate the crankshaft of the engine 40. The motor generator 10 can also generate power using the power of the engine 40. The AC power generated by the motor generator 10 is converted into DC power by the PCU 200 and charged to the assembled battery 100. Further, the AC power generated by the motor generator 10 may be supplied to the motor generator 20.

  Motor generator 20 rotates the drive shaft using at least one of the electric power from battery pack 100 and the electric power generated by motor generator 10. The motor generator 20 can also generate power by regenerative braking. The AC power generated by the motor generator 20 is converted into DC power by the PCU 200 and charged to the assembled battery 100.

  Power split device 30 is, for example, a planetary gear mechanism, and mechanically connects the three elements of the crank shaft of engine 40, the rotation shaft of motor generator 10, and the drive shaft. The engine 40 is an internal combustion engine such as a gasoline engine, and generates a driving force for the vehicle 1 to travel in response to a control signal from the ECU 300.

  PCU 200 converts electric power between assembled battery 100 and motor generators 10 and 20. Although neither is shown, an inverter and a converter are included. The inverter is a general three-phase inverter. During the boosting operation, the converter boosts the voltage supplied from the assembled battery 100 and supplies the boosted voltage to the inverter. During the step-down operation, the converter steps down the voltage supplied from the inverter and charges the assembled battery 100. The SMR 150 is electrically connected to a current path connecting the assembled battery 100 and the PCU 200. When SMR 150 is closed in response to a control signal from ECU 300, power can be exchanged between assembled battery 100 and PCU 200.

  In the assembled battery 100, a plurality of cells 101 are connected in series to form a block (module), and a plurality of blocks are connected in series to form the assembled battery 100. Each cell 101 is a nickel metal hydride battery. The configuration of the cell 101 will be described in more detail with reference to FIG.

  The assembled battery 100 is provided with a voltage sensor 110, a current sensor 120, and a temperature sensor 130. The monitoring units of the voltage sensor 110 and the temperature sensor 130 are not particularly limited, and may be, for example, for each block, for each of a plurality of adjacent cells 101 (number of cells less than the number of cells in the block), or for each cell. Or you may. In the present embodiment, since the internal configuration of the assembled battery 100 does not particularly affect, it is not necessary to distinguish a plurality of blocks from each other or to distinguish a plurality of cells 101 from each other. Therefore, in the following, in order to facilitate understanding of the description, the battery pack is collectively referred to as an assembled battery 100.

  The voltage sensor 110 detects the voltage VB of the assembled battery 100. The current sensor 120 detects a current IB input to and output from the assembled battery 100. The temperature sensor 130 detects the temperature TB of the assembled battery 100. Each sensor outputs the detection result to ECU 300. ECU 300 calculates the SOC (State Of Charge) of battery pack 100 based on the detection results of the sensors. Further, as will be described below, ECU 300 estimates internal pressure P of battery pack 100 based on the detection results of the sensors.

  The ECU 300 includes a CPU (Central Processing Unit) 301, a memory 302, an input / output buffer (not shown), and the like. ECU 300 controls each device so that vehicle 1 is in a desired state based on a signal received from each sensor, a map (including maps MP1 to MP4 described later) and a program stored in memory 302. As main control executed by the ECU 300, charge / discharge control of the assembled battery 100 is exemplified. For example, for the purpose of protecting the assembled battery 100, the ECU 300 controls the charging power of the assembled battery 100 so that the charging power to the assembled battery 100 does not exceed the charging power upper limit Win (described later). This charge control will be described later in detail.

  FIG. 2 is a diagram illustrating a configuration of the cell 101 included in the assembled battery 100. Since the configuration of each cell 101 is common, only one cell 101 is representatively shown in FIG. The cell 101 is, for example, a square sealed cell, and includes a case 102, a safety valve 103 provided in the case 102, an electrode body 104 and an electrolytic solution (not shown) accommodated in the case 102. In FIG. 2, the electrode body 104 is shown by seeing through a part of the case 102.

  The case 102 includes a case main body and a lid made of metal, and the lid is hermetically sealed by being welded all around the opening of the case book. However, the material of the case 102 is not limited to metal, and a resin or the like may be employed as long as the gas permeation amount through the case 102 can be suppressed to a predetermined amount or less. When the internal pressure P of the case 102 exceeds a predetermined value, the safety valve 103 discharges a part of the gas (oxygen gas, hydrogen gas, nitrogen gas, etc.) inside the case 102 to the outside. The electrode body 104 includes a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate is inserted into a bag-shaped separator, and the positive electrode plate and the negative electrode plate inserted into the separator are alternately laminated. The positive electrode plate and the negative electrode plate are electrically connected to a positive electrode terminal and a negative electrode terminal (not shown), respectively.

Various conventionally known materials can be used as the material for the electrode body 104 and the electrolytic solution. In this embodiment, as an example, an electrode plate including a positive electrode active material layer containing nickel hydroxide (Ni (OH) ₂ or NiOOH) and an active material support such as foamed nickel is used for the positive electrode plate. It is done. As the negative electrode plate, an electrode plate containing a hydrogen storage alloy (for example, LaNi ₅ or ReNi ₅ ) as a negative electrode active material is used. For the separator, a nonwoven fabric made of a synthetic fiber that has been subjected to a hydrophilic treatment is used. An alkaline aqueous solution containing potassium hydroxide (KOH) or sodium hydroxide (NaOH) is used for the electrolytic solution. However, the configuration of the cell 101 illustrated in FIG. 2 is merely an example, and a nickel metal hydride battery having an arbitrary configuration can be adopted as the cell 101.

  In the secondary battery system 2 configured as described above, charging control of the assembled battery 100 as described below is executed.

<Charge control>
FIG. 3 is a flowchart for illustrating charging control of assembled battery 100 in the present embodiment. The flowchart shown in FIG. 3 and FIG. 6 to be described later is called from a main routine (not shown) and executed every predetermined cycle (“predetermined time” according to the present disclosure). Note that each step (hereinafter abbreviated as “S”) included in these flowcharts is basically realized by software processing by the ECU 300, but realized by dedicated hardware (electric circuit) produced in the ECU 300. May be.

  In S10, ECU 300 acquires voltage VB, current IB, and temperature TB of battery pack 100 from voltage sensor 110, current sensor 120, and temperature sensor 130, respectively. In addition, the ECU 300 calculates the internal resistance R of the assembled battery 100.

  The internal resistance R of the assembled battery 100 can be calculated as follows, for example. That is, when the detected values of a plurality of voltages VB and current IB are plotted on the voltage-current coordinates and an approximate expression of each plotted point is obtained, the slope of the straight line represented by this approximate expression is used as the internal resistance R. Can be calculated. In general, the internal resistance of the secondary battery has temperature dependence. Therefore, a map (not shown) indicating the correlation between the internal resistance R and the temperature TB may be stored in the memory 302 of the ECU 300. The ECU 300 can calculate the internal resistance R from the temperature TB detected by the temperature sensor 130 by referring to this map.

In S20, the ECU 300 calculates the electrode plate voltage V0 of the assembled battery 100 (cell 101). The electrode plate voltage V0 is a voltage between the positive electrode and the negative electrode of the battery pack 100 (cell 101). As shown in the following formula (1), the electrode plate voltage V0 is obtained from the voltage VB (terminal voltage) of the assembled battery 100 detected by the voltage sensor 110 and the voltage change due to the internal resistance R (IB × R). Can be calculated. In addition, regarding the current IB, the charging direction of the assembled battery 100 is set to the negative direction. That is, VB <V0 when discharging the assembled battery 100, and VB> V0 when charging.
V0 = VB + (IB × R) (1)

  In S <b> 30, ECU 300 (“estimation device” according to the present disclosure) executes “internal pressure estimation processing” for estimating internal pressure P of battery pack 100. The internal pressure estimation process will be described later in detail.

  In S <b> 40, ECU 300 calculates charging power upper limit Win of assembled battery 100 based on internal pressure P of assembled battery 100. The charging power upper limit value Win is a control upper limit value of charging power that is set so that the internal pressure P of the assembled battery 100 does not increase to a pressure at which the safety valve 103 operates (opens). More specifically, a map (not shown) indicating the correlation between the internal pressure P of the assembled battery 100 and the charging power upper limit Win is prepared in advance and stored in the memory 302 of the ECU 300 (for example, see Patent Document 1). (See FIG. 4). In this map, when the internal pressure P is lower than the predetermined value PB, the charging power upper limit Win is constant. When the internal pressure P becomes equal to or greater than the predetermined value PB, the charging power upper limit Win decreases as the internal pressure P increases. By referring to a map (not shown) showing the correlation between the internal pressure P and the charging power upper limit value Win, the charging power upper limit value Win can be calculated from the internal pressure P.

  In S50, ECU 300 compares internal pressure P of battery pack 100 with a predetermined reference value. When internal pressure P is higher than the reference value (YES in S50), ECU 300 limits the charging power of assembled battery 100 based on charging power upper limit Win (S60). On the other hand, when internal pressure P is equal to or lower than the reference value (NO in S50), ECU 300 returns the process to the main routine without executing the process of S60 (S70).

<Change in internal pressure of battery pack>
Although it has been described that the internal pressure estimation process is executed in S30, the assembled battery 100, which is a nickel metal hydride battery, contains oxygen gas, hydrogen gas, nitrogen gas, and water vapor. The influence of the partial pressure of each gas in the internal pressure estimation will be described below.

  FIG. 4 is a diagram illustrating an example of results obtained by attaching various sensors to the assembled battery 100 and measuring time-dependent changes in parameters (current IB, voltage VB, and internal pressure P). In FIG. 4, the horizontal axis indicates the elapsed time. The vertical axis indicates the current IB, voltage VB, and internal pressure P of the battery pack 100 in order from the top.

FIG. 4 shows the measurement results (or calculation results) of each parameter when the assembled battery 100 is repeatedly charged and discharged. As described above, in the current IB, the charging direction of the assembled battery 100 is set to the negative direction. The internal pressure P that is the sum of the partial pressures of the gases in the assembled battery 100 includes a hydrogen partial pressure P _H2 , an oxygen partial pressure P _O2 , a nitrogen partial pressure P _N2, and a water vapor pressure P _H2O .

In FIG. 4, the water vapor pressure PH _{2 O} is a value calculated using a saturated water vapor pressure when a temperature sensor and a humidity sensor (both not shown) are installed in the assembled battery 100. Since the water vapor amount inside the assembled battery 100 is negligibly small compared to the oxygen amount and the hydrogen amount, the water vapor pressure P _H2O = 0 can be considered.

The nitrogen partial pressure P _N2 is calculated as follows. That is, the internal pressure P, the hydrogen concentration, the oxygen concentration, the temperature TB and the humidity were measured before charging and discharging the assembled battery 100, and the initial value of the nitrogen partial pressure P _N2 was calculated from these measurement results. Since nitrogen does not participate in the charge / discharge reaction of the assembled battery 100, the nitrogen partial pressure _PN2 was calculated from the temperature TB, assuming that it is determined according to the temperature TB during the charge / discharge of the assembled battery 100.

The oxygen partial pressure P _O2 and the hydrogen partial pressure P _H2 are provided with a large number of sensors (pressure sensor, oxygen concentration sensor, hydrogen concentration sensor, temperature sensor, and humidity sensor) in the assembled battery 100, similarly to the water vapor pressure P _H2O. It is a value measured by doing.

If the battery pack 100 is charged and discharged repeatedly, but the amount of increase in the oxygen partial pressure P _O2 during charging is large, therewith lowering the amount of oxygen partial pressure P _O2 in the discharge to the same extent also large. In contrast, the amount of increase in the hydrogen partial pressure P _H2 in the charging large increase amount about the same oxygen partial pressure P _O2 Nevertheless, the amount of decrease in the hydrogen partial pressure P _H2 in the discharge of oxygen partial pressure P It is smaller than the amount of decrease in _O2 . This is presumably because the rate at which hydrogen is absorbed by the hydrogen storage alloy is slower than the rate at which oxygen reacts with the hydrogen storage alloy of the negative electrode.

According to the measurement results of the present inventors, as shown in FIG. 4, the hydrogen partial pressure _PH2 can rise with time or with an increase in current value. Therefore, it can be seen that in estimating the internal pressure P of the assembled battery 100, it is important to calculate the change in the hydrogen partial pressure _PH2 with high accuracy.

In the in-vehicle secondary battery system 2, it is difficult to install a large number of sensors inside the assembled battery 100 for calculating the hydrogen partial pressure _PH2 . On the other hand, as the method of calculating the hydrogen partial pressure P _H2, previously determined temperature dependence of the hydrogen partial pressure P _H2, technique is also conceivable to calculate the hydrogen partial pressure P _H2 from temperature TB measured by the temperature sensor 130 (e.g. Patent Document 1). However, such a simple method may not reflect the change in the hydrogen partial pressure _PH2 over time, in other words, may not reflect the change in the hydrogen partial pressure _PH2 associated with the charge / discharge history of the nickel metal hydride battery. is there. Therefore, there is a possibility that the hydrogen partial pressure _PH2 cannot be accurately calculated. In this regard, there is room for improvement in the estimation accuracy of the internal pressure P in the method disclosed in Patent Document 1.

<Calculation of hydrogen partial pressure>
Therefore, in the present embodiment, as described below, the hydrogen gas generation rate (hydrogen gas generation amount per unit time) α and the hydrogen gas absorption rate (hydrogen gas absorption amount or decrease amount per unit time) A configuration is employed in which γ is calculated and the hydrogen partial pressure _PH2 is calculated based on the calculation results. This will be described in more detail below.

First, the hydrogen gas generation rate α is calculated according to the following formula (2). In the formula (2), the ratio of the current flowing through the negative electrode active material in the total current is represented by η ₁ . For this reason, (1-η ₁ ) indicates a current ratio (hereinafter also referred to as “hydrogen current ratio”) consumed for generating hydrogen gas as a side reaction on the negative electrode. K1 is a predetermined constant.
α = (− IB) × (1-η ₁ ) × K1 (2)

Next, the hydrogen gas absorption rate γ is calculated. When the hydrogen partial pressure _PH2 is repeatedly calculated in a predetermined unit time (corresponding to the “predetermined period” according to the present disclosure), the hydrogen gas absorption rate γ is the previous calculation period (the nth calculation period, where n is It can be calculated using the difference (P _H2 (n) −P _eq ) between the hydrogen partial pressure P _H2 (n) calculated by (natural number) and the equilibrium hydrogen pressure P _eq . More specifically, the hydrogen gas absorption rate γ can be calculated using a map MP1 indicating a correlation between the difference (P _H2 (n) −P _eq ) and the temperature TB.

FIG. 5 is a diagram showing an example of a map MP1 for calculating the hydrogen gas absorption rate γ. A map MP1 as shown in FIG. 5 is obtained in advance by experiments and stored in the memory 302 of the ECU 300. The ECU 300 can calculate the hydrogen gas absorption rate γ from the difference (P _H2 (n) −P _eq ) and the temperature TB by referring to the map MP1. Note that the specific numerical values shown in FIG. 5 are merely examples, and in fact, the same correlation can be obtained in a wider temperature range with a narrower temperature interval. The same applies to the numerical values described in FIG. 7 and FIG.

Since the hydrogen gas change rate (change amount of hydrogen gas per unit time) is represented by (α−γ), when the time width of the unit time is represented by Δt, the change amount of hydrogen gas is (α−γ). X Δt. Therefore, the hydrogen partial pressure P _H2 (n + 1) at the time of the current calculation (at the time of the (n + 1) th calculation) can be calculated by the following equation (3). K2 is a constant for converting the change amount of the hydrogen gas into the change amount of the hydrogen partial pressure, and can be obtained, for example, by an experiment. By employing such an approach, it becomes possible to sequential calculation over time the change in the hydrogen partial pressure P _H2, it is possible to improve the estimation accuracy of the pressure P.
P _H2 (n + 1) = P _H2 (n) + K2 × (α−γ) × Δt (3)

<Internal pressure estimation processing flow>
FIG. 6 is a flowchart for explaining in detail the internal pressure estimation process (the process of S30) shown in FIG. 6, in S310, ECU 300 calculates the nitrogen partial pressure _{P N2} of the battery pack 100. The nitrogen partial pressure P _N2 is calculated based on the actually measured temperature TB. By _obtaining the temperature dependency of the nitrogen partial pressure P _N2 in advance and storing it in the memory 302 as a map (not shown), You may calculate from the temperature TB of the assembled battery 100. FIG.

In S320, the ECU 300 calculates the hydrogen current ratio (1-η ₁ ) on the negative electrode, and the ratio of current consumed for oxygen gas generation as a side reaction on the positive electrode (hereinafter referred to as “oxygen current ratio”). (1-η ₂ ) is calculated (η ₂ is the rate of normal reaction on the positive electrode). The oxygen current ratio (1-η ₂ ) can be calculated using, for example, a map MP3 indicating the relationship between the electrode plate voltage V0 of the assembled battery 100 and (1-η ₂ ).

FIG. 7 is a diagram illustrating an example of a map showing a relationship between the electrode plate voltage V0 and the current ratios (1-η ₁ ), (1-η ₂ ) of the assembled battery 100. FIG. 7A shows a map MP2 showing the relationship between the electrode plate voltage V0 and the hydrogen current ratio (1-η ₁ ) for the detected values of the plurality of temperatures TB. By referring to the map MP2, the hydrogen current ratio (1-η ₁ ) can be calculated from the temperature TB and the electrode plate voltage V0. Similarly, the oxygen current ratio (1-η ₂ ) can be calculated using a map MP3 as shown in FIG. 7B (refer to FIG. 5 of Patent Document 1 for details).

Returning to FIG. 6, in S330, the ECU 300 calculates the oxygen gas generation rate δ of the assembled battery 100 based on the oxygen current ratio (1-η ₂ ) and the current IB. The oxygen gas generation rate δ can be calculated in the same manner as the hydrogen gas generation rate α, using an equation in which the constant K1 in Equation (2) is appropriately changed to another constant in order to calculate the oxygen gas generation amount. (For details, see Equation (2) or Equation (3) in Patent Document 1).

In S340, ECU 300 calculates oxygen gas absorption rate ε of battery pack 100. For the calculation of the oxygen gas absorption rate ε, for example, a map MP4 representing the relationship between the oxygen partial pressure _PO2 in the assembled battery 100 and the oxygen gas absorption rate ε can be used.

FIG. 8 is a diagram showing an example of a map MP4 for calculating the oxygen gas absorption rate ε. By referring to the map MP4 as shown in FIG. 8, the oxygen gas absorption rate ε can be calculated from the oxygen partial pressure _P02 . Since the relationship between the oxygen partial pressure PO ₂ and the oxygen gas absorption rate ε has temperature dependence, it is desirable to obtain the relationship for each temperature TB of the assembled battery 100 as shown in FIG.

Returning to FIG. 6, in S350, the ECU 300 determines the oxygen content based on the difference (δ−ε) between the oxygen gas generation rate δ and the oxygen gas absorption rate ε, that is, based on the oxygen gas change rate in the assembled battery 100. The pressure _PO2 is calculated. More specifically, the oxygen partial pressure P _O2 can be calculated by the following equation (4). K3 is a constant for converting the change amount of the oxygen gas into the change amount of the oxygen partial pressure _PO2 . P _O2 (n + 1) represents the oxygen partial pressure at the time of the current calculation, and P _O2 (n) represents the oxygen partial pressure at the time of the previous calculation (at the time of calculation before the unit time).
P _O2 (n + 1) = P _O2 (n) + K3 × (δ−ε) × Δt (4)

In S360, ECU 300 calculates hydrogen gas generation rate α of battery pack 100 based on the hydrogen current ratio (1-η ₁ ) calculated in S320 and current IB. Since the calculation method of the hydrogen gas generation rate α has been described in detail in Equation (2), description thereof will not be repeated here.

  In S370, the ECU 300 calculates the hydrogen gas absorption rate γ of the battery pack 100 from the temperature TB by referring to the map MP1 (see FIG. 5).

In S380, the ECU 300 calculates the hydrogen partial pressure _PH2 based on the hydrogen gas generation rate α and the hydrogen gas absorption rate γ according to the above equation (3).

In S390, the ECU 300 calculates the sum of the nitrogen partial pressure P _N2 calculated in S310, the oxygen partial pressure P _O2 calculated in S350, and the hydrogen partial pressure P _H2 calculated in S380. The internal pressure P is calculated (P = P _N2 + P _O2 + P _H2 ). Thereafter, the process returns to S40 shown in FIG.

  FIG. 9 is a diagram showing an estimation result of the internal pressure P by the internal pressure estimation process in the present embodiment. FIG. 9A shows an estimation result of the internal pressure P (and each partial pressure) when a voltage VB that increases the internal pressure P is applied. FIG. 9B shows an estimation result of the internal pressure P (and each partial pressure) when a voltage VB that reduces the internal pressure P is applied.

Referring to FIG. 9A, it can be seen that the hydrogen partial pressure P _H2 (and the internal pressure P) increases following the applied voltage VB. In addition, referring to FIG. 9B, it can be seen that the hydrogen partial pressure _PH2 (and the internal pressure P) decreases following the applied voltage VB.

As described above, according to the present embodiment, the hydrogen partial pressure _PH2 is calculated based on the hydrogen gas generation rate α and the hydrogen gas absorption rate γ. Thus, compared from temperature TB of the battery pack 100 by using the temperature dependence of the hydrogen partial pressure P _H2 configured to calculate the hydrogen partial pressure P _H2, it is possible to improve the accuracy of estimating the hydrogen partial pressure P _H2. In addition, as shown in the measurement results in FIG. 4, the accuracy can be obtained without installing a pressure sensor, an oxygen concentration sensor, a hydrogen concentration sensor, a temperature sensor, and a humidity sensor (all of which are not shown) in the assembled battery 100. It is possible to calculate the hydrogen partial pressure PH ₂ well. Therefore, the estimation accuracy of the internal pressure P can be improved. As a result, the process (the process shown in FIG. 3) for limiting the charging power of the assembled battery 100 based on the internal pressure P can be executed with high accuracy.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description of the embodiments but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Secondary battery system 10, 20 Motor generator, 30 Power split mechanism, 40 Engine, 50 Driving wheel, 100 Battery assembly, 101 cell, 102 Case, 103 Safety valve, 104 Electrode body, 110 Voltage sensor, 120 Current Sensor, 130 Temperature sensor, 300 ECU, 301 CPU, 302 Memory.

Claims (4)

A secondary battery that is a nickel metal hydride battery;
A voltage sensor for detecting a voltage of the secondary battery;
A current sensor for detecting a current input to and output from the secondary battery;
A temperature sensor for detecting a temperature of the secondary battery;
An estimation device that estimates an internal pressure of the secondary battery using detected values of voltage, current, and temperature of the secondary battery;
The estimation device includes:
Calculate the nitrogen partial pressure of the secondary battery using the detected value of the temperature of the secondary battery,
Calculate the oxygen partial pressure of the secondary battery using the detected values of the voltage, current and temperature of the secondary battery,
Calculate the hydrogen partial pressure of the secondary battery using the detected values of the voltage, current and temperature of the secondary battery,
A secondary battery system that estimates an internal pressure of the secondary battery by calculating a sum of the nitrogen partial pressure, the oxygen partial pressure, and the hydrogen partial pressure.   The estimation device calculates a hydrogen gas generation rate and a hydrogen gas absorption rate in the secondary battery using detected values of the voltage, current, and temperature of the secondary battery, and calculates the calculated hydrogen gas generation rate and the hydrogen gas. The secondary battery system according to claim 1, wherein a hydrogen partial pressure of the secondary battery is calculated from a gas absorption rate. The estimation device includes:
Using the parameter indicating the ratio of the current flowing in the negative electrode active material out of the total current of the secondary battery calculated from the detected value of the voltage and current of the secondary battery, and the detected value of the current of the secondary battery Calculating the hydrogen gas generation rate,
Using the difference between the hydrogen partial pressure of the secondary battery calculated before a predetermined time and the equilibrium hydrogen pressure calculated from the temperature of the secondary battery, and the detected value of the temperature of the secondary battery, The secondary battery system according to claim 2, wherein a hydrogen gas absorption rate is calculated. The estimation device includes:
The amount of change in the hydrogen gas in the secondary battery is calculated by multiplying the difference between the hydrogen gas generation rate and the hydrogen gas absorption rate by the predetermined time,
Calculating the amount of change in the hydrogen partial pressure during the predetermined time by multiplying the calculated amount of change in the hydrogen gas by a predetermined constant;
The hydrogen partial pressure after the predetermined time has elapsed is calculated by adding the calculated amount of change in the hydrogen partial pressure to the hydrogen partial pressure calculated before the predetermined time. Secondary battery system.

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