JP6743577B2 - Battery system - Google Patents

Description

The present disclosure relates to battery systems, and more particularly to battery systems that include a plurality of cells, each of which is a nickel metal hydride battery.

In order to appropriately protect the nickel-hydrogen battery, it is desirable to estimate the positive electrode potential and the negative electrode potential of the nickel-hydrogen battery and use them so that both of these potentials fall within an appropriate range. Since the positive electrode potential of a nickel-hydrogen battery can change due to SOC (State Of Charge) and memory effect, a technique for highly accurately estimating the positive electrode potential of a nickel-hydrogen battery is required. For example, Japanese Unexamined Patent Application Publication No. 2016-091978 (Patent Document 1) discloses a technique of estimating the negative electrode potential based on the negative electrode open potential, the negative electrode resistance, and the current value, and estimating the positive electrode potential from the negative electrode potential.

JP, 2016-091978, A

According to Patent Document 1, the negative electrode resistance is estimated from the temperature by previously obtaining the correspondence relationship (map or arithmetic expression) between the negative electrode resistance and the temperature based on the temperature dependency of the negative electrode resistance. ..

Generally, when manufacturing a nickel-hydrogen battery, various gases are adsorbed on the surface of the negative electrode (the surface of the hydrogen storage alloy) and the surface of the negative electrode is covered with an oxide film, so that it is possible to store hydrogen in the negative electrode. An activation process (so-called initial activation process) is performed. This activation of the negative electrode can further proceed as the usage period of the nickel-hydrogen battery elapses.

As the activation of the negative electrode progresses, hydrogen is likely to be occluded, whereby the negative electrode resistance decreases, which may reduce the overvoltage to the negative electrode during charging and discharging. As described above, the progress of the negative electrode activation gradually decreases the negative electrode resistance, and as a result, the estimation accuracy of the negative electrode potential (and thus the positive electrode potential) may be reduced. Since Patent Document 1 does not particularly consider the progress of negative electrode activation, there is room for improvement in the accuracy of negative electrode potential estimation.

The present disclosure has been made to solve the above problems, and an object thereof is to provide a technique capable of improving the estimation accuracy of a negative electrode potential in a battery system including a plurality of cells of a nickel hydrogen battery. Is.

A battery system according to an aspect of the present disclosure includes first and second cells each being a nickel-hydrogen battery, and an estimation device that estimates a negative electrode potential. The negative electrode estimation device includes a memory that stores data defining the negative electrode resistance using the temperature as a parameter for the first and second cells, and estimates the negative electrode potential using the data. The estimation device estimates the resistance of the first cell from the voltage and the current of the first cell, and estimates the resistance of the second cell from the voltage and the current of the second cell. A first resistance difference from the resistance of the second cell is calculated. The estimation device estimates the negative resistance of the first cell corresponding to the temperature of the first cell using the data, and the negative resistance of the second cell corresponding to the temperature of the second cell using the data. The second resistance difference between the negative resistance of the first cell and the negative resistance of the second cell is estimated and calculated. The estimation device calculates an activation coefficient indicating the degree of progress of the negative electrode activation of the first and second cells from the ratio of the first and second resistance differences, and corrects the data using the calculated activation coefficient. To do.

The present inventor has noticed that the difference in positive electrode resistance is extremely small even when there is temperature variation between the first cell and the second cell. Based on this finding, according to the above configuration, the difference in the negative electrode resistance can be obtained by calculating the first resistance difference (see the equation (3) described later). The difference in the negative electrode resistance reflects the influence of the change over time in the negative electrode activation, and thus can be used for calculating the activation coefficient. Then, by correcting the above data using the activation coefficient, it becomes possible to estimate the negative electrode resistance with high accuracy even when the negative electrode activation progresses. Therefore, the estimation accuracy of the negative electrode potential can be improved.

According to the present invention, the accuracy of estimating the negative electrode potential can be improved in a battery system including a plurality of cells of a nickel hydrogen battery.

FIG. 1 is a block diagram schematically showing an overall configuration of a hybrid vehicle equipped with a battery system according to the present embodiment. It is a figure which shows the structure of each cell contained in an assembled battery. It is a figure for demonstrating the correction method of the map in this Embodiment. It is a flowchart which shows the map correction process which concerns on this Embodiment. 5 is a flowchart showing discharge control of the assembled battery according to the present embodiment.

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

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

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

Each of motor generators 10 and 20 is, for example, a three-phase AC rotating electric machine. Motor generator 10 is connected to a crankshaft of engine 40 via power split device 30. When starting the engine 40, the motor generator 10 uses the electric power of the battery pack 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 the assembled battery 100 is charged. In addition, 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 electric power by regenerative braking. The AC power generated by the motor generator 20 is converted into DC power by the PCU 200 to charge the assembled battery 100.

The power split mechanism 30 is, for example, a planetary gear mechanism, and mechanically connects the three elements of the crankshaft of the engine 40, the rotation shaft of the 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 battery pack 100 and motor generators 10 and 20. PCU 200 includes an inverter and a converter (both not shown). 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 battery pack 100. SMR 150 is electrically connected to a current path connecting assembled battery 100 and PCU 200. When SMR 150 is closed according to a control signal from ECU 300, electric power can be exchanged between battery pack 100 and PCU 200.

The assembled battery 100 includes a plurality of cells (two cells 101 and 102 are shown in FIG. 1) each being a nickel hydrogen battery. The configuration of each cell will be described with reference to FIG. The cell 101 corresponds to the “first cell” according to the present disclosure, and the cell 102 corresponds to the “second cell” according to the present disclosure.

The assembled battery 100 is provided with a voltage sensor 110, a current sensor 120, and a temperature sensor 130. The voltage sensor 110 detects the voltage of each cell included in the battery pack 100 (in FIG. 1, the voltage Vb1 of the cell 101 and the voltage Vb2 of the cell 102 are shown). The current sensor 120 detects the current Ib input/output to/from the battery pack 100. The temperature sensor 130 detects the temperature Tb of the battery pack 100 (including the temperature Tb1 of the cell 101 and the temperature Tb2 of the cell 102). Each sensor outputs the detection result to ECU 300. The ECU 300 calculates the SOC (State Of Charge) of the battery pack 100 (more specifically, each cell 101) based on the detection result of each sensor.

ECU 300 includes a CPU (Central Processing Unit) 301, a memory 302, and an input/output buffer (not shown). ECU 300 controls each device so that vehicle 1 is in a desired state based on a signal received from each sensor and a map (a map MP0 described later) and a program stored in memory 302. As a main process executed by the ECU 300, a process of estimating the positive electrode potential Vp1 and the negative electrode potential Vn1 of the cell 101 can be mentioned. This estimation process will be described later in detail. The ECU 300 corresponds to the “estimation device” according to the present disclosure.

FIG. 2 is a diagram showing a configuration of each cell included in the assembled battery 100. Since the configuration of each cell is common, the configuration of the cell 101 is shown in FIG. 2 as a representative. The cell 101 is, for example, a prismatic closed cell, and includes a case 101A, a safety valve 101B provided in the case 101A, an electrode body 101C housed in the case 101A, and an electrolytic solution (not shown). In FIG. 2, a part of the case 101A is seen through to show the electrode body 101C.

The case 101A includes a case main body and a lid body, both of which are made of metal, and is hermetically sealed by welding the entire circumference of the lid body on the opening of the case book. When the pressure inside the case 101A exceeds a predetermined value, the safety valve 101B discharges a part of the gas (hydrogen gas or the like) inside the case 101A to the outside. The electrode body 101C includes a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate is inserted in the bag-shaped separator, and the positive electrode plate and the negative electrode plate inserted in 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.

As the material of the electrode body 101C and the electrolytic solution, various conventionally known materials can be used. In the present 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 as the positive electrode plate. To be 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 negative electrode plate. As the separator, a nonwoven fabric made of hydrophilized synthetic fibers is used. An alkaline aqueous solution containing potassium hydroxide (KOH) or sodium hydroxide (NaOH) is used as the electrolytic solution.

<Estimation of negative electrode potential>
In the battery system 2 configured as described above, it is conceivable to execute the discharge control of the assembled battery 100 as follows. That is, since the negative electrode resistance of the nickel-hydrogen battery has temperature dependency (correspondence relationship), this temperature dependency is obtained in advance as a map MP0 (described later in FIG. 3) and the negative electrode resistance is estimated from the temperature Tb1. .. Further, the negative electrode potential Vn1 of the cell 101 is estimated from the negative electrode resistance, and the positive electrode potential Vp1 of the cell 101 is estimated from the negative electrode potential Vn1. Then, the discharge of the assembled battery 100 is controlled based on the positive electrode potential Vp1 (see, for example, Patent Document 1).

Generally, when manufacturing a nickel-hydrogen battery, various gases are adsorbed on the surface of the negative electrode (the surface of the hydrogen storage alloy) and the surface of the negative electrode is covered with an oxide film, so that it is possible to store hydrogen in the negative electrode. An activation process (so-called initial activation process) is performed. The present inventor has paid attention to the fact that the negative electrode activation can further progress with the lapse of the usage period of the nickel hydrogen battery.

As the negative electrode activation of the cell 101 progresses, hydrogen is likely to be occluded and the negative electrode resistance Rn is lowered, whereby, for example, the negative electrode potential Vn during discharging is calculated to be higher than the true value. As a result, the positive electrode potential Vp calculated from the sum of the cell voltage Vb1 (the detection value of the voltage sensor 110) and the negative electrode potential Vn can be high. If the map MP obtained in advance is continuously used without considering such progress of the negative electrode activation, the negative electrode resistance Rn gradually decreases, and as a result, the estimation accuracy of the negative electrode potential Vn and the positive electrode potential Vp decreases. obtain.

Therefore, in the present embodiment, a method of appropriately correcting (or updating) the map MP is adopted in order to reflect the change over time of the negative electrode resistance Rn. In the present embodiment, the activation coefficient k indicating the degree of progress of the negative electrode activation is calculated from the temperatures (Tb1, Tb2) of the two cells 101 and 102 and the negative electrode resistance, and the map MP0 is calculated using the activation coefficient k. Will be corrected. Hereinafter, a method of correcting the map MP0 according to the present embodiment will be described in detail.

FIG. 3 is a diagram for explaining the correction method of the map MP0 in the present embodiment. 3A shows the map MP0 (initial map) before correction, and FIG. 3B shows the map MP after correction. The horizontal axis of each map represents the temperature Tb of the cell (cell 101 or cell 102), and the vertical axis represents the negative electrode resistance Rn of the cell.

Hereinafter, the positive electrode resistance and the negative electrode resistance of the cell 101 are represented by Rp1 and Rn1, respectively, and the positive electrode resistance and the negative electrode resistance of the cell 102 are represented by Rp2 and Rn2, respectively. Further, the resistance of the entire cell 101 (cell resistance) is represented by R1, and the resistance of the entire cell 102 (cell resistance) is represented by R2. For each of the cells 101 and 102, the relationships of the following equations (1) and (2) are established between the cell resistance, the positive electrode resistance, and the negative electrode resistance.

R1=Rp1+Rn1 (1)
R2=Rp2+Rn2 (2)
In the present embodiment, first, voltage Vb1, current Ib and temperature Tb1 of cell 101 are acquired, and voltage Vb2, current Ib and temperature Tb2 of cell 102 are acquired. Then, the cell resistance R1 is calculated from the voltage Vb1 and the current Ib of the cell 101 (R1=Vb1/Ib). Similarly, for the cell 102, the cell resistance R1 is calculated from the voltage Vb2 and the current Ib (R2=Vb2/Ib). Further, the absolute value (|R1-R2|) of the difference ΔR (first resistance difference) between the cell resistance R1 and the cell resistance R2 is calculated.

Here, as a result of the experiments by the present inventors, in the positive electrode material of the nickel-hydrogen battery, the temperature dependence of the positive electrode resistance (Rp1, Rp2) is extremely small, and the positive electrode resistance is increased even when the temperature variation occurs between the cells. It became clear that the two were almost equal to each other. That is, Rp1≈Rp2. Therefore, the absolute value of the difference ΔR between the cell resistance R1 and the cell resistance R2 represents the difference between the negative electrode resistance Rn1 and the negative electrode resistance Rn2, as shown in the following formula (3).

ΔR=|Rn1-Rn2| (3)
Then, in the present embodiment, the negative resistance Rn10 is estimated from the temperature Tb1 of the cell 101 using the map MP0 before correction (see FIG. 3A) stored in advance in the memory 302, and The negative electrode resistance Rn20 is estimated from the temperature Tb2. More specifically, in the map MP before correction, the temperature dependence of the negative electrode resistance Rn0 is represented by a curve C0:Rn0=f(Tb). By using it, it is estimated that Rn10=f(Tb1) and Rn20=f(Tb2).

Further, the absolute value of the difference ΔRn0 (second resistance difference) between the negative electrode resistance Rn10 and the negative electrode resistance Rn20 is calculated (see the following equation (4)).

ΔRn0=|Rn10−Rn20| (4)
The difference ΔRn0 is an initial parameter that does not reflect the effect of negative electrode activation (change over time), whereas the difference ΔR is a parameter that reflects the effect of negative electrode activation. Therefore, the progress degree of the negative electrode activation can be estimated by comparing the difference ΔRn0 and the difference ΔR. More specifically, as shown in the following equation (5), the ratio of the difference ΔR to the difference ΔRn0 is calculated as the activation coefficient k.

k=ΔR/ΔRn0 (5)
Further, as shown in FIG. 3B, the map MP0 is corrected using the activation coefficient k. In the corrected map MP, the curve C is expressed as Rn=k×Rn0.

FIG. 4 is a flowchart showing the map correction processing according to this embodiment. The flowchart shown in FIG. 4 and FIG. 5, which will be described later, is executed by being called from the main routine when a predetermined condition is satisfied or at predetermined intervals. Further, 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) created in the ECU 300. May be done.

In S101, the ECU 300 acquires the voltage Vb1 and the temperature Tb1 of the cell 101 from the voltage sensor 110 and the temperature sensor 130 provided in the cell 101, respectively. Further, the ECU 300 acquires the current Ib flowing through the battery pack 100 from the current sensor 120.

In S102, the ECU 300 acquires the voltage Vb2, the current Ib, and the temperature Tb2 of the cell 102, as in S101. The order of the processes of S101 and S102 may be exchanged, or these processes may be executed simultaneously.

In S103, ECU 300 estimates cell resistance R1 from voltage Vb1 and current Ib, and estimates cell resistance R2 from voltage Vb2 and current Ib. Further, the ECU 300 calculates the resistance difference ΔR (absolute value |R1-R2|) based on the difference between the cell resistance R1 and the cell resistance R2 (S104).

In S105, the ECU 300 estimates the negative electrode resistance Rn10 from the temperature Tb1 of the cell 101 and the negative electrode resistance Rn20 from the temperature Tb2 of the cell 102 with reference to the map MP (see FIG. 3A). Further, the ECU 300 calculates (the absolute value |Rn10−Rn20|) of the resistance difference ΔRn0 from the difference between the negative electrode resistance Rn10 and the negative electrode resistance Rn20 (S106). The order of the processes of S103, S104 and S105, S106 may be exchanged.

In S107, ECU 300 calculates activation coefficient k (=ΔR/Rn0) using resistance difference ΔR calculated in S104 and resistance difference ΔRn0 calculated in S106.

In S108, ECU 300 corrects map MP0 using activation coefficient k. More specifically, by multiplying the right side of the relational expression (Rn0=f(Tb)) represented by the curve C0 by the activation coefficient k, the relational expression (Rn=k×Rn0=k×f(Tb) ) (Curve C). The relationship represented by the curve C is stored in the memory 302 as the map MP.

FIG. 5 is a flowchart showing discharge control of the battery pack 100 according to the present embodiment. Although a configuration for estimating the negative electrode potential Vn1 and the positive electrode potential Vp1 of the cell 101 will be described below as an example, the negative electrode potential and the positive electrode potential of another cell (cell 102 or the like) may be estimated.

In S201, the ECU 300 estimates the negative electrode potential Vn1 of the cell 101. More specifically, the ECU 300 adds the product of the current Ib detected by the current sensor 120 and the negative electrode resistance Rn1 calculated in S105 (see FIG. 4) to the negative electrode open potential OCVn1 to determine the negative electrode potential Vn1. Calculate (see formula (6) below). Note that the negative electrode open-circuit potential OCVn1 is constant regardless of the SOC within a predetermined SOC range, and thus can be obtained in advance by an experiment.

Vn1=OCVn1+Ib×Rn1 (6)
In step S202, the ECU 300 estimates the positive electrode potential Vp1 of the cell 101. More specifically, the ECU 300 calculates the positive electrode potential Vp1 by adding the voltage Vb1 of the cell 101 detected by the voltage sensor 110 to the negative electrode potential Vn1 calculated in S201 (see the following formula (7)). ..

Vp1=Vn1+Vb1 (7)
In S203, ECU 300 determines whether negative electrode potential Vn1 is lower than a predetermined negative electrode protective potential and positive electrode potential Vp1 is higher than a predetermined positive electrode protective potential. Note that the negative electrode protection potential is a potential set in advance in consideration of a potential at which the negative electrode of the cell 101 may deteriorate. Similarly, the positive electrode protection potential is a potential set in advance in consideration of a potential at which deterioration of the positive electrode of the cell 101 (for example, elution of the conductive material in the positive electrode active material layer) may occur.

When negative electrode potential Vn1 is lower than negative electrode protective potential and positive electrode potential Vp1 is higher than positive electrode protective potential (YES in S203), ECU 300 skips the process of S204 below and returns the process to the main routine. As a result, the processing shown in FIG. 5 is repeatedly executed.

On the other hand, when the negative electrode potential Vn1 is equal to or higher than the negative electrode protection potential, or when the positive electrode potential Vp1 is equal to or lower than the positive electrode protection potential (including both cases), the ECU 300 advances the process to S201 and normally (in S203). The output from the assembled battery 100 is suppressed as compared with the case (NO). In the present embodiment, ECU 300 causes discharge power upper limit value Wout, which is the control upper limit value of discharge power from assembled battery 100, to be lower than the reference value Wref in the normal state, and the output from assembled battery 100 is suppressed. Make it easier. The reference value Wref is defined in advance by experiments or simulations according to the temperature and SOC of the battery pack 100, and is stored in the memory 302.

As described above, according to the present embodiment, attention is paid to the fact that the change in the positive electrode resistance is extremely small even when the temperature varies between cells (between the cells 101 and 102) (Rp1≈ Rp2) and the difference in cell resistance (ΔR) are taken to obtain the difference in negative electrode resistance (|Rn1-Rn2|) (see the above equation (3)). Since the difference in the negative electrode resistance reflects the influence of the change in the negative electrode activation over time, it can be used to calculate the activation coefficient k. Then, by correcting the map MP0 using the activation coefficient k, it becomes possible to accurately estimate the negative electrode resistance even when the negative electrode activation progresses. Therefore, the estimation accuracy of the negative electrode potential can be improved.

It should be considered that the embodiments disclosed this time are exemplifications in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

1 vehicle, 2 battery system, 10, 20 motor generator, 30 power split mechanism, 40 engine, 50 drive wheels, 100 battery pack, 101, 102 cells, 101A case, 101B safety valve, 101C electrode body, 110 voltage sensor, 120 current Sensor, 130 temperature sensor, 200 PCU, 300 ECU, 301 CPU, 302 memory.

Claims (1)

First and second cells, each of which is a nickel metal hydride battery;
A estimating device that includes a memory that stores data defining the negative electrode resistance with respect to the first and second cells using temperature as a parameter, and that estimates the negative electrode potential using the data;
The estimation device is
The resistance of the first cell is estimated from the voltage and the current of the first cell, and the resistance of the second cell is estimated from the voltage and the current of the second cell, and the resistance of the first cell is estimated. And a first resistance difference between the resistance of the second cell and the resistance of the second cell,
The negative resistance of the first cell corresponding to the temperature of the first cell is estimated using the data, and the negative resistance of the second cell corresponding to the temperature of the second cell is calculated using the data. Estimate using, calculate a second resistance difference between the negative electrode resistance of the first cell and the negative electrode resistance of the second cell,
An activation coefficient indicating the degree of progress of the negative electrode activation of the first and second cells is calculated from the ratio of the first and second resistance differences, and the data is corrected using the calculated activation coefficient. , Battery system.

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