JP2018010758A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in generation amount of NiOH in a positive electrode of a nickel hydrogen battery, in a battery system including the nickel hydrogen battery.SOLUTION: An ECU performs control processing including: a step (S100) of acquiring voltage Vb, current Ib, and temperature Tb; a step (S102) of calculating a positive electrode potential U; a step (S104) of calculating an upper limit Up of the positive electrode potential U; a step (S108) of, if the positive electrode potential Uexceeds the upper limit Up (Yes in S106), controlling a PCU so as to limit the positive electrode potential Uto a predetermined value or less; and a step (S110) of, if the positive electrode potential Uis equal to or less than the upper limit Up (Yes in S106), performing normal control.SELECTED DRAWING: Figure 3

Description

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

  Conventionally, a technique for controlling charge / discharge of a battery based on the positive electrode potential or the negative electrode potential of the battery is known. For example, JP 2013-171691 A (Patent Document 1) estimates either the positive electrode potential or the negative electrode potential, calculates the other potential from the measured voltage and the estimated one potential, A device that limits charge / discharge in response to the electrode potential reaching a threshold value is disclosed.

JP2013-171691A

Meanwhile, when the battery system is constituted by a nickel-hydrogen battery, there is a case where Ni 2 _O 3 _H is generated in the positive electrode of the nickel hydrogen battery. When the amount of Ni ₂ O ₃ H produced increases, the capacity of the nickel-metal hydride battery may decrease and deterioration may proceed. Therefore, it is necessary to estimate the positive electrode potential with high accuracy in order to estimate the production amount of Ni ₂ O ₃ H.

However, in Patent Document 1 described above, since the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery is not taken into consideration, an increase in the amount of Ni ₂ O ₃ H produced cannot be suppressed, There are cases where charge / discharge control of a nickel metal hydride battery cannot be performed properly.

The present invention has been made to solve the above-described problems, and an object of the present invention is to suppress an increase in the amount of Ni ₂ O ₃ H generated in the positive electrode of a nickel metal hydride battery in a battery system including the nickel metal hydride battery. It is to provide a battery system.

A battery system according to an aspect of the present invention includes a nickel metal hydride battery and a memory, and a control device that performs any one of charging and discharging of the nickel metal hydride battery and suspension of charge and discharge using information stored in the memory. With. The memory stores data indicating the correspondence between the temperature of the nickel metal hydride battery and the upper limit of the positive electrode potential of the nickel metal hydride battery. The upper limit value is set so that an increase in the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery is suppressed under the corresponding temperature environment. The controller removes the influence of the voltage change derived from the metal resistance from the voltage of the nickel metal hydride battery, calculates the positive electrode potential from the negative electrode potential of the nickel metal hydride battery, and refers to the data from the current temperature to set the upper limit value. When the calculated positive electrode potential exceeds the upper limit value, any one of charging and discharging and charging / discharging is paused so that the positive electrode potential decreases.

According to the present invention, it is possible to remove the influence of the voltage change derived from the metal resistance from the voltage of the nickel metal hydride battery and calculate the positive electrode potential with high accuracy from the potential of the negative electrode of the nickel metal hydride battery. When the calculated positive electrode potential exceeds the upper limit value, the generation amount of Ni ₂ O ₃ H is increased by performing any one of charging and discharging and charging / discharging so that the positive electrode potential decreases. Can be suppressed. Therefore, a decrease in the capacity of the nickel metal hydride battery can be suppressed and the battery charge / discharge control can be appropriately executed.

According to the present invention, it is possible to provide the battery system including a nickel hydride battery, a battery system for suppressing the increase of the amount of Ni 2 _O 3 _H in the positive electrode of the nickel hydrogen battery.

It is a block diagram which shows roughly the whole structure of the electric vehicle carrying the battery system which concerns on this Embodiment. It is a diagram showing an example of experimental results on the relationship between the presence ratio and the full charge capacity of Ni 2 _O 3 _H in the positive electrode. In this embodiment, it is a flowchart showing the processing content of Ni 2 _O 3 _H generation suppression control. It is a figure which shows an example of RC circuit used in order to provide a time delay component to the overvoltage contained in a negative electrode potential. It is a figure which shows notionally an example of the map produced in this Embodiment. Is a flowchart showing the processing content of Ni 2 _O 3 _H generation suppression control according to a modification.

  Hereinafter, embodiments of the present invention 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.

  Hereinafter, a configuration in which the battery system according to the embodiment of the present invention is mounted on an electric vehicle will be described as an example. Is not to be done. The vehicle may be, for example, a hybrid vehicle (including a plug-in hybrid vehicle) equipped with a drive motor and an engine, or a hybrid vehicle equipped with a fuel cell. Moreover, the use of the battery system is not limited to the vehicle, but may be stationary.

<Battery system configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of an electric vehicle 1 (hereinafter simply referred to as a vehicle 1) on which a battery system 2 according to the present embodiment is mounted. The vehicle 1 includes a motor generator (MG) 10, a power transmission gear 20, drive wheels 30, a power control unit (PCU) 40, and a system main relay (SMR) 50. And a battery system 2. The battery system 2 includes an assembled battery 100, a voltage sensor 210, a current sensor 220, a temperature sensor 230, and an electronic control unit (ECU) 300.

  MG10 is, for example, a three-phase AC rotating electric machine. The output torque of MG 10 is transmitted to drive wheel 30 via power transmission gear 20 configured to include a reduction gear and a power split mechanism. The MG 10 can also generate power by the rotational force of the drive wheels 30 during the regenerative braking operation of the vehicle 1. 1 shows a configuration in which only one motor generator is provided, the number of motor generators is not limited to this, and a plurality of (for example, two) motor generators may be provided.

  PCU 40 includes, for example, an inverter and a converter that operate based on a control signal from ECU 300. When the battery pack 100 is discharged, the converter boosts the voltage supplied from the battery pack 100 and supplies it to the inverter. The inverter converts the DC power supplied from the converter into AC power and drives motor generator 10. On the other hand, when charging the assembled battery 100, the inverter converts AC power generated by the motor generator 10 into DC power and supplies it to the converter. The converter steps down the voltage supplied from the inverter to a voltage suitable for charging the battery pack 100 and supplies the voltage to the battery pack 100. PCU 40 stops charging and discharging by stopping the operation of the inverter and the converter based on a control signal from ECU 300. The PCU 40 may have a configuration in which a converter is omitted.

  The SMR 50 is electrically connected to a power line connecting the assembled battery 100 and the PCU 40. When SMR 50 is closed in accordance with a control signal from ECU 300, power can be exchanged between assembled battery 100 and PCU 40.

  The assembled battery 100 is a rechargeable DC power source and includes a nickel metal hydride battery. The assembled battery 100 is configured by connecting a plurality (n) of nickel-metal hydride batteries (single cells) 110 (hereinafter referred to as cells 110) in series.

  The voltage sensor 210 detects voltages Vb (1) to Vb (n) between the terminals of the plurality of cells 110. The current sensor 220 detects a current Ib input / output to / from the assembled battery 100. The temperature sensor 230 detects the temperatures Tb (1) to Tb (n) of each of the plurality of cells 110. In the following description, voltages Vb (1) to Vb (n) of each cell 110 may be described as voltage Vb, and temperatures Tb (1) to Tb (n) may be described as temperature Tb. Each sensor outputs the detection result to ECU 300.

  ECU 300 includes a CPU (Central Processing Unit) 301, a memory (ROM (Read Only Memory) and RAM (Random Access Memory)) 302, and an input / output buffer (not shown). ECU 300 controls each device so that vehicle 1 and battery system 2 are in a desired state based on signals received from each sensor and information such as a map and a program stored in memory 302.

<Production of Ni ₂ O ₃ H>
When Ni 2 _O 3 _H is generated in the positive electrode of the nickel hydrogen battery, the Ni 2 _O 3 _H because that does not contribute to the battery reaction, the full charge capacity decreases (deterioration of the battery).

FIG. 2 is a diagram illustrating an example of experimental results regarding the relationship between the abundance ratio of Ni ₂ O ₃ H in the positive electrode and the full charge capacity. In FIG. 2, the horizontal axis indicates the abundance ratio of Ni ₂ O ₃ H in the positive electrode, and the vertical axis indicates the full charge capacity. From this experimental result, it can be seen that the lower the Ni ₂ O ₃ H abundance ratio, the higher the full charge capacity, and the full charge capacity decreases as the abundance ratio increases.

Therefore, when performing various charging / discharging control of the assembled battery 100, it is desirable to consider the reduction of the full charge capacity resulting from the generation of Ni ₂ O ₃ H. For example, Ni 2 _O 3 when the full charge capacity due to the generation of _H was decreased to some extent, inhibit so an increase in the amount of Ni 2 _O 3 _H before below the required amount of the full charge capacity It is required to perform charge / discharge control.

However, the amount of Ni ₂ O ₃ H produced is determined based on the positive electrode potential U ₊ . Therefore, in order to realize highly accurate estimation and suppression control of the production amount of Ni ₂ O ₃ H, it is desirable to estimate the positive electrode potential U ₊ with high accuracy.

Therefore, in the present embodiment, ECU 300 subtracts voltage change ΔVm derived from metal resistance from voltage Vb of each cell 110 to remove the influence and negative electrode potential U ₋ (1) to (1) ˜ of each cell 110. The positive electrode potential U ₊ (1) to U ₊ (n) of each cell 110 is calculated from U ₋ (n). The ECU 300 calculates upper limit values Up (1) to Up (n) of the positive electrode potentials U ₊ (1) to U ₊ (n) with reference to the data from the current temperature Tb, and calculates the calculated positive electrode potential U _+. When at least one of (1) to U ₊ (n) exceeds the corresponding upper limit value, charging is performed so that the positive electrode potential does not exceed the upper limit value.

Thus, the positive electrode potentials U ₊ (1) to U ₊ (n) of each cell 110 can be calculated with high accuracy. Further, when at least one of the calculated positive electrode potentials U ₊ (1) to U ₊ (n) exceeds a corresponding upper limit value, charging is performed so that the positive electrode potential does not exceed the upper limit value. , An increase in the amount of Ni ₂ O ₃ H produced can be suppressed. In the following description, positive electrode potentials U ₊ (1) to U ₊ (n) are described as positive electrode potentials U _+, and negative electrode potentials U ₋ (1) to U ₋ (n) are described as negative electrode potentials U ₋ . The upper limit Up (1) to Up (n) may be described as the upper limit Up.

<Ni ₂ O ₃ H production suppression control>
FIG. 3 is a flowchart showing the processing content of the Ni ₂ O ₃ H generation suppression control. The processing shown in this flowchart is called from a main routine (not shown) and executed every predetermined control cycle (= unit time). Each step included in these flowcharts is basically realized by software processing by the ECU 300, but a part or all of the steps may be realized by hardware (electric circuit) produced in the ECU 300.

  In step (hereinafter, step is referred to as “S”) 100, ECU 300 acquires voltage Vb, current Ib, and temperature Tb of cell 110. ECU 300 acquires voltage Vb, current Ib, and temperature Tb from voltage sensor 210, current sensor 220, and temperature sensor 230, respectively.

In S102, ECU 300 calculates positive electrode potential U ₊ of cell 110. ECU 300 calculates the positive electrode potential from the value obtained by removing the influence of the voltage change derived from the metal resistance from the voltage of the nickel metal hydride battery and the negative electrode potential of the nickel metal hydride battery. That is, the positive electrode potential U ₊ can be calculated based on the relationship expressed by the following equation.

Vb = U ₊ -U ₋ + ΔVm (1)
That is, the positive electrode potential U ₊ can be calculated by rewriting the equation (1) into the following equation (2).

U ₊ = Vb + U ₋ −ΔVm (2)
Note that ΔVm at the time of charging is a positive value, and ΔVm at the time of discharging is a negative value.

The negative electrode potential U ₋ can be expressed by the following formula (3).
U ₋ = EP ₋ + η ₋ (η during charging is a negative value, positive during discharging) Formula (3)
In the above formula (3), EP ₋ represents a negative electrode equilibrium potential, and η ₋ represents an overvoltage. Here, the negative electrode equilibrium potential EP ₋ of a hydrogen storage alloy generally used in the negative electrode of a nickel metal hydride battery can be regarded as constant in the normal battery SOC range (for example, −0.9 V (vs Hg / HgO)). If necessary, the negative electrode equilibrium potential EP ₋ may be given SOC dependency (hydrogen amount dependency).

In the present embodiment, ECU 300 calculates η ₋ using an equation of η ₋ = current Ib × negative electrode resistance value R ₋ when a predetermined condition for the state of cell 110 is satisfied. The predetermined condition is, for example, a condition that a time delay hardly occurs in the change of η _{− at} the temperature Tb (for example, a threshold value or more). ECU 300 determines that a time delay is likely to occur in the change in η ₋ when a predetermined condition is not satisfied for the state of cell 110. Therefore, ECU 300, when a predetermined condition is not satisfied, for example, eta using the equivalent circuit shown in FIG. 4 _- can estimate the overvoltage change during energized by applying a two-hour delay component .

  The equivalent circuit shown in FIG. 4 includes an RC circuit (1) in which a resistor R1 and a capacitor C1 are connected in parallel, an RC circuit (2) in which a resistor R2 and a capacitor C2 are connected in parallel, a resistor R3 and a capacitor C3. The RC circuit (3) connected in parallel is connected in series. The number of RC circuits is set based on the number of resistance factors having different time constants. For this reason, FIG. 4 shows an example in which there are three RC circuits, but the number is not particularly limited to three. For example, when there are many resistance components having different time constants, four or more RC circuits may be set. When there are few resistance components having different time constants, two or less RC circuits may be set.

  The capacitances of R1 to R3 and capacitors C1 to C3 may be predetermined values, for example, or may be set as a map of temperature Tb or SOC when having temperature characteristics or SOC characteristics. The map may be adapted, for example, by design or experiment.

In S104, ECU 300 sets an upper limit value Up of positive electrode potential U ₊ . ECU 300 refers to, for example, a map stored in memory 302, identifies a value corresponding to temperature Tb acquired in S100, and sets the identified value as upper limit value Up.

FIG. 5 is a diagram illustrating an example of a map used for setting the upper limit value Up of the positive electrode potential U ₊ according to the temperature Tb. Referring to FIG. 5, the lower value in map 200 indicates temperature Tb, and the upper value indicates upper limit value Up of positive electrode potential U ₊ corresponding to temperature Tb immediately below.

More specifically, in the map 200, values (Up0, Up1, Up2,...) Indicating the upper limit value Up of the positive electrode potential U ₊ correspond to values (T0, T1, T2,...) Indicating the temperature Tb. It is attached. It is assumed that the map 200 has a magnitude relationship of T0 <T1 <T2. In the map 200, for example, the upper limit value Up of the positive electrode potential U ₊ is set so as to decrease as the temperature Tb increases. The upper limit value Up of the positive electrode potential U ₊ may be set so as to monotonously decrease with respect to the increase in the temperature Tb. The upper limit value Up is kept constant up to a predetermined temperature and exceeds the predetermined temperature. The temperature Tb may be set to decrease, or the temperature Tb may be set to decrease stepwise.

  In battery system 2 in the present embodiment, map 200 is created in advance by experiments or the like, and created map 200 is stored in memory 302. The map 200 corresponds to “data” according to the present invention, but a function may be defined instead of the map.

In S106, ECU 300 determines whether or not positive electrode potential U ₊ calculated in S102 is greater than upper limit value Up set in S104. For example, ECU 300 determines that positive electrode potential U ₊ is greater than upper limit value Up when at least one of positive electrode potentials U ₊ (1) to U ₊ (n) is greater than the corresponding upper limit value.

Note that ECU 300 determines that positive electrode potential U ₊ is an upper limit value when each of a predetermined number or more of positive electrode potentials among positive electrode potentials U ₊ (1) to U ₊ (n) is greater than a corresponding upper limit value. It may be determined that it is larger than Up. If it is determined that positive electrode potential U ₊ is larger than upper limit value Up (YES in S106), the process proceeds to S108.

In S108, ECU 300 controls PCU 40 such that positive electrode potential U _{+ of} cell 110 is limited to a predetermined value or less.

The ECU 300 controls the PCU 40 by setting the limit value Win of the charging power to a limit value smaller than the normal value, for example. ECU 300 maintains the limit value until all of positive electrode potentials U ₊ (1) to U ₊ (n) of cell 110 fall below a predetermined value. The ECU 300 limits all the positive electrode potentials U ₊ (1) to U ₊ (n) of the cell 110 to a predetermined value or less, and also sets all the temperatures Tb (1) to Tb (n) to a predetermined value. You may restrict to the following. In this case, for example, the ECU 300 determines that all of the positive electrode potentials U ₊ (1) to U ₊ (n) are equal to or lower than a predetermined value and the temperatures Tb (1) to Tb (n) are equal to or lower than the predetermined value. The limit value is maintained until. Thereafter, ECU 300 returns the process to the main routine.

If positive electrode potential U ₊ is equal to or lower than upper limit value Up (NO in S106), the process proceeds to S110. In S110, ECU 300 performs normal control (that is, sets normal value as charging power limit value Win and controls PCU 40). Thereafter, ECU 300 returns the process to the main routine.

  An operation of battery system 2 according to the present embodiment based on the configuration and flowchart as described above will be described.

For example, assume that the cell 110 is being charged. When the Ni ₂ O ₃ H generation suppression control of the cell 110 is started, the voltage Vb, the current Ib, and the temperature Tb are acquired based on the detection results of the voltage sensor 210, the current sensor 220, and the temperature sensor 230 (S100).

In accordance with the above formula (2), the negative electrode potential U ₋ is added to the voltage Vb of the cell 110, and the positive electrode potential U ₊ is calculated by subtracting the voltage change ΔVm derived from the metal resistance (S102).

Further, the upper limit value Up of the positive electrode potential U ₊ of the cell 110 is set based on the acquired temperature Tb and the map 200 shown in FIG. 5 (S104). Then, it is determined whether or not the calculated positive electrode potential U ₊ is larger than the set upper limit value Up (S106).

When it is determined that calculated positive electrode potential U ₊ is larger than set upper limit value Up (YES in S106), PCU 40 is controlled so that positive electrode potential U ₊ is limited to a predetermined value or less (S108). ).

On the other hand, when it is determined that positive electrode potential U ₊ is equal to or lower than set upper limit value Up (NO in S106), normal control is performed (S110).

As described above, according to the battery system of the present embodiment, the negative electrode potential U on actual voltage Vb of the nickel hydrogen battery _- with adding, positive electrode potential by subtracting the voltage variation ΔVm derived from metallic resistance U ₊ can be calculated with high accuracy. In addition, when the calculated positive electrode potential U ₊ exceeds the upper limit value Up, the positive electrode potential U ₊ is limited to a threshold value or less, thereby suppressing an increase in the amount of Ni ₂ O ₃ H generated. it can. Therefore, a decrease in capacity of the assembled battery 100 can be suppressed, and charge / discharge control of the assembled battery 100 can be appropriately executed. Therefore, in a battery system including a nickel metal hydride battery, a battery system that suppresses an increase in the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery can be provided.

Hereinafter, modifications will be described.
In the above-described embodiment, for example, when the positive electrode potential U ₊ is larger than the upper limit value Up, it has been described that charging is performed so that the positive electrode potential U ₊ becomes a predetermined value or less. It may be discharged to actively lower U ₊ , or charging / discharging may be suspended.

In the above embodiment, the negative electrode potential U to the voltage of the cell 110 _- with adding, has been described as to estimate the positive electrode potential U ₊ by subtracting the voltage variation ΔVm from metal resistor, the negative electrode The negative electrode resistance used for calculating the potential U ₋ may be calculated in consideration of aging degradation.

The negative electrode resistance has a characteristic that changes due to aging. This is because, for example, the reaction surface area increases as cracks occur in the negative electrode active material. Therefore, when the negative electrode resistance calculates the positive electrode potential U ₊ as not aging from the initial value, deviate from the actual values calculated value of the positive potential U ₊ is with the passage of time, possible to estimate the potential of the positive electrode U ₊ excessively small There is sex. That is, there is a concern that generation of Ni ₂ O ₃ H occurs.

  Therefore, for example, ECU 300 estimates the stress generated in the negative electrode active material of cell 110, estimates the negative electrode resistance according to the crack occurrence state in the active material, and determines the negative electrode potential based on the estimated negative electrode resistance. May be calculated.

FIG. 6 is a flowchart showing the processing content of Ni ₂ O ₃ H generation suppression control according to the modification. Note that the processing of S100 to S110 in the flowchart shown in FIG. 6 is the same as the processing of S100 to S110 in FIG. Therefore, detailed description thereof will not be repeated.

  After acquiring voltage Vb, current Ib, and temperature Tb in S100, ECU 300 estimates the negative electrode resistance of each cell 110 in S200. Specifically, ECU 300 calculates the stress generated in the active material of each cell 110 from voltage Vb, current Ib, and temperature Tb acquired in S100. ECU 300 calculates the difference between the calculated stress generated in each cell 110 and the limit value at which a crack occurs, and calculates the excess amount. ECU 300 calculates the damage amount of each cell 110 based on the calculated excess amount and excess time. ECU 300 adds the calculated damage amount to the previous integrated value to calculate the integrated value of the current damage amount of each cell 110. ECU 300 calculates the value of the negative electrode resistance of each cell 110 using a map in which the calculated integrated value and the negative electrode resistance are associated with each other. A map indicating the relationship between the negative electrode resistance and the integrated value is created in advance by experiments or the like and stored in the memory 302.

At S202, ECU 300 is the negative electrode potential U of each cell 110 by using the estimated value of the anode resistance calculated _- is calculated.

In this way, the negative electrode resistance that changes due to aging can be accurately estimated by estimating the negative electrode resistance based on the amount of damage received by the stress in the active material. As a result, since the positive electrode potential U ₊ can be estimated with high accuracy even after a lapse of time, an increase in the amount of Ni ₂ O ₃ H generated at the positive electrode can be suppressed.

  The method for estimating the negative electrode resistance is not limited to the method based on the stress in the active material, as long as the negative electrode resistance can be estimated in consideration of aging degradation. A load (current, voltage, temperature, or SOC) on the battery and a negative electrode resistance may be mapped in advance based on a durability experiment or the like.

  The embodiment disclosed this time should be considered as illustrative 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 scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 2 Battery system, 10 Motor generator, 20 Power transmission gear, 30 Drive wheel, 40 PCU, 50 SMR, 100 Battery, 110 Battery cell, 200 Map, 210 Voltage sensor, 220 Current sensor, 230 Temperature sensor, 300 ECU , 301 CPU, 302 memory.

Claims (1)

A nickel metal hydride battery,
A control device that includes a memory and performs any one of charging and discharging of the nickel metal hydride battery and suspension of charging and discharging using information stored in the memory,
The memory stores data indicating a correspondence relationship between the temperature of the nickel metal hydride battery and the upper limit of the positive electrode potential of the nickel metal hydride battery,
The upper limit is set so that an increase in the amount of Ni ₂ O ₃ H produced in the positive electrode of the nickel metal hydride battery is suppressed under a corresponding temperature environment,
The control device removes the influence of the voltage change derived from the metal resistance from the voltage of the nickel metal hydride battery, calculates the positive electrode potential from the potential of the negative electrode of the nickel metal hydride battery, and calculates the data from the current temperature. The upper limit value is calculated with reference, and when the calculated positive electrode potential exceeds the upper limit value, any one of the charging and discharging and the charging / discharging pause so that the positive electrode potential decreases. Do the battery system.

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