JP2017168357A - Control device for nickel hydrogen battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for a nickel hydrogen battery that more surely controls a negative electrode potential to be equal to an upper limit potential or less by accurately estimating the negative electrode potential during discharging of the nickel hydrogen battery.SOLUTION: In a secondary battery system 10 of a vehicle 1, ECU 300 calculates a negative electrode potential increase amount ΔV per unit time from discharge current I detected by a monitoring unit 200 during discharging in a low temperature range, and integrates ΔV to calculate a negative electrode potential increase amount ΣΔV over time. ECU calculates, as a negative electrode potential V(-), a value obtained by adding ΣΔV (a negative electrode potential increase amount peculiar to the nickel hydrogen battery) to the sum of a negative electrode opening potential OCP(-) and a negative electrode potential increase amount IRCT(-) caused by reaction resistance (that is, an equivalent negative electrode potential estimated value in the past). When the calculated negative electrode potential V(-) exceeds an upper limit potential V(-) max, ECU performs discharge current limitation for limiting discharge current I to a predetermined value Imax or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for controlling charge / discharge of a nickel metal hydride battery.

  Japanese Patent No. 576378 (Patent Document 1) discloses a controller for controlling charge / discharge of a lithium ion battery. This controller estimates the negative electrode potential from the state of the lithium ion battery, and controls charging / discharging of the lithium ion battery so that the estimated negative electrode potential changes within a predetermined range (range between the lower limit potential and the upper limit potential). . Thereby, the fall of the battery performance by lithium precipitation etc. is suppressed.

Japanese Patent No. 576378

  Conventionally, as a secondary battery for a hybrid vehicle, not only a lithium ion battery but also a nickel metal hydride battery has been widely used. It is known that the negative electrode potential increases at the time of discharge of the nickel metal hydride battery, and that the negative electrode deteriorates and the battery characteristics deteriorate when the negative electrode potential increases excessively at the time of discharge. Therefore, it is important to estimate the negative electrode potential and control the estimated negative electrode potential to be equal to or lower than the upper limit potential as in Patent Document 1 even when the nickel metal hydride battery is discharged.

  However, in general, carbon is used for a negative electrode of a lithium ion battery, whereas a hydrogen storage alloy (MH) is used for a negative electrode of a nickel metal hydride battery. Due to such a difference in structure, the negative electrode potential of the nickel metal hydride battery can exhibit a unique behavior different from the negative electrode potential of the lithium ion battery under a predetermined condition. Therefore, if the estimation method of Patent Document 1 based on a lithium ion battery is applied to a nickel metal hydride battery as it is, there is a concern that the estimation accuracy of the negative electrode potential is lowered. Therefore, development of a method for estimating the negative electrode potential more suitable for nickel metal hydride batteries is desired.

  The present invention has been made in order to solve the above-described problems. The object of the present invention is to accurately estimate the negative electrode potential during discharge of the nickel-metal hydride battery, thereby more reliably setting the negative electrode potential to the threshold potential. The control is as follows.

  (1) A control device according to the present invention is a control device for a nickel-metal hydride battery in which a hydrogen storage alloy is used for the negative electrode, the temperature detection unit configured to be able to detect the temperature of the nickel-metal hydride battery, A current detection unit configured to detect the discharge current; and a control unit configured to control the discharge current. When the nickel hydride battery is discharging and the temperature is equal to or lower than the threshold temperature, the control unit calculates the increase amount of the negative electrode potential per unit time from the discharge current, and integrates the increase amount of the negative electrode potential per unit time. As a result, the amount of increase in negative electrode potential over time is calculated. The control unit calculates the sum of the open circuit potential of the negative electrode, the product of the reaction resistance and discharge current of the negative electrode, and the amount of increase in the negative electrode potential over time as the potential of the negative electrode. The control unit limits the discharge current to a predetermined value or less when the calculated potential of the negative electrode exceeds the threshold potential.

  During the discharge of the nickel metal hydride battery, it is known that the negative electrode potential increases more than the open-circuit potential (the potential during non-energization). Conventionally, the amount of increase in negative electrode potential during discharge is uniquely determined by the product of the discharge current and the reaction resistance of the negative electrode (charge transfer resistance generated in the active material of the negative electrode). If the discharge current and the reaction resistance of the negative electrode are constant, the negative electrode The potential was also thought to be constant. However, in a nickel metal hydride battery in which a hydrogen storage alloy is used for the negative electrode, the discharge current and the reaction resistance of the negative electrode are constant under conditions where the temperature is equal to or lower than a threshold temperature (for example, 0 ° C.) and the discharge current is higher than a predetermined value. Even if the negative electrode potential gradually increases with the passage of time, the negative electrode potential behavior peculiar to a nickel metal hydride battery occurs that the increase amount of the negative electrode potential per unit time is larger as the discharge current is larger. Newly discovered.

  The control unit having the above configuration calculates the potential of the negative electrode in consideration of the above-described behavior specific to the nickel metal hydride battery. Specifically, during discharge in a low temperature range where the temperature is equal to or lower than the threshold temperature, the amount of increase in negative electrode potential per unit time is calculated from the discharge current, and the time is calculated by integrating the amount of increase in negative electrode potential per unit time. The amount of increase in negative electrode potential over time (that is, the amount of increase in negative electrode potential peculiar to nickel metal hydride batteries) is calculated. Then, the control unit further adds the negative electrode potential increase amount over time (specific to the nickel metal hydride battery) to the sum of the product of the open circuit potential of the negative electrode and the product of the discharge current and the reaction resistance of the negative electrode (that is, the estimated value of the negative electrode potential corresponding to the prior art). The value obtained by adding the negative electrode potential increase amount) is calculated as the negative electrode potential. Thereby, the negative electrode potential can be accurately calculated (estimated) in consideration of the negative electrode potential behavior unique to the nickel metal hydride battery.

  And a control part restrict | limits a discharge current below to predetermined value, when the electric potential of the negative electrode calculated accurately exceeds a threshold electric potential. Thereby, since the increase amount of a negative electrode potential is reduced, the potential of a negative electrode is controlled below a threshold potential. As a result, by accurately estimating the potential of the negative electrode during the discharge of the nickel metal hydride battery, the potential of the negative electrode can be controlled more reliably below the threshold potential.

  (2) Preferably, a control part calculates the negative electrode activation rate which shows the fall degree from the initial value of the reaction resistance of a negative electrode from the voltage change amount log | history of a nickel metal hydride battery, and uses a negative electrode activation rate and is negative electrode Correct the reaction resistance.

  In general, when the battery is repeatedly charged and discharged, the reaction resistance of the negative electrode tends to increase due to deterioration. However, in a nickel metal hydride battery in which a hydrogen storage alloy is used for the negative electrode, by repeating charge and discharge, the surface of the hydrogen storage alloy can be activated and the reaction resistance of the negative electrode can be reduced. Considering this point, the control unit calculates the negative electrode activation rate indicating the degree of decrease from the initial value of the reaction resistance of the negative electrode from the history of the voltage change amount of the nickel metal hydride battery, and uses the negative electrode activation rate, The reaction resistance of the negative electrode used for calculation of the negative electrode potential is corrected. This makes it possible to estimate the potential of the negative electrode with higher accuracy in consideration of a decrease in reaction resistance due to the activation of the negative electrode.

1 is a block diagram schematically showing the configuration of a vehicle. It is a figure which shows the structure of a battery unit in detail. It is a figure which shows schematically the internal structure of a battery cell. It is a figure which shows typically the positive electrode potential and negative electrode potential at the time of non-energization, and the positive electrode potential and negative electrode potential at the time of discharge. It is a figure which shows an example of the correspondence of the discharge current I in a low temperature area, and negative electrode potential increase amount (DELTA) V per unit time. It is a flowchart (the 1) which shows an example of the process sequence of ECU. It is a figure which shows typically the calculation method of negative electrode electric potential increase amount (sigma) (DELTA) V with time passage. It is a figure which shows typically the positive electrode potential and negative electrode potential at the time of discharge in an initial state, and the positive electrode potential and negative electrode potential at the time of discharge after long-term use. It is a flowchart (the 2) which shows an example of the process sequence of ECU.

  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.

[Embodiment 1]
<Vehicle configuration>
FIG. 1 is a block diagram schematically showing a configuration of a vehicle 1 on which a nickel-hydrogen battery control device according to the present embodiment is mounted. FIG. 1 shows a system configuration related to charge / discharge control of the electric system in the vehicle 1.

  Although the vehicle 1 shown in FIG. 1 is an electric vehicle, the vehicle to which the present invention can be applied is not limited to an electric vehicle, but is applied to any electric vehicle equipped with a nickel hydrogen battery, such as a hybrid vehicle and a fuel cell vehicle. It is possible.

  The vehicle 1 includes a secondary battery system 10, a system main relay (SMR) 20, a power control unit (PCU) 30, a motor generator (MG) 40, and driving wheels. 50. The secondary battery system 10 includes a battery unit 100, a monitoring unit 200, and an electronic control unit (ECU) 300.

  Battery unit 100 includes a plurality of nickel metal hydride battery cells 110 (see FIG. 2) connected in series.

  Monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. Voltage sensor 210 is configured to detect the voltage of each cell in battery unit 100 (hereinafter also referred to as “cell voltage VC”). Current sensor 220 is configured to detect a current discharged from secondary battery system 10 (hereinafter also referred to as “discharge current I”). The temperature sensor 230 is configured to detect the temperature in the battery unit 100 (hereinafter also referred to as “battery temperature T”). Each sensor outputs a signal indicating the detection result to ECU 300.

  The SMR 20 is electrically connected between the battery unit 100 and the PCU 30. The SMR 20 is turned on / off in response to a control signal from the ECU 300. Thereby, conduction | electrical_connection and interruption | blocking between the battery unit 100 and PCU30 are switched.

  PCU 30 includes, for example, a converter and an inverter (both not shown). The PCU 30 is configured to be capable of bi-directional power conversion between the battery unit 100 and the MG 40 in accordance with a switching command from the ECU 300. The converter is configured to perform bidirectional DC voltage conversion between the battery unit 100 and the inverter. The inverter is configured to perform bidirectional power conversion between DC power and AC power input / output to / from the MG 40.

  More specifically, the inverter converts DC power supplied from the battery unit 100 via the converter into AC power and supplies the AC power to the MG 40. Thereby, the MG 40 generates the driving force of the driving wheel 50. On the other hand, at the time of regenerative braking of vehicle 1, the inverter converts AC power (regenerative power) generated by MG 40 into DC power and supplies it to the converter. Thereby, the battery unit 100 is charged.

  ECU 300 includes a CPU (Central Processing Unit) (not shown), a memory 310, and an input / output interface (not shown). ECU 300 controls charging / discharging of battery unit 100 by controlling PCU 30 based on signals from each sensor and information stored in the memory. Note that at least a part of the ECU 300 may be configured by hardware such as an electronic circuit.

<Configuration of battery unit>
FIG. 2 is a diagram showing the configuration of the battery unit 100 in more detail. Battery unit 100 includes a plurality of nickel metal hydride battery cells 110 (hereinafter also simply referred to as “battery cells 110”), a pair of end plates 112, a restraining band 114, and a plurality of bus bars 116. The number of cells is not particularly limited. The x axis, the y axis, and the z axis are orthogonal to each other. The upper vertical direction is the positive direction of the z-axis.

  Each of the plurality of battery cells 110 has a flat rectangular shape, for example. The plurality of battery cells 110 are stacked in the y direction so that the side surfaces having the largest area face each other with a distance therebetween. In FIG. 2, one end in the stacking direction is partially shown in the stack configured by stacking a plurality of battery cells 110. A pair of end plates 112 (only one is shown in FIG. 2) are disposed so as to face one end and the other end in the stacking direction (y direction), respectively. The pair of end plates 112 are restrained by the restraining band 114 with all the battery cells 110 sandwiched therebetween.

  Each cell 110 has a positive electrode terminal and a negative electrode terminal, and is arranged so that the positive electrode terminal faces the negative electrode terminal of an adjacent cell. A positive electrode terminal of a certain cell and a negative electrode terminal of an adjacent cell are electrically connected by being fastened by a bus bar 116 using a bolt and a nut (both not shown). Thereby, in the battery unit 100, the some battery cell 110 is mutually connected in series.

  FIG. 3 is a diagram schematically showing the internal configuration of the battery cell 110. A positive electrode 130, a negative electrode 140, and a separator 150 are accommodated in the battery cell 110. As described above, the battery cell 110 is a nickel metal hydride battery, nickel oxide or nickel hydroxide is used for the positive electrode 130, and hydrogen storage alloy (MH) is used for the negative electrode 140. The positive electrode 130 and the negative electrode 140 are laminated in multiple layers with a separator 150 in a state of being immersed in an electrolytic solution. An alkaline electrolyte such as an aqueous potassium hydroxide solution is used as the electrolyte.

Hereinafter, the potential of the positive electrode 130 is described as “positive electrode potential V ₍₊₎ ”, and the potential of the negative electrode 140 is described as “negative electrode potential V ₍₋₎ ”. Further, the potential of the positive electrode 130 when not energized is described as “positive electrode open potential OCP ₍₊₎ ”, and the potential of the negative electrode 140 when deenergized is described as “negative electrode open potential OCP ₍₋₎ ”.

<Restriction of discharge current>
4 is not energized when the positive electrode potential V ₍₊₎ and negative potentials V _(-) and, during discharge of the positive electrode potential V ₍₊₎ and negative potentials V _(-) and a diagram showing schematically.

At the time of non-energization, the negative electrode potential V ₍₋₎ becomes the negative electrode open potential OCP ₍₋₎ , and the positive electrode potential V ₍₊₎ becomes the positive electrode open potential OCP ₍₊₎ . The difference between the negative electrode potential V ₍₋₎ and the positive electrode potential V ₍₊₎ is the cell voltage VC.

The negative electrode potential V ₍₋₎ during discharge is the negative electrode open-circuit potential due to the influence of charge transfer resistance (hereinafter also referred to as “negative electrode reaction resistance R _{CT (−)} ” ₎ generated in the hydrogen storage alloy that is the active material of the negative electrode 140. OCP _(-). increases than the reaction resistance due anode potential _{V (-)} increase in the discharge current I and the anode reaction resistance _{R CT} represented by _{(- -)} product of ₍₎ = I _{· R CT ()} It is.

When a negative electrode of a hydrogen storage alloy is used in an alkaline electrolyte as in a nickel metal hydride battery, if the negative electrode potential V _(-) increases excessively during discharge, the hydrogen storage alloy is oxidized and deteriorates, resulting in a decrease in battery characteristics. It is known. Therefore, the ECU 300 estimates the negative electrode potential V ₍₋₎ by a method described later, and the estimated negative electrode potential V ₍₋₎ is an upper limit value of the negative electrode potential that can prevent the oxidation of the hydrogen storage alloy (hereinafter referred to as “upper limit potential V”). _The discharge current I is limited so as not to exceed _{(−) max} ”.

<Estimation of negative electrode potential>
Conventionally, the amount of increase in the negative electrode potential V ₍₋₎ during discharge is uniquely determined by the amount of increase in the negative electrode potential V ₍₋₎ due to reaction resistance (= I · R _{CT (−)} ). If the resistance R _{CT (−)} is constant, the negative electrode potential V ₍₋₎ is also considered to be constant.

However, in the nickel-metal hydride battery in which hydrogen-absorbing alloy used for the negative electrode, the battery temperature T is the threshold temperature T1 (e.g. 0 ° C.) in the following and under a discharge current I is larger than the predetermined value I _max, the discharge current I and Even if the negative electrode reaction resistance R _{CT (−)} is constant, the negative electrode potential V ₍₋₎ gradually increases as time passes, and the amount of increase in the negative electrode potential per unit time at that time increases as the discharge current I increases. It has been newly found by the present applicant that the negative electrode potential behavior peculiar to the nickel-metal hydride battery is generated.

  FIG. 5 is a diagram illustrating an example of a correspondence relationship between the discharge current I and the negative electrode potential increase amount ΔV per unit time in a low temperature range where the battery temperature T is equal to or lower than the threshold temperature T1.

If the discharge current I is below the predetermined value I _max is the anode potential increase ΔV per unit time is 0. That is, the discharge current I in is equal to or less than the predetermined value I _max, even in a low temperature range, there is no negative electrode potential increases by similarly time and the normal temperature range.

On the other hand, if the discharge current I is not less than the predetermined value I _max is the negative electrode potential increases per unit time ΔV is larger than 0, and the discharge current I is negative electrode potential increases ΔV per unit larger the time increased Become. That is, in the low temperature range, when the discharge current I is larger than the predetermined value I _max , the negative electrode potential V ₍₋₎ increases as the negative electrode potential increases ΔV per unit time even if the discharge current I is constant. The negative electrode potential increase amount ΔV per unit time at this time increases in proportion to the discharge current I.

Further, correspondence between the negative electrode potential increase ΔV per discharge current I and the unit time (including the magnitude of the predetermined value I _max) became also clear that changes according to the battery temperature T.

Further, it has been clarified that the increase amount of the negative electrode potential V _{(−) with} the lapse of time decreases with a predetermined time constant when the discharge current I is limited to a predetermined value I _max or less.

The ECU 300 estimates the negative electrode potential V ₍₋₎ in consideration of the negative electrode potential behavior specific to the nickel metal hydride battery as described above. Specifically, ECU 300 uses a map (hereinafter also referred to as “I-ΔV map”) that defines the correspondence shown in FIG. 5 for each battery temperature T (temperatures T1, T2, T3, T4... In the example shown in FIG. 5). (Every T1 <T2 <T3 <T4...), And an I-ΔV map corresponding to the actual battery temperature T is specified during discharging in the low temperature range. The ECU 300 calculates the negative electrode potential increase amount ΔV per unit time from the discharge current I with reference to the specified I-ΔV map, and integrates the negative electrode potential increase amount ΔV per unit time. A negative electrode potential increase amount ΣΔV is calculated.

ECU 300 then adds the negative electrode open-circuit potential OCP ₍₋₎ and the negative electrode potential increase amount I · R _{CT (−)} due to reaction resistance (that is, the estimated value of the negative electrode potential corresponding to the conventional value) to the negative electrode potential increase over time. A value obtained by adding an amount ΣΔV (a negative electrode potential increase amount peculiar to a nickel metal hydride battery ₎ is calculated as a negative electrode potential V ₍₋₎ . Accordingly, the negative electrode potential V ₍₋₎ can be calculated (estimated) with high accuracy in consideration of the negative electrode potential behavior unique to the nickel metal hydride battery.

Then, the ECU 300 limits the discharge current I to a predetermined value I _max or less (hereinafter “discharge current limitation” ₎ when the negative electrode potential V ₍₋₎ accurately calculated exceeds the upper limit potential V _{(−) max.} (Also called). The discharge current I by the discharge current limit is limited below a predetermined value I _max, the reaction resistance due to the negative electrode potential increase I · R _{CT (-)} with decreases, when also the anode potential increase with time of a predetermined constant Decrease. Therefore, the negative electrode potential V ₍₋₎ can be controlled below the upper limit potential V _{(−) max} . As a result, during the discharge of the nickel metal hydride battery, the negative electrode potential V ₍₋₎ can be accurately controlled to be equal to or lower than the upper limit potential V _{(−) max} by accurately estimating the negative electrode potential V ₍₋₎ .

  Furthermore, in view of the fact that the amount of increase in the negative electrode potential with the passage of time decreases with a predetermined time constant due to the discharge current limitation, the ECU 300 has a predetermined period during which the discharge current limitation is continued (hereinafter also referred to as “limit period”). When the threshold value is exceeded, the discharge current limitation is canceled assuming that the increase in the negative electrode potential over time has been eliminated. As a result, unnecessary limitation of the discharge current I is suppressed.

<Flowchart of negative electrode potential estimation and discharge current limitation>
FIG. 6 is a flowchart illustrating an example of a processing procedure when ECU 300 estimates the negative electrode potential V ₍₋₎ to limit the discharge current. This flowchart is executed every time a predetermined calculation cycle Δt elapses.

  In step (hereinafter, step is abbreviated as “S”) 10, ECU 300 determines whether or not battery cell 110 is being discharged. If not discharging (NO in S10), ECU 300 ends the process.

If it is being discharged (YES in S10), ECU 300, at S20, determines whether it is during the execution of the discharge current limit above (process for limiting the discharge current I to a predetermined value or less _{I max).}

  If the discharge current is not being restricted (NO in S20), ECU 300 acquires discharge current I and battery temperature T from monitoring unit 200 in S30.

  In S40, ECU 300 determines whether or not battery temperature T is equal to or lower than threshold temperature T1. This determination is a process for determining whether or not the temperature is in a low temperature range where an increase in negative electrode potential can occur over time.

When battery temperature T is higher than threshold temperature T1 (NO in S40), ECU 300 causes negative electrode potential V ₍₋₎ to be set as follows in S50 because the negative electrode potential does not increase over time. This is calculated using Equation (1).

_{V (-) = OCP (-} ) + I · R CT (-) ... (1)
In the formula (1), “OCP ₍₋₎ ” is the potential of the negative electrode 140 when not energized as described above. For example, ECU 300 refers to a T-OCP ₍₋₎ map (data indicating a correspondence relationship between battery temperature T and negative electrode open-circuit potential OCP ₍₋₎ obtained by experiment or the like ₎ stored in advance in a memory. A negative electrode open-circuit potential OCP ₍₋₎ corresponding to the temperature T is calculated.

In the formula (1), “I · R _{CT (−)} ” is the product of the discharge current I and the negative electrode reaction resistance R _{CT (−)} and represents the amount of increase in the negative electrode potential due to the reaction resistance. For example, ECU 300 refers to a TR- _{CT (−)} map (data indicating a correspondence relationship between battery temperature T and negative-electrode reaction resistance R _{CT (−)} obtained by experiment or the like ₎ stored in advance in a memory. The negative electrode reaction resistance R _{CT (−)} corresponding to the battery temperature T is calculated.

Formula (1) is a value obtained by adding a negative electrode potential increase amount I · R _{CT (−)} due to reaction resistance to the negative electrode open-circuit potential OCP as a negative electrode potential V ₍₋₎ . Expression (1) represents a method for estimating the conventional negative electrode potential V ₍₋₎ .

On the other hand, when battery temperature T is equal to or lower than threshold temperature T1 (YES in S40), ECU 300 has a negative electrode potential V in S60 to S65, which will be described later, because it is a low temperature region in which the negative electrode potential may increase with time. ₍₋₎ Is calculated.

At S60, ECU 300 from the battery temperature T acquired in S30, and calculates the predetermined value _{I max} (maximum value of the discharge current I negative electrode potential increases with time in a low temperature region does not occur). Specifically, the ECU 300 specifies an I-ΔV map corresponding to the battery temperature T acquired in S30 from a plurality of I-ΔV maps (see FIG. 5) stored in the memory for each battery temperature T, The predetermined value I _max stored in the specified I-ΔV map is read out.

At S61, ECU 300 determines whether the discharge current I acquired in S30 exceeds the predetermined value _{I max} calculated in S60.

When the discharge current I is greater than the predetermined value _{I max} (YES at S61), ECU 300, at S62, the battery temperature T and discharge current I obtained at S30, the negative electrode potential increases per unit in the current cycle time The amount ΔV _(n) is calculated. The ECU 300 refers to the I-ΔV map specified in S60, calculates the negative electrode potential increase amount ΔV corresponding to the discharge current I of the current cycle, and sets the calculated ΔV to ΔV _(n) in the current cycle. To do.

In S63, ECU 300 calculates negative electrode potential increase amount ΣΔV _(n) over time using the following equation (2a).

ΣΔV _(n) = ΣΔV _(n−1) + {ΔV _(n) · Δt} (2a)
In the equation (2a), “ΣΔV _(n−1) ” is the amount of increase in the negative electrode potential over time calculated in the previous cycle. “ΔV _(n) · Δt” is the amount of increase in the negative electrode potential due to the elapse of the calculation cycle Δt of the current cycle.

FIG. 7 is a diagram schematically illustrating a method of calculating the negative electrode potential increase amount ΣΔV _(n) over time. The ECU 300 calculates a value (= ΔV _(n) · Δt) obtained by multiplying the negative electrode potential increase amount ΔV _(n) per unit time in the current cycle by the calculation cycle Δt of the current cycle as the negative electrode potential increase amount in the current cycle. . ECU 300 then adds a negative electrode potential increase amount ΔV _(n) · Δt of the current cycle to the negative electrode potential increase amount ΣΔV _(n−1) over the time period calculated in the previous cycle, and calculates the time elapsed in the current cycle. Is calculated as the negative electrode potential increase amount ΣΔV _(n) . That is, ECU 300 calculates negative electrode potential increase amount ΣΔV _(n) over time by integrating negative electrode potential increase amount ΔV per unit time for each calculation cycle.

When discharge current I is equal to or _smaller than predetermined value Imax (NO in S61), ECU 300 considers that the increase amount of the negative electrode potential over time gradually decreases with a predetermined time constant, in S64, ECU 300 Using formula (2b), the amount of increase in negative electrode potential ΣΔV _{(n) over time} is calculated.

ΣΔV _(n) = Max [{ΣΔV _(n−1) −α}, 0] (2b)
In the formula (2b), “α” is a decrease amount of the negative electrode potential with the elapse of the current calculation cycle Δt. The right side of the equation (2b) means that the larger one of “ΣΔV _(n−1) −α” and “0” is selected. That is, when “ΣΔV _(n−1) −α” becomes a value of 0 or less, it is assumed that the increase in the negative electrode potential over time has completely disappeared, and the negative electrode potential increase amount over time ΣΔV _{( n)} is set to zero.

Note that ΣΔV _(n) calculated in S63 or S64 is stored in the memory and used as “ΣΔV _(n−1) calculated in the previous cycle” in the next cycle.

In S65, ECU 300 calculates negative electrode potential V ₍₋₎ using the following equation (2).
V _(-) = OCP _{( -)} + IRCT _{( -)} + ΣΔV _(n) (2)
That is, the ECU 300 adds the negative electrode open-circuit potential OCP ₍₋₎ and the negative electrode potential increase amount I · R _{CT (−)} due to the reaction resistance (that is, the estimated value of the conventional negative electrode potential) to the negative electrode potential increase over time. A value obtained by adding an amount ΣΔV (a negative electrode potential increase amount peculiar to a nickel metal hydride battery ₎ is calculated as a negative electrode potential V ₍₋₎ . Thereby, the negative electrode potential V ₍₋₎ is calculated (estimated) with high accuracy in consideration of the negative electrode potential behavior peculiar to the nickel metal hydride battery.

In S70, ECU 300 determines whether or not negative electrode potential V ₍₋₎ calculated in S50 or S65 exceeds upper limit potential V _{(−) max} .

If negative electrode potential V ₍₋₎ does not exceed upper limit potential V _{(−) max} (NO in S70), ECU 300 ends the process.

If negative electrode potential V ₍₋₎ exceeds upper limit potential V _{(−) max} (YES in S70), ECU 300 limits the above-described discharge current (discharge current I to a predetermined value I _max or less) in S80. Process).

  If the discharge current is already being limited (YES in S20), ECU 300 determines in S81 whether or not the above-described limiting period (the period during which the discharge current limiting process is continued) has exceeded a predetermined threshold value. judge. This determination is a process for determining whether or not the increase in the negative electrode potential over time has been eliminated by the discharge current limiting process.

  If the limit period does not exceed the threshold value (NO in S81), ECU 300 continues the discharge current limit in S84.

If the limit period exceeds the threshold value (YES in S81), ECU 300 resets ΣΔV _(n) stored in the memory to 0 in S82). Thereafter, ECU 100 cancels the discharge current limitation in S83.

As described above, the ECU 300 according to the present embodiment estimates the negative electrode potential V ₍₋₎ in consideration of the negative electrode potential behavior unique to the nickel metal hydride battery. Specifically, the ECU 300 calculates the negative electrode potential increase amount ΔV per unit time from the discharge current I during discharge in a low temperature range where the battery temperature T is the threshold temperature T1 or less, and the negative electrode potential per unit time. By integrating the increase amount ΔV, the negative electrode potential increase amount ΣΔV (that is, the negative electrode potential increase amount peculiar to the nickel metal hydride battery) is calculated. ECU 300 then adds the negative electrode open-circuit potential OCP ₍₋₎ and the negative electrode potential increase amount I · R _{CT (−)} due to reaction resistance (ie, the conventional negative electrode potential estimated value) to the negative electrode potential increase amount over time. A value obtained by adding ΣΔV (a negative electrode potential increase amount peculiar to a nickel metal hydride battery ₎ is calculated as a negative electrode potential V ₍₋₎ . Thereby, the negative electrode potential can be accurately calculated (estimated) in consideration of the negative electrode potential behavior unique to the nickel metal hydride battery.

Then, ECU 300 performs discharge current limitation when negative electrode potential V ₍₋₎ accurately calculated exceeds upper limit potential V _{(−) max} . This makes it possible to control the negative electrode potential V ₍₋₎ to be lower than or equal to the upper limit potential V _{(−) max} more reliably than in the case of using a conventional estimated value of the negative electrode potential that does not take into account the increase in negative electrode potential ΣΔV over time. Can do.

[Embodiment 2]
Generally, when a battery is used for a long time, the negative electrode reaction resistance increases due to deterioration. However, in a nickel metal hydride battery, the charge and discharge are repeated over a long period of time, so that the surface of the hydrogen storage alloy used for the negative electrode is activated and the negative electrode reaction resistance R _{CT (−)} decreases. Battery-specific phenomena can occur.

8, the positive electrode potential at the time of discharging in the initial state V ₍₊₎ and negative potentials V _- and the positive electrode potential at the time of discharge after long-term use V ₍₊₎ and negative potentials V _{() (-)} and, schematically FIG. In FIG. 8, “R _{CT (−) ini} ” is the negative electrode reaction resistance (initial value) in the initial state, and “R _{CT (−)} ” is the negative electrode reaction resistance after long-term use. FIG. 8 illustrates the case where the amount of increase in negative electrode potential does not occur over time.

The negative electrode potential V ₍₋₎ at the time of discharge increases by the negative electrode potential increase amount I · R _{CT (−)} due to the reaction resistance than the negative electrode open-circuit potential OCP ₍₋₎ . However, as described above, in the nickel metal hydride battery, the negative electrode reaction resistance R _{CT (−)} can be lower than the initial value R _{CT (−) ini} due to the activation of the negative electrode due to long-term use. Therefore, when the discharge current I is the same, the negative electrode potential increase amount I · R _{CT (−)} due to the reaction resistance after long-term use is greater than the negative electrode potential increase amount I · R _{CT (−) ini} due to the reaction resistance in the initial state. Becomes smaller.

Therefore, if the negative electrode potential V ₍₋₎ is estimated using the initial value R _{CT (−) ini} even after long-term use, the estimated value of the negative electrode potential V ₍₋₎ becomes larger than the actual value. Therefore, the actual negative electrode potential is less likely to exceed the upper limit potential V _{(−) max,} which is preferable from the viewpoint of preventing deterioration, but on the other hand, the discharge current I is unnecessarily limited and the original battery performance cannot be used up. It will be. Moreover, the negative electrode potential V from the cell voltage VC _(-) when calculating the estimated value of the positive potential V ₍₊₎ by subtracting an estimate of, than the estimated value of the actual positive electrode potential of the positive electrode potential V ₍₊₎ There is also a concern that the actual positive electrode potential becomes lower than the lower limit potential V _{(+) max} and the positive electrode is deteriorated.

Therefore, the ECU 300 according to the second embodiment corrects the negative electrode reaction resistance R _{CT (−)} used for the estimation of the negative electrode potential V ₍₋₎ according to the degree of activation of the negative electrode. Specifically, the ECU 300 calculates the minimum value Ymin of the negative electrode activation rate indicating the degree of decrease from the initial value of the negative electrode reaction resistance R _{CT (−)} from the history of the change amount of the cell voltage VC of the nickel metal hydride battery. The negative electrode reaction resistance R _{CT (−)} is corrected using the minimum value Ymin of the negative electrode activation rate. Thereby, the negative electrode potential V ₍₋₎ can be estimated with higher accuracy in consideration of the decrease in the negative electrode reaction resistance R _{CT (−)} due to the negative electrode activation.

FIG. 9 is a flowchart showing a processing procedure when ECU 300 according to the second embodiment corrects negative electrode reaction resistance R _{CT (−)} . This flowchart is repeatedly executed at a predetermined cycle.

  In S90, ECU 300 determines whether or not it is time to start discharging battery cell 110. If not at the start of discharging (NO in S90), ECU 300 ends the process.

  When it is time to start discharging (YES in S90), ECU 300 in S91, discharge current I and battery temperature T when predetermined time t1 has elapsed from the start of discharging, and until predetermined time t1 has elapsed from the start of discharging. The cell voltage change amount VC is obtained.

In S92, ECU 300 calculates a value (= VC / I) obtained by dividing cell voltage change VC acquired in S91 by discharge current I as battery resistance R _(t1) when predetermined time t1 has elapsed, and is calculated. The battery resistance R _(t1) is stored in the memory in association with the battery temperature T.

In S93, ECU 300 determines whether or not the number of data of battery resistance R _(t1) stored in the memory exceeds a predetermined number N. If the number of data is N or less (NO in S93), ECU 300 ends the process.

If the number of data exceeds N (YES in S93), ECU 300 determines the maximum value of battery resistance R _(t1) (hereinafter, “battery resistance maximum value R _{(t1)) for} each battery temperature T in S94. _max ”). Here, specifying the maximum value of the battery resistance R _(t1) avoids erroneous recognition that the battery resistance is excessively lower than the actual value in consideration of detection errors and variations. Because. Note that the battery resistance maximum value R _{(t1) max} in the temperature region where the data of the battery resistance R _(t1) does not exist is complementarily calculated using the battery resistance maximum value R _{(t1) max} in the temperature region where the data exists. Is done.

In S95, for each battery temperature T, ECU 300 calculates maximum value R _{CT (−) max} of negative electrode reaction resistance using the following equation (3).

_{RCT (-) max} = R _{(t1) max-} {R _{(+) ini} + R _{(L) ini} + _{RM (-) ini} } ... (3)
In Expression (3), “R _{(t1) max} ” is the maximum value of the battery resistance specified in S94. “R _{(+) ini} ” is an initial value of the resistance R ₍₊₎ (including reaction resistance and metal resistance ₎ of the positive electrode 130 at the time of discharging, and is stored in advance in a memory. “R _{(L) ini} ” is an initial value of the resistance R _(L) of the electrolytic solution at the time of discharging, and is stored in advance in a memory. “R _{M (−) ini} ” is an initial value of the metal resistance R _{M (−)} of the negative electrode 140 at the time of discharging, and is stored in the memory in advance. That is, in view of the fact that the battery resistance is the sum of positive electrode resistance R ₍₊₎ , electrolyte resistance R _(L) , negative electrode metal resistance R _{M (−)} , negative electrode reaction resistance R _{CT (−)} , ECU 300 Is a value obtained by subtracting a resistance component other than the negative electrode reaction resistance R _{CT (−)} from the battery resistance maximum value R _{(t1) max} specified in S94, and the current maximum value R _{CT (−)} of the negative electrode reaction resistance. Calculated as _max .

In S96, ECU 300 calculates lower limit value Ymin of the negative electrode activation rate for each battery temperature T using the following equation (4). The negative electrode activation rate is an index indicating the degree of decrease from the initial value of the negative electrode reaction resistance R _{CT (−)} .

Ymin = R _{CT (−) ini} / R _{CT (−) max} (4)
In Expression (4), “R _{CT (−) ini} ” is an initial value of the negative electrode reaction resistance R _{CT (−)} and is stored in the memory in advance. “R _{CT (−) max} ” is the maximum value of the negative electrode reaction resistance calculated in S95.

In S97, ECU 300 corrects negative electrode reaction resistance R _{CT (−)} used for calculation of negative electrode potential V ₍₋₎ in S50 or S65 of FIG. 6 described above using lower limit value Ymin of the negative electrode activation rate. . For example, the ECU 300 calculates the negative electrode reaction resistance R _{CT (−)} of each battery temperature T stored in the T-R _{CT (−)} map used for calculation of the negative electrode reaction resistance R _{CT (−)} by the following formula ( 5) to correct.

R _{CT (−)} = R _{CT (−) ini} / Ymin (5)
As described above, the ECU 300 according to the second embodiment corrects the negative electrode reaction resistance R _{CT (−)} used for the estimation of the negative electrode potential V ₍₋₎ according to the degree of activation of the negative electrode 140. Specifically, the ECU 300 calculates the negative electrode activation rate Ymin from the history of the cell voltage change amount VC of the nickel metal hydride battery, and corrects the negative electrode reaction resistance R _{CT (−)} using the negative electrode activation rate Ymin. Thereby, the negative electrode potential V ₍₋₎ can be estimated with higher accuracy in consideration of a decrease in reaction resistance due to the negative electrode activation.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Vehicle, 10 Secondary battery system, 50 Driving wheel, 100 Battery unit, 110 Nickel metal hydride battery cell, 112 End plate, 114 Restraint band, 116 Bus bar, 130 Positive electrode, 140 Negative electrode, 150 Separator, 200 Monitoring unit, 210 Voltage sensor 220, current sensor, 230 temperature sensor, 300 ECU, 310 memory.

Claims (2)

A control device for a nickel metal hydride battery in which a hydrogen storage alloy is used for the negative electrode,
A temperature detector configured to be able to detect the temperature of the nickel metal hydride battery;
A current detector configured to be able to detect the discharge current of the nickel metal hydride battery;
A controller configured to control the discharge current,
When the controller is discharging the nickel metal hydride battery and the temperature is equal to or lower than a threshold temperature,
The amount of increase in negative electrode potential per unit time is calculated from the discharge current,
Calculate the amount of increase in negative electrode potential over time by integrating the amount of increase in negative electrode potential per unit time,
Calculate the sum of the open-circuit potential of the negative electrode, the product of the reaction resistance of the negative electrode and the discharge current, and the increase in negative electrode potential over time as the potential of the negative electrode,
A control device for a nickel metal hydride battery, wherein the discharge current is limited to a predetermined value or less when the calculated potential of the negative electrode exceeds a threshold potential. The controller is
From the voltage change history of the nickel metal hydride battery, calculate the negative electrode activation rate indicating the degree of decrease from the initial value of the reaction resistance of the negative electrode,
The control apparatus for a nickel-metal hydride battery according to claim 1, wherein the negative electrode activation rate is used to correct a reaction resistance of the negative electrode.

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