JP6662228B2 - Battery system - Google Patents

Description

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

  Japanese Patent Laying-Open No. 2011-222133 (Patent Document 1) discloses an electric vehicle equipped with a battery pack (assembled battery). The battery pack includes a plurality of unit batteries (unit cells). A plurality of temperature sensors are provided in the battery pack in order to accurately detect the temperatures of the plurality of unit batteries. In this electric vehicle, the internal resistance of each unit battery is estimated. The input / output of the battery pack is limited by using the maximum value of the detection results of the plurality of temperature sensors and the estimated internal resistance of each unit battery (see Patent Document 1).

JP 2011-222133 A

  In a nickel-metal hydride battery, the repetition of charge and discharge activates the negative electrode (hydrogen storage alloy), and the reaction resistance of the negative electrode decreases. As the reaction resistance of the negative electrode decreases, the internal resistance of the nickel-metal hydride battery also decreases.

  By the way, even in a battery system including a nickel-metal hydride battery, it is conceivable that input / output of the nickel-metal hydride battery is limited by estimating the internal resistance of the nickel-metal hydride battery as in the electric vehicle disclosed in Patent Document 1. Can be As described above, the internal resistance of the nickel-metal hydride battery decreases as charging and discharging of the nickel-metal hydride battery are repeated. Therefore, if the internal resistance after the decrease is not accurately estimated, the input / output of the nickel-metal hydride battery may be unnecessarily severely restricted.

  The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a battery system including a nickel-metal hydride battery, thereby reducing the reaction resistance of the negative electrode to improve the estimation accuracy of the internal resistance. It is to improve.

  A battery system according to the present invention includes a nickel-metal hydride battery and a control device. The control device is configured to estimate an internal resistance of the nickel-metal hydride battery. The control device monitors a current change amount and a voltage change amount of the nickel-metal hydride battery during a predetermined time. The predetermined time is set to be different depending on the temperature of the nickel-metal hydride battery. When the first time is set as the predetermined time, the control device determines whether or not the magnitude of the current change amount is equal to or more than the first predetermined amount and the magnitude of the current change amount is the maximum. When the fluctuation range of the current of the nickel-metal hydride battery is equal to or smaller than a second predetermined amount smaller than the first predetermined amount, the current change amount and the voltage change amount are stored. The control device estimates the internal resistance of the nickel-metal hydride battery using the stored current change amount and voltage change amount. The control device, when the second time shorter than the first time is set as the predetermined time, when the magnitude of the current change is equal to or larger than the third predetermined amount, The amount of change is stored. The control device estimates the internal resistance of the nickel-metal hydride battery using the stored current change amount and voltage change amount.

  The input / output of the nickel-metal hydride battery is easily affected by past input / output (hysteresis). Even if the control device estimates the internal resistance of the nickel-metal hydride battery by using the current change amount and the voltage change amount detected at the timing at which the influence of the past input / output is large, the control device determines the decrease in the negative electrode reaction resistance by the internal resistance. Can not be accurately reflected on. As a result, the control device cannot accurately estimate the internal resistance of the nickel-metal hydride battery. In this battery system, a timing at which a current change amount in a predetermined time satisfies a predetermined condition (a condition that the influence of the reaction resistance of the negative electrode becomes dominant in the internal resistance estimated from the current change amount and the voltage change amount). Are used for estimating the internal resistance. Therefore, according to this battery system, a decrease in the reaction resistance of the negative electrode can be considered in estimating the internal resistance.

  According to the present invention, in a battery system including a nickel-metal hydride battery, it is possible to improve the accuracy of estimating the internal resistance by considering a decrease in the reaction resistance of the negative electrode.

FIG. 1 is a block diagram schematically showing a configuration of a vehicle on which a battery system is mounted. FIG. 3 is a diagram for explaining conditions under which the influence of reaction resistance of a negative electrode is likely to appear when the temperature of a nickel-metal hydride cell is normal temperature. FIG. 3 is a diagram for explaining conditions under which the influence of the reaction resistance of the negative electrode is likely to appear when the temperature of the nickel-metal hydride cell is low. FIG. 9 is a diagram for explaining a condition in which a current change amount and a voltage change amount are stored for internal resistance estimation when a first time is set as a predetermined time. FIG. 8 is a diagram for explaining a condition in which a current change amount and a voltage change amount are stored for estimating an internal resistance when a second time is set as a predetermined time. It is a flowchart which shows the estimation process procedure of the internal resistance of the nickel hydride single battery in a battery system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated.

[Configuration of Battery System]
FIG. 1 is a block diagram schematically showing a configuration of a vehicle 1 on which a battery system according to the present embodiment is mounted. 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, and is applicable to any electric vehicle equipped with a nickel-metal hydride battery, such as a hybrid vehicle and a fuel cell vehicle. It is possible.

  Referring to FIG. 1, vehicle 1 includes a battery system 10, a power control unit (PCU) 20, a motor generator (MG) 30, and drive wheels 40. The battery system 10 includes a battery pack 100, a monitoring unit 200, and an electronic control unit (ECU: Electronic Control Unit) 300.

  The battery pack 100 includes a plurality of nickel-metal hydride cells (single cells) connected in series. Monitoring unit 200 includes a voltage sensor 210, a current sensor 220, and a temperature sensor 230. Voltage sensor 210 detects a voltage of each cell in battery pack 100 (hereinafter, also referred to as “cell voltage”). The current sensor 220 detects a charge / discharge current of the battery pack 100. The temperature sensor 230 detects the temperature of each cell in the battery pack 100 (hereinafter, also referred to as “cell temperature”). Each sensor outputs a signal indicating the detection result to ECU 300. Note that it is not always necessary to monitor the voltage and the temperature on a cell-by-cell basis. For example, the voltage and temperature may be monitored on a module-by-module basis or a battery pack-by-cell basis.

  MG 30 is driven by electric power supplied from battery pack 100. The driving force of MG 30 is transmitted to driving wheels 40 via a driving shaft. When the vehicle 1 is braked, the MG 30 operates as a generator by being driven by the rotational force of the drive wheels 40. The power generated by MG 30 is charged to battery pack 100 via PCU 20.

  PCU 20 includes, for example, a converter and an inverter (neither is shown). PCU 20 is configured to be capable of bidirectional power conversion between battery pack 100 and MG 30 in accordance with a switching command from ECU 300. The converter is configured to perform bidirectional DC voltage conversion between the battery pack 100 and the inverter. The inverter is configured to perform bidirectional power conversion between DC power and AC power input / output to / from MG 30.

  ECU 300 includes a CPU (Central Processing Unit), a memory, and an input / output interface (neither is shown). ECU 300 controls charging and discharging of battery pack 100 by controlling PCU 20 based on signals from the respective sensors and information stored in the memory.

[Improved estimation accuracy of internal resistance]
As described above, in the battery system 10, the assembled battery 100 includes a nickel-metal hydride unit cell. In a nickel-metal hydride single cell, the charge and discharge are repeated to activate the negative electrode (hydrogen storage alloy), and the reaction resistance of the negative electrode decreases. As the reaction resistance of the negative electrode decreases, the internal resistance of the nickel-metal hydride cell decreases. Therefore, in order to accurately estimate the internal resistance of the nickel-metal hydride cell, it is necessary to sufficiently consider the reduction in the reaction resistance of the negative electrode.

  Incidentally, the input / output of the nickel-metal hydride single cell is easily affected by past input / output (hysteresis). Therefore, even if the internal resistance of the nickel-metal hydride cell is estimated from the current change amount and the voltage change amount detected at the timing when the influence of the past input / output is large, the decrease in the reaction resistance of the negative electrode is accurately represented by the internal resistance. Is not reflected.

  In battery system 10 according to the present embodiment, ECU 300 stores a current change amount and a voltage change amount when a condition in which the influence of the reaction resistance of the negative electrode of the nickel-metal hydride battery is dominant is satisfied. ECU 300 estimates the internal resistance of the nickel-metal hydride battery using the stored current change amount and voltage change amount. Since the internal resistance of the nickel-metal hydride cell is estimated using the current change and the voltage change detected at the timing when the influence of the reaction resistance of the negative electrode becomes dominant, the battery system 10 estimates the internal resistance. In this case, a reduction in the reaction resistance of the negative electrode can be sufficiently considered. ECU 300 stores, for example, a current change amount and a voltage change amount for each nickel-metal hydride cell included in battery pack 100, and estimates the internal resistance for each nickel-metal hydride cell.

  The present inventor has further found that conditions under which the influence of the reaction resistance of the negative electrode of the nickel-metal hydride cell dominates differ depending on the temperature of the nickel-metal hydride cell.

  FIG. 2 is a diagram for explaining conditions under which the influence of the reaction resistance of the negative electrode is likely to appear when the temperature of the nickel-metal hydride cell is normal temperature (for example, 25 ° C.). Referring to FIG. 2, the horizontal axis indicates whether the target nickel-metal hydride cell is a new or collected product, and the vertical axis indicates the internal resistance of the nickel-metal hydride cell.

  The recovered product is a single cell repeatedly charged and discharged. Originally, in a nickel-metal hydride cell, the reaction resistance of the negative electrode decreases as charge and discharge are repeated. Therefore, the collected product should have lower internal resistance than the new product.

  The internal resistance of the new product and the collected product on the right side is a value estimated by detecting a current change amount and a voltage change amount for one second at room temperature in each of the new product and the collected product. Originally, the collected product should have lower internal resistance than the new product as described above, but in this case, there is almost no difference between the two. This is considered to be because the estimated internal resistance largely reflected the influence of the past input / output of the nickel-metal hydride single cell at a relatively long time of 1 second at room temperature.

  The internal resistance of the new product and the recovered product on the left side is a value estimated by detecting a current change amount and a voltage change amount for 0.1 second at room temperature in each of the new product and the recovered product. In this case, the internal resistance of the recovered product is lower than that of the new product, and it can be said that the estimated internal resistance reflects a decrease in the reaction resistance of the negative electrode. Therefore, in order to accurately estimate the decrease in the reaction resistance of the negative electrode, it is necessary to detect the amount of current change and the amount of voltage change in a short time of 0.1 second at normal temperature.

  FIG. 3 is a diagram for explaining conditions under which the influence of the reaction resistance of the negative electrode is likely to appear when the temperature of the nickel-metal hydride single cell is low (for example, minus (−) 30 ° C.). Referring to FIG. 3, similarly to FIG. 2, the horizontal axis indicates whether the target nickel-metal hydride cell is a new or collected product, and the vertical axis indicates the internal resistance of the nickel-metal hydride cell.

  The internal resistance of the new product and the recovered product on the left side is a value estimated by detecting a current change amount and a voltage change amount for 0.1 second at a low temperature in each of the new product and the recovered product. In this case, there is almost no difference in the estimated internal resistance between the new product and the recovered product. This is considered to be because the effect of the reaction resistance of the negative electrode did not sufficiently appear in a short time of 0.1 second at a low temperature.

  The internal resistance of the new product and the collected product on the right side is a value estimated by detecting the amount of current change and the amount of voltage change for one second at a low temperature in each of the new product and the collected product. In this case, the internal resistance of the recovered product is lower than that of the new product, and it can be said that the estimated internal resistance reflects a decrease in the reaction resistance of the negative electrode. Therefore, in order to accurately estimate the decrease in the reaction resistance of the negative electrode, it is necessary to detect the amount of change in current and the amount of change in voltage for a relatively long time of 1 second at low temperatures.

  Therefore, in battery system 10 according to the present embodiment, ECU 300 monitors the amount of current change and the amount of voltage change of the nickel-metal hydride battery for a predetermined time in order to estimate the internal resistance of the nickel-metal hydride battery. The setting is made different depending on the temperature of the nickel-metal hydride cell. Thus, the interval for determining whether to store the current change amount and the voltage change amount is appropriately set according to the temperature. For example, when the temperature of the nickel-metal hydride cell is low, 1 second is set as the predetermined time, and when the temperature of the nickel-metal hydride cell is normal temperature, 0.1 second is set as the predetermined time. .

  When a first time (for example, one second) is set as the predetermined time (for example, when the temperature is low), ECU 300 determines the amount of change in current of the nickel-metal hydride battery when both of the following two conditions are satisfied. And the amount of voltage change is stored for estimating the internal resistance. The first condition is that the magnitude of the current change in the predetermined time is equal to or greater than the first predetermined amount. The second condition is that the fluctuation range of the current after the time when the magnitude of the current change in the predetermined time becomes maximum is equal to or smaller than a second predetermined amount (second predetermined amount <first predetermined amount). It is.

  FIG. 4 is a diagram for explaining a condition under which the current change amount and the voltage change amount are stored for estimating the internal resistance when the first time is set as the predetermined time. Referring to FIG. 4, the horizontal axis represents time, and the vertical axis represents current of the nickel-metal hydride battery.

  It is assumed that one second from time t01 to t01 + 1 second is a predetermined time. In this case, the “magnitude of the current change amount in the predetermined time” under the first condition is ΔI0 obtained by subtracting the current I10 at the time t01 from the current I11 at the time t01 + 1 second. Therefore, when ΔI0 is equal to or more than the first predetermined amount, the first condition is satisfied. When the first condition is satisfied, it is considered that the influence of the reaction resistance of the negative electrode on the internal resistance estimated from the current change amount and the voltage change amount has increased to some extent.

  Between time t01 and time t01 + 1 second, the time at which the magnitude of the current change from time t01 is maximum is t02. Therefore, the “fluctuation width of the current after the time point when the magnitude of the current change amount in the predetermined time becomes maximum” under the second condition is ΔI1 which is the fluctuation width from time t02 to t01 + 1 second. Therefore, when ΔI1 is equal to or less than the second predetermined amount, the second condition is satisfied. When the second condition is not satisfied (when ΔI1 fluctuates greatly), the influence of diffusion resistance (a time constant is slower than the reaction resistance) on the internal resistance estimated from the current change amount and the voltage change amount. It is thought that it is getting bigger. Therefore, the ECU 300 cannot accurately estimate a decrease in the reaction resistance of the negative electrode depending on the current change amount and the voltage change amount when the second condition is not satisfied.

  When the first time is set as the predetermined time, it is considered that the influence of the reaction resistance of the negative electrode becomes dominant when the first and second conditions are satisfied. By estimating the internal resistance using the current change amount and the voltage change amount stored at this timing, the ECU 300 can sufficiently consider the decrease in the reaction resistance of the negative electrode.

  When the second time (for example, 0.1 second) is set as the predetermined time (for example, at normal temperature), ECU 300 determines that the magnitude of the current change in the predetermined time is equal to or greater than the third predetermined amount. At one time, the amount of change in current and the amount of change in voltage of the nickel-metal hydride battery are stored for estimating the internal resistance. If the magnitude of the current change during the predetermined time is equal to or larger than the third predetermined amount, it is considered that the influence of the reaction resistance of the negative electrode is dominant. By estimating the internal resistance using the current change amount and the voltage change amount stored at this timing, the ECU 300 can sufficiently consider the decrease in the reaction resistance of the negative electrode.

  FIG. 5 is a diagram for explaining conditions under which the current change amount and the voltage change amount are stored for estimating the internal resistance when the second time is set as the predetermined time. Referring to FIG. 5, the horizontal axis represents time, and the vertical axis represents current of the nickel-metal hydride cell.

  It is assumed that 0.1 second from time t0 to t0 + 0.1 second is the predetermined time. In this case, a value obtained by subtracting the current I0 at the time t0 from the current I1 at the time t0 + 0.1 seconds is the magnitude of the current change amount in the predetermined time. Therefore, when this value is equal to or larger than the third predetermined amount, ECU 300 stores the current change amount and the voltage change amount for estimating the internal resistance.

  Note that when the second time (for example, 0.1 second) is set as the predetermined time, unlike the case where the first time (for example, 1 second) is set, the second condition is set. Is not imposed. This is because, when the predetermined time is short, the influence of the diffusion resistance having a slow time constant on the internal resistance estimated from the current change amount and the voltage change amount is unlikely to increase.

  As described above, the ECU 300 stores the current change amount and the voltage change amount when the condition in which the influence of the reaction resistance of the negative electrode of the nickel-metal hydride battery is dominant is satisfied, and stores the stored current change amount and the voltage change amount. Is used to estimate the internal resistance of the nickel-metal hydride cell. Therefore, according to the battery system 10, a reduction in the reaction resistance of the negative electrode can be sufficiently considered in estimating the internal resistance.

[Processing procedure for internal resistance estimation]
FIG. 6 is a flowchart showing a procedure for estimating the internal resistance of the nickel-metal hydride battery in the battery system 10. Referring to FIG. 6, the processing shown in this flowchart is repeatedly executed by ECU 300 during the operation of the vehicle system.

  ECU 300 obtains a signal indicating a cell voltage, a signal indicating a current, and a signal indicating a cell temperature from voltage sensor 210, current sensor 220, and temperature sensor 230, respectively (step S100). The ECU 300 determines whether the temperature of the nickel-metal hydride battery is low or normal by referring to the obtained cell temperature (step S110). For example, ECU 300 determines that the temperature is equal to or higher than 0 ° C. as normal temperature, and determines that the temperature is lower than 0 ° C. as low temperature.

  When it is determined that the temperature of the nickel-metal hydride battery is low (“low temperature” in step S110), ECU 300 sets a first time (for example, 1 second) as the above-mentioned predetermined time (step S120).

  Thereafter, the ECU 300 determines the absolute value of the difference between the current detected before the first time (stored in the internal memory of the ECU 300) and the current detected in the current cycle (the current change amount in the predetermined time). It is determined whether or not the (size) is equal to or more than a first predetermined amount (step S130). If it is determined that the magnitude of the current change in the predetermined time is less than the first predetermined amount (NO in step S130), the process proceeds to return.

  If it is determined that the magnitude of the current change in the predetermined time is equal to or greater than the first predetermined amount (YES in step S130), ECU 300 has maximized the magnitude of the current change since the first time before. It is determined whether or not the current fluctuation range from the time point to the current cycle is equal to or less than a second predetermined value (step S140). If it is determined that the fluctuation range of the current exceeds the second predetermined value (NO in step S140), the process proceeds to return.

  If it is determined that the current fluctuation width is equal to or smaller than the second predetermined value (YES in step S140), ECU 300 determines the voltage change amount and the current change amount (the voltage in the predetermined time) from the first time before to the current cycle. The amount of change and the amount of current change) are stored in the internal memory in order to estimate the internal resistance (step S150).

  Thereafter, the ECU 300 uses the voltage change amount and the current change amount stored in step S150 in the current cycle, and the voltage change amount and the current change amount stored in step S150 in the past cycle, so that the nickel hydrogen The internal resistance of the cell is estimated (step S160). For example, the ECU 300 uses the voltage change amount and the current change amount stored in the past and the voltage change amount and the current change amount stored this time after appropriately weighting them to use the internal resistance of the nickel-metal hydride unit cell. Is estimated. The internal resistance estimated here is a resistance value of t seconds (first time), and is a resistance value obtained from the voltage change amount and the current change amount in the first time.

  ECU 300 updates the input / output limit value of the nickel-metal hydride battery based on the estimated internal resistance (step S170).

  If it is determined in step S110 that the temperature of the nickel-metal hydride cell is normal temperature (“normal temperature” in step S110), ECU 300 sets a second time (eg, 0.1 second) as the above-described predetermined time. (Step S180).

  Subsequent processes in steps S190 to S220 are substantially the same as the processes in steps S130 and S150 to S170, respectively. The difference is, for example, that the predetermined time in steps S190 to S220 is the first time, while the predetermined time in steps S130 and S150 to S170 is the second time, and the threshold value in step S130 is different. There is a point that the threshold value in step S190 is the third predetermined amount, while the threshold value is the first predetermined amount.

  If the temperature of the nickel-metal hydride battery is normal temperature, the determination as in step S140 is not performed. This is because, as described above, when the predetermined time is short (for example, 0.1 second), the influence of the diffusion resistance having a slow time constant may increase on the internal resistance estimated from the current change and the voltage change. This is because the nature is low.

  As described above, in battery system 10 according to the present embodiment, ECU 300 stores the amount of change in current and the amount of change in voltage at the timing at which the effect of the reaction resistance of the negative electrode of the nickel-metal hydride cell is dominant. The internal resistance of the nickel-metal hydride cell is estimated using the current change and the voltage change. Therefore, according to the battery system 10, a reduction in the reaction resistance of the negative electrode can be sufficiently considered in estimating the internal resistance.

  Note that the procedure for estimating the internal resistance of the nickel-metal hydride cell does not necessarily need to be divided into low temperature and normal temperature. For example, the processing procedure for estimating the internal resistance may be divided into a very low temperature (for example, −30 ° C. or less), a low temperature (for example, less than 0 ° C.), and a normal temperature (for example, 0 ° C. or more).

  The embodiments disclosed this time are to be considered in all respects as illustrative 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.

  1 vehicle, 10 battery system, 20 PCU, 30 MG, 40 driving wheels, 100 assembled battery, 200 monitoring unit, 210 voltage sensor, 220 current sensor, 230 temperature sensor, 300 ECU.

Claims (1)

Nickel-metal hydride batteries,
A control device configured to estimate the internal resistance of the nickel-metal hydride battery,
The control device monitors a current change amount and a voltage change amount of the nickel-metal hydride battery during a predetermined time,
The predetermined time is set to be different depending on the temperature of the nickel-metal hydride battery,
The control device includes:
When the first time is set as the predetermined time,
The variation range of the current of the nickel-metal hydride battery after the time when the magnitude of the current change amount is equal to or more than the first predetermined amount and the magnitude of the current change amount is the maximum is the first predetermined amount. When the current change amount and the voltage change amount are equal to or smaller than a second predetermined amount which is smaller than the second predetermined amount, the internal resistance is estimated using the stored current change amount and the voltage change amount,
The first predetermined amount is a value for determining that a reaction resistance is dominant in the internal resistance,
The second predetermined amount is a value for determining that diffusion resistance is not dominant in the internal resistance,
When a second time shorter than the first time is set as the predetermined time, when the magnitude of the current change is equal to or greater than a third predetermined amount, the current change and the current storing the voltage change amount, the current change amount stored and using the voltage variation estimating the internal resistance,
The battery system , wherein the third predetermined amount is a value for determining that a reaction resistance is dominant in the internal resistance .

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