JP2018050373A - Battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery system capable of more effectively utilizing a power storage device including a two-phase coexistence battery.SOLUTION: A battery system comprises: a power storage device including a two-phase coexistence battery; and a charge/discharge controller for performing control of charge/discharge on the power storage device. The charge/discharge controller comprises: a storage unit 36 that stores history data 64 in which a charge/discharge history of the power storage device is recorded; a standard value calculation unit 52 that calculates a standard value for a charge/discharge power allowable value for the power storage device; a correction value calculation unit 54 that on the basis of the history data 64, calculates a correction coefficient for correcting the standard value, the correction value calculation unit 54 calculating the correction coefficient for making the discharge power allowable value be larger and charge power allowable value be smaller when the power storage device is in an overcharge state than those when the power storage device is in an overdischarge state; and a charge/discharge control unit 56 that calculates the charge/discharge power allowable value on the basis of the standard value and the correction value and controls charge/discharge of the power storage device so that charge/discharge power does not exceed the charge/discharge power allowable value.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a battery system including a power storage device including a lithium ion secondary battery using a dual coexistence-type positive electrode active material, and a charge / discharge control device that controls charge / discharge of the power storage device.

  Conventionally, an electric vehicle (for example, a hybrid vehicle or an electric vehicle) using a rotating electric machine as a power source is widely known. Such an electric vehicle includes a power storage device that supplies power to the rotating electrical machine and a charge / discharge control device that controls charging / discharging of the power storage device. The charge / discharge control device controls the charge / discharge of the power storage device so that the charge / discharge power of the power storage device does not exceed the set charge / discharge power allowable values Win, Wout.

  Here, various techniques have been proposed for setting the allowable charge / discharge power values Win and Wout. For example, Patent Document 1 discloses a charge / discharge power allowable value Win, Wout based on a root mean square value of a charge / discharge current of a power storage device, a current SOC (State Of Charge), and a current temperature of the power storage device. Techniques for determining are disclosed. As represented by Patent Document 1, in the prior art, charge / discharge power allowable values Win and Wout are set mainly based on the current state of the power storage device.

JP 2007-288906 A

  When such a conventional technology is applied to a power storage device using a lithium ion secondary battery (hereinafter referred to as “two-phase coexisting battery”) using a two-phase coexisting positive electrode active material, the battery performance cannot be sufficiently utilized. was there. That is, in such a two-phase coexistence type battery, the influence of past charge / discharge continues for a long time. As a result, in the two-phase coexistence type battery, the battery behavior at the current time (for example, lithium diffusion in the active material having a long time constant) greatly changes depending on the past charge / discharge history.

  Specifically, in the case of a two-phase coexistence type battery, if charging is continued after a predetermined SOC is continued, input characteristics are low (polarization is large), while high output characteristics are exhibited during discharge (polarization is small). In addition, when charging is performed after discharging is continued up to a predetermined SOC, for example, 70%, input characteristics are high, while output characteristics during discharging are low. In other words, after continuing charging, it is possible to discharge with higher power than after continuing discharging, and after continuing discharging, it is possible to charge with larger power than after continuing charging. is there.

  However, many of the prior arts determine the allowable charge / discharge power value only from the current state of the power storage device. Therefore, when the conventional technology is applied to a two-phase coexistence type battery, the discharge power is excessively limited after the continuous charging, compared to the actual discharge characteristics of the battery. Compared to the above, there is a possibility that the charging power is excessively limited and the power storage device cannot be used to the maximum extent.

  Accordingly, an object of the present invention is to provide a battery system that can more effectively use a power storage device including a two-phase coexisting battery.

  A battery system of the present invention includes a power storage device that is mounted on a vehicle and includes a lithium ion secondary battery using a two-phase coexistence-type positive electrode active material, and a charge / discharge control device that controls charge / discharge of the power storage device. The charging / discharging control device stores a storage unit that stores history data of a past fixed period of charging / discharging of the power storage device, and calculates a standard value of a charge / discharge power allowable value of the power storage device. And a correction value deriving unit that calculates a correction coefficient for correcting the standard value based on the history data, and the discharge power is higher when the power storage device is excessively charged than when the discharge is excessive. When the allowable value is increased and the charging power allowable value is decreased, and the power storage device is excessively discharged, the charging power allowable value is increased and the discharging power allowable value is decreased as compared with the case of excessive charging. Calculate the correction factor. The charge / discharge power of the power storage device is calculated such that the charge / discharge power allowable value is calculated based on the correction value calculation unit, the standard value, and the correction value, and the charge / discharge power does not exceed the charge / discharge power allowable value. And a charge / discharge control unit for controlling the operation.

  In a preferred aspect, the power storage device is configured by connecting a plurality of single cells each made of a lithium ion secondary battery using a dual coexistence-type positive electrode active material, and a specific voltage among the plurality of single cells. The storage unit includes an equalization circuit that equalizes the voltages of the plurality of single cells by discharging a single cell having a higher voltage, and the storage unit also stores information on the discharge of the single cells by the equalization circuit. Store as data.

  According to the present invention, the allowable charge / discharge power value can be made to follow the charge / discharge characteristics (input / output characteristics) of the two-phase coexistence type battery that changes depending on the charge / discharge history. Can be used more effectively.

It is a block diagram which shows the structure of the battery system which is embodiment of this invention. It is a figure which shows the structure of the monitoring unit and the equalization unit. It is a figure which shows the voltage change at the time of the pulse discharge in a two-phase coexistence type battery. It is a figure which shows the voltage change at the time of pulse charge in a two-phase coexistence type battery. (A) is a model figure which shows the two-phase coexistence type battery after charge continuation, and (b) the two-phase coexistence type battery after continuation of discharge. It is a functional block diagram of a control part. It is a figure which shows an example of a standard value map. It is a figure which shows an example of a correction coefficient map. It is a flowchart which shows the flow of calculation of charging / discharging electric power allowable value.

[Example 1]
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a battery system 10 according to an embodiment of the present invention. The battery system 10 is mounted on an electric vehicle (for example, an electric vehicle or a hybrid vehicle) on which the rotating electrical machine 100 is mounted as one of power sources.

  The battery system 10 includes a power storage device 12 that supplies power to the rotating electrical machine 100 for traveling. The power storage device 12 is configured by connecting a plurality of single cells 14 in series or in parallel (in the illustrated example, in series). The number of single cells 14 constituting one power storage device 12 can be set as appropriate based on the required output of the power storage device 12 and the like.

  The unit cell 14 is a chargeable / dischargeable lithium ion secondary battery. There are various types of lithium ion secondary batteries. In this embodiment, a lithium ion secondary battery using a two-phase coexisting material as the positive electrode active material of the battery (hereinafter referred to as “two-phase coexisting battery”). Is used as the single cell 14. The characteristics of the two-phase coexistence type battery will be described in detail later.

  An equalization unit 16 and a monitoring unit 18 are connected to the power storage device 12. FIG. 2 is a diagram showing the configuration of the equalization unit 16 and the monitoring unit 18. As shown in FIG. 2, the monitoring unit 18 has a plurality of voltage monitoring ICs 37 provided for each single cell 14. This voltage monitoring IC 37 is connected in parallel to each cell 14, detects the voltage of each cell 14, and outputs it to the control unit 32 described later. The monitoring unit 18 also detects the voltage of the entire power storage device 12 and outputs it to the control unit 32. In the following description, among the voltages detected by the monitoring unit 18, the voltage of the entire power storage device 12 is referred to as “battery voltage Vb”, and the voltage of each cell 14 is referred to as “cell voltage Vc”.

  The equalization unit 16 includes a plurality of equalization circuits 38 provided for each single cell 14. Each equalizing circuit 38 is configured by connecting an equalizing resistor 40 and an equalizing switch 42 in series, and the equalizing circuit 38 is connected in parallel with the single cell 14. The equalization circuit 38 is a circuit for equalizing the voltages (cell voltages Vc) of the plurality of single cells 14. The control unit 32 compares the cell voltages Vc of the plurality of single cells 14, and for the single cell 14 higher than a specific cell voltage Vc (for example, the minimum cell voltage Vc among the plurality of cell voltages Vc), the corresponding equalization is performed. The equalizing switch 42 of the circuit 38 is turned on. When the equalizing switch 42 is turned on, the corresponding single cell 14 is discharged, and the cell voltage Vc decreases. More specifically, when the cell voltage Vc of the three single cells 14 is 3.6V and the cell voltage Vc of the remaining seven single cells 14 is 3.7V among the 10 single cells 14. The control unit 32 turns on the equalization switch 42 of the equalization circuit 38 corresponding to the seven single cells 14 for a predetermined period. The time during which the equalizing switch 42 is kept on is the difference value (in this example, 3.7V) between the minimum voltage (3.6V in this example) and the cell voltage Vc (3.7V in this example) of the single cell 14 to be discharged. , 0.1V). Hereinafter, voltage equalization using the equalization circuit 38 is referred to as “equalization processing”. This equalization processing is normally performed during a system off period described later. The cell voltage Vc here is equivalent to a value obtained in a state where the battery is sufficiently relaxed, that is, an open circuit voltage OCV.

  Returning to FIG. 1 again, the battery system 10 will be described. A temperature sensor 28 that detects the temperature of the power storage device 12 is provided in the vicinity of the power storage device 12. One or more temperature sensors 28 may be provided. The detection value by the temperature sensor 28 is sent to the control unit 32, and this detection value becomes the battery temperature Tb. When there are a plurality of temperature sensors 28 and a plurality of detection values, a statistical value of the plurality of detection values, for example, an average value, a minimum value, a maximum value, etc. may be handled as the battery temperature Tb. The battery system 10 also includes a current sensor 30 that detects a current value flowing through the power storage device 12. The detection value of the current sensor 30 is the battery current Ib.

  The power storage device 12 is connected to a load (the inverter 102 and the rotating electrical machine 100) via a system main relay (hereinafter referred to as “SMR”) 20. When the SMR 20 is turned on, power supply from the power storage device 12 to the rotating electrical machine 100 and charging of the power storage device 12 by power regenerated by the rotating electrical machine 100 are allowed. ON / OFF of the SMR 20 is controlled by the control unit 32.

  A charging circuit 21 is connected between the power storage device 12 and the SMR 20. The charging circuit 21 is a circuit including a connector (inlet 26) that can be connected to an external commercial power source, a charger 24, and a charging relay 22. By connecting the inlet 26 to an external power source and turning on the charging relay 22, the power storage device 12 can be charged by external power. The charger 24 converts external power, which is AC power, into DC power and outputs the DC power to the power storage device 12.

  Here, when both the SMR 20 and the charging relay 22 are turned off, the power storage device 12 is not charged / discharged in principle (however, strictly speaking, there is discharge of some single cells 14 due to equalization processing). . Hereinafter, a state in which both the relays 20 and 22 are turned off and charging / discharging is prohibited is referred to as a state in which the battery system 10 is turned off, that is, “system off”, and at least one of the SMR 20 and the charging relay 22. The state where is turned on is called “system on”. In the case of a battery system that cannot perform external charging (battery system that does not have a charging circuit) or a battery system in which the charging circuit is connected to the load side with respect to SMR 20, if SMR 20 is turned off, power storage is possible. Charging / discharging of the device 12 is prohibited. Therefore, in such a battery system, the state where the SMR 20 is turned on is “system on”, and the state where the SMR 20 is turned off is “system off”.

  The power storage device 12 is connected to various loads via the SMR 20. Among these loads are the inverter 102 and the rotating electrical machine 100. Inverter 102 performs current control between power storage device 12 and rotating electrical machine 100 while converting power from direct current to alternating current or from alternating current to direct current. The rotating electrical machine 100 functions as a motor that outputs power for driving the vehicle and also functions as a generator that converts the power into electric power. The electric power generated by the rotating electrical machine 100 is sent to the power storage device 12 via the inverter 102 and the SMR 20, thereby charging the power storage device 12. Further, when rotating electric machine 100 functions as a motor, it is driven by electric power sent from power storage device 12. In FIG. 1, the number of rotating electric machines 100 is one, but a plurality of rotating electric machines 100 may be provided. For example, a first rotary electric machine that mainly functions as a motor and a second rotary electric machine that mainly functions as a generator may be provided. In FIG. 1, only the inverter 102 and the rotating electrical machine 100 are illustrated as loads connected to the power storage device 12, but other loads may be connected. Examples of other loads include an auxiliary power storage device that supplies power to the auxiliary machinery, a heater and a fan for controlling the temperature of the power storage device 12, and the like.

  The charge / discharge of the power storage device 12 is managed and controlled by the control unit 32. The control unit 32 includes a CPU 34 that performs various calculations and a storage unit 36 that stores various programs and parameters. In FIG. 1, the control unit 32 is illustrated as a single unit, but the control unit 32 may be configured by combining a plurality of control units each having a CPU 34 and a storage unit 36. Therefore, the control unit 32 may include a plurality of CPUs 34 and storage units 36.

  Battery voltage Vb, battery current Ib, and battery temperature Tb are input to control unit 32 from monitoring unit 18, current sensor 30, and temperature sensor 28 provided in power storage device 12. Control unit 32 calculates an SOC (State Of Charge) of power storage device 12 based on the information acquired by these sensors. Further, as will be described in detail later, control unit 32 calculates an allowable value of charge / discharge power of power storage device 12, that is, allowable charge power value Win and allowable discharge power value Wout. Control unit 32 controls charging / discharging of power storage device 12 so that the charge / discharge power of power storage device 12 does not exceed these charge / discharge power allowable values Win, Wout. In order to calculate the charge / discharge power allowable values Win and Wout, the control unit 32 stores the charge / discharge history of the power storage device 12 as the history data 64, which will be described later.

Next, a two-phase coexistence type battery will be described. As described above, the single cell 14 of the present embodiment is a lithium ion secondary battery (two-phase coexisting battery) using a two-phase coexisting material as a positive electrode active material. The two-phase coexisting positive electrode active material is an active material in which two phases (first phase and second phase) can stably coexist. For example, the first phase is a state in which a large amount of lithium is inserted into the positive electrode active material, and the second phase is a state in which the amount of lithium insertion is small compared to the first phase (for example, a state in which lithium is almost zero). . In this state, lithium ions are released from the positive electrode active material. The two-phase coexisting positive electrode active material is a compound containing lithium. As this positive electrode active material, for example, a spinel type compound containing Ni or Mn or an olivine type compound containing Fe (LiFePO ₄ or the like) is used. Can do.

  Specifically, when the two-phase coexistence battery (single cell 14) is almost completely discharged, the entire positive electrode active material is almost in the first phase (a state in which a large amount of lithium is inserted), whereas the two-phase coexistence type When the battery is almost fully charged, the whole positive electrode active material is in the second phase (a state where the amount of inserted lithium is small—for example, a state where the amount of lithium is substantially zero). When the two-phase coexistence type battery is charged, the first phase decreases and the second phase increases. When the battery is discharged, the second phase decreases and the first phase increases.

  In the two-phase coexistence type battery, the charge / discharge characteristics of the two-phase coexistence type battery change according to the past history (charge / discharge history) when the two-phase coexistence type battery is charged / discharged. The charge / discharge characteristics of the two-phase coexistence type battery will be described with reference to FIGS.

  FIG. 3 shows a voltage behavior when discharging (here, pulse discharge) is performed using a two-phase coexistence type battery when SOC is A (A> 0) [%]. FIG. 4 shows the voltage behavior when charging (here, pulse charging) is performed using the two-phase coexistence type battery when the SOC is A (A> 0) [%]. 3 and 4, the vertical axis represents voltage change ΔVb accompanying discharge or charging, and the horizontal axis represents time. Note that the SOC is the ratio of the current charge capacity to the full charge capacity. The voltage change ΔVb is a difference value between the voltage before the start of charging / discharging and the voltage at the current time. In the case of discharge from time t0 to time t1 (that is, during energization) in FIGS. 3 and 4, ΔVb Decreases, and in the case of charging, ΔVb increases.

  In FIGS. 3 and 4, the thick line indicates the voltage behavior of the two-phase coexistence type battery after continuing the charge, and the thin line indicates the voltage behavior of the two-phase coexistence type battery after continuing the discharge. Here, “after charging is continued” means after charging is continued. In this example, as shown in FIG. 5A, the SOC is 0% from the state where the SOC is 0%. It shows the state of charging until. Further, “after the discharge is continued” means after the discharge is continuously performed. In this example, as shown in FIG. 5B, the SOC is almost 100%, and the SOC is A%. It shows the state where the discharge was performed until. In FIG. 5, the hatched portion indicates the first phase, that is, the phase with a large amount of lithium insertion, and the white portion illustrates the second phase, that is, the state where the lithium insertion amount is substantially zero. .

  In FIG. 3, discharge is performed at time t0 to time t1, and after time t1, there is a pause period during which no charge / discharge is performed. As shown in FIG. 3, even when the SOC at the start of discharge (time t0) is the same A%, the amount of voltage change ΔVb is larger after continuing discharge (thin line) than after continuing charging (thick line). I understand. A large amount of voltage change ΔVb associated with discharge means that the polarization generated with discharge is large. That is, it can be seen that the output characteristics are lower after the discharge is continued (thin line) than when the charge is continued (thick line).

  In FIG. 4, charging is performed at time t0 to time t1, and after time t1, there is a pause period during which charging / discharging is not performed. As shown in FIG. 4, even if the SOC at the start of charging (time t0) is the same A%, the amount of voltage change ΔVb is greater after continuing charging (thick line) than after continuing discharging (thin line). I understand. A large amount of voltage change ΔVb associated with charging means that the polarization generated with charging is large. That is, it can be seen that the input characteristics are deteriorated after the charging is continued (thick line) compared to after the discharging is continued (thin line).

  Thus, in the two-phase coexistence type battery, the charge / discharge characteristics change depending on the past charge / discharge history. In such a two-phase coexistence type battery, when the allowable charge / discharge power values Win and Wout are the same after the charge is continued and after the discharge is continued, the performance of the power storage device 12 may not be effectively used. For example, since the input characteristics are high after the discharge is continued, the allowable charging power value Win can be set relatively high. However, when the allowable charge power value Win is set as a constant value regardless of the charge / discharge history, the allowable charge power value Win is set to a low value for battery protection in accordance with the charge continuation state with low input characteristics. There is a need. As a result, after the discharge is continued, the allowable charge power value Win is excessively limited as compared with the actual charge characteristic (input characteristic) of the power storage device 12 (two-phase coexistence type battery). Similarly, when the discharge power allowable value Wout is set as a constant value regardless of the charge / discharge history, after the charge is continued, compared to the actual discharge characteristics (output characteristics) of the power storage device 12 (two-phase coexistence type battery), Discharge power allowable value Wout is excessively limited.

  Therefore, in this embodiment, the charge / discharge history of the power storage device 12 is stored, and the charge / discharge power allowable values Win, Wout are corrected according to the charge / discharge history. As a result, it is possible to maximize input / output performance while appropriately protecting the battery. Hereinafter, the setting of the allowable charge / discharge power values Win and Wout will be described.

  First, the functional configuration of the control unit 32 of the present embodiment will be described. FIG. 6 is a functional block diagram of the control unit 32. Although the control unit 32 originally has various functions, FIG. 6 particularly shows only functions related to the calculation of the charge / discharge power allowable values Win and Wout. As shown in FIG. 6, the control unit 32 includes an SOC calculation unit 50, a standard value calculation unit 52, a correction value calculation unit 54, a charge / discharge control unit 56, an equalization control unit 58, and a storage unit 36. Have. The SOC calculation unit 50 calculates the SOC of the power storage device 12. Specifically, a known method is used in which the current acquired by the current sensor 30 is integrated as needed and divided by the full charge capacity. Alternatively, for example, even if the positive electrode is made of a two-phase coexisting material and the equilibrium potential of the positive electrode is flat with respect to the amount of lithium, the following method may be used as long as the equilibrium potential of the negative electrode is inclined. That is, the SOC calculation unit 50 calculates the OCV by removing the influence of the voltage change derived from the internal resistance from the battery voltage Vb detected by the monitoring unit 18, and stores the calculated OCV in the storage unit 36. The SOC of power storage device 12 is calculated in light of map 60. Furthermore, a method of appropriately mixing the SOC values calculated from these two methods may be used. The calculated SOC is used for controlling the power storage device 12 and the like. The calculated SOC is stored in the history data 64 described later.

  The standard value calculation unit 52 calculates a charge standard value Win_st and a discharge standard value Wout_st which are standard values of the charge / discharge power allowable values Win and Wout. The charge / discharge standard values Win_st and Wout_st are both candidate values of the charge / discharge power allowable values Win and Wout calculated regardless of the charge / discharge history of the power storage device 12. There are various methods for calculating the charge / discharge standard values Win_st and Wout_st. In this embodiment, as an example, the charge / discharge standard values Win_st and Wout_st are calculated based on the battery temperature Tb. Specifically, in the present embodiment, a standard value map 62 indicating the relationship between the battery temperature Tb and the charge / discharge standard values Win_st, Wout_st is stored in the storage unit 36 in advance. FIG. 7 is a diagram illustrating an example of the standard value map 62. As shown in FIG. 7, in general, the absolute values of the charge / discharge standard values Win_st and Wout_st are greatly limited at extremely low temperatures, but as the temperature rises, the absolute values of the charge / discharge standard values Win_st and Wout_st also increase. I will do it. However, if the temperature becomes a certain level or higher, the charge / discharge standard values Win_st and Wout_st may be limited to substantially constant values. The standard value calculation unit 52 compares the battery temperature Tb detected by the temperature sensor 28 with the standard value map 62 to calculate the charge / discharge standard values Win_st and Wout_st. The charge / discharge standard values Win_st and Wout_st described here are examples, and may be changed as appropriate. For example, in the present embodiment, the charge / discharge standard values Win_st and Wout_st are specified based on the battery temperature Tb. However, other parameters such as the SOC of the power storage device 12, the running state of the vehicle, the deterioration amount of the power storage device 12, etc. In consideration of the above, the charge / discharge standard values Win_st and Wout_st may be calculated.

  The correction value calculation unit 54 calculates a charge correction coefficient Kin that corrects the charge standard value Win_st calculated by the standard value calculation unit 52 and a discharge correction coefficient Kout that corrects the discharge standard value Wout_st. That is, as described above, the power storage device 12 of the present embodiment is configured by a two-phase coexistence type battery, and the two-phase coexistence type battery has its charge / discharge characteristics (input) according to the past charge / discharge history. The output characteristics change. If the charge / discharge power allowable values Win and Wout are set without taking such charge / discharge characteristics into consideration, there may be a situation where the performance of the power storage device 12 cannot be exhibited to the maximum and there is a concern that battery deterioration will progress.

  Therefore, the correction value calculation unit 54 calculates charge / discharge correction coefficients Kin, Kout for correcting the charge / discharge standard values Win_st, Wout_st according to the past charge / discharge history of the power storage device 12. In order to calculate the charge / discharge correction coefficients Kin and Kout, the storage unit 36 stores history data 64 and a correction coefficient map 66.

  The history data 64 is data for storing a charge / discharge history of the power storage device 12 for a certain period in the past. More specifically, the history data 64 includes the amount of change in the SOC (ΔSOC) of the power storage device 12 during the past certain period and the battery current Ib during the past certain period. Here, in this embodiment, the discharge current is positive and the charge current is negative. It is desirable to determine the period during which the history data 64 continues to be stored according to the characteristics (long time constant) of the two-phase coexisting battery constituting the power storage device 12. In order to reduce the data size, it is desirable to forget past data further than a certain period in the past.

  However, the configuration of the history data 64 described here is an example, and may be changed as appropriate. For example, in the present embodiment, both the SOC and the battery current Ib are recorded as the history data 64, but only one of them may be recorded. Further, in addition to or instead of the SOC and the battery current Ib, other parameters such as the total charge / discharge time may be stored. Further, in a battery system in which the battery rest time (no-load time) affects, the influence may be taken into consideration. Note that the charge / discharge history stored in the history data 64 includes a discharge history by the equalization process, which will be described in detail later.

  The correction coefficient map 66 is a map showing the relationship between the SOC and the battery current Ib and the charge / discharge correction coefficients Kin and Kout. FIG. 8 is a diagram illustrating an example of the correction coefficient map 66. In FIG. 8, the horizontal line indicates ΔSOC in a certain period. If the battery is used for excessive discharge during the past certain period, the difference value ΔSOC is negative, and if it is used for excessive charge, the difference value ΔSOC is positive.

  In FIG. 8, the thick line indicates the charge correction coefficient Kin, and the thin line indicates the discharge correction coefficient Kout. The alternate long and short dash line indicates the average value of the battery current Ib for a certain period in the past, that is, when the absolute value (| I_ave |) of the current average value I_ave is large, and the solid line indicates the two values when | I_ave | Dotted lines indicate charge / discharge correction coefficients Kin and Kout when | I_ave | is small.

  In the present embodiment, values obtained by multiplying charge / discharge standard values Win_st, Wout_st by charge / discharge correction coefficients Kin, Kout are used as allowable charge / discharge power values Win, Wout. Therefore, as the charge correction coefficient Kin increases, the absolute value of the charge power allowable value Win increases. Similarly, as the discharge correction coefficient Kout increases, the absolute value of the discharge power allowable value Wout also increases.

  As is apparent from FIG. 8, in this embodiment, the larger the difference value ΔSOC, the larger the discharge correction coefficient Kout and the smaller the charge correction coefficient Kin, and the smaller the difference value ΔSOC, the smaller the discharge correction coefficient Kout, The correction coefficient Kin increases. When the difference value ΔSOC is positive, that is, when the charge is excessive, the discharge correction coefficient Kout is larger than 1 (Kout> 1), and the charge correction coefficient Kin is smaller than 1 (Kin <1). In this case, the absolute value of the discharge power allowable value Wout finally calculated is larger than the absolute value of the discharge standard value Wout_st, and the absolute value of the charge power allowable value Win is larger than the absolute value of the charge standard value Win_st. Get smaller. This is because, when the difference value ΔSOC is positive and excessively charged, the power storage device 12 is considered to have improved input characteristics and lower input characteristics than the standard state (Win_st, Wout_st). . In such a case, it is possible to limit the charging by lowering the absolute value of the allowable charge power value Win, and to effectively use the battery while suppressing the battery deterioration by increasing the absolute value of the allowable discharge power value Wout. it can.

  Similarly, when the difference value ΔSOC is negative, that is, when the discharge is excessive, Kout <1, Kin> 1. For this reason, the absolute value of the allowable discharge power value Wout becomes lower and discharge is restricted, while the absolute value of the allowable charge power value Win is increased, so that the allowable range of charging is expanded. Thereby, a battery can be used effectively, suppressing battery deterioration.

  In the present embodiment, the charge / discharge correction coefficients Kin and Kout are changed not only by the SOC difference value ΔSOC but also by the absolute value of the average value I_ave of the battery current Ib. Specifically, as the absolute value | I_ave | of the current average value I_ave is larger, the slope of the change with respect to the difference value ΔSOC of the charge / discharge correction coefficients Kin and Kout is steeper. Thus, the charge / discharge history of the power storage device 12 can be more accurately charged / discharged by changing the charge / discharge correction coefficients Kin, Kout not only by the SOC difference value ΔSOC but also by the absolute value of the current average value I_ave. It can be reflected in the correction coefficients Kin and Kout.

  Note that the calculation method of the charge / discharge correction coefficients Kin and Kout described here is an example, and based on the charge / discharge history of the power storage device 12, the discharge power allowable value is greater in the case of excessive charge than in the case of excessive discharge. As long as Wout is large and the charge / discharge correction coefficients Kin and Kout can be calculated such that the allowable charge power value Win is small, the charge / discharge correction coefficients Kin and Kout may be calculated by other methods. For example, in the present embodiment, the charge / discharge correction coefficients Kin and Kout are changed according to the current average value I_ave with all the battery currents Ib in the past fixed period having the same weight. However, in general, the most recent charge / discharge has a greater effect on the charge / discharge characteristics of the power storage device 12 than the charge / discharge performed in the past. Therefore, the weighted addition value of the current added to the battery current Ib with a weight that becomes heavier as it gets closer is calculated, and the charge / discharge correction coefficients Kin and Kout are changed according to the weighted addition value of the current. Also good. In the present embodiment, the charge / discharge correction coefficients Kin and Kout are specified in consideration of both the SOC and the battery current Ib. However, according to the characteristics of the battery to be used, only one of the charge / discharge correction coefficients is corrected. The coefficients Kin and Kout may be specified.

  The charge / discharge control unit 56 multiplies the charge / discharge standard values Win_st, Wout_st calculated by the standard value calculation unit 52 by the charge / discharge correction coefficients Kin, Kout calculated by the correction value calculation unit 54 to allow charge / discharge power allowance. The values Win and Wout are calculated. That is, Win = Win_st × Kin and Wout = Wout_st × Kout. Charging / discharging control unit 56 controls charging / discharging of power storage device 12 so that the charging / discharging power of power storage device 12 does not exceed calculated charge / discharge power allowable values Win, Wout. The equalization control unit 58 will be described in detail later.

  Next, the flow of calculating the charge / discharge power allowable values Win and Wout in the battery system 10 having the above configuration will be described. FIG. 9 is a flowchart showing a flow of calculation of allowable charge / discharge power values Win and Wout.

  In principle, the flow shown in FIG. 9 is repeatedly executed at a predetermined control period during a period in which charging / discharging of the power storage device 12 is permitted, that is, in a system-on period in which at least one of the SMR 20 and the charging relay 22 is turned on. . On the other hand, in the system off period in which both the SMR 20 and the charging relay 22 are turned off, the charge / discharge power allowable values Win and Wout do not need to be calculated, and therefore the flow of FIG. 9 is not executed.

  In order to calculate the allowable charge / discharge power values Win and Wout, the control unit 32 determines the battery current Ib detected by the current sensor 30, the battery temperature Tb detected by the temperature sensor 28, and the battery voltage detected by the monitoring unit 18. Vb is acquired (S10).

  Subsequently, the control unit 32 calculates the SOC of the power storage device 12 based on the acquired battery current Ib and battery voltage Vb (S12). If the SOC can be calculated, the control unit 32 updates the history data 64 (S14). Specifically, the current SOC calculated in the history data 64 and the battery current Ib are recorded, and the past SOC and battery current Ib past the storage period are forgotten.

  Subsequently, the control unit 32 calculates the charge standard value Win_st and the discharge standard value Wout_st by comparing the battery temperature Tb with the standard value map 62 stored in the storage unit 36 (S16).

  Next, the control unit 32 refers to the history data 64 and calculates the charge correction coefficient Kin and the discharge correction coefficient Wout from ΔSOC and | I_ave | (S18). If the charge / discharge standard values Win_st, Wout_st and the charge / discharge correction coefficients Kin, Kout can be calculated, the control unit 32 multiplies them to calculate the charge power allowable value Win and the discharge power allowable value Wout (S20). That is, the calculation of Win = Win_st × Kin and Wout = Wout_st × Kout is performed. If the allowable charging power value Win and the allowable discharging power value Wout can be calculated, the process returns to step S10, and thereafter, steps S10 to S20 are repeated until the system is turned off (SMR 20 is turned off and the charging relay 22 is turned off).

  As is clear from the above description, in this embodiment, the charge / discharge power allowable values Win, Wout are corrected according to the charge / discharge history of the power storage device 12 in the past certain period. Here, the charge / discharge characteristics of the two-phase coexistence type battery change according to the past charge / discharge history. In the present embodiment, the allowable charge / discharge power values Win and Wout are corrected according to the charge / discharge history, and therefore the allowable charge / discharge power values Win and Wout can follow the changing charge / discharge characteristics. As a result, the power storage device 12 can be used more effectively while preventing the power storage device 12 from deteriorating.

[Example 2]
Next, Example 2 will be described. The charge / discharge power allowable values Win, Wout need only be calculated only during a period during which the power storage device 12 can be charged / discharged, that is, the system on period. During the system off period, the charge / discharge power allowable values Win, Wout are calculated. It becomes unnecessary. However, even during this system off period, an equalization process in which some of the single cells 14 are discharged may be performed.

  This equalization process will be briefly described. As shown in FIG. 6, the control unit 32 has an equalization control unit 58. The equalization control unit 58 controls driving of the equalization circuit 38 in order to equalize the voltage values of the plurality of single cells 14 constituting the power storage device 12. The equalization process by the equalization circuit 38 is performed during a period in which charging / discharging of the power storage device 12 is prohibited, specifically, during a system off period in which the SMR 20 is off and the charging relay 22 is off.

  There are various variations in the flow of the equalization process. Basically, the equalization process is performed in the following procedure. In the system off period, the equalization control unit 58 acquires the cell voltages Vc of the plurality of single cells 14 from the monitoring unit 18. Here, the cell voltage Vc can be regarded as substantially equivalent to the open circuit voltage OCV. The equalization control unit 58 specifies a specific cell voltage Vc, for example, the minimum cell voltage Vc among the plurality of cell voltages Vc as the reference voltage Vdef. Subsequently, a differential voltage ΔVc between the reference voltage Vdef and the cell voltage Vc of each cell 14 is calculated. Then, the equalization control unit 58 specifies the single cell 14 in which the differential voltage ΔVc is equal to or greater than a predetermined threshold, and the cell voltage Vc is used as the reference for the equalization switch 42 of the equalization circuit 38 corresponding to the single cell 14. It keeps on until it reaches the voltage Vdef. Thereby, the voltage variation of the single cell 14 is eliminated.

  Here, when such an equalization process is performed, naturally, a current flows through the cell subjected to the equalization process, and the SOC decreases. The equalization control unit 58 calculates the current value flowing at this time and ΔSOC of the equalized cell, and stores it in the history data 64.

  Here, the charge / discharge characteristics of the power storage device 12 also change due to the discharge caused by the equalization process. Therefore, in the present embodiment, the discharge history by this equalization processing is also recorded in the history data 64 and used for the subsequent calculation of allowable charge / discharge power values Win and Wout. However, during the equalization process, only some of the single cells 14 are discharged, and the current sensor 30 cannot detect the discharge current at this time. Therefore, in the present embodiment, the current and ΔSOC during the equalization process are acquired by the following procedure.

  Usually, the resistance value of the equalizing resistor 40 provided in the equalizing circuit 38 can be considered to be sufficiently larger than the internal resistance of the battery. In this case, the discharge current Ic flowing during the equalization process can be expressed as Vc_def = Ic × Re where the cell voltage before the equalization process is Vc_def and the resistance value of the equalization resistor 40 is Re. Therefore, during the equalization process, the control unit 32 calculates the discharge current Ic of each cell based on Ic = Vc_def / Re. Further, if the discharge current Ic is multiplied by the equalization execution time and the value is divided by the full charge capacity of the power storage device 12, the SOC change ΔSOC due to the equalization process can be obtained. The control unit 32 calculates the discharge current Ic and ΔSOC at the time when the equalization process is completed, and records it in the history data 64. After the system is turned on, the control unit 32 refers to the history data 64 and calculates the charge / discharge correction coefficients Kin and Kout.

  In addition, even when the positive electrode is a two-phase coexisting material and the equilibrium potential is flat with respect to the amount of lithium, when the equilibrium potential of the negative electrode is inclined and the batteries OCV and SOC are uniquely determined, This method is also conceivable. That is, the SOC change (ΔSOC) associated with the equalization process may be calculated based on the change in the OCV (battery voltage Vb) of the entire power storage device 12 before and after the execution of the equalization process. In this case, the current (discharge current Ic) flowing through the single cell 14 during the equalization processing period is calculated by multiplying ΔSOC corresponding to the amount of change in OCV by the full charge amount and dividing that value by the equalization execution time. it can.

  In addition, after the equalization process is completed, since the power storage device 12 is not charged / discharged, the SOC does not change, and the battery current Ib remains zero. In the case of the battery system in which the charging / discharging period, that is, the time when the battery is not loaded (resting time) also affects the input / output characteristics as a history, the history data 64 may be updated in consideration of this effect. .

  As is apparent from the above description, the current value and SOC that flow during the system off period, particularly during the execution of the equalization process, are also stored in the history data 64 as the charge / discharge history, whereby the power storage device resulting from the equalization process Thus, charging / discharging power allowable values Win, Wout reflecting the change of 12 charging / discharging characteristics are obtained. Thus, the power storage device 12 can be used more effectively while preventing the power storage device 12 from being deteriorated.

DESCRIPTION OF SYMBOLS 10 Battery system 12 Power storage device 14 Single cell 16 Equalization unit 18 Monitoring unit 20 System main relay 21 Charging circuit 22 Charging relay 24 Charger 26 Inlet 28 Temperature sensor 30 Current sensor 32 Control unit, 34 CPU, 36 storage unit, 38 equalization circuit, 40 equalization resistor, 42 equalization switch, 50 SOC calculation unit, 52 standard value calculation unit, 54 correction value calculation unit, 56 charge / discharge control unit, 58 equalization Control unit, 60 SOC-OCV map, 62 standard value map, 64 history data, 66 correction coefficient map, 100 rotating electrical machine, 102 inverter.

Claims (2)

A power storage device including a lithium ion secondary battery mounted on a vehicle and using a two-phase coexisting positive electrode active material,
A charge / discharge control device for controlling charge / discharge of the power storage device;
The charge / discharge control device comprises:
A storage unit that stores history data in which a history of a past fixed period of charge and discharge of the power storage device is recorded;
A standard value calculation unit for calculating a standard value of the charge / discharge power allowable value of the power storage device;
A correction value devising unit that calculates a correction coefficient for correcting the standard value based on the history data, and when the power storage device is overcharged, the discharge power allowable value is set more than in the case of overdischarge. A correction that increases the allowable charging power value and decreases the allowable charging power value, and increases the allowable charging power value and decreases the allowable discharging power value when the power storage device is excessively discharged compared to excessive charging. A correction value calculation unit for calculating a coefficient;
A charge / discharge control unit that calculates the allowable charge / discharge power based on the standard value and the correction value, and controls charge / discharge of the power storage device so that the charge / discharge power does not exceed the allowable charge / discharge power. When,
A battery system comprising: The battery system according to claim 1,
The power storage device is configured by connecting a plurality of single cells each made of a lithium ion secondary battery using a dual coexistence-type positive electrode active material,
Furthermore, the discharge circuit of a single cell having a voltage higher than a specific voltage among the plurality of single cells is provided with an equalization circuit that equalizes the voltage of the plurality of single cells,
The storage unit also stores information regarding discharge of the single cell by the equalization circuit as the history data.
A battery system characterized by that.

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