JP2016225306A - Charge/discharge system of electric storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for managing a plurality of secondary batteries connected in series.SOLUTION: A BMS 20 includes a voltmeter 24 for individually measuring voltage values V of a plurality of secondary batteries 50 connected in series, and a time keeping unit 42 measures time difference between from when a time rate of change of the voltage value V of any one of the secondary batteries 50 reaches a reference value K to when a time rate of change of the voltage value V of the other secondary battery 50 reaches the reference value K. The BMS 20 detects deterioration of the secondary battery 50 on the basis of a comparison between a time point when the time rate of change of the voltage of any one of storage elements reaches the reference value and a time point when the voltage of the secondary battery 50 reaches a voltage at which charge/discharge is terminated.SELECTED DRAWING: Figure 1

Description

  The invention disclosed in this specification relates to a technique for charging and discharging a plurality of power storage elements connected in series.

  Conventionally, power storage elements that can be used repeatedly have been used. The power storage element can be used many times by repeating charging and discharging, is more environmentally friendly than a battery that cannot be charged and discharged, and is currently expanding its field of use such as electric vehicles.

  In an apparatus in which a plurality of power storage elements are used, the capacity of the power storage elements may become uneven due to variations in initial capacity and deterioration rate of each power storage element. If the capacities of the storage elements become uneven, the voltage of one or several storage elements reaches the fully charged voltage before or after other storage elements at the time of charging, and charging ends, The power storage element may not be fully charged. Further, at the time of discharging, the voltage of one or several power storage elements reaches the discharge end voltage before or after the other power storage elements and the discharge ends, and the power charged in all the power storage elements is reduced. You may not be able to use up. As described above, when the capacities of the power storage elements are uneven, it is not possible to maximize the capacity of the power storage elements. 2. Description of the Related Art Conventionally, a technique is known in which a secondary battery with an uneven capacity is discharged using a discharge circuit such as a resistor to equalize the capacity of the secondary battery (for example, cited reference 1). In this technique, the remaining battery capacity of the secondary battery is obtained from the voltage information of the secondary battery obtained in a no-current state, and each secondary battery is discharged based on the difference in capacity, whereby the capacity of the secondary battery is obtained. Is said to equalize.

JP 2011-19329 A

  In recent years, olivine iron-based lithium ion secondary batteries (hereinafter referred to as olivine iron-based batteries) have attracted attention as secondary batteries for electric vehicles and the like. The olivine iron-based battery is a kind of lithium ion battery, and olivine-type iron phosphate is used for the positive electrode and, for example, a graphite-based material is used for the negative electrode. For this reason, the olivine iron-based battery does not need to use a cobalt-based electrode material as an electrode, and has an advantage that the cost is low and the safety is high compared to a secondary battery using a cobalt-based electrode material.

  The olivine iron-based battery has a region in which the voltage rapidly increases with respect to the increase in the remaining capacity (hereinafter referred to as a change region). For example, when a graphite-based material is used as the negative electrode, the SOC indicating the remaining capacity of the secondary battery Is known to be a change region in a region of less than 10% and a region of 90% or more. If the change region exists in a relatively high SOC region or a relatively low SOC region, even if an attempt is made to equalize the storage element capacity from the voltage information of the storage element in the change region, The SOC of the power storage element reaches approximately 100% or approximately 0%, and charging / discharging of the power storage element ends. When the charging / discharging of the power storage element is finished, the equalization of the capacity of the power storage element is also finished, so that it is difficult to sufficiently equalize the capacity of the power storage element. Therefore, a technique for equalizing the capacities of the power storage elements using an area other than the change area is desired.

  On the other hand, the olivine iron-based battery has a plateau region in combination with the negative electrode. For example, when a graphite-based material is used as the negative electrode, the plateau in which the SOC indicating the remaining capacity of the secondary battery extends from 10% to 90%. Known to have territory. Here, the plateau region means a region where the voltage of the secondary battery is substantially constant even when the SOC of the secondary battery changes. Therefore, in a power storage element such as a secondary battery having a plateau area, it is difficult to estimate the capacity of the power storage element from the voltage information of the power storage element acquired in the plateau area during charging, and the capacity of the power storage element is equalized. Difficult to do.

  In this specification, the technique of charging / discharging a some electrical storage element is disclosed.

  The charge / discharge system disclosed in the present specification manages the state of a plurality of power storage elements connected in series, and the time change of the voltage of any one power storage element during charging or discharging of the power storage element The deterioration of the power storage element is detected based on a comparison between the time when the rate reaches a reference value and the time when the total voltage of the power storage element or the voltage of any one of the power storage elements reaches a voltage at which charging / discharging is terminated.

  In this charging / discharging system, when the time change rate of the voltage of each storage element reaches a reference value at the time of charging or discharging, and the voltage at which the total voltage of the storage element or the voltage of any one of the storage elements ends charging / discharging. Compare with the point in time. As the deterioration progresses, the latter time becomes faster compared to the former time, so that the degree of deterioration can be determined, and based on this, it is possible to warn of the deterioration of the power storage element or to promote the replacement.

  In addition, at the time of charging or discharging the storage element, when the time change rate of the voltage of any one storage element reaches the reference value and when the change rate of the voltage of the other storage element reaches the reference value It is also possible to provide a charge / discharge system that calculates a capacity difference between the one power storage element and the other power storage element based on the time difference between the first power storage element and the other power storage element. This is because the time difference reflects the difference in SOC between the two power storage elements. In addition, when the charge / discharge current is measured during the time difference, the capacity difference can be calculated by multiplying the time difference by the charge / discharge current.

  When the voltage of a plurality of power storage elements connected in series is measured and provided with a discharge unit that individually discharges the power storage elements, the power storage is performed on the condition that the time change rate of the voltage of the power storage elements has reached a reference value. By discharging the elements, the state of charge between the power storage elements can be equalized.

  In the state management device, the plurality of power storage elements include a first power storage element and a second power storage element, and the discharge control unit is configured so that a time change rate of the first power storage element reaches a reference value. In addition, the first time difference until the time change rate of the second power storage element reaches the reference value may be acquired and the reference time may be included. When the plurality of power storage elements are being charged and the first time difference is greater than or equal to the reference time, the first power storage element is discharged using the first time difference, and the first time difference is If it is acceptable that the first power storage element and the second power storage element are not discharged when the time is less than the reference time, the plurality of power storage elements are being discharged, and the first time difference is equal to or greater than the reference time. The second power storage element is discharged using the first time difference, and the first power storage element and the second power storage element are not discharged when the first time difference is less than the reference time. It is good also as a structure.

  In this state management device, the first power storage element or the second power storage element is discharged when the first time difference is greater than or equal to the reference time. In general, the difference in arrival time indicating the time from when the storage element starts to charge or discharge until it reaches a certain state indicates the difference in capacity of the storage element due to deterioration. According to this state management device, the first power storage element and the second power storage element are discharged by discharging the first power storage element or the second power storage element when the first time difference that is the difference in arrival time is equal to or greater than the reference time. The difference between the capacities charged to and discharged from the storage element can be kept within a certain capacity difference corresponding to the reference time.

  The state management device further includes a deterioration determination unit that determines deterioration of the power storage element, wherein the deterioration determination unit is charging the plurality of power storage elements and is a time of the voltage of the second power storage element. A configuration in which when the charging of the plurality of power storage elements is completed and the charging of the second power storage element is completed before the rate of change reaches the reference value, it is determined that the second power storage element has deteriorated If so, the plurality of power storage elements are being discharged, and the discharge of the plurality of power storage elements is completed before the time change rate of the voltage of the second power storage element reaches the reference value. When the discharge of the second power storage element is completed, the first power storage element may be determined to be deteriorated.

  When charging the power storage element, if charging of the first power storage element is completed before the time rate of change of the voltage of the second power storage element exceeds the reference value, the first power storage element and the second power storage element It can be seen that the difference in capacity from the storage element differs by more than a certain capacity difference corresponding to the reference time. In addition, when the discharge of the first power storage element is completed before the time change rate of the voltage of the second power storage element changes beyond the reference value at the time of discharging the power storage element, the first power storage element It can be seen that the capacity difference from the second power storage element is different by more than a certain capacity difference corresponding to the reference time. According to this state management device, by determining that the first power storage element or the second power storage element has deteriorated in the above case, the capacity of the power storage elements is equalized and the use of the plurality of power storage elements is prohibited. Thus, necessary measures can be taken for the plurality of power storage elements.

  The state management device further includes a deterioration determination unit that determines deterioration of the power storage element, wherein the deterioration determination unit is charging the plurality of power storage elements and is a time of the voltage of the second power storage element. If the elapsed time after the time change rate of the voltage of the first power storage element reaches the reference value before the change rate reaches the reference value reaches a specified time, the second power storage element If it is acceptable to determine that the battery has deteriorated, the plurality of power storage elements are being discharged, and the time change rate of the voltage of the second power storage element reaches the reference value before the first storage element. A configuration may be adopted in which it is determined that the first power storage element has deteriorated when an elapsed time after the time change rate of the voltage of the power storage element reaches the reference value reaches a specified time.

  When the elapsed time after the time change rate of the voltage of the first power storage element reaches the reference value before the time change rate of the voltage of the second power storage element exceeds the reference value has reached the specified time The charging time of the second power storage element is prolonged due to deterioration, or the discharge time of the first power storage element is shortened, and the time change rate of the voltage of the second power storage element does not reach the reference value within the specified time. I understand that. According to this state management device, by determining that the first power storage element or the second power storage element has deteriorated in the above case, the capacity of the power storage elements is equalized and the use of the plurality of power storage elements is prohibited. Thus, necessary measures can be taken for the plurality of power storage elements.

  In the state management device, the discharge control unit may set a discharge time for discharging the first power storage element or the second power storage element using the first time difference. According to this state management device, the first power storage element is obtained using the capacity difference between the capacity charged / discharged in the first secondary battery corresponding to the first time difference and the capacity charged / discharged in the second secondary battery. Alternatively, since the discharge time for discharging the second power storage element is set, the capacities charged and discharged to the first power storage element and the second power storage element can be equalized.

  In the state management device, the timing unit may be configured such that when the voltage of the power storage element reaches a reference voltage and the time change rate of the voltage of the power storage element reaches a reference value, the voltage of the power storage element It is good also as a structure which judges that the time change rate of this reached | attained the reference value. According to this state management device, since discharge is controlled based on the voltage of the storage element in addition to the time change rate of the voltage of the storage element, for example, when the time change rate reaches a reference value multiple times Therefore, a specific one can be selected from the plurality of times, and the capacities charged and discharged by the plurality of power storage elements can be equalized with high accuracy.

  In the above state management device, the power storage element may be configured to be subjected to constant current charging or constant current discharging. According to this state management device, the power storage element is charged / discharged with a constant current, so that the time difference and the capacity difference between the power storage elements can be easily matched, and the capacity charged / discharged to the power storage elements can be easily equalized.

  In the above-described state management device, the charge / discharge rate of the power storage element may be set to 1C or less, and more preferably set to less than 0.9C. When the storage element is charged / discharged at a constant current, the lower the charge / discharge rate, the greater the rate of time change in the voltage of the storage element during charging / discharging. According to this state management device, since the charge / discharge rate is set to be relatively low, it is easy to detect the time change rate of the power storage element and to easily obtain the time difference.

  In the state management device, the negative electrode of the power storage element may be formed of a graphite material. A power storage element in which the negative electrode is formed of a graphite-based material includes a change point where the time change rate of the power storage element is larger than that in other regions. According to this state management device, it is easy to detect the time change rate of the power storage element by using the inflection point, and to easily obtain the time difference.

  In said state management apparatus, each said electrical storage element is good also as an olivine iron-type lithium ion secondary battery. The olivine iron-based lithium ion secondary battery has a plateau region in which the SOC extends from 10% to 90%, and the SOC value of the power storage device is estimated based on the voltage value of the power storage device in the plateau region. It is difficult. In this state management device, since the SOC value of the power storage element is estimated based on the rate of change of the voltage of the power storage element with time, the capacity charged and discharged to the power storage element can be equalized even in the plateau region.

  The state management device disclosed in the present specification is also a state management device that manages the states of a plurality of power storage elements connected in series, and a voltage measurement unit that individually measures the voltage of each power storage element; A discharge unit that discharges each storage element individually, a storage unit that stores discharge times in association with the order in which the time change rate of the voltage of each storage element reaches a reference value, and a discharge that controls the discharge unit A control unit, wherein the discharge control unit discharges the power storage element over the discharge time stored in association with the order in which the time change rate of the voltage of each power storage element reaches the reference value. It is good also as a structure.

  In this state management device, the voltage of each power storage element is measured, and the discharge of each power storage element is controlled using the order in which the time change rate of the voltage reaches the reference value. According to this state management device, even when the power storage element has a plateau region and it is difficult to control the equalization based on the voltage, the discharge is controlled based on the time change rate of the voltage of the power storage element. And the capacity charged and discharged by the power storage elements can be equalized. Moreover, when setting discharge time, discharge time can be set using the discharge time previously memorize | stored in the memory | storage part, and discharge time can be set early.

  The state management device disclosed in the present specification is also a state management device that manages the states of a plurality of power storage elements connected in series, and a voltage measurement unit that individually measures the voltage of each power storage element; A discharge unit that individually discharges each storage element; and a discharge control unit that controls the discharge unit, the discharge control unit, when the rate of time change of the voltage of each storage element reaches a reference value, It may be configured to start discharging the power storage element.

  In this state management device, the voltage of each power storage element is measured, and when the time change rate of the voltage reaches a reference value, the power storage element is discharged. According to this state management device, even when the power storage element has a plateau region and it is difficult to control the equalization based on the voltage, the discharge is controlled based on the time change rate of the voltage of the power storage element. And the capacity charged and discharged by the power storage elements can be equalized. In addition, since the discharge of the power storage element is started when the time change rate of the voltage of the power storage element reaches the reference value, the discharge start timing of the power storage element can be advanced.

  The present invention is also embodied in a storage element equalization method realized by using the state management device. The method for equalizing power storage elements disclosed in this specification is a method for equalizing power storage elements that equalizes the states of a plurality of power storage elements connected in series. And the time difference from when the time change rate of the voltage of any one storage element reaches the reference value until the time change rate of the voltage of the other storage element reaches the reference value is measured. And a discharging step of individually discharging each power storage device using the time difference.

  Further, the storage element equalization method disclosed in this specification is a storage element equalization method for equalizing the states of a plurality of storage elements connected in series, and the voltage of each storage element during charge / discharge Voltage measurement step for individually measuring each of the storage elements, and a discharge step for discharging each of the storage elements individually. In the discharge process, the time change rate of the voltage of each of the storage elements reaches the reference value. It is good also as a structure which discharges the said electrical storage element over the discharge time preset in association.

  Further, the storage element equalization method disclosed in this specification is a storage element equalization method for equalizing the states of a plurality of storage elements connected in series, and the voltage of each storage element during charge / discharge A voltage measuring step for individually measuring each of the storage elements, and a discharging step for discharging each of the storage elements individually. In the discharging step, when the time change rate of the voltage of each of the storage elements reaches the reference value, It may be configured to start discharging the power storage element.

  According to the present invention, it is possible to appropriately manage the states of a plurality of power storage elements.

Charge system (discharge system) block diagram Schematic diagram of discharge circuit The flowchart which shows the equalization process of 1st Embodiment. The figure which shows the charging / discharging characteristic of a secondary battery The figure which shows the charging / discharging characteristic of a secondary battery The figure which shows the charging / discharging characteristic of a secondary battery The flowchart which shows the equalization process of 2nd Embodiment. The flowchart which shows the equalization process of 3rd Embodiment. The flowchart which shows the equalization process of 4th Embodiment The flowchart which shows the equalization process of other embodiment

<Embodiment 1>
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 6.

1. Configuration of State Determination Device FIG. 1 is a diagram illustrating a configuration of a charging system (discharge system) 10 according to the present embodiment. The charging system (discharge system) 10 includes a battery group 12, a state management device (hereinafter referred to as BMS) 20, and a charger (load) 18. The battery group 12 is mounted on an electric vehicle,
It includes a plurality of secondary batteries 50 (an example of a power storage element) connected in series inside. The battery group 12 is charged with a constant current by being connected to a charger 18 provided inside or outside the electric vehicle or the like, and connected to a load 18 such as a power source provided inside the electric vehicle or the like. Is discharged at a constant current. The BMS 20 monitors the voltage value V and current value I of each secondary battery 50 of the battery group 12 being charged, manages the remaining capacity (SOC) indicating the charge / discharge state of the secondary battery 50, and equalizes the SOC. Turn into.

  In the present embodiment, an example in which an olivine iron-based lithium ion secondary battery (hereinafter referred to as an olivine iron-based battery) is used as the secondary battery 50 will be described. The secondary battery 50 is a kind of lithium ion battery, in which olivine-type iron phosphate is used for the positive electrode and graphite-based material is used for the negative electrode. As shown in FIG. 4, the secondary battery 50 is a battery with respect to an increase in SOC in an initial charge stage (an end stage of discharge) in which the SOC is less than 10% and an end stage of charge (an initial stage of discharge) in which the SOC is 90% or more. It has a region where the voltage rises rapidly. In addition, there is a region where the battery voltage is substantially constant (hereinafter referred to as a plateau region) with respect to an increase in the SOC in the middle of charging (the middle discharging) where the SOC is 10% or more and less than 90%.

  The BMS 20 includes a central processing unit (hereinafter referred to as CPU) 30, an analog-digital converter (hereinafter referred to as ADC) 34, an ammeter 22, a voltmeter (an example of a voltage measuring unit) 24, a discharge circuit (an example of a discharge unit) 26, A thermometer 28 is included.

  The CPU 30 includes a memory (an example of a storage unit) 32 such as a ROM or a RAM, and the memory 32 stores various programs for controlling the operation of each component of the BMS 20. The CPU 30 functions as a timer unit 42, an equalization control unit 44, a deterioration determination unit 46, and the like according to the program read from the memory 32, and controls each unit in the BMS 20 including the discharge circuit 26.

  The thermometer 28 measures the temperature of the battery group 12 by a contact method or a non-contact method, and stores the measured temperature in the memory 32. As shown in FIG. 2, the voltmeter 24 is directly connected to both ends of each secondary battery 50 via a wiring 54, and the voltage value V of the secondary battery 50 being charged / discharged is individually set for each predetermined period. taking measurement. The battery group 12 includes N (N: 2 or more) secondary batteries 50A, 50B,... 50N, and the voltmeter 24 includes voltages VA, VB,. Each voltage value of VN is measured. The voltmeter 24 transmits these measured voltage values V to the ADC 34.

  The wiring 54 that connects the secondary battery 50 and the voltmeter 24 is provided with a discharge circuit 26 that discharges the secondary battery 50 individually. As shown in FIG. 2, the discharge circuit 26 includes discharge circuits 26A, 26B,... 26N for discharging each secondary battery 50 between wirings 54 connected to both ends of each secondary battery 50. Is provided. Each discharge circuit 26 includes a resistor R and a switch Q. The switch Q of the discharge circuit 26 is controlled to open and close by the CPU 30 functioning as an equalization control unit 44 that is a discharge control unit that controls the discharge of the secondary battery 50, and when the switch Q is closed by the CPU 30. Then, current flows from the secondary battery 50 through the wiring 54 and the resistor R, and the corresponding secondary battery 50 is discharged. Further, when the switch Q is opened by the CPU 30, the discharge from the corresponding secondary battery 50 is stopped.

  The ammeter 22 measures the current flowing through the wiring 52 that connects the battery group 12 and the charger 18, and measures the current value of the charge / discharge current ZI that flows in common to the secondary battery 50. Further, the ammeter 22 measures current values IA, IB,... IN of currents (hereinafter referred to as equalized discharge currents) HI discharged individually from the respective secondary batteries 50 via the wiring 54. The ammeter 22 transmits these measured current values I to the ADC 34.

  The ADC 34 is connected to the ammeter 22, the voltmeter 24, and the CPU 30. The ADC 34 converts the current value I and the voltage value V, which are analog data transmitted from the ammeter 22 and the voltmeter 24, into digital data. The current value I and the voltage value V are stored in the memory 32. The CPU 30 functioning as the time measuring unit 42, the deterioration determining unit 46, and the like executes equalization processing described later using the current value I and the voltage value V stored in the memory 32.

2. Equalization process The equalization process performed in BMS20 when charging the battery group 12 is demonstrated using FIG. 3 or FIG. In this embodiment, the battery group 12 is charged with a constant current by a low-speed charge of 0.5 C. The equalization process is executed in association with the charging control process for the battery group 12. FIG. 3 shows a flowchart of a charging control process for the battery group 12 executed by the CPU 30.

  When the battery group 12 is connected to the charger 18 by the user and power supply from the charger 18 to the battery group 12 is started, the CPU 30 executes the charge control process and the equalization process. When the equalization process is started, the CPU 30 repeatedly measures the voltage value V of each secondary battery 50 every predetermined time ΔX, and calculates the absolute value of the difference value ΔV of the continuously measured voltage value V for the predetermined time ΔX. The time change rate DV of the voltage value V divided by is calculated. The CPU 30 detects that the calculated time change rate DV reaches the reference value K (K> 0) (S2: NO).

  As described above, in the plateau region, since the voltage value V of the secondary battery 50 is substantially constant with respect to the increase in SOC, it is detected that the voltage value V of the secondary battery 50 has reached the reference voltage value. However, the SOC of the secondary battery 50 cannot be estimated with high accuracy.

  In this embodiment, as shown in FIG. 5, in the plateau region of the olivine iron-based battery using a graphite-based material for the negative electrode, the time change rate of the voltage value V of the secondary battery 50 during charging is higher than that in other regions. We noticed that there are changing points. In a battery using a graphite-based material for the negative electrode, there is a change point at which the rate of change with time changes greatly compared to other ranges. In the olivine iron-based battery using a graphite-based material for the negative electrode, attention is paid to the change point located in the plateau region. That is, in the olivine iron-based battery, there are two change points (KS1, KS2) where the rate of change with time exceeds the reference value K in the plateau region. In the following description, a case will be described in which the change point KS2 having the larger voltage value corresponding to the change point is reached among the change points KS1 and KS2. That is, the CPU 30 detects that the voltage value V rises to a voltage value (an example of a reference voltage) KV2 corresponding to the change point KS2, and the time change rate DV reaches the reference value K. A similar process may be performed when the change point KS1 is reached.

  When detecting that the time change rate DV of any one of the secondary batteries 50 has reached the reference value K (S2: YES), the CPU 30 starts measuring the time since the arrival (S4). The CPU 30 functioning as the time measuring unit 42 is from the time change rate DV of one secondary battery 50 reaching the reference value K to the time change rate DV of the other secondary battery 50 reaching the reference value K. The elapsed time (an example of a time difference) ΔT is counted, and the elapsed time ΔT is compared with the reference time KT stored in the memory 32 (S6).

  In the following description, for the sake of understanding, the secondary battery 50 whose time change rate DV has reached the reference value K earliest is the first secondary battery 50, and one of the other secondary batteries 50 is the second secondary battery. The equalization process in the first secondary battery 50 and the second secondary battery 50 will be described as the battery 50. That is, in the first secondary battery 50, the voltage value V rises to the change point KS2 earliest among the plurality of secondary batteries 50 (that is, SOC is large), and the second secondary battery 50 Is assumed that the voltage value V rises to the latest change point KS2 among the plurality of secondary batteries 50 (that is, the SOC is small).

  As shown in FIG. 6, the time change rate of the first secondary battery 50 is a time change rate DV1, the time change rate of the second secondary battery 50 is a time change rate DV2, and the time change rate DV1 is a reference value. The elapsed time from reaching K to the time change rate DV2 reaching the reference value K is defined as elapsed time (an example of a first time difference) ΔT1. In the following description, the first secondary battery 50 is applied to each of the secondary batteries 50 other than the second secondary battery 50, so that all the secondary batteries 50 existing in a plurality will be described. be able to.

  When the time change rate DV2 reaches the reference value K before the reference time KT elapses and the elapsed time ΔT1 becomes less than the reference time KT (S6: NO), the CPU 30 determines that the first secondary battery 50 and the second The secondary battery 50 is determined to be charged evenly. In this case, the CPU 30 ends the equalization process without discharging any secondary battery 50.

  On the other hand, when the time change rate DV2 does not reach the reference value K before the reference time KT elapses, and the elapsed time ΔT1 becomes equal to or greater than the reference time KT (S6: YES), the time change rate DV2 is the reference. It is monitored that the value K has been reached and the total voltage, which is the sum of the voltage values V of the secondary battery 50, has increased to reach the charge end voltage (S8, S10).

  When the time change rate DV2 reaches the reference value K before the total voltage reaches the end-of-charge voltage and the elapsed time ΔT1 is timed (S8: YES, S10: NO), the CPU 30 determines the first secondary battery. 50 and the second secondary battery 50 are determined to be charged unevenly. The CPU 30 sets a discharge time HT for discharging the first secondary battery 50 in order to equalize the SOCs of the first secondary battery 50 and the second secondary battery 50. The discharge time HT can also be referred to as a homogenization control time for making the SOCs of the first secondary battery 50 and the second secondary battery 50 uniform.

  The memory 32 of the CPU 30 stores in advance a correspondence table in which the elapsed time ΔT1 is associated with the discharge time HT. The CPU 30 functioning as the equalization control unit 44 sets the discharge time HT based on the elapsed time ΔT1 and the correspondence table (S12). After setting the discharge time HT, the CPU 30 starts discharging the first secondary battery 50 (S14). Specifically, the CPU 30 closes the switch Q of the discharge circuit 26 corresponding to the first secondary battery 50, and measures an elapsed time ΔT2 since the switch Q is closed (S16). The CPU 30 discharges the first secondary battery 50 until the elapsed time ΔT2 reaches the discharge time HT (S16: NO). When the elapsed time ΔT2 reaches the discharge time HT (S16: YES), the first time is reached. The discharge of the secondary battery 50 is finished (S18), and the equalization process is finished.

  On the other hand, when the total voltage reaches the end-of-charge voltage before the time change rate DV2 reaches the reference value K (S8: NO, S10: YES), the CPU 30 functioning as the deterioration determination unit 46 performs the first secondary operation. It is detected that the deterioration of the second secondary battery 50 is progressing as compared with the battery 50, and it is determined that the battery group 12 has a lifetime (S20). The CPU 30 notifies the user that the battery group 12 has deteriorated and the battery group 12 needs to be replaced via a display unit such as a display, and ends the equalization process.

3. Effects of this embodiment (1) In the BMS 20 of this embodiment, the BMS 20 measures the voltage value V of the secondary battery 50 being charged, and the time change rate DV calculated from the voltage value V reaches the reference value K. The equalization of the secondary batteries 50 is controlled using the elapsed time ΔT1 that is the time difference. According to this BMS 20, even in a plateau region where it is difficult to perform equalization control of the secondary battery 50 based on the voltage value V, it is possible to equalize and charge the SOC of the plurality of secondary batteries 50 being charged.

  In particular, in this embodiment, an olivine iron-based lithium ion secondary battery is used as the secondary battery 50, and has a plateau region in which the SOC extends in the range of 10% to less than 90%. On the other hand, in the olivine iron-based lithium ion secondary battery, the battery voltage rapidly rises with respect to the increase in SOC at the end of charging when the SOC is 90% or more. Therefore, even when trying to equalize the plurality of secondary batteries 50 using the voltage value V of the secondary battery 50 at the end of charging, the SOC reaches almost 100% due to a slight increase in the SOC, and the plurality of 2 The equalization process of the secondary battery 50 cannot be completed. Therefore, it is desirable to equalize the plurality of secondary batteries 50 using a plateau region that exists in a range where the SOC is lower than the end of charging.

In this BMS 20, the discharge of the secondary battery 50 is controlled using the time change rate DV. Furthermore, in the present embodiment, an olivine iron-based lithium ion secondary battery using a graphite-based material for the negative electrode is used as the secondary battery 50, and the change point at which the rate of time change exceeds the reference value K in the plateau region. KS1 and KS2 exist. Therefore, the SOC of the secondary battery 50 can be estimated from the time change rate DV using the change points KS1 and KS2, and the SOC of the plurality of secondary batteries 50 is equalized once using the plateau region. The secondary battery 50 can be charged by completing the conversion process.
(2) In the BMS 20 of this embodiment, when the elapsed time ΔT1 that is the time difference between the first secondary battery 50 and the second secondary battery 50 is equal to or greater than the reference time KT, the BMS 20 The secondary battery 50 is discharged. In general, the elapsed time ΔT <b> 1 indicates the difference in SOC of these secondary batteries 50. According to this BMS 20, the first secondary battery 50 and the second secondary battery 50 when charging the battery group 12 are discharged by discharging the first secondary battery 50 when the elapsed time ΔT1 is equal to or longer than the reference time KT. The difference in SOC with the secondary battery 50 can be kept within a certain capacity difference corresponding to the reference time KT.
(3) In the BMS 20 of the present embodiment, the first secondary battery 50 using the elapsed time ΔT1, that is, the time difference corresponding to the difference between the SOC of the first secondary battery 50 and the SOC of the second secondary battery 50. Since the discharge time HT for equalizing is set, the discharge time HT can be set with high accuracy, and the SOC charged in the first secondary battery 50 and the second secondary battery 50 can be equalized. it can.
(4) In the BMS 20 of the present embodiment, the elapsed time ΔT1, that is, the time change rate DV2 of the second secondary battery 50 after the time change rate DV1 of the first secondary battery 50 reaches the reference value K is the reference. When the time until the value K is reached is equal to or longer than the reference time KT, it is determined that these secondary batteries 50 are charged unevenly. In the BMS 20, by discharging the first secondary battery 50 in the above case, when charging the battery group 12, the secondary batteries 50 included in the battery group 12 can be equalized and charged. it can.
(5) In the BMS 20 of this embodiment, before the time change rate DV2 of the second secondary battery 50 reaches the reference value K, the total voltage of the plurality of secondary batteries 50 reaches the charge end voltage and is charged. When is completed, it is determined that the second secondary battery 50 has deteriorated and the SOCs of the first secondary battery 50 and the second secondary battery 50 cannot be equalized. In this BMS 20, it is determined that the second secondary battery 50 has deteriorated in the above-described case, thereby suppressing the use of the battery group 12 including the secondary batteries 50 that cannot be equalized due to deterioration. can do.
(6) In the BMS 20 of the present embodiment, when detecting whether or not the secondary battery 50 being charged / discharged has reached the change point, it is detected that the time change rate DV has reached the reference value K, It is confirmed whether the voltage value V has increased to the voltage value KV2. Therefore, for example, when the second secondary battery 50 reaches the change point KS1 after the first secondary battery 50 reaches the change point KS2, the time difference between them is measured, so that the different change point is reached. The measured time difference is measured, and the secondary battery 50 can be prevented from being equalized inaccurately.
(7) In the BMS 20 of the present embodiment, the battery group 12 is charged at a constant current by 0.5C charge, so it is larger than 1C charge, and further compared to a case where it is charged at a relatively high speed of 0.9C charge or more. A large time change rate can be generated. In the secondary battery 50, the time change rate DV generated due to deterioration decreases, and it becomes difficult to detect whether the time change rate DV has reached the reference value K or not. In this BMS 20, since the secondary battery 50 is charged at a relatively low speed, it is easy to detect whether or not the time change rate DV has reached the reference value K even when the secondary battery 50 is deteriorated.
<Embodiment 2>
A second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the contents described using the charging system 10 in the first embodiment will be described using the discharging system 10. That is, the equalization process performed accompanying the discharge control process using the discharge system 10 is demonstrated.

  In the present embodiment, the battery group 12 is discharged at a constant current. Further, in the present embodiment, a case will be described in which the voltage value corresponding to the change point among the change points KS1 and KS2 existing in the plateau region reaches the change point KS1 on the smaller side. That is, the CPU 30 detects that the voltage value V drops to the voltage value KV1 corresponding to the change point KS1 and the time change rate DV reaches the reference value K. Also in this embodiment, the secondary battery 50 whose time change rate DV has reached the reference value K earliest is the first secondary battery 50, and the secondary battery 50 whose time change rate DV has reached the reference value K is the latest. 50 is a second secondary battery 50. In other words, the first secondary battery 50 is assumed to have the voltage value V that drops the earliest among the plurality of secondary batteries 50 (that is, the SOC is small), and the second secondary battery 50 includes the plurality of 2 It is assumed that the voltage value V decreases most slowly in the secondary battery 50 (that is, SOC is large). In the following description, the same description as that of the first embodiment will not be repeated.

1. Equalization Process FIG. 7 shows a flowchart of the equalization process of the present embodiment executed by the CPU 30.

  The CPU 30 functioning as the time measuring unit 42 monitors the time rate of change DV2 of the second secondary battery 50 reaching the reference value K and decreases the total voltage that is the sum of the voltage values V of the secondary battery 50. Then, it is monitored that the discharge end voltage is reached (S8, S22). When the time change rate DV2 reaches the reference value K and the elapsed time ΔT1 is measured before the total voltage reaches the discharge end voltage, the CPU 30 functioning as the equalization control unit 44 (S8: YES, S22: NO). ), It is determined that the first secondary battery 50 and the second secondary battery 50 are discharged unevenly. The CPU 30 sets a discharge time HT for discharging the second secondary battery 50 in order to equalize the SOC of the first secondary battery 50 and the second secondary battery 50 (S12), and the discharge time The second secondary battery 50 is discharged over HT (S24, S16, S26).

  On the other hand, when the total voltage reaches the discharge end voltage before the time change rate DV2 reaches the reference value K (S8: NO, S22: YES), the CPU 30 functioning as the deterioration determination unit 46 performs the second secondary operation. It is detected that the deterioration of the first secondary battery 50 is progressing compared to the battery 50, and it is determined that the battery group 12 has a lifetime (S28). The CPU 30 notifies the user that the battery group 12 has deteriorated and the battery group 12 needs to be replaced via a display unit such as a display, and ends the equalization process.

2. Advantages of the present embodiment (1) In the BMS 20 of the present embodiment, the BMS 20 detects the time change rate DV of the secondary battery 50 being discharged, and uses the elapsed time ΔT1 calculated from the time change rate DV to perform the secondary operation. The equalization of the batteries 50 is controlled. According to the BMS 20, even in the plateau region, the SOC of the plurality of secondary batteries 50 being discharged can be equalized and discharged.
(2) In the present embodiment, an olivine iron-based lithium ion secondary battery is used as the secondary battery 50, and has a plateau region in which the SOC extends in the range of 10% to less than 90%. On the other hand, in the olivine iron-based lithium ion secondary battery, the battery voltage rapidly decreases with respect to the decrease in SOC at the end of discharge when the SOC is less than 10%. Therefore, even when trying to equalize the plurality of secondary batteries 50 using the voltage value V of the secondary battery 50 at the end of discharge, the SOC reaches almost 0% due to a slight decrease in the SOC, and the plurality of 2 The equalization process of the secondary battery 50 cannot be completed. Therefore, it is desirable to equalize the plurality of secondary batteries 50 using a plateau region that exists in a range where the SOC is greater than the end of discharge.

In this BMS 20, the discharge of the secondary battery 50 is controlled using not the voltage value V of the secondary battery 50 but the time change rate DV. Therefore, using the plateau region, the SOC equalization of the plurality of secondary batteries 50 can be completed in one equalization process, and the secondary battery 50 can be discharged.
(3) In the BMS 20 of the present embodiment, the first secondary battery 50 when discharging the battery group 12 by discharging the second secondary battery 50 when the elapsed time ΔT1 is equal to or longer than the reference time KT. And the second secondary battery 50 can be kept within a certain capacity difference corresponding to the reference time KT.
(4) In the BMS 20 of this embodiment, when the elapsed time ΔT1 is equal to or longer than the reference time KT, it is determined that the first secondary battery 50 and the second secondary battery 50 are discharged unevenly. By discharging the second secondary battery 50, when the battery group 12 is discharged, the secondary batteries 50 included in the battery group 12 can be equalized and discharged.
(5) In the BMS 20 of this embodiment, before the time change rate DV2 of the second secondary battery 50 reaches the reference value K, the total voltage of the plurality of secondary batteries 50 reaches the discharge end voltage and discharges. If the first secondary battery 50 is judged to have deteriorated when the battery is terminated, the battery group 12 including the secondary batteries 50 that cannot be equalized due to deterioration is prevented from being used. Can do.
<Embodiment 3>
A third embodiment of the present invention will be described with reference to FIG. The charging system 10 of the present embodiment is different from the charging system 10 of the first embodiment in that the discharge time HT is set during the equalization process in that the discharge time HT is set based on the discharge time HT stored in the memory 32 in advance. Different. In the following description, the same description as that of the first embodiment will not be repeated.

1. Equalization Processing FIG. 8 shows a flowchart of the equalization processing of this embodiment executed by the CPU 30.

  When the CPU 30 functioning as the time measuring unit 42 detects that the time change rate DV1 of the first secondary battery 50 has reached the reference value K (S2: YES), the CPU 30 starts measuring the time since the arrival. Together with (S4), discharging of the first secondary battery 50 is started (S14). Further, the CPU 30 detects the order of the secondary batteries 50 at which the time change rate DV has reached the reference value K for all the secondary batteries 50 including the first and second secondary batteries 50, and stores the memory. 32 is temporarily stored.

  Next, the CPU 30 functioning as the equalization control unit 44 sets the discharge time HT of each secondary battery 50 (S32). As shown by a dotted line in FIG. 1, the memory 32 of the CPU 30 stores the discharge time HT in association with the rank of the secondary battery 50 at which the time change rate DV has reached the reference value K, and the secondary battery. The discharge time HT is set to increase as the rank of 50 increases. The CPU 30 sets the discharge time HT stored in the memory 32 corresponding to the rank of each secondary battery 50 as the discharge time HT of each secondary battery 50, and the first discharge time HT is set over the set discharge time HT. The secondary battery 50 is discharged (S34, S18), and the equalization process ends.

  In the charging system 10, the battery group 12 is repeatedly charged a plurality of times, and the CPU 30 repeats the charge control process and the equalization process each time the battery group 12 is charged. When repeating the equalization process, the CPU 30 repeats the equalization process using the discharge time HT stored in the memory 32.

2. Effects of the present embodiment (1) In the BMS 20 of the present embodiment, when the time change rate DV of the first secondary battery 50 reaches the reference value K during charging, the discharge of the first secondary battery 50 is started. . Therefore, the discharge of the first secondary battery 50 can be started before the time rate of change DV of the other secondary battery 50 reaches the reference value K, and in the equalization process when charging the battery group 12 The discharge start time of the first secondary battery 50 can be advanced.
(2) In the BMS 20 of the present embodiment, the discharge time HT of each secondary battery 50 is set from the order in which the time change rate DV reaches the reference value K during charging and the discharge time HT stored in the memory 32 in advance. Therefore, the discharge time HT of each secondary battery 50 can be set easily and early.
<Embodiment 4>
Embodiment 4 of the present invention will be described with reference to FIG. In the present embodiment, the contents described using the charging system 10 in the third embodiment will be described using the discharging system 10. That is, the equalization process performed accompanying the discharge control process using the discharge system 10 is demonstrated.

  In the present embodiment, a case where the change point KS1 is reached will be described. Also in this embodiment, the secondary battery 50 whose voltage change rate DV has reached the reference value K earliest is the first secondary battery 50, and the secondary battery 50 whose voltage change rate DV has reached the reference value K is the latest. 50 is a second secondary battery 50. In the following description, duplicate descriptions are omitted for the same contents as in the first and third embodiments.

1. Equalization Processing FIG. 9 shows a flowchart of the equalization processing of the present embodiment executed by the CPU 30.

  When detecting that the time change rate DV1 of the second secondary battery 50 has reached the reference value K (S42: YES), the CPU 30 functioning as the time measuring unit 42 starts measuring the time since the arrival. Together with (S4), discharging of the second secondary battery 50 is started (S24). Next, the CPU 30 functioning as the equalization control unit 44 sets the discharge time HT stored in the memory 32 corresponding to the rank of each secondary battery 50 as the discharge time HT of each secondary battery 50 (S32). ), The second secondary battery 50 is discharged over the set discharge time HT (S34, S26), and the equalization process is terminated. The discharge time HT is stored in the memory 32 of the CPU 30 in association with the rank of the secondary battery 50 at which the time change rate DV has reached the reference value K. As the rank of the secondary battery 50 decreases, the discharge time HT The HT is set to be long.

2. Effects of this Embodiment In the BMS 20 of this embodiment, the discharge start timing of each secondary battery 50 can be advanced during discharge, and the second secondary battery 50 is equalized in the equalization process when the battery group 12 is discharged. The discharge start time can be advanced.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and the drawings, and for example, the following various aspects are also included in the technical scope of the present invention.
(1) In the above embodiment, the charging system (discharging system) 10 has one BMS 20, and the functions of the time measuring unit 42, the equalization control unit 44, the deterioration determining unit 46, etc. are executed by one CPU 30 having the BMS 20. Although shown using an example, the present invention is not limited to this. For example, if each unit may be configured by different CPUs, BMSs, etc., these units may be configured using independent devices.
(2) Although the above embodiment has been described using an example in which an olivine iron-based battery using a graphite-based material for the negative electrode is used as the secondary battery 50, the present invention is not limited thereto. For example, it can be used in other batteries using a graphite-based material for the negative electrode, and can also be used in batteries that do not have a plateau region. In this case, the reference value K is appropriately set based on the charge / discharge characteristics of each battery.
(3) In the above embodiment, the secondary battery 50 has been described using an example in which the secondary battery 50 is charged with constant current (constant current discharge). However, the charging method (discharge method) of the secondary battery 50 is not limited thereto. . For example, the secondary battery 50 may be charged with a constant voltage (constant voltage discharge) or may be charged with a constant power (constant power discharge).
(4) In the above embodiment, the example in which the charging system (discharge system) 10 performs the equalization process on the battery group 12 mounted on the electric vehicle has been described. It is not limited to the embodiment.
(5) In the above embodiment, when measuring the elapsed time ΔT, the time measurement starts after the time change rate DV of the voltage value V of any one secondary battery 50 reaches the reference value K. However, the time may be measured from the start of the charge control process (discharge control process). That is, the CPU 30 functioning as the time measuring unit 42 measures the time from the start of the charge control process (discharge control process) until the time change rate DV of the voltage value V of each secondary battery 50 reaches the reference value K. The arrival time may be measured, and the elapsed time ΔT may be measured as a difference between the arrival times.
(6) In the first embodiment, the description has been given by using the example of starting the discharge of the first secondary battery 50 after setting the discharge time HT. For example, as shown in FIG. Discharging may be started before setting, and discharging time HT may be set after starting discharging.

  FIG. 10 shows a flowchart of equalization processing of another embodiment.

  When detecting that the time change rate DV1 of the first secondary battery 50 has reached the reference value K (S2: YES), the CPU 30 starts measuring the time since the arrival (S4). The secondary battery 50 starts to be discharged (S14).

  Next, the CPU 30 monitors that the time change rate DV2 of the second secondary battery 50 reaches the reference value K, and the total voltage, which is the sum of the voltage values V of the secondary battery 50, is increased and charged. The arrival of the end voltage is monitored (S8, S10). When the time change rate DV2 reaches the reference value K before the total voltage reaches the end-of-charge voltage and the elapsed time ΔT1 is timed (S8: YES, S10: NO), the CPU 30 determines the first secondary battery. A discharge time HT for discharging 50 is set (S12). Then, the first secondary battery 50 is discharged over the set discharge time HT (S16, S18), and the equalization process is terminated.

On the other hand, when the total voltage reaches the charge end voltage before the time change rate DV2 reaches the reference value K (S8: NO, S10: YES), the CPU 30 stops discharging the first secondary battery 50. Along with (S42), it is detected that the deterioration of the second secondary battery 50 has progressed compared to the first secondary battery 50, and it is determined that the battery group 12 has a life (S20). The CPU 30 notifies the user that the battery group 12 has deteriorated and the battery group 12 needs to be replaced via a display unit such as a display, and ends the equalization process.
(7) In the first and second embodiments described above, an example in which the life determination of the battery group 12 is performed when the total voltage of the plurality of secondary batteries 50 reaches the charge end voltage (discharge end voltage) will be described. However, the end-of-life voltage of the battery group 12 may be determined when a termination voltage is set for each secondary battery 50 and any one of the secondary batteries 50 reaches the termination voltage. That is, after the time change rate DV1 of the first secondary battery 50 reaches the reference value K, the first secondary battery 50 before the time change rate DV2 of the second secondary battery 50 reaches the reference value K. When the voltage value V of 50 reaches the charge upper limit voltage (end-of-discharge voltage), the life of the battery group 12 may be determined.
(8) In the first and second embodiments, the elapsed time ΔT is measured and the discharge time HT is set from the correspondence table stored in the memory 32 with the elapsed time ΔT. It is not limited to this. For example, the charging / discharging current ZI to the battery group 12 is measured, the charging / discharging current ZI is multiplied by the elapsed time ΔT to calculate the capacity difference ΔY, and the capacity difference ΔY is closed with the switch Q of the discharging circuit 26 closed. The discharge time HT may be obtained by dividing by the equalization control current HI that flows in the state. Furthermore, it is possible to discharge only the discharge time HT determined by a predetermined elapsed time ΔT.
Discharge time HT = capacity difference ΔY / equalization control current HI

10: Charging system (discharge system), 12: Battery group, 20: BMS, 22: Ammeter, 24: Voltmeter, 26: Discharge circuit, 30: CPU, 42: Timekeeping unit, 44: Equalization control unit, 46 : Degradation judgment unit, 50: Secondary battery, DV: Time change rate, HT: Discharge time, KT: Reference time, K: Reference value, ΔT: Elapsed time

Claims (10)

A charge / discharge system for controlling charge / discharge of a plurality of power storage elements connected in series,
At the time of charging or discharging the storage element, when the time rate of change of the voltage of any one storage element reaches a reference value, the total voltage of the storage element or the voltage of any storage element is charged / discharged. A charge / discharge system that detects deterioration of the power storage element based on a comparison with a point in time at which a voltage to be terminated is reached. A charge / discharge system for controlling charge / discharge of a plurality of power storage elements connected in series,
At the time of charging or discharging the storage element, when the time change rate of the voltage of any one of the storage elements reaches a reference value, and when the change rate of the voltage of the other storage element reaches a reference value The charge / discharge system which calculates the capacity | capacitance difference of said one electrical storage element and said other electrical storage element based on the time difference of. A charging / discharging system that controls charging / discharging of a plurality of power storage elements connected in series, a voltage measuring unit that measures a voltage of the power storage element, a discharge unit that individually discharges the power storage element, and the discharge unit A discharge control unit for controlling
The discharge control unit is a charge / discharge system that starts discharging of the power storage element on condition that the time change rate of the voltage of the power storage element reaches a reference value. The charge / discharge system according to any one of claims 1 to 3,
The charging / discharging rate of the said electrical storage element is a charging / discharging system set to 1 C or less. The charge / discharge system according to any one of claims 1 to 3,
The charge / discharge rate of the said electrical storage element is a charge / discharge system set to less than 0.9C.   6. The charge / discharge system according to claim 1, wherein a negative electrode of the power storage element is formed of a graphite-based material.   It is a charging / discharging system as described in any one of Claims 1 thru | or 6, Comprising: The said electrical storage element is a charging / discharging system which is an olivine iron-type lithium ion secondary battery. A method for diagnosing deterioration of a plurality of power storage elements connected in series,
At the time of charging or discharging the storage element, when the time rate of change of the voltage of any one storage element reaches a reference value, the total voltage of the storage element or the voltage of any storage element is charged / discharged. A method for diagnosing deterioration of a storage element, wherein the deterioration of the storage element is diagnosed based on a comparison with a point in time when a voltage to be terminated is reached. A method for calculating a capacity difference between a plurality of power storage elements connected in series,
At the time of charging or discharging the storage element, when the time change rate of the voltage of any one of the storage elements reaches a reference value, and when the change rate of the voltage of the other storage element reaches a reference value A method for calculating a capacity difference between power storage elements, wherein a capacity difference between the one power storage element and the other power storage element is calculated on the basis of the time difference.   A charge / discharge control method for controlling charging / discharging of a plurality of power storage elements connected in series, wherein the voltage of the power storage element is measured, and when the time change rate of the voltage of the power storage element reaches a reference value, A charge / discharge control method for discharging individual storage elements.

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