JP7652129B2 - Battery System - Google Patents

Description

This disclosure relates to a battery system, and in particular to a battery system equipped with a battery pack.

In JP 2020-119820 A (Patent Document 1), in an assembled battery in which multiple stacked cells (single cells) are restrained by restraining members, the degree of deterioration, temperature, and SOC (State Of Charge) of the assembled battery are used to estimate the restraining load of the restraining members, thereby determining fatigue failure of the restraining members.

JP 2020-119820 A

In this patent document 1, fatigue failure of the restraining member is diagnosed by estimating the restraining load of the restraining member. The restraining load is estimated using the degree of deterioration, temperature, and SOC estimated from the capacity maintenance rate. Therefore, in order to accurately estimate the restraining load, it is necessary to calculate the capacity maintenance rate with high accuracy.

To obtain a highly accurate capacity maintenance rate, it is preferable to perform charge/discharge control suitable for calculating the capacity maintenance rate (hereinafter, also referred to as diagnosis mode charge/discharge control). However, diagnosis mode charge/discharge control is different from charge/discharge control when the battery pack is in use. For this reason, frequently performing diagnosis mode charge/discharge control results in a waste of power and time.

The objective of this disclosure is to improve diagnostic accuracy while reducing diagnostic labor by diagnosing the battery pack at appropriate times in a battery system equipped with a battery pack.

The battery system disclosed herein includes a battery pack in which a plurality of stacked single cells are restrained by restraining members, and a control device that controls the battery pack. The control device includes a restraining load estimation unit that estimates the restraining load caused by the restraining members, and a diagnosis mode processing unit that performs diagnosis of the battery pack when the restraining load estimated by the restraining load estimation unit is equal to or greater than a predetermined value.

When a single cell is used for a long period of time, the electrodes expand and gas is generated within the battery, causing the cell to expand. Furthermore, when the SOC of a single cell is high, the electrodes expand, causing the cell to expand. When a single cell expands, the restraining load of the restraining members increases, and the mechanical load (load, pressure, stress, etc.) applied to the restraining members and the single cell is large, creating a harsh environment, which is likely to cause various malfunctions in the battery pack.

According to this configuration, when the restraint load estimated by the restraint load estimation unit of the control device is equal to or greater than a predetermined value, the diagnosis mode processing unit of the control device executes diagnosis of the battery pack. Therefore, because the battery pack diagnosis is executed when the restraint load of the restraining member is large and there is a high possibility that various malfunctions of the battery pack will occur, diagnosis of the battery pack is performed at an appropriate time, and labor saving of diagnosis is achieved. In addition, because diagnosis of the battery pack is performed in a harsh environment, improvement of diagnostic accuracy can be expected.

Preferably, the diagnosis performed by the diagnosis mode processing unit is a diagnosis of a restraint load, and the diagnosis mode processing unit may include a first voltage acquisition unit that performs discharging of the battery pack so that the SOC of the battery pack is equal to or less than a first predetermined value, and acquires a first battery voltage that is the voltage of the battery pack when charging and discharging of the battery pack is suspended for a first predetermined time while the SOC is equal to or less than the first predetermined value, a charging current integration unit that performs charging of the battery pack after acquiring the first battery voltage and integrates the charging current, a second voltage acquisition unit that stops charging when the SOC becomes equal to or greater than a second predetermined value, and acquires a second battery voltage that is the voltage of the battery pack when charging and discharging of the battery pack is suspended for a second predetermined time, and a restraint load calculation unit that calculates the restraint load based on the charging current integration value calculated by the charging current integration unit, the first battery voltage, and the second battery voltage.

According to this configuration, the diagnostic mode processing unit executes diagnosis of the restraint load. The first voltage acquisition unit of the diagnostic mode processing unit executes discharge of the battery pack so that the SOC of the battery pack is equal to or less than a first predetermined value, and acquires a first battery voltage, which is the voltage when charging and discharging of the battery pack is suspended for a first predetermined time while the SOC is equal to or less than the first predetermined value. The charging current integration unit executes charging of the battery pack after acquiring the first battery voltage, and integrates the charging current. When the SOC becomes equal to or greater than a second predetermined value, the second voltage acquisition unit stops charging and acquires a second battery voltage, which is the voltage when charging and discharging of the battery pack is suspended for a second predetermined time. The restraint load calculation unit calculates the restraint load based on the charging current integration value, the first battery voltage, and the second battery voltage.

The diagnostic mode processing unit performs charge and discharge control for the diagnostic mode in order to calculate the restraint load. Then, the diagnostic mode processing unit calculates the restraint load from the charge current integrated value, the first battery voltage, and the second battery voltage during the charge and discharge control for the diagnostic mode. The first battery voltage is the voltage when the charge and discharge of the battery pack is suspended for a first predetermined time, and the second battery voltage is the voltage when the charge and discharge of the battery pack is suspended for a second predetermined time, and is the voltage after the polarization is eliminated. Therefore, the restraint load can be calculated with high accuracy. Furthermore, when the restraint load estimated by the restraint load estimation unit becomes equal to or exceeds a predetermined value and a highly accurate restraint load is required, such as for predicting the breakage of the restraint member, the diagnostic mode processing unit performs charge and discharge control for the diagnostic mode and calculates the restraint load, thereby reducing waste of power and time.

Preferably, the first battery voltage and the second battery voltage are voltages of the single cells, and the restraint load calculation unit may estimate the full charge capacity of the single cells based on the charging current integrated value, the first battery voltage, and the second battery voltage, and calculate the restraint load using the smallest value of the estimated full charge capacities.

According to this configuration, the full charge capacity of the cells is estimated, and the smallest value of the estimated full charge capacities is used to calculate the restraint load, so the restraint load is calculated based on the state of the most deteriorated cell. The restraint load calculated for predicting the breakage of the restraint member is preferably the restraint load under the most severe conditions, which is expected to improve the diagnostic accuracy of the battery pack.

Preferably, the diagnosis performed by the diagnosis mode processing unit is a diagnosis of a micro-short circuit in the battery pack, and the diagnosis mode processing unit may include a threshold setting unit that sets a smaller threshold value when the restraint load is large compared to when the restraint load is small, and a micro-short circuit detection unit that determines that a micro-short circuit has occurred when a parameter indicating a micro-short circuit in the battery pack is equal to or greater than the threshold value.

According to this configuration, the diagnostic mode processing unit executes a diagnosis of a micro-short circuit in the battery pack. The micro-short circuit detection unit of the diagnostic mode processing unit determines that a micro-short circuit has occurred when a parameter indicating a micro-short circuit in the battery pack is equal to or greater than a threshold value. The threshold setting unit sets a smaller threshold value when the restraining load is large compared to when the restraining load is small, so that the detection sensitivity of the micro-short circuit is high when the restraining load is large. This makes it possible to detect a micro-short circuit with high accuracy. Furthermore, when the restraining load estimated by the restraining load estimation unit is equal to or greater than a predetermined value and a micro-short circuit is likely to occur, the diagnostic mode processing unit diagnoses a micro-short circuit, so that the diagnosis of a micro-short circuit in the battery pack can be performed at an appropriate time, thereby reducing the labor required for diagnosis.

According to the present disclosure, in a battery system equipped with a battery pack, by diagnosing the battery pack at an appropriate time, it is possible to reduce the labor required for diagnosis while improving the accuracy of the diagnosis.

1 is a diagram illustrating a schematic configuration of a power system including a battery system according to an embodiment of the present invention. 1 is a perspective view showing a schematic structure of a battery pack according to an embodiment of the present invention; FIG. 2 is a diagram illustrating functional blocks configured in a control device in the present embodiment. 4 is a flowchart showing an example of a process executed by a control device in the present embodiment. FIG. 11 is a diagram illustrating functional blocks configured in a control device in a second embodiment. 11 is a flowchart showing an example of a process executed by a control device in the second embodiment. FIG. 13 is a diagram showing the configuration of an electric vehicle equipped with a battery system according to a modified example.

The following describes in detail the embodiments of the present disclosure with reference to the drawings. Note that in the embodiments described below, identical or common parts are given the same reference numerals in the drawings, and their description will not be repeated.

(Embodiment 1)
Fig. 1 is a diagram showing a schematic configuration of a power system including a battery system according to the present embodiment. As shown in Fig. 1, the power system 1 includes a house 10, a power grid (power system) 20, a distribution transformer (pole transformer) 30, a smart meter 40, and a battery system 50.

The power grid 20 is a power system consisting of power plants, transmission lines, high-voltage substations, etc., and is a power grid managed by a power retailer, etc. The power of the power grid 20, which is stepped down to a voltage of, for example, 6.6 kV by a distribution substation, is stepped down to, for example, single-phase three-wire 100V/200V by a pole transformer 30, and is connected to the home power line 4 via a smart meter 40. The smart meter 40 is an electronic power meter with a communication function, which measures the amount of power exchanged between the power grid 20 and the home 10 during a specified measurement period (for example, 30 minutes), and transmits the measured amount of power to a server under the jurisdiction of the power retailer at specified intervals (for example, every 60 minutes).

In a house 10 connected to a power grid 20 via a smart meter 40, various electrical appliances (household loads) such as a power conditioner (PCS) 12, a photovoltaic power generation device 13, a heat pump water heater 14, a refrigerator 15, and an air conditioner (heating and cooling device) 16 are connected using a home power line via a distribution board 11 compatible with a HEMS (Home Energy Management Service). A battery system 50 is also connected to the distribution board 11 via a home power line. This makes it possible to consume power supplied from the power grid 20, and to supply (reverse flow) power generated by the photovoltaic power generation device 13 and power discharged from the battery system 50 to the power grid 20. The power generated by the photovoltaic power generation device 13 is consumed by the home loads and stored in the battery system 50. The power discharged from the battery system 50 is also consumed by the home loads.

The house 10 is provided with a HEMS controller 60. The HEMS controller 60 is configured to be able to communicate with each electrical device, such as a HEMS-compatible distribution board 11, PCS 12, refrigerator 15, and air conditioner 16, and with a battery system 50. The HEMS controller 60 acquires information about each electrical device and controls the operation of each electrical device.

The battery system 50 includes a battery 51, a monitoring unit 52, a charger/discharger 53, and a control device 55. The battery 51 is composed of a battery pack in which multiple single cells are stacked.

Figure 2 is a perspective view showing a schematic structure of a battery pack according to this embodiment. The battery pack 510 includes a plurality of cells (single cells) 81, a plurality of resin frames 82, a pair of end plates 83, and a pair of restraining bands 84. In the battery pack 510, the cells 81 and the resin frames 82 are stacked to form a laminate.

Each of the multiple cells 81 is a secondary battery such as a lithium ion battery or a nickel-metal hydride battery. The number of cells included in the battery pack 510 is not particularly limited. Each cell 81 has a common configuration, and each stacked cell 81 is electrically connected in series.

Each of the multiple resin frames 82 is disposed between two adjacent cells 81 in the stacking direction. A pair of end plates 83 are disposed at one end and the other end of the stack in the stacking direction. The end plates 83 are disposed so as to sandwich the stack from both sides in the stacking direction.

Multiple restraining bands (restraining members) 84 are arranged on the upper and lower surfaces of the resin frame 82. The restraining bands 84 restrain the pair of end plates 83 that sandwich the laminate together.

The battery 51 may be a battery pack in which multiple battery packs 510 are connected in series or parallel, or may be a battery module consisting of one battery pack 510.

Referring to FIG. 1, the monitoring unit 52 includes a voltage sensor, a current sensor, and a temperature sensor, which are not shown. The voltage sensor detects the voltage Vb of the battery pack 510 (more specifically, the voltage of each cell 81). The current sensor detects the current Ib input to and output from the battery pack 510. The temperature sensor detects the temperature Tb of the battery pack 510. Each sensor outputs a signal indicating the detection result or measurement result to the control device 55.

The charger/discharger 53 charges and discharges the battery 51 (battery pack 510). The charger/discharger 53 is connected to the distribution board 11 and the PCS 12 via the in-house power line, and includes a relay that switches between connecting and disconnecting the power path, and a power conversion circuit (e.g., a bidirectional converter). The charger/discharger 53 charges the battery pack 510 using power from the power grid 20 and power generated by the solar power generation device 13 (charging mode). The charger/discharger 53 supplies power to the household load or the power grid 20 by discharging the power stored in the battery pack 510 (discharging mode). The charger/discharger 53 is controlled by the control device 55.

The control device 55 is configured, for example, by an electronic control unit (ECU) and is capable of communicating with the HEMS controller 60. The control device 55 controls the charger/discharger 53 to control the charging and discharging of the battery pack 510, and also diagnoses the battery pack 510.

As shown in FIG. 2, the battery pack 510 is restrained by a restraining band (restraining member) 84. When a cell (single cell) 81 is used for a long period of time, the electrodes expand and gas is generated within the cell 81, causing the cell 81 to expand. Furthermore, when the SOC of the cell 81 is high, the electrodes expand and the cell 81 expands. When the cell 81 expands, the restraining load of the restraining band 84 increases, and the mechanical load (load, pressure, stress, etc.) applied to the restraining band 84 and the cell 81 increases, which may cause the restraining band 84 to break, for example.

In this embodiment, by diagnosing the restraining load of the restraining band 84, it is possible to predict the breakage of the restraining band 84.

Figure 3 is a diagram illustrating the functional blocks configured in the control device 55 in this embodiment. The SOC calculation unit 55a calculates the SOC of the battery pack 510. The SOC calculation method may be a known coulomb counting method that integrates charge and discharge currents, or may be calculated from the SOC-OCV (Open Circuit Voltage) characteristics. Alternatively, the SOC-OCV characteristics and the coulomb counting method may be combined.

The restraint load estimation unit 55b estimates the restraint load (estimated restraint load Le) of the restraint band 84. In this embodiment, the estimation is based on the usage period of the battery pack 510. As the deterioration of the cells (single cells) 81 progresses with the use of the battery pack 510, the electrodes expand and gas is generated in the cells 81, causing the cells 81 to expand and increasing the restraint load. The relationship between the usage period of the battery pack 510 and the restraint load is obtained in advance by experiments, simulations, etc. When the battery pack 510 is new, an initial restraint load (design restraint load) is set in the restraint load estimation unit 55b. Then, the restraint load estimation unit 55b estimates the estimated restraint load Le so that the restraint load increases as the usage period of the battery pack 510 progresses.

When the estimated restraint load Le becomes equal to or greater than the predetermined value X, the diagnostic mode processing unit 55c executes a diagnosis of the restraint load (restraint load Ls) of the restraint band 84. The diagnostic mode processing unit 55c performs charge/discharge control for the diagnostic mode and calculates the restraint load Ls of the restraint band 84.

The diagnostic mode processing unit 55c includes a first voltage acquisition unit 551, a charging current integration unit 552, a second voltage acquisition unit 553, and a restraint load calculation unit 554. The first voltage acquisition unit 551 discharges the battery pack 510 until the SOC of the battery pack 510 becomes equal to or less than a first predetermined value α. The first predetermined value α may be, for example, 5%. The charger/discharger 53 is set to a discharge mode, and discharges the battery pack 510. The power discharged from the battery pack 510 is consumed, for example, by a household load. When the SOC of the battery pack 510 drops to the first predetermined value α, the first voltage acquisition unit 551 stops discharging the battery pack 510 and suspends charging and discharging. Then, the first voltage acquisition unit 551 acquires a first battery voltage V1, which is the voltage Vb when the state in which the discharge of the battery pack 510 is suspended (the state in which charging and discharging are suspended) has elapsed for a first predetermined time T1. In this embodiment, the first battery voltage V1 is the voltage of each cell 81. The first predetermined time T1 may be, for example, one hour, and the first battery voltage V1 is the voltage Vb when polarization is eliminated.

After the first voltage acquisition unit 551 acquires the first battery voltage V1, the charging current accumulator 552 charges the assembled battery 510 and accumulates the current Ib (charging current) to calculate the charging current accumulated value ΣI. The charging current accumulator 552 sets the charger/discharger 53 to a charging mode and charges the assembled battery 510. The charging power may be the power of the power grid 20 or may be the power generated by the solar power generation device 13. The charging current accumulator 552 accumulates the current Ib output from the monitoring unit 52 to calculate the charging current accumulated value ΣI. The charging current accumulated value ΣI is the time integral value of the current Ib and corresponds to the amount of change in the capacity [Ah] of the assembled battery 510 (cell 81).

The second voltage acquisition unit 553 stops charging and suspends charging and discharging when the SOC of the assembled battery 510 increases to a second predetermined value β by charging and the SOC becomes equal to or greater than the second predetermined value β. The second predetermined value β may be, for example, 85%. The second voltage acquisition unit 553 acquires the second battery voltage V2, which is the voltage Vb when the charging of the assembled battery 510 has been stopped (charging and discharging have been suspended) for a second predetermined time T2. In this embodiment, the second battery voltage V2 is the voltage of each cell 81. The second predetermined time T2 may be, for example, one hour, and the second battery voltage V2 is the voltage Vb when polarization is eliminated. When charging is stopped, the charging current integration unit 552 stops integrating the current Ib (charging current).

The constraint load calculation unit 554 calculates the constraint load Ls based on the integrated current value ΣI, the first battery voltage V1, and the second battery voltage V2. In this embodiment, the full charge capacity FC of each cell 81 is estimated from the integrated current value ΣI, the first battery voltage V1, and the second battery voltage V2. Then, the constraint load Ls is calculated using the minimum value FCmin of the estimated full charge capacities FC. For example, the SOC change amount ΔS (=SOC2-SOC1) is calculated, which is the difference between SOC1, which is the SOC of the cell 81 calculated from the first battery voltage V1, and SOC2, which is the SOC of the cell 81 calculated from the second battery voltage V2. Then, the full charge capacity FC of the cell 81 is estimated as FC=ΣI/(ΔS/100).

The restraint load calculation unit 554 estimates the full charge capacity FC for each cell 81, and calculates the restraint load Ls using the minimum value FCmin of the estimated full charge capacity FC. For example, the relationship between the full charge capacity FC and the restraint load Ls is calculated in advance by experiments, etc., and this relationship is mapped and stored in the memory unit of the control device 55. The minimum value FCmin is then used to search the map to calculate the restraint load Ls.

The control device 55 may predict the breakage of the restraint band 84 using the restraint load Ls calculated by the restraint load calculation unit 554. For example, when the restraint load Ls exceeds a preset allowable value, it may determine that there is a possibility of the restraint band 84 breaking, and may turn on a Malfunction Indication Lamp (MIL) (not shown).

Figure 4 is a flowchart showing an example of processing executed by the control device 55 in this embodiment. This flowchart is repeatedly processed at predetermined intervals. In step (hereinafter, step is abbreviated as "S") 10, the estimated restraint load Le is calculated. The estimated restraint load Le is calculated by the restraint load estimation unit 55b so that the restraint load increases as the usage period of the battery pack 510 elapses. In the following S11, it is determined whether the estimated restraint load Le is equal to or greater than a predetermined value X. If the estimated restraint load Le is less than the predetermined value X, a negative determination is made and the current routine is terminated. If the estimated restraint load Le is equal to or greater than the predetermined value X, a positive determination is made and the routine proceeds to S12.

In S12, the battery pack 510 is discharged, and the process proceeds to S13. In S13, it is determined whether the SOC of the battery pack 510 is equal to or less than a predetermined value α. If the SOC is greater than the predetermined value α, a negative determination is made, and the process returns to S12, and the discharge of the battery pack 510 continues. When the SOC falls to the predetermined value α due to the discharge of the battery pack 510, the SOC falls to or less than the predetermined value α, a positive determination is made in S13, and the process proceeds to S14.

In S14, discharging of the battery pack 510 is stopped, charging and discharging are suspended, and then the process proceeds to S15. In S15, it is determined whether the state in which discharging of the battery pack 510 has been stopped (charging and discharging are suspended) has continued for a first predetermined time T1. If the state in which charging and discharging of the battery pack 510 has been suspended has continued for the first predetermined time T1, a positive determination is made in S15, and the process proceeds to S16.

In S16, the voltage Vb is acquired as the first battery voltage V1, and the process proceeds to S17. In S17, the battery pack 510 is charged, and the current Ib is accumulated to calculate the accumulated charging current value ΣI.

In the next step S18, it is determined whether the SOC of the battery pack 510 is equal to or greater than a predetermined value β. If the SOC is less than the predetermined value β, a negative determination is made and the process returns to S17, where charging of the battery pack 510 continues and calculation of the charging current integrated value ΣI continues. When the SOC increases to the predetermined value β as a result of charging the battery pack 510, the SOC becomes equal to or greater than the predetermined value β, a positive determination is made in S18, and the process proceeds to S19.

In S19, charging of the battery pack 510 is stopped, charging and discharging are suspended, and the process proceeds to S20. In S20, it is determined whether the state in which charging of the battery pack 510 has been stopped (charging and discharging are suspended) has elapsed for a second predetermined time T2. If the state in which charging and discharging of the battery pack 510 has been suspended has elapsed for the second predetermined time T2, a positive determination is made in S20 and the process proceeds to S21.

In S21, the voltage Vb is acquired as the second battery voltage V2, and the process proceeds to S22. In S22, as described above, the full charge capacity FC of each cell 81 is estimated using the charging current integrated value ΣI, the first battery voltage V1, and the second battery voltage V2.

In the next step S23, a map search is performed using the minimum value FCmin of the full charge capacity FC of each cell 81, the restraining load Ls is calculated, and then the routine ends.

According to this embodiment, when the estimated restraint load Le estimated by the restraint load estimation unit 55b is equal to or greater than a predetermined value X, the diagnosis mode processing unit 55c executes diagnosis of the battery pack. Therefore, when the restraint load of the restraint bands 84 is large and there is a high possibility that various malfunctions of the battery pack 510 will occur, diagnosis of the battery pack 510 is executed at an appropriate timing, and the labor required for diagnosis is reduced.

According to this embodiment, the diagnostic mode processing unit 55c performs charge and discharge control for the diagnostic mode by the first voltage acquisition unit 551, the charge current integration unit 552, and the second voltage acquisition unit 553 in order to calculate the restraint load Ls. Then, the restraint load Ls is calculated from the charge current integration value ΣI, the first battery voltage V1, and the second battery voltage V2 during the charge and discharge control for the diagnostic mode. The first battery voltage V1 is the voltage when the charge and discharge of the battery pack 510 is suspended for a first predetermined time T1, and the second battery voltage V2 is the voltage when the charge and discharge of the battery pack 510 is suspended for a second predetermined time T2, and is the voltage after the polarization is eliminated. Therefore, the restraint load Ls can be calculated with high accuracy. In addition, when the estimated restraint load Le estimated by the restraint load estimation unit 55b exceeds a predetermined value X and it becomes necessary to calculate the restraint load Ls with high accuracy, such as to predict the breakage of the restraint band 84, the diagnosis mode processing unit 55c performs charge and discharge control for the diagnosis mode and calculates the restraint load Ls, thereby reducing the waste of power and time.

In the above embodiment, the restraint load estimation unit 55b estimates the estimated restraint load Le based on the period of use of the battery pack 510. However, the restraint load estimation unit 55b may calculate the estimated restraint load Le using the method described in the above Patent Document 1. For example, the capacity maintenance rate of the battery pack 510 is calculated by dividing the current integrated value between two appropriate points when the battery pack 510 is being charged and discharged by the SOC difference between the two points. Then, the deterioration degree of the battery pack 510 is calculated from the capacity maintenance rate, and the estimated restraint load Le may be calculated from the deterioration degree, the SOC, and the temperature Tb of the battery pack 510. The restraint load estimation unit 55b may also calculate the estimated restraint load Le using the output signal (output voltage) of a strain gauge provided in the battery pack 510.

(Embodiment 2)
In the second embodiment, a diagnosis mode processing unit 55c of a control device 55 diagnoses a micro-short circuit in a battery pack 510. The configurations of the battery system and the power system in the second embodiment are similar to those of the battery system and the power system in the first embodiment, and therefore, differences from the first embodiment will be described below.

Figure 5 is a diagram illustrating the functional blocks configured in the control device in the second embodiment. The control device 55 in the second embodiment includes a restraint load estimation unit 55b and a diagnosis mode processing unit 55c. The restraint load estimation unit 55b is the same as in the first embodiment.

In the second embodiment, the diagnostic mode processing unit 55c executes a diagnosis of a micro-short circuit of the battery pack 510 when the estimated restraining load Le becomes equal to or greater than a predetermined value Y. The diagnostic mode processing unit 55c includes a threshold setting unit 561, a cell voltage acquisition unit 562, a voltage difference calculation unit 563, and a micro-short circuit detection unit 564.

The threshold setting unit 561 sets the threshold S using the estimated restraint load Le estimated by the restraint load estimation unit 55b. The threshold S is set to a smaller value as the estimated restraint load Le increases.

The cell voltage acquisition unit 562 acquires the voltage (cell voltage) of each cell 81 using the voltage Vb output from the monitoring unit 52. The cell voltage acquisition unit 562 acquires the voltage of each cell 81, for example, from the voltage Vb when the battery pack 510 is being charged.

The voltage difference calculation unit 563 calculates the voltage difference ΔVb, which is the difference between the maximum and minimum voltages of each cell 81 acquired by the cell voltage acquisition unit 562.

The micro-short circuit detection unit 564 detects a micro-short circuit in the battery pack 510 (cell 81) by comparing the voltage difference ΔVb with the threshold value S. When the voltage difference ΔVb is equal to or greater than the threshold value S (ΔVb≧S), the micro-short circuit detection unit 564 determines that a micro-short circuit has occurred and detects a micro-short circuit. A micro-short circuit may be a micro-short circuit between the terminals of the cell 81 (within the circuit of the battery pack 510) or a micro-short circuit inside the cell 81. When the micro-short circuit detection unit 564 detects a micro-short circuit in the battery pack 510, the diagnosis mode processing unit 55c turns on the MIL 57.

Figure 6 is a flowchart showing an example of processing executed by the control device 55 in the second embodiment. This flowchart is repeatedly processed at predetermined intervals. In S40, the estimated restraint load Le is calculated. The estimated restraint load Le is calculated by the restraint load estimation unit 55b so that the restraint load increases as the usage period of the battery pack 510 elapses. In the following S41, it is determined whether the estimated restraint load Le is equal to or greater than a predetermined value Y. If the estimated restraint load Le is less than the predetermined value Y, a negative determination is made and the current routine is terminated. If the estimated restraint load Le is equal to or greater than the predetermined value Y, a positive determination is made and the routine proceeds to S42.

In S42, a threshold value S is set. The threshold value S is set to a smaller value as the estimated restraining load Le is larger. Once the threshold value S is set, the process proceeds to S43, where it is determined whether the battery pack 510 is being charged. If the battery pack 510 is not being charged, the process waits until the battery pack 510 is being charged, and once the battery pack 510 is being charged, a positive determination is made in S43, and the process proceeds to S44.

In S44, the voltage (cell voltage) of each cell 81 is obtained using the voltage Vb output from the monitoring unit 52. The voltage of the cell 81 is obtained while the battery pack 510 is being charged because, when the battery pack 510 is being charged, CC (constant current) charging or CCCV (constant current, constant voltage) charging is performed, and the voltage of the cell 81 does not change suddenly.

In the next S45, the voltage difference ΔVb, which is the difference between the maximum and minimum voltages of each cell 81 obtained in S44, is calculated, and then the process proceeds to S46. In S46, it is determined whether the voltage difference ΔVb is equal to or greater than the threshold value S. If the voltage difference ΔVb is smaller than the threshold value S (ΔVb<S), a negative determination is made in S46 and the current routine is terminated. If the voltage difference ΔVb is equal to or greater than the threshold value S (ΔVb≧S), it is determined that a micro-short circuit has occurred in the battery pack 510, and the process proceeds to S47, where the MIL is turned on, and the current routine is terminated.

According to this second embodiment, when the estimated restraint load Le estimated by the restraint load estimation unit 55b is equal to or greater than a predetermined value Y, the diagnosis mode processing unit 55c executes diagnosis of the battery pack. Therefore, when the restraint load of the restraint bands 84 is large and there is a high possibility that various malfunctions of the battery pack 510 may occur, diagnosis of the battery pack 510 is executed at an appropriate timing, and the labor required for diagnosis is reduced.

According to this embodiment 2, the diagnostic mode processing unit 55c executes a diagnosis of a micro-short circuit of the battery pack 510. The micro-short circuit detection unit 564 of the diagnostic mode processing unit 55c determines that a micro-short circuit has occurred when the parameter (the voltage difference ΔVb calculated by the voltage difference calculation unit 563) indicating a micro-short circuit of the battery pack 510 is equal to or greater than the threshold value S. The threshold setting unit 561 sets the threshold value S to a smaller value as the estimated restraint load Le increases, so that the threshold value S becomes smaller when the estimated restraint load Le is large than when the estimated restraint load Le is small. Therefore, when the restraint load of the restraint band 84 is large, the detection sensitivity of the micro-short circuit is high, and the micro-short circuit can be detected with high accuracy. In addition, when the estimated restraint load Le estimated by the restraint load estimation unit 55b becomes equal to or greater than the predetermined value Y and a micro-short circuit is likely to occur, the diagnostic mode processing unit 55c diagnoses a micro-short circuit, so that the diagnosis of the micro-short circuit of the battery pack 510 can be performed at an appropriate timing, and the labor required for diagnosis is reduced.

In this second embodiment, a micro-short circuit is detected using the voltage difference ΔVb. However, it is also possible to monitor the voltage drop of the cells 81 when charging/discharging of the battery pack 510 is suspended, and determine that a micro-short circuit has occurred if there is a cell 81 whose voltage drop is equal to or greater than a threshold value. It is also possible to calculate the resistance value of each cell 81 from the current and voltage when the battery pack 510 is charging/discharging, and determine that a micro-short circuit has occurred if there is a cell 81 whose resistance value is equal to or greater than a threshold value.

In this second embodiment, detection (diagnosis) of a micro-short circuit in the battery pack 510 is performed when the estimated restraining load Le is equal to or greater than a predetermined value Y. However, a micro-short circuit in the battery pack 510 may be detected when the estimated restraining load Le is smaller than the predetermined value Y. In this case, the threshold value to be compared with the voltage difference ΔVb is set to a value that is a certain amount larger than the maximum value of the threshold value S set by the threshold setting unit 561 to detect a micro-short circuit in the battery pack 510. This allows the detection sensitivity of a micro-short circuit to be appropriately set, and erroneous detection to be suppressed.

The control device 55 may diagnose the restraint load in embodiment 1 and the micro-short circuit in embodiment 2. In this case, the predetermined value Y may be set to be greater than the predetermined value X. With this configuration, the threshold setting unit 561 can set the threshold S using the restraint load Ls calculated by the restraint load calculation unit 554 (Figure 3: embodiment 1), making it possible to set the threshold S using the restraint load with high accuracy.

(Modification)
In each of the above-described embodiments, the battery system 50 (battery pack 510) is a stationary battery installed in the house 10. However, the battery system (battery pack) may be mounted on a vehicle.

Figure 7 is a diagram showing the schematic configuration of an electric vehicle equipped with a battery system according to a modified example. In this modified example, an example is described in which the electric vehicle 100 is an electric vehicle (BEV: Battery Electric Vehicle), but the electric vehicle 100 is not limited to being a BEV and may be, for example, a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle), an externally chargeable fuel cell electric vehicle (FCEV: Fuel Cell Electric Vehicle), etc.

The electric vehicle 100 includes a battery pack 101, a boost converter 102, an inverter 103, a motor generator 104, a transmission gear 105, drive wheels 106, and a control device 200.

The battery pack 101 is mounted on the electric vehicle 100 as a driving power source (i.e., a power source) for the electric vehicle 100. The battery pack 101 is a battery pack in which a battery pack similar to the battery pack 510 in the above embodiment is connected in series or parallel. A monitoring unit 107 is arranged in the battery pack 101, and detects the voltage Vb of the battery pack (the voltage of each cell), the current Ib input/output to/from the battery pack, and the temperature Tb.

The battery pack 101 is connected to the boost converter 102 via system main relays 108a and 108b. The boost converter 102 is connected to an inverter 103, which converts the DC power from the boost converter 102 into AC power.

The motor generator (three-phase AC motor) 104 receives AC power from the inverter 103 and generates kinetic energy for propelling the electric vehicle 100. The kinetic energy generated by the motor generator 104 is transmitted to the drive wheels 106. On the other hand, when the electric vehicle 100 is decelerated or stopped, the motor generator 104 converts the kinetic energy of the electric vehicle 100 into electrical energy. The AC power generated by the motor generator 104 is converted to DC power by the inverter 103 and supplied to the battery pack 101 via the boost converter 102. This allows regenerative power to be stored in the battery pack 101.

The electric vehicle 100 is configured to have an external charging function for charging the battery pack 101 with an external power source 90. The electric vehicle 100 is equipped with a charger 109 and charging relays 110a and 110b. The external power source 90 is a power source provided outside the vehicle, and an example of the external power source 90 is a commercial power source. The charger 109 converts power from the external power source 90 into charging power for the battery pack 101. The charger 109 is connected to the battery pack 101 via the charging relays 110a and 110b. When the charging relays 110a and 110b are on, the battery pack 101 can be charged with power from the external power source 90.

The battery pack 101 is connected to the auxiliary battery 112 and the auxiliary load 113 via the DC/DC converter 111. The power stored in the battery pack 101 is stepped down by the DC/DC converter 111 to charge the auxiliary battery 112 and drive the auxiliary load 113.

The control device 200 is composed of a battery ECU 201 and a vehicle ECU 202. Either the battery ECU 201 or the vehicle ECU 202 is configured with functional blocks similar to the functional blocks configured in the control device 55 of the above embodiment. For example, the SOC calculation unit 55a and the restraint load estimation unit 55b may be configured in the battery ECU 201, and the diagnosis mode processing unit 55c may be configured in the vehicle ECU 202.

In the modified example, when the estimated restraint load Le estimated by the restraint load estimation unit 55b configured in the control device 200 is equal to or greater than a predetermined value X, the diagnosis mode processing unit 55c configured in the control device 200 diagnoses the restraint load Ls of the restraint member (restraint band). In this case, it is preferable that the processing from S12 (FIG. 4) onwards is executed when the electric vehicle 100 is stopped (parked). For example, when the electric vehicle 100 is stopped (parked) and the external power supply 90 is connected, charging is performed to the auxiliary battery 112 and discharging is performed by driving the auxiliary load 113, and the processing from S12 to S16 is executed. After that, charging is performed by the external power supply 90, and the processing from S17 to S23 is executed. Note that a charger/discharger may be provided instead of the charger 109, and power supply (discharge) to the outside of the electric vehicle 100 is enabled, discharging is performed by the external power supply, and the processing from S12 to S16 may be executed.

In a modified example, when the estimated restraint load Le estimated by the restraint load estimation unit 55b configured in the control device 200 is equal to or greater than a predetermined value Y, the diagnosis mode processing unit 55c configured in the control device 200 diagnoses a micro-short circuit in the battery pack. In this case, it is preferable to execute the processing from S42 (FIG. 6) onwards when external charging is being performed by the external power source 90. When charging while the electric vehicle 100 is traveling (for example, when charging using regenerative power), there is a possibility that the voltage fluctuation of the battery pack 101 (battery pack) will be large. However, when the electric vehicle 100 is externally charged, CC charging or CCCV charging is performed, and the voltage of the battery pack does not change suddenly.

The embodiments disclosed herein are illustrative in all respects and are not limiting. The scope of the present disclosure is defined by the claims, and includes all modifications within the meaning and scope of the claims.

1 Power system, 4 In-house power line, 10 House, 11 Distribution board, 12 Power conditioner, 13 Photovoltaic power generation device, 14 Heat pump water heater, 15 Refrigerator, 16 Air conditioner, 20 Power grid, 30 Pole transformer, 40 Smart meter, 50 Battery system, 51 Battery, 52 Monitoring unit, 53 Charger/discharger, 55 Control device, 55a SOC calculation unit, 55b Restraint load estimation unit, 55c Diagnostic mode processing unit, 60 HEMS controller, 57 MIL, 81 Cell (single cell), 82 Resin frame, 83 End plate, 84 Restraint band, 90 External power source, 100 Electric vehicle, 101 Battery pack, 102 Boost converter, 103 Inverter, 104 Motor generator, 105 Transmission gear, 106 Drive wheel, 107 Monitoring unit, 108a, 108b system main relay, 109 charger, 110a, 110b charging relay, 111 DC/DC converter, 112 auxiliary battery, 113 auxiliary load, 200 control device, 201 battery ECU, 202 vehicle ECU, 510 assembled battery, 551 first voltage acquisition unit, 552 charging current integration unit, 553 second voltage acquisition unit, 554 restraint load calculation unit, 561 threshold setting unit, 562 cell voltage acquisition unit, 563 voltage difference calculation unit, 564 micro-short circuit detection unit.

Claims (4)

a battery pack in which a plurality of stacked unit cells are restrained by a restraining member;
A control device for controlling the battery pack,
The control device includes:
a restraint load estimation unit that estimates a restraint load caused by the restraint member;
a diagnosis mode processing unit that executes a diagnosis of the battery pack when the restraint load estimated by the restraint load estimation unit is equal to or greater than a predetermined value,
the diagnosis executed by the diagnosis mode processing unit is a diagnosis of the restraining load,
The diagnostic mode processing unit:
a first voltage acquisition unit that executes discharging of the battery pack so that an SOC of the battery pack becomes equal to or less than a first predetermined value, and acquires a first battery voltage that is a voltage when charging and discharging of the battery pack is suspended for a first predetermined time in a state in which the SOC is equal to or less than the first predetermined value;
a charging current integrating unit that, after acquiring the first battery voltage, charges the battery pack and integrates a charging current;
a second voltage acquisition unit that stops the charging when the SOC becomes equal to or greater than a second predetermined value and acquires a second battery voltage that is a voltage when charging and discharging of the battery pack is suspended for a second predetermined time;
a restraint load calculation unit that calculates the restraint load based on the charging current integrated value calculated by the charging current integration unit, the first battery voltage, and the second battery voltage. the first battery voltage and the second battery voltage are voltages of the single cells,
2. The battery system according to claim 1, wherein the restraint load calculation unit estimates a full charge capacity of the single battery based on the charging current integrated value, the first battery voltage, and the second battery voltage, and calculates the restraint load using the smallest value among the estimated full charge capacities. a battery pack in which a plurality of stacked unit cells are restrained by a restraining member;
A control device for controlling the battery pack,
The control device includes:
a restraint load estimation unit that estimates a restraint load caused by the restraint member;
a diagnosis mode processing unit that executes a diagnosis of the battery pack when the restraint load estimated by the restraint load estimation unit is equal to or greater than a predetermined value,
the diagnosis executed by the diagnosis mode processing unit is a diagnosis of a micro-short circuit of the battery pack,
The diagnostic mode processing unit:
a threshold setting unit that sets a smaller threshold when the restraint load is large compared to when the restraint load is small;
a micro-short circuit detection unit that determines that the micro-short circuit has occurred when a parameter indicating a micro-short circuit of the battery pack is equal to or greater than the threshold value. The battery system according to claim 3 , wherein the parameter indicative of a micro-short circuit in the battery pack is a voltage difference between the cells.

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