JP6711238B2 - Battery pack disconnection detection system - Google Patents

Description

The present invention relates to a disconnection detection system for a battery pack in which a plurality of battery cells are connected in parallel.

A hybrid vehicle or an electric vehicle that uses a rotating electric machine as a drive source is equipped with a battery module (battery module) that is a power source. The battery module may be composed of a plurality of battery packs connected in series. For example, several tens of battery cells (unit cells) are connected in parallel to each battery pack.

For example, in Patent Document 1, the presence or absence of disconnection in the battery pack is detected based on the internal resistance of the battery pack, that is, the combined internal resistance of the battery cells connected in parallel. The disconnection includes the case where the electrodes of the battery cells are disengaged from the wiring inside the battery pack and the case where the electrodes of the battery cells are in an insulated state (non-conductive state).

For example, the combined resistance R1 of the internal resistances r1, r2, and r3 of three parallel-connected battery cells is represented by the following formula (1), and when one of the three parallel-connected battery cells is broken, the combined resistance R2 is It is expressed as Equation (2).

The ratio R2/R1 (rate of change in internal resistance) between the two is expressed by the following mathematical expression (3).

Here, assuming that all internal resistances are equal (r1=r2=r3=r), Equation (3) becomes Equation (4) below.

That is, the internal resistance change rate (increase rate) is represented by the initial battery cell number/(initial battery cell number-disconnected battery cell number). In Patent Document 1, when the internal resistance value of the battery pack exceeds a predetermined threshold value, it is determined that a disconnection has occurred in the battery pack.

JP, 2008-27658, A

By the way, as the number of battery cells connected in parallel in the battery pack increases, it becomes more difficult to detect disconnection based on the internal resistance. For example, when 20 battery cells are arranged in parallel, if one battery cell is disconnected, the increase rate of the internal resistance becomes 20/19≈1.05, which is only about 5%. Such an increase rate may be on the order (accuracy) equal to or less than the error associated with the calculation of the internal resistance, and as a result, it becomes difficult to detect the disconnection.

Therefore, it is an object of the present invention to provide a battery pack disconnection detection system capable of more reliable disconnection detection than before.

The disconnection detection system for a battery pack according to the present invention includes a disconnection determination unit, a current determination unit, a timer, and a discharge time determination unit. The disconnection determination unit determines the presence or absence of disconnection of the battery pack based on the internal resistance of the battery pack in which a plurality of battery cells are connected in parallel. The current determination unit determines whether or not the discharge current of the battery pack is in a large current discharge state in which the discharge current is equal to or higher than a predetermined current threshold value. The timer measures the duration of the large current discharge state. The discharge time determination unit permits the disconnection determination unit to perform the disconnection presence/absence determination of the battery pack when the duration of the high current discharge state is equal to or longer than a predetermined threshold time.

According to the present invention, the presence or absence of disconnection of the battery pack is determined when the high current discharge state continues for a long period of time. When the high-current discharge state continues for a long period of time, the salt concentration distribution in each battery cell spreads, and a low concentration region with low ionic conductivity (so-called salt-dead region) occurs in the battery cell. As a result, the internal resistance of each battery cell increases, and the internal resistance difference between when the battery pack is disconnected and when the disconnection occurs becomes larger than before the low-concentration region occurs. As a result, it becomes possible to detect the disconnection with higher reliability than before.

It is a figure which illustrates the disconnection detection system of the battery pack which concerns on this embodiment, and the structure of the vehicle carrying this. It is a figure (current graph, voltage graph) explaining the voltage drop of a battery cell. It is a graph which illustrates the relationship between the salt concentration of a battery cell, and ionic conductivity. It is a figure which illustrates the functional block of a control part. It is a figure which illustrates the disconnection determination permission flow. It is a figure which shows another example of the functional block of a control part. It is a figure which shows another example of a disconnection determination permission flow. It is a figure which shows another example of a functional block of a control part. It is a figure which shows the further another example of a disconnection determination permission flow. It is a figure which illustrates the time chart when another example of a disconnection determination permission flow is performed.

FIG. 1 illustrates a configuration of a battery pack disconnection detection system according to the present embodiment and a vehicle equipped with the system. Note that, for simplification of the illustration, in FIG. 1, a configuration having a low relevance to the disconnection detection system according to the present embodiment is omitted as appropriate. The arrow lines represent signal lines.

The vehicle shown in FIG. 1 is a vehicle that uses a rotating electric machine as a drive source, such as a hybrid vehicle, a plug-in hybrid vehicle, and an electric vehicle. In this vehicle, electric power is supplied from the battery module 10 (main battery) to the loads such as the rotary electric machines MG1 and MG2 that are drive sources. Specifically, the DC power output from the battery module 10 is boosted by the step-up/down DC/DC converter 12. The boosted DC power is orthogonally converted by the inverter 14. The converted AC power is supplied to at least one of the rotary electric machines MG1 and MG2. Since the power transmission path from the rotary electric machines MG1 and MG2 to the wheels 16 is known, the description thereof is omitted here.

In the hybrid vehicle and the plug-in hybrid vehicle, an EV traveling mode in which only the rotary electric machine MG2 is used as a drive source and an HV traveling mode in which the rotary electric machine MG2 and the internal combustion engine 17 are used as drive sources are selected as the traveling modes of the vehicle. Compared to the HV traveling mode, a large current is supplied from the battery module 10 to the rotary electric machine MG2 in the EV traveling mode (large current discharging). As will be described later, the presence or absence of disconnection of the battery pack 33 is determined when the large current discharge state during execution of the EV running mode is continued for a long time.

A branch circuit is provided that branches from a circuit connecting the battery module 10 and the step-up/down DC/DC converter 12 and is connected to the step-down DC/DC converter 18. The high-voltage power of the battery module 10 is stepped down by the step-down DC/DC converter 18 and supplied to the sub-battery 20, the control unit 22, the voltage sensor unit 24, and other accessories.

A system main relay SMR is provided between the battery module 10 and the step-up/down DC/DC converter 12 and the step-down DC/DC converter 18. When the system main relay SMR is brought into the connected state, the high voltage system loads such as the rotary electric machines MG1 and MG2, the low voltage system loads such as the control unit 22 and auxiliary machines, and the battery module 10 are brought into the connected state. Become. For example, when the driver turns on a start switch (not shown), the system main relay SMR is switched from the disconnected state to the connected state. Further, when the driver turns off the start switch, the system main relay SMR is switched from the connected state to the disconnected state.

The battery module 10 is configured to include a laminated body in which a plurality of secondary battery cells 32 are laminated. In the example shown in FIG. 1, a plurality of battery packs 33 including a plurality of battery cells 32 connected in parallel are connected in series. For example, several tens of battery cells 32 are connected in parallel per one battery pack 33.

The battery cell 32 is composed of, for example, a lithium ion battery. Since the detailed structure of the lithium-ion battery is known, it will be briefly described here. A lithium ion battery includes a positive electrode plate made of a material such as lithium cobalt oxide, a negative electrode plate made of a material such as graphite, and an insulating paper (separator) separating the two. The layer in which the positive electrode plate, the insulating paper, and the negative electrode plate are bundled is housed in a cylindrical metal case in a wound state, for example. Further, the metal case is filled with a lithium salt organic electrolyte.

FIG. 2 illustrates the voltage characteristics of the lithium ion battery. Basically, it is known that in a lithium-ion battery, the energizing current and the degree of voltage drop (ΔV) due to the energizing current are approximately in a proportional relationship. For example, the voltage drop of the solid line (B) of relatively large current becomes larger than the voltage drop of the broken line (A) of relatively small current.

Further, it is known that in a lithium ion battery, a salt concentration distribution occurs with energization. The spread of this salt concentration distribution changes according to the applied current. For example, when the large current discharge is continued, the salt concentration distribution is expanded accordingly. On the other hand, when high-current charging is performed after high-current discharging, the once-widened salt concentration distribution is narrowed.

FIG. 3 illustrates the change in ionic conductivity according to the salt concentration. As shown in this graph, the ionic conductivity sharply decreases on the low concentration side. When a low-concentration region (so-called salt-depleted region) occurs in the battery cell 32 due to the spread of the salt concentration distribution, the ionic conductivity of the region decreases, so that the internal resistance of the battery cell 32 increases. Along with this, the voltage drop of the solid line (B) becomes steep as shown by the broken line circle in FIG.

As will be described later, in the present embodiment, attention is paid to the characteristic that the internal resistance of the battery cell 32 increases with the occurrence of the salt withdrawal region, and the presence or absence of disconnection of the battery pack 33 is determined when the salt withdrawal region occurs.

<Disconnection detection system>
The disconnection detection system according to this embodiment includes a voltage sensor unit 24, a current sensor 42, a timer 40, and a control unit 22.

The voltage sensor unit 24 measures the voltage (voltage between terminals) of each battery pack 33 of the battery module 10. In other words, the combined voltage of the battery cells 32 connected in parallel in the battery pack 33 is measured. The difference between the voltage (CCV) of the battery pack 33 and the previously detected open circuit voltage (OCV) becomes the voltage drop due to the internal resistance. This internal resistance becomes a combined internal resistance of the plurality of battery cells 32 connected in parallel. The measured voltage of each battery pack 33 is sent to the control unit 22.

The control unit 22 is configured by a computer, for example, and includes a CPU 36 that is an arithmetic circuit and a storage unit 38. The control unit 22 may be a so-called battery ECU that mainly manages the battery module 10. The storage unit 38 includes a volatile memory such as SRAM and a non-volatile memory such as ROM and hard disk. The storage unit 38 stores a program for executing a disconnection detection process and a disconnection determination permission flow which will be described later.

The control unit 22 also receives detection values from various sensors mounted on the vehicle. Specifically, the current value Ib and the temperature Tb of the battery module 10 are received from the current sensor 42 and the temperature sensor 44, respectively. Also, the voltage value Vb of each battery pack 33 is received from the voltage sensor unit 24.

By executing the disconnection detection process and the disconnection determination permission flow program stored in the storage unit 38 of the control unit 22, the control unit 22 includes a plurality of functional units as illustrated in FIG. 4. That is, the control unit 22 includes a current determination unit 52, a discharge time determination unit 54, and a disconnection determination unit 56.

The disconnection determination unit 56 executes a disconnection presence/absence determination (disconnection determination) that determines whether or not the battery pack 33 is disconnected. The disconnection determination unit 56 uses the voltage Vb (=CCV) of the battery pack 33 acquired from the voltage sensor unit 24, the current value Ib acquired from the current sensor 42, and the open circuit of the battery pack 33 previously measured when the vehicle is stopped. The disconnection determination is performed according to the voltage (OCV).

Specifically, the disconnection determination unit 56 subtracts the current voltage (CCV) of the battery pack 33 from the previously obtained open circuit voltage (OCV) of the battery pack 33 to obtain the voltage drop ΔV based on the internal resistance. Further, the disconnection determination unit 56 obtains the current value Ib from the current sensor 42 and divides the voltage drop ΔV by the current value Ib to obtain the internal resistance r. When the calculated internal resistance r is equal to or higher than a predetermined resistance threshold, the disconnection determination unit 56 determines that the battery pack 33 has disconnection and outputs a disconnection warning signal. For example, a message urging the dealer to inspect is displayed on the display in the vehicle.

Generally, when a disconnection occurs in any of the battery cells 32 in the battery pack 33, the current density per one battery cell 32 increases and the internal resistance of the entire battery pack 33 increases. In addition, as described above, when the salt withdrawal region occurs in the battery cell 32, the internal resistance of the battery cell 32 increases. Since the internal resistance of each battery cell 32 increases due to the occurrence of the salt withdrawal region, the difference in the internal resistance of the battery pack 33 between when there is no disconnection and when the disconnection occurs is greater than the internal resistance difference before the salt withdrawal region occurs. Also grows. Based on this, the disconnection detection system according to the present embodiment determines the presence/absence of a disconnection, aiming at the timing when the salt withered region occurs in the battery cell 32.

<First disconnection determination permission flow>
The current determination unit 52 and the discharge time determination unit 54 cooperate with the timer 40 to determine whether the disconnection determination unit 56 can execute the disconnection determination. FIG. 5 exemplifies a flow for determining whether or not to execute the disconnection determination (disconnection determination permission flow).

When the start button (not shown) in the vehicle is turned on and the system main relay SMR is switched from the cut-off state to the conductive state, the battery module 10 and the loads of the rotary electric machines MG1, MG2, etc. are connected. The current determination unit 52 activates the flow of FIG. 5 according to the ON operation of the start button.

The discharge time t at the time of starting the flow of FIG. 5 is set to an initial value t=0. Further, the flow of FIG. 5 is terminated by turning off the start button.

The current determination unit 52 receives an EV traveling mode on/off command from a host controller (not shown) of the vehicle and determines whether the vehicle is in the EV traveling mode implementation (S10). When the EV traveling mode is not executed, the discharge time t is reset to 0 (S20). If the vehicle is an electric vehicle, step S10 is omitted.

When the EV traveling mode is being executed, the current determination unit 52 determines whether the energized state of the battery pack 33 is the large current discharge state. That is, the current determination unit 52 acquires the current Ib of the battery module 10 (hence the battery pack 33) from the current sensor 42 and determines whether or not the current Ib is greater than or equal to a predetermined current threshold Ib_th (S12). When the current Ib is less than the current threshold value Ib_th, the discharge time t is reset to 0 (S20).

When the current Ib is greater than or equal to the current threshold Ib_th, the current determination unit 52 outputs to the timer 40 a count command to start measuring the duration of the large current discharge state (discharge time t). As a result, the discharge time t is counted up (S14).

Next, the discharge time determination unit 54 determines whether or not a so-called salt-dead region has occurred in the battery pack 33. That is, the discharge time determination unit 54 determines whether the discharge time t counted by the timer 40 is equal to or longer than a predetermined threshold time t_th (S16). When the discharge time t is less than the threshold time t_th, the disconnection determination unit 56 is caused to suspend the execution of the disconnection determination (disconnection presence determination) (S22). For example, the disconnection determination unit 56 is not permitted to acquire measurement values from the voltage sensor unit 24 and the current sensor 42.

When the discharge time t is equal to or longer than the threshold time t_th in step S16, the discharge time determination unit 54 permits the disconnection determination unit 56 to perform the disconnection determination (disconnection presence determination) (S18). In response to this, the disconnection determination unit 56 determines whether or not the battery pack 33 is disconnected as described above.

<Second disconnection determination permission flow>
As described above, the way the salt concentration distribution spreads changes depending on the magnitude of the energizing current. Specifically, the salt withered region is generated earlier as the current is larger. Therefore, a plurality of pairs of current value and discharge time may be set to determine the possibility of disconnection determination in multiple stages.

FIG. 6 illustrates a functional block diagram of the control unit 22 that executes the second disconnection determination permission flow. Compared with the functional block diagram of FIG. 4, a second timer 58 is added in addition to the timer 40 (first timer).

The current determination unit 52 also stores a first current threshold value Ib_th1 and a second current threshold value Ib_th2 as threshold values for large current discharge. Further, the discharge time determination unit 54 stores a first threshold time t_th1 and a second threshold time t_th2. The magnitude relationship between these thresholds is Ib_th1>Ib_th2 and t_th1<t_th2.

FIG. 7 illustrates the second disconnection determination permission flow. Similar to the flow of FIG. 5, when the start button (not shown) in the vehicle is turned on, the flow of FIG. 7 is activated. The discharge time t at the start of the flow is set to the initial value t=0. The flow of FIG. 7 is terminated by turning off the start button.

The current determination unit 52 receives an ON/OFF command for the EV traveling mode from a host controller (not shown) of the vehicle and determines whether the vehicle is in the EV traveling mode implementation (S30). When the EV traveling mode is not executed, the first discharge time t1 and the second discharge time t2, which are the durations of the large current discharge state, are reset to 0 (S52, S54). Further, the execution of the disconnection determination (determination of presence or absence of disconnection) is suspended (S50). If the vehicle is an electric vehicle, step S30 is omitted.

When the EV traveling mode is being performed, the current determination unit 52 acquires the current Ib of the battery module 10 from the current sensor 42 and determines whether or not the current Ib is the first current threshold value Ib_th1 or more (S32).

When the current Ib is equal to or greater than the first current threshold value Ib_th1, the current determination unit 52 outputs a count command to start measuring the duration of the large current discharge state to the timer 40 (first timer). As a result, the discharge time t1 is counted up (S34).

The discharge time determination unit 54 determines whether the discharge time t1 counted by the timer 40 is equal to or longer than the first threshold time t_th1 (S36). If the discharge time t1 is less than the first threshold time t_th1, the disconnection determination unit 56 is made to suspend the execution of the disconnection determination (disconnection presence determination) (S50). When the discharge time t1 is the first threshold time t_th1 or more, the discharge time determination unit 54 permits the disconnection determination unit 56 to execute the disconnection determination (S38).

Returning to step S32, when the current Ib is less than the first current threshold value Ib_th1, the count t1 of the timer 40 is reset to 0 (S40). Further, the current determination unit 52 causes the current Ib to be the second current threshold value Ib_th2 or more. It is determined whether or not (S42). When the current Ib is less than the second current threshold value Ib_th2, the count t2 of the second timer 58 is reset to 0 (S48). Further, the execution of the disconnection determination is suspended (S50).

When the current Ib is greater than or equal to the second current threshold value Ib_th2 in step S42, the current determination unit 52 outputs to the second timer 58 a count command to start measuring the duration of the large current discharge state. As a result, the discharge time t2 is counted up (S44).

The discharge time determination unit 54 determines whether the discharge time t2 counted by the second timer 58 is equal to or greater than the second threshold time t_th2 (S46). If the discharge time t2 is less than the second threshold time t_th2, the execution of the disconnection determination is suspended (S50). When the discharge time t2 is equal to or longer than the second threshold time t_th2, the discharge time determination unit 54 permits the disconnection determination unit 56 to execute the disconnection determination (S38).

<Third disconnection determination permission flow>
In the flows of FIGS. 5 and 7, if the current Ib falls below the current threshold value (Ib_th, Ib_th1, Ib_th2) even once during the discharge time measurement, the execution of the disconnection determination is suspended. In order to increase the chances of executing the disconnection determination, whether or not to execute the disconnection determination may be determined based on the integrated current ΣIb instead of the current Ib.

FIG. 8 illustrates a functional block diagram of the control unit 22 that executes the third disconnection determination permission flow. Compared to the functional block diagram of FIG. 4, a current accumulating unit 60 is provided in the previous stage of the current determining unit 52. In addition, a third timer 62 and a fourth timer 64 are provided.

FIG. 9 illustrates the third disconnection determination permission flow. The flow in FIG. 9 is activated in response to an operation of turning on a start button (not shown) in the vehicle. The discharge time t at the time of starting the flow, the current integration time t_ΣIb, and the current integration value ΣIb are set to the initial value 0. Further, the flow of FIG. 9 is terminated by turning off the start button.

The current integration unit 60 determines whether the vehicle is in the EV traveling mode (S60). When the EV traveling mode is not executed, the discharge time t, the current integration time t_ΣIb, and the current integration value ΣIb are all reset to 0 (S80, S82, S84). Further, the execution of disconnection determination (disconnection presence/absence determination) is suspended (S86). If the vehicle is an electric vehicle, step S60 is omitted.

When the EV traveling mode is being executed in step S60, the current integration unit 60 outputs a count command to start counting the current integration time t_ΣIb to the third timer 62. As a result, the current integration time t_ΣIb is counted up (S62). Further, the current integration unit 60 adds the current current Ib to the previous value of the current integration value ΣIb (S64).

The current determination unit 52 determines whether the current integration time t_ΣIb by the third timer 62 is equal to or longer than the predetermined threshold time t_ΣIb_th (S66). When the current integration time t_ΣIb has not reached the threshold time t_ΣIb_th, the execution of the disconnection determination is suspended (S86).

When the integrated current time t_ΣIb is equal to or longer than the threshold time t_ΣIb_th, the current determination unit 52 determines whether or not the integrated current value ΣIb is equal to or larger than a predetermined integrated current threshold ΣIb_th (S68). When the integrated current value ΣIb is less than the integrated current threshold value ΣIb_th, the discharge time t is reset to 0 (S88), and the process proceeds to step S72.

When the integrated current value ΣIb is greater than or equal to the integrated current threshold value ΣIb_th, the current determination unit 52 outputs a count command to the fourth timer 64 to start counting the discharge time t. As a result, the discharge time t, which is the duration of the large current discharge state, is counted up (S70), and then the current integration time t_ΣIb and the current integration value ΣIb are reset to 0 (S72, S74).

The discharge time determination unit 54 determines whether the discharge time t counted by the fourth timer 64 is the threshold time t_th or more (S76). If the discharge time t is less than the threshold time t_th, the execution of the disconnection determination (disconnection presence determination) is suspended (S86). If the discharge time t is equal to or longer than the threshold time t_th, execution of the disconnection determination is permitted (S78).

As described above, in the third disconnection determination permission flow, the integrated current value ΣIb is used instead of the current value Ib. As a result, as shown in FIG. 10, even if the current value Ib falls below the current threshold value Ib_th set in the first disconnection determination permission flow during the current integration time t_ΣIb, the current integration when the threshold time t_ΣIb_th is reached. If the value ΣIb is greater than or equal to the integrated current threshold value ΣIb_th, the discharge time t is not reset. As a result, it is possible to obtain more opportunities to execute the disconnection determination.

10 battery module, 22 control unit, 24 voltage sensor unit, 32 battery cell, 33 battery pack, 40 timer (first timer), 42 current sensor, 52 current determination unit, 54 discharge time determination unit, 56 disconnection determination unit, 58 2nd timer, 60 electric current integration part, 62 3rd timer, 64 4th timer.

Claims (1)

A disconnection determination unit that determines the presence or absence of disconnection of the battery pack based on the internal resistance of the battery pack in which a plurality of battery cells are connected in parallel,
A current determination unit that determines whether or not the discharge current of the battery pack is in a high current discharge state that is equal to or greater than a predetermined current threshold value,
A timer for measuring the duration of the high current discharge state,
When the duration of the high-current discharge state is equal to or more than a predetermined threshold time, a discharge time determination unit that permits the disconnection determination unit to perform disconnection presence/absence determination of the battery pack,
A disconnection detection system for a battery pack, comprising: