JP2013192389A - Discharge control system and discharge control method for battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more properly discharge a battery pack as a whole when a plurality of lithium-ion cells are used as the battery pack by being connected in series.SOLUTION: A discharge control system for a battery pack comprises: voltmeters 4 for monitoring voltages of respective cells 2; step-down converters 3 which are arranged at the respective cells 2 and are capable of individually stepping down the voltages of the cells 2; and a controller 5 for controlling the respective step-down converters 3 on the basis of the voltages of the respective cells 2. When voltages of some of the cells 2 are lower than a first predetermined voltage V, the controller 5 controls the step-down converters 3 so that the voltages of the some of the cells 2 are stepped down.

Description

  The present invention relates to an assembled battery discharge control system and a discharge control method for controlling discharge of an assembled battery in which a plurality of secondary batteries are connected in series.

  As secondary batteries, lithium ion secondary batteries (lithium ion cells) and lead acid batteries are known. For example, lithium ion cells have advantages such as high energy density and low self-discharge amount, and are widely used as automobile storage batteries, storage batteries for electric / electronic devices, and the like. Here, in order to obtain a voltage according to the purpose of use, a plurality of lithium ion cells (hereinafter simply referred to as “cells”) are connected in series to form a lithium ion assembled battery (hereinafter simply referred to as “assembled battery”). There is a case. When used as an assembled battery in this way, charging is performed on the entire assembled battery, and the charging voltage of each cell cannot be controlled, so the charging voltage between series cells (between cells in the same assembled battery) Variation, a cell having a high voltage, that is, a cell having a high SOC (state of charge) and a cell having a low voltage, that is, a cell having a low SOC are mixed. In addition, due to variations in manufacturing of the cells, installation environment during operation, etc., the deterioration state may vary between the series cells, and the upper limit value of the SOC may be different.

  Moreover, in the assembled battery comprised by the cell, when the cell which comprises an assembled battery reaches even a discharge end voltage, it is necessary to stop discharge of the whole assembled battery in order to maintain safety | security. Specifically, for example, as shown in FIG. 8, at the time of discharging a battery pack 220 configured by connecting a plurality of cells 210, the controller 230 monitors the cell voltage of each cell 210, and the cell voltage is a predetermined voltage. When there is a lower cell 210, the switch 240 is turned off (opened) so that the discharge from the assembled battery 220 is stopped.

  For this reason, at the time of discharge, the cell with low SOC reaches the discharge end voltage earlier than the other cells, so that the entire assembled battery stops discharging. That is, a cell with a low SOC becomes a bottleneck, and the entire battery pack stops discharging even though other cells can be discharged, so the discharge capacity of the battery pack decreases. If the use of the cells with such variations is left unattended, there is a problem that the discharge capacity of the assembled battery is lowered and becomes inefficient, and the use of energy becomes inefficient.

  Such a problem is particularly noticeable in a high voltage direct current (HVDC) configured by connecting a large number of cells (about 100), an uninterruptible power supply (UPS), and the like.

  In order to solve the above problems, when charging an assembled battery having a variation in voltage, for example, an assembled battery of a lithium ion secondary battery and an assembled battery that can safely charge the assembled battery and reduce the weight of the assembled battery. A technique related to a charging method is known (for example, see Patent Document 1). In this technology, a switch is installed in a discharge line that discharges to a load in an assembled battery configured by connecting a plurality of single cells in series, and the voltage of each cell in the assembled battery is monitored. A battery monitoring control unit having a function of sending a control signal for opening and closing the switch according to the voltage is provided, and charging is performed independently for each cell by the charging wiring connected to the positive and negative terminals of each cell. That's it.

JP 2007-166747 A

  However, in the technique of Patent Document 1, although each cell can be charged uniformly to the fully charged state (upper limit value of SOC) by charging each cell, there are variations in manufacturing of the cell, Due to differences in installation environment, etc., the degradation state varies among the series cells, and a difference occurs in the upper limit value of the SOC. For this reason, at the time of discharging, the SOC of the cell whose deterioration has progressed is depleted earlier than the others, so that the discharge capacity of the entire assembled battery is restricted and the use of energy becomes inefficient.

  Therefore, the present invention eliminates the variation in SOC caused by the variation in charging voltage when using a plurality of cells in series as an assembled battery, and causes the cells in the assembled battery to be in a deteriorated state (upper limit value of SOC). Even when variation occurs, the battery pack discharge control system and the discharge enable to discharge the battery pack more efficiently by avoiding a decrease in the discharge capacity of the battery pack as a whole due to the progress of deterioration. An object is to provide a control method.

  In order to achieve the above object, the invention according to claim 1 is an assembled battery discharge control system for controlling discharge of an assembled battery in which a plurality of secondary batteries are connected in series, wherein each of the secondary batteries Monitoring means for monitoring the voltage; voltage reducing means disposed in each secondary battery and capable of individually lowering the voltage of the secondary battery; and controlling each voltage reducing means based on the voltage of each secondary battery And a control unit configured to reduce the voltage of the part of the secondary batteries when the voltage of the part of the secondary batteries is lower than the first predetermined voltage. The battery pack discharge control system is characterized by controlling the means.

  According to the present invention, when the voltage of some of the secondary batteries is lower than the first predetermined voltage, the step-down means is controlled by the control means so as to step down the voltage of the some secondary batteries. .

  According to a second aspect of the present invention, in the assembled battery charge control system according to the first aspect, the control means is configured such that the voltage of the other secondary battery is lower than the voltage of the partial secondary battery. In this case, the step-down means is controlled to step down the voltage of the other secondary battery.

  According to a third aspect of the present invention, in the battery pack discharge control system according to the first or second aspect, the first predetermined voltage is a voltage drop in a final discharge state of the secondary battery. It is characterized in that it is set to a value equal to or higher than the discharge end voltage in the early voltage range.

  According to a fourth aspect of the present invention, in the assembled battery charge control system according to any one of the first to third aspects, the control means is configured such that the voltage of at least one of the secondary batteries is the end of discharge. When the voltage is lower than the voltage, the step-down unit is controlled so as to stop the step-down of the voltage of all the secondary batteries, and the output of the step-down unit is disconnected.

  The invention according to claim 5 is an assembled battery discharge control method for controlling discharge of an assembled battery in which a plurality of secondary batteries are connected in series, wherein the voltage of the secondary battery can be individually stepped down. Means is provided in each secondary battery, the voltage of each secondary battery is monitored, and when the voltage of some of the secondary batteries is lower than the first predetermined voltage, the secondary battery The battery pack discharge control method is characterized in that the step-down means is controlled so that the voltage of the battery is stepped down.

  According to a sixth aspect of the present invention, in the battery pack charging control method according to the fifth aspect, when the voltage of the other secondary battery is lower than the voltage of the partial secondary battery, The step-down means is controlled to step down the voltage of the secondary battery.

  A seventh aspect of the present invention is the battery pack discharge control method according to any one of the fifth and sixth aspects, wherein the first predetermined voltage is reduced in the final discharge state of the secondary battery. In the early voltage range, it is set to a value equal to or higher than the discharge end voltage.

  The invention according to claim 8 is the battery pack charge control method according to any one of claims 4 and 5, wherein the voltage of the at least one secondary battery is lower than a discharge end voltage. In this case, the step-down means is controlled to stop the step-down of the voltages of all the secondary batteries, and the output of the step-down means is disconnected.

  According to the first or fifth aspect of the present invention, since the load is constant power, when the voltage of some of the secondary batteries is lower than the first predetermined voltage, the voltage of the some of the secondary batteries By reducing the voltage, the discharge currents of the other secondary batteries become relatively larger than the discharge currents of the partial secondary batteries. Thereby, the discharge current of some secondary batteries decreases, and the voltage drop of some secondary batteries becomes gentle. Therefore, since the time until the discharge end voltage is reached is increased, the time until the entire assembled battery reaches the discharge end voltage can also be increased. For this reason, the discharge of some secondary batteries with a low voltage is suppressed, the discharge of other secondary batteries with a high voltage is promoted, the voltage drops to an appropriate value, or the voltage of each secondary battery varies. Or the secondary battery can be discharged more appropriately. As a result, the variation in the SOC due to the variation in the charging voltage is eliminated, and even if the variation in the deterioration state (the upper limit value of the SOC) occurs in the cells in the assembled battery, the combination of the cells in which the deterioration has progressed. A reduction in the discharge capacity of the entire battery can be avoided, and the assembled battery can be discharged more efficiently.

  According to the invention of claim 2 or 6, when the voltage of the other secondary battery is lower than the voltage of some of the secondary batteries, the voltage of the other secondary battery is stepped down. The voltage step-down of the other secondary battery can be stopped at the timing when the variation is eliminated. Therefore, since it is not necessary to discharge other secondary batteries whose voltage variation has been reduced by eliminating the voltage variation, it is possible to suppress the discharge current by stepping down, and the entire assembled battery can be suppressed. It is possible to lengthen the time until the discharge end voltage is reached. Moreover, useless discharge current is reduced, which is economical. As a result, even when the voltage of another secondary battery is stepped down to eliminate the voltage variation, the battery pack can be discharged more efficiently by stopping the step-down when the voltage variation is resolved. Is possible.

  According to the invention described in claim 3 or 7, since the first predetermined voltage is set in a voltage region in which the voltage drop is early in the end-of-discharge state of the secondary battery, the SOC difference is the voltage difference. Thus, the SOC can be easily adjusted by detecting the voltage at the end of discharge that clearly appears.

  According to the invention described in claim 4 or 8, when the voltage of any one of the secondary batteries becomes the discharge end voltage, the step-down of the voltages of all the secondary batteries is stopped, and the output of the step-down means Since the discharge from the assembled battery can be stopped, the secondary battery can be prevented from being deteriorated due to overdischarge and kept safe.

It is an example of the schematic block diagram which shows the state which applied the discharge control system of the lithium ion assembled battery which concerns on embodiment of this invention to the DC power supply system. It is a flowchart which shows the process and effect | action of the discharge mode of the system of FIG. It is a figure which shows the cell voltage, assembled battery voltage, and discharge current before step-down operation start in the system of FIG. FIG. 2 is a diagram illustrating a cell voltage, an assembled battery voltage, and a discharge current immediately after the step-down operation is started in the system of FIG. 1. It is a figure which shows the cell voltage at the time of discharge at the time of discharge in the system of FIG. It is a figure which shows the cell voltage at the time of discharge at the time of discharge in the system of FIG. It is a figure which expands and shows the cell voltage shown in FIG. It is an example of the schematic block diagram which shows the state which applied the conventional assembled battery to the DC power supply system.

  The present invention will be described below based on the illustrated embodiments.

  FIG. 1 is an example of a schematic configuration diagram showing a state in which a discharge control system (hereinafter simply referred to as “discharge control system”) 1 for a lithium ion battery pack according to an embodiment of the present invention is applied to a DC power supply system. The discharge control system 1 is a system that controls the discharge of a battery pack 20 in which a plurality of cells 2 (for example, 12 cells) that are unit cells are connected in series. In this embodiment, the cell 2 has a rated voltage of 3.7 [V] (full charge voltage 4.1 [V]), and 12 cells 2 are connected in series to form an assembled battery having a rated voltage of 48 [V]. 20 is constituted.

  Here, the AC / DC converter 101 and the load facility 102 are connected, and in a normal state, power from a commercial power source (not shown) is converted into DC by the AC / DC converter 101 and supplied to the load facility 102. It has come to be. In the event of a power failure, power is supplied from the assembled battery 20 to the load facility 102. In this embodiment, it is assumed that the load facility 102 has a constant power of Q [W].

  The discharge control system 1 mainly includes a step-down converter (step-down means) 3 and a voltmeter (monitoring means) 4 provided in each cell 2 and a controller (control means) 5. Each step-down converter 3 and each voltmeter 4 are connected to the controller 5 so as to be able to communicate (data transmission).

  The step-down converter 3 is a DC / DC converter connected in parallel to the corresponding cell 2 and capable of individually stepping down the output voltage of the cell 2, and is controlled by a controller 5 described later. When the step-down converter 3 receives the step-down signal from the controller 5, the step-down converter 3 steps down the output voltage of the corresponding cell 2 by the step-down circuit and outputs it. Further, in a normal state (a state where a step-down signal is not received from the controller 5), the input and output of the converter are in a direct connection state so that the step-down circuit does not operate, and the output of the corresponding cell 2 The voltage is output as it is. Further, in the charged state, the input and output of the converter are in a direct connection state, so that the step-down circuit does not operate.

  The voltmeter 4 is connected in parallel to the corresponding cell 2, and always measures and monitors the voltage of the cell 2, not only during charging or discharging, and transmits the measurement result to the controller 5 in real time. Moreover, although not shown in figure, each is equipped with the measuring device which measures the total voltage and discharge current of the assembled battery 20, and the temperature of each cell 2, and the measurement result from these measuring devices is transmitted to the controller 5 in real time. It has become so.

The controller 5 is a device that controls each step-down converter 3 based on the measurement result from each voltmeter 4, and performs processing so as to obtain the operation and operation shown in FIG. The controller 5 is in a discharged state, when the output voltage of some cells 2 is lower than the first predetermined voltage V _1, the step-down so that the output voltage of the cell 2 (a part of the cell 2) is a step-down The converter 3 is controlled. As a result, the output voltage of some of the cells 2 is stepped down by the step-down converter 3 and output from the step-down converter 3. On the other hand, the output voltage of the other cells 2 is output from the step-down converter 3 as it is without being stepped down. Here, the first predetermined voltage _{V 1} was, and in this embodiment for example 3.2 [V]. Some of the cells 2 are one or more.

The controller 5 is, as specifically shown in FIG. 2, first, whether the discharge end voltage V _E less than the cell 2 exists, i.e., the output voltage (cell voltage) of discharge end voltage V _E following cell 2 is determined (step S1). In this case, it is because the assembled battery 20 needs to stop discharge. Here, the end-of-discharge voltage _VE is, for example, 3.0 [V] in this embodiment. When the cells 2 than the discharge end voltage V _E is determined to be present ( "YES"), the process proceeds to step S10. If the cell 2 than the discharge end voltage V _E is determined not to exist ( "NO") determines whether the output voltage of the cell 2 is a first predetermined voltages V ₁ following cell 2 exists Is determined (step S2).

When it is determined in step S2 that the cell 2 having the _first predetermined voltage V1 or less does not exist (in the case of “NO”), the process proceeds to step S3, whether or not the output of the rectifier 101 is recovered, Then, it is determined whether or not the charging current is zero or more (step S3). When it is determined that the output of the rectifier 101 has recovered (in the case of “YES”), the processing of this task is terminated. If it is determined that the output of the rectifier 101 has not recovered (in the case of “NO”), the process returns to step S1 and the process is repeated.

If it is determined in step S2 that the cell 2 having the _first predetermined voltage V1 or less exists ("YES"), the process proceeds to step S4. Then, the step-down converter 3 of the cell 2 having the _first predetermined voltage V1 or less is controlled to perform a step-down operation (step S4).

  Then, it is determined whether or not the step-down operation start condition is satisfied (step S5). Here, the start condition of the step-down operation is that the cell voltage of the cells (other cells) 2 that are not stepped down is equal to or less than the minimum value of the cell voltages of the cells that are stepped down (some cells) 2. It is determined that the cell (other cells) 2 that has not been stepped down is “step-down operation start”. In this case, if other cells 2 whose cell voltages are lower than some of the cells 2 are not stepped down, the other cells 2 continue to have an increased discharge current and quickly reach the discharge end voltage. Since there is a risk of reaching, the step-down is started when the value becomes the minimum value or less.

If it is determined in step S5 that the step-down operation start condition is not satisfied (in the case of “NO”), the process waits until the step-down operation start condition is satisfied. At this time, the other cells 2 still have a high discharge surplus and promote discharge. At this time, whether the discharge end voltage V _E less than the cell 2 exists, the output of the rectifier 101 is constantly determines whether or not recovered, the cell 2 than the discharge end voltage V _E is present If it is determined, the process proceeds to step S10, and if it is determined that the output of the rectifier 101 has been recovered, the process proceeds to step S8. This is to prevent overdischarge of the cell 2 and resume charging when the rectifier 101 is restored.

  In step S5, when it is determined that the step-down operation start condition is satisfied (in the case of “YES”), the target cell 2 from among other cells 2, that is, the cell voltage of some cells 2 or less The detected cell 2 is detected, and the step-down converter 3 is controlled to start the step-down operation of the cell 2 (step S6).

Then, it is determined whether or not the output of the rectifier 101 has been recovered, that is, whether or not the charging current is zero or more (step S7). When it is determined that the output of the rectifier 101 has recovered (in the case of “YES”), the step-down converter 3 is controlled to stop the step-down operation of the step-down converters 3 of all the cells 2 and to “directly connect” (step S8). ), The process of this task is terminated. If the output of the rectifier 101 is determined not to be recovered (in the case of "NO"), the discharge end voltage V _E less than the cell 2 determines whether there (step S9). ( "NO") if the cell 2 than the discharge end voltage V _E is determined not to exist, the process returns to step S5. If the cell 2 than the discharge end voltage V _E is determined to be present (in the case of "YES"), stops the step-down operation of the step-down converter 3 of all cells 2, "Output separating" (step S10). Here, “output disconnection” may disconnect the output of the step-down converter 3 or may open a switch of the assembled battery 20 (for example, corresponding to the switch 240 of the assembled battery 220 shown in FIG. 8).

  Then, it is determined whether or not the output of the rectifier 101 has been recovered, that is, whether or not the charging current is greater than or equal to zero (step S11). When it is determined that the output of the rectifier 101 has not recovered (in the case of “NO”), the process waits until the output of the rectifier 101 recovers. If it is determined that the output of the rectifier 101 has been restored (in the case of “YES”), “output separation” is canceled (step S12), and the processing of this task ends.

  By performing the processing in this manner, when the predetermined cell 2 is stepped down and the voltage variation is eliminated, the step-down is stopped. Here, if the voltage variation is not eliminated even after the voltage is lowered for a predetermined time, an alarm may be output and the discharge may be stopped. Here, the alarm is output by turning on an alarm lamp (not shown) of the controller 5 or notifying a computer of the management center. Further, the predetermined time is a time estimated to have a possibility of an abnormality of the step-down converter 3, an internal abnormality of the cell 2, an abnormal connection between the cells 2, and the like, and is set according to the characteristics and capacity of the cell 2.

  Next, an operation of the discharge control system 1 having such a configuration, a discharge control method by the discharge control system 1 and the like will be described. Here, in the charging state, the input and output of each step-down converter 3 are directly connected, and control is performed so that the step-down circuit does not operate. When the supply of power from the commercial power supply is stopped due to a power failure or the like, power is supplied from the assembled battery 20 to the load facility 102 and the discharge control system 1 is activated.

  First, the voltage of each cell 2 is constantly monitored by the voltmeter 4 and the measurement result is transmitted to the controller 5 in real time. Based on the voltage of each cell 2, the above control is performed.

Specifically, for example, first, reduced to 3 to 5 as shown in the cell ₂ 1 voltage of the cell _{2 1} in the _{~ 2 12} a first predetermined voltage _V 1 (3.2 _[V]) The case will be described.

Figure 3 shows the step-down operation before the start of the step-down converter 3 during charging of the battery pack 20 (time t ₁ before). At this time, the output voltage of the cell _{2 1} is 3.2 [V], the output voltage of the other cells _{2 2-2 12} is 3.5 [V], one each buck converter ₃ 1 _{to 3 12} Is not operating, the output voltages of the cells 2 ₁ to 2 ₁₂ are output as they are. In this case, the total voltage of the assembled battery 20 is 41.7 [V], and the discharge current is I _1T [A]. Here, the discharge current I _1T [A] is calculated by Q [W] ÷ 41.7 [V].

Then, the controller 5, at time _{t 1} shown in FIG. 5, the voltage of the cell _{2 1} is determined to be lower than the first predetermined voltage _{V 1 (3.2 [V])} ( step S2), the cell _{2 1} buck converter 3 ₁ is controlled so that the voltage of the buck (step S4). Specifically, the step-down signal is transmitted to the step-down converter 3 _1.

Figure 4 shows the immediately following step-down operation start of the step-down converter 3 (immediately after time t _1). At this time, since the step-down converters 3 _{2 to} 3 ₁₂ are not operated in the other cells 2 ₂ to 2 ₁₂ , the output voltage 3.4 [V] is output as it is. On the other hand, some of the cells _{2 1} the output voltage is 3.3 [V], is stepped down by the step-down converter 3 becomes 3.0 [V]. Here, the voltage of the cell _{2 1} is higher than before the start down operation of the step-down converter 3 is to the cell discharge current _I 21 [A] is reduced _(I 11 _{<I 21).} The cell discharge current _I 22 _{~I 212} of the other cells ₂ 2-2 ₁₂ [A] is equal to the discharge current _I 2T [A] Since the cell ₂ 2-2 ₁₂ is not stepped down is directly connected. That is, in the other cells 2 _{2 to} 2 ₁₂ , the voltage decreases slightly (3.4 V) as the discharge current I _2T [A] increases, but the discharge current I _2T is directly connected to the step-down converter 3. It becomes equal to [A]. In this case, the total voltage of the assembled battery 20 is 40.4 [V], and the discharge current I _2T [A] is calculated by Q [W] ÷ 40.4 [V]. Furthermore, some of the cells _{2 1} cell discharge current _I 21 [A] is the cell voltage, output voltage, the discharge _{current, 3.0 [V] × I 2T} [A] ÷ 3.3 [V] ÷ ( It is calculated by the efficiency of the step-down converter 3 and is stepped down, so that I ₂₁ <I _2n .

Thereafter, in a while the discharge state from the assembled battery 20 is continued, since the cell discharge current is I _{21 <I 2n,} with cells 2 ₁ discharge is inhibited, the other cells 2 _{2-2 12} discharges are promoted. As a result, than the cell discharge current _{I 21} of the cell _{2 1,} cell discharge current _{I 2n} of the other cells _{2 2-2 12} that is large, with the cells _{2 1} discharge is inhibited, the other cells The discharge of 2 _{2 to} 2 ₁₂ is promoted. Thus, the drop of the cell 2 ₁ voltage is suppressed, since the descent of the other cells 2 _{2-2 12} voltage is facilitated, the variation of each cell 2 ₁ to 2 ₁₂ of voltage is suppressed.

Here, explaining the changes of the cells ₂ 1 _{to 2 12} of the voltage in the step-down operation of the step-down converter _{3 1.} First, to indicate the 5, a case where step-down the cell 2 ₁ voltage reaches the early discharge end voltage V _E than the voltage of the cell 2 _{2-2 12.} In this case, at time _{t 2, the} it is determined that the voltage of the cell _{2 1} reaches the discharge end voltage _{V E (3.0 [V])} ( step S9), and the step-down operation of the cell _{2 1} voltage buck converter 3 ₁ is controlled so as to stop to "output separating" (step S10). Then, at time t _3, the output of the rectifier 101 is determined to be a chargeable state restored (step S11), and "Output disconnection" is released (step S12).

Next, the 6 and 7, at the time of step-down operation of the step-down converter 3 ₁ (after time t _1), when the voltage of the cell 2 ₂ is the cell 2 ₁ voltage below with drops sharply is there. In this case At time t _4, the cell 2 ₂ voltage is lower than the voltage of the cell 2 _1, i.e., it is determined that the voltage has reversed (step S5), and to the cell 2 ₂ voltage becomes "buck" buck converter _{3 2} is controlled (step S6). At this time, the voltage of the cell 2 ₁ is continued step-down is. Then, at time t _5, the cells 2 ₁ voltage is determined to reach the discharge end voltage V _E (step S9), and stops the step-down operation of the voltage step-down of all the cells 2 ₁ to 2 ₁₂ Thus, step-down converters 3 _{1 to} 3 ₁₂ are controlled so as to “cut off the output” (step S10). Then, at time t _6, the output of the rectifier 101 is determined to be a chargeable state restored (step S11), and "Output disconnection" is released (step S12).

Next, the case where the voltages of the plurality of cells 2 _{11 and} 2 ₁₂ among the cells 2 _{1 to} 2 ₁₂ are reduced to the _first predetermined voltage V ₁ will be described. In this case, the controller 5 determines that the voltages of the plurality of cells 2 and the cells 2 _{11 and} 2 ₁₂ are lower than the first predetermined voltage V ₁ (step S2), and the voltages of the cells 2 _{11 and} 2 ₁₂ are stepped down. Thus, step-down converters 3 ₁₁ , 3 ₁₂ are controlled (step S 4). In this case, in step S5, among the cells 2 ₁ to 2 ₁₀ that have not been stepped down, the cell whose voltage is equal to or lower than the minimum voltage of the cells 2 _{11 and} 2 ₁₂ that have been stepped down is determined to be “step-down”. The For example, the voltage of the cell _{2 10,} cell _{2 11, 2 12} the minimum value of the voltage when it is determined that (cell _{2 12} voltage) or less, the step-down converter the voltage of the cell _{2 10} so that the "buck" 3 ₁₀ is controlled (step S6).

As described above, according to the discharge control system 1 and the discharge control method, since the load facility 102 has constant power (Q [W]), the voltages of some of the cells 2 are higher than the first predetermined voltage V ₁ . If the voltage is lower, the voltages of some cells 2 are stepped down, so that the discharge currents of other cells 2 are relatively larger than the discharge currents of some cells 2. As a result, the discharge current of some of the cells 2 decreases, and the voltage drop of some of the cells 2 becomes gentle. Therefore, since the time until the discharge end voltage is reached can be lengthened, the time until the entire assembled battery 20 reaches the discharge end voltage can also be lengthened. For this reason, the discharge of some of the cells 2 having a low voltage is suppressed, the discharge of other cells 2 having a high voltage is promoted, the voltage drops to an appropriate value, or the variation in the voltage of each cell 2 converges. Thus, each cell 2 can be discharged more appropriately. As a result, even if there is a difference in the upper limit value of the SOC due to variations in the deteriorated state or variations in the deteriorated state (upper limit value of the SOC), the assembly by the lithium ion cell in which the deterioration has progressed A reduction in the discharge capacity of the entire battery 20 can be avoided, and the assembled battery 20 can be discharged more efficiently. That is, since the backup time can be extended, the stability and quality of the assembled battery 20 can be improved.

  In addition, when the voltages of other cells 2 are lower than the voltages of some of the cells 2, the voltages of the other cells 2 are stepped down. Therefore, the voltage of the other cells 2 is reduced at the timing when the voltage variation is eliminated. The step-down can be stopped. Therefore, since it is not necessary to discharge the other cells 2 in which the voltage variation is eliminated and the voltage is reduced, it is possible to suppress the discharge current by stepping down, and the assembled battery 20 as a whole. It is possible to lengthen the time until the discharge end voltage is reached. Moreover, useless discharge current is reduced, which is economical. As a result, even when the voltage of other cells 2 is stepped down to eliminate the voltage variation, when the voltage variation is resolved, the step-down is stopped to discharge the assembled battery 20 more efficiently. Is possible.

  In addition, since the first predetermined voltage V1 is set in a voltage region in which the voltage drop is early in the end-of-discharge state of the cell 2, the end-of-discharge voltage that clearly shows the difference in SOC as the voltage difference is detected. By doing so, the SOC can be adjusted easily.

  Further, when the voltage of any one of the cells 2 becomes the discharge end voltage, the voltage step-down of all the other cells 2 is stopped and the output of the step-down converter 3 is disconnected, that is, the discharge from the assembled battery 20 Therefore, it is possible to prevent the secondary battery from being deteriorated due to overdischarge and keep it safe.

  Furthermore, if the abnormal voltage of the cell 2 or the abnormal variation of the voltage between the cells 2 is not solved even after the discharge in the state where the discharge current of the other cells 2 is increased for a predetermined time, an alarm is issued. Is output and the discharge is stopped, so that a prompt and appropriate response can be made. That is, in such a case, there is a possibility that an abnormality such as an internal short circuit or connection failure may exist in the cell 2, and an alarm output or discharge stop is performed, so that quick and proper inspection, cell replacement, etc. are possible. At the same time, it becomes possible to avoid damage to the cell 2 or abnormal temperature rise. On the other hand, when the abnormal voltage of the cell 2 or the abnormal variation of the voltage between the cells 2 is resolved within a predetermined time, the step-down operation is terminated, so that unnecessary discharge of the cell 2 is prevented. Thus, it is possible to properly maintain the state of charge of the entire assembled battery 20.

  Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there is a design change or the like without departing from the gist of the present invention, Included in the invention. For example, in the above-described embodiment, the case of having one set of assembled batteries 20 has been described, but the present invention can also be applied to the case where a plurality of assembled batteries 20 are connected in parallel. In this case, the discharge control system 1 as described above is provided for each assembled battery 20. Moreover, not only the lithium ion cell 2, but in order to eliminate the variation in the discharge state between the series cells, it can be widely applied to secondary batteries in general. Furthermore, although the case where the discharge control system 1 is applied to a DC power supply system has been described, the present invention can also be applied to an uninterruptible power supply (UPS), a storage battery for automobiles, and the like.

  Of course, the number of lithium ion cells is not limited to twelve, and a discharge control system is also used for high-voltage direct current or uninterruptible power supply devices configured by connecting a large number of lithium ion cells (about 100). 1 can be applied.

Further, in the above embodiment, the first predetermined voltage V _{1 is set} to 3.2 [V]. However, the first predetermined voltage V ₁ is set to the threshold value V _{X at} which the voltage variation of the cell 2 occurs. May be. Here, the threshold value V _X is a value set according to the characteristics, capacity, etc. of the cell 2 or the assembled battery 20, and is a voltage at which the voltage drop of the cell 2 tends to be accelerated at the end of discharge. It is set to less than [V] and the discharge end voltage of 3.0 [V] or more.

1 Lithium ion battery discharge control system 2 Lithium ion cell (cell, secondary battery)
20 Lithium ion battery pack (battery pack)
3 Step-down converter (step-down means)
4 Voltmeter (monitoring means)
5 Controller (control means)
V ₁ first predetermined voltage V ₂ second predetermined voltage V _E discharge end voltage V _A average voltage

Claims (8)

A discharge control system for an assembled battery that controls the discharge of the assembled battery in which a plurality of secondary batteries are connected in series,
Monitoring means for monitoring the voltage of each secondary battery;
Step-down means arranged in each secondary battery and capable of stepping down the voltage of the secondary battery individually;
Control means for controlling each step-down means based on the voltage of each secondary battery;
With
The control means controls the step-down means so that the voltages of some of the secondary batteries are stepped down when the voltages of some of the secondary batteries are lower than a first predetermined voltage;
A discharge control system for an assembled battery. The control means controls the step-down means so as to step down the voltage of the other secondary battery when the voltage of the other secondary battery is lower than the voltage of the partial secondary battery.
The discharge control system for an assembled battery according to claim 1. The first predetermined voltage is set to a value equal to or higher than a discharge end voltage in a voltage region in which a voltage drop is early in the end-of-discharge state of the secondary battery.
The assembled battery discharge control system according to any one of claims 1 and 2. The control means controls the step-down means to stop stepping down to all the secondary batteries when the voltage of at least one of the secondary batteries is lower than a discharge end voltage, and the step-down means The output of
The discharge control system for an assembled battery according to any one of claims 1 to 3. A discharge control method for an assembled battery for controlling discharge of the assembled battery in which a plurality of secondary batteries are connected in series,
A step-down means capable of individually lowering the voltage of the secondary battery is disposed in each secondary battery,
Monitoring the voltage of each secondary battery,
When the voltage of some of the secondary batteries is lower than the first predetermined voltage, the step-down means is controlled so as to step down the voltage of the some secondary batteries;
A discharge control method for an assembled battery. When the voltage of the other secondary battery is lower than the voltage of the partial secondary battery, the step-down means is controlled to step down the voltage of the other secondary battery;
The discharge control method for an assembled battery according to claim 5. The first predetermined voltage is set to a value equal to or higher than a discharge end voltage in a voltage region in which a voltage drop is early in the end-of-discharge state of the secondary battery;
The discharge control method for an assembled battery according to any one of claims 5 and 6. When the voltage of the at least one secondary battery is lower than the end-of-discharge voltage, the step-down means is controlled to stop the step-down of the voltages of all the secondary batteries, and the output of the step-down means is Disconnect,
The discharge control method for an assembled battery according to any one of claims 5 to 7,

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