JP2022113030A - Secondary battery system - Google Patents

Abstract

To suppress an increase in the variation in voltages of a plurality of secondary batteries while suppressing the weight of a charging cable that connects a secondary battery system and a charger in the secondary battery system in which the plurality of secondary batteries are connected in series or in parallel with each other.SOLUTION: During constant-voltage charge control after constant-current charge control, when a current flowing through a plurality of secondary batteries B becomes equal to or less than a switching current which is a value obtained by dividing a constant current by the number of secondary batteries B, the current flowing through the plurality of secondary batteries B is gradually reduced after controlling the operation of a switching circuit such that the plurality of secondary batteries B are connected in parallel with each other and increasing the total current flowing through the plurality of secondary batteries B to a constant current.SELECTED DRAWING: Figure 1

Description

The present invention relates to a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel.

As a secondary battery system, at the start of charging, a plurality of secondary batteries are connected in series and a constant current is passed through each secondary battery. , the current flowing through each secondary battery is gradually reduced, and when the current flowing through each secondary battery falls below the value obtained by dividing the maximum current value that can be supplied to the secondary battery by the number of secondary batteries, each secondary battery In some cases, batteries are connected in parallel and the charging of each secondary battery is terminated when at least one of the currents flowing in each secondary battery becomes equal to or less than the final current. As a related technology, there is Patent Document 1.

However, in the above secondary battery system, the larger the maximum current value that can be supplied to the secondary batteries, the larger the total current that flows through each secondary battery when switching from series connection to parallel connection. It is necessary to increase the rated current of the charging cable that connects the system and the charger, and there is concern about the weight of the charging cable.

Further, in the secondary battery system, when the total current flowing through each secondary battery after switching from series connection to parallel connection is made smaller than a constant current, each secondary battery flows after switching from series connection to parallel connection. Since the current becomes smaller and the period in which the secondary batteries are connected in parallel becomes shorter, there is a possibility that the voltages of the secondary batteries may vary widely.

JP 2008-278635 A

An object according to one aspect of the present invention is to provide a secondary battery system in which a plurality of secondary batteries are connected in series or parallel to each other, while suppressing weight increase of a charging cable connecting the secondary battery system and a charger. It is to suppress an increase in variation in each voltage of the secondary battery.

A secondary battery system according to one aspect of the present invention includes a plurality of secondary batteries, a switching circuit that connects the plurality of secondary batteries in series or parallel connection, and a control unit that controls the operation of the switching circuit. and

The control unit controls the operation of the switching circuit so that the plurality of secondary batteries are connected in parallel to each other during discharging of the plurality of secondary batteries, and controls the operation of the switching circuit during charging of the plurality of secondary batteries. secondary batteries are connected in series with each other, a constant current is passed through the plurality of secondary batteries, and at least one voltage among the voltages of the plurality of secondary batteries is When the voltage reaches the predetermined voltage or higher, the current flowing through the plurality of secondary batteries is gradually reduced while maintaining the at least one voltage at the predetermined voltage, and the current flowing through the plurality of secondary batteries reduces the constant current to the second voltage. When the switching current becomes equal to or less than the value obtained by dividing the number of secondary batteries, the operation of the switching circuit is controlled so that the plurality of secondary batteries are connected in parallel, and the total current flowing through the plurality of secondary batteries is reduced. After increasing the current to the constant current, the current flowing through the plurality of secondary batteries is gradually decreased, and at least one current among the currents flowing through the plurality of secondary batteries becomes equal to or lower than the cut-off current that is smaller than the switching current. Then, the current flowing through the plurality of secondary batteries is made zero.

As a result, it is possible to suppress an increase in the rated current of the charging cable, thereby suppressing an increase in the weight of the charging cable. Moreover, since it is possible to suppress shortening of the period in which the secondary batteries are connected in parallel, it is possible to suppress an increase in variation in the voltages of the secondary batteries.

Further, when the current flowing through the plurality of secondary batteries becomes equal to or less than the switching current during charging of the plurality of secondary batteries, the control unit causes the current flowing through the plurality of secondary batteries to become zero, and then The operation of the switching circuit may be controlled so that the plurality of secondary batteries are connected in parallel with each other, and the total current flowing through the plurality of secondary batteries may be increased to the constant current.

As a result, it is possible to prevent an inrush current from flowing through each secondary battery when the secondary batteries are switched from series connection to parallel connection during charging of each secondary battery.

According to the present invention, in a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel, each secondary battery can An increase in voltage variation can be suppressed.

It is a figure which shows an example of the secondary battery system of embodiment. 4 is a flow chart showing an example of the operation of a control unit; 9 is a flow chart showing a modification of the operation of the control unit; FIG. 3 is a diagram showing an example of the current flowing through a secondary battery being charged and the voltage of the secondary battery being charged; It is a figure which shows the modification of the secondary battery system of embodiment.

Embodiments will be described in detail below with reference to the drawings.
FIG. 1 is a diagram showing an example of a secondary battery system according to an embodiment.

A secondary battery system 1 shown in FIG. 1 is mounted in a vehicle Ve such as an industrial vehicle such as a forklift or an electric vehicle, and supplies electric power to a load Lo such as a driving motor.

Further, the secondary battery system 1 is supplied with electric power through a charging cable Ca from a charger Ch provided outside the vehicle Ve.

The secondary battery system 1 also includes secondary batteries B1 to B4, a positive charge terminal Tip, a negative charge terminal Tin, a positive discharge terminal Top, a negative discharge terminal Ton, and a first output switch. S11 to S14, second output section switches S21 to S24, series connection switches S31 to S33, switches S41 and S42, ammeters Si1 to Si4, storage section 2, and control section 3.

A switching circuit is composed of the first output section switches S11 to S14, the second output section switches S21 to S24, and the series connection switches S31 to S33.
Further, the series connection switches S31 to S33 may be replaced with diodes.

Further, the secondary batteries B1 to B4 are simply referred to as a secondary battery B when not specifically distinguished. Further, when the first output section switches S11 to S14 are not particularly distinguished, they will simply be referred to as the first output section switch S1. Further, when the second output section switches S21 to S24 are not particularly distinguished, they are simply referred to as the second output section switch S2. Further, when the series connection switches S31 to S33 are not particularly distinguished, the series connection switch S3 is simply referred to. Further, when the ammeters Si1 to Si4 are not particularly distinguished, they are simply referred to as ammeters Si.

Also, the number of each of the secondary battery B, the first output switch S1, the second output switch S2, and the ammeter Si is not limited to four. Also, the number of series connection switches S3 is not limited to three. For example, when the number of each of the secondary battery B, the first output switch S1, the second output switch S2, and the ammeter Si is two, and the series connection switch S3 is one, the secondary battery system 1 includes secondary batteries B1 and B2, first output switches S11 and S12, second output switches S21 and S22, ammeters Si1 and Si2, and a series connection switch S31.

The secondary battery B is composed of one or more chargeable/dischargeable batteries (modules) such as lithium ion batteries or nickel-metal hydride batteries.

The first output switch S1, the second output switch S2, the series connection switch S3, and the switches S41 and S42 are semiconductor switches such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or mechanical switches (electromagnetic relays). ).

Ammeter Si<b>1 detects current flowing through secondary battery B<b>1 and sends the detected current to control unit 3 . Ammeter Si<b>2 also detects the current flowing through secondary battery B<b>2 and sends the detected current to control unit 3 . Ammeter Si<b>3 detects current flowing through secondary battery B<b>3 and sends the detected current to control unit 3 . Ammeter Si<b>4 detects current flowing through secondary battery B<b>4 and sends the detected current to control unit 3 .

That is, one terminal of the first output switch S11 is connected to the positive terminal of the secondary battery B1, one terminal of the first output switch S12 is connected to the positive terminal of the secondary battery B2, and the first output switch S13 is connected to the positive terminal of the secondary battery B2. is connected to the positive terminal of the secondary battery B3, and one terminal of the first output switch S14 is connected to the positive terminal of the secondary battery B4. Further, the other terminals of the first output section switches S11 to S14 are connected to each other. Further, the connection point of the other terminal of each of the first output section switches S11 to S14 is connected to the positive terminal of the charger Ch via the positive charging terminal Tip, and is connected to the load via the positive discharging terminal Top. It is connected to the positive terminal of Lo. One terminal of the second output switch S21 is connected to the negative terminal of the secondary battery B1 through the ammeter Si1, and one terminal of the second output switch S22 is connected to the negative terminal of the secondary battery B2 through the ammeter Si2. One terminal of the second output switch S23 is connected to the negative terminal of the secondary battery B3 via an ammeter Si3, and one terminal of the second output switch S24 is connected to the negative terminal of the secondary battery B3 via an ammeter Si4. It is connected to the negative terminal of the secondary battery B4. Further, the other terminals of the second output section switches S21 to S24 are connected to each other. Further, the connection point of the other terminals of the second output section switches S21 to S24 is connected to the negative terminal of the charger Ch via the switch S41 and the negative charging terminal Tin, and the switch S42 and the negative charging terminal Tin. It is connected to the negative terminal of the load Lo via the terminal Ton. One terminal of the series connection switch S31 is connected to the negative terminal of the secondary battery B1 via the ammeter Si1, and the other terminal of the series connection switch S31 is connected to the positive terminal of the secondary battery B2. One terminal of the series connection switch S32 is connected to the negative terminal of the secondary battery B2 via the ammeter Si2, and the other terminal of the series connection switch S32 is connected to the positive terminal of the secondary battery B3. One terminal of the series connection switch S33 is connected to the negative terminal of the secondary battery B3 via the ammeter Si3, and the other terminal of the series connection switch S33 is connected to the positive terminal of the secondary battery B4.

The storage unit 2 is composed of RAM (Random Access Memory) or ROM (Read Only Memory), and stores a constant current, a predetermined voltage, a predetermined current, a switching current, an end current, and the like, which will be described later.

The control unit 3 is configured by a CPU (Central Processing Unit) or a programmable device (FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)) or the like, and controls the operation of the switching circuit.

<Regarding operation control of the switching circuit during discharging of the secondary batteries B1 and B2>
The control unit 3 controls the operation of the switching circuit so that the secondary batteries B1 to B4 are connected in parallel while the secondary batteries B1 to B4 are being discharged, and connects the secondary batteries B1 to B4 to the load Lo. . That is, while the secondary batteries B1 to B4 are being discharged, the control unit 3 turns on the first output unit switches S11 to S14, the second output unit switches S21 to S24, and the switch S42, and the series connection switches S31 to S33 and The switch S41 is turned off. As a result, from the positive terminal of the secondary battery B1 through the first output switch S11, the positive discharge terminal Top, the load Lo, the negative discharge terminal Ton, the switch S42, the second output switch S21, and the ammeter Si1, A current can flow to the negative terminal of the secondary battery B1. Further, from the positive electrode terminal of the secondary battery B2, a second output switch S12, a positive discharge terminal Top, a load Lo, a negative discharge terminal Ton, a switch S42, a second output switch S22, and an ammeter Si2 are connected. A current can flow to the negative terminal of the secondary battery B2. Further, from the positive electrode terminal of the secondary battery B3, a second output switch S13, a positive discharge terminal Top, a load Lo, a negative discharge terminal Ton, a switch S42, a second output switch S23, and an ammeter Si3 are connected. A current can flow to the negative terminal of the secondary battery B3. Further, from the positive electrode terminal of the secondary battery B4, a second output switch S14, a positive discharge terminal Top, a load Lo, a negative discharge terminal Ton, a switch S42, a second output switch S24, and an ammeter Si4 are connected. A current can flow to the negative terminal of the secondary battery B4. Thus, by connecting the secondary batteries B1 to B4 in parallel while the secondary batteries B1 to B4 are being discharged, the total capacity of the secondary batteries B1 to B4 can be increased.

<Regarding operation control of the switching circuit during charging of the secondary batteries B1 to B4>
First, when charging of the secondary batteries B1 to B4 is started, the control unit 3 controls the operation of the switching circuit so that the secondary batteries B1 to B4 are connected in series with each other, and the secondary batteries B1 to B4 are connected to the charger. Connect to Ch. That is, when the charging of the secondary batteries B1 to B4 is started, the control unit 3 turns on the first output switch S11, the series connection switches S31 to S33, the second output switch S24, and the switch S41. The output section switches S12 to S14, the second output section switches S21 to S23, and the switch S42 are turned off.

Next, the controller 3 sends a current command value to the charger Ch so that a constant current flows through the secondary battery system 1 . The charger Ch supplies a constant current to the secondary battery system 1 based on the current command value. Then, from the positive terminal of the charger Ch to the positive side charging terminal Tip, the first output section switch S11, the secondary battery B1, the ammeter Si1, the series connection switch S31, the secondary battery B2, the ammeter Si2, the series connection switch S32, secondary battery B3, ammeter Si3, series connection switch S33, secondary battery B4, ammeter Si4, second output section switch S24, switch S41, and negative electrode of charger Ch via negative charging terminal Tin A constant current flows through the terminals to charge the secondary batteries B1 to B4, respectively, thereby increasing the voltages of the secondary batteries B1 to B4. It should be noted that the constant current is determined in advance by the rated current of the charging cable Ca and the like. In this way, when the secondary batteries B1 to B4 are charged in a state in which the secondary batteries B1 to B4 are connected in series, the voltage applied to the entire secondary batteries B1 to B4 can be relatively high. The current flowing through the secondary batteries B1 to B4 can be made relatively small. Therefore, since the charging cable Ca can be made smaller, the charging workability for the user can be improved.

Next, when the voltage of at least one of the voltages of the secondary batteries B1 to B4 becomes equal to or higher than a predetermined voltage while a constant current is flowing through the secondary batteries B1 to B4, the control unit 3 A current command value is sent to the charger Ch so that the current flowing through the secondary batteries B1 to B4 gradually decreases while maintaining the voltage at a predetermined voltage.

Then, when at least one of the currents flowing through the secondary batteries B1 to B4 becomes the terminal current, the control unit 3 causes at least one of the secondary batteries B1 to B4 to reach a fully charged state. Then, a current command value is sent to the charger Ch so that the current flowing through the secondary batteries B1-B4 becomes zero, and the charging of the secondary batteries B1-B4 is completed. Note that the final current is a current value for determining that the secondary batteries B1 to B4 have reached a fully charged state.

That is, while the secondary batteries B1 to B4 are being charged, the controller 3 performs constant-current charging control and then constant-voltage charging control.

By the way, during the charging of the secondary batteries B1 to B4, the charging rate of each of the secondary batteries B1 to B4 (the ratio of the current capacity to the full charge capacity) varies due to the influence of variations in manufacturing and aging deterioration of the secondary batteries B1 to B4. ratio) are different from each other, and there is a possibility that the respective voltages of the secondary batteries B1 to B4 are different from each other. Further, in a state where the secondary batteries B1 to B4 have different voltages, if the secondary batteries B1 to B4 are connected in parallel to discharge the secondary batteries B1 to B4, the secondary battery B having the higher voltage A return current flows from the secondary battery B having a lower voltage, and the charging rates (voltages) of the secondary batteries B1 to B4 are equalized. Therefore, when the secondary batteries B1 to B4 are discharged after the charging of the secondary batteries B1 to B4 is completed, the overall charging rate (voltage) of the secondary batteries B1 to B4 at the start of discharging is the same as that immediately after charging is completed. There is a possibility that the charging rate (voltage) of the following batteries B1 to B4 may be lower than that of the entire batteries B1 to B4.

Therefore, in the control unit 3 of the embodiment, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current during the constant voltage charging control after the constant current charging control, the secondary batteries B1 to B4 are connected in parallel with each other. It controls the operation of the switching circuit so that it is connected. As a result, the secondary batteries B1 to B4 are applied with the same voltage, a relatively large current flows through the secondary battery B that has not yet reached a fully charged state, and a relatively small current flows through the secondary battery B that is almost fully charged. Since the current flows, the voltages of the secondary batteries B1 to B4 can be equalized while the secondary batteries B1 to B4 are being charged. Therefore, it is possible to reduce the return current flowing between the secondary batteries B1 to B4 at the start of discharging after the end of charging, and the charging rate (voltage) of the entire secondary batteries B1 to B4 at the start of discharging after the end of charging can be reduced. It is possible to suppress the decrease.

Further, in the embodiment, a value obtained by dividing a constant current by the number of secondary batteries B is used as a switching current. For example, when the constant current is 200 [A], the switching current is 50 [A]=200 [A]/4. As a result, when the secondary batteries B1 to B4 are switched from series connection to parallel connection, the total current flowing through the secondary batteries B1 to B4 increases to a constant current, so the rated current of the charging cable Ca is set to a value higher than the constant current. Therefore, the weight of the charging cable Ca can be suppressed.

Further, in the control unit 3 of the embodiment, after switching the secondary batteries B1 to B4 from series connection to parallel connection during the constant voltage charging control, the total current flowing through the secondary batteries B1 to B4 is increased to a constant current. . For example, after switching the secondary batteries B1 to B4 from series connection to parallel connection, the control unit 3 sends a current command value equal to the constant current to the charger Ch. As a result, compared to the case where the total current flowing through the secondary batteries B1 to B4 after switching from the series connection to the parallel connection of the secondary batteries B1 to B4 is made smaller than a constant current, the secondary batteries B1 to B4 are switched from the series connection to the parallel connection. After switching to parallel connection, the current flowing through each of the secondary batteries B1 to B4 does not decrease, and the period during which the secondary batteries B1 to B4 are connected in parallel during the constant voltage charging control does not become shorter. It is possible to suppress an increase in the variation of each voltage of .

FIG. 2 is a flow chart showing an example of the operation of the control section 3. As shown in FIG.

When the control unit 3 receives an instruction to start supplying power to the load Lo from the secondary battery system 1 (step S1: Yes), the control unit 3 operates the switching circuit so that the secondary batteries B1 to B4 are connected in parallel with each other. In addition, the operations of the switches S41 and S42 are controlled so that the secondary batteries B1 to B4 are connected to the load Lo (step S2).

Next, when an instruction to end the power supply to the load Lo is input from the secondary battery system 1 (step S3: Yes), the control unit 3 cuts off the switches S41 and S42 to discharge the secondary batteries B1 to B4. terminate.

Further, when the control unit 3 receives an instruction to start charging the secondary batteries B1 to B4 (step S1: No, step S4: Yes), the control unit 3 switches the switching circuit so that the secondary batteries B1 to B4 are connected in series with each other. and control the operations of the switches S41 and S42 so that the secondary batteries B1 to B4 are connected to the charger Ch (step S5).

Next, the control unit 3 performs constant current charging control to supply a constant current to the secondary batteries B1 to B4 (step S6). No), the constant current charging control is continued.

Next, when at least one of the voltages of the secondary batteries B1 to B4 reaches or exceeds a predetermined voltage (step S7: Yes), the control unit 3 keeps the at least one voltage at the predetermined voltage and Constant voltage charge control is performed to reduce the current flowing through the batteries B1 to B4 by a predetermined amount (step S8).

Next, when the current flowing through the secondary batteries B1 to B4 is greater than the switching current (step S9: No), the control unit 3 continues constant voltage charging control.

On the other hand, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current (step S9: Yes), the control unit 3 controls the operation of the switching circuit so that the secondary batteries B1 to B4 are connected in parallel with each other. After increasing the total current flowing through the secondary batteries B1 to B4 to a constant current (step S10), while maintaining at least one of the voltages of the secondary batteries B1 to B4 at a predetermined voltage, the secondary battery B1 A constant voltage charging control is performed to reduce the current flowing through B4 by a predetermined amount (step S11). The predetermined current in step S8 and the predetermined current in step S11 are arbitrary values determined in advance according to the characteristics of the secondary battery B and the charging time, and may be the same value or different values.

Next, when the current flowing through each of the secondary batteries B1 to B4 is greater than the final current (step S12: No), the control unit 3 continues constant voltage charging control.

On the other hand, when at least one of the currents flowing through the secondary batteries B1 to B4 becomes equal to or less than the final current (step S12: Yes), the control unit 3 causes the current flowing through the secondary batteries B1 to B4 to become zero. Charging of the secondary batteries B1 to B4 ends (step S13).

Note that, as in the modified example of the operation of the control unit 3 shown in FIG. After setting the current flowing through B4 to zero (step S10'), secondary batteries B1 to B4 may be connected in parallel (step S10). For example, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current, the control unit 3 sends a current command value indicating zero to the charger Ch, and the currents detected by the ammeters Si1 to Si4 become zero. Then, the secondary batteries B1 to B4 are connected in parallel with each other. With this configuration, it is possible to prevent a rush current from flowing through the secondary batteries B1 to B4 when the secondary batteries B1 to B4 are switched from series connection to parallel connection while the secondary batteries B1 to B4 are being charged. be able to.

FIG. 4(a) is a diagram showing an example of changes in the current flowing through the secondary batteries B1 to B4 during charging. Note that the horizontal axis of the two-dimensional coordinates shown in FIG. 4A indicates time, and the vertical axis indicates current. Further, the solid line shown in FIG. 4(a) indicates the total current flowing through the secondary batteries B1 to B4, and the dashed line shown in FIG. 4(a) indicates one current ( individual current). FIG. 4B is a diagram showing an example of voltage changes of the secondary batteries B1 to B4 during charging. Note that the horizontal axis of the two-dimensional coordinates shown in FIG. 4B indicates time, and the vertical axis indicates voltage. Further, the solid line shown in FIG. 4(b) indicates the voltage of the secondary battery B1, the dashed line shown in FIG. 4(b) indicates the voltage of the secondary battery B2, and the dashed line shown in FIG. The voltage of the battery B3 is shown, and the two-dot chain line shown in FIG. 4(b) shows the voltage of the secondary battery B4.

First, at time t0, control unit 3 connects secondary batteries B1 to B4 in series with each other.

Next, the control unit 3 performs constant current charging control in a period from time t0 to time t1. In the period from time t0 to time t1, the voltages of secondary batteries B1 to B4 gradually increase. Also, at time t1, the voltage (charging rate) of secondary battery B1 is the highest, the voltage (charging rate) of secondary battery B2 is the second highest, and the voltage (charging rate) of secondary battery B3 is three. It is assumed that the voltage (charging rate) of the secondary battery B4 is the smallest.

Next, when the voltage of the secondary battery B1 becomes equal to or higher than a predetermined voltage at time t1, the control unit 3 performs constant voltage charging control during the period from time t1 to time t2. In the period from time t1 to time t2, the voltage of the secondary battery B1 is maintained at a predetermined voltage, and the voltages of the secondary batteries B2 to B4 are the same as the voltages of the secondary batteries B2 to B4 at time t1. shall be kept at

Next, at time t2, when the current (individual current) flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current, the control unit 3 connects the secondary batteries B1 to B4 in parallel and switches the secondary batteries B1 to B4. increase the total current flowing through to a constant current.

Next, the control unit 3 performs constant voltage charging control during the period from time t2 to time t3. At this time, the largest amount of charging current flows through secondary battery B4, the second largest amount of charging current flows through secondary battery B3, the third largest amount of charging current flows through secondary battery B2, and the smallest amount of charging current flows through secondary battery B1. charging current flows. Therefore, the voltages of the secondary batteries B2 to B4 gradually approach the voltage of the secondary battery B1, and the voltages of the secondary batteries B1 to B4 are equalized.

At time t3, when the current (individual current) flowing through the secondary batteries B1-B4 becomes equal to or less than the final current, the control unit 3 causes the current (individual current) flowing through the secondary batteries B1-B4 to be zero.

As described above, in the secondary battery system 1 of the embodiment, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current during the constant voltage charging control after the constant current charging control, the secondary batteries B1 to B4 are This configuration controls the operation of the switching circuits so that they are connected in parallel and increases the total current flowing through the secondary batteries B1 to B4 to a constant current. As a result, it is possible to suppress an increase in variation in the voltages of the secondary batteries B1 to B4 while suppressing the weight of the charging cable Ca.

The present invention is not limited to the above embodiments, and various improvements and modifications are possible without departing from the gist of the present invention.

<Modification>
FIG. 5 is a diagram showing a modification of the secondary battery system of the embodiment. In the secondary battery system 1 shown in FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The secondary battery system 1 shown in FIG. 5 differs from the secondary battery system 1 shown in FIG. 1 in that the positive electrode side charging terminal Tip is connected to the positive electrode terminal of the secondary battery B1 and one terminal of the first output section switch S11. and that the negative charge terminal Tin is connected to the connection point between the negative terminal of the secondary battery B4 and one terminal of the second output switch S24. The switch S41 is connected between the connection point between the negative terminal of the secondary battery B4 and one terminal of the second output switch S24 and the negative charging terminal Tin. Further, the operation control of the switching circuit during discharging of the secondary batteries B1 to B4 in the secondary battery system 1 shown in FIG. This is the same as the operation control of the circuit, so its explanation is omitted.

<Regarding operation control of the switching circuit during charging of the secondary batteries B1 to B4>
First, when charging of the secondary batteries B1 to B4 is started, the control unit 3 turns on the series connection switches S31 to S33 and the switch S41, and the first output unit switches S11 to S14 and the second output unit switches S21 to S24. , and the switch S42 is cut off. Thereby, the secondary batteries B1 to B4 are connected in series with each other, and the secondary batteries B1 to B4 are connected to the charger Ch.

Next, the controller 3 sends a current command value to the charger Ch so that a constant current flows through the secondary batteries B1 to B4. The charger Ch supplies a constant current to the secondary battery system 1 based on the current command value. Then, from the positive terminal of the charger Ch to the positive side charging terminal Tip, secondary battery B1, ammeter Si1, series connection switch S31, secondary battery B2, ammeter Si2, series connection switch S32, secondary battery B3, A constant current flows through the negative terminal of the charger Ch through the ammeter Si3, the switch S33 for series connection, the secondary battery B4, the ammeter Si4, the switch S41, and the negative charging terminal Tin, and the secondary batteries B1 to B4 are charged. By being charged, the voltages of the secondary batteries B1 to B4 rise.

Next, when the voltage of at least one of the voltages of the secondary batteries B1 to B4 becomes equal to or higher than a predetermined voltage while a constant current is flowing through the secondary batteries B1 to B4, the control unit 3 A current command value is sent to the charger Ch so that the current flowing through the secondary batteries B1 to B4 gradually decreases while maintaining the voltage at a predetermined voltage.

Next, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current, the control unit 3 conducts the first output unit switches S11 to S14, the second output unit switches S21 to S24, and the switch S41, and switches the switches in series. The connection switches S31 to S33 and the switch S42 are turned off. Thereby, the secondary batteries B1 to B4 are connected in parallel with each other, and the secondary batteries B1 to B4 are connected to the charger Ch. When the current flowing through the secondary batteries B1-B4 becomes equal to or less than the switching current, the control unit 3 temporarily reduces the current flowing through the secondary batteries B1-B4 to zero, and then connects the secondary batteries B1-B4 in parallel. may be configured to be connected.

Next, the control unit 3 sends a current command value to the charger Ch so that the total current flowing through the secondary batteries B1 to B4 increases to a constant current. The charger Ch supplies a constant current to the secondary battery system 1 based on the current command value. Then, from the positive terminal of the charger Ch through the positive charging terminal Tip, the secondary battery B1, the ammeter Si1, the second output section switch S21, the second output section switch S24, the switch S41, and the negative charging terminal Tin, , a current flows to the negative terminal of the charger Ch. Further, from the positive terminal of the charger Ch to the positive side charging terminal Tip, the first output section switch S11, the first output section switch S12, the secondary battery B2, the ammeter Si2, the second output section switch S22, the second output section switch A current flows to the negative terminal of the charger Ch via S24, the switch S41, and the negative charging terminal Tin. Further, from the positive terminal of the charger Ch to the positive side charging terminal Tip, the first output section switch S11, the first output section switch S13, the secondary battery B3, the ammeter Si3, the second output section switch S23, the second output section switch A current flows to the negative terminal of the charger Ch via S24, the switch S41, and the negative charging terminal Tin. Also, from the positive terminal of the charger Ch through the positive side charging terminal Tip, the first output section switch S11, the first output section switch S14, the secondary battery B4, the ammeter Si4, the switch S41, and the negative side charging terminal Tin. , a current flows to the negative terminal of the charger Ch.

Next, the control unit 3 maintains at least one of the voltages of the secondary batteries B1 to B4 at a predetermined voltage, and controls the current command value so that the currents flowing through the secondary batteries B1 to B4 gradually decrease. to the charger Ch.

Then, when at least one of the currents flowing through the secondary batteries B1 to B4 becomes the terminal current, the control unit 3 sets the current command value so that the currents flowing through the secondary batteries B1 to B4 become zero. The secondary batteries B1 to B4 are sent to the charger Ch to finish charging.

In the secondary battery system 1 shown in FIG. 5, when the secondary batteries B1 to B4 are connected in parallel during constant voltage charging control, the total current flowing through the secondary batteries B2 to B4 is the first output. flow to the internal switch S11. Therefore, it is assumed that the rated current of the first output section switch S11 is determined based on the total current flowing through each of the secondary batteries B2 to B4.

Further, in the secondary battery system 1 shown in FIG. 5, when the secondary batteries B1 to B4 are connected in parallel during constant voltage charging control, the total current flowing through each of the secondary batteries B1 to B3 is the second output. flow to the internal switch S24. Therefore, it is assumed that the rated current of the second output section switch S24 is determined based on the total current flowing through each of the secondary batteries B1 to B3.

Further, in the secondary battery system 1 shown in FIG. 5, the switching current is determined based on the rated current of the charging cable Ca or the rated current of the first output section switch S11 and the second output section switch S24. .

For example, when the rated current of the charging cable Ca is 200 [A] and the rated current of the first output switch S11 and the second output switch S24 is 160 [A], the switching current is 50 [A]=200 [A]/4 and 40[A]=160[A]/4 are considered. Both 150 [A]=50 [A]×3 and 120 [A]=40 [A]×3 are below the rated currents of the first output section switch S11 and the second output section switch S24. Therefore, between 50 [A] and 40 [A], 50 [A], which is the larger value, is used as the switching current. A constant current is 200 [A]=50 [A]×4.

Further, when the rated current of the charging cable Ca is 200 [A] and the rated current of the first output section switch S11 and the second output section switch S24 is 120 [A], the switching current is 50 [A] = 200 [A]/4 and 30[A]=120[A]/4 are considered. Also, 90 [A] = 30 [A] x 3 is below the rated current of the first output section switch S11 and the second output section switch S24, but 150 [A] = 50 [A] x 3 is the It becomes larger than the rated current of the 1st output switch S11 and the 2nd output switch S24. Therefore, 30 [A] out of 50 [A] and 30 [A] is set as the switching current. A constant current is 120 [A]=30 [A]×4.

As described above, in the secondary battery system 1 shown in FIG. 5 as well, during the constant voltage charging control after the constant current charging control, when the current flowing through the secondary batteries B1 to B4 becomes equal to or less than the switching current, the secondary batteries B1 to In this configuration, the operation of the switching circuit is controlled so that the secondary batteries B4 are connected in parallel with each other, and the total current flowing through the secondary batteries B1 to B4 is increased to a constant current. As a result, it is possible to suppress an increase in variation in the voltages of the secondary batteries B1 to B4 while suppressing the weight of the charging cable Ca.

1 Secondary battery system 2 Storage unit 3 Control unit B1 to B4 Secondary battery Ve Vehicle Lo Load Ch Charger Ca Charging cable Tip Positive side charging terminal Tin Negative side charging terminal Top Positive side discharging terminal Ton Negative side discharging terminal S11 to S14 First output section switches S21 to S24 Second output section switches S31 to S33 Series connection switches S41 and S42 Switches

Claims (2)

a plurality of secondary batteries;
a switching circuit that connects the plurality of secondary batteries in series or in parallel;
a control unit that controls the operation of the switching circuit;
with
The control unit
controlling the operation of the switching circuit so that the plurality of secondary batteries are connected in parallel to each other during discharging of the plurality of secondary batteries;
During charging of the plurality of secondary batteries, the operation of the switching circuit is controlled so that the plurality of secondary batteries are connected in series with each other, and a constant current is passed through the plurality of secondary batteries, and the plurality of secondary batteries is charged. When at least one of the voltages of the batteries reaches a predetermined voltage or higher, the current flowing through the plurality of secondary batteries is gradually reduced while maintaining the at least one voltage at the predetermined voltage, When the current flowing through the battery becomes equal to or less than the switching current obtained by dividing the constant current by the number of the secondary batteries, the operation of the switching circuit is controlled so that the plurality of secondary batteries are connected in parallel with each other. and increasing the total current flowing through the plurality of secondary batteries to the constant current, then gradually decreasing the current flowing through the plurality of secondary batteries, and at least one of the currents flowing through the plurality of secondary batteries A secondary battery system characterized in that the current flowing through the plurality of secondary batteries is set to zero when one current becomes equal to or lower than a final current that is smaller than the switching current. The secondary battery system according to claim 1,
When the current flowing through the plurality of secondary batteries becomes equal to or less than the switching current during charging of the plurality of secondary batteries, the control unit reduces the current flowing through the plurality of secondary batteries to zero, and then secondary batteries are connected in parallel with each other, and the operation of the switching circuit is controlled, and the total current flowing through the plurality of secondary batteries is increased to the constant current.

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