JP7318548B2 - Secondary battery system and industrial vehicle - Google Patents

Description

The present invention relates to a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel, and an industrial vehicle equipped with the secondary battery system.

As a secondary battery system, when charging a plurality of secondary batteries, a plurality of secondary batteries are connected in series with each other, and when discharging a plurality of secondary batteries, a plurality of secondary batteries are connected in parallel with each other. . As a related technology, there is Patent Document 1.

By the way, if a plurality of secondary batteries are connected in series and charged, the voltages of the secondary batteries may differ from each other at the end of charging due to variations in manufacturing and deterioration of the secondary batteries. .

Therefore, in the above secondary battery system, when the voltages of the secondary batteries at the end of charging are different from each other, if the secondary batteries are connected in parallel to discharge the secondary batteries, the voltage between the secondary batteries will increase. A return current may flow in the

JP 2016-123228 A

An object according to one aspect of the present invention is to switch from series connection to parallel connection after charging is finished in a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel and an industrial vehicle provided with the secondary battery system. It is to suppress the return current from sometimes flowing between the secondary batteries.

A secondary battery system according to one aspect of the present invention includes a connection circuit for connecting a plurality of secondary batteries in series or in parallel, and a control unit for controlling the operation of the connection circuit so that the secondary batteries are connected in parallel when discharging the plurality of secondary batteries.

When charging a plurality of secondary batteries, the control unit charges a plurality of secondary batteries connected in series each time charging of a predetermined secondary battery among the plurality of secondary batteries is completed. It controls the operation of the connecting circuit so that it is disconnected from the next battery.

As a result, the voltages of the secondary batteries can be made uniform when the charging of the secondary batteries is finished, so that it is possible to suppress the return current from flowing between the secondary batteries when switching from series connection to parallel connection. can be done.

Further, when charging a plurality of secondary batteries, the control unit controls the operation of the connection circuit so that the plurality of secondary batteries are connected in series with each other, and causes a constant current to flow through the plurality of secondary batteries. When the voltage of a predetermined secondary battery among the secondary batteries reaches or exceeds the threshold voltage, the current flowing through the plurality of secondary batteries is gradually decreased while the voltage of the predetermined secondary battery is maintained at the threshold voltage. For all secondary batteries, the operation of the connection circuit is controlled such that when the current flowing through the secondary battery becomes equal to or less than the cut-off current, a predetermined secondary battery is disconnected from the plurality of secondary batteries connected in series with each other. You may comprise so that it may repeat until charge is complete|finished.

As a result, the voltages of the secondary batteries can be made uniform when the charging of the secondary batteries is finished, so that it is possible to suppress the return current from flowing between the secondary batteries when switching from series connection to parallel connection. can be done.

Further, when charging a plurality of secondary batteries, the control unit controls the operation of the connection circuit so that the plurality of secondary batteries are connected in series with each other, and causes a constant current to flow through the plurality of secondary batteries. The operation of the connection circuit is controlled so that the predetermined secondary battery is disconnected from the plurality of secondary batteries connected in series each time the voltage of the predetermined secondary battery among the secondary batteries reaches or exceeds the threshold voltage. Then, when the voltage of the last rechargeable battery that has not been charged reaches the threshold voltage or more, the operation of the connection circuit is controlled so that the plurality of rechargeable batteries are connected in series with each other, and each of the plurality of rechargeable batteries is connected in series. While maintaining the voltage of the secondary battery at the threshold voltage, the current flowing through the secondary batteries is gradually reduced. can be configured to

As a result, the voltages of the secondary batteries can be made uniform when the charging of the secondary batteries is finished, so that it is possible to suppress the return current from flowing between the secondary batteries when switching from series connection to parallel connection. can be done. Also, the charging time of each secondary battery can be shortened.

Further, the connection circuit includes a plurality of first output section switches each having one terminal connected to the positive terminal of each of the plurality of secondary batteries, and a plurality of first output section switches each having one terminal connected to each of the negative terminals of the plurality of secondary batteries. and a plurality of series connection elements respectively connected between a negative terminal of one of the adjacent secondary batteries and a positive terminal of the other secondary battery, and a plurality of Through a positive discharge output section connected to the other terminal of the first output section switch, a negative discharge output section connected to the other terminal of the plurality of second output section switches, and a plurality of series connection elements a positive side charge input section connected between a positive terminal of a secondary battery provided at one end of a plurality of series-connected secondary batteries and one terminal of a first output section switch; The negative electrode side connected between the negative terminal of the secondary battery provided at the other end of the plurality of secondary batteries connected in series via the series connection element and the one terminal of the second output section switch a charging input unit, wherein when the plurality of secondary batteries are connected in series, the control unit cuts off the plurality of first output section switches and the plurality of second output section switches to connect the plurality of secondary batteries in parallel with each other; When connecting, the plurality of first output section switches and the plurality of second output section switches are conductive, and the plurality of series connection elements may be diodes.

As a result, compared to the case where a plurality of series connection elements are configured by switches, it is possible to suppress complicated switching control between series connection and parallel connection of the secondary batteries, and the secondary battery system can be improved. It can be configured inexpensively.

According to another aspect of the present invention, there is provided an industrial vehicle including the secondary battery system.

According to the present invention, in a secondary battery system in which a plurality of secondary batteries are connected in series or in parallel and an industrial vehicle provided with the secondary battery system, the secondary battery is switched from series connection to parallel connection after charging is completed. It is possible to suppress the return current from flowing between them.

It is a figure showing an example of vehicles provided with a rechargeable battery system of an embodiment. 4 is a diagram showing an example of voltage change of a secondary battery in the charging method of Example 1. FIG. FIG. 10 is a diagram showing an example of voltage change of a secondary battery in the charging method of Example 2; FIG. 10 is a diagram showing an example of voltage change of a secondary battery in the charging method of Example 3;

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

An industrial vehicle Ve shown in FIG. 1 is an industrial vehicle such as a forklift, and includes a secondary battery system 1 and a load Lo.

The secondary battery system 1 supplies power to a load Lo such as a driving motor, and the power is supplied from an external charger Ch. Note that the charger Ch may be provided inside the vehicle Ve.

Further, the secondary battery system 1 includes secondary batteries B1 to B3, a positive electrode side charging input portion Tip, a negative electrode side charging input portion Tin, a positive electrode side discharge output portion Top, a negative electrode side discharge output portion Ton, and a second 1 output section switches S11 to S13, second output section switches S21 to S23, series connection elements Ss1 and Ss2, and a control section 2 are provided.

A positive charge input section Tip, a negative charge input section Tin, a positive discharge output section Top, a negative discharge output section Ton, first output section switches S11 to S13, and a second output section switch S21. , S23, and series connection elements Ss1 and Ss2 to form a connection circuit.

Further, the secondary batteries B1 to B3 are simply referred to as a secondary battery B when not specifically distinguished. Further, when the first output section switches S11 to S13 are not particularly distinguished, they are simply referred to as the first output section switch S1. Further, when the second output section switches S21 to S23 are not particularly distinguished, they are simply referred to as the second output section switch S2. Further, when the series connection elements Ss1 and Ss2 are not particularly distinguished, the series connection element Ss is simply referred to. Also, the number of each of the secondary battery B, the first output switch S1, and the second output switch S2 is not limited to three. Also, the number of series connection elements Ss is not limited to two.

Each of the secondary batteries B1 to B3 is composed of one or more chargeable/dischargeable batteries such as lithium ion batteries or nickel metal hydride batteries. It is conceivable to adopt LFP (LiFePO4), NMC (Nickel Manganese Cobalt), etc. as the lithium ion battery.

For example, the first output switches S11 to S13 each include a first semiconductor switch (such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor)) to which a first diode is connected in parallel, a first diode and a forward current is connected in series with a second semiconductor switch (such as a MOSFET) to which a second diode in which the current flows in the opposite direction is connected in parallel. The drain terminal of the first semiconductor switch is connected to the cathode terminal of the first diode, the source terminal of the first semiconductor switch is connected to the anode terminal of the first diode, the source terminal of the second semiconductor switch, and the second semiconductor switch. It is connected to the anode terminal of the diode and the drain terminal of the second semiconductor switch is connected to the cathode terminal of the second diode. One terminal of each of the first output switches S11 to S13 (the drain terminal of the first semiconductor switch) is connected to the positive terminal of each of the secondary batteries B1 to B3. (drain terminal of the second semiconductor switch) is connected to the positive discharge output section Top. That is, one terminal of the first output switch S11 is connected to the positive terminal of the secondary battery B1, and the other terminal of the first output switch S11 is connected to the positive discharge output Top. One terminal of the first output switch S12 is connected to the positive terminal of the secondary battery B2, and the other terminal of the first output switch S12 is connected to the positive discharge output Top. One terminal of the first output switch S13 is connected to the positive terminal of the secondary battery B3, and the other terminal of the first output switch S13 is connected to the positive discharge output Top. Note that the first output unit switches S11 to S13 may be mechanical switches (electromagnetic relays) capable of electrically switching between conduction and interruption by a signal from the control unit 2, for example.

For example, like the first output switches S11 to S13, the second output switches S21 to S23 are each a first semiconductor switch (such as a MOSFET) in which a first diode is connected in parallel and a first diode. and a second semiconductor switch (such as a MOSFET) connected in parallel with a second diode in which the forward current flows in the opposite direction are connected in series. One terminal of each of the second output switches S21 to S23 (drain terminal of the first semiconductor switch) is connected to the negative terminal of each of the secondary batteries B1 to B3, and the other terminal of each of the second output switches S11 to S13. The terminal (drain terminal of the second semiconductor switch) is connected to the negative discharge output section Ton. That is, one terminal of the second output switch S21 is connected to the negative terminal of the secondary battery B1, and the other terminal of the second output switch S21 is connected to the negative discharge output Ton. One terminal of the second output switch S22 is connected to the negative terminal of the secondary battery B2, and the other terminal of the second output switch S22 is connected to the negative discharge output Ton. One terminal of the second output switch S23 is connected to the negative terminal of the secondary battery B3, and the other terminal of the second output switch S23 is connected to the negative discharge output Ton. The second output section switches S21 to S23 may be mechanical switches capable of electrically switching between conduction and interruption by a signal from the control section 2, for example.

The series connection elements Ss1 and Ss2 are elements that allow current to flow from the negative terminal of one of the adjacent secondary batteries B to the positive terminal of the other secondary battery B, For example, it is composed of a diode. The series connection elements Ss1 and Ss2 are connected between the negative terminal of one of the adjacent secondary batteries B and the positive terminal of the other secondary battery. That is, the anode terminal of the series connection element Ss1 is connected to the negative terminal of the secondary battery B1 of the adjacent secondary batteries B1 and B2, and the cathode terminal of the series connection element Ss1 is connected to the positive terminal of the secondary battery B2. Connected. The anode terminal of the series connection element Ss2 is connected to the negative terminal of the secondary battery B2 of the adjacent secondary batteries B2 and B3, and the cathode terminal of the series connection element Ss2 is connected to the positive terminal of the secondary battery B3. Connected. The series connection elements Ss1 and Ss2 may each be composed of a switch such as a semiconductor switch (MOSFET) or a mechanical switch that can switch between conduction and interruption in response to a signal from the control section 1. FIG. That is, when the secondary batteries B are connected in series, the series connection elements Ss1 and Ss2 move from the negative terminal of one of the adjacent secondary batteries B to the positive terminal of the other secondary battery B. current can flow, while the current does not flow from the positive terminal of the other of the adjacent secondary batteries B to the negative terminal of one of the secondary batteries B when connected in parallel. good. When the series connection elements Ss1 and Ss2 are composed of diodes, compared to the case where the series connection elements Ss1 and Ss2 are composed of switches, switching control between the series connection and the parallel connection of the secondary batteries B1 to B3 is performed. Complications can be suppressed, and the secondary battery system 1 can be configured at low cost.

The positive electrode side charging input section Tip is the positive electrode of the secondary battery B1 provided at one end of the secondary batteries B1 to B3 provided in the order of the secondary battery B1, the secondary battery B2, and the secondary battery B3. It is connected between the terminal and one terminal of the first output switch S11 corresponding to the secondary battery B1. In other words, the positive charge input section Tip is connected to the positive terminal of the secondary battery B1 provided at one end of the secondary batteries B1 to B3 connected in series via the series connection elements Ss1 and Ss2, and the positive terminal of the secondary battery B1. It is connected between one terminal of the first output section switch S11 corresponding to the secondary battery B1.

The negative electrode side charging input portion Tin is the negative electrode of the secondary battery B3 provided at the other end of the secondary batteries B1 to B3 provided in the order of the secondary battery B1, the secondary battery B2, and the secondary battery B3. terminal and the second output switch S23 corresponding to the secondary battery B3. In other words, the negative charge input section Tin is connected to the negative terminal of the secondary battery B3 provided at the other end of the secondary batteries B1 to B3 connected in series via the series connection elements Ss1 and Ss2, and the negative terminal of the secondary battery B3. It is connected between the second output section switch S23 corresponding to the secondary battery B3.

The control unit 2 is composed of a CPU (Central Processing Unit) or a programmable device (FPGA (Field Programmable Gate Array) or PLD (Programmable Logic Device)), and according to the charging or discharging of the secondary batteries B1 to B3, It controls the operation of the first output section switches S11-S13 and the second output section switches S21-S23. When the series connection elements Ss1 and Ss2 are configured by switches, the control unit 2 controls the operations of the series connection elements Ss1 and Ss2 according to the charge or discharge of the secondary batteries B1 to B3.

That is, when the secondary batteries B1 to B3 are to be charged, the control unit 2 connects the secondary batteries B1 to B3 in series with each other. When connecting the secondary batteries B1 to B3 in series, the controller 2 turns off the first output switches S11 to S13 and the second output switches S21 to S23. When the series connection elements Ss1 and Ss2 are configured by switches, the control unit 2 causes the series connection elements Ss1 and Ss2 to conduct. At this time, when power is supplied from the charger Ch to the secondary battery system 1, the positive terminal of the charger Ch is connected to the positive electrode side charging input tip Tip, the secondary battery B1, the series connection element Ss1, the secondary battery B2, A current flows to the negative terminal of the charger Ch via the series connection element Ss2, the secondary battery B3, and the negative charge input section Tin. In this way, when the secondary batteries B1 to B3 are charged, by connecting the secondary batteries B1 to B3 in series with each other, the voltage applied to the entire secondary batteries B1 to B3 can be made relatively high. The current flowing through the secondary batteries B1 to B3 can be reduced. Therefore, it is possible to reduce the size of the charging cable that connects the charger Ch, the positive charging input section Tip, and the negative charging input section Tin, thereby improving the charging workability.

Further, when charging only the secondary batteries B2 and B3, the control unit 2 connects only the secondary batteries B2 and B3 in series with each other. When only the secondary batteries B2 and B3 are connected in series, the control unit 2 turns on the first output unit switches S11 and S12 and cuts off the first output unit switch S13 and the second output unit switches S21 to S23. . At this time, when power is supplied from the charger Ch to the secondary battery system 1, the positive terminal of the charger Ch is connected to the positive terminal Tip, the first output switch S11, the first output switch S12, the secondary A current flows to the negative terminal of the charger Ch through the battery B2, the series connection element Ss2, the secondary battery B3, and the negative charging input section Tin.

When only the secondary battery B3 is to be charged, the control section 2 turns on the first output section switches S11 and S13 and cuts off the first output section switch S12 and the second output section switches S21 to S23. At this time, when power is supplied from the charger Ch to the secondary battery system 1, from the positive terminal of the charger Ch, the positive electrode side charging input Tip, the first output switch S11, the first output switch S13, the secondary A current flows to the negative terminal of the charger Ch via the battery B3 and the negative charging input Tin.

It is assumed that the power supplied from the charger Ch to the secondary battery system 1 is not directly supplied to the load Lo.

Further, when the secondary batteries B1 to B3 are to be discharged, the control unit 2 connects the secondary batteries B1 to B3 in parallel. When the secondary batteries B1 to B3 are connected in parallel, the control section 2 turns on the first output section switches S11 to S13 and the second output section switches S21 to S23. At this time, when power is supplied from the secondary battery system 1 to the load Lo, the negative terminal of the load Lo is connected to the negative electrode side discharge output section Ton, the second output section switch S21, the secondary battery B1, and the first output section switch S11. , and the positive electrode discharge output portion Top to the positive terminal of the load Lo. Also, from the negative terminal of the load Lo to the positive terminal of the load Lo through the negative discharge output section Ton, the second output section switch S22, the secondary battery B2, the first output section switch S12, and the positive discharge output section Top. current flows. Also, from the negative terminal of the load Lo to the positive terminal of the load Lo via the negative discharge output section Ton, the second output section switch S23, the secondary battery B3, the first output section switch S13, and the positive discharge output section Top. current flows. Thus, when the secondary batteries B1 to B3 are discharged, the capacity of the entire secondary battery B can be increased by connecting the secondary batteries B1 to B3 in parallel.

<Charging Method of Embodiment 1>
When charging the secondary batteries B1 to B3, the control unit 2 controls the operation of the connection circuit so that the secondary batteries B1 to B3 are connected in series with each other, and supplies a constant current to the secondary battery B to charge the secondary batteries B1 to B3. When the voltage of a predetermined secondary battery B (for example, a secondary battery B connected to the positive terminal of the charger Ch) among the batteries B1 to B3 reaches or exceeds the threshold voltage Vth, the voltage of the predetermined secondary battery B is increased. The current flowing through the secondary battery B is gradually reduced while maintaining the threshold voltage Vth, and when the current flowing through the secondary battery B becomes equal to or less than the final current, the predetermined secondary batteries B are connected in series with each other as the secondary battery B1. The control of the operation of the connection circuit is repeated until charging of all the secondary batteries B is completed. It is assumed that the threshold voltage Vth is set by the voltage of the secondary battery B in a fully charged state.

FIG. 2 is a diagram showing voltage changes of the secondary batteries B1 to B3 when the secondary batteries B1 to B3 are charged by the charging method of the first embodiment. Note that the horizontal axis of the two-dimensional coordinates shown in FIG. 2 indicates time, and the vertical axis indicates voltage. The solid line shown in FIG. 2 indicates changes in the voltage of the secondary battery B1, the dashed line shown in FIG. 2 indicates changes in the voltage of the secondary battery B2, and the dashed-dotted line shown in FIG. shows the conversion.

First, at time t0, the control unit 2 connects the secondary batteries B1 to B3 in series by turning off the first output unit switches S11 to S13 and the second output unit switches S21 to S23.

Next, the control unit 2 sends an instruction to the charger Ch so that a constant current flows from the charger Ch to the secondary battery system 1, and starts constant current charging control of the secondary batteries B1 to B3. Then, a constant current flows through the secondary batteries B1 to B3, and the voltage of each of the secondary batteries B1 to B3 gradually increases.

Next, at time t1, when the voltage of the secondary battery B1 becomes equal to or higher than the threshold voltage Vth, the control unit 2 keeps the voltage of the secondary battery B1 at the threshold voltage Vth and gradually increases the current flowing through the secondary batteries B1 to B3. , the constant current charging control of the secondary batteries B1 to B3 is terminated, and the constant voltage charging control of the secondary batteries B1 to B3 is started. At time t1, the secondary battery B1 has the highest voltage, the secondary battery B2 has the second highest voltage and the secondary battery B3 shall have the lowest voltage.

Next, at time t2, when the current flowing through the secondary batteries B1 to B3 becomes equal to or less than the final current, the control unit 2 turns on the first output unit switches S11 and S12, and the first output unit switch S13 and the second output unit switch By turning off the output unit switches S21 to S23, the secondary battery B1, which is a predetermined secondary battery B, is removed from the secondary batteries B1 to B3 connected in series with each other (the constant voltage charging control of the secondary battery B1 is performed). end). Further, the control unit 2 sends an instruction to the charger Ch to cause a constant current to flow from the charger Ch to the secondary battery system 1, terminates the constant voltage charging control of the secondary batteries B2 and B3, and controls the secondary battery B2. , B3 start the constant current charging control. Then, a constant current flows through the secondary batteries B2 and B3, and the voltages of the secondary batteries B2 and B3 gradually rise. It is assumed that when the charging of the secondary battery B1 is completed, the voltage of the secondary battery B2 is lower than the threshold voltage Vth, and the voltage of the secondary battery B3 is lower than the voltage of the secondary battery B2. It is also assumed that when the current stops flowing through the secondary battery B1, the voltage of the secondary battery B1 decreases to near the predetermined voltage V1 due to the influence of the internal resistance and polarization of the secondary battery B1. Threshold voltage Vth>predetermined voltage V1.

Next, when the voltage of the secondary battery B2 becomes equal to or higher than the threshold voltage Vth at time t3, the control unit 2 keeps the voltage of the secondary battery B2 at the threshold voltage Vth and gradually increases the current flowing through the secondary batteries B2 and B3. , the constant current charging control of the secondary batteries B2 and B3 is terminated, and the constant voltage charging control of the secondary batteries B2 and B3 is started. It is assumed that at time t3, the voltage of secondary battery B2 becomes higher than the voltage of secondary battery B3 due to manufacturing variations and deterioration variations of secondary batteries B2 and B3.

Next, at time t4, when the current flowing through the secondary batteries B2 and B3 becomes equal to or less than the final current, the control unit 2 turns on the first output unit switches S11 and S13, By shutting off the output unit switches S21 to S23, the secondary battery B2, which is a predetermined secondary battery B, is removed from the secondary batteries B2 and B3 connected in series (the constant voltage charging control of the secondary battery B2). end). Further, the control unit 2 sends an instruction to the charger Ch to cause a constant current to flow from the charger Ch to the secondary battery system 1, terminates the constant voltage charging control of the secondary battery B3, and controls the constant voltage of the secondary battery B3. Start current charge control. Then, a constant current flows through the secondary battery B3, and the voltage of the secondary battery B3 gradually increases. It is assumed that the voltage of the secondary battery B3 is lower than the threshold voltage Vth when the charging of the secondary battery B2 is completed. It is also assumed that when the current stops flowing through the secondary battery B2, the voltage of the secondary battery B2 decreases to near the predetermined voltage V1 due to the influence of the internal resistance and polarization of the secondary battery B2.

Next, when the voltage of the secondary battery B3 becomes equal to or higher than the threshold voltage Vth at time t5, the control unit 2 keeps the voltage of the secondary battery B3 at the threshold voltage Vth while the current flowing through the secondary battery B3 gradually decreases. Then, the constant current charging control of the secondary battery B3 is terminated and the constant voltage charging control of the secondary battery B3 is started.

At time t6, when the current flowing through the secondary battery B3 becomes equal to or less than the final current, the control unit 2 sends an instruction to the charger Ch so that the current flowing from the charger Ch to the secondary battery system 1 becomes zero. , terminates the constant voltage charging control of the secondary battery B3. It is assumed that when the current stops flowing through the secondary battery B3, the voltage of the secondary battery B3 decreases to near the predetermined voltage V1 due to the influence of the internal resistance and polarization of the secondary battery B3.

As a result, after the constant current charging control of the secondary battery B3 is completed, the voltage of each of the secondary batteries B1 to B3 can be brought close to the predetermined voltage V2. That is, after charging the secondary batteries B1 to B3, the voltages of the secondary batteries B1 to B3 can be equalized. Therefore, it is possible to suppress the return current from flowing between the secondary batteries B when switching from the series connection of the secondary batteries B1 to B3 to the parallel connection.

Further, the charging method of the first embodiment can fully charge the secondary batteries B1 to B3 after charging the secondary batteries B1 to B3. As described above, the charging method of the first embodiment can fully charge each of the secondary batteries B1 to B3, so that the error in the voltage detected in a state other than the fully charged state becomes relatively large. This is suitable when the secondary batteries B1 to B3 are configured with LFPs or the like in which the error in the voltage detected by is relatively small.

<Charging Method of Embodiment 2>
When charging the secondary batteries B1 to B3, the control unit 2 controls the operation of the connection circuit so that the secondary batteries B1 to B3 are connected in series with each other, and supplies a constant current to the secondary batteries B1 to B3, Each time the voltage of a predetermined secondary battery B among the secondary batteries B1 to B3 (for example, the secondary battery B connected to the positive terminal of the charger Ch) reaches or exceeds the threshold voltage Vth, the predetermined secondary battery B controls the operation of the connection circuit so that the secondary battery B is disconnected from the secondary batteries B connected in series with each other, and when the voltage of the last secondary battery B that has not been charged reaches the threshold voltage Vth or higher, the secondary battery The operation of the connection circuit is controlled so that B1 to B3 are connected in series with each other, and the current flowing through the secondary batteries B1 to B3 is gradually reduced while maintaining the voltage of each of the secondary batteries B1 to B3 at the threshold voltage Vth. , the current flowing through the secondary batteries B1-B3 becomes zero when the current flowing through the secondary batteries B1-B3 becomes equal to or less than the final current.

FIG. 3 is a diagram showing voltage changes of the secondary batteries B1 to B3 when the secondary batteries B1 to B3 are charged by the charging method of the second embodiment. Note that the horizontal axis of the two-dimensional coordinates shown in FIG. 3 indicates time, and the vertical axis indicates voltage. Further, the solid line shown in FIG. 3 indicates changes in the voltage of the secondary battery B1, the dashed line shown in FIG. 3 indicates changes in the voltage of the secondary battery B2, and the dashed-dotted line shown in FIG. shows the conversion.

First, at time t0, the control unit 2 connects the secondary batteries B1 to B3 in series by turning off the first output unit switches S11 to S13 and the second output unit switches S21 to S23.

Next, the control unit 2 sends an instruction to the charger Ch so that a constant current flows from the charger Ch to the secondary battery system 1, and starts constant current charging control of the secondary batteries B1 to B3. Then, a constant current flows through the secondary batteries B1 to B3, and the voltage of each of the secondary batteries B1 to B3 gradually increases.

Next, at time t1, when the voltage of the secondary battery B1 becomes equal to or higher than the threshold voltage Vth, the control section 2 turns on the first output section switches S11 and S12, and switches the first output section switch S13 and the second output section switch S13 to the second output section switch. By disconnecting the switches S21 to S23, the secondary battery B1, which is a predetermined secondary battery B, is disconnected from the secondary batteries B1 to B3 connected in series (end of constant current charging control of the secondary battery B1). . Then, a constant current flows only through the secondary batteries B2 and B3, and the respective voltages of the secondary batteries B2 and B3 gradually rise. It is assumed that when the voltage of the secondary battery B1 becomes equal to or higher than the threshold voltage Vth, the voltage of the secondary battery B2 is lower than the threshold voltage Vth, and the voltage of the secondary battery B3 is lower than the voltage of the secondary battery B2. It is also assumed that when the current stops flowing through the secondary battery B1, the voltage of the secondary battery B1 decreases due to the influence of the internal resistance and polarization of the secondary battery B1.

Next, at time t2, when the voltage of the secondary battery B2 becomes equal to or higher than the threshold voltage Vth, the control unit 2 turns on the first output unit switches S11 and S13, and switches the first output unit switch S12 and the second output unit switch S12 to the second output unit. By disconnecting the switches S21 to S23, the secondary battery B2, which is a predetermined secondary battery B, is disconnected from the secondary batteries B2 and B3 connected in series (end of constant current charging control of the secondary battery B2). . Then, a constant current flows only through the secondary battery B3, and the voltage of the secondary battery B3 gradually increases. It is assumed that when the voltage of the secondary battery B2 becomes equal to or higher than the threshold voltage Vth, the voltage of the secondary battery B3 is lower than the threshold voltage Vth. It is also assumed that when the current stops flowing through the secondary battery B2, the voltage of the secondary battery B2 decreases due to the influence of the internal resistance and polarization of the secondary battery B2.

Next, when the voltage of the secondary battery B3 becomes equal to or higher than the threshold voltage Vth at time t3, the control unit 2 cuts off the first output unit switches S11 to S13 and the second output unit switches S21 to S23. An instruction is sent to the charger Ch so that the secondary batteries B1 to B3 are connected in series with each other, and the current flowing through the secondary batteries B1 to B3 is gradually decreased while the voltage of the secondary batteries B1 to B3 is maintained at the threshold voltage Vth. , the constant current charging control of the secondary battery B3 is terminated and the constant voltage charging control of the secondary batteries B1 to B3 is started.

Then, at time t4, when the current flowing through the secondary batteries B1 to B3 becomes equal to or less than the final current, the control unit 2 instructs the charger Ch so that the current flowing from the charger Ch to the secondary battery system 1 becomes zero. is sent to terminate the constant voltage charging control of the secondary batteries B1 to B3. It should be noted that when the current stops flowing through the secondary batteries B1 to B3, the voltages of the secondary batteries B1 to B3 decrease to near the predetermined voltage V2 due to the influence of the internal resistance and polarization of the secondary batteries B1 to B3. do.

As a result, after the constant voltage charging control of the secondary batteries B1 to B3 is completed, the voltage of each of the secondary batteries B1 to B3 can be brought close to the predetermined voltage V2. That is, after charging the secondary batteries B1 to B3, the voltages of the secondary batteries B1 to B3 can be equalized. Therefore, it is possible to suppress the return current from flowing between the secondary batteries B when switching from the series connection of the secondary batteries B1 to B3 to the parallel connection. In the charging method of the second embodiment, the voltage of the secondary batteries B1 to B3 can be maintained at the threshold voltage Vth in the constant voltage charging control. The voltages of B1 to B3 can be further uniformed, and the flow of return current between the secondary batteries B can be further suppressed when the secondary batteries B1 to B3 are switched from series connection to parallel connection. .

Further, the charging method of the second embodiment can fully charge the secondary batteries B1 to B3 after charging the secondary batteries B1 to B3. As described above, the charging method of the second embodiment can fully charge each of the secondary batteries B1 to B3, and is suitable when the secondary batteries B1 to B3 are configured by LFPs or the like.

In addition, since the charging method of the second embodiment can perform constant voltage charging control of the secondary batteries B1 to B3 at the same time, compared to the charging method of the first embodiment, the total charging time of the secondary batteries B1 to B3 is longer. can be shortened. As described above, the charging method of the second embodiment can relatively shorten the overall charging time of the secondary batteries B1 to B3, and is suitable for the industrial vehicle Ve, which does not have much charging time.

<Charging Method of Embodiment 3>
When charging the secondary batteries B1 to B3, the control unit 2 charges a predetermined secondary battery B (for example, the secondary battery B connected to the positive terminal of the charger Ch) among the secondary batteries B1 to B3. The operation of the connection circuit is controlled so that the predetermined secondary battery B is separated from the secondary battery B1 connected in series each time the voltage becomes equal to or higher than the threshold voltage Vth.

FIG. 4 is a diagram showing voltage changes of the secondary batteries B1 to B3 when the secondary batteries B1 to B3 are charged by the charging method of the third embodiment. Note that the horizontal axis of the two-dimensional coordinates shown in FIG. 4 indicates time, and the vertical axis indicates voltage. Further, the solid line shown in FIG. 4 indicates changes in the voltage of the secondary battery B1, the dashed line shown in FIG. 4 indicates changes in the voltage of the secondary battery B2, and the dashed-dotted line shown in FIG. shows the conversion.

First, at time t0, the control unit 2 connects the secondary batteries B1 to B3 in series by turning off the first output unit switches S11 to S13 and the second output unit switches S21 to S23.

Next, the control unit 2 sends an instruction to the charger Ch so that a constant current flows from the charger Ch to the secondary battery system 1, and starts constant current charging control of the secondary batteries B1 to B3. Then, a constant current flows through the secondary batteries B1 to B3, and the voltage of each of the secondary batteries B1 to B3 gradually increases.

Next, at time t1, when the voltage of the secondary battery B1 becomes equal to or higher than the threshold voltage Vth, the control section 2 turns on the first output section switches S11 and S12, and switches the first output section switch S13 and the second output section switch S13 to the second output section switch. By disconnecting the switches S21 to S23, the secondary battery B1, which is a predetermined secondary battery B, is disconnected from the secondary batteries B1 to B3 connected in series (end of constant current charging control of the secondary battery B1). . Then, a constant current flows only through the secondary batteries B2 and B3, and the respective voltages of the secondary batteries B2 and B3 gradually rise. It is assumed that when the voltage of the secondary battery B1 becomes equal to or higher than the threshold voltage Vth, the voltage of the secondary battery B2 is lower than the threshold voltage Vth, and the voltage of the secondary battery B3 is lower than the voltage of the secondary battery B2. It is also assumed that when the current stops flowing through the secondary battery B1, the voltage of the secondary battery B1 decreases to near the predetermined voltage V3 due to the influence of the internal resistance and polarization of the secondary battery B1.

Next, at time t2, when the voltage of the secondary battery B2 becomes equal to or higher than the threshold voltage Vth, the control unit 2 turns on the first output unit switches S11 and S13, and switches the first output unit switch S12 and the second output unit switch S12 to the second output unit. By disconnecting the switches S21 to S23, the secondary battery B2, which is a predetermined secondary battery B, is disconnected from the secondary batteries B2 and B3 connected in series (end of constant current charging control of the secondary battery B2). . Then, a constant current flows only through the secondary battery B3, and the voltage of the secondary battery B3 gradually increases. It is assumed that when the voltage of the secondary battery B2 becomes equal to or higher than the threshold voltage Vth, the voltage of the secondary battery B3 is lower than the threshold voltage Vth. It is also assumed that when the current stops flowing through the secondary battery B2, the voltage of the secondary battery B2 decreases to near the predetermined voltage V3 due to the influence of the internal resistance and polarization of the secondary battery B2.

Then, when the voltage of the secondary battery B2 reaches or exceeds the threshold voltage Vth at time t3, the control unit 2 sends an instruction to the charger Ch so that the constant current does not flow from the charger Ch to the secondary battery system 1, The constant current charging control of the secondary battery B3 is terminated. It is assumed that when the current stops flowing through the secondary battery B3, the voltage of the secondary battery B3 decreases to near the predetermined voltage V3 due to the influence of the internal resistance and polarization of the secondary battery B3.

As a result, after the constant current charging control of the secondary battery B3 is completed, the voltage of each of the secondary batteries B1 to B3 can be brought close to the predetermined voltage V3. That is, after charging the secondary batteries B1 to B3, the voltages of the secondary batteries B1 to B3 can be equalized. Therefore, it is possible to suppress the return current from flowing between the secondary batteries B when switching from the series connection of the secondary batteries B1 to B3 to the parallel connection.

In addition, since the charging method of Example 3 does not perform constant voltage charging control of the secondary batteries B1 to B3, compared to the charging method of Example 2, the charging time of the entire secondary batteries B1 to B3 is longer. can be shortened. As described above, the charging method of the third embodiment, like the charging method of the second embodiment, can relatively shorten the overall charging time of the secondary batteries B1 to B3, and is therefore suitable for the industrial vehicle Ve. is.

That is, when charging the secondary batteries B1 to B3, the control unit 2 of the secondary battery system 1 of the embodiment, whenever charging of a predetermined secondary battery B among the secondary batteries B1 to B3 is completed, The operation of the connection circuit is controlled so that a predetermined secondary battery B is separated from the secondary batteries B1 to B3 connected in series with each other.

As a result, the secondary batteries B1 to B3 can be charged until the voltage of each of the secondary batteries B1 to B3 reaches the threshold voltage Vth. can be equalized. Therefore, after charging the secondary batteries B1 to B3, even if the secondary batteries B1 to B3 are connected in parallel to discharge the secondary batteries B1 to B3, a relatively large current flow is generated between the secondary batteries B1 to B3. It is possible to suppress the flow of current.

Moreover, 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.

1 Secondary battery system 2 Control unit Tip Positive electrode side charging input portion Tin Negative electrode side charging input portion Top Positive electrode side discharge output portion Ton Negative electrode side discharge output portion Tp Positive electrode side input/output portion Tn Negative electrode side input/output portions S11 to S13 First output Section switches S21 to S23 Second output section switches Ss1 and Ss2 Series connection elements B1 to B3 Secondary battery Lo Load Ch Charger

Claims (4)

a connection circuit for connecting a plurality of secondary batteries in series or in parallel;
When charging the plurality of secondary batteries, controlling the operation of the connection circuit so that the plurality of secondary batteries are connected in series with each other; a controller for controlling the operation of the connection circuit so that the batteries are connected in parallel;
with
When charging the plurality of secondary batteries, the control unit causes the predetermined secondary batteries to be connected in series each time charging of a predetermined secondary battery among the plurality of secondary batteries is completed. controlling the operation of the connection circuit so as to disconnect from the plurality of secondary batteries ,
The connection circuit is
a plurality of first output switches each having one terminal connected to the positive terminal of each of the plurality of secondary batteries;
a plurality of second output switches each having one terminal connected to a negative terminal of each of the plurality of secondary batteries;
a plurality of series connection elements respectively connected between the negative terminal of one of the adjacent secondary batteries and the positive terminal of the other secondary battery;
a positive discharge output section connected to the other terminal of the plurality of first output section switches;
a negative discharge output section connected to the other terminal of the plurality of second output section switches;
Between the positive terminal of the secondary battery provided at one end of the plurality of secondary batteries connected in series via the plurality of series connection elements and one terminal of the first output section switch a positive charging input connected to the
Between the negative terminal of the secondary battery provided at the other end of the plurality of secondary batteries connected in series via the plurality of series connection elements and one terminal of the second output section switch a negative charging input connected to the
with
When the plurality of secondary batteries are connected in series, the controller cuts off the plurality of first output section switches and the plurality of second output section switches, and connects the plurality of secondary batteries in parallel with each other. , the plurality of first output section switches and the plurality of second output section switches are rendered conductive
A secondary battery system characterized by: The secondary battery system according to claim 1,
When charging the plurality of secondary batteries, the control unit controls the operation of the connection circuit so that the plurality of secondary batteries are connected in series with each other and supplies a constant current to the plurality of secondary batteries. and when the voltage of a predetermined secondary battery among the plurality of secondary batteries reaches a threshold voltage or higher, the current flowing through the plurality of secondary batteries is gradually reduced while the voltage of the predetermined secondary battery is maintained at the threshold voltage. and when the current flowing through the plurality of secondary batteries becomes equal to or less than the final current, the operation of the connection circuit is operated such that the predetermined secondary battery is disconnected from the plurality of secondary batteries connected in series with each other. A secondary battery system, characterized in that the control is repeated until charging of all the secondary batteries is completed. The secondary battery system according to claim 1,
When charging the plurality of secondary batteries, the control unit controls the operation of the connection circuit so that the plurality of secondary batteries are connected in series with each other and supplies a constant current to the plurality of secondary batteries. , so that each time the voltage of a predetermined secondary battery among the plurality of secondary batteries becomes equal to or higher than a threshold voltage, the predetermined secondary battery is disconnected from the plurality of secondary batteries connected in series with each other; The operation of the connection circuit is controlled, and when the voltage of the last rechargeable battery that has not been charged reaches the threshold voltage or higher, the operation of the connection circuit is controlled so that the plurality of secondary batteries are connected in series with each other. While controlling and maintaining the voltage of each of the plurality of secondary batteries at the threshold voltage, the current flowing through the plurality of secondary batteries is gradually reduced, and when the current flowing through the plurality of secondary batteries becomes equal to or less than the final current , a secondary battery system characterized in that the current flowing through the plurality of secondary batteries is set to zero. An industrial vehicle comprising the secondary battery system according to any one of claims 1 to 3 .

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