Control circuit of parallel lithium battery pack

Abstract

The utility model provides a control circuit of a parallel lithium battery pack, the control circuit comprises at least two lithium battery pack access interfaces and a charge-discharge control unit, each lithium battery pack access interface comprises a lithium battery pack access end and a voltage output end, the lithium battery pack is accessed to the lithium battery pack access interface through the lithium battery pack access end, and the charge-discharge control unit is connected to the lithium battery pack access interface through the voltage output end. The charging and discharging control unit comprises switch elements with the same number as the lithium battery pack access interfaces, each switch element corresponds to one lithium battery pack access interface, and the control end of each switch element is connected with the voltage output end of the corresponding lithium battery pack access interface. And each switch element also comprises a control signal end for receiving a control signal. According to the utility model, the charging and discharging of each lithium battery pack can be respectively controlled through the switch element, when the lithium battery packs with different voltages are connected in parallel, the sequence of each lithium battery pack participating in discharging can be controlled according to the voltage difference, and the charging and discharging safety of the lithium battery packs is ensured.

Description

Technical Field

[0001] The utility model relates to the technical field of lithium battery charge and discharge control, in particular to a control circuit for a parallel lithium battery pack. Background Art

[0002] When lithium battery packs are produced, lithium battery cells of the same voltage need to be connected in parallel through sorting to form a lithium battery pack, and a protection board needs to be set up to provide charging protection for the lithium battery pack. However, in the actual use of lithium battery packs, there will be scenarios where lithium battery packs of different voltages are used to power the same product. When lithium battery packs of different voltages are connected together, the high-voltage lithium battery pack will charge the low-voltage lithium battery pack. The internal resistance of lithium battery packs is generally very small. This charging phenomenon between lithium battery packs will bring a large charging current, which is likely to trigger the charging protection of the low-voltage lithium battery pack, and even cause the low-voltage lithium battery pack to heat up and be damaged. Utility Model Content

[0003] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a control circuit for parallel lithium battery packs, which controls the charging and discharging of each lithium battery pack separately through switching elements. When lithium battery packs with different voltages are connected in parallel, the order in which each lithium battery pack participates in the discharge can be controlled according to the voltage difference between them. This can solve the problem of high current charging and discharging caused by the charging phenomenon between lithium batteries caused by the voltage difference between lithium battery packs when lithium battery packs with different voltages are used for power supply at the same time, and ensure the charging and discharging safety of the lithium battery packs.

[0004] The purpose of this utility model is achieved through the following technical solutions:

[0005] A control circuit for a parallel lithium battery pack includes at least two lithium battery pack access interfaces and a charge and discharge control unit, each lithium battery pack access interface includes a lithium battery pack access terminal and a voltage output terminal, the lithium battery pack is connected to the lithium battery pack access interface via the lithium battery pack access terminal, the charge and discharge control unit includes switch elements whose number is the same as the lithium battery pack access interface, and each switch element corresponds to a lithium battery pack access interface, the control terminal of each switch element is connected to the voltage output terminal of the corresponding lithium battery pack access interface, and each switch element also includes a control signal terminal for receiving a control signal.

[0006] Furthermore, the lithium battery pack access interface includes a first lithium battery pack access interface and a second lithium battery pack access interface.

[0007] Furthermore, it also includes a battery status detection unit, which is connected to the voltage output end of the first lithium battery pack access interface and the voltage output end of the second lithium battery pack access interface at the same time, and the battery status detection unit also includes a signal output end for outputting a battery status detection signal.

[0008] Furthermore, the battery status detection unit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5 and an operational amplifier U1, one end of the resistor R1 is connected to the second end of the first lithium battery pack access interface, the other end of the resistor R1 is connected to the second end of the second lithium battery access interface, one end of the resistor R2 is connected to one end of the resistor R1, the other end of the resistor R2 is connected to the positive input end of the operational amplifier U1, the positive input end of the operational amplifier U1 is also connected to the follower unit through the resistor R4, one end of the resistor R3 is connected to the other end of the resistor R1, the other end of the resistor R3 is connected to the negative input end of the operational amplifier U1, the negative input end of the operational amplifier U1 is also connected to the output end of the operational amplifier U1 through the resistor R5, and the output end of the operational amplifier U1 is a signal output end of the battery status detection unit to output a battery status detection signal.

[0009] Furthermore, it also includes a follower unit, which is connected to the battery status detection unit to provide a reference voltage for the operational amplifier U1 in the battery status detection unit.

[0010] Furthermore, the follower unit includes a resistor R6, a resistor R7 and an operational amplifier U2, one end of the resistor R6 is connected to the 5V voltage output terminal, the other end of the resistor R6 is connected to the positive input terminal of the operational amplifier U2, the other end of the resistor R6 is also grounded through the resistor R7, the negative input terminal of the operational amplifier U2 is also connected to the output terminal of the operational amplifier U2, the output terminal of the operational amplifier U2 is connected to the battery status detection unit, the positive power supply input terminal of the operational amplifier U2 is connected to the 5V voltage output terminal, and the negative power supply input terminal of the operational amplifier U2 is grounded.

[0011] Furthermore, when the voltage at the signal output end of the battery status detection unit is lower than the reference voltage of the operational amplifier U2, the switch element corresponding to the first lithium battery pack access interface is turned on, and when the voltage at the signal output end of the battery status detection unit reaches the reference voltage of the operational amplifier U2, the switch element corresponding to the second lithium battery pack access interface is turned on.

[0012] Furthermore, when the voltage at the signal output end of the battery status detection unit is higher than the reference voltage of the operational amplifier U2, the switch element corresponding to the second lithium battery pack access interface is turned on, and when the voltage at the signal output end of the battery status detection unit reaches the reference voltage of the operational amplifier U2, the switch element corresponding to the first lithium battery pack access interface is turned on.

[0013] Furthermore, the voltage at the signal output terminal of the battery status detection unit is equal to the reference voltage of the operational amplifier U2, and the switch element corresponding to the first lithium battery pack access interface and the switch element corresponding to the second lithium battery pack access interface are turned on at the same time.

[0014] The beneficial effects of the utility model are:

[0015] The charging and discharging of each lithium battery pack is controlled separately through switching elements. When lithium battery packs with different voltages are connected in parallel, the order in which each lithium battery pack participates in the discharge can be controlled according to their voltage difference. This can avoid the problem of high current charging and discharging caused by charging between lithium batteries, and can also ensure the charging and discharging safety of the lithium battery pack while further reducing energy loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the utility model;

[0017] Figure 2 It is a circuit diagram of a control circuit of a parallel lithium battery pack according to an embodiment of the utility model;

[0018] Figure 3 The invention is a circuit diagram of a control circuit of a parallel lithium battery pack using a voltage-dividing resistor as a battery status detection unit according to an embodiment of the present invention.

[0019] Among them: 1. lithium battery pack access interface, 11. lithium battery pack access terminal, 12. voltage output terminal, 2. charge and discharge control unit, 21. switch element, 211. control terminal, 212. control signal terminal, 3. lithium battery pack. DETAILED DESCRIPTION

[0020] The utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0021] Example:

[0022] A control circuit for a parallel lithium battery pack, such as Figure 1As shown, it includes at least two lithium battery pack access interfaces 1 and a charge and discharge control unit 2, each lithium battery pack access interface includes a lithium battery pack access terminal 11 and a voltage output terminal 12, and the lithium battery pack 3 is connected to the lithium battery pack access interface through the lithium battery pack access terminal. The charge and discharge control unit includes switch elements 21 with the same number as the lithium battery pack access interface, and each switch element corresponds to a lithium battery pack access interface. The control terminal 211 of each switch element is connected to the voltage output terminal of the corresponding lithium battery pack access interface, and each switch element also includes a control signal terminal 212 for receiving a control signal.

[0023] In this embodiment, a MOS tube is specifically arranged as a switch element, so as to reduce the power consumption of the lithium battery pack as much as possible during the application process.

[0024] Taking the first lithium battery pack access interface and the second lithium battery pack access interface as an example, the charge and discharge control unit specifically includes a MOS tube Q1 and a MOS tube Q2, the drain of the MOS tube Q1 is connected to the voltage output end of the first lithium battery pack access interface, the source of the MOS tube Q1 is grounded, and the gate of the MOS tube Q1 is the control signal end BA1MG for receiving the control signal, the drain of the MOS tube Q2 is connected to the voltage output end of the first lithium battery pack access interface, the source of the MOS tube Q2 is grounded, and the gate of the MOS tube Q2 is the control signal end BA2MG for receiving the control signal.

[0025] In this embodiment, a single chip microcomputer is specifically used to process the battery status detection signal outputted from the signal output terminal of the battery status detection unit, and formulates and sends a control signal to the control signal terminal of the corresponding switch element according to the battery status detection signal.

[0026] It also includes a battery status detection unit, which is connected to the voltage output end of the first lithium battery pack access interface and the voltage output end of the second lithium battery pack access interface at the same time. The battery status detection unit also includes a signal output end for outputting a battery status detection signal.

[0027] Specifically, the single-chip microcomputer can change the corresponding pin level according to the voltage of the signal output terminal of the receiving battery status detection unit, thereby changing the control signal terminal voltage of the corresponding connected switch element, that is, changing the corresponding MOS tube gate voltage, and realizing the conduction control of the MOS tube. A resistor R8 is also connected in series between the MOS tube Q1 and the control unit, a resistor R9 is also connected in series between the gate and the source of the MOS tube Q1, a resistor R10 is also connected in series between the MOS tube Q2 and the control unit, and a resistor R11 is also connected in series between the gate and the source of the MOS tube Q1, so as to ensure that the MOS tube Q1 and the MOS tube Q2 can be normally controlled to be turned on and off.

[0028] The battery also includes a follower unit, which is connected to the battery status detection unit to provide a reference voltage for the operational amplifier U1 in the battery status detection unit. In this embodiment, the reference voltage value is specifically 2.5V.

[0029] The battery status detection unit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5 and an operational amplifier U1, one end of the resistor R1 is connected to the second end of the first lithium battery pack access interface, the other end of the resistor R1 is connected to the second end of the second lithium battery access interface, one end of the resistor R2 is connected to one end of the resistor R1, the other end of the resistor R2 is connected to the positive input end of the operational amplifier U1, the positive input end of the operational amplifier U1 is also connected to the follower unit through the resistor R4, one end of the resistor R3 is connected to the other end of the resistor R1, the other end of the resistor R3 is connected to the negative input end of the operational amplifier U1, the negative input end of the operational amplifier U1 is also connected to the output end of the operational amplifier U1 through the resistor R5, and the output end of the operational amplifier U1 is a signal output end V_DIFF12 of the battery status detection unit outputting a battery status detection signal.

[0030] The follower unit includes a resistor R6, a resistor R7 and an operational amplifier U2, one end of the resistor R6 is connected to the 5V voltage output terminal, the other end of the resistor R6 is connected to the positive input terminal of the operational amplifier U2, the other end of the resistor R6 is also connected to the ground through the resistor R7, the negative input terminal of the operational amplifier U2 is also connected to the output terminal of the operational amplifier U2, the output terminal of the operational amplifier U2 is connected to the battery status detection unit, the positive power supply input terminal of the operational amplifier U2 is connected to the 5V voltage output terminal, and the negative power supply input terminal of the operational amplifier U2 is grounded.

[0031] In this embodiment, the circuit diagram of the control circuit of the parallel lithium battery pack is as follows: Figure 2 shown.

[0032] When two lithium battery packs with a large voltage difference are connected, that is, the voltage difference between the first lithium battery pack and the second lithium battery pack is greater than 1.5 V. When there is no load and MOS tube Q1 and MOS tube Q2 are not turned on, the output voltage of operational amplifier U1 is 2.5±βUd, and the control unit can recognize this voltage.

[0033] If it is identified as 2.5-βUd, it means that the voltage of the first lithium battery pack connected is higher. At this time, the MOS tube Q1 can be controlled to open, so that the loss can be reduced when the lithium battery pack is discharged. At this time, since the MOS tube Q2 is in the off state, the inter-battery charging process will not occur because the voltage of the first lithium battery pack is higher than that of the second lithium battery pack. And because the voltage of the first lithium battery pack is higher, it will give priority to output current when used. As the voltage of the first lithium battery pack is used, the voltage will decrease. When the voltage difference between the two lithium battery packs is less than a certain value, both MOS tubes can be turned on.

[0034] If it is identified as 2.5+βUd, it means that the voltage of the connected second lithium battery pack is higher. At this time, the MOS tube Q2 can be controlled to open, so that the loss can be reduced when the lithium battery pack is discharged. At this time, since the MOS tube Q1 is in the closed state, the inter-battery charging process will not occur because the voltage of the second lithium battery pack is higher than that of the first lithium battery pack. And because the voltage of the second lithium battery pack is higher, it will give priority to output current when used. As the voltage of the second lithium battery pack is used, the voltage will decrease. When the voltage difference between the two lithium battery packs is less than a certain value, both MOS tubes can be turned on.

[0035] Therefore, the voltage at the signal output end of the battery state detection unit is lower than the reference voltage of the operational amplifier U2, turning on the MOS tube Q1, and when the voltage at the signal output end of the battery state detection unit reaches the reference voltage of the operational amplifier U2, turning on the MOS tube Q2.

[0036] When the voltage at the signal output end of the battery status detection unit is higher than the reference voltage of the operational amplifier U2, the MOS tube Q2 is turned on, and when the voltage at the signal output end of the battery status detection unit reaches the reference voltage of the operational amplifier U2, the MOS tube Q1 is turned on.

[0037] The voltage at the signal output terminal of the battery status detection unit is equal to the reference voltage of the operational amplifier U2, and the MOS transistor Q1 and the MOS transistor Q2 are turned on at the same time.

[0038] In addition to the operational amplifier U2, the battery status detection unit can also realize the voltage detection of the first lithium battery pack and the second lithium battery pack through the corresponding two voltage-dividing resistors connected in series, and the signal output end of the battery status detection signal is respectively set in the middle of the two corresponding voltage-dividing resistors connected in series. Specifically, the voltage-dividing resistor R12, the voltage-dividing resistor R13, the voltage-dividing resistor R14 and the voltage-dividing resistor R15 are connected in series with each other, and one end of the series connection is connected to the voltage output end of the first lithium battery pack access interface, and the other end is grounded; the voltage-dividing resistor R13 and the voltage-dividing resistor R14 are connected in series with each other, and one end of the series connection is connected to the voltage output end of the second lithium battery pack access interface, and the other end is grounded. And different from using an operational amplifier as the battery status detection unit, the lithium battery pack access end and the voltage output end of the first lithium battery access interface share a pin port, and similarly, the lithium battery pack access end and the voltage output end of the second lithium battery access interface also share a pin port. And because the operational amplifier is not used as the battery status detection unit, the follower unit is also cancelled. In order to ensure the normal operation of the circuit, a pin header J1 is also provided to connect the MOS tube Q1 and the MOS tube Q2. The circuit diagram is as follows Figure 3 As shown, it is also possible to turn on the MOS tube corresponding to the lithium battery pack with a high voltage first to reduce the output conduction loss.

[0039] In addition to being applicable to the control scenario of two parallel-connected lithium battery packs, this embodiment is also applicable to the scenario of only connecting one lithium battery pack.

[0040] When only one lithium battery pack is connected, if the load current is very small, when neither MOS tube Q1 nor MOS tube Q2 is turned on, the output current of the lithium battery pack will flow back to the lithium battery pack through the body diode of the MOS tube, but because the current is very small, the body diode voltage drop of the two MOS tubes is not much different, so the voltage difference across the resistor R1 is 0, and the output voltage of the operational amplifier U1 is 2.5V. When a load is connected, taking the case where the lithium battery pack is connected to the first lithium battery pack access interface and the second lithium battery pack access interface is not connected to the lithium battery pack as an example, when the MOS tube Q1 is not turned on, the body diode voltage drop of the MOS tube Q1 is greater than the body diode voltage drop of the MOS tube Q2, and the voltage at the upper end of the resistor R1 is lower than the voltage at the lower end by Ud, and the maximum Ud is about 1.5V, which can be set according to the parameters of the MOS tube. After being reduced by the operational amplifier U1, the voltage output by the operational amplifier U1 should be 2.5-βUd, and the microcontroller can identify the battery status through this voltage, thereby controlling the MOS tube Q1 to turn on to reduce the conduction power consumption.

[0041] Similarly, this embodiment is also applicable to the control of two lithium battery packs with similar voltages. When two lithium battery packs with similar voltages are connected, the voltage difference across the resistor R1 is 0, and the output of the operational amplifier U1 is 2.5V. The microcontroller can identify the battery status through this voltage, thereby controlling the MOS tube Q1 and the MOS tube Q2 to be turned on at the same time to reduce the conduction power consumption.

[0042] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A control circuit for a parallel lithium battery pack, characterized in that: It includes at least two lithium battery pack access interfaces and a charge and discharge control unit, each lithium battery pack access interface includes a lithium battery pack access terminal and a voltage output terminal, the lithium battery pack is connected to the lithium battery pack access interface via the lithium battery pack access terminal, the charge and discharge control unit includes switch elements with the same number as the lithium battery pack access interface, and each switch element corresponds to a lithium battery pack access interface, the control end of each switch element is connected to the voltage output terminal of the corresponding lithium battery pack access interface, and each switch element also includes a control signal terminal for receiving a control signal.

2. The control circuit of a parallel lithium battery pack according to claim 1, characterized in that: The lithium battery pack access interface includes a first lithium battery pack access interface and a second lithium battery pack access interface.

3. The control circuit of a parallel lithium battery pack according to claim 2, characterized in that: It also includes a battery status detection unit, which is connected to the voltage output end of the first lithium battery pack access interface and the voltage output end of the second lithium battery pack access interface at the same time, and the battery status detection unit also includes a signal output end for outputting a battery status detection signal.

4. The control circuit of a parallel lithium battery pack according to claim 3, characterized in that: The battery status detection unit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5 and an operational amplifier U1, one end of the resistor R1 is connected to the second end of the first lithium battery pack access interface, the other end of the resistor R1 is connected to the second end of the second lithium battery access interface, one end of the resistor R2 is connected to one end of the resistor R1, the other end of the resistor R2 is connected to the positive input end of the operational amplifier U1, the positive input end of the operational amplifier U1 is also connected to the follower unit through the resistor R4, one end of the resistor R3 is connected to the other end of the resistor R1, the other end of the resistor R3 is connected to the negative input end of the operational amplifier U1, the negative input end of the operational amplifier U1 is also connected to the output end of the operational amplifier U1 through the resistor R5, and the output end of the operational amplifier U1 is a signal output end of the battery status detection unit to output a battery status detection signal.

5. The control circuit of a parallel lithium battery pack according to claim 4, characterized in that: It also includes a follower unit, which is connected to the battery status detection unit to provide a reference voltage for the operational amplifier U1 in the battery status detection unit.

6. The control circuit of a parallel lithium battery pack according to claim 5, characterized in that: The follower unit includes a resistor R6, a resistor R7 and an operational amplifier U2, one end of the resistor R6 is connected to the 5V voltage output terminal, the other end of the resistor R6 is connected to the positive input terminal of the operational amplifier U2, the other end of the resistor R6 is also connected to the ground through the resistor R7, the negative input terminal of the operational amplifier U2 is also connected to the output terminal of the operational amplifier U2, the output terminal of the operational amplifier U2 is connected to the battery status detection unit, the positive power supply input terminal of the operational amplifier U2 is connected to the 5V voltage output terminal, and the negative power supply input terminal of the operational amplifier U2 is grounded.

7. The control circuit of a parallel lithium battery pack according to claim 6, characterized in that: When the voltage at the signal output end of the battery status detection unit is lower than the reference voltage of the operational amplifier U2, the switch element corresponding to the first lithium battery pack access interface is turned on. When the voltage at the signal output end of the battery status detection unit reaches the reference voltage of the operational amplifier U2, the switch element corresponding to the second lithium battery pack access interface is turned on.

8. The control circuit of a parallel lithium battery pack according to claim 6, characterized in that: The voltage at the signal output end of the battery status detection unit is higher than the reference voltage of the operational amplifier U2, turning on the switch element corresponding to the second lithium battery pack access interface, and when the voltage at the signal output end of the battery status detection unit reaches the reference voltage of the operational amplifier U2, turning on the switch element corresponding to the first lithium battery pack access interface.

9. The control circuit of a parallel lithium battery pack according to claim 6, characterized in that: The voltage at the signal output terminal of the battery status detection unit is equal to the reference voltage of the operational amplifier U2, and the switch element corresponding to the first lithium battery pack access interface and the switch element corresponding to the second lithium battery pack access interface are turned on at the same time.

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