Active equalization circuit of single battery cell group and active equalization device of battery pack group

Abstract

The invention aims to provide the active equalization circuit of the single cell group and the active equalization device of the battery pack group, which are simple in structure, low in cost, good in efficiency and good in equalization effect. The active equalization circuit of the single cell group comprises a first bus (a) and a second bus (b), two ends of any cell (Bn) are respectively connected to the first bus (a) or the second bus (b) through two connecting lines (1), each connecting line (1) is provided with a gating switch (2), the on-off of the gating switch (2) is controlled by a switching circuit (3), and the on-off of the gating switch (2) is controlled by the switching circuit (3). The other end of the first bus (a) and the other end of the second bus (b) are connected with a first flyback switching circuit (5) through an H bridge (4), and the output end of the first flyback switching circuit is connected with an energy storage module (6); the active equalization device of the battery pack group comprising the active equalization circuit further comprises a second flyback switch circuit (8) and a voltage comparator (9). The invention relates to the technical field of battery equalization.

Description

Technical Field

[0001] The present invention relates to the technical field of battery balancing, and in particular to an active balancing circuit for a single cell group and an active balancing device for a battery pack group. Background Art

[0002] In the energy storage system, the battery cells are unbalanced due to long-term use. In order to ensure the service life of the battery and the stability of the operating voltage, a balancing strategy is generally used to balance the battery cells. Generally, there are the following methods: 1. Passive balancing is usually used, that is, the method of discharging the battery cell with high energy through a resistor. Specifically, the battery cell with higher voltage is discharged by turning on the MOS and using a resistor by using the balancing foot on the AFE (front-end analog chip) board on the BMS (battery management system) board. The energy in the battery cell is transferred to the air for consumption by heating. However, this method will cause energy loss and the balancing rate is too slow. 2. Inductive and capacitive active balancing generally only balances with adjacent batteries, which is difficult to control through software algorithms, and the control level is low. Although the voltage difference between two adjacent batteries can be controlled, the batteries connected in series will produce cumulative errors, and the overall voltage difference is difficult to control. 3. The use of flyback active balancing requires a large number of flyback transformers and MOS tubes, which is too expensive. Each sampling channel is equipped with a standard DC-DC and requires the addition of additional energy carriers to store the power released by high-energy cells and charge low-power cells, making the system cost extremely expensive.

[0003] There are also companies in this field who have made efforts to this end. For example, the Chinese invention patent document with publication number CN104184192A discloses an active equalization circuit for charging and discharging of lithium-ion power battery packs. The active equalization circuit is provided with a voltage acquisition module and a voltage equalization circuit for each battery pack of the power battery pack; the voltage acquisition module collects the voltage of each battery cell in real time and sends it to the battery management system, and performs voltage equalization when the voltage of the battery cell, battery pack or power battery pack exceeds the set upper and lower limits; the voltage equalization circuit includes a transformer and an equalization switch MOS tube, and each battery cell in the power pack, each battery pack in the power battery pack, and the entire power battery pack are respectively connected to a winding of the same core transformer through two equalization switch MOS tubes, and the corresponding equalization voltage is coupled on the transformer by controlling the on and off of the equalization switch MOS tube to realize charging and discharging. However, this solution also has a complex structure and requires the provision of multiple windings, which greatly increases the cost.

[0004] Therefore, it is urgent to design a new balancing device to solve the above problems. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an active balancing circuit for a single cell group and an active balancing device for a battery pack group, which have simple structure, low cost, high efficiency and good balancing effect.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the active balancing circuit of the single cell group of the present invention is: an active balancing circuit of a single cell group, the single cell group is composed of n cells connected in series, wherein n is a natural number representing the number of cells connected in series, the active balancing circuit of the single cell group is connected to the peripheral BMS system, the active balancing circuit includes a first bus and a second bus, the two ends of any of the cells are respectively connected to the first bus or the second bus through two connecting wires, a selection switch is arranged on each of the connecting wires, the selection switch is controlled by a switching circuit, the other end of the first bus and the second bus is connected to the first flyback switch circuit through an H bridge, and the output end of the first flyback switch circuit is connected to an energy storage module.

[0007] The first flyback switch circuit includes a first transformer including a first primary side and a first secondary side, a first primary MOS tube connected to the loop of the first primary side, a first primary PWM connected to the G pole of the first primary MOS tube, a first secondary MOS tube connected to the loop of the first secondary side, and a first secondary PWM connected to the G pole of the first secondary MOS tube, and the energy storage module is connected to the loop of the first secondary side.

[0008] The four bridge arms of the H bridge are each composed of two bridge arm MOS tubes connected in series, the other ends of the two bridge arms connected to the first bus are respectively connected to the loop of the first primary side, and the other ends of the two bridge arms connected to the second bus are respectively connected to the loop of the first primary side.

[0009] The selection switch is composed of two NMOS tubes connected in series, and the G poles of the two NMOS tubes constituting the selection switch with a common connection line are connected to the switch circuit, and the two NMOS tubes rely on the internal PN junction to jointly control the on and off of one end of the single cell; when the single cell group is connected in series with n+1 cells, at the positive end of the single cell group, the selection switch is composed of a PMOS tube, the G pole of the PMOS tube is connected to the AFE chip, and the G pole of the PMOS tube is connected to the Sn+1 pin of the AFE chip, wherein n is a natural number representing the number of cells connected in series.

[0010] The switch circuit includes an AFE chip and two voltage-dividing resistors respectively led out from the AFE chip, and the other ends of the voltage-dividing resistors are output to the selection switch to control the on-off of the selection switch.

[0011] The energy storage module is the single cell group formed by connecting B1 to Bn+1 in series.

[0012] The switch circuit is provided with a control output pin, and the two voltage-dividing resistors are connected in series, and the control output pin is led out from the series connection point to output a control signal to the selection switch.

[0013] An active balancing device for a battery pack group including the active balancing circuit of the above-mentioned single cell group, wherein the battery pack group is composed of a plurality of battery packs connected in series through a series bus, and the active balancing device for the battery pack group also includes a second flyback switch circuit and a voltage comparator connected between any two adjacent battery packs, the two input ends of the voltage comparator are respectively connected to the positive electrodes of the two adjacent battery packs, the output end of the voltage comparator is respectively connected to the two control ends of the second flyback switch circuit, and one of the control ends of the flyback switch circuit is controlled to operate according to the output value of the voltage comparator.

[0014] The second flyback switch circuit includes a first transformer including a second primary side and a second secondary side, a second primary MOS tube connected to the loop of the second primary side, a second primary PWM connected to the G pole of the second primary MOS tube, a second secondary MOS tube connected to the loop of the second secondary side, and a second secondary PWM connected to the G pole of the second secondary MOS tube. A first loop is formed between the positive pole of the battery pack connected to the second primary side, the second primary side, the second primary MOS tube, and the negative pole of the battery pack connected to the second primary side. A second loop is formed between the positive pole of the battery pack connected to the second secondary side, the second secondary side, the second secondary MOS tube, and the negative pole of the battery pack connected to the second secondary side. The output end of the voltage comparator is respectively connected to the connection point of the second primary MOS tube and the second primary PWM and the connection point of the second secondary MOS tube and the second secondary PWM.

[0015] The beneficial effects of the present invention are as follows: in the active balancing circuit of the single cell group of the present invention, the balancing type of the corresponding cell is confirmed by the BMS system to confirm whether the cell is discharging outward or charging the cell. By setting the first bus and the second bus, the positive and negative poles of each cell are connected to different buses respectively. When a cell is to be balanced, the selection switch is controlled by the switch circuit to select the corresponding cell. The selection switch connects the positive and negative poles of the cell to the two buses, and then the four bridge arms of the H bridge are used to determine whether to connect to the positive end or the negative end of the first flyback switch circuit according to the positive and negative poles of the cell. After the determination is made, the first flyback switch circuit charges the energy storage module according to the determined balancing type, or the energy storage module charges the selected connected cell to supplement the electric energy of the cell. Compared with the prior art, the active balancing circuit of the single cell group of the present invention has a simple structure and low cost, and energy storage is achieved through the energy storage module, which improves energy efficiency and also makes the balancing effect of the entire circuit excellent.

[0016] The active balancing device of the battery pack group including the active balancing circuit of the above-mentioned single cell group confirms the positive voltage of the two battery packs connected thereto through a voltage comparator. When it is confirmed that the voltage of a certain battery pack is higher, the control end of the battery pack with higher voltage in the second flyback switch circuit is opened, and the energy of the battery pack with higher voltage is driven to couple to the battery pack with lower voltage through the second flyback switch circuit, so as to charge the battery pack with lower voltage. Similarly, when there is a voltage difference between any two adjacent battery packs, electric energy can be transferred, thereby ensuring that all battery packs connected in series can be actively balanced. It simplifies the balancing structure, greatly reduces the cost, and realizes automatic balancing with high precision by using the flyback circuit in combination with the comparator. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of the active equalization circuit of the present invention; Figure 2 is a schematic diagram of the switching circuit; Figure 3 It is the schematic diagram of the active balancing device of the battery pack. DETAILED DESCRIPTION

[0018] like Figure 1 and Figure 2As shown, in the active balancing circuit of the monomer battery group of the present invention, the monomer battery group is composed of n battery cells Bn connected in series, wherein n is a natural number representing the number of battery cells connected in series, and in this embodiment, the number of battery cells is 16. The active balancing circuit of the monomer battery group is connected to the peripheral BMS system, and the active balancing circuit includes a first bus a and a second bus b, and the two ends of any of the battery cells Bn are respectively connected to the first bus a or the second bus b through two connecting wires 1, and a selection switch 2 is provided on each of the connecting wires 1, and the selection switch 2 is controlled by a switch circuit 3. The other end of the first bus a and the second bus b is connected to the first flyback switch circuit 5 through an H bridge 4, and the output end of the first flyback switch circuit 5 is connected to an energy storage module 6.

[0019] The first flyback switch circuit 5 includes a first transformer 51 including a first primary side 511 and a first secondary side 512, a first primary side MOS tube 52 connected to the loop of the first primary side 511, a first primary side PWM53 connected to the G pole of the first primary side MOS tube 52, a first secondary side MOS tube 54 connected to the loop of the first secondary side 512, and a first secondary side PWM55 connected to the G pole of the first secondary side MOS tube 54. The energy storage module 6 is connected to the loop of the first secondary side 512.

[0020] The four bridge arms of the H bridge 4 are each composed of two bridge arm MOS tubes 41 connected in series, and the other ends of the two bridge arms connected to the first bus a are respectively connected to the loop of the first primary side 511, and the other ends of the two bridge arms connected to the second bus b are respectively connected to the loop of the first primary side 511.

[0021] The selection switch 2 is composed of two NMOS tubes 21 connected in series, and the G poles of the two NMOS tubes 21 constituting the selection switch 2 with a common connection line are both connected to the switch circuit 3, and the two NMOS tubes 21 rely on the internal PN junction to jointly control the on and off of one end of the single cell. When the single cell group is connected in series with n+1 cells Bn+1, at the positive end of the single cell group, the selection switch 2 is composed of a PMOS tube 22, and the G pole of the PMOS tube 22 is connected to the AFE chip 31, and the G pole of the PMOS tube 22 is connected to the Sn+1 pin of the AFE chip 31, wherein n is a natural number, representing the number of cells connected in series. At this time, when it is necessary to connect the Bn+1 cell to the primary side of the transformer, it only needs to change the Sn+1 of the AFE chip 31 to a low level to complete this operation, which is optimized in terms of structure and cost.

[0022] The switch circuit 3 includes an AFE chip 31 and two voltage-dividing resistors 32 respectively led from the AFE chip 31, and the other end of the voltage-dividing resistor 32 is output to the selection switch 2 to control the on and off of the selection switch 2. Here, for the nth battery cell, when the AFE chip 31 turns on the balance, its balance pins Sn and Cn are respectively connected to the two voltage-dividing resistors 32, and then the control amount is output to the selection switch 2, and one of the selection switches 2 is selected to be turned on, so that the corresponding battery cell is turned on.

[0023] The energy storage module 6 is the single cell group formed by connecting B1 to Bn+1 in series.

[0024] The switch circuit 3 is provided with a control output pin 33 . After the two voltage-dividing resistors 32 are connected in series, the control output pin 33 is led out from the series connection point to output a control signal to the selection switch 2 .

[0025] When the BMS system turns on balancing, when it is confirmed that a certain battery cell needs to be balanced, the AFE chip in the switch circuit 3 corresponding to the battery cell sends a drive signal to the selection switch corresponding to the battery cell, so that the positive and negative electrodes of the battery cell are respectively connected to the first bus and the second bus. At this time, the positive electrode of the battery cell may be mounted on the first bus, or the positive electrode of the battery cell may be mounted on the second bus. For this reason, the positive and negative electrodes of the battery cell can be matched with the positive and negative electrodes of the first primary side through the setting of the H-bridge to avoid wrong connection of electrodes. The positive and negative electrodes of the first primary side of the first flyback switch circuit 5 confirmed by the H-bridge are connected, so that an energy coupling link is established between the battery cell and the energy storage module through the H-bridge and the first flyback switch circuit. When the selected battery cell needs to be charged, the first secondary side PWM located on one side of the energy storage module sends a PWM wave, driving the energy storage module to couple electric energy to the first primary side through the first secondary side, and then store the electric energy in the selected battery cell to achieve balancing. Otherwise, the electric energy in the selected battery cell is coupled to the first secondary side and stored in the energy storage module.

[0026] like Figure 3 As shown, an active balancing device for a battery pack group including the active balancing circuit of the above-mentioned single cell group, wherein the battery pack group is composed of a plurality of battery packs connected in series through a series bus 7, and the active balancing device for the battery pack group also includes a second flyback switch circuit 8 and a voltage comparator 9 connected between any two adjacent battery packs, the two input ends of the voltage comparator 9 are respectively connected to the positive electrodes of the two adjacent battery packs, and the output end of the voltage comparator 9 is respectively connected to the two control ends of the second flyback switch circuit 8, and one of the control ends of the flyback switch circuit 8 is controlled to operate according to the output value of the voltage comparator 9.

[0027] The second flyback switch circuit 8 includes a first transformer 81 including a second primary side 811 and a second secondary side 812, a second primary side MOS transistor 82 connected to the loop of the second primary side 811, a second primary side PWM83 connected to the G pole of the second primary side MOS transistor 82, a second secondary side MOS transistor 84 connected to the loop of the second secondary side 812, and a second secondary side PWM85 connected to the G pole of the second secondary side MOS transistor 84. A first loop is formed between the positive pole of the battery pack connected to the second primary side 811, the second primary side 811, the second primary side MOS transistor 82, and the negative pole of the battery pack connected to the second primary side 811. A second loop is formed between the positive pole of the battery pack connected to the second secondary side 812, the second secondary side 812, the second secondary side MOS transistor 84, and the negative pole of the battery pack connected to the second secondary side 812. The output end of the voltage comparator 9 is respectively connected to the connection point between the second primary side MOS transistor 82 and the second primary side PWM83 and the second secondary side MOS transistor 84 and the second secondary side PWM At the connection point of 85.

[0028] Similarly, here, through the setting of the first loop and the second loop, bidirectional DC-DC module control is achieved between the battery packs, so that the voltage of each battery pack in the entire battery pack group can be balanced and consistent, and the battery cells in the module are kept consistent through cell-level balancing.

[0029] Compared with the prior art, the present invention has the following characteristics: 1. Abandoning the embarrassment of the traditional passive balancing energy utilization rate of 0%, the energy utilization rate is increased to more than 85% at the cell level through the setting of energy storage modules. In the battery pack group, the energy is directly balanced between battery packs, which also greatly improves the energy utilization rate.

[0030] 2. Set a selection switch at the connection point of two adjacent battery cells, control the selection to the bus through a pair of MOS tubes, and then select the H bridge, so that the DC-DC works within the positive voltage range. This allows the entire module to only require one transformer instead of equipping each battery cell with a transformer, which can greatly save the investment cost of transformers and MOS tubes.

[0031] 3. Compared with the prior art, the balancing current in the present invention is 100 times larger than that of passive balancing, and the balancing action can be completed very quickly, so that large-capacity batteries can be balanced quickly.

[0032] 4. For the battery pack, the present invention uses an active balancing device to transfer the energy in the battery cells with high cell voltage to charge the entire battery pack through a transformer. The entire battery pack (battery cluster) can balance the voltage of all cells and maintain it at a fixed value without cumulative error.

[0033] The above description is only the optimal solution embodiment of the present invention and is not intended to limit the present invention. Various modifications or substitutions made by those skilled in the art to the present invention without departing from the essence and protection scope of the present invention should also be within the protection scope of the present invention.

Claims

1. An active balancing circuit for a single cell group, wherein the single cell group is composed of n cells (Bn) connected in series, wherein n is a natural number representing the number of cells connected in series, and the active balancing circuit for the single cell group is connected to an external BMS system, and is characterized in that: The active balancing circuit comprises a first bus (a) and a second bus (b), the two ends of any of the battery cells (Bn) are connected to the first bus (a) or the second bus (b) via two connecting wires (1), a selection switch (2) is provided on each of the connecting wires (1), the selection switch (2) is controlled to be on and off by a switch circuit (3), the other ends of the first bus (a) and the second bus (b) are connected to a first flyback switch circuit (5) via an H bridge (4), and the output end of the first flyback switch circuit (5) is connected to an energy storage module (6).

2. The active balancing circuit of a single cell group according to claim 1, characterized in that: The first flyback switch circuit (5) comprises a first transformer (51) comprising a first primary side (511) and a first secondary side (512), a first primary side MOS tube (52) connected to the loop of the first primary side (511), a first primary side PWM (53) connected to the G pole of the first primary side MOS tube (52), a first secondary side MOS tube (54) connected to the loop of the first secondary side (512), and a first secondary side PWM (55) connected to the G pole of the first secondary side MOS tube (54), and the energy storage module (6) is connected to the loop of the first secondary side (512).

3. The active balancing circuit of a single cell group according to claim 2, characterized in that: The four bridge arms of the H-bridge (4) are each composed of two bridge arm MOS tubes (41) connected in series, the other ends of the two bridge arms connected to the first bus (a) are respectively connected to the loop of the first primary side (511), and the other ends of the two bridge arms connected to the second bus (b) are respectively connected to the loop of the first primary side (511).

4. The active balancing circuit of a single cell group according to claim 1, characterized in that: The selection switch (2) is formed by two NMOS tubes (21) connected in series, the G poles of the two NMOS tubes (21) forming the selection switch (2) having a common connection line are both connected to the switch circuit (3), and the two NMOS tubes (21) rely on internal PN junctions to jointly control the on / off of one end of the single cell. When the single cell group is connected in series with n+1 cells (Bn+1), at the positive end of the single cell group, the selection switch (2) is formed by a PMOS tube (22), the G pole of the PMOS tube (22) is connected to an AFE chip (31), and the G pole of the PMOS tube (22) is connected to the Sn+1 pin of the AFE chip (31), wherein n is a natural number representing the number of cells connected in series.

5. The active balancing circuit of a single cell group according to claim 4, characterized in that: The switch circuit (3) comprises an AFE chip (31) and two voltage-dividing resistors (32) respectively led from the AFE chip (31), and the other end of the voltage-dividing resistor (32) is output to the selection switch (2) to control the on and off of the selection switch (2).

6. The active balancing circuit of a single cell group according to claim 1, characterized in that: The energy storage module (6) is the single cell group formed by connecting B1 to Bn+1 in series.

7. The active balancing circuit of a single cell group according to claim 5, characterized in that: The switch circuit (3) is provided with a control output pin (33), and the two voltage-dividing resistors (32) are connected in series, and the control output pin (33) is led out from the series connection point to output a control signal to the selection switch (2).

8. An active balancing device for a battery pack comprising the active balancing circuit for a single cell group as claimed in any one of claims 1 to 7, wherein: The battery pack group is composed of a plurality of battery packs connected in series via a series busbar (7), and is characterized in that: the active balancing device of the battery pack group also includes a second flyback switch circuit (8) and a voltage comparator (9) connected between any two adjacent battery packs (packs), the two input ends of the voltage comparator (9) are respectively connected to the positive electrodes of the two adjacent battery packs (packs), the output end of the voltage comparator (9) is respectively connected to the two control ends of the second flyback switch circuit (8), and one of the control ends of the flyback switch circuit (8) is controlled to operate according to the output value of the voltage comparator (9).

9. The active equalization device for a battery pack according to claim 8, characterized in that: The second flyback switch circuit (8) comprises a first transformer (81) comprising a second primary side (811) and a second secondary side (812), a second primary side MOS tube (82) connected to the loop of the second primary side (811), a second primary side PWM (83) connected to the G pole of the second primary side MOS tube (82), a second secondary side MOS tube (84) connected to the loop of the second secondary side (812), and a second secondary side PWM (85) connected to the G pole of the second secondary side MOS tube (84), a positive pole of the battery pack (pack) connected to the second primary side (811), the second primary side (811), and the second primary side MOS tube (83). A first loop is formed between the second primary MOS tube (82) and the negative electrode of the battery pack (pack) connected to the second primary side (811), and a second loop is formed between the positive electrode of the battery pack (pack) connected to the second secondary side (812), the second secondary side (812), the second secondary side MOS tube (84) and the negative electrode of the battery pack (pack) connected to the second secondary side (812), and the output end of the voltage comparator (9) is respectively connected to the connection point between the second primary MOS tube (82) and the second primary side PWM (83) and the connection point between the second secondary side MOS tube (84) and the second secondary side PWM (85).

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