CN105098845B - Battery management system - Google Patents

Abstract

The invention discloses a battery management system, which is used for power balance of at least two groups of battery groups, each battery group includes at least two battery cells, and the battery management system includes a central control unit and batteries corresponding to each battery group The management unit, the central control unit and each battery management unit are connected through the CAN bus. The battery management unit is used to balance the battery cells in the corresponding battery pack. Power balance between groups. Through the above method, the battery management system of the present invention can realize the power balance within the battery pack and the power balance between the battery packs at the same time, effectively improving the power balance effect.

Description

battery management system

technical field

The invention relates to the field of battery management, in particular to a battery management system.

Background technique

In the existing technical field of batteries, a storage battery is widely used in various fields because it is a convenient, safe and reliable DC energy source. A battery can convert electrical energy into chemical energy and store it, and convert chemical energy into electrical energy when in use. However, since the storage battery is a chemical reaction device, it is generally difficult to detect the internal chemical reaction in time, and the defects in daily use often need long-term and frequent use to appear. Furthermore, the chemical characteristics of the battery determine that the range of its working voltage is strictly limited. When the working voltage of the battery is higher than the maximum voltage limit value, a safety accident will occur, and when the working voltage of the battery is lower than the minimum voltage limit value, an irreversible reaction will occur. , thus easily damaging the battery.

In traditional technology, online monitoring is generally used for battery fault diagnosis. On-line monitoring is mainly based on RS-232 (a serial bus) bus or RS-485 bus to balance the batteries. However, these methods can only adopt a master-slave system structure, collect data in a polling manner, and do not have active coordination capabilities. Moreover, the power balance effect is poor, and only the power balance between the battery cells can be realized, and the power balance between the battery packs cannot be realized.

Contents of the invention

The main technical problem to be solved by the present invention is to provide a battery management system that can realize power balance within and between battery packs, has low cost and high reliability, and can effectively improve the power balance effect.

In order to solve the above-mentioned technical problems, a technical solution adopted by the present invention is to provide a battery management system for power balance of at least two groups of battery packs, each battery pack includes at least two battery cells, and the battery management system includes The central control unit and the battery management unit corresponding to each battery pack are connected through the CAN bus between the central control unit and each battery management unit. Power balance, the central control unit is used to balance the power between the battery packs.

Among them, the battery management unit is used to collect the state information of each battery cell in the battery pack, and determine the battery cells that need to be balanced according to the state information of the battery cells, and control the battery cells with high power to balance the battery cells with low power. The battery cells perform power balance within the group.

Wherein, the status information includes at least one of a voltage value, a current value and a temperature value.

Among them, the central control unit is used to obtain the total state information of each battery pack from the battery management unit through the CAN bus, and determine the battery pack that needs to be balanced according to the total state information of the battery pack, and control the battery pack with high power to the battery pack Low battery packs are used for power balance among the packs.

Wherein, the battery management unit includes a first microcontroller, a first transformer, a first triode, a first capacitor, a second capacitor, a third capacitor, and at least two first A switch group and at least two second switch groups, the first transformer includes a primary coil and a secondary coil, the two ends of the primary coil of the first transformer are respectively connected to the two ends of the first capacitor, and are connected to each The two poles of a battery cell are connected, the two ends of the secondary coil of the first transformer are respectively connected to the two ends of the second capacitor, and are connected to the two poles of each battery cell through the corresponding second switch group, and the first triode Connected in series between a plurality of first switch groups and the primary coil of the first transformer, the first micro-controller is respectively connected to the battery group, the first switch group and the second switch group, and connected to the first triode through the third capacitor The control terminal is connected; when the first microcontroller collects the state information of each battery cell in the battery pack, and determines the battery cell that needs to be balanced according to the state information of the battery cell, the first microcontroller controls the battery cell The first switch group corresponding to the high battery cell is connected to the primary coil of the first transformer, and controls the second switch group corresponding to the low battery cell to be connected to the secondary coil of the first transformer, and controls the first three-pole The tube is intermittently turned on, so that the battery cell with high power stores the electric energy in the primary coil of the first transformer when the first triode is turned on, and passes through the secondary coil of the first transformer when the first triode is turned off. The coil charges the low battery cells.

Wherein, the battery management unit further includes a first feedback unit, the first feedback unit is connected in series between the secondary coil of the first transformer and the second switch group, the first micro-controller is connected to the first feedback unit, and feeds back The current information of the first triode controls the first duty ratio of the first triode, so that the first triode is controlled to be turned on and off by the first duty ratio.

Wherein, the battery management unit further includes a first diode, and the first diode is connected in series between the secondary coil of the first transformer and the second switch group, so as to prevent the current of the battery cell from flowing backward to the secondary coil of the first transformer.

Wherein, the central control unit includes a second microcontroller, a second transformer, a second triode, a fourth capacitor, a fifth capacitor, a sixth capacitor, at least two third switch groups corresponding to the number of battery packs, and at least two A fourth switch group, the second transformer includes a primary coil and a secondary coil, the two ends of the primary coil of the second transformer are respectively connected to the two ends of the fourth capacitor, and are connected to the two poles of each battery group through the corresponding third switch group connected, the two ends of the secondary coil of the second transformer are respectively connected to the two ends of the fifth capacitor, and are connected to the two poles of each battery group through the corresponding fourth switch group, and the second triode is connected in series with a plurality of third switches Between the group and the primary coil of the second transformer, the second microcontroller is respectively connected to the first microcontroller, the third switch group and the fourth switch group, and is connected to the control terminal of the second triode through the sixth capacitor; When the central control unit obtains the total status information of each battery pack from the battery management unit through the CAN bus, and determines the battery pack that needs to be balanced according to the total status information of the battery packs, the second microcontroller controls the battery pack with high power The corresponding third switch group is connected to the primary coil of the second transformer, and controls the battery pack with low power. The corresponding fourth switch group is connected to the secondary coil of the second transformer, and is intermittently turned on by controlling the second triode. In order to make the battery pack with high power store the electric energy in the primary coil of the second transformer during the conduction phase of the second triode, and to store the electric energy in the secondary coil of the second transformer during the close phase of the second triode. Battery pack charging.

Wherein, the central control unit further includes a second feedback unit, the second feedback unit is connected in series between the secondary coil of the second transformer and the fourth switch group, the second micro-controller is connected to the second feedback unit, and feeds back The current information of the second triode controls the second duty ratio of the second triode, so that the second duty ratio controls the turn-on and shutdown of the second triode.

Wherein, the central control unit further includes a second diode, and the second diode is connected in series between the secondary coil of the second transformer and the fourth switch group, so as to prevent the current of the battery pack from flowing back into the secondary coil of the second transformer.

The beneficial effects of the present invention are: different from the situation in the prior art, the battery management unit of the present invention determines the battery cells that need to be balanced according to the state information of the battery cells by collecting the state information of each battery cell in the battery pack body, and control the battery cells with high power to charge the battery cells with low power; at the same time, the central control unit obtains the total state information of each battery pack from the battery management unit through the CAN bus, and determines the battery pack according to the total state information of the battery pack The battery pack that needs to be balanced, and the battery pack with high power is controlled to charge the battery pack with low power. Through the above method, the battery management system of the present invention can more accurately realize power balance within and between battery packs without affecting the normal operation of the battery pack, and has low cost and high reliability, and can effectively improve the power balance effect.

Description of drawings

Fig. 1 is a schematic structural diagram of the connection between the battery management system and the battery pack of the present invention;

Fig. 2 is a schematic structural diagram of the connection between the battery management unit and the battery pack in Fig. 1;

Fig. 3 is a schematic diagram of the connection between the central control unit and the battery pack in Fig. 1 .

Detailed ways

Referring to FIG. 1 , FIG. 1 is a schematic structural diagram of the connection between the battery management system and the battery pack of the present invention. The battery management system is used for power balance of at least two groups of battery packs M, each battery pack M including at least two battery cells B. In this embodiment, the battery pack M preferably includes 12 battery cells B1-B12, and the battery cell B is preferably a storage battery. Of course, in other embodiments, the battery cell B can also be other rechargeable batteries. The battery management system includes at least two battery management units 11 and a central control unit 12 . Each battery management unit 11 corresponds to each battery pack M, and the battery management unit 11 is connected to the corresponding battery pack M, and the central control unit 12 is connected to each battery management unit 11 through a CAN bus 13 . Preferably, the central control unit 12 is connected to each battery management unit 11 through the first CAN bus 131 and the second CAN bus 132 . Of course, the central control unit 12 can also be connected to the battery management unit 11 through other buses. Wherein, the battery management unit 11 is used to balance the battery cells B in the corresponding battery pack M within the battery pack, and the central control unit 12 is used to balance the battery pack M among battery packs.

The battery management unit 11 is used to collect the state information of each battery cell B in the battery pack M, determine the battery cell B that needs to be balanced according to the state information of the battery cell B, and control the battery cell B with high power In-group power balance is performed on battery cell B with low power. In this embodiment, the state information includes at least one of a voltage value, a current value and a temperature value.

Please refer to FIG. 2 together. FIG. 2 is a schematic structural diagram of the connection between the battery management unit and the battery pack in FIG. 1 . The battery management unit 11 includes a first microcontroller 111, a first transformer 112, a first feedback unit 113, a first diode D1, a first transistor Q1, a first capacitor C1, a second capacitor C2, and a third capacitor C3, the number of the first switch group 114 and the second switch group 115 corresponding to the battery cells B in the battery pack M. The first transformer 112 includes a primary winding Np1 and a secondary winding Ns1 , there are at least two first switch groups 114 , and there are at least two second switch groups 115 . Wherein, the first switch group 114 includes a first switch A1 and a second switch A2; the second switch group 115 includes a third switch A3 and a fourth switch A4. The first diode D1 is connected in series between the secondary winding Ns1 of the first transformer 112 and the second switch group 115 to prevent the current of the battery cell B from flowing back into the secondary winding Ns1 of the first transformer 112 .

The first microcontroller 111 is respectively connected to the first feedback unit 113 , one end of the third capacitor C3 , the battery pack M, the first switch group 114 and the second switch group 115 . The first feedback unit 113 is respectively connected to one end of the second capacitor C2 , one end of the secondary winding Ns1 of the first transformer 112 and one side of the fourth switch A4 of the second switch group 115 . The other end of the second capacitor C2 is respectively connected to the negative end of the first diode D1 and one side of the third switch A3 of the second switch group 115 . The positive end of the first diode D1 is connected to the other end of the secondary winding Ns1 of the first transformer 112 . The other side of the third switch A3 of the second switch group 115 is connected to the positive terminal of the corresponding battery cell B; the other side of the fourth switch A4 of the second switch group 115 is connected to the negative terminal of the corresponding battery cell B.

One end of the primary winding Np1 of the first transformer 112 is respectively connected to one end of the first capacitor C1 and one side of the first switch A1 of the first switch group 114 . The other end of the primary coil Np1 of the first transformer 112 is connected to the other end of the first capacitor C1 and the first pin of the first transistor Q1 respectively. The second pin of the first transistor Q1 is connected to the other end of the third capacitor C3. The third pin of the first transistor Q1 is connected to one side of the second switch A2 of the first switch group 114 . The other side of the first switch A1 of the first switch group 114 is connected to the positive terminal of the corresponding battery cell B. The other side of the second switch A2 of the first switch group 114 is connected to the negative terminal of the corresponding battery cell B.

In this embodiment, the first triode Q1 is an NMOS transistor, the first pin of the first triode Q1 is the drain, and the second pin of the first triode Q1 is the gate, that is, the control terminal. The third pin of the first triode Q1 is the source.

The central control unit 12 is used to obtain the overall state information of each battery pack M from the battery management unit 11 through the CAN bus 13, and determine the battery pack M that needs to be balanced according to the overall state information of the battery pack M, and control the battery pack M with high power. The battery pack M performs inter-group power balance for the battery pack M with low power.

Please refer to FIG. 3 together. FIG. 3 is a schematic structural diagram of the connection between the central control unit and the battery pack in FIG. 1 . The central control unit 12 includes a second microcontroller 121, a second transformer 122, a second feedback unit 123, a second diode D2, a second transistor Q2, a fourth capacitor C4, a fifth capacitor C5, and a sixth capacitor C6, the third switch group 124 and the fourth switch group 125 corresponding in quantity to the battery pack M. The second transformer 122 includes a primary coil Np2 and a secondary coil Ns2 , there are at least two third switch groups 124 , and at least two fourth switch groups 125 . Wherein, the third switch group 124 includes the fifth switch E1 and the sixth switch E2; the fourth switch group 125 includes the seventh switch E3 and the eighth switch E4. The second diode D2 is connected in series between the secondary winding Ns2 of the second transformer 122 and the fourth switch group 125 to prevent the current of the battery pack M from flowing back into the secondary winding Ns2 of the second transformer 122 .

The second microcontroller 121 is connected to the first microcontroller 111 of the battery management unit 11 through the CAN bus 13 . In this embodiment, the second microcontroller 121 is connected to the first microcontroller 111 through the first CAN bus 131 and the second CAN bus 132 . Certainly, in other embodiments, the second microcontroller 121 may also be connected to the first microcontroller 111 through other buses.

The second microcontroller 121 is respectively connected to the second feedback unit 123 , one end of the sixth capacitor C6 , the third switch group 124 and the fourth switch group 125 . The second feedback unit 123 is respectively connected to one end of the fifth capacitor C5 , one end of the secondary winding Ns2 of the second transformer 122 and one side of the eighth switch E4 of the fourth switch group 125 . The other end of the fifth capacitor C5 is respectively connected to the negative end of the second diode D2 and one side of the seventh switch E3 of the fourth switch group 125 . The positive end of the second diode D2 is connected to the other end of the secondary winding Ns2 of the second transformer 122 . The other side of the seventh switch E3 of the fourth switch group 125 is connected to the positive terminal of the corresponding battery M. The other side of the eighth switch E4 of the fourth switch group 125 is connected to the negative terminal of the corresponding battery M.

One end of the primary winding Np2 of the second transformer 122 is respectively connected to one end of the fourth capacitor C4 and one side of the fifth switch E1 of the third switch group 124 . The other end of the primary winding Np2 of the second transformer 122 is connected to the other end of the fourth capacitor C4 and the first pin of the second transistor Q2 respectively. The second pin of the second transistor Q2 is connected to the other end of the sixth capacitor C6. The third pin of the second transistor Q2 is connected to one side of the sixth switch E2 of the third switch group 124 . The other side of the fifth switch E1 of the third switch group 124 is connected to the positive terminal of the battery M. The other side of the sixth switch E2 of the third switch group 124 is connected to the negative terminal of the battery M.

In this embodiment, the second triode Q2 is an NMOS transistor, the first pin of the second triode Q2 is the drain, and the second pin of the second triode Q2 is the gate, that is, the control terminal. The third pin of the second triode Q2 is the source.

The working principle of the battery management system will be described below in combination with embodiments.

When the battery pack M does not carry out power balance within and between packs, the first switch A1 and the second switch A2 of the first switch group 114, the third switch A3 and the fourth switch A4 of the second switch group 115, and the third switch The fifth switch E1 and the sixth switch E2 of the group 124 and the seventh switch E3 and the eighth switch E4 of the fourth switch group 125 are all open.

When the battery pack M performs power balance within the pack: the first microcontroller 111 collects state information of each battery cell B in the battery pack M. The first microcontroller 111 determines the battery cell B that needs to be balanced according to the state information of the battery cell B. If it is determined that the first battery cell B1 is the battery cell B with high power, the twelfth battery cell B12 is the battery cell B with low power. The first microcontroller 111 controls the first switch A1 and the second switch A2 of the first switch group 114 corresponding to the first battery cell B1 to close; the first microcontroller 111 controls the second switch group 114 corresponding to the twelfth battery cell B12 to close; The third switch A3 and the fourth switch A4 of the switch group 115 are closed. At the same time, the first microcontroller 111 outputs the first duty ratio to the third capacitor C3, and the first triode Q1 is turned on at the first level of the first duty ratio, so that the first battery cell B1 During the conduction phase of the transistor Q1, the electric energy is stored in the primary coil Np1 of the first transformer 112; when the first duty ratio is at the second level, the first transistor Q1 is not conducted, so that the first transistor Q1 In the off stage, the secondary winding Ns1 of the first transformer 112 is used to charge the twelfth battery unit B12.

In addition, the first feedback unit 113 feeds back the current information of charging the twelfth battery cell B12 by the first transformer 112 in the group to the first micro-controller 111 in real time, and the first micro-controller 111 according to the current fed back by the first feedback unit 113 The information controls the first duty cycle of the first triode Q1, so that the first transformer 112 is controlled to output a constant current to charge the twelfth battery unit B12. In this embodiment, the first level of the first duty cycle is a high level, and the second level of the first duty cycle is a low level. Certainly, in other embodiments, the first level may also be set as a low level and the second level as a high level according to control requirements.

When the battery pack M is performing inter-group power balance: the second microcontroller 121 actively acquires the overall state information of each battery pack M from the first microcontroller 111 through the first CAN bus 131 and the second CAN bus 132 in real time, or The first microcontroller 111 actively transmits the overall state information of each battery pack M to the second microcontroller 121 through the first CAN bus 131 and the second CAN bus 132 in real time. The second microcontroller 121 determines the battery pack M that needs to be balanced according to the overall state information of the battery pack M. If it is determined that the first battery pack M1 is a battery pack M with high power, the Nth battery pack Mn is a battery pack M with low power. The second microcontroller 121 controls the fifth switch E1 and the sixth switch E2 of the third switch group 124 corresponding to the first battery group M1 to close; the second microcontroller 121 controls the fourth switch group 125 corresponding to the Nth battery group Mn The seventh switch E3 and the eighth switch E4 are closed. At the same time, the second microcontroller 121 outputs the second duty cycle to the sixth capacitor C6, and the second triode Q2 is turned on at the first level of the second duty cycle, so that the first battery pack M1 The electric energy is stored in the primary coil Np2 of the second transformer 122 during the conduction phase of the transistor Q2; the second transistor Q2 is not conducted at the second level of the second duty cycle, so that the second transistor Q2 is turned off stage, the Nth battery pack Mn is charged through the secondary winding Ns2 of the second transformer 122 .

In addition, the second feedback unit 123 feeds back the current information of charging the N-th battery pack Mn by the second transformer 122 between groups in real time to the second microcontroller 121, and the second microcontroller 121 controls the current according to the current information fed back by the second feedback unit 123. The second duty ratio of the second transistor Q2 is such that the second transformer 122 is controlled to output a constant current to charge the Nth battery pack Mn. In this embodiment, the first level of the second duty cycle is a high level, and the second level of the second duty cycle is a low level. Certainly, in other embodiments, the first level may also be set as a low level and the second level as a high level according to control needs.

In this embodiment, the battery management system based on the CAN bus 13 can monitor the battery pack M on-line and in real time, and can realize the power balance within the battery pack M and the power balance between the battery packs M alone, and can also realize the power balance of the battery pack M at the same time. Intra-group power balance of M and inter-group power balance of battery pack M. CAN bus 13 is a multi-master control local area network standard, which has the characteristics of physical layer and data link layer network protocol, multi-master nodes, lossless arbitration, high reliability and good expansion performance. The battery management system based on the CAN bus 13 can continuously and effectively perform high-current power balance, and can control the overall service life of the battery cell B and the battery pack M. At the same time, the battery management system based on the CAN bus 13 can reliably monitor the working status and health status of the battery pack M online, which is convenient for the maintenance of the battery pack M and guarantees the safety of operation, and achieves a large power balance without heat loss. It solves the reliable online monitoring of the battery pack M, and also solves the problem of power balance between the battery cell B and the battery pack M.

To sum up, the battery management unit of the present invention collects the state information of each battery cell in the battery pack, determines the battery cell that needs to be balanced according to the state information of the battery cell, and controls the battery cell with high power Charge the battery cells with low power; at the same time, the central control unit obtains the overall status information of each battery pack from the battery management unit through the CAN bus, determines the battery pack that needs to be balanced according to the overall status information of the battery pack, and controls The high battery pack charges the low battery pack. Through the above method, the battery management system of the present invention can more accurately realize power balance within and between battery packs without affecting the normal operation of the battery pack, and has low cost and high reliability, and can effectively improve the power balance effect.

The above is only an embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related technologies fields, all of which are equally included in the scope of patent protection of the present invention.

Claims (5)

1. A battery management system, which is used to balance the power of at least two groups of battery packs, each of which includes at least two battery cells, characterized in that, The battery management system includes a central control unit and a battery management unit corresponding to each of the battery packs, and the central control unit is connected to each of the battery management units through a CAN bus; The battery management unit is used to collect the state information of each of the battery cells in the battery pack, and determine the battery cells that need to be balanced according to the state information of the battery cells, and control the high power The battery cells with low power balance the battery cells within the group, and the state information includes at least one of a voltage value, a current value, and a temperature value; The central control unit is used to obtain the overall state information of each of the battery packs from the battery management unit through the CAN bus, and determine the battery packs that need to be balanced according to the overall state information of the battery packs , and controlling the battery pack with high power to balance the power between the battery packs with low power; The battery management unit includes a first microcontroller, a first transformer, a first triode, a first capacitor, a second capacitor, a third capacitor, and at least two capacitors whose number corresponds to the battery cells in the battery pack. A first switch group and at least two second switch groups, the first transformer includes a primary coil and a secondary coil, and the two ends of the primary coil of the first transformer are respectively connected to the two ends of the first capacitor, and through The corresponding first switch group is connected to the two poles of each of the battery cells, and the two ends of the secondary coil of the first transformer are respectively connected to the two ends of the second capacitor, and through the corresponding first Two switch groups are connected to the two poles of each of the battery cells, the first triode is connected in series between the plurality of first switch groups and the primary coil of the first transformer, and the first microcontroller connected to the battery pack, the first switch group and the second switch group, and connected to the control terminal of the first triode through the third capacitor; When the first microcontroller collects the state information of each of the battery cells in the battery pack, and determines the battery cells that need to be balanced according to the state information of the battery cells, the The first micro-controller controls the first switch group corresponding to the battery cell with high power to be connected to the primary coil of the first transformer, and controls the second switch group corresponding to the battery cell with low power connected to the secondary coil of the first transformer, and by controlling the intermittent conduction of the first triode, so that the battery cell with high power stores the electric energy during the conduction phase of the first triode In the primary coil of the first transformer, and during the off stage of the first triode, charge the battery cell with low power through the secondary coil of the first transformer; The central control unit includes a second microcontroller, a second transformer, a second triode, a fourth capacitor, a fifth capacitor, a sixth capacitor, at least two third switch groups corresponding to the number of the battery pack, and At least two fourth switch groups, the second transformer includes a primary coil and a secondary coil, the two ends of the primary coil of the second transformer are respectively connected to the two ends of the fourth capacitor, and through the corresponding first The three switch groups are connected to the two poles of each battery group, the two ends of the secondary coil of the second transformer are respectively connected to the two ends of the fifth capacitor, and the corresponding fourth switch group is connected to each The two poles of the battery pack are connected, the second triode is connected in series between the plurality of third switch groups and the primary coil of the second transformer, and the second micro-controller is respectively connected to the first A microcontroller, the third switch group, and the fourth switch group are connected to the control terminal of the second triode through the sixth capacitor; When the central control unit obtains the overall status information of each battery pack from the battery management unit through the CAN bus, and determines the battery pack that needs to be balanced according to the overall status information of the battery packs , the second microcontroller controls the third switch group corresponding to the battery pack with high power to be connected to the primary coil of the second transformer, and controls the fourth switch group corresponding to the battery pack with low power connected to the secondary coil of the second transformer, and by controlling the intermittent conduction of the second triode, so that the battery pack with high power stores the electric energy in the conduction stage of the second triode the primary coil of the second transformer, and charge the battery pack with low power through the secondary coil of the second transformer when the second triode is turned off. 2. The battery management system according to claim 1, wherein the battery management unit further comprises a first feedback unit, the first feedback unit is connected in series with the secondary coil of the first transformer and the second Between the switch groups, the first micro-controller is connected to the first feedback unit, and controls the first duty ratio of the first triode according to the current information fed back by the first feedback unit, so that through The first duty cycle controls the turn-on and turn-off of the first triode. 3. The battery management system according to claim 2, wherein the battery management unit further comprises a first diode, and the first diode is connected in series with the secondary coil of the first transformer and the Between the second switch group, so as to prevent the current of the battery cell from flowing backward to the secondary coil of the first transformer. 4. The battery management system according to claim 1, wherein the central control unit further comprises a second feedback unit, the second feedback unit is connected in series with the secondary coil of the second transformer and the fourth Between the switch groups, the second micro-controller is connected to the second feedback unit, and controls the second duty ratio of the second triode according to the current information fed back by the second feedback unit, so that through The second duty cycle controls the turn-on and turn-off of the second triode. 5. The battery management system according to claim 4, wherein the central control unit further comprises a second diode, the second diode is connected in series with the secondary coil of the second transformer and the between the fourth switch group, so as to prevent the current of the battery pack from flowing backward to the secondary coil of the second transformer.