Balancing circuit and balancing control method based on forward and flyback principle

Abstract

The application discloses an equalization circuit and an equalization control method based on a forward and reverse flyback principle. The equalization circuit comprises a battery pack unit, a switch matrix unit and an energy storage unit. The equalization circuit can flexibly transfer energy between different equalization objects and adjust the equalization type in real time according to the condition of the battery pack, so that the equalization circuit always works in the best state, the rapid equalization of the battery pack is realized, the problem of the reduction of the equalization efficiency caused by the frequent on-off of switches in the equalization circuit is effectively solved, the switch loss is effectively reduced, and the efficiency of the equalization circuit is improved.

Description

Technical Field

[0001] This invention relates to the field of power electronic conversion technology, and in particular to equalization circuits and equalization control methods based on the flyback principle. Background Technology

[0002] Currently, energy storage technology has become a key core technology for realizing new power systems, and the development of energy storage battery technology is of great strategic significance for promoting the development of new energy power generation such as wind power and photovoltaic power. To meet the voltage and capacity requirements of energy storage systems, lithium batteries typically appear in the form of series battery packs, battery cells, and modular designs. Due to differences in manufacturing processes and external environments during the production of lithium batteries, variations exist in their capacity, internal resistance, and self-discharge rate. These variations gradually increase during cyclic use, leading to inconsistencies within the battery pack. Furthermore, according to the "barrel effect" theory, the lifespan of a battery pack can be drastically reduced due to a single battery cell with poor performance parameters, potentially causing serious safety issues such as fires and explosions.

[0003] Currently, battery balancing technology is one of the most effective methods to solve the problem of inconsistency between individual cells in battery packs, and research on battery balancing technology is of great significance to the development of battery energy storage systems. Among these methods, active balancing is the mainstream approach, using energy storage elements to transfer balancing energy between the cells being balanced. Compared to passive balancing, which utilizes resistance to dissipate energy, active balancing offers higher efficiency and speed. Depending on the type of balancing, active balancing is divided into three categories: cell-to-cell, cell-to-pack, and cell-to-pack-to-cell.

[0004] Depending on the energy storage element, active balancing can be divided into inductive topology, capacitive topology, and transformer topology. Among them, transformer-type balancing topology has the advantages of simple structure, fast balancing speed, high efficiency, short balancing path, and electrical isolation between the battery discharge circuit and the charging circuit during the balancing process. However, in the battery balancing design of the transformer-type balancing topology, the controllable energy is difficult to transfer flexibly between different balancing objects, and it is impossible to adjust the balancing type in real time according to the condition of the battery pack to ensure that the balancing circuit always works in the optimal state. The switch in the balancing circuit needs to be frequently turned on and off, resulting in reduced efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide an equalization circuit and equalization control method based on the flyback principle. It can control the flexible transfer of energy between different equalization objects and adjust the equalization type in real time according to the condition of the battery pack, so that the equalization circuit always works in the optimal state, realizes the rapid equalization of the battery pack, and can effectively solve the problem of reduced equalization efficiency caused by frequent switching in the equalization circuit, effectively reduce switching losses, and improve the efficiency of the equalization circuit.

[0006] To achieve the above objectives, this invention discloses an equalization circuit based on the flyback principle, comprising a battery pack unit, a switch matrix unit, and an energy storage unit. The battery pack unit includes multiple battery cells connected in series. The switch matrix unit includes multiple first switch units, multiple second switch units, a third switch unit, a fourth switch unit, a fifth switch unit, a first diode, and a second diode. Each battery cell corresponds to one first switch unit and one second switch unit. The energy storage unit includes a first winding, a second winding, and a third winding. The first winding and the second winding are located on opposite sides of the third winding. The positive terminal of the battery pack unit is electrically connected to the corresponding terminal of the third winding, and the negative terminal is electrically connected to the third winding through the fifth switch unit. The positive terminal of each battery cell is connected in parallel through a corresponding first switching unit, and then electrically connected to the same-name terminal of the first winding through a third switching unit, and electrically connected to the opposite-name terminal of the second winding through a fourth switching unit. The negative terminal of each battery cell is connected in parallel through a corresponding second switching unit, and then electrically connected to the negative terminal of the first diode and the positive terminal of the second diode. The positive terminal of the first diode is electrically connected to the opposite-name terminal of the first winding, and the negative terminal of the second diode is electrically connected to the same-name terminal of the second winding. The positive terminal of the battery pack unit is electrically connected to the same-name terminal and the negative terminal of the third winding. The switching matrix unit can selectively control the energy transfer between any battery cells and the energy transfer between any battery cell and the battery pack unit.

[0007] Preferably, the third switching unit includes a first MOSFET, a third diode, a first capacitor, and a first inductor. The source (S) terminal of the first MOSFET and the negative terminal of the third diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the first MOSFET and the positive terminal of the third diode are connected in parallel and then electrically connected to the same-name terminal of the first winding through the first inductor. The first capacitor is connected in parallel with the first MOSFET.

[0008] Preferably, the fourth switching unit includes a second MOSFET, a fourth diode, a second capacitor, and a second inductor. The source (S) terminal of the second MOSFET and the positive terminal of the fourth diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the second MOSFET and the negative terminal of the fourth diode are connected in parallel and then electrically connected to the opposite terminal of the second winding through the second inductor. The second capacitor is connected in parallel with the second MOSFET.

[0009] Preferably, the energy storage unit is a transformer with three windings.

[0010] Preferably, each switch in the switch matrix unit is independently controlled by a control signal.

[0011] The first switching unit, the second switching unit, and the fifth switching unit are all switching transistors.

[0012] Accordingly, this invention also discloses an equalization control method for an equalization circuit based on the flyback principle, applied to the equalization circuit based on the flyback principle as described above. The equalization circuit includes a first mode, a second mode, and a third mode. The first mode is used for energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC. The second mode is used for energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC. The third mode is used for energy transfer between the battery pack unit and the battery cell with the lowest SOC. Each of the first, second, and third modes sequentially has a first stage and a second stage within one switching cycle. The equalization control method for the equalization circuit based on the flyback principle includes the following steps:

[0013] For the first mode:

[0014] Phase 1:

[0015] By controlling the third switching unit, the fifth switching unit, and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit.

[0016] Phase Two:

[0017] By controlling the fourth switching unit, the fifth switching unit, and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the excitation current of the first winding is reduced to zero through the second winding, thereby completing the core reset of the forward circuit in the first stage, and completing the energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC.

[0018] For the second mode:

[0019] Phase 1:

[0020] By controlling the third switching unit and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding and stored by the second winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit.

[0021] Phase Two:

[0022] By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the current of the first winding is cut off, thereby enabling energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC.

[0023] For the third mode:

[0024] Phase 1:

[0025] The fifth switching unit is turned on by a control signal, and the other switching units are turned off. The second winding and the third winding together form a flyback circuit so that the energy of the battery pack unit is released to the third winding and stored by the second winding.

[0026] Phase Two:

[0027] By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC through the control signal, the current of the third winding is cut off. The magnetic field energy of the third winding is released to the battery cell with the lowest SOC through the second winding, so as to complete the energy transfer between the battery pack unit and the battery cell with the lowest SOC.

[0028] Compared with the prior art, the present invention can control the flexible transfer of energy between different equalization objects and adjust the equalization type in real time according to the condition of the battery pack, so that the equalization circuit always works in the best state, realizes the rapid equalization of the battery pack, and can effectively solve the problem of reduced equalization efficiency caused by frequent switching in the equalization circuit, effectively reduce switching losses and improve the efficiency of the equalization circuit. Attached Figure Description

[0029] Figure 1 This is a topology diagram of the equalization circuit based on the flyback principle of the present invention;

[0030] Figure 2 The control signal waveform of the equalization circuit based on the flyback principle of the present invention in the first mode;

[0031] Figure 3 The current flow direction of the equalization circuit based on the flyback principle of the present invention in the first mode;

[0032] Figure 4 The control signal waveform of the equalization circuit based on the flyback principle of the present invention in the second mode;

[0033] Figure 5 The current flow direction of the equalization circuit based on the flyback principle of the present invention in the second mode;

[0034] Figure 6 The control signal waveform of the equalization circuit based on the flyback principle of the present invention in the third mode;

[0035] Figure 7 The current flow direction of the equalization circuit based on the flyback principle of the present invention in the third mode. Detailed Implementation

[0036] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0037] Please see Figures 1-7As shown, the equalization circuit based on the flyback principle in this embodiment includes a battery pack unit, a switch matrix unit, and an energy storage unit. The battery pack unit includes multiple battery cells connected in series. The switch matrix unit includes multiple first switch units, multiple second switch units, a third switch unit, a fourth switch unit, a fifth switch unit, a first diode, and a second diode. Each battery cell corresponds to one first switch unit and one second switch unit. The energy storage unit includes a first winding, a second winding, and a third winding. The first winding and the second winding are located on opposite sides of the third winding. The positive terminal of the battery pack unit is electrically connected to the same-name terminal of the third winding, and the negative terminal is electrically connected to the opposite-name terminal of the third winding through the fifth switch unit. The positive terminal of each battery cell is connected in parallel through a corresponding first switching unit, and then electrically connected to the same-name terminal of the first winding through a third switching unit, and electrically connected to the opposite-name terminal of the second winding through a fourth switching unit. The negative terminal of each battery cell is connected in parallel through a corresponding second switching unit, and then electrically connected to the negative terminal of the first diode and the positive terminal of the second diode. The positive terminal of the first diode is electrically connected to the opposite-name terminal of the first winding, and the negative terminal of the second diode is electrically connected to the same-name terminal of the second winding. The positive terminal of the battery pack unit is electrically connected to the same-name terminal and the negative terminal of the third winding. The switching matrix unit can selectively control the energy transfer between any battery cells and the energy transfer between any battery cell and the battery pack unit.

[0038] Preferably, the third switching unit includes a first MOSFET, a third diode, a first capacitor, and a first inductor. The source (S) terminal of the first MOSFET and the negative terminal of the third diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the first MOSFET and the positive terminal of the third diode are connected in parallel and then electrically connected to the same-name terminal of the first winding through the first inductor. The first capacitor is connected in parallel with the first MOSFET.

[0039] Preferably, the fourth switching unit includes a second MOSFET, a fourth diode, a second capacitor, and a second inductor. The source (S) terminal of the second MOSFET and the positive terminal of the fourth diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the second MOSFET and the negative terminal of the fourth diode are connected in parallel and then electrically connected to the opposite terminal of the second winding through the second inductor. The second capacitor is connected in parallel with the second MOSFET.

[0040] Preferably, the energy storage unit is a transformer with three windings.

[0041] Preferably, each switch in the switch matrix unit is independently controlled by a control signal.

[0042] This embodiment uses three battery cells connected in series as an example for illustration. These three battery cells are referred to as B1, B2 and B3 respectively. Battery cell B1 is set as the battery cell with the highest SOC and battery cell B3 is set as the battery cell with the lowest SOC. Let switch S1 be the first switching unit corresponding to battery cell B1, and switch S2 be the second switching unit corresponding to it; let switch S3 be the first switching unit corresponding to battery cell B2, and switch S4 be the second switching unit corresponding to it; let switch S5 be the first switching unit corresponding to battery cell B3, and switch S6 be the second switching unit corresponding to it; let switch S7 be the fifth switching unit; let W1 be the first winding, W2 be the second winding, W3 be the third winding; let D1 be the first diode, D2 be the second diode, D3 be the third diode, D4 ​​be the fourth diode; let C1 be the first capacitor, M1 be the first MOSFET, L1 be the first inductor, C2 be the second capacitor, M2 be the second MOSFET, L2 be the second inductor, and W1 be the first winding, W2 be the second winding, and W3 be the third winding. The resulting circuit diagram is as follows: Figure 1 As shown, C1, C2, L1, and L2 in the switch matrix unit provide a quasi-resonant effect for the zero-voltage conduction of M1 and M2, which helps to reduce switching losses and improve equalization efficiency. Among them, M1, C1, L1, and D1 mainly serve the discharge process of the battery pack unit, while M2, C2, L2, and D2 mainly serve the charging process of the battery pack unit.

[0043] In addition, to prevent transformer core saturation and ensure circuit balance accuracy, the topology operates in flyback mode and discontinuous current mode, while assuming that the MOSFET and energy storage unit operate under ideal conditions.

[0044] Accordingly, the equalization control method for the equalization circuit based on the flyback principle disclosed in this embodiment is applied to the equalization circuit based on the flyback principle as described above. The equalization circuit includes a first mode, a second mode, and a third mode. The first mode is used for energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC. The second mode is used for energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC. The third mode is used for energy transfer between the battery pack unit and the battery cell with the lowest SOC. Each of the first, second, and third modes has a first stage and a second stage sequentially within one switching cycle. This equalization circuit based on the flyback principle has two control signals: one is PWM+, and the other is PWM-. PWM+ and PWM- are complementary signals. T is the switching period of all switches, and D is the duty cycle of PWM+. The equalization control method for the equalization circuit based on the flyback principle includes the following steps:

[0045] For the first mode:

[0046] Phase 1:

[0047] By controlling the third switching unit, the fifth switching unit, and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit.

[0048] Phase Two:

[0049] By controlling the fourth and fifth switching units and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the excitation current of the first winding is reduced to zero through the second winding, thereby completing the core reset of the forward circuit in the first stage, and completing the energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC.

[0050] It is understandable that PWM1+ and PWM1- are the first mode control signals, T1 is the switching period, D1 is the duty cycle of the control signal PWM1+, and PWM1+ and PWM1- are complementary signals. The control signal waveform is as follows: Figure 2 As shown;

[0051] The operation of this mode within one switching cycle can be divided into two stages, and its working principle diagram is as follows: Figure 3 As shown;

[0052] Phase 1 (0 to D1T1): Its current loop is as follows Figure 3 As shown by the dashed line, at time t=0, PWM1+ applies a high level to M1, S1, S2, and S7, turning these switches on while de-energizing the others. Figure 3 As shown, W1 and W3 form a forward converter circuit. B1 releases energy and supplies it to W1. The voltage across B1 is positive at the top and negative at the bottom. The voltage across W3, which is coupled to B1, is also positive at the top and negative at the bottom. The current in W3 gradually increases, thereby transferring the energy of the high SOC battery cell to the entire battery pack.

[0053] The second stage (D1T1 to T1): its circuit loop is as follows Figure 3As shown by the dashed line, at time t = D1T1, PWM1+ applies a low level to all switches (except S7) turned on in the first stage, turning them off, while PWM1- applies a high level to M2, S5, and S6, turning them on. At this time, starting from time 0, the magnetizing current of W1 increases linearly with time until the end of the first stage. In the second stage, W2 reduces the magnetizing current of W1 to zero, thus completing the necessary core reset process in the forward transformer. Simultaneously, it transfers some energy from the high-SOC battery cells to the low-SOC battery cells, completing the energy balancing process between battery cells.

[0054] In summary, the first mode involves high-SOC batteries releasing energy to the battery pack and low-SOC batteries absorbing it. During operation in this mode, the energy of the balancing circuit comes from the highest-SOC battery in the battery pack, and the balancing energy is distributed in two parts: most of the energy is used to charge the entire battery pack via W3, and a small portion of the energy is used to charge the lowest-SOC battery via W2. This process can cause the high-SOC battery to drop rapidly, which is the characteristic of this first mode.

[0055] For the second mode:

[0056] Phase 1:

[0057] By controlling the third switching unit and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding and stored by the second winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit.

[0058] Phase Two:

[0059] By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the current of the first winding is cut off, thereby enabling energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC.

[0060] It is understandable that PWM2+ and PWM2- are the second-mode control signals, T2 is the switching period, D2 is the duty cycle of the control signal PWM2+, and PWM2+ and PWM2- are complementary signals. The control signal waveform is as follows: Figure 4 As shown.

[0061] The operation of this mode within one switching cycle can be divided into two stages, and its working principle diagram is as follows: Figure 4 As shown.

[0062] Phase 1 (0 to D2T2): Its current loop is as follows Figure 5 As shown by the dashed line, at time t=0, PWM2+ applies a high level to M1, S1, and S2, turning these switches on while de-energizing the others. Figure 4 As shown, W1 and W2 form a flyback circuit. B1 releases energy and supplies it to W1. The transformer in the flyback circuit acts as an energy storage element. The current of W1 increases linearly, and the energy stored in W2 increases.

[0063] The second stage (D2T2 to T2): its circuit loop is as follows Figure 5 As shown by the dashed line, at time t = D2T2, PWM2+ applies a low level to all the switches turned on in the first stage, turning them off, while PWM2- applies a high level to M2, S5, and S6, turning them on. At this time, the current in W1 is cut off, and the magnetic field energy in the transformer is released to B3 through W2, realizing the energy balancing process from battery cell to battery cell.

[0064] In summary, the second mode involves high-SOC battery cells releasing energy for low-SOC battery cells to absorb, belonging to the cell-to-cell balancing type, which is currently the most widely used balancing type. Its circuit current flow direction is as follows... Figure 5 As shown by the dashed line, W1 and W2 constitute a flyback circuit.

[0065] For the third mode:

[0066] Phase 1:

[0067] The fifth switching unit is turned on by a control signal, and the other switching units are turned off. The second winding and the third winding together form a flyback circuit so that the energy of the battery pack unit is released to the third winding and stored by the second winding.

[0068] Phase Two:

[0069] By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC through the control signal, the current of the third winding is cut off. The magnetic field energy of the third winding is released to the battery cell with the lowest SOC through the second winding, so as to complete the energy transfer between the battery pack unit and the battery cell with the lowest SOC.

[0070] It is understandable that PWM3+ and PWM3- are the third-mode control signals, T3 is the switching period, D3 is the duty cycle of the control signal PWM3+, and PWM3+ and PWM3- are complementary signals. The control signal waveform is as follows: Figure 6 As shown.

[0071] The operation of this mode within one switching cycle can be divided into two stages, and its working principle diagram is as follows: Figure 7 As shown.

[0072] Phase 1 (0 to D3T3): Its current loop is as follows Figure 7 As shown by the dashed line, at t=0, PWM3+ applies a high level to S7, turning on the switching transistor, while other switching transistors remain off. Figure 7 As shown, W2 and W3 form a flyback circuit. The battery pack unit releases energy and supplies it to W3. The transformer in the flyback circuit acts as an energy storage element. The current in W3 increases linearly, and the energy stored in W2 increases.

[0073] The second stage (D3T3 to T3): its circuit loop is as follows Figure 7 As shown by the dashed line, at time t = D3T3, PWM3+ applies a low level to S7 in the first stage to turn it off, while PWM3- applies a high level to M2, S5, and S6 to turn them on. At this time, the current to W3 is cut off, and the magnetic field energy in the transformer is released to B3 through W2, realizing the energy balancing process from the overall battery pack unit to individual battery cells.

[0074] Combination Figures 1-7 This invention can control the flexible transfer of energy between different equalization objects and adjust the equalization type in real time according to the condition of the battery pack, so that the equalization circuit always works in the best state, realizes the rapid equalization of the battery pack, and can effectively solve the problem of reduced equalization efficiency caused by frequent switching in the equalization circuit, effectively reduce switching losses and improve the efficiency of the equalization circuit.

[0075] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An equalization circuit based on the flyback / forward principle, characterized in that: The system includes a battery pack unit, a switch matrix unit, and an energy storage unit. The battery pack unit comprises multiple battery cells connected in series. The switch matrix unit includes multiple first switch units, multiple second switch units, a third switch unit, a fourth switch unit, a fifth switch unit, a first diode, and a second diode. Each battery cell corresponds to one first switch unit and one second switch unit. The energy storage unit includes a first winding, a second winding, and a third winding. The first and second windings are located on opposite sides of the third winding. The positive terminal of the battery pack unit is electrically connected to the same-name terminal of the third winding, and the negative terminal is electrically connected to the opposite-name terminal of the third winding through the fifth switch unit. The positive terminal of each battery cell... After the electrodes are connected in parallel through the corresponding first switching unit, they are electrically connected to the same-name terminal of the first winding through the third switching unit and to the opposite-name terminal of the second winding through the fourth switching unit. After the negative terminal of each battery cell is connected in parallel through the corresponding second switching unit, it is electrically connected to the negative terminal of the first diode and to the positive terminal of the second diode. The positive terminal of the first diode is electrically connected to the opposite-name terminal of the first winding, and the negative terminal of the second diode is electrically connected to the same-name terminal of the second winding. The positive terminal of the battery pack unit is electrically connected to the same-name terminal and the negative terminal of the third winding. The switching matrix unit can selectively control the energy transfer between any battery cells and the energy transfer between any battery cell and the battery pack unit.

2. The equalization circuit based on the flyback principle as described in claim 1, characterized in that: The third switching unit includes a first MOSFET, a third diode, a first capacitor, and a first inductor. The source (S) terminal of the first MOSFET and the negative terminal of the third diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the first MOSFET and the positive terminal of the third diode are connected in parallel and then electrically connected to the same-name terminal of the first winding through the first inductor. The first capacitor is connected in parallel with the first MOSFET.

3. The equalization circuit based on the flyback principle as described in claim 1, characterized in that: The fourth switching unit includes a second MOSFET, a fourth diode, a second capacitor, and a second inductor. The source (S) terminal of the second MOSFET and the positive terminal of the fourth diode are connected in parallel and then electrically connected to the positive terminal of the corresponding battery cell through the corresponding first switching unit. The drain (D) terminal of the second MOSFET and the negative terminal of the fourth diode are connected in parallel and then electrically connected to the opposite terminal of the second winding through the second inductor. The second capacitor is connected in parallel with the second MOSFET.

4. The equalization circuit based on the flyback principle as described in claim 1, characterized in that: The energy storage unit is a transformer with three windings.

5. The equalization circuit based on the forward / flyback principle as described in claim 1, characterized in that: Each switch in the switch matrix unit is independently controlled by a control signal.

6. The equalization circuit based on the flyback principle as described in claim 1, characterized in that: The first switching unit, the second switching unit, and the fifth switching unit are all switching transistors.

7. A method for equalization control of an equalization circuit based on the flyback principle, applied to an equalization circuit based on the flyback principle as described in any one of claims 1-6, characterized in that: The equalization circuit based on the flyback principle includes a first mode, a second mode, and a third mode. The first mode is used for energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC. The second mode is used for energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC. The third mode is used for energy transfer between the battery pack unit and the battery cell with the lowest SOC. The first mode, the second mode, and the third mode each have a first stage and a second stage sequentially within one switching cycle. The equalization control method of the equalization circuit based on the flyback principle includes the following steps: For the first mode: Phase 1: By controlling the third switching unit, the fifth switching unit, and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit. Phase Two: By controlling the fourth switching unit, the fifth switching unit, and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the excitation current of the first winding is reduced to zero through the second winding, thereby completing the core reset of the forward circuit in the first stage, and completing the energy transfer between the battery cell with the highest SOC and the battery pack unit and the battery cell with the lowest SOC. For the second mode: Phase 1: By controlling the third switching unit and the first and second switching units corresponding to the battery cell with the highest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the first winding and the second winding together form a forward circuit, so that the energy of the battery cell with the highest SOC is released to the first winding and stored by the second winding, thereby transferring the energy of the battery cell with the highest SOC to the battery pack unit. Phase Two: By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC to be turned on by the control signal, and controlling the remaining switching units to be turned off, the current of the first winding is cut off, thereby enabling energy transfer between the battery cell with the highest SOC and the battery cell with the lowest SOC. For the third mode: Phase 1: The fifth switching unit is turned on by a control signal, and the other switching units are turned off. The second winding and the third winding together form a flyback circuit so that the energy of the battery pack unit is released to the third winding and stored by the second winding. Phase Two: By controlling the fourth switching unit and the first and second switching units corresponding to the battery cell with the lowest SOC to conduct through the control signal, the current of the third winding is cut off. The magnetic field energy of the third winding is released to the battery cell with the lowest SOC through the second winding, so as to complete the energy transfer between the battery pack unit and the battery cell with the lowest SOC.

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