Lithium battery active equalization circuit with small volume, high efficiency and large current and control method thereof

Abstract

The invention discloses a small-size high-efficiency large-current lithium battery active equalization circuit and a control method thereof, the small-size high-efficiency large-current lithium battery active equalization circuit comprises active equalization modules which are connected in parallel between two connected battery cells, and each active equalization module is composed of four switching tubes and a group of resonance branch circuit which is formed by connecting an inductor and a capacitor in series; n-1 active equalization modules are needed for a battery pack composed of N battery cells. The LC series branch serves as an energy temporary storage unit to replace a traditional inductance type single inductor or capacitance type multiple capacitors, the number of elements is reduced, meanwhile, low-loss energy transfer is achieved through resonance characteristics, and the equalization scheme has the advantages of being small in size, large in equalization current, small in equalization energy loss between battery cells, high in efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery balancing technology, specifically relating to a small-volume, high-efficiency, high-current active balancing circuit for lithium batteries and its control method. Background Technology

[0002] Lithium-ion batteries are widely used. To improve their lifespan and safety, balancing technology must be used between individual cells. For larger cells, a larger current balancing technology is required, hence the development of active balancing technology. Currently, the mainstream active balancing technologies for lithium-ion batteries fall into two categories: One type is inductive active balancing technology: This technology uses a single or multiple inductors as the core energy transfer component, and establishes an energy path through 2 to 4 switching transistors. A typical scheme is to connect an "inductor + switching transistor group" module in parallel between two adjacent cells. When the voltage of cell 1 is higher than that of cell 2, the corresponding switching transistor is turned on, and the energy of cell 1 is stored through the inductor. Subsequently, the state of the switching transistor is switched, and the energy stored in the inductor is released to cell 2, completing the unidirectional energy transfer. For example, Chinese invention patent CN115864606B proposes an inductive lithium battery active balancing circuit and its control method. Its core components include an inductor L, MOSFET switching transistors Q1~Q4, and cells Cell1~Cell2. The switching transistors are controlled by a PWM signal to realize the transfer of energy between cells.

[0003] Another type is capacitive active balancing technology: using capacitors as energy storage elements, and employing multiple sets of switching transistors to form a switching matrix. For example, in a battery pack with k cells connected in series, a common balancing capacitor C is set up, and the capacitor is connected to each cell through k sets of switching transistors respectively. When the voltage of cell 3 is abnormal, the corresponding switching transistor is controlled to turn on, and cell 3 and capacitor C form a circuit. The capacitor is charged to the voltage of cell 3. Then, the switching transistor is switched to make the capacitor conduct with the low-voltage cell (such as cell 5), and the capacitor discharges to cell 5, realizing the transfer of energy from the high-voltage cell to the low-voltage cell.

[0004] Switched capacitor active balancing technology was once considered to have potential in terms of circuit integration and cost control because it does not require magnetic components such as inductors and transformers. As early as 2014, Kim et al. systematically discussed the topological characteristics of bidirectional battery balancing structures, which require two additional switches for each additional battery (Kim M, Kim JH, Moon G W. Center-Cell Concentration Structure of a Cell-to-Cell Balancing Circuit With a Reduced Number of Switches. IEEE Transactions on Power Electronics, 2014, 29(10):5285-5297), and clearly pointed out that the increase in the number of switches would inevitably lead to a simultaneous increase in cost and size. However, there has been a long-standing consensus in academia and industry regarding the limitations of this technology: an excessive number of switching transistors is an inherent drawback, and the negative impact of a large number of switching transistors is multi-dimensional: First, each switching transistor has on-resistance and switching losses, and the series path of multiple transistors leads to the superposition of on-resistance, making the overall efficiency of capacitive equalization schemes generally lower than that of inductive schemes; Second, a large number of switching transistors and their driving circuits occupy PCB area, and even with integrated chip solutions, each additional equalization channel still requires additional pins and peripheral circuits, and the area expansion problem remains prominent when the number of battery strings is large; Third, the number of switching transistors is strongly correlated with system cost, becoming a key obstacle to the large-scale application of capacitive equalization in high-capacity battery packs.

[0005] Therefore, the existing active balancing technology has the following process and performance defects, which cannot meet the needs of large battery cells and high integration scenarios.

[0006] (1) Small balancing current: Inductive active balancing technology is limited by the saturation current of the inductor. The balancing current of conventional solutions is mostly 1~3A, which cannot meet the fast balancing requirements of large capacity cells (such as power batteries with a capacity of 100Ah or more); Capacitor active balancing technology is limited by the capacitive reactance of the capacitor charging and discharging current, and the balancing current is usually less than 1A, resulting in slow balancing speed.

[0007] (2) Low efficiency: Both technologies use hard switching control. When the switching transistor is turned on / off, there are sudden changes in current / voltage in the inductor / capacitor, resulting in large switching losses. In the inductor scheme, when energy is transferred through “cell → inductor → cell”, the copper loss and iron loss of the inductor account for about 15%~20%. In the capacitor scheme, due to the large number of switching transistors, the overall efficiency is often less than 80% after the conduction loss is superimposed.

[0008] (3) Large size and inconvenient layout: The inductor volume of the inductor solution increases significantly with the increase of the balancing current; the capacitor solution requires a large number of switching transistors, which leads to an increase in PCB area. Both are difficult to adapt to scenarios with strict space requirements, such as new energy vehicle battery packs and small energy storage devices. Summary of the Invention

[0009] In view of the above, the present invention provides a small-volume, high-efficiency, high-current active balancing circuit for lithium batteries and its control method. The balancing circuit completes the energy transfer between connected cells, so that any unbalanced cell can achieve the purpose of balancing through the present invention.

[0010] A small-volume, high-efficiency, high-current active balancing circuit for lithium batteries, comprising N-1 active balancing modules B1~B2. N-1 N represents the number of cells in the lithium battery pack, wherein the lithium battery pack consists of N cells Vb1~Vb N The modules are connected in series; for any active equalization module B i Its relationship with the cell Vb i and Vb i+1 Connected to implement Vb i With Vb i+1 Energy transfer between them, where i is a natural number and 1≤i≤N-1.

[0011] Furthermore, the active balancing module B i Includes four switching transistors Q i_1 ~Q i_4 Inductor L i and capacitor C i Q i_1 Drain and Vb i The positive terminals are connected, Q i_1 The source and Q i_2 The drain and L i One end is connected, L i The other end and C i Connect one end to Q i_2 The source and Q i_3 Drain, Vb i The negative electrode and Vb i+1 The positive terminals are connected, Q i_3 The source and Q i_4 The drain and C i The other end is connected, Q i_4 The source and Vb i+1 The negative terminal is connected, Q i_1 ~Q i_4 The gate is connected to the drive signal provided by the control unit.

[0012] Furthermore, the inductor L i and capacitor Ci Form a resonant branch to buffer Vb i With Vb i+1 The energy to be transferred between them.

[0013] Furthermore, the switching transistor Q i_1 ~Q i_4 The duty cycle of the drive signal is about 50%.

[0014] Furthermore, the switching transistor Q i_1 and Q i_3 Using drive signal Φ1, switching transistor Q i_2 and Q i_4 The drive signal Φ2 is used, and the switching phases of the drive signals Φ1 and Φ2 are complementary.

[0015] Furthermore, the resonant frequency of the resonant branch is close to the switching frequency of the switching transistor, so as to realize soft switching of the switching transistor and improve working efficiency.

[0016] Furthermore, the switching transistor Q i_1 ~Q i_4 It employs IGBT (Insulated Gate Bipolar Transistor), BJT (Bipolar Junction Transistor), MOSFET (Metal-Oxide-Semiconductor Transistor), or third-generation semiconductor transistors such as GaN (Gallium Nitride) and SiC (Silicon Carbide).

[0017] The control method for the above-mentioned lithium battery active balancing circuit includes: Vb i Energy transferred to Vb i+1 First, Q is turned on simultaneously. i_1 and Q i_3 This allows energy to be transferred to the resonant branch for storage. When the current in the resonant branch drops to near zero, Q is simultaneously disconnected. i_1 and Q i_3 and conduct Q i_2 and Q i_4 This causes the energy stored in the resonant branch to be transferred to Vb. i+1 Complete the Vb i Energy transferred to Vb i+1 middle; Vb i+1 Energy transferred to Vb i First, Q is turned on simultaneously. i_2 and Q i_4 This allows energy to be transferred to the resonant branch for storage. When the current in the resonant branch drops to near zero, Q is simultaneously disconnected. i_2 and Q i_4 and conduct Q i_1 and Q i_3 This causes the energy stored in the resonant branch to be transferred to Vb.i Complete the Vb i+1 Energy transferred to Vb i middle.

[0018] This invention temporarily stores the energy to be transferred between battery cells in a resonant branch. This resonant branch controls the resonant cavity current to exhibit a sinusoidal change, controlling the switching transistor to turn on or off around the current zero point to achieve soft switching. Since the switching transistor operates under soft-switching conditions, the switching loss is almost zero. Therefore, by increasing the switching frequency, the volume of the inductor and capacitor in the resonant branch can be reduced, thereby reducing the overall weight and size.

[0019] Meanwhile, this invention can control the energy transfer direction of the battery cells by controlling the sequence of switching transistor actions, and control the energy transfer magnitude between battery cells by controlling the switching transistor action time, thereby achieving rapid balancing between battery cells and improving balancing efficiency. Furthermore, this invention can also control the magnitude of the current flowing into or out of the battery cells when the switching transistor is turned on by controlling the switching time of the switching transistor and the magnitude of the inductance of the resonant branch, thereby controlling the magnitude of the balancing current.

[0020] This invention is applicable to scenarios that rely on lithium batteries for power supply, such as new energy vehicles, energy storage systems, and portable electronic devices. By using balancing technology, the voltage / capacity consistency of each cell in the lithium battery pack can be ensured, thereby extending the battery pack's lifespan and improving safety. Especially for large-capacity cells, balancing technology is needed to avoid charging and discharging limitations caused by cell imbalance.

[0021] The inventiveness and core key points of this invention are mainly reflected in the following aspects: 1. Modular architecture design: In this invention, the number of balancing modules is strictly matched with the number of battery cells (N cells require N-1 modules). Each module is only responsible for balancing two adjacent battery cells, without the need for common energy components (such as common inductors / capacitors), which simplifies the circuit topology and makes it easy to expand to battery packs with any number of series connections.

[0022] 2. Core structure of "four switching transistors + LC resonant branch": This invention uses an LC series branch as an energy storage unit to replace the traditional single inductor or multiple capacitors of the inductor type, reducing the number of components, and at the same time achieving low-loss energy transfer through resonant characteristics. 3. Bidirectional energy transfer control: This invention can achieve bidirectional energy transfer between adjacent cells simply by switching the on and off sequence of the switching transistors, without the need for additional reverse switches or paths, thus reducing circuit complexity.

[0023] 4. Application of soft-switching technology: This invention controls the LC resonant frequency to match the operating frequency of the switching transistor, so that the switching transistor turns on and off near the current zero point, with almost zero switching loss, significantly improving the equalization efficiency.

[0024] 5. Optimized switching transistor drive logic: The drive logic within the same module is such that "the first and third switches are driven in the same way, and the second and fourth switches are driven in the same way; the first and second switches are driven in opposite ways, and the third and fourth switches are driven in opposite ways". This avoids the risk of short circuits caused by simultaneous conduction of switches, and the duty cycle of about 50% ensures that the energy transfer is stable and controllable.

[0025] 6. Wide range of switching transistors compatible: This invention supports ordinary MOSFETs, IGBTs and third-generation semiconductors (GaN / SiC), allowing for flexible selection based on application scenarios (such as high voltage, high current, low cost), balancing efficiency and cost requirements.

[0026] Therefore, compared with existing active balancing technologies, this invention has significant advantages in performance, size, and compatibility, with the specific effects as follows: (1) Significantly increased equalization current: This invention adapts the high-frequency characteristics of the LC resonant branch to high-power switching transistors (such as GaN / SiC), thereby increasing the equalization current; compared with the traditional inductor type, it is 1.5 to 3 times higher, which is fully adapted to the fast equalization requirements of large-capacity cells with a capacity of 100Ah or more.

[0027] (2) Significantly improved balancing efficiency: The soft-switching design of this invention makes the switching loss almost zero. The energy loss in the transfer between the battery cell and the LC branch comes only from the component's own losses (such as inductor copper loss and capacitor dielectric loss). The overall balancing efficiency can reach more than 90%, which is an improvement compared to the traditional capacitor type.

[0028] (3) The overall volume is greatly reduced: Because the soft switch supports high-frequency design, the volume of the inductor and capacitor of the LC resonant branch is significantly reduced, and the modular design reduces the overall volume of the battery pack equalization circuit of N=4 by more than 30%, which is convenient for compact space layout.

[0029] (4) Strong application compatibility: This invention can be adapted to battery packs with different series numbers (from 2 cells to dozens of cells), and the selection of switching transistors is flexible. It can meet the high current and high reliability requirements of new energy vehicle power batteries, as well as the low cost and long life requirements of energy storage systems.

[0030] (5) Improved reliability: This invention eliminates the risk of overall balance failure caused by the failure of common energy components (such as the failure of the common capacitor in traditional capacitor-type batteries, which would lead to the paralysis of the entire battery pack balance). The failure of a single module only affects the two adjacent cells and does not affect the entire battery pack, thus improving the system's fault tolerance. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the three-cell active balancing circuit structure in Embodiment 1 of the present invention.

[0032] Figure 2This is a schematic diagram of the two-cell active balancing circuit structure in Embodiment 2 of the present invention.

[0033] Figure 3 This is a schematic diagram of the four-cell active balancing circuit structure in Embodiment 3 of the present invention.

[0034] Figure 4 This is a schematic diagram of the active balancing circuit structure of the K-cell in Embodiment 4 of the present invention.

[0035] Figure 5 This is a schematic diagram of the equalization working principle between Vb1 and Vb2 in Embodiment 1 of the present invention, where (a) corresponds to the discharge state of Vb1, (b) corresponds to the charging state of Vb2, (c) corresponds to the discharge state of Vb2, and (d) corresponds to the charging state of Vb1.

[0036] Figure 6 This is a schematic diagram of the equalization working principle between Vb2 and Vb3 in Embodiment 1 of the present invention, where (a) corresponds to the discharge state of Vb2, (b) corresponds to the charging state of Vb3, (c) corresponds to the discharge state of Vb3, and (d) corresponds to the charging state of Vb2.

[0037] Figure 7 This is a schematic diagram of the equalization working principle between Vb1 and Vb2 in Embodiment 2 of the present invention, where (a) corresponds to the discharge state of Vb1, (b) corresponds to the charging state of Vb2, (c) corresponds to the discharge state of Vb2, and (d) corresponds to the charging state of Vb1.

[0038] Figure 8 This is a schematic diagram of the waveforms of key components during the active balancing process of two battery cells in Embodiment 2 of the present invention, where (a) corresponds to Vb1 discharging to charge Vb2, and (b) corresponds to Vb2 discharging to charge Vb1. Detailed Implementation

[0039] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] Example 1: Three-cell active balancing circuit (B12+B23 module) like Figure 1 As shown, this embodiment is an active balancing circuit adapted to three series-connected battery cells (Vb1, Vb2, Vb3), and its core consists of one balancing main module (B12) and one balancing extension module (B23).

[0041] Connection between battery cells and modules: The positive terminal of battery cell Vb1 is connected to the positive input port of main module B12; the negative terminal of battery cell Vb1 and the positive terminal of battery cell Vb2 are connected to the negative input port of main module B12; the negative terminal of battery cell Vb2 and the positive terminal of battery cell Vb3 are connected to the positive input port of expansion module B23; the negative terminal of battery cell Vb3 is connected to the negative input port of expansion module B23.

[0042] Connections of module B12: The drain of switch Q1 is connected to the positive terminal of cell Vb1; the source of switch Q1 is connected to the drain of switch Q2 and the first terminal of inductor L1; the source of switch Q2 is connected to the negative terminal of cell Vb1; the drain of switch Q2 is connected to the source of switch Q1 and the first terminal of inductor L1; the second terminal of inductor L1 is connected in series with the first terminal of capacitor C1; the second terminal of capacitor C1 is connected to the source of switch Q3; the drain of switch Q3 is connected to the source of switch Q2 and the positive terminal of cell Vb2; the source of switch Q3 is connected to the drain of switch Q4 and the second terminal of capacitor C1; the source of switch Q4 is connected to the negative terminal of cell Vb2.

[0043] Connections of module B23: The drain of switch Q3a is connected to the negative terminal of cell Vb2; the source of switch Q3a is connected to the drain of switch Q4a and the first terminal of inductor L2; the source of switch Q4a is connected to the positive terminal of cell Vb3; the drain of switch Q4a is connected to the source of switch Q3a and the first terminal of inductor L2; the second terminal of inductor L2 is connected in series with the first terminal of capacitor C2; the second terminal of capacitor C2 is connected to the source of switch Q5a; the drain of switch Q5a is connected to the source of switch Q4a and the positive terminal of cell Vb3; the source of switch Q5a is connected to the drain of switch Q6a; and the source of switch Q6a is connected to the negative terminal of cell Vb3.

[0044] Three-cell positive energy transfer refers to the energy transfer from high-voltage cells to low-voltage cells: In this embodiment, when the voltage of cell Vb1 is higher than the voltages of cells Vb2 and Vb3, graded energy transfer is initiated. The specific process is as follows: When energy is transferred from cell Vb1 to cell Vb2, the switches Q1 and Q3 in the control module are turned on. The energy of cell Vb1 is transferred to the resonant branch composed of inductor L1 and capacitor C1. The current in this branch gradually increases during the resonance process to store energy. After the current in the resonant branch decreases to a preset threshold, the switches Q1 and Q3 are turned off, and the switches Q2 and Q4 are turned on simultaneously. The energy stored in the resonant branch is transferred to cell Vb2 to release energy.

[0045] When energy is transferred from cell Vb2 to cell Vb3, the switches Q3a and Q5a in the control extension module B23 are turned on. The electrical energy of cell Vb2 is transferred to the resonant branch composed of inductor L2 and capacitor C2. The current in this branch gradually increases during the resonance process to store energy. After the current in the resonant branch decreases to a preset threshold, the switches Q3a and Q5a are turned off, and the switches Q4a and Q6a are turned on simultaneously. The electrical energy stored in the resonant branch is transferred to cell Vb3 to release energy.

[0046] Repeat the above graded transfer process. When the voltage difference between cells Vb1, Vb2, and Vb3 decreases to within the preset threshold, the main module and module 23 stop working simultaneously, completing the active balancing of the three cells.

[0047] Three-cell reverse energy transfer refers to the energy transfer from low-voltage cells to high-voltage cells: This embodiment is applicable to scenarios where the voltage of cell Vb3 is higher than that of cell Vb1. The connection relationship is the same as in Embodiment 1, only the conduction logic of the switching transistor is adjusted. The specific process is as follows: When energy is transferred from cell Vb3 to cell Vb2, the switches Q4a and Q6a in the control expansion module B23 are turned on, and the electrical energy of cell Vb3 is transferred to the resonant branch composed of inductor L2 and capacitor C2. After the current in the resonant branch decreases to a preset threshold, the switches Q4a and Q6a are turned off, and the switches Q3a and Q5a are turned on simultaneously, and the electrical energy stored in the resonant branch is transferred to cell Vb2.

[0048] When energy is transferred from cell Vb2 to cell Vb1, the switching transistors Q2 and Q4 in the main control module are turned on, and the electrical energy of cell Vb2 is transferred to the resonant branch composed of inductor L1 and capacitor C1. After the current in the resonant branch decreases to a preset threshold, the switching transistors Q2 and Q4 are turned off, and the switching transistors Q1 and Q3 are turned on simultaneously, and the electrical energy stored in the resonant branch is transferred to cell Vb1.

[0049] After multiple energy transfer cycles, the voltage difference between cells Vb1, Vb2, and Vb3 can be reduced to within a preset threshold, achieving voltage consistency regulation of the three cells.

[0050] like Figure 5 and Figure 6 As shown, in this embodiment, the active balancing of the three battery cells (Vb1, Vb2, Vb3) is achieved through a two-stage hierarchical transfer of "bidirectional balancing between Vb1 and Vb2" and "bidirectional balancing between Vb2 and Vb3", ultimately reducing the voltage difference among the three cells. The specific working principle is as follows: The first-level equilibrium is the bidirectional energy transfer between Vb1 and Vb2, such as... Figure 5 As shown, the three-cell equalization prioritizes adjusting the voltage difference between Vb1 and Vb2, which is divided into two scenarios: "Vb1 discharging to charge Vb2" and "Vb2 discharging to charge Vb1". Both are completed in two stages: "energy storage - energy release". The specific process is as follows: When Vb1 discharges and Vb2 charges (corresponding to...) Figure 5 In (a) and (b), when the main control module switches Q1 and Q3 are turned on, the electrical energy of Vb1 flows out through its positive terminal, passing sequentially through Q1, inductor L1, capacitor C1, and Q3, and finally returns to the negative terminal of Vb1. During this process, the electrical energy is stored in the resonant branch formed by L1 and C1, completing energy storage. When Q1 and Q3 are turned off and switches Q2 and Q4 are turned on, the electrical energy stored in the resonant branch flows out through Q2, passing sequentially through the negative terminals of Vb1 and Vb2, and Q4, and finally returns to C1. During this process, the electrical energy is released to Vb2, completing the energy transfer from Vb1 to Vb2.

[0051] When Vb2 discharges and Vb1 charges (corresponding to...) Figure 5 (c) and (d) control the switching transistors Q2 and Q4 in the main module to conduct, allowing the electrical energy of Vb2 to flow out through its positive terminal, sequentially through Q4, capacitor C1, inductor L1, and Q2, finally returning to the negative terminal of Vb2. During this process, the electrical energy is stored in the resonant branch formed by L1 and C1, completing energy storage. Figure 4 When Q2 and Q4 are turned off, and Q1 and Q3 are turned on, the electrical energy stored in the resonant branch flows out through Q1, passes through the positive terminal of Vb1, the negative terminal of Vb1, and Q3 in sequence, and finally returns to C1. During this process, electrical energy is released to Vb1, completing the energy transfer from Vb2 to Vb1.

[0052] The second-level equilibrium is the bidirectional energy transfer between Vb2 and Vb3, such as... Figure 6 As shown, after the voltage difference between Vb1 and Vb2 decreases, bidirectional balancing between Vb2 and Vb3 is initiated. This is also accomplished through two stages: "energy storage - energy release," using the switching transistor and resonant element in extension module B23. The specific process is as follows: Vb2 discharges, Vb3 charges (corresponding to...) Figure 6 When (a) and (b) are executed, the switches Q3a and Q5a in the control expansion module B23 are turned on, and the electrical energy of Vb2 flows out through its positive terminal, passing sequentially through Q3a, inductor L2, capacitor C2, and Q5a, finally returning to the negative terminal of Vb2. During this process, the electrical energy is stored in the resonant branch formed by L2 and C2, completing energy storage. When Q3a and Q5a are turned off and the switches Q4a and Q6a are turned on, the electrical energy stored in the resonant branch flows out through Q4a, passing sequentially through the negative terminal of Vb2, the negative terminal of Vb3, and Q6a, finally returning to C2. During this process, the electrical energy is released to Vb3, completing the energy transfer from Vb2 to Vb3.

[0053] Vb3 discharges, Vb2 charges (corresponding to...) Figure 6 When (c) and (d) are executed, the switches Q4a and Q6a in the control expansion module B23 are turned on, and the electrical energy of Vb3 flows out through its positive terminal, passing sequentially through Q6a, capacitor C2, inductor L2, and Q4a, finally returning to the negative terminal of Vb3. During this process, the electrical energy is stored in the resonant branch formed by L2 and C2, completing energy storage. When Q4a and Q6a are turned off and the switches Q3a and Q5a are turned on, the electrical energy stored in the resonant branch flows out through Q3a, passing sequentially through the positive terminal of Vb2, the negative terminal of Vb2, and Q5a, finally returning to C2. During this process, the electrical energy is released to Vb2, completing the energy transfer from Vb3 to Vb2.

[0054] Through a hierarchical cyclic switching of "first stage (Vb1-Vb2) → second stage (Vb2-Vb3)," bidirectional energy transfer between the three battery cells is achieved: if Vb1 has the highest voltage, energy is first transferred to Vb2 through the first stage, and then transferred to Vb3 through the second stage; if Vb3 has the highest voltage, energy is first transferred to Vb2 through the second stage, and then transferred to Vb1 through the first stage; the above "storage-release" process is repeated until the voltage difference between Vb1, Vb2, and Vb3 is reduced to a preset threshold, thus completing the active balancing of the three battery cells.

[0055] Example 2: Two-cell active balancing circuit (B12 module) like Figure 2 As shown, this embodiment is an active balancing circuit adapted to two series-connected battery cells (Vb1, Vb2), and its core consists of one balancing main module.

[0056] Connection between battery cell and module: The positive terminal of battery cell Vb1 is connected to the positive input port of the main module; the negative terminal of battery cell Vb1 and the positive terminal of battery cell Vb2 are connected to the middle port of the main module; the negative terminal of battery cell Vb2 is connected to the negative input port of the main module.

[0057] Main module connections: The drain of switch Q1 is connected to the positive terminal of battery cell Vb1; the source of switch Q1 is connected to the drain of switch Q2 and the first terminal of inductor L1; the source of switch Q2 is connected to the negative terminal of battery cell Vb1; the drain of switch Q2 is connected to the source of switch Q1 and the first terminal of inductor L1; the second terminal of inductor L1 is connected in series with the first terminal of capacitor C1; the second terminal of capacitor C1 is connected to the source of switch Q3; the drain of switch Q3 is connected to the source of switch Q2 and the positive terminal of battery cell Vb2; the source of switch Q3 is connected to the drain of switch Q4 and the second terminal of capacitor C1; the source of switch Q4 is connected to the negative terminal of battery cell Vb2.

[0058] Forward energy transfer between two battery cells refers to the energy transfer from the high-voltage cell to the low-voltage cell: In this embodiment, when the voltage of cell Vb1 is higher than that of cell Vb2, an energy transfer process is initiated, specifically as follows: Switches Q1 and Q3 in the main module are turned on, and the energy in cell Vb1 is transferred to the resonant branch composed of inductor L1 and capacitor C1. The current in this branch gradually increases during the resonance process to store energy. Once the current in the resonant branch decreases to a preset threshold, switches Q1 and Q3 are turned off, and simultaneously switches Q2 and Q4 are turned on, transferring the stored energy in the resonant branch to cell Vb2 for energy release. This process is repeated until the voltage difference between cells Vb1 and Vb2 decreases to within the preset threshold, at which point the main module stops operating, completing the active balancing of the two cells.

[0059] Reverse energy transfer between two battery cells, i.e., energy transfer from the low-voltage cell to the high-voltage cell: This embodiment is applicable to scenarios where the voltage of cell Vb2 is higher than that of cell Vb1. The connection relationship remains the same as described above, only the conduction logic of the switching transistors is adjusted. The specific process is as follows: Switches Q2 and Q4 in the main control module are turned on, and the energy of cell Vb2 is transferred to the resonant branch composed of inductor L1 and capacitor C1. After the resonant branch current decreases to a preset threshold, switches Q2 and Q4 are turned off, and simultaneously switches Q1 and Q3 are turned on, transferring the energy stored in the resonant branch to cell Vb1. After multiple energy transfer cycles, the voltage difference between cells Vb1 and Vb2 can be reduced to within the preset threshold, achieving voltage consistency regulation between the two cells.

[0060] like Figure 7 As shown, in this embodiment, the active balancing of the two battery cells (Vb1, Vb2) is achieved through two scenarios: "Vb1 discharging to charge Vb2" and "Vb2 discharging to charge Vb1". Each scenario corresponds to two stages: "energy storage - energy release". The switching transistor drive waveform and the resonant branch current waveform are coordinated. The specific process is as follows: Vb1 discharges, Vb2 charges (corresponding to...) Figure 7 In (a) and (b)), during the energy storage stage: the switching transistors Q1 and Q3 in the control module are turned on, and the electrical energy of Vb1 flows out through its positive terminal, sequentially through Q1, inductor L1, capacitor C1, and Q3, and finally returns to the negative terminal of Vb1. During this process, the electrical energy is stored in the resonant branch formed by L1 and C1; the corresponding waveform is as follows. Figure 8As shown in (a): VOQ1 / 3 (the drive signals controlling Q1 and Q3) is at a high level, and IL1 (the current waveform of L1) rises with the resonance process. Energy release stage: Controlling Q1 and Q3 is turned off, and switching transistors Q2 and Q4 are turned on. The electrical energy stored in the resonant branch flows out through Q2, sequentially through the negative terminals of Vb1 and Vb2, and Q4, finally returning to C1. During this process, electrical energy is released to Vb2; the corresponding waveform is as follows. Figure 8 As shown in (a): VOQ1 / 3 switches to low level, VOQ2 / 4 (the drive signals that control Q2 and Q4) switches to high level, and IL1 decreases during the resonance process.

[0061] Vb2 discharges, Vb1 charges (corresponding to) Figure 7 During (c) and (d) the energy storage stage: Switches Q2 and Q4 in the control module are turned on, and the electrical energy of Vb2 flows out through its positive terminal, sequentially through Q4, capacitor C1, inductor L1, and Q2, finally returning to the negative terminal of Vb2. During this process, the electrical energy is stored in the resonant branch formed by L1 and C1; the corresponding waveform is as follows: Figure 8 As shown in (b): VOQ2 / 4 is at a high level, and IL1 rises during the resonance process. Energy release stage: Controls Q2 and Q4 are turned off, and switches Q1 and Q3 are turned on. The electrical energy stored in the resonant branch flows out through Q1, sequentially through the positive terminal of Vb1, the negative terminal of Vb1, and Q3, finally returning to C1. During this process, electrical energy is released to Vb1; the corresponding waveform is as follows. Figure 8 As shown in (b): VOQ2 / 4 switches to low level, VOQ1 / 3 switches to high level, and IL1 decreases during the resonance process.

[0062] like Figure 8 As shown, the switching transistor drive waveforms (VOQ1 / 3 and VOQ2 / 4) are complementary waveforms with no overlapping high levels, avoiding simultaneous short circuits of the switching transistors; the resonant branch current waveform (IL1) exhibits a periodic sinusoidal change, and its "rising-falling" rhythm is completely synchronized with the "high-level-low-level" switching of the drive waveform, ensuring stable energy flow during the "storage-release" phase and achieving bidirectional voltage balance between Vb1 and Vb2.

[0063] Example 3: Four-cell active balancing circuit (B12+B23+B34 modules) like Figure 3 As shown, this embodiment is an active balancing circuit adapted to four series-connected battery cells (Vb1, Vb2, Vb3, Vb4). Its core consists of one main balancing module (module B12), one balancing extension module (module B23), and one balancing module (module B34).

[0064] Connection of battery cells to modules: The positive terminal of battery cell Vb1 is connected to the positive input port of module B12; the negative terminal of battery cell Vb1 and the positive terminal of battery cell Vb2 are connected to the middle port of module B12; the negative terminal of battery cell Vb2 and the positive terminal of battery cell Vb3 are connected to the positive input port of module B23; the negative terminal of battery cell Vb3 and the positive terminal of battery cell Vb4 are connected to the middle port of module B34; the negative terminal of battery cell Vb4 is connected to the negative input port of module B34.

[0065] Connections of module B12: The drain of switch Q1 is connected to the positive terminal of cell Vb1; the source of switch Q1 is connected to the drain of switch Q2 and the first terminal of inductor L1; the source of switch Q2 is connected to the negative terminal of cell Vb1; the drain of switch Q2 is connected to the source of switch Q1 and the first terminal of inductor L1; the second terminal of inductor L1 is connected in series with the first terminal of capacitor C1; the second terminal of capacitor C1 is connected to the source of switch Q3; the drain of switch Q3 is connected to the source of switch Q2 and the positive terminal of cell Vb2; the source of switch Q3 is connected to the drain of switch Q4 and the second terminal of capacitor C1; the source of switch Q4 is connected to the negative terminal of cell Vb2.

[0066] Connections of module B23: The drain of switch Q3a is connected to the negative terminal of cell Vb2; the source of switch Q3a is connected to the drain of switch Q4a and the first terminal of inductor L2; the source of switch Q4a is connected to the positive terminal of cell Vb3; the drain of switch Q4a is connected to the source of switch Q3a and the first terminal of inductor L2; the second terminal of inductor L2 is connected in series with the first terminal of capacitor C2; the second terminal of capacitor C2 is connected to the source of switch Q5a; the drain of switch Q5a is connected to the source of switch Q4a and the positive terminal of cell Vb3; the source of switch Q5a is connected to the drain of switch Q6a; and the source of switch Q6a is connected to the negative terminal of cell Vb3.

[0067] Connections of module B34: The drain of switch Q5 is connected to the negative terminal of cell Vb3; the source of switch Q5 is connected to the drain of switch Q6 and the first terminal of inductor L3; the source of switch Q6 is connected to the positive terminal of cell Vb4; the drain of switch Q6 is connected to the source of switch Q5 and the first terminal of inductor L3; the second terminal of inductor L3 is connected in series with the first terminal of capacitor C3; the second terminal of capacitor C3 is connected to the source of switch Q7; the drain of switch Q7 is connected to the positive terminal of cell Vb4; the source of switch Q7 is connected to the drain of switch Q8 and the second terminal of capacitor C3; the source of switch Q8 is connected to the negative terminal of cell Vb4.

[0068] Four-cell positive energy transfer refers to the energy transfer from high-voltage cells to low-voltage cells: In this embodiment, when the voltage of cell Vb1 is higher than the voltages of cells Vb2, Vb3, and Vb4, graded energy transfer is initiated. The specific process is as follows: Energy transfer from Vb1 to Vb2: Switches Q1 and Q3 in module B12 are turned on, and the energy in cell Vb1 is transferred to the resonant branch composed of inductor L1 and capacitor C1. The current in this branch gradually increases during the resonance process to store energy. After the current in the resonant branch decreases to a preset threshold, switches Q1 and Q3 are turned off, and switches Q2 and Q4 are turned on simultaneously. The energy stored in the resonant branch is transferred to cell Vb2 for energy release.

[0069] Energy transfer from Vb2 to Vb3: Switches Q3a and Q5a in module B23 are turned on, and the energy in cell Vb2 is transferred to the resonant branch composed of inductor L2 and capacitor C2. The current in this branch gradually increases during the resonance process to store energy. After the current in the resonant branch decreases to a preset threshold, switches Q3a and Q5a are turned off, and switches Q4a and Q6a are turned on simultaneously. The energy stored in the resonant branch is transferred to cell Vb3 for energy release.

[0070] Energy transfer from Vb3 to Vb4: Switches Q5 and Q7 in module B34 are turned on, and the energy in cell Vb3 is transferred to the resonant branch composed of inductor L3 and capacitor C3. The current in this branch gradually increases during the resonance process to store energy. After the current in the resonant branch decreases to a preset threshold, switches Q5 and Q7 are turned off, and switches Q6 and Q8 are turned on simultaneously. The energy stored in the resonant branch is transferred to cell Vb4 for energy release.

[0071] Repeat the above graded transfer process. When the voltage difference between cells Vb1, Vb2, Vb3, and Vb4 decreases to within a preset threshold, modules B12, B23, and B34 simultaneously stop working, completing the active balancing of the four cells.

[0072] Four-cell reverse energy transfer refers to the energy transfer from low-voltage cells to high-voltage cells: This embodiment is applicable to scenarios where the voltage of cell Vb4 is higher than that of cell Vb1. The connection relationship is the same as described above, only the conduction logic of the switching transistor is adjusted. The specific process is as follows: Energy transfer from Vb4 to Vb3: Switches Q6 and Q8 in module B34 are turned on, and the energy in cell Vb4 is transferred to the resonant branch formed by inductor L3 and capacitor C3. After the current in the resonant branch decreases to a preset threshold, switches Q6 and Q8 are turned off, and switches Q5 and Q7 are turned on simultaneously, and the energy stored in the resonant branch is transferred to cell Vb3.

[0073] Energy transfer from Vb3 to Vb2: Switches Q4a and Q6a in module B23 are turned on, and the energy in cell Vb3 is transferred to the resonant branch composed of inductor L2 and capacitor C2. After the current in the resonant branch decreases to a preset threshold, switches Q4a and Q6a are turned off, and switches Q3a and Q5a are turned on simultaneously, and the energy stored in the resonant branch is transferred to cell Vb2.

[0074] Energy transfer from Vb2 to Vb1: Switches Q2 and Q4 in module B12 are turned on, and the energy in cell Vb2 is transferred to the resonant branch composed of inductor L1 and capacitor C1. After the current in the resonant branch decreases to a preset threshold, switches Q2 and Q4 are turned off, and switches Q1 and Q3 are turned on simultaneously, and the energy stored in the resonant branch is transferred to cell Vb1.

[0075] After multiple energy transfer cycles, the voltage difference between cells Vb1, Vb2, Vb3, and Vb4 can be reduced to within a preset threshold, achieving voltage consistency regulation of the four cells.

[0076] Example 4: Active balancing circuit for K-cells like Figure 4 As shown, this embodiment is an active balancing circuit adapted to K series-connected battery cells (BT1, BT2...BT(K-2), BT(K-1), BTK). Its core consists of K-1 balancing modules, namely balancing module 1, balancing module 2... balancing module K-3, balancing module K-2, balancing module K-1, etc. Each module corresponds to the balancing control of two adjacent battery cells.

[0077] Connection between battery cells and modules: The positive terminal of battery cell BT1 is connected to the positive input port of equalization module 1; The negative terminal of cell BT1 and the positive terminal of cell BT2 are connected to the middle port of equalization module 1. The negative terminal of cell BT2 and the positive terminal of cell BT3 are connected to the middle port of equalization module 2. ...(The connection between adjacent cells and modules follows the same principle) The negative terminal of cell BT(K-2) and the positive terminal of cell BT(K-1) are connected to the middle port of equalization module K-3; The negative terminal of cell BT(K-1) and the positive terminal of cell BTK are connected to the middle port of equalization module K-2; The negative terminal of the BTK battery cell is connected to the negative input port of the equalization module K-1.

[0078] The general connection of the equalization module (taking the m-th equalization module as an example, m∈[1,K-1], corresponding to cells BTm and BT(m+1)) is as follows: Each equalization module consists of four switching transistors and a set of resonant branches with "inductor + capacitor" connected in series. The specific connection is as follows: The drain of switch Q1 is connected to the positive terminal of cell BTm. The source of switch Q1 is also connected to the drain of switch Q2 and the first terminal of inductor Lm. The source of switch Q2 is connected to the negative terminal of cell BTm. The drain of switch Q2 is connected to the source of switch Q1 and the first terminal of inductor Lm. The second terminal of inductor Lm is connected in series with the first terminal of capacitor Cm. The second terminal of capacitor Cm is connected to the drain of switch Q3. The source of switch Q3 is connected to the positive terminal of cell BT(m+1). The drain of switch Q3 is connected to the second terminal of capacitor Cm. The drain of switch Q4 is connected to the positive terminal of cell BT(m+1). The source of switch Q4 is connected to the negative terminal of cell BT(m+1).

[0079] Through the distributed connection of the above K-1 balancing modules, active balancing can be achieved among K series-connected cells, which has the characteristics of small size, large balancing current, low energy loss and high efficiency.

[0080] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.

Claims

1. A small-volume, high-efficiency, high-current active balancing circuit for lithium batteries, characterized in that, Includes N-1 active balancing modules B1~B N-1 N represents the number of cells in the lithium battery pack, wherein the lithium battery pack consists of N cells Vb1~Vb N The modules are connected in series; for any active equalization module B i Its relationship with the cell Vb i and Vb i+1 Connected to implement Vb i With Vb i+1 Energy transfer between them, where i is a natural number and 1≤i≤N-1.

2. The lithium battery active balancing circuit according to claim 1, characterized in that: The active balancing module B i Includes four switching transistors Q i_1 ~Q i_4 Inductor L i and capacitor C i Q i_1 Drain and Vb i The positive terminals are connected, Q i_1 The source and Q i_2 The drain and L i One end is connected, L i The other end and C i Connect one end to Q i_2 The source and Q i_3 Drain, Vb i The negative electrode and Vb i+1 The positive terminals are connected, Q i_3 The source and Q i_4 The drain and C i The other end is connected, Q i_4 The source and Vb i+1 The negative terminal is connected, Q i_1 ~Q i_4 The gate is connected to the drive signal provided by the control unit.

3. The lithium battery active balancing circuit according to claim 2, characterized in that: The inductor L i and capacitor C i Form a resonant branch to buffer Vb i With Vb i+1 The energy to be transferred between them.

4. The lithium battery active balancing circuit according to claim 2, characterized in that: The switching transistor Q i_1 ~Q i_4 The duty cycle of the drive signal is about 50%.

5. The lithium battery active balancing circuit according to claim 2, characterized in that: The switching transistor Q i_1 and Q i_3 Using drive signal Φ1, switching transistor Q i_2 and Q i_4 The drive signal Φ2 is used, and the switching phases of the drive signals Φ1 and Φ2 are complementary.

6. The lithium battery active balancing circuit according to claim 3, characterized in that: The resonant frequency of the resonant branch is close to the switching frequency of the switching transistor, so as to realize the soft switching of the switching transistor.

7. The lithium battery active balancing circuit according to claim 2, characterized in that: The switching transistor Q i_1 ~Q i_4 It uses IGBT, BJT, MOSFET or third-generation semiconductor transistors.

8. The control method for the lithium battery active balancing circuit as described in any one of claims 2 to 7, characterized in that, include: Vb i Energy transferred to Vb i+1 First, Q is turned on simultaneously. i_1 and Q i_3 This allows energy to be transferred to the resonant branch for storage. When the current in the resonant branch drops to near zero, Q is simultaneously disconnected. i_1 and Q i_3 and conduct Q i_2 and Q i_4 This causes the energy stored in the resonant branch to be transferred to Vb. i+1 Complete the Vb i Energy transferred to Vb i+1 middle; Vb i+1 Energy transferred to Vb i First, Q is turned on simultaneously. i_2 and Q i_4 This allows energy to be transferred to the resonant branch for storage. When the current in the resonant branch drops to near zero, Q is simultaneously disconnected. i_2 and Q i_4 and conduct Q i_1 and Q i_3 This causes the energy stored in the resonant branch to be transferred to Vb. i Complete the Vb i+1 Energy transferred to Vb i middle.

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