Active equalization circuit for series battery pack based on zeta converter

Abstract

The application discloses a series battery pack active equalization circuit based on a Zeta converter, which comprises an n-way output Zeta converter, n cross connection capacitors and n battery units; the n-way output Zeta converter comprises an inductor L, a power switch S and a first-way output diode D1, a first-way output capacitor C1, a first-way cross connection capacitor C p1 , a first-way clamping diode D p1 ; a second-way output diode D2, a second-way output capacitor C2, a second-way cross connection capacitor C p2 , a second-way clamping diode D p2 ; a third-way output diode D3, a third-way output capacitor C3, a third-way cross connection capacitor C p3 , a third-way clamping diode D p3 ; and a fourth-way output diode D n , a fourth-way output capacitor C n , a fourth-way cross connection capacitor C pn , a fourth-way clamping diode D pn . The application realizes automatic voltage equalization among the battery units through the cross connection capacitors, does not need complex sampling and control algorithms, avoids the end voltage imbalance problem caused by the cross regulation ratio of a transformer in a multi-winding output, effectively reduces voltage deviation and improves battery equalization precision.

Description

Technical Field

[0001] This invention relates to battery pack balancing circuits, and more specifically to an active balancing circuit for series battery packs based on a Zeta converter. Background Technology

[0002] Lithium-ion batteries dominate the electric vehicle (EV) battery market due to their superior energy density, long cycle life, lack of memory effect, and high efficiency and environmental friendliness. However, the voltage and capacity of individual cells limit their ability to directly meet the high-performance requirements of EVs. Therefore, battery packs composed of multiple cells connected in series and parallel have become a necessary choice. But this combination method also brings new challenges: differences in manufacturing processes, usage environments, and charge / discharge modes lead to variations in the performance of individual cells within the battery pack, such as mismatches in capacity, voltage, and internal resistance. This not only affects the durability and reliability of the battery pack but also poses a threat to safety.

[0003] To address this issue, battery balancing technology has emerged, aiming to ensure the performance balance of individual cells within a battery pack. Currently, balancing technologies are mainly divided into two categories: passive balancing and active balancing. Passive balancing dissipates excess energy through resistors, but this method not only wastes energy but may also damage battery performance due to high-temperature environments. In contrast, active balancing technology achieves this through energy transfer, such as the balancing control method based on a buck-boost converter proposed in patent CN113489083A. This method introduces energy storage inductors, diodes, and balancing control switches into the battery pack. By controlling the opening and closing of these switches, energy transfer is achieved from high-energy cells to low-energy cells, effectively promoting battery balancing. Furthermore, by combining individual cells into modules of different levels and achieving balancing between these levels through logic control, not only is the energy distribution between adjacent cells optimized, but balancing of non-adjacent cells is also indirectly achieved, significantly improving the balancing efficiency of the battery pack.

[0004] However, the complexity of this method lies in its equalization circuit design, which involves the fine logic control of multiple control switches, which undoubtedly increases the difficulty of technical implementation. Summary of the Invention

[0005] To address the shortcomings of existing battery pack balancing technologies, this invention proposes an active balancing circuit for series battery packs based on a Zeta converter. This balancing circuit consists of a multi-output converter and multiple bridging capacitors. Based on the Zeta circuit, this active balancing circuit employs a multi-output Zeta circuit topology, achieving voltage equalization (identical voltage) between the battery cells within the battery pack by adding a bridging capacitor between each output. Compared to traditional multi-series Zeta circuit balancing structures, this invention achieves automatic voltage equalization between battery cells through bridging capacitors, eliminating the need for complex sampling and control algorithms. Furthermore, it avoids the voltage imbalance problem caused by cross-regulation in multi-series Zeta circuits, effectively reducing voltage deviation and improving battery balancing accuracy.

[0006] The technical solution adopted in this invention is as follows:

[0007] An active balancing circuit for series battery packs based on a Zeta converter, the balancing circuit including:

[0008] An n-output zeta converter, n crossover capacitors, and n battery cells;

[0009] The n-channel output zeta converter includes an inductor L, a power switch S, and:

[0010] First output diode D1, first output capacitor C1, first bridging capacitor C p1 First clamping diode D p1 ;

[0011] Second output diode D2, second output capacitor C2, second bridging capacitor C p2 Second clamping diode D p2 ;

[0012] Third output diode D3, third output capacitor C3, third bridging capacitor C p3 Third clamping diode D p3 ;

[0013] ...and so on,

[0014] nth output diode D n The nth output capacitor C n The nth bridging capacitor C pn The nth clamping diode D pn ;

[0015] The drain of switch S is connected to the cathode of output diode D1 and one end of output capacitor C1, respectively; the source of switch S is connected to one end of inductor L and the first-path bridging capacitor C, respectively. p1 One end,

[0016] First-stage bridging capacitor C p1 The other end is connected to the first clamping diode D. p1 The cathode of output diode D1 is connected to one end of output capacitor C1 and the positive terminal of lithium battery B1, respectively. The negative terminal of lithium battery B1 is connected to the other end of output capacitor C1 and the first clamping diode D. p1 anode;

[0017] Second bridging capacitor C p2 The other end is connected to the second clamping diode D. p2 The cathode of output diode D2 is connected to one end of output capacitor C2 and the positive terminal of lithium battery B2, respectively. The negative terminal of lithium battery B2 is connected to the other end of output capacitor C2 and the second clamping diode D. p2 anode;

[0018] Third-channel bridging capacitor C p3 The other end is connected to the third clamping diode D. p3 The cathode of output diode D3 is connected to one end of output capacitor C3 and the positive terminal of lithium battery B3, respectively. The negative terminal of lithium battery B3 is connected to the other end of output capacitor C3 and the third clamping diode D. p3 anode;

[0019] ...and so on,

[0020] The nth bridging capacitor C pn The other end is connected to the nth clamping diode D. pn Cathode, output diode D n Anode, output diode D n The cathodes are connected to the output capacitor C. n One end, lithium battery B n Positive electrode, lithium battery B n The negative terminals are connected to the output capacitor C. n At the other end, the nth clamping diode D pn anode;

[0021] First-stage bridging capacitor C p1 One end is connected to the second bridging capacitor C. p2 One end, third-way bridging capacitor C p3 One end, ... and so on, the nth bridging capacitor C pn One end;

[0022] The other end of output capacitor C1 is connected to one end of output capacitor C2;

[0023] The other end of output capacitor C2 is connected to one end of output capacitor C3;

[0024] The other end of output capacitor C3 is connected to one end of output capacitor C4;

[0025] ...and so on,

[0026] Output capacitor C n-1 The other end is connected to the output capacitor C. n One end;

[0027] The drain of switch S is connected to the positive terminal of lithium battery B1, and the other end of inductor L is connected to lithium battery B1. n negative electrode.

[0028] The gate of the power switch S is connected to a controller, and its duty cycle can vary between 0 and 1.

[0029] An active balancing circuit for four single-cell series battery packs based on a Zeta converter, the balancing circuit including:

[0030] A 4-output zeta converter, 4 bridging capacitors, and 4 battery cells;

[0031] The n-channel output zeta converter includes an inductor L, a power switch S, and:

[0032] First output diode D1, first output capacitor C1, first bridging capacitor C p1 First clamping diode D p1 ;

[0033] Second output diode D2, second output capacitor C2, second bridging capacitor C p2 Second clamping diode D p2 ;

[0034] Third output diode D3, third output capacitor C3, third bridging capacitor C p3 Third clamping diode D p3 ;

[0035] Fourth output diode D4, fourth output capacitor C4, fourth bridging capacitor C p4 Fourth clamping diode D p4 ;

[0036] The drain of switch S is connected to the cathode of output diode D1 and one end of output capacitor C1, respectively; the source of switch S is connected to one end of inductor L and the first-path bridging capacitor C, respectively. p1 One end,

[0037] First-stage bridging capacitor C p1 The other end is connected to the first clamping diode D. p1The cathode of output diode D1 is connected to one end of output capacitor C1 and the positive terminal of lithium battery B1, respectively. The negative terminal of lithium battery B1 is connected to the other end of output capacitor C1 and the first clamping diode D. p1 anode;

[0038] Second bridging capacitor C p2 The other end is connected to the second clamping diode D. p2 The cathode of output diode D2 is connected to one end of output capacitor C2 and the positive terminal of lithium battery B2, respectively. The negative terminal of lithium battery B2 is connected to the other end of output capacitor C2 and the second clamping diode D. p2 anode;

[0039] Third-channel bridging capacitor C p3 The other end is connected to the third clamping diode D. p3 The cathode of output diode D3 is connected to one end of output capacitor C3 and the positive terminal of lithium battery B3, respectively. The negative terminal of lithium battery B3 is connected to the other end of output capacitor C3 and the third clamping diode D. p3 anode;

[0040] Fourth bridging capacitor C p4 The other end is connected to the fourth clamping diode D. p4 The cathode of output diode D4 is connected to one end of output capacitor C4 and the positive terminal of lithium battery B4, respectively. The negative terminal of lithium battery B4 is connected to the other end of output capacitor C4 and the fourth clamping diode D. p4 anode;

[0041] First-stage bridging capacitor C p1 One end is connected to the second bridging capacitor C. p2 One end, third-way bridging capacitor C p3 One end, fourth-channel bridging capacitor C p4 One end;

[0042] The other end of output capacitor C1 is connected to one end of output capacitor C2;

[0043] The other end of output capacitor C2 is connected to one end of output capacitor C3;

[0044] The other end of output capacitor C3 is connected to one end of output capacitor C4;

[0045] The drain of switch S is connected to the positive terminal of lithium battery B1, and the other end of inductor L is connected to the negative terminal of lithium battery B4.

[0046] Taking a battery pack consisting of four single cells B1, B2, B3, and B4 connected in series as an example, when the power switch S is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned on, and the clamping diode D... p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 Turn off. Power is supplied to the energy storage inductor L and the bridging capacitor C. p2 1. Cross capacitor C p3 and the bridging capacitor C p4 Charging. Connecting capacitor C. p1 Charge output capacitor C1 and lithium battery B1. Output capacitor C2 charges lithium battery B2, output capacitor C3 charges lithium battery B3, and output capacitor C4 charges lithium battery B4.

[0047] Taking a battery pack consisting of four individual cells B1, B2, B3, and B4 connected in series as an example, when the power switch S is turned off, the clamping diode D... p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 When the circuit is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned off. The energy storage inductor L connects to the bridging capacitor C. p1 Charging; bridging capacitor C p2 Charge output capacitor C2 and lithium battery B2; bridge capacitor C p3 Charge output capacitor C3 and lithium battery B3; bridge capacitor C p4 Charge the output capacitor C4 and the lithium battery B4.

[0048] The principle of battery balancing is to keep the individual lithium battery cells in the series battery pack in a balanced state. Currently, the balance of the entire lithium battery pack is mainly judged by whether the terminal voltage of the lithium battery cells is balanced.

[0049] When switch S is on, there exists a loop C1→B1, C p1 →D1→C1→D2→C p2 According to the KVL theorem, u B1 =u C1 =u Cp2 -u Cp1 There exists a loop C. p2 →D2→C2→D3→C p3 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp3-uCp2; A cycle exists; A cycle exists Cp3→D3→C3→D4→Cp4, C3→B3. By the KVL theorem, u B3 =u C3 =u Cp4 -u Cp3 There exists a loop C4→B4, and by the KVL theorem, u B4 =u C4 .

[0050] When switch S is off, a loop C1→B1 exists. According to the KVL theorem, the voltage of lithium battery B1 is equal to the voltage of output capacitor C1, i.e., u B1 =u C1 There exists a loop C. p1 →D p1 →C2→D p2 →C p2 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp2 -u Cp1 There exists a loop C. p2 →D p2 →C3→D p3 →C p3 C3→B3, according to the KVL theorem, u B3 =u C3 =u Cp3 -u Cp2 There exists a loop C. p3 →D p3 →C4→D p4 →C p4 From C4 to B4, by the KVL theorem, we know that uB4 = uC4 = uC p 4-uC p 3.

[0051] Throughout the entire switching cycle, based on the capacitor ampere-second balance principle and the above analysis, the voltage of lithium battery B1 is equal to the voltage of lithium battery B2, equal to the voltage of lithium battery B3, and equal to the voltage of lithium battery B4, i.e., u B1 =u B2 =u B3 =u B4 The voltage of each lithium battery cell is equal, thus achieving balance in the lithium battery pack.

[0052] This invention discloses an active balancing circuit for a series battery pack based on a Zeta converter, with the following technical advantages:

[0053] 1) The active equalization circuit of this invention can effectively reduce the problem of unbalanced terminal voltage caused by cross-regulation in multi-output zeta converters, reduce voltage deviation, and improve battery equalization accuracy.

[0054] 2) The active equalization circuit of this invention is simple to control. It achieves automatic voltage equalization between battery cells by bridging capacitors, without the need for complex sampling and control algorithms. Attached Figure Description

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0056] Figure 1 This is the circuit schematic diagram of the present invention;

[0057] Figure 2 This is a circuit diagram illustrating the balanced operation of a battery pack consisting of four connected battery cells, as described in this invention.

[0058] Figure 3 This is a simulation diagram illustrating the balanced operation of a battery pack consisting of four connected battery cells, as described in this invention. Detailed Implementation

[0059] The invention will now be described in further detail with reference to the accompanying drawings. Figure 2 As shown, this is the active balancing circuit for a battery pack containing four battery cells according to the present invention. The circuit includes a four-output zeta converter, four bridging capacitors, and four battery cells, wherein:

[0060] The n-channel output zeta converter includes an inductor L, a power switch S, and:

[0061] First output diode D1, first output capacitor C1, first bridging capacitor C p1 First clamping diode D p1 ;

[0062] Second output diode D2, second output capacitor C2, second bridging capacitor C p2 Second clamping diode D p2 ;

[0063] Third output diode D3, third output capacitor C3, third bridging capacitor C p3 Third clamping diode D p3 ;

[0064] Fourth output diode D4, fourth output capacitor C4, fourth bridging capacitor C p4 Fourth clamping diode D p4 ;

[0065] The drain of switch S is connected to the cathode of output diode D1 and one end of output capacitor C1, respectively; the source of switch S is connected to one end of inductor L and the first-path bridging capacitor C, respectively. p1 One end,

[0066] First-stage bridging capacitor Cp1 The other end is connected to the first clamping diode D. p1 The cathode of output diode D1 is connected to one end of output capacitor C1 and the positive terminal of lithium battery B1, respectively. The negative terminal of lithium battery B1 is connected to the other end of output capacitor C1 and the first clamping diode D. p1 anode;

[0067] Second bridging capacitor C p2 The other end is connected to the second clamping diode D. p2 The cathode of output diode D2 is connected to one end of output capacitor C2 and the positive terminal of lithium battery B2, respectively. The negative terminal of lithium battery B2 is connected to the other end of output capacitor C2 and the second clamping diode D. p2 anode;

[0068] Third-channel bridging capacitor C p3 The other end is connected to the third clamping diode D. p3 The cathode of output diode D3 is connected to one end of output capacitor C3 and the positive terminal of lithium battery B3, respectively. The negative terminal of lithium battery B3 is connected to the other end of output capacitor C3 and the third clamping diode D. p3 anode;

[0069] Fourth bridging capacitor C p4 The other end is connected to the fourth clamping diode D. p4 The cathode of output diode D4 is connected to one end of output capacitor C4 and the positive terminal of lithium battery B4, respectively. The negative terminal of lithium battery B4 is connected to the other end of output capacitor C4 and the fourth clamping diode D. p4 anode;

[0070] First-stage bridging capacitor C p1 One end is connected to the second bridging capacitor C. p2 One end, third-way bridging capacitor C p3 One end, fourth-channel bridging capacitor C p4 One end;

[0071] The other end of output capacitor C1 is connected to one end of output capacitor C2;

[0072] The other end of output capacitor C2 is connected to one end of output capacitor C3;

[0073] The other end of output capacitor C3 is connected to one end of output capacitor C4;

[0074] The drain of switch S is connected to the positive terminal of lithium battery B1, and the other end of inductor L is connected to the negative terminal of lithium battery B4.

[0075] When power switch S is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned on, and the clamping diode D... p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 Turn off. Power is supplied to the energy storage inductor L and the bridging capacitor C. p2 1. Cross capacitor C p3 and the bridging capacitor C p4 Charging. Connecting capacitor C. p1 Charge output capacitor C1 and lithium battery B1. Output capacitor C2 charges lithium battery B2, output capacitor C3 charges lithium battery B3, and output capacitor C4 charges lithium battery B4.

[0076] When power switch S is turned off, clamping diode D p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 When the circuit is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned off. The energy storage inductor L connects to the bridging capacitor C. p1 Charging; bridging capacitor C p2 Charge output capacitor C2 and lithium battery B2; bridge capacitor C p3 Charge output capacitor C3 and lithium battery B3; bridge capacitor C p4 Charge the output capacitor C4 and the lithium battery B4.

[0077] The principle of battery balancing is to keep the individual lithium battery cells in the series battery pack in a balanced state. Currently, the balance of the entire lithium battery pack is mainly judged by whether the terminal voltage of the lithium battery cells is balanced.

[0078] When switch S is on, there exists a loop C1→B1, C p1 →D1→C1→D2→C p2 According to the KVL theorem, u B1 =u C1 =u Cp2 -u Cp1 There exists a loop C. p2 →D2→C2→D3→C p3 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp3 -uCp2; A cycle exists; A cycle exists Cp3→D3→C3→D4→Cp4, C3→B3. By the KVL theorem, u B3 =uC3 =u Cp4 -u Cp3 There exists a loop C4→B4, and by the KVL theorem, u B4 =u C4 .

[0079] When switch S is off, a loop C1→B1 exists. According to the KVL theorem, the voltage of lithium battery B1 is equal to the voltage of output capacitor C1, i.e., u B1 =u C1 There exists a loop C. p1 →D p1 →C2→D p2 →C p2 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp2 -u Cp1 There exists a loop C. p2 →D p2 →C3→D p3 →C p3 C3→B3, according to the KVL theorem, u B3 =u C3 =u Cp3 -u Cp2 There exists a loop C. p3 →D p3 →C4→D p4 →C p4 From C4 to B4, by the KVL theorem, we know that uB4 = uC4 = uC p 4-uC p 3.

[0080] Throughout the entire switching cycle, based on the capacitor ampere-second balance principle and the above analysis, the voltage of lithium battery B1 is equal to the voltage of lithium battery B2, equal to the voltage of lithium battery B3, and equal to the voltage of lithium battery B4, i.e., u B1 =u B2 =u B3 =u B4 The voltage of each lithium battery cell is equal, thus achieving balance in the lithium battery pack.

[0081] Figure 3 This is a simulation diagram illustrating the balanced operation of a battery pack consisting of four connected battery cells, as described in this invention. Figure 3 It can be seen that when charging multiple battery groups, due to the different initial state of charge (SOC) of each battery, the charging rate of each battery is different under the action of the balancing topology. As charging progresses, the SOC of each battery gradually converges and quickly reaches a relatively stable and close SOC value, indicating that the topology has a good balancing charging effect and fast speed.

[0082] Compared with the traditional multi-channel series equalization structure, this invention achieves automatic voltage equalization between battery cells by bridging capacitors, eliminating the need for complex sampling and control algorithms. It also avoids the problem of unbalanced terminal voltage caused by cross-regulation when the transformer has multiple windings, effectively reducing voltage deviation and improving battery equalization accuracy.

Claims

1. An active balancing circuit for a series battery pack based on a Zeta converter, characterized in that... The equalization circuit includes: An n-output zeta converter, n crossover capacitors, and n battery cells; The n-channel output zeta converter includes an inductor L, a power switch S, and: First output diode D1, first output capacitor C1, first bridging capacitor C p1 First clamping diode D p1 ; Second output diode D2, second output capacitor C2, second bridging capacitor C p2 Second clamping diode D p2 ; Third output diode D3, third output capacitor C3, third bridging capacitor C p3 Third clamping diode D p3 ; ...and so on, nth output diode D n The nth output capacitor C n The nth bridging capacitor C pn The nth clamping diode D pn ; The drain of switch S is connected to the cathode of output diode D1 and one end of output capacitor C1, respectively; the source of switch S is connected to one end of inductor L and the first-path bridging capacitor C, respectively. p1 One end, First-stage bridging capacitor C p1 The other end is connected to the first clamping diode D. p1 The cathode of output diode D1 is connected to one end of output capacitor C1 and the positive terminal of lithium battery B1, respectively. The negative terminal of lithium battery B1 is connected to the other end of output capacitor C1 and the first clamping diode D. p1 anode; Second bridging capacitor C p2 The other end is connected to the second clamping diode D. p2 The cathode of output diode D2 is connected to one end of output capacitor C2 and the positive terminal of lithium battery B2, respectively. The negative terminal of lithium battery B2 is connected to the other end of output capacitor C2 and the second clamping diode D. p2 anode; Third-channel bridging capacitor C p3 The other end is connected to the third clamping diode D. p3 The cathode of output diode D3 is connected to one end of output capacitor C3 and the positive terminal of lithium battery B3, respectively. The negative terminal of lithium battery B3 is connected to the other end of output capacitor C3 and the third clamping diode D. p3 anode; ...and so on, The nth bridging capacitor C pn The other end is connected to the nth clamping diode D. pn Cathode, output diode D n Anode, output diode D n The cathodes are connected to the output capacitor C. n One end, lithium battery B n Positive electrode, lithium battery B n The negative terminals are connected to the output capacitor C. n At the other end, the nth clamping diode D pn anode; First-stage bridging capacitor C p1 One end is connected to the second bridging capacitor C. p2 One end, third-way bridging capacitor C p3 One end, ... and so on, the nth bridging capacitor C pn One end; The other end of output capacitor C1 is connected to one end of output capacitor C2; The other end of output capacitor C2 is connected to one end of output capacitor C3; The other end of output capacitor C3 is connected to one end of output capacitor C4; ...and so on, Output capacitor C n-1 The other end is connected to the output capacitor C. n One end; The drain of switch S is connected to the positive terminal of lithium battery B1, and the other end of inductor L is connected to lithium battery B1. n negative electrode.

2. The active balancing circuit for a series battery pack based on a Zeta converter according to claim 1, characterized in that: The gate of the power switch S is connected to a controller, and its duty cycle can vary between 0 and 1.

3. An active balancing circuit for four single-cell series-connected battery packs based on a Zeta converter, characterized in that: The equalization circuit includes: A 4-output zeta converter, 4 bridging capacitors, and 4 battery cells; The 4-output zeta converter includes an inductor L, a power switch S, and: First output diode D1, first output capacitor C1, first bridging capacitor C p1 First clamping diode D p1 ; Second output diode D2, second output capacitor C2, second bridging capacitor C p2 Second clamping diode D p2 ; Third output diode D3, third output capacitor C3, third bridging capacitor C p3 Third clamping diode D p3 ; Fourth output diode D4, fourth output capacitor C4, fourth bridging capacitor C p4 Fourth clamping diode D p4 ; The drain of switch S is connected to the cathode of output diode D1 and one end of output capacitor C1, respectively; the source of switch S is connected to one end of inductor L and the first-path bridging capacitor C, respectively. p1 One end, First-stage bridging capacitor C p1 The other end is connected to the first clamping diode D. p1 The cathode of output diode D1 is connected to one end of output capacitor C1 and the positive terminal of lithium battery B1, respectively. The negative terminal of lithium battery B1 is connected to the other end of output capacitor C1 and the first clamping diode D. p1 anode; Second bridging capacitor C p2 The other end is connected to the second clamping diode D. p2 The cathode of output diode D2 is connected to one end of output capacitor C2 and the positive terminal of lithium battery B2, respectively. The negative terminal of lithium battery B2 is connected to the other end of output capacitor C2 and the second clamping diode D. p2 anode; Third-channel bridging capacitor C p3 The other end is connected to the third clamping diode D. p3 The cathode of output diode D3 is connected to one end of output capacitor C3 and the positive terminal of lithium battery B3, respectively. The negative terminal of lithium battery B3 is connected to the other end of output capacitor C3 and the third clamping diode D. p3 anode; Fourth bridging capacitor C p4 The other end is connected to the fourth clamping diode D. p4 The cathode of output diode D4 is connected to one end of output capacitor C4 and the positive terminal of lithium battery B4, respectively. The negative terminal of lithium battery B4 is connected to the other end of output capacitor C4 and the fourth clamping diode D. p4 anode; First-stage bridging capacitor C p1 One end is connected to the second bridging capacitor C. p2 One end, third-way bridging capacitor C p3 One end, fourth-channel bridging capacitor C p4 One end; The other end of output capacitor C1 is connected to one end of output capacitor C2; The other end of output capacitor C2 is connected to one end of output capacitor C3; The other end of output capacitor C3 is connected to one end of output capacitor C4; The drain of switch S is connected to the positive terminal of lithium battery B1, and the other end of inductor L is connected to the negative terminal of lithium battery B4.

4. The active balancing circuit for four single-cell series battery packs based on a Zeta converter according to claim 3, characterized in that: When power switch S is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned on, and the clamping diode D... p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 Turn off; power supply to energy storage inductor L and bridging capacitor C p2 1. Cross capacitor C p3 and the bridging capacitor C p4 Charging; bridging capacitor C p1 Charge output capacitor C1 and lithium battery B1; output capacitor C2 charges lithium battery B2, output capacitor C3 charges lithium battery B3, and output capacitor C4 charges lithium battery B4. When power switch S is turned off, clamping diode D p1 Clamping diode D p2 Clamping diode D p3 and clamping diode D p4 When the circuit is turned on, the first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode D4 are turned off; the energy storage inductor L connects to the bridging capacitor C. p1 Charging; bridging capacitor C p2 Charge output capacitor C2 and lithium battery B2; bridge capacitor C p3 Charge output capacitor C3 and lithium battery B3; bridge capacitor C p4 Charge the output capacitor C4 and the lithium battery B4.

5. The active balancing circuit for four single-cell series battery packs based on a Zeta converter according to claim 3, characterized in that: When switch S is on, there exists a loop C1→B1, C p1 →D1→C1→D2→C p2 According to the KVL theorem, u B1 =u C1 =u Cp2 -u Cp1 There exists a loop C. p2 →D2→C2→D3→C p3 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp3 -uCp2; A cycle exists; A cycle exists Cp3→D3→C3→D4→Cp4, C3→B3. By the KVL theorem, u B3 =u C3 =u Cp4 -u Cp3 There exists a loop C4→B4, and by the KVL theorem, u B4 =u C4 ; When switch S is off, a loop C1→B1 exists. According to the KVL theorem, the voltage of lithium battery B1 is equal to the voltage of output capacitor C1, i.e., u B1 = u C1 There exists a loop C. p1 →D p1 →C2→D p2 →C p2 C2→B2, according to the KVL theorem, u B2 =u C2 =u Cp2 -u Cp1 There exists a loop C. p2 →D p2 →C3→D p3 →C p3 C3→B3, according to the KVL theorem, u B3 =u C3 =u Cp3 -u Cp2 There exists a loop C. p3 →D p3 →C4→D p4 →C p4 C4→B4, according to the KVL theorem, u B4 =u C4 =u Cp4 -u Cp3 .

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