Sepic multi-port series lithium ion battery pack equalization circuit

Abstract

A Sepic multi-port series lithium ion battery pack equalization circuit comprises an n-path output Sepic converter, n bridging capacitors and n lithium battery units, the n-path output Sepic converter comprises a direct current input source uin, inductors L1 and L2, a power switch S1, a capacitor C1, a first-path bridging capacitor Cp1, first-path output diodes D11 and D12, a first-path output capacitor C2 and a lithium battery B1, the first path of bridge connection capacitor Cp (n-1), the second path of bridge connection capacitor Cp2, the second path of output diodes D21 and D22, the second path of output capacitor C3, the lithium battery B2,..., and the like, the (n-1) th path of bridge connection capacitor Cp (n-1), the (n-1) th path of output diodes D (n-1) 1 and D (n-1) 2, the (n-1) th path of output capacitor Cn, and the lithium battery Bn-1; and the nth path is bridged with a capacitor Cpn, the second path of output diodes Dn1 and Dn2, a second path of output capacitor Cn + 1 and a lithium battery Bn. Automatic charging voltage sharing between the battery units is achieved through the bridging capacitor, no complex sampling and control algorithm is needed, expansibility is high, power switches and magnetic elements do not need to be added along with increasing of the number of the series battery packs, voltage deviation is effectively reduced, and battery equalization precision is improved.

Description

Technical Field

[0001] The invention relates to a battery pack equalization circuit, and in particular to a Sepic multi-port series-connected lithium-ion battery pack equalization circuit. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, low self-discharge rate, and long cycle life, and are widely used in transportation, aerospace and other fields. However, there are differences in the production of batteries. With use, the inconsistency of battery packs gradually increases. Inconsistency can lead to overcharging and discharging of batteries, damage battery life and safety hazards, reduce battery energy utilization, accelerate battery aging and performance degradation, and even create thermal runaway risks. Therefore, balanced management of battery packs is a necessary technology to extend battery life and improve battery pack performance.

[0003] Therefore, in order to maintain the balance of single cells in lithium-ion battery packs, researchers have proposed many balancing circuits, devices and methods. The current battery balancing technology is mainly divided into passive balancing and active balancing. Passive balancing is to consume excess energy in the form of heat through resistance, but this method will cause energy loss of the battery pack, and the high temperature environment caused by improper heat dissipation will damage the performance of the battery pack. Active balancing technology is to transfer energy from higher battery cells to lower battery cells. For example, the patent document with application publication number CN118117693A discloses a modular reconfigurable battery balancing circuit. This method connects the positive and negative electrodes of two adjacent series-connected single cells in each battery pack to the same CUK balancing circuit, and then connects 3 power switches and 1 energy storage inductor for balancing. The energy of the single cell with higher energy storage is stored in the energy storage inductor of the balancing circuit and the external energy storage inductor through the balancing circuit, and then controls the external power switch to transfer the energy in the inductor to the single cell with lower energy storage, forming a balancing control of the series lithium-ion battery pack. However, for every 4 batteries added to the balancing circuit, an additional 3 CUK balancing circuits, 3 power switches, and 1 external energy storage inductor are required. The structure is complex and many components are used. Moreover, as the number of power switches increases, the control method becomes more complex. Summary of the invention

[0004] In order to solve the shortcomings of the existing lithium battery pack balancing technology, the present invention proposes a Sepic multi-port series lithium-ion battery pack balancing circuit, which is composed of a multi-output SEPIC converter and multiple jumper capacitors and diodes. The balancing circuit is based on the Sepic balancing circuit, and the rectifier output side is replaced with an expandable structure composed of capacitors and diodes. The battery packs are connected by jumper capacitors to achieve terminal voltage balancing (same) of the battery cells inside the battery pack. Compared with the traditional expandable balancing structure, the balancing circuit of the present invention realizes automatic charging voltage balancing between battery cells through jumper capacitors, without the need for complex sampling and control algorithms; and avoids the efficiency reduction caused by the introduction of non-energy storage elements, effectively reduces voltage deviation, and improves battery balancing accuracy.

[0005] The technical solution adopted by the present invention is:

[0006] A Sepic multi-port series lithium-ion battery pack equalization circuit, the equalization circuit comprising:

[0007] An n-output Sepic converter, n jumper capacitors and n lithium battery cells, where:

[0008] The n-way output Sepic converter includes a DC input source u in , inductors L1, L2, power switch S1, capacitor C1,

[0009] The first bridge capacitor C p1 , the first output diode D 11 , D 12 , the first output capacitor C2, lithium battery B1,

[0010] The second bridge capacitor C p2 , the second output diode D 21 , D 22 , the second output capacitor C3, lithium battery B2,

[0011] ... and so on, the n-1th bridge capacitor C p(n-1) , the n-1th output diode D (n-1)1 , D (n-1)2 , the n-1th output capacitor C n , lithium battery B n-1 ;

[0012] The nth cross-connect capacitor C pn , the second output diode D n1 , D n2 , the second output capacitor C n+1 , lithium battery B n ;

[0013] The connection form of n-way output Sepic converter is as follows:

[0014] One end of inductor L1 is connected to the DC input source u in The positive electrode and the other end of the inductor L1 are connected to the drain of the power switch S1 and one end of the capacitor C1. The other end of the capacitor C1 is connected to one end of the inductor L2 and the first bridge capacitor C p1 One end, the first cross-connect capacitor C p1 The other end is connected to the first output diode D 12 Cathode, first output diode D 11 Anode, first output diode D 11 The cathode is connected to one end of the first output capacitor C2 and the positive electrode of the lithium battery B1, and the negative electrode of the lithium battery B1 is connected to the other end of the first output capacitor C2 and the first output diode D 12 Anode, the other end of inductor L2, source of power switch S1, DC input source u in negative electrode;

[0015] The second bridge capacitor C p2 The other end is connected to the second output diode D 22 Cathode, second output diode D 21 Anode, second output diode D 21 The cathode is connected to one end of the second output capacitor C3, and the other end of the second output capacitor C3 is connected to the second output diode D 22 Anode, negative electrode of lithium battery B2;

[0016] The third bridge capacitor C p3 The other end is connected to the third output diode D 32 Cathode, third output diode D 31 Anode, the third output diode D 31 The cathode is connected to one end of the third output capacitor C4, and the other end of the third output capacitor C4 is connected to the third output diode D 32 Anode, negative electrode of lithium battery B3;

[0017] ... and so on.

[0018] The nth cross-connect capacitor C pn The other end is connected to the nth output diode D n2 Cathode, nth output diode D n1 Anode, nth output diode D n1 The cathode is connected to the nth output capacitor C n+1 One end, the nth output capacitor C n+1 The other end is connected to the nth output diode D n2 Anode, lithium battery B n negative electrode;

[0019] Among the n jumper capacitors:

[0020] The second bridge capacitor C p2 One end, the third way cross-connect capacitor C p3 One end, ... and so on, the nth path is connected across the capacitor C pn One end is connected to the first cross-capacitor C p1 one end;

[0021] The other end of the first output capacitor C2 is connected to one end of the second output capacitor C3;

[0022] The other end of the second output capacitor C3 is connected to one end of the third output capacitor C4;

[0023] The other end of the third output capacitor C4 is connected to one end of the fourth output capacitor C5;

[0024] ... and so on.

[0025] Output capacitor C of the n-1th channel n The other end is connected to the nth output capacitor C n+1 one end;

[0026] Among n lithium battery cells:

[0027] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2;

[0028] The negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3;

[0029] The negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4;

[0030] ... and so on.

[0031] Lithium battery B n-1 Negative connection to lithium battery B n positive electrode.

[0032] DC input source u in The power switch S1 is outputting when it is turned on or off. The battery acts as a load and is charged evenly through the circuit energy storage element.

[0033] The principle of battery balancing is to keep each battery cell in a series battery pack in a balanced state. At present, the balance of the entire battery pack is mainly judged by whether the terminal voltage of the battery cell is balanced (same). In a switching cycle, according to the inductor volt-second balance principle, the average voltage of the inductor L1 is 0. According to L2→C p1 → Based on the KVL principle of C2 circuit, the cross-connected capacitor C can be obtained p1 Voltage voltage u cp1 Equal to the voltage u of lithium battery B1 B1 Similarly, the cross-connect capacitor Cp2 The voltage u cp2 Equal to the voltage u of lithium battery B2 B2 , ... and so on, the jumper capacitor C pn The voltage u cpn Equal to lithium battery B n Voltage u Bn .

[0034] When the capacitor is connected across C p1 , C p2 ,......,C pn When the voltage of each lithium battery cell is large enough, the voltage of each lithium battery cell is equal. If there is a relatively low voltage lithium battery cell, then when the power switch S1 is turned on, the cross-connected capacitor C p1 , C p2 ,......,C pn Energy is released to the inductor L1 and stored. When the power switch S1 is turned off, the energy is transferred to the lithium battery cells with lower voltage. Therefore, part of the energy of the series lithium battery pack can be transferred to the lithium battery cells with lower energy, thus achieving balance of the lithium battery pack.

[0035] A battery pack balancing circuit containing four lithium batteries connected in series, the balancing circuit comprising:

[0036] A 4-way output Sepic converter, 4 jumper capacitors and 4 lithium battery cells, where:

[0037] The n-way output Sepic converter includes a DC input source u in , inductors L1, L2, power switch S1, capacitor C1,

[0038] The first bridge capacitor C p1 , the first output diode D 11 , D 12 , the first output capacitor C2, lithium battery B1,

[0039] The second bridge capacitor C p2 , the second output diode D 21 , D 22 , the second output capacitor C3, lithium battery B2,

[0040] The third bridge capacitor C p3 , the third output diode D 31 , D 32 , the second output capacitor C4, lithium battery B3,

[0041] The fourth bridge capacitor C p4 , the fourth output diode D 41 , D 42, the second output capacitor C5, lithium battery B4,

[0042] The connection form of 4-way output Sepic converter is as follows:

[0043] One end of inductor L1 is connected to the DC input source u in The positive electrode and the other end of the inductor L1 are connected to the drain of the power switch S1 and one end of the capacitor C1. The other end of the capacitor C1 is connected to one end of the inductor L2 and the first bridge capacitor C p1 One end, the first cross-connect capacitor C p1 The other end is connected to the first output diode D 12 Cathode, first output diode D 11 Anode, first output diode D 11 The cathode is connected to one end of the first output capacitor C2 and the positive electrode of the lithium battery B1, and the negative electrode of the lithium battery B1 is connected to the other end of the first output capacitor C2 and the first output diode D 12 Anode, the other end of inductor L2, source of power switch S1, DC input source u in negative electrode;

[0044] The second bridge capacitor C p2 The other end is connected to the second output diode D 22 Cathode, second output diode D 21 Anode, second output diode D 21 The cathode is connected to one end of the second output capacitor C3, and the other end of the second output capacitor C3 is connected to the second output diode D 22 Anode, negative electrode of lithium battery B2;

[0045] The third bridge capacitor C p3 The other end is connected to the third output diode D 32 Cathode, third output diode D 31 Anode, the third output diode D 31 The cathode is connected to one end of the third output capacitor C4, and the other end of the third output capacitor C4 is connected to the third output diode D 32 Anode, negative electrode of lithium battery B3;

[0046] The fourth bridge capacitor C p4 The other end is connected to the fourth output diode D 42 Cathode, fourth output diode D 41 Anode, fourth output diode D 41 The cathode is connected to one end of the fourth output capacitor C5, and the other end of the fourth output capacitor C5 is connected to the fourth output diode D 42 Anode, negative electrode of lithium battery B4;

[0047] Among the 4 jumper capacitors:

[0048] The second bridge capacitor C p2 One end, the third way cross-connect capacitor C p3 One end, the fourth cross-connect capacitor C p4 One end is connected to the first cross-capacitor C p1 one end;

[0049] The other end of the first output capacitor C2 is connected to one end of the second output capacitor C3;

[0050] The other end of the second output capacitor C3 is connected to one end of the third output capacitor C4;

[0051] The other end of the third output capacitor C4 is connected to one end of the fourth output capacitor C5;

[0052] In 4 lithium battery cells:

[0053] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2;

[0054] The negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3;

[0055] The negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4.

[0056] Take a battery pack consisting of four cells B1, B2, B3, and B4 connected in series as an example. When the power switch S1 is turned on, the output diode D 11 , D 21 , D 31 , D 41 Turn off, output diode D 12 , D 22 , D 32 , D 42 On, DC input source u in Charge the inductor L1, capacitor C1, and jumper capacitor C p1 , C p2 , C p3 , C p4 Discharging, inductor L2 is charged, and output capacitors C2, C3, C4, and C5 provide energy to lithium batteries B1, B2, B3, and B4;

[0057] When the power switch S1 is turned off, the output diode D 11 , D 21 , D 31 , D 41 Conducting, output diode D 12 , D 22 , D 32 , D 42 Shutdown, DC input source u in To inductor L1, capacitor C1, jumper capacitor Cp1 , C p2 , C p3 , C p4 It is charged and combines with inductor L2 to provide energy to output capacitors C2, C3, C4, C5, and lithium batteries B1, B2, B3, and B4.

[0058] The present invention provides a Sepic multi-port series-connected lithium-ion battery pack equalization circuit, and the technical effects are as follows:

[0059] 1) The balancing circuit of the present invention can effectively solve the problem that as the number of battery packs increases in the non-isolated balancing circuit, the expansion structure becomes complex and the cost increases dramatically;

[0060] 2) The balancing circuit of the present invention is simple to control and realizes automatic voltage balancing between battery cells through cross-connected capacitors without the need for complex sampling and control algorithms. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0062] Figure 1 It is the circuit principle diagram of the present invention;

[0063] Figure 2 The circuit schematic diagram of the present invention for realizing the balancing of a battery pack with four battery cells connected in series;

[0064] Figure 3 This is a simulation diagram of the present invention realizing balancing of a battery pack with four battery cells connected in series. DETAILED DESCRIPTION

[0065] like Figure 2 As shown, a battery pack balancing circuit containing 4 lithium batteries connected in series, the balancing circuit comprises:

[0066] A 4-way output Sepic converter, 4 jumper capacitors and 4 lithium battery cells, where:

[0067] The n-way output Sepic converter includes a DC input source u in , inductors L1, L2, power switch S1, capacitor C1,

[0068] The first bridge capacitor C p1 , the first output diode D 11 , D 12 , the first output capacitor C2, lithium battery B1,

[0069] The second bridge capacitor C p2 , the second output diode D 21 , D 22 , the second output capacitor C3, lithium battery B2,

[0070] The third bridge capacitor C p3 , the third output diode D 31 , D 32 , the second output capacitor C4, lithium battery B3,

[0071] The fourth bridge capacitor C p4 , the fourth output diode D 41 , D 42 , the second output capacitor C5, lithium battery B4,

[0072] The connection form of 4-way output Sepic converter is as follows:

[0073] One end of inductor L1 is connected to the DC input source u in The positive electrode and the other end of the inductor L1 are connected to the drain of the power switch S1 and one end of the capacitor C1. The other end of the capacitor C1 is connected to one end of the inductor L2 and the first bridge capacitor C p1 One end, the first cross-connect capacitor C p1 The other end is connected to the first output diode D 12 Cathode, first output diode D 11 Anode, first output diode D 11 The cathode is connected to one end of the first output capacitor C2 and the positive electrode of the lithium battery B1, and the negative electrode of the lithium battery B1 is connected to the other end of the first output capacitor C2 and the first output diode D 12 Anode, the other end of inductor L2, source of power switch S1, DC input source u in negative electrode;

[0074] The second bridge capacitor C p2 The other end is connected to the second output diode D 22 Cathode, second output diode D 21 Anode, second output diode D 21 The cathode is connected to one end of the second output capacitor C3, and the other end of the second output capacitor C3 is connected to the second output diode D 22 Anode, negative electrode of lithium battery B2;

[0075] The third bridge capacitor C p3 The other end is connected to the third output diode D 32 Cathode, third output diode D 31 Anode, the third output diode D 31 The cathode is connected to one end of the third output capacitor C4, and the other end of the third output capacitor C4 is connected to the third output diode D 32 Anode, negative electrode of lithium battery B3;

[0076] The fourth bridge capacitor C p4The other end is connected to the fourth output diode D 42 Cathode, fourth output diode D 41 Anode, fourth output diode D 41 The cathode is connected to one end of the fourth output capacitor C5, and the other end of the fourth output capacitor C5 is connected to the fourth output diode D 42 Anode, negative electrode of lithium battery B4;

[0077] Among the 4 jumper capacitors:

[0078] The second bridge capacitor C p2 One end, the third way cross-connect capacitor C p3 One end, the fourth path crosses the capacitor C p4 One end is connected to the first cross-capacitor C p1 one end;

[0079] The other end of the first output capacitor C2 is connected to one end of the second output capacitor C3;

[0080] The other end of the second output capacitor C3 is connected to one end of the third output capacitor C4;

[0081] The other end of the third output capacitor C4 is connected to one end of the fourth output capacitor C5;

[0082] In 4 lithium battery cells:

[0083] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2;

[0084] The negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3;

[0085] The negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4.

[0086] When the power switch S1 is turned on, the output diode D 11 , D 21 , D 31 , D 41 Turn off, output diode D 12 , D 22 , D 32 , D 42 On, DC input source u in Charge the inductor L1, capacitor C1, and jumper capacitor C p1 , C p2 , C p3 , C p4 Discharging, inductor L2 is charged, and output capacitors C2, C3, C4, and C5 provide energy to lithium batteries B1, B2, B3, and B4.

[0087] When the power switch S1 is turned off, the output diode D 11 , D 21, D 31 , D 41 Conducting, output diode D 12 , D 22 , D 32 , D 42 Shutdown, DC input source u in To inductor L1, capacitor C1, jumper capacitor C p1 , C p2 , C p3 , C p4 It is charged and combines with inductor L2 to provide energy to output capacitors C2, C3, C4, C5, and lithium batteries B1, B2, B3, and B4.

[0088] The principle of lithium battery balancing is to keep each lithium battery unit in a series battery pack in a balanced state. At present, the balance of the entire lithium battery pack is mainly judged by whether the terminal voltage of the lithium battery unit is balanced (same). In a switching cycle, according to the inductor volt-second balance principle, the average voltage of the inductor L1 is 0. According to L2→C p1 → The KVL principle of C2 circuit can be used to obtain the cross-over capacitor C p1 Voltage voltage u cp1 Equal to the voltage u of lithium battery B1 B1 Similarly, the cross-connect capacitor C p2 The voltage u cp2 Equal to the voltage u of lithium battery B2 B2 , ... and so on, the jumper capacitor C pn The voltage u cpn Equal to lithium battery B n Voltage u Bn When the capacitor is connected across C p1 , C p2 ,......,C pn When the voltage of each lithium battery cell is large enough, the voltage of each lithium battery cell is equal. If there is a relatively low voltage lithium battery cell, then when the power switch S1 is turned on, the cross-connected capacitor C p1 , C p2 ,......,C pn Energy is released to the inductor L1 and stored. When the power switch S1 is turned off, the energy is transferred to the lithium battery cells with lower voltage. Therefore, part of the energy of the series lithium battery pack can be transferred to the lithium battery cells with lower energy, thus achieving balance of the lithium battery pack.

[0089] Figure 3 This is a simulation diagram of the present invention to achieve balancing of a battery pack with four battery cells in series. Figure 3It can be seen that when charging multiple groups of batteries with different initial SOC (State of Charge), the battery SOC is constantly balanced and charged to the same SOC, and quickly reaches a relatively stable and close SOC value, indicating that the topology has a good balanced charging effect and a fast speed.

[0090] Compared with the traditional non-isolated balancing structure, the present invention realizes automatic charging and voltage balancing between battery cells through jumper capacitors, does not require complex sampling and control algorithms, and has strong scalability. As the number of series battery packs increases, there is no need to increase power switches and magnetic components, which effectively reduces voltage deviation and improves battery balancing accuracy.

Claims

1. A Sepic multi-port series lithium-ion battery pack equalization circuit, characterized in that: The equalization circuit includes: An n-output Sepic converter, n jumper capacitors and n lithium battery cells, where: The n-way output Sepic converter includes a DC input source u in , inductors L1, L2, power switch S1, capacitor C1, The first bridge capacitor C p1 , the first output diode D 11 , D 12 , the first output capacitor C2, lithium battery B1, the second jumper capacitor C p2 , the second output diode D 21 , D 22 , the second output capacitor C3, lithium battery B2, ... and so on, The n-1th cross-connect capacitor C p(n-1) , the n-1th output diode D (n-1)1 , D (n-1)2 , the n-1th output capacitor C n , lithium battery B n-1 ; The nth cross-connect capacitor C pn , the second output diode D n1 , D n2 , the second output capacitor C n+1 , lithium battery B n ; The connection form of n-way output Sepic converter is as follows: One end of inductor L1 is connected to the DC input source u in The positive electrode and the other end of the inductor L1 are connected to the drain of the power switch S1 and one end of the capacitor C1. The other end of the capacitor C1 is connected to one end of the inductor L2 and the first bridge capacitor C p1 One end, the first cross-connect capacitor C p1 The other end is connected to the first output diode D 12 Cathode, first output diode D 11 Anode, first output diode D 11 The cathode is connected to one end of the first output capacitor C2 and the positive electrode of the lithium battery B1, and the negative electrode of the lithium battery B1 is connected to the other end of the first output capacitor C2 and the first output diode D 12 Anode, the other end of inductor L2, source of power switch S1, DC input source u in negative electrode; The second bridge capacitor C p2 The other end is connected to the second output diode D 22 Cathode, second output diode D 21 Anode, second output diode D 21 The cathode is connected to one end of the second output capacitor C3, and the other end of the second output capacitor C3 is connected to the second output diode D 22 Anode, negative electrode of lithium battery B2; The third bridge capacitor C p3 The other end is connected to the third output diode D 32 Cathode, third output diode D 31 Anode, the third output diode D 31 The cathode is connected to one end of the third output capacitor C4, and the other end of the third output capacitor C4 is connected to the third output diode D 32 Anode, negative electrode of lithium battery B3; ... and so on. The nth cross-connect capacitor C pn The other end is connected to the nth output diode D n2 Cathode, nth output diode D n1 Anode, nth output diode D n1 The cathode is connected to the nth output capacitor C n+1 One end, the nth output capacitor C n+1 The other end is connected to the nth output diode D n2 Anode, lithium battery B n negative electrode; Among the n jumper capacitors: The second bridge capacitor C p2 One end, the third way cross-connect capacitor C p3 One end, ... and so on, the nth path is connected across the capacitor C pn One end is connected to the first cross-capacitor C p1 one end; The other end of the first output capacitor C2 is connected to one end of the second output capacitor C3; The other end of the second output capacitor C3 is connected to one end of the third output capacitor C4; The other end of the third output capacitor C4 is connected to one end of the fourth output capacitor C5; ... and so on. Output capacitor C of the n-1th channel n The other end is connected to the nth output capacitor C n+1 one end; Among n lithium battery cells: The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2; The negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3; The negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4; ... and so on. Lithium battery B n-1 Negative connection to lithium battery B n positive electrode.

2. According to claim 1, a Sepic multi-port series lithium-ion battery pack equalization circuit is characterized in that: DC input source u in The power switch S1 is outputting when it is turned on or off. The battery acts as a load and is charged evenly through the circuit energy storage element.

3. According to claim 1, a Sepic multi-port series lithium-ion battery pack equalization circuit is characterized in that: In one switching cycle, the average voltage of inductor L1 is 0. p1 →C2 circuit KVL principle, jumper capacitor C p1 Voltage voltage u cp1 Equal to the voltage u of lithium battery B1 B1 Similarly, the cross-connect capacitor C p2 The voltage u cp2 Equal to the voltage u of lithium battery B2 B2 , ... and so on, the jumper capacitor C pn The voltage u cpn Equal to lithium battery B n Voltage u Bn ; When the capacitor is connected across C p1 , C p2 ,......,C pn When the voltage of each lithium battery cell is large enough, the voltage of each lithium battery cell is equal. If there is a relatively low voltage lithium battery cell, then when the power switch S1 is turned on, the cross-connected capacitor C p1 , C p2 ,......,C pn Energy is released to the inductor L1 and stored. When the power switch S1 is turned off, the energy is transferred to the lithium battery cells with lower voltage. Therefore, part of the energy of the series lithium battery pack is transferred to the lithium battery cells with lower energy, thus achieving balance of the lithium battery pack.

4. A battery pack balancing circuit containing 4 lithium batteries connected in series, characterized in that: The equalization circuit includes: A 4-way output Sepic converter, 4 jumper capacitors and 4 lithium battery cells, where: The n-way output Sepic converter includes a DC input source u in , inductors L1, L2, power switch S1, capacitor C1, The first bridge capacitor C p1 , the first output diode D 11 , D 12 , the first output capacitor C2, lithium battery B1, the second jumper capacitor C p2 , the second output diode D 21 , D 22 , the second output capacitor C3, lithium battery B2, the third jumper capacitor C p3 , the third output diode D 31 , D 32 , the second output capacitor C4, lithium battery B3, the fourth jumper capacitor C p4 , the fourth output diode D 41 , D 42 , the second output capacitor C5, lithium battery B4, 4-way output Sepic converter connection form is as follows: One end of inductor L1 is connected to the DC input source u in The positive electrode and the other end of the inductor L1 are connected to the drain of the power switch S1 and one end of the capacitor C1. The other end of the capacitor C1 is connected to one end of the inductor L2 and the first bridge capacitor C p1 One end, the first cross-connect capacitor C p1 The other end is connected to the first output diode D 12 Cathode, first output diode D 11 Anode, first output diode D 11 The cathode is connected to one end of the first output capacitor C2 and the positive electrode of the lithium battery B1, and the negative electrode of the lithium battery B1 is connected to the other end of the first output capacitor C2 and the first output diode D 12 Anode, the other end of inductor L2, source of power switch S1, DC input source u in negative electrode; The second bridge capacitor C p2 The other end is connected to the second output diode D 22 Cathode, second output diode D 21 Anode, second output diode D 21 The cathode is connected to one end of the second output capacitor C3, and the other end of the second output capacitor C3 is connected to the second output diode D 22 Anode, negative electrode of lithium battery B2; The third bridge capacitor C p3 The other end is connected to the third output diode D 32 Cathode, third output diode D 31 Anode, the third output diode D 31 The cathode is connected to one end of the third output capacitor C4, and the other end of the third output capacitor C4 is connected to the third output diode D 32 Anode, negative electrode of lithium battery B3; The fourth bridge capacitor C p4 The other end is connected to the fourth output diode D 42 Cathode, fourth output diode D 41 Anode, fourth output diode D 41 The cathode is connected to one end of the fourth output capacitor C5, and the other end of the fourth output capacitor C5 is connected to the fourth output diode D 42 Anode, negative electrode of lithium battery B4; Among the 4 jumper capacitors: The second bridge capacitor C p2 One end, the third way cross-connect capacitor C p3 One end, the fourth path crosses the capacitor C p4 One end is connected to the first cross-capacitor C p1 one end; The other end of the first output capacitor C2 is connected to one end of the second output capacitor C3; The other end of the second output capacitor C3 is connected to one end of the third output capacitor C4; The other end of the third output capacitor C4 is connected to one end of the fourth output capacitor C5; In 4 lithium battery cells: The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2; The negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3; The negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4.

5. A battery pack balancing circuit comprising four lithium batteries connected in series according to claim 4, characterized in that: When the power switch S1 is turned on, the output diode D 11 , D 21 , D 31 , D 41 Turn off, output diode D 12 , D 22 , D 32 , D 42 On, DC input source u in Charge the inductor L1, capacitor C1, and jumper capacitor C p1 , C p2 , C p3 , C p4 Discharging, inductor L2 is charged, and output capacitors C2, C3, C4, and C5 provide energy to lithium batteries B1, B2, B3, and B4; When the power switch S1 is turned off, the output diode D 11 , D 21 , D 31 , D 41 Conducting, output diode D 12 , D 22 , D 32 , D 42 Shutdown, DC input source u in To inductor L1, capacitor C1, jumper capacitor C p1 , C p2 , C p3 , C p4 It is charged and combines with inductor L2 to provide energy to output capacitors C2, C3, C4, C5, and lithium batteries B1, B2, B3, and B4.

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