Lithium ion battery pack charging equalization optimization circuit

Abstract

A lithium ion battery pack charging equalization optimization circuit comprises a basic Sepic converter, n-1 bridging capacitors, n-1 output expansion units and n lithium ion batteries. The basic Sepic converter comprises an inductor L1, a Lin, a capacitor C1, a capacitor Cin, a switch S1 and a diode D1. Compared with a traditional DC / DC converter circuit equalization structure, voltage equalization between the battery units is achieved by adding a bridging capacitor between the output units, complex sampling and control algorithms are not needed, voltage deviation is effectively reduced, the battery equalization precision is improved, equalization of the battery pack is achieved only through one switch, and the cost is reduced. And the control difficulty and cost of the circuit are reduced.

Description

Technical Field

[0001] The invention relates to a battery pack equalization circuit, in particular to a lithium ion battery pack charging equalization optimization circuit. Background Art

[0002] In order to meet the performance requirements of energy storage systems, lithium-ion batteries usually need to be used in groups, but there are inconsistencies between different battery cells, such as differences in performance such as capacity, internal resistance, and voltage. These differences will reduce the capacity utilization of the battery pack, and will also cause overcharging and over-discharging of the battery, accelerate battery aging, and endanger the safety of the battery system. At present, battery balancing technology is most effective in optimizing inconsistencies. Battery balancing technology is mainly divided into passive balancing and active balancing. Passive balancing, also known as energy-consuming balancing, refers to consuming all the excess energy of the battery cells in the form of heat, but this method will cause large battery energy loss, and the high temperature environment caused by improper heat dissipation will damage the battery performance. Active balancing, as a non-energy-consuming balancing, refers to the transfer of energy through energy storage elements, thereby reducing the inconsistency of the battery pack and achieving battery energy balance. Active balancing is a hot spot in battery balancing technology due to its high energy utilization and flexible energy transfer. Summary of the invention

[0003] The present invention proposes a lithium-ion battery pack charging equalization optimization circuit, which is based on the equalization circuit of the converter, adopts a multi-output Sepic converter equalization topology, and realizes the terminal voltage equalization of the battery cells inside the lithium-ion battery pack by adding a jumper capacitor between each output unit. Compared with the traditional DC / DC converter circuit equalization structure, the circuit of the present invention realizes automatic voltage equalization between battery cells through jumper capacitors, does not require complex sampling and control algorithms, and avoids the terminal voltage imbalance problem caused by the cross-regulation rate of the converter when there are multiple outputs; effectively reduces voltage deviation and improves the equalization accuracy of lithium-ion batteries. The circuit is simple and only uses one switch to achieve the equalization of the lithium-ion battery pack, reducing the control difficulty and cost of the circuit.

[0004] The technical solution adopted by the present invention is:

[0005] A lithium-ion battery pack charging equalization optimization circuit includes: a basic Sepic converter, n-1 cross-connected capacitors, n-1 output expansion units, and n lithium-ion batteries;

[0006] The basic Sepic converter includes an inductor L 1 , L in , capacitor C 1 , C in , switch S 1 and diode D 1 ;

[0007] DC input source u in Positive connection inductor L in One end, inductor L in The other end is connected to the switch S 1 Drain, capacitor C in One end, capacitor C in The other end is connected to diode D 1 Anode, inductor L 1 One end, diode D 1 Cathode connection capacitor C 1 One end, capacitor C 1 The other end is connected to the inductor L 1 The other end, switch S 1 Source and DC input source u in cathode;

[0008] In n-1 output expansion units:

[0009] The first output expansion unit includes an inductor L 2 , capacitor C 2 、Diode D 2 ; Among them, the inductance L 2 One end is connected to diode D 2 Anode, inductance L 2 The other end is connected to capacitor C 2 The other end, capacitor C 2 One end is connected to diode D 2 cathode;

[0010] The second output expansion unit includes an inductor L 3 , capacitor C 3 、Diode D 3 ; Among them, the inductance L 3 One end is connected to diode D 3 Anode, inductance L 3 The other end is connected to capacitor C 3 The other end, capacitor C 3 One end is connected to diode D 3 cathode;

[0011] ... and so on.

[0012] The n-1th output expansion unit includes an inductor L n , capacitor C n 、Diode D n ; Among them, the inductance L n One end is connected to diode D n Anode, inductance L n The other end is connected to capacitor C n The other end, capacitor C n One end is connected to diode D n cathode.

[0013] Among n-1 jumper capacitors:

[0014] Capacitor C VB1 The upper end and the diode D 1 Anode connection, capacitor C VB1 The lower end and diode D 2 Anode connection;

[0015] Capacitor C VB2 The upper end and the diode D 2 Anode connection, capacitor C VB2 The lower end and diode D 3 Anode connection;

[0016] Capacitor C VB3 The upper end and the diode D 3 Anode connection, capacitor C VB3 The lower end and diode D 4 Anode connection;

[0017] ... and so on.

[0018] Capacitor C VB(n-1) The upper end and the diode D n-1 Anode connection, capacitor C VB(n-1) The lower end and diode D n Anode connection;

[0019] Lithium-ion battery B 1 The positive pole is connected to the capacitor C 1 One end, diode D 1 Cathode, Li-ion Battery B 1 The negative pole is connected to capacitor C 1 The other end, inductor L 1 The other end;

[0020] Lithium-ion battery B 2 The positive pole is connected to the capacitor C 2 One end, diode D 2 Cathode, Li-ion Battery B 2 The negative pole is connected to capacitor C 2 The other end, inductor L 2 The other end;

[0021] Lithium-ion battery B 3 The positive pole is connected to the capacitor C 3 One end, diode D 3 Cathode, Li-ion Battery B 3 The negative pole is connected to capacitor C 3 The other end, inductor L 3 The other end;

[0022] ... and so on.

[0023] Lithium-ion battery B n-1 The positive pole is connected to the capacitor C n-1 One end, diode D n-1 Cathode, Li-ion Battery B n-1 The negative pole is connected to capacitor C n-1 The other end, inductor L n-1 The other end;

[0024] Lithium-ion battery B n The positive pole is connected to the capacitor C n One end, diode D n Cathode, Li-ion Battery B n The negative pole is connected to capacitor C n The other end, inductor L n The other end.

[0025] Among n lithium-ion batteries:

[0026] Lithium-ion battery B 1 Negative connection to lithium-ion battery B 2 Positive electrode, lithium-ion battery B 2 Negative connection to lithium-ion battery B 3 Positive electrode, lithium-ion battery B 3 Negative connection to lithium-ion battery B 4 Positive electrode... and so on, lithium-ion battery B n-1 Negative connection to lithium-ion battery B n positive electrode.

[0027] The switch S 1 The gate of the controller is connected and its duty cycle can be varied between 0 and 1.

[0028] A lithium-ion battery pack charging equalization optimization circuit, characterized in that it includes: the circuit includes a basic Sepic converter, three cross-connected capacitors, three output expansion units, and four lithium-ion batteries;

[0029] The basic Sepic converter includes an inductor L 1 , L in , capacitor C 1 , C in , switch S 1 and diode D 1 ;

[0030] DC input source u in Positive connection inductor L in One end, inductor L in The other end is connected to the switch S 1 Drain, capacitor C in One end, capacitor C inThe other end is connected to diode D 1 Anode, inductor L 1 One end, diode D 1 Cathode connection capacitor C 1 One end, capacitor C 1 The other end is connected to the inductor L 1 The other end, switch S 1 Source and DC input source u in cathode;

[0031] 3 output expansion units:

[0032] The first output expansion unit includes an inductor L 2 , capacitor C 2 、Diode D 2 ; Among them, the inductance L 2 One end is connected to diode D 2 Anode, inductance L 2 The other end is connected to capacitor C 2 The other end, capacitor C 2 One end is connected to diode D 2 cathode;

[0033] The second output expansion unit includes an inductor L 3 , capacitor C 3 、Diode D 3 ; Among them, the inductance L 3 One end is connected to diode D 3 Anode, inductance L 3 The other end is connected to capacitor C 3 The other end, capacitor C 3 One end is connected to diode D 3 cathode;

[0034] The third output expansion unit includes an inductor L 4 , capacitor C 4 、Diode D 4 ; Among them, the inductance L 4 One end is connected to diode D 4 Anode, inductance L 4 The other end is connected to capacitor C 4 The other end, capacitor C 4 One end is connected to diode D 4 cathode;

[0035] Among the 3 jumper capacitors:

[0036] Capacitor C VB1 The upper end and the diode D 1 Anode connection, capacitor C VB1 The lower end and diode D 2 Anode connection;

[0037] Capacitor C VB2 The upper end and the diode D 2 Anode connection, capacitor C VB2 The lower end and diode D 3 Anode connection;

[0038] Capacitor C VB3 The upper end and the diode D 3 Anode connection, capacitor C VB3 The lower end and diode D 4 Anode connection;

[0039] Lithium-ion battery B 1 The positive pole is connected to the capacitor C 1 One end, diode D 1 Cathode, Li-ion Battery B 1 The negative pole is connected to capacitor C 1 The other end, inductor L 1 The other end;

[0040] Lithium-ion battery B 2 The positive pole is connected to the capacitor C 2 One end, diode D 2 Cathode, Li-ion Battery B 2 The negative pole is connected to capacitor C 2 The other end, inductor L 2 The other end;

[0041] Lithium-ion battery B 3 The positive pole is connected to the capacitor C 3 One end, diode D 3 Cathode, Li-ion Battery B 3 The negative pole is connected to capacitor C 3 The other end, inductor L 3 The other end;

[0042] Lithium-ion battery B 4 The positive pole is connected to the capacitor C 4 One end, diode D 4 Cathode, Li-ion Battery B 4 The negative pole is connected to capacitor C 4 The other end, inductor L 4 One end.

[0043] Of the 4 lithium-ion batteries:

[0044] Lithium-ion battery B 1 Negative connection to lithium-ion battery B 2 Positive electrode, lithium-ion battery B 2 Negative connection to lithium-ion battery B 3 Positive electrode, lithium-ion battery B 3 Negative connection to lithium-ion battery B4 positive electrode.

[0045] When the switch S 1 When conducting, diode D 1 , D 2 , D 3 , D 4 Withstand reverse voltage cutoff, capacitor C in Discharge, capacitor C VB1 , C VB2 , C VB3 Charging, capacitor C 1 , C 2 , C 3 , C 4 Provides energy to lithium-ion battery packs;

[0046] When the switch S 1 When off, the diode D 1 , D 2 , D 3 , D 4 On, input source u in Through inductor L in Provides energy for the lithium-ion battery pack, capacitor C in Charging, capacitor C VB1 , C VB2 , C VB3 Discharge, capacitor C 1 , C 2 , C 3 , C 4 Charging, inductance L 1 , L 2 , L 3 , L 4 Through diode D 1 , D 2 , D 3 , D 4 Provides energy to the lithium-ion battery pack.

[0047] Assume that the single lithium-ion battery B in the series lithium-ion battery pack 1 If the SOC is higher than the average value, the initial voltage u B1 >u B2 When the switch S 1 When turned off, due to the cross-capacitor C VB1 The role of the diode D in the circuit 1 It is not turned on, and the current is first given to the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u CVB1 rises to the output voltage u of the circuit B1 When the diode D 1 Start conducting.

[0048] Assuming the output capacitor C 1 If the output voltage ripple is large enough, it is much smaller than the cross-capacitor C VB1 The voltage ripple can be considered as u B1 The average voltage across the capacitor C VB1 In switch S 1 The peak voltage during the turn-off phase. Therefore, u B1 and u B2 The voltage deviation Δu is equal to the difference between the peak voltage and the average value, that is, the cross-capacitor C VB1 The voltage ripple peak-to-peak value is half. VB1 As the capacitance increases, the capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with C VB1 As the capacitance increases, u decreases. B1 and u B2 The voltage of capacitor C will be closer. VB1 , C VB2 , C VB3 When it is large enough, the voltages of the lithium-ion battery cells are equal, achieving voltage balance among the battery cells in the lithium-ion battery pack.

[0049] The present invention provides a lithium-ion battery pack charging equalization optimization circuit, and the technical effects are as follows:

[0050] 1) The battery balancing circuit converter of the present invention solves the problem of terminal voltage imbalance caused by cross regulation rate when there are multiple outputs, effectively reduces voltage deviation and improves battery balancing accuracy.

[0051] 2) Compared with the traditional DC / DC converter circuit balancing structure, the present invention realizes voltage balancing between lithium-ion battery cells through cross-connected capacitors, without the need for complex sampling and control algorithms.

[0052] 3) The circuit of the present invention is simple and only one switch is used to achieve the balance of the lithium-ion battery pack, thereby reducing the control difficulty and cost of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0054] Figure 1 It is the circuit principle diagram of the present invention;

[0055] Figure 2 The schematic diagram of the present invention is a battery pack balancing converter with four battery cells connected in series.

[0056] Figure 3 This is a simulation diagram of a battery pack balancing converter that realizes four battery cells in series according to the present invention. DETAILED DESCRIPTION

[0057] The present invention will be further described in detail below in conjunction with the accompanying drawings. Figure 2 As shown, the battery pack charge equalization optimization circuit of the present invention contains 4 battery cells, and the circuit includes a basic Sepic converter, 3 cross-connected capacitors, 3 output expansion units, and 4 lithium-ion batteries, wherein:

[0058] The basic Sepic converter includes an inductor L 1 , L in , capacitor C 1 , C in , switch S 1 and diode D 1 ;

[0059] DC input source u in Positive connection inductor L in One end, inductor L in The other end is connected to the switch S 1 Drain, capacitor C in One end, capacitor C in The other end is connected to diode D 1 Anode, inductor L 1 One end, diode D 1 Cathode connection capacitor C 1 One end, capacitor C 1 The other end is connected to the inductor L 1 The other end, switch S 1 Source and DC input source u in cathode;

[0060] 3 output expansion units:

[0061] The first output expansion unit includes an inductor L 2 , capacitor C 2 、Diode D 2 ; Among them, the inductor L 2 One end is connected to diode D 2 Anode, inductance L 2 The other end is connected to capacitor C 2 The other end, capacitor C 2 One end is connected to diode D 2 cathode;

[0062] The second output expansion unit includes an inductor L 3 , capacitor C 3 、Diode D 3 ; Among them, the inductor L 3 One end is connected to diode D 3 Anode, inductance L 3 The other end is connected to capacitor C 3 The other end, capacitor C3 One end is connected to diode D 3 cathode;

[0063] The third output expansion unit includes an inductor L 4 , capacitor C 4 、Diode D 4 ; Among them, the inductor L 4 One end is connected to diode D 4 Anode, inductance L 4 The other end is connected to capacitor C 4 The other end, capacitor C 4 One end is connected to diode D 4 cathode;

[0064] Among the 3 jumper capacitors:

[0065] Capacitor C VB1 The upper end and the diode D 1 Anode connection, capacitor C VB1 The lower end and diode D 2 Anode connection;

[0066] Capacitor C VB2 The upper end and the diode D 2 Anode connection, capacitor C VB2 The lower end and diode D 3 Anode connection;

[0067] Capacitor C VB3 The upper end and the diode D 3 Anode connection, capacitor C VB3 The lower end and diode D 4 Anode connection;

[0068] Lithium-ion battery B 1 The positive pole is connected to the capacitor C 1 One end, diode D 1 Cathode, Li-ion Battery B 1 The negative pole is connected to capacitor C 1 The other end, inductor L 1 The other end;

[0069] Lithium-ion battery B 2 The positive pole is connected to the capacitor C 2 One end, diode D 2 Cathode, Li-ion Battery B 2 The negative pole is connected to capacitor C 2 The other end, inductor L 2 The other end;

[0070] Lithium-ion battery B 3 The positive pole is connected to the capacitor C 3 One end, diode D 3Cathode, Li-ion Battery B 3 The negative pole is connected to capacitor C 3 The other end, inductor L 3 The other end;

[0071] Lithium-ion battery B 4 The positive pole is connected to the capacitor C 4 One end, diode D 4 Cathode, Li-ion Battery B 4 The negative pole is connected to capacitor C 4 The other end, inductor L 4 One end.

[0072] Of the 4 lithium-ion batteries:

[0073] Lithium-ion battery B 1 Negative connection to lithium-ion battery B 2 Positive electrode, lithium-ion battery B 2 Negative connection to lithium-ion battery B 3 Positive electrode, lithium-ion battery B 3 Negative connection to lithium-ion battery B 4 positive electrode.

[0074] When the switch S 1 When conducting, diode D 1 , D 2 , D 3 , D 4 Withstand reverse voltage cutoff, capacitor C in Discharge, capacitor C VB1 , C VB2 , C VB3 Charging, capacitor C 1 , C 2 , C 3 , C 4 Provides energy to lithium-ion battery packs;

[0075] When the switch S 1 When off, the diode D 1 , D 2 , D 3 , D 4 On, input source u in Through inductor L in Provides energy for the lithium-ion battery pack, capacitor C in Charging, capacitor C VB1 , C VB2 , C VB3 Discharge, capacitor C 1 , C 2 , C 3 , C 4 Charging, inductance L 1 , L 2 , L3 , L 4 Through diode D 1 , D 2 , D 3 , D 4 Provides energy to the lithium-ion battery pack.

[0076] The principle of battery balancing is to keep the lithium-ion battery cells in a series-connected lithium-ion battery pack in a balanced state. At present, the balance of the entire lithium-ion battery pack is mainly judged by whether the terminal voltage of the lithium-ion battery cells is balanced (same). 1 If the SOC is higher than the average value, the initial voltage u B1 >u B2 When the switch S 1 When turned off, due to the cross-capacitor C VB1 The role of the diode D in the circuit 1 It is not turned on, and the current is first given to the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u CVB1 rises to the output voltage u of the circuit B1 When the diode D 1 Assuming the output capacitor C 1 If the output voltage ripple is large enough, it is much smaller than the cross-capacitor C VB1 The voltage ripple can be considered as u B1 The average voltage across the capacitor C VB1 In switch S 1 The peak voltage during the turn-off phase. Therefore, u B1 and u B2 The voltage deviation Δu is equal to the difference between the peak voltage and the average value, that is, the cross-capacitor C VB1 The voltage ripple peak-to-peak value is half. VB1 As the capacitance increases, the capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with C VB1 As the capacitance increases, u decreases. B1 and u B2 The voltage of capacitor C will be closer. VB1 , C VB2 , C VB3 When it is large enough, the voltages of the lithium-ion battery cells are equal, achieving voltage balance among the battery cells in the lithium-ion battery pack.

[0077] Depend on Figure 3It can be seen that the SOCs of the four lithium-ion batteries in the series lithium-ion battery pack are different, and the other parameters are the same, among which the SOCs of lithium-ion battery B1 are 85, the SOCs of lithium-ion battery B2 are 83, the SOCs of lithium-ion battery B3 are 80, and the SOCs of lithium-ion battery B4 are 75. The converter circuit proposed in the present invention can achieve SOC balancing of the four lithium-ion battery units.

Claims

1. A lithium-ion battery pack charging equalization optimization circuit, characterized in that: It includes Sepic converter, n-1 jumper capacitors, n-1 output expansion units, and n lithium-ion batteries; The Sepic converter includes an inductor L1, L in , capacitors C1, C in , switch S1 and diode D1; DC input source u in Positive connection inductor L in One end, inductor L in The other end is connected to the drain of switch S1 and capacitor C in One end, capacitor C in The other end is connected to the anode of diode D1 and one end of inductor L1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the other end of inductor L1, the source of switch S1 and the DC input source u. in cathode; In n-1 output expansion units: The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; wherein one end of the inductor L2 is connected to the anode of the diode D2, the other end of the inductor L2 is connected to the other end of the capacitor C2, and one end of the capacitor C2 is connected to the cathode of the diode D2; The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; wherein one end of the inductor L3 is connected to the anode of the diode D3, the other end of the inductor L3 is connected to the other end of the capacitor C3, and one end of the capacitor C3 is connected to the cathode of the diode D3; ... and so on. The n-1th output expansion unit includes an inductor L n , capacitor C n 、Diode D n ; Among them, the inductor L n One end is connected to diode D n Anode, inductance L n The other end is connected to capacitor C n The other end, capacitor C n One end is connected to diode D n cathode; Among n-1 jumper capacitors: Capacitor C VB1 The upper end is connected to the anode of diode D1, and the capacitor C VB1 The lower end is connected to the anode of diode D2; Capacitor C VB2 The upper end is connected to the anode of diode D2, and the capacitor C VB2 The lower end is connected to the anode of diode D3; Capacitor C VB3 The upper end is connected to the anode of diode D3, and the capacitor C VB3 The lower end is connected to the anode of diode D4; ... and so on. Capacitor C VB(n-1) The upper end and the diode D n-1 Anode connection, capacitor C VB(n-1) The lower end and diode D n Anode connection; The positive electrode of the lithium-ion battery B1 is connected to one end of the capacitor C1 and the cathode of the diode D1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and the other end of the inductor L1; The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2 and the cathode of the diode D2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and the other end of the inductor L2; The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3 and the cathode of the diode D3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3 and the other end of the inductor L3; ... and so on. Lithium-ion battery B n-1 The positive pole is connected to the capacitor C n-1 One end, diode D n-1 Cathode, Li-ion Battery B n-1 The negative pole is connected to capacitor C n-1 The other end, inductor L n-1 The other end; Lithium-ion battery B n The positive pole is connected to the capacitor C n One end, diode D n Cathode, Li-ion Battery B n The negative pole is connected to capacitor C n The other end, inductor L n The other end; Among n lithium-ion batteries: The negative electrode of lithium-ion battery B1 is connected to the positive electrode of lithium-ion battery B2, the negative electrode of lithium-ion battery B2 is connected to the positive electrode of lithium-ion battery B3, the negative electrode of lithium-ion battery B3 is connected to the positive electrode of lithium-ion battery B4... and so on. n-1 Negative connection to lithium-ion battery B n positive electrode.

2. A lithium-ion battery pack charging equalization optimization circuit according to claim 1, characterized in that: The gate of the switch S1 is connected to a controller, and its duty cycle can be changed between 0 and 1.

3. A lithium-ion battery pack charging equalization optimization circuit, characterized in that: The circuit includes a Sepic converter, three jumper capacitors, three output expansion units, and four lithium-ion batteries; The Sepic converter includes an inductor L1, L in , capacitors C1, C in , switch S1 and diode D1; DC input source u in Positive connection inductor L in One end, inductor L in The other end is connected to the drain of switch S1 and capacitor C in One end, capacitor C in The other end is connected to the anode of diode D1 and one end of inductor L1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the other end of inductor L1, the source of switch S1 and the DC input source u. in cathode; 3 output expansion units: The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; wherein one end of the inductor L2 is connected to the anode of the diode D2, the other end of the inductor L2 is connected to the other end of the capacitor C2, and one end of the capacitor C2 is connected to the cathode of the diode D2; The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; wherein one end of the inductor L3 is connected to the anode of the diode D3, the other end of the inductor L3 is connected to the other end of the capacitor C3, and one end of the capacitor C3 is connected to the cathode of the diode D3; The third output expansion unit includes an inductor L4, a capacitor C4, and a diode D4; wherein one end of the inductor L4 is connected to the anode of the diode D4, the other end of the inductor L4 is connected to the other end of the capacitor C4, and one end of the capacitor C4 is connected to the cathode of the diode D4; Among the 3 jumper capacitors: Capacitor C VB1 The upper end is connected to the anode of diode D1, and the capacitor C VB1 The lower end is connected to the anode of diode D2; Capacitor C VB2 The upper end is connected to the anode of diode D2, and the capacitor C VB2 The lower end is connected to the anode of diode D3; Capacitor C VB3 The upper end is connected to the anode of diode D3, and the capacitor C VB3 The lower end is connected to the anode of diode D4; The positive electrode of the lithium-ion battery B1 is connected to one end of the capacitor C1 and the cathode of the diode D1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and the other end of the inductor L1; The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2 and the cathode of the diode D2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and the other end of the inductor L2; The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3 and the cathode of the diode D3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3 and the other end of the inductor L3; The positive electrode of the lithium-ion battery B4 is connected to one end of the capacitor C4 and the cathode of the diode D4, and the negative electrode of the lithium-ion battery B4 is connected to the other end of the capacitor C4 and one end of the inductor L4; Of the 4 lithium-ion batteries: The negative electrode of lithium-ion battery B1 is connected to the positive electrode of lithium-ion battery B2, the negative electrode of lithium-ion battery B2 is connected to the positive electrode of lithium-ion battery B3, and the negative electrode of lithium-ion battery B3 is connected to the positive electrode of lithium-ion battery B4.

4. A lithium-ion battery pack charging equalization optimization circuit according to claim 3, characterized in that: When the switch S1 is turned on, the diodes D1, D2, D3, and D4 are cut off due to the reverse voltage, and the capacitor C in Discharge, capacitor C VB1 , C VB2 , C VB3 Charging, capacitors C1, C2, C3, and C4 provide energy for the lithium-ion battery pack; When the switch S1 is turned off, the diodes D1, D2, D3, and D4 are turned on, and the input source u in Through inductor L in Provides energy for the lithium-ion battery pack, capacitor C in Charging, capacitor C VB1 , C VB2 , C VB3 Discharging, capacitors C1, C2, C3, and C4 are charged, and inductors L1, L2, L3, and L4 provide energy to the lithium-ion battery pack through diodes D1, D2, D3, and D4 respectively.

5. The lithium-ion battery pack charging equalization optimization circuit according to claim 3, characterized in that: Assume that the SOC of the single lithium-ion battery B1 in the series lithium-ion battery pack is higher than the average value, then the initial voltage u B1 >u B2 ; When switch S1 is turned off, due to the cross-connected capacitor C VB1 The diode D1 in the circuit is not turned on, and the current is first fed to the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u CVB1 rises to the output voltage u of the circuit B1 When they are equal, diode D1 starts to conduct; Assuming the output capacitor C1 is large enough, the output voltage ripple is much smaller than the cross-capacitor C VB1 The voltage ripple can be considered as u B1 The average voltage across the capacitor C VB1 The peak voltage during the turn-off phase of switch S1; therefore, u B1 and u B2 The voltage deviation Δu is equal to the difference between the peak voltage and the average value, that is, the cross-capacitor C VB1 Half of the peak-to-peak voltage ripple; with the capacitance C VB1 As the capacitance increases, the capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with C VB1 As the capacitance increases, u decreases. B1 and u B2 The voltage of capacitor C will be closer; VB1 , C VB2 , C VB3 When it is large enough, the voltages of the lithium-ion battery cells are equal, achieving voltage balance among the battery cells in the lithium-ion battery pack.

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