Lithium ion battery pack energy equalization circuit

Abstract

An energy balancing circuit of a lithium ion battery pack comprises a direct current input source, a basic Buck-Boost converter, n-1 bridging capacitors, n-1 output expansion units and n lithium ion batteries, and the basic Buck-Boost converter comprises an inductor L1, a capacitor C1, a switch S1 and a diode D1. According to the energy equalization circuit, automatic voltage equalization is realized by adding a bridging capacitor between the output units. Compared with a traditional converter type equalization structure, equalization of the battery pack is achieved only through one switch, and the control difficulty and cost of the circuit are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery balancing, and in particular to an energy balancing circuit for a lithium-ion battery pack. Background Art

[0002] In recent years, the new energy industry is in a period of rapid development. Lithium-ion batteries are widely used in automobiles, power grids, communications, power monitoring systems and energy storage fields due to their advantages such as high energy density, long cycle life, no memory effect and low self-discharge rate. However, the voltage and capacity of each single lithium-ion battery are small, and the battery pack will be connected in parallel and then in series. However, due to factors such as production process and material properties, the cells in the battery pack have differences in performance. Moreover, due to the differences in working environment and the unique chemical properties of the battery itself, these differences in characteristics become more obvious during the operation of the battery pack, showing inconsistency. With use, the inconsistency of the battery pack gradually increases, which will lead to excessive charging and discharging of the battery, damage the battery life and safety hazards, reduce the energy utilization rate of the battery, accelerate battery aging and performance degradation, and even produce thermal runaway risks. Therefore, equalization management of the battery pack is a necessary technology to extend the battery life and improve the performance of the battery pack. At present, 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 CN116247925A discloses a battery balancing bidirectional DC-DC converter control method. This method adds multiple balancing control switches on the basis of lithium-ion battery packs and integrates multiple working modes. By controlling the switch closure, the circuit topology is reconstructed to change the working mode, including charging mode, external power supply mode, battery pack function mode, battery pack voltage balancing mode, and energy recovery mode. It can realize the bidirectional flow of energy, as well as the boost and buck functions, and there are many different combinations of energy supply methods to increase backup and improve fault tolerance; the battery pack achieves voltage balancing through the energy storage inductor and switch tube of the bidirectional DC-DC converter, thereby improving the utilization rate of the device. However, the balancing circuit adopted by the control method uses fourteen switch tubes for only three battery packs, and the logic control is very complicated. Summary of the invention

[0003] In order to solve the shortcomings of the existing lithium-ion battery pack balancing technology, the present invention proposes a lithium-ion battery pack energy balancing circuit, which is composed of a multi-output Buck-Boost converter and a plurality of cross-over capacitors. The balancing circuit is based on converter-type balancing, adopts a Buck-Boost converter balancing topology, and realizes SOC balancing of the series battery pack by adding a cross-over capacitor between each output unit. Compared with the traditional balancing structure, the battery pack is balanced by only one switch, which reduces the control difficulty and cost of the circuit; effectively reduces the voltage deviation and improves the battery balancing accuracy.

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

[0005] A lithium-ion battery pack energy balancing circuit includes a DC input source, a basic Buck-Boost converter, n-1 cross-connected capacitors, n-1 output expansion units, and n lithium-ion batteries, wherein:

[0006] The basic Buck-Boost converter includes an inductor L1, a capacitor C1, a switch S1, and a diode D1;

[0007] DC input source u in The positive electrode is connected to the drain of switch S1, the source of switch S1 is connected to one end of inductor L1 and the cathode of diode D1, one end of capacitor C1 is connected to the anode of diode D1, and the other end of inductor L1 and capacitor C1 are connected to the DC input source u in negative electrode.

[0008] The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; one end of the inductor L2 is connected to the cathode of the diode D2, one end of the capacitor C2 is connected to the anode of the diode D2, and the other end of the capacitor C2 is connected to the other end of the inductor L2;

[0009] The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3;

[0010] ... and so on.

[0011] The n-1th output expansion unit includes an inductor L n , capacitor C n 、Diode D n ; Inductor L n One end is connected to diode D n The cathode of the capacitor C n One end of the diode D n The anode of the capacitor C n The other end of the inductor is connected ton The other end.

[0012] The connection between the jumper capacitor and each output expansion unit is as follows:

[0013] Cross-over capacitor C VB1 One end of the diode D1 is connected to the cathode, one end of the inductor L1, and the capacitor C VB1 The other end is connected to the cathode of diode D2 and one end of inductor L2 respectively;

[0014] Cross-over capacitor C VB2 One end of the diode D2 is connected to the cathode, one end of the inductor L2, and the capacitor C is connected across the VB2 The other end is connected to the cathode of diode D3 and one end of inductor L3 respectively;

[0015] Cross-over capacitor C VB(n-2) One end of each diode D n-2 The cathode, inductance L n-2 One end, across the capacitor C VB(n-2) The other end is connected to the diode D n-1 The cathode, inductance L n-1 One end.

[0016] ... and so on.

[0017] Cross-over capacitor C VB(n-1) One end of each diode D n-1 The cathode, inductance L n-1 One end, across the capacitor C VB(n-1) The other end is connected to the diode D n The cathode, inductance L n one end;

[0018] The connection between the lithium-ion battery and each output expansion unit is as follows:

[0019] The positive electrode of the lithium-ion battery B1 is connected to the anode of the diode D1 and one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and one end of the inductor L1;

[0020] The positive electrode of the lithium-ion battery B2 is connected to the anode of the diode D2 and one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and one end of the inductor L2;

[0021] Lithium-ion battery B n-1 The positive poles of the diodes D n-1 Anode, capacitor C n-1 One end of the lithium-ion battery B n-1 The negative electrodes are connected to capacitor C n-1 The other end of the inductor Ln-1 one end of

[0022] ... and so on.

[0023] Lithium-ion battery B n The positive poles of the diodes D n Anode, capacitor C n One end of the lithium-ion battery B n The negative electrodes are connected to capacitor C n The other end of the inductor L n one end.

[0024] The gates of the switches S1 are connected to a controller, and the duty cycle of the switches S1 can be changed between 0 and 1.

[0025] A lithium-ion battery pack energy balancing circuit includes a DC input source, a basic Buck-Boost converter, three jumper capacitors, three output expansion units, and four lithium-ion batteries, wherein:

[0026] A basic Buck-Boost converter includes inductor L1, capacitor C1, switch S1, and diode D1.

[0027] DC input source u in The positive electrode is connected to the drain of switch S1, the source of switch S1 is connected to one end of inductor L1 and the cathode of diode D1, one end of capacitor C1 is connected to the anode of diode D1, and the other end of inductor L1 and capacitor C1 are connected to the DC input source u in negative electrode;

[0028] The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; one end of the inductor L2 is connected to the cathode of the diode D2, one end of the capacitor C2 is connected to the anode of the diode D2, and the other end of the capacitor C2 is connected to the other end of the inductor L2;

[0029] The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3;

[0030] The third output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3;

[0031] The connection between the jumper capacitor and each output expansion unit is as follows:

[0032] Cross-over capacitor C VB1One end of the diode D1 is connected to the cathode, one end of the inductor L1, and the capacitor C VB1 The other end is connected to the cathode of diode D2 and one end of inductor L2 respectively;

[0033] Cross-over capacitor C VB2 One end of the diode D2 is connected to the cathode, one end of the inductor L2, and the capacitor C is connected across the VB2 The other end is connected to the cathode of diode D3 and one end of inductor L3 respectively;

[0034] Cross-over capacitor C VB3 One end of the diode D3 and one end of the inductor L3 are connected to the cathode of the diode D3 and one end of the inductor L3, and the capacitor C VB3 The other end is connected to the cathode of the diode D4 and one end of the inductor L4 respectively.

[0035] The connection between the lithium-ion battery and each output expansion unit is as follows:

[0036] The positive electrode of the lithium-ion battery B1 is connected to the anode of the diode D1 and one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and one end of the inductor L1;

[0037] The positive electrode of the lithium-ion battery B2 is connected to the anode of the diode D2 and one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and one end of the inductor L2;

[0038] The positive electrode of the lithium-ion battery B3 is connected to the anode of the diode D3 and one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3 and one end of the inductor L3;

[0039] The positive electrode of the lithium-ion battery B4 is connected to the anode of the diode D4 and one end of the capacitor C4, respectively, 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, respectively.

[0040] Take the battery pack composed of four single batteries B1, B2, B3, and B4 connected in series as an example:

[0041] In a switching cycle, according to the inductor volt-second balance principle, the average voltage of inductors L1, L2, L3, and L4 is 0, and the following is written: L1→C2→L2→C VB1 The loop KVL equation can be obtained by the cross-capacitance C VB1 The voltage u VB1 Equal to the output voltage u B2 Similarly, the cross-connect capacitor C VB2 The voltage u VB2 Equal to the output voltage u B3 , the cross-capacitor C VB3 The voltage u VB3 Equal to the output voltage uB4 .

[0042] When the switch S1 is turned on, the diodes D1, D2, D3, and D4 are turned off, and the DC input source u in The inductors L1, L2, L3, L4 and capacitors C1, C2, C3, C4 supply power to the load. When the switch S1 is turned off, the diodes D1, D2, D3, D4 are turned on, and the inductor L i Through the loop L i →C i →D i →L i To capacitor C i Charging, if the SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value, the initial voltage u VB1 <u VB2 .

[0043] When switch S1 is turned off, the capacitor C VB1 The diode D1 in the circuit is not conducting, and the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u VB1 The output voltage u of the circuit drops to B1 When the output capacitor C1 is large enough, the output voltage ripple is much smaller than the cross-capacitor C1. VB1 The voltage ripple can be approximately considered as u B1 The average voltage is equal to the capacitance C VB1 The minimum voltage during the switch off phase, therefore, u VB1 and u VB2 The voltage deviation Δu is equal to the difference between the minimum voltage and the average value, that is, the cross-capacitor capacitance C VB1 The voltage ripple peak-to-peak value is half. With the cross-capacitor C VB1 As the capacitance increases, the cross-capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with the cross-connect capacitor C VB1 As the capacitance increases, u decreases. VB1 and u VB2 The voltages will be closer.

[0044] Therefore, when the capacitor C VB1 , C VB2 , C VB3 When large enough, the voltages of the individual lithium-ion battery cells are equal.

[0045] Assume that the SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value. When the switch S1 is turned on, the DC input source charges the jumper capacitor and inductor. After the switch is turned off, the auxiliary capacitor C VBThe introduction of can greatly reduce the inter-electrode voltage deviation caused by load imbalance, so that the lithium-ion battery cells with lower energy in the lithium-ion battery pack can obtain more energy and achieve SOC balance of the lithium-ion battery pack.

[0046] The present invention provides a lithium-ion battery pack energy balancing circuit, and the technical effects are as follows:

[0047] 1) The balancing circuit of the present invention achieves the effect of automatic voltage balancing of the output voltages of multi-channel output Buck-Boost converters by connecting a jumper capacitor between adjacent output units of the Buck-Boost converter, thereby improving the balancing degree of the lithium-ion battery;

[0048] 2) The balancing circuit of the present invention has a simple topology and uses only one switch, which reduces the difficulty of control system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0050] Figure 1 It is the circuit principle diagram of the present invention;

[0051] Figure 2 This is the schematic diagram of the traditional Buck-Boost converter circuit.

[0052] Figure 3 The circuit schematic diagram of the present invention is a circuit schematic diagram of a lithium-ion battery pack with four single lithium-ion batteries connected in series to achieve SOC balancing.

[0053] Figure 4 This is a simulation diagram of the present invention realizing balancing of a lithium-ion battery pack with four lithium-ion battery cells connected in series. DETAILED DESCRIPTION

[0054] like Figure 3 As shown, a lithium-ion battery pack energy balancing circuit includes: a DC input source, a basic Buck-Boost converter, 3 cross-capacitors, 3 output expansion units, and 4 lithium-ion batteries, wherein:

[0055] A basic Buck-Boost converter includes inductor L1, capacitor C1, switch S1, and diode D1.

[0056] The basic Buck-Boost converter is connected as follows:

[0057] DC input source u in The positive electrode is connected to the drain of switch S1, the source of switch S1 is connected to one end of inductor L1 and the cathode of diode D1, one end of capacitor C1 is connected to the anode of diode D1, and the other end of inductor L1 and capacitor C1 are connected to the DC input source u in negative electrode.

[0058] The connection form of each output expansion unit is as follows: the first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; one end of the inductor L2 is connected to the cathode of the diode D2, one end of the capacitor C2 is connected to the anode of the diode D2, and the other end of the capacitor C2 is connected to the other end of the inductor L2; the second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3; the third output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3.

[0059] The connection between the jumper capacitor and each output expansion unit is as follows:

[0060] Cross-over capacitor C VB1 One end of the diode D1 is connected to the cathode, one end of the inductor L1, and the capacitor C VB1 The other end is connected to the cathode of diode D2 and one end of inductor L2 respectively; the capacitor C VB2 One end of the diode D2 is connected to the cathode, one end of the inductor L2, and the capacitor C is connected across the VB2 The other end is connected to the cathode of diode D3 and one end of inductor L3 respectively; the cross-capacitor C VB3 One end of the diode D3 and one end of the inductor L3 are connected to the cathode of the diode D3 and one end of the inductor L3, and the capacitor C VB3 The other end is connected to the cathode of the diode D4 and one end of the inductor L4 respectively.

[0061] The connection between the lithium-ion battery and each output expansion unit is as follows:

[0062] The positive electrode of the lithium-ion battery B1 is respectively connected to the anode of the diode D1 and one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is respectively connected to the other end of the capacitor C1 and one end of the inductor L1; the positive electrode of the lithium-ion battery B2 is respectively connected to the anode of the diode D2 and one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is respectively connected to the other end of the capacitor C2 and one end of the inductor L2; the positive electrode of the lithium-ion battery B3 is respectively connected to the anode of the diode D3 and one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is respectively connected to the other end of the capacitor C3 and one end of the inductor L3; the positive electrode of the lithium-ion battery B4 is respectively connected to the anode of the diode D4 and one end of the capacitor C4, and the negative electrode of the lithium-ion battery B4 is respectively connected to the other end of the capacitor C4 and one end of the inductor L4.

[0063] In a switching cycle, according to the inductor volt-second balance principle, the average voltage of inductors L1, L2, L3, and L4 is 0, and the following is written: L1→C2→L2→C VB1 The KVL equation of the loop gives the capacitance C VB1 The voltage u VB1 Equal to the output voltage u B2 Similarly, the capacitor C VB2 The voltage u VB2 Equal to the output voltage u B3 , capacitor C VB3 The voltage u VB3 Equal to the output voltage u B4 When switch S1 is turned on, diodes D1, D2, D3, and D4 are turned off, and the DC input source u in Inductors L1, L2, L3, L4, and cross-capacitor C VB1 , C VB2 , C VB3 When the switch S1 is turned off, the diodes D1, D2, D3, D4 are turned on, and the inductor L i Through the loop L i →C i →D i →L i To capacitor C i Charging, if the SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value, the initial voltage u VB1 <u VB2 When switch S1 is turned off, due to the cross-connect capacitor C VB1 The diode D1 in the circuit is not conducting, and the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u VB1 The output voltage u of the circuit drops to B1 When they are equal, diode D1 starts conducting.

[0064] 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 approximately considered as u B1 The average voltage across the capacitor C VB1 The minimum voltage during the switch off phase, therefore, u VB1 and u VB2 The voltage deviation Δu is equal to the difference between the minimum voltage and the average value, that is, the cross-capacitor C VB1 The voltage ripple peak-to-peak value is half. With the cross-capacitor C VB1 As the capacitance increases, the cross-capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with the cross-connect capacitor C VB1As the capacitance increases, u decreases. VB1 and u VB2 The voltage will be closer. So when the capacitor C is connected VB1 , C VB2 , C VB3 When the voltage of each lithium-ion battery cell is large enough, the voltage of each lithium-ion battery cell is equal. Assuming that the SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value, when the switch S1 is turned on, the DC input source charges the jumper capacitor and inductor. After the switch is turned off, the auxiliary capacitor C VB The introduction of can greatly reduce the inter-electrode voltage deviation caused by load imbalance, so that the lithium-ion battery cells with lower energy in the lithium-ion battery pack can obtain more energy and achieve SOC balance of the lithium-ion battery pack.

[0065] Figure 4 This is a simulation diagram of the present invention realizing the balancing of a lithium-ion battery pack with four lithium-ion battery cells connected in series. Figure 4 It can be seen that the starting SOCs of the four battery cells in the battery pack are different, and the other parameters are the same. The SOC of the single lithium-ion battery B1 is higher than the average value. The converter proposed in the present invention can enable the lithium-ion battery cells with lower energy in the lithium-ion battery pack to obtain more energy, and finally the SOCs of the four battery cells are balanced.

[0066] Compared with the traditional converter type balancing structure, the lithium ion battery pack energy balancing circuit of the present invention realizes the balancing of the battery pack by using only one switch, thereby reducing the control difficulty and cost of the circuit.

Claims

1. A lithium-ion battery pack energy balancing circuit, characterized in that: Contains a DC input source, a Buck- Boost converter, n-1 jumper capacitors, n-1 output expansion units, n lithium-ion batteries, where: The Buck-Boost converter includes an inductor L1, a capacitor C1, a switch S1, and a diode D1; DC input source u in The positive electrode is connected to the drain of switch S1, the source of switch S1 is connected to one end of inductor L1 and the cathode of diode D1, one end of capacitor C1 is connected to the anode of diode D1, and the other end of inductor L1 and capacitor C1 are connected to the DC input source u in negative electrode; The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; one end of the inductor L2 is connected to the cathode of the diode D2, one end of the capacitor C2 is connected to the anode of the diode D2, and the other end of the capacitor C2 is connected to the other end of the inductor L2; The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3; ... and so on. The n-1th output expansion unit includes an inductor L n , capacitor C n 、Diode D n ; Inductor L n One end is connected to diode D n The cathode of the capacitor C n One end of the diode D n The anode of the capacitor C n The other end of the inductor is connected to n The other end; The connection between the jumper capacitor and each output expansion unit is as follows: Cross-over capacitor C VB1 One end of the diode D1 is connected to the cathode, one end of the inductor L1, and the capacitor C VB1 The other end is connected to the cathode of diode D2 and one end of inductor L2 respectively; Cross-over capacitor C VB2 One end of the diode D2 is connected to the cathode, one end of the inductor L2, and the capacitor C is connected across the VB2 The other end is connected to the cathode of diode D3 and one end of inductor L3 respectively; Cross-over capacitor C VB(n-2) One end of each diode D n-2 The cathode, inductance L n-2 One end, across the capacitor C VB(n-2) The other end is connected to the diode D n-1 The cathode, inductance L n-1 one end; ... and so on. Cross-over capacitor C VB(n-1) One end of each diode D n-1 The cathode, inductance L n-1 One end, across the capacitor C VB(n-1) The other end is connected to the diode D n The cathode, inductance L n one end; The connection between the lithium-ion battery and each output expansion unit is as follows: The positive electrode of the lithium-ion battery B1 is connected to the anode of the diode D1 and one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and one end of the inductor L1; The positive electrode of the lithium-ion battery B2 is connected to the anode of the diode D2 and one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and one end of the inductor L2; Lithium-ion battery B n-1 The positive poles of the diodes D n-1 Anode, capacitor C n-1 One end of the lithium-ion battery B n-1 The negative electrodes are connected to capacitor C n-1 The other end of the inductor L n-1 one end of ... and so on. Lithium-ion battery B n The positive poles of the diodes D n Anode, capacitor C n One end of the lithium-ion battery B n The negative electrodes are connected to capacitor C n The other end of the inductor L n one end.

2. The lithium-ion battery pack energy balancing circuit according to claim 1, characterized in that: The gates of the switches S1 are connected to a controller, and the duty cycle of the switches S1 can be changed between 0 and 1.

3. A lithium-ion battery pack energy balancing circuit, characterized in that: It includes a DC input source, a Buck-Boost converter, 3 jumper capacitors, 3 output expansion units, and 4 lithium-ion batteries, including: A Buck-Boost converter includes an inductor L1, a capacitor C1, a switch S1, and a diode D1; DC input source u in The positive electrode is connected to the drain of switch S1, the source of switch S1 is connected to one end of inductor L1 and the cathode of diode D1, one end of capacitor C1 is connected to the anode of diode D1, and the other end of inductor L1 and capacitor C1 are connected to the DC input source u in negative electrode; The first output expansion unit includes an inductor L2, a capacitor C2, and a diode D2; one end of the inductor L2 is connected to the cathode of the diode D2, one end of the capacitor C2 is connected to the anode of the diode D2, and the other end of the capacitor C2 is connected to the other end of the inductor L2; The second output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3; The third output expansion unit includes an inductor L3, a capacitor C3, and a diode D3; one end of the inductor L3 is connected to the cathode of the diode D3, one end of the capacitor C3 is connected to the anode of the diode D3, and the other end of the capacitor C3 is connected to the other end of the inductor L3; The connection between the jumper capacitor and each output expansion unit is as follows: Cross-over capacitor C VB1 One end of the diode D1 is connected to the cathode, one end of the inductor L1, and the capacitor C VB1 The other end is connected to the cathode of diode D2 and one end of inductor L2 respectively; Cross-over capacitor C VB2 One end of the diode D2 is connected to the cathode, one end of the inductor L2, and the capacitor C is connected across the VB2 The other end is connected to the cathode of diode D3 and one end of inductor L3 respectively; Cross-over capacitor C VB3 One end of the diode D3 and one end of the inductor L3 are connected to the cathode of the diode D3 and one end of the inductor L3, and the capacitor C VB3 The other end is connected to the cathode of diode D4 and one end of inductor L4 respectively; The connection between the lithium-ion battery and each output expansion unit is as follows: The positive electrode of the lithium-ion battery B1 is connected to the anode of the diode D1 and one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1 and one end of the inductor L1; The positive electrode of the lithium-ion battery B2 is connected to the anode of the diode D2 and one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2 and one end of the inductor L2; The positive electrode of the lithium-ion battery B3 is connected to the anode of the diode D3 and one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3 and one end of the inductor L3; The positive electrode of the lithium-ion battery B4 is connected to the anode of the diode D4 and one end of the capacitor C4, respectively, 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, respectively.

4. The lithium-ion battery pack energy balancing circuit according to claim 3, characterized in that: In a switching cycle, according to the inductor volt-second balance principle, the average voltage of inductors L1, L2, L3, and L4 is 0, and the following is written: L1→C2→L2→ C VB1 The loop KVL equation can be obtained by the cross-connected capacitance C VB1 The voltage u VB1 Equal to the output voltage u B2 Similarly, the cross-connect capacitor C VB2 The voltage u VB2 Equal to the output voltage u B3 , the cross-capacitor C VB3 The voltage u VB3 Equal to the output voltage u B4 ; When the switch S1 is turned on, the diodes D1, D2, D3, and D4 are turned off, and the DC input source u in Inductors L1, L2, L3, L4 and capacitors C1, C2, C3, C4 supply power to the load. When switch S1 is turned off, diodes D1, D2, D3, D4 are turned on, and inductors L i Through the loop L i →C i →D i →L i To capacitor C i Charging, if the SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value, the initial voltage u VB1 <u VB2 ; When switch S1 is turned off, the capacitor C VB1 The diode D1 in the circuit is not conducting, and the capacitor C VB1 Discharge until the capacitor C VB1 The voltage u VB1 The output voltage u of the circuit drops to B1 When the voltage is equal to the value of the diode D1, it starts to conduct. Assuming that 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 approximately considered as u B1 The average voltage is equal to the capacitance C VB1 The minimum voltage during the switch off phase, therefore, u VB1 and u VB2 The voltage deviation Δu is equal to the difference between the minimum voltage and the average value, that is, the cross-capacitor capacitance C VB1 Half of the peak-to-peak voltage ripple; with the cross-connect capacitor C VB1 As the capacitance increases, the cross-capacitor C VB1 The voltage ripple will become smaller and smaller, so the output voltage deviation will increase with the cross-connect capacitor C VB1 As the capacitance increases, u decreases. VB1 and u VB2 The voltages will be closer; Therefore, when the capacitor C VB1 , C VB2 , C VB3 When large enough, the voltages of the individual lithium-ion battery cells are equal.

5. The lithium-ion battery pack energy balancing circuit according to claim 3, characterized in that: The SOC of the single lithium-ion battery B1 in the lithium-ion battery pack is lower than the average value. When the switch S1 is turned on, the DC input source charges the jumper capacitor and inductor. After the switch is turned off, the auxiliary capacitor C VB The introduction of can greatly reduce the inter-electrode voltage deviation caused by load imbalance, so that the lithium-ion battery cells with lower energy in the lithium-ion battery pack can obtain more energy and achieve SOC balance of the lithium-ion battery pack.

Images