Lithium ion battery SOC active equalization circuit based on improved Sepic converter

Abstract

A lithium ion battery SOC active equalization circuit based on an improved Sepic converter comprises an n-path output improved Sepic converter, n-1 bridging capacitors and n lithium ion batteries, and the n-path output improved Sepic converter comprises a direct current input source Vin, two input inductors L1 and L2, a power switch S1, two input capacitors C1 and C2, a first capacitor C1, a second capacitor C2 and a third capacitor C1, the first output diodes D11 and D12, the output capacitor C11, the second output diodes D21 and D22, the output capacitor C21,..., and so on; and the nth path outputs diodes Dn1 and Dn2 and an output capacitor Cn1. Compared with a traditional multi-path series equalization structure, automatic voltage equalization between the battery units is achieved through the bridging capacitors, complex sampling and control algorithms are not needed, voltage deviation is effectively reduced, and the battery equalization precision is improved.

Description

Technical Field

[0001] The invention relates to the technical field of battery equalization, and in particular to a lithium-ion battery SOC active equalization circuit based on an improved Sepic converter. Background Art

[0002] Lithium-ion batteries occupy a core position in the electric vehicle power battery market due to their outstanding energy density, long-term cycle stability, no memory effect, and high efficiency and environmentally friendly characteristics. However, the voltage and capacity limitations of single cells make it difficult to directly meet the high performance requirements of electric vehicles. Therefore, building a battery pack composed of multiple batteries in series and parallel has become an inevitable choice. However, this combination strategy also raises new problems: manufacturing differences, operating environment differences, and different charging and discharging strategies lead to mismatches in capacity, voltage, internal resistance, etc. among the single cells in the battery pack, which not only weakens the overall durability and reliability of the battery pack, but also poses a severe challenge to the safety of the system. Therefore, in order to maintain the balance of single cells in lithium-ion battery packs, researchers have proposed many balancing circuits, devices, and methods. Current battery balancing technologies are mainly divided into passive balancing and active balancing. Passive balancing consumes excess energy in the form of heat through resistance, but this method will cause energy loss in the battery pack, and the high temperature environment caused by improper heat dissipation will damage the performance of the battery pack.

[0003] Active balancing technology is to transfer energy from a higher battery cell to a lower battery cell. For example, the patent document with application publication number CN113489083A discloses a hierarchical balancing control method for lithium-ion battery packs based on a buck-boost converter. This method adds multiple energy storage inductance elements, diodes, and balancing control switches to the lithium-ion battery pack. By controlling the switch to close, the single battery with higher energy storage stores excess energy in the corresponding inductance, and then controls the switch to close to transfer the energy in the inductance to the single battery with lower energy storage, forming a balancing control of the series lithium-ion battery pack. In addition, two adjacent single batteries are formed into a small module, and then the adjacent small modules are formed into a large module. Through logical control, each level is balanced to achieve three-level balancing control. The balancing control method proposed in this patent can not only achieve balancing between two adjacent single batteries, but also indirectly achieve balancing between two non-adjacent single batteries through balancing control between adjacent modules, shortening the energy transmission path and improving the efficiency of the battery pack balancing system. However, the balancing circuit used in this control method includes multiple control switches, and the logical control is very complex. Summary of the invention

[0004] In order to solve the shortcomings of the existing lithium-ion battery pack balancing technology, the present invention proposes a lithium-ion battery SOC active balancing circuit based on an improved Sepic converter, and the active balancing circuit is composed of a multi-channel output improved Sepic converter and a plurality of cross-over capacitors. The active balancing circuit is based on the improved Sepic converter circuit, and proposes a lithium-ion battery SOC active balancing circuit based on the improved Sepic converter. The circuit includes an n-channel output improved Sepic converter, n cross-over capacitors and n lithium-ion batteries, and output consistency is achieved by adding a cross-over capacitor between each channel. Compared with the traditional multi-series Sepic circuit balancing structure, the present invention realizes automatic voltage balancing between battery cells through cross-over capacitors, does not require complex sampling and control algorithms, and avoids the problem of terminal voltage imbalance caused by cross-regulation rate when the multi-series Sepic circuit outputs; effectively reduces voltage deviation and improves battery balancing accuracy.

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

[0006] The lithium-ion battery SOC active balancing circuit based on the improved Sepic converter includes an n-way output improved Sepic converter, n-1 cross-connected capacitors, and n lithium-ion batteries, wherein:

[0007] An n-output improved Sepic converter includes a DC input source V in , 2 input inductors L1 and L2, a power switch S1, 2 input capacitors C1 and C2, and:

[0008] The first output diode D 11 and D 12 , output capacitor C 11 ,

[0009] The second output diode D 21 and D 22 , output capacitor C 21 ,

[0010] ... and so on;

[0011] The nth output diode D n1 and D n2 , output capacitor C n1 ;

[0012] The connection form of the n-way output improved Sepic converter is as follows:

[0013] DC input source V inThe positive electrode of the input inductor L1 is connected to the input end of the input inductor L1, the output end of the input inductor L1 is connected to the intersection of the drain of the power switch S1 and the input end of the input capacitor C1, the output end of the input capacitor C1 is connected to one end of the input inductor L2, the other end of the input inductor L2 is connected to one end of the input capacitor C2, and the other end of the input capacitor C2 is connected to the DC input source V in The negative electrode of is connected to the intersection of the source of the power switch S1, and the gate of the power switch S1 is connected to the controller;

[0014] Diode D 11 The cathode of the diode D 12 The anode of the diode D 12 The cathode and output capacitor C 11 One end of the output capacitor C 11 The other end of the diode D 11 Anode connection;

[0015] Diode D 21 The cathode of the diode D 22 The anode of the diode D 22 The cathode and output capacitor C 21 One end of the output capacitor C 21 The other end of the diode D 21 Anode connection;

[0016] ... and so on;

[0017] Diode D n1 The cathode of the diode D n2 The anode of the diode D n2 The cathode and output capacitor C n1 One end of the output capacitor C n1 The other end of the diode D n1 anode connection.

[0018] Diode D n1 The anode of is connected to the other end of the input capacitor C2;

[0019] The connection between the jumper capacitor and each output is as follows:

[0020] Capacitor C m1 One end of the capacitor is connected to the output end of the input capacitor C1. m1 The other end of the diode D 11 The cathode of the diode D 12 The intersection of the anode is connected;

[0021] Capacitor C m2 One end of the capacitor C m1 One end of the capacitor C m2The other end of the diode D 21 The cathode of the diode D 22 The intersection of the anode is connected;

[0022] ... and so on;

[0023] Capacitor C mn One end of the capacitor C m(n-1) One end of the capacitor C mn The other end of the diode D n1 The cathode of the diode D n2 The intersection of the anodes is connected.

[0024] The connection form of n lithium-ion batteries and n-output improved Sepic converter is as follows:

[0025] One end of the lithium-ion battery B1 is connected to the diode D 12 The cathode and capacitor C 11 The other end of the lithium-ion battery B1 is connected to the intersection of the diode D 11 The anode and capacitor C 11 The other end of the intersection is connected;

[0026] One end of the lithium-ion battery B2 is connected to the diode D 22 The cathode and capacitor C 21 The other end of the lithium-ion battery B2 is connected to the intersection of the diode D 21 The anode and capacitor C 21 The other end of the intersection is connected;

[0027] ... and so on;

[0028] Lithium-ion battery B n One end of the diode D n2 The cathode and capacitor C n1 One end of the lithium-ion battery B is connected to the intersection of n The other end of the diode D n1 The anode and capacitor C n1 The other end of the intersection is connected;

[0029] The connection between n lithium-ion batteries is as follows:

[0030] The other end of the lithium-ion battery B1 is connected to one end of the lithium-ion battery B2;

[0031] The other end of the lithium-ion battery B2 is connected to one end of the lithium-ion battery B3;

[0032] ... and so on;

[0033] Lithium-ion battery B n-1The other end of the lithium-ion battery B n one end of the .

[0034] The gate of the power switch S1 is connected to a controller, and its duty cycle can be changed between 0 and 1.

[0035] The lithium-ion battery SOC active balancing circuit based on the improved Sepic converter includes a 4-way output improved Sepic converter, 4 cross-connected capacitors, and 4 lithium-ion batteries, wherein:

[0036] A 4-way output improved Sepic converter consists of a DC input source V in , 2 input inductors L1 and L2, a power switch S1, 2 input capacitors C1 and C2, the first output diode D 11 and D 12 , output capacitor C 11 , the second output diode D 21 and D 22 , output capacitor C 21 , the third output diode D 31 and D 32 , output capacitor C 31 , the fourth output diode D 41 and D 42 , output capacitor C 41 .

[0037] The connection form of the 4-way output improved Sepic converter is as follows:

[0038] DC input source V in The positive electrode of the input inductor L1 is connected to the input end of the input inductor L1, the output end of the input inductor L1 is connected to the intersection of the drain of the power switch S1 and the input end of the input capacitor C1, the output end of the input capacitor C1 is connected to one end of the input inductor L2, the other end of the input inductor L2 is connected to one end of the input capacitor C2, and the other end of the input capacitor C2 is connected to the DC input source V in The cathode of the diode D is connected to the intersection of the source of the power switch S1, and the gate of S1 is connected to the controller. 11 The cathode of the diode D 12 The anode of the diode D 12 The cathode and output capacitor C 11 One end of the output capacitor C 11 The other end of the diode D 11 Anode connection of diode D 21 The cathode of the diode D 22 The anode of the diode D 22 The cathode and output capacitor C 21 One end of the output capacitor C 21The other end of the diode D 21 Anode connection of diode D 31 The cathode of the diode D 32 The anode of the diode D 32 The cathode and output capacitor C 31 One end of the output capacitor C 31 The other end of the diode D 31 Anode connection of diode D 41 The cathode of the diode D 42 The anode of the diode D 42 The cathode and output capacitor C 41 One end of the output capacitor C 41 The other end of the diode D 41 The anode of diode D is connected. 41 The anode of is connected to the other end of the input capacitor C2.

[0039] The connection between the jumper capacitor and each output is as follows:

[0040] Capacitor C m1 One end of the capacitor is connected to the output end of the input capacitor C1. m1 The other end of the diode D 11 The cathode of the diode D 12 The intersection of the anode of m2 One end of the capacitor C m1 One end of the capacitor C m2 The other end of the diode D 21 The cathode of the diode D 22 The intersection of the anode of m3 One end of the capacitor C m2 One end of the capacitor C m3 The other end of the diode D 31 The cathode of the diode D 32 The anode of capacitor C is connected to the intersection of m4 One end of the capacitor C m3 One end of the capacitor C m4 The other end of the diode D 41 The cathode of the diode D 42 The intersection of the anodes is connected.

[0041] The connection between 4 lithium-ion batteries and the 4-way output improved Sepic converter is as follows:

[0042] One end of the lithium-ion battery B1 is connected to the diode D 12 The cathode and capacitor C 11 The other end of the lithium-ion battery B1 is connected to the intersection of the diode D11 The anode and capacitor C 11 The other end of the lithium ion battery B2 is connected to the intersection of the diode D 22 The cathode and capacitor C 21 The other end of the lithium-ion battery B2 is connected to the intersection of the diode D 21 The anode and capacitor C 21 The other end of the lithium ion battery B3 is connected to the intersection of the diode D 32 The cathode and capacitor C 31 The other end of the lithium-ion battery B3 is connected to the intersection of the diode D 31 The anode and capacitor C 31 The other end of the lithium ion battery B4 is connected to the intersection of the diode D 42 The cathode and capacitor C 41 The other end of the lithium-ion battery B4 is connected to the intersection of the diode D 41 The anode and capacitor C 41 The other end is connected to the intersection point.

[0043] The connection between the 4 lithium-ion batteries is as follows:

[0044] The other end of lithium ion battery B1 is connected to one end of lithium ion battery B2, the other end of lithium ion battery B2 is connected to one end of lithium ion battery B3, and the other end of lithium ion battery B3 is connected to one end of lithium ion battery B4.

[0045] Take the battery pack composed of four single lithium-ion batteries B1, B2, B3, and B4 connected in series as an example.

[0046] When the power switch S1 is in the on mode, the diode D 11 , D 21 , D 31 , D 41 Conducting, diode D 12 , D 22 , D 32 , D 42 Shutdown. Input voltage source V in , inductor L1 and power switch S1 form a closed loop, inductor L1 is charged. Power switch S1, capacitor C1, capacitor C2 and inductor L2 form a closed loop, capacitor C1 is charged, inductor L2 is discharged, and capacitor C2 is charged. Inductor L2 charges capacitor C m1 , capacitor C m2 , capacitor C m3 and capacitor C m4 Charging, inductor L2 to capacitor C 11 And lithium-ion battery B1, capacitor C 21 And lithium-ion battery B2, capacitor C31 And lithium-ion battery B3, capacitor C 41 And charge the lithium-ion battery B4.

[0047] When the power switch S1 is in the off mode, the diode D 11 , D 21 , D 31 , D 41 Turn off, diode D 12 , D 22 , D 32 , D 42 The input voltage source V in , inductor L1 and capacitor C1, capacitor C2 and inductor L2 form a closed loop, inductor L1 discharges, capacitor C1, capacitor C2 and inductor L2 charge. m1 、Diode D 12 and capacitor C 11 , C 21 , C 31 , C 41 The inductor L2, the capacitor C2, and the capacitor C m2 、Diode D 22 , capacitor C 21 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m2 , C 21 , C 31 , C 41 Charging. Inductor L2, capacitor C2, capacitor C m3 、Diode D 32 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m3 , C 31 , C 41 Charging. Inductor L2, capacitor C2, capacitor C m4 、Diode D 42 , capacitor C 41 The circuit is composed of capacitor C m4 , C 41 Charge.

[0048] The principle of battery balancing is to maintain the various lithium-ion battery cells in a series-connected lithium-ion battery pack in a balanced state. Currently, the balance of the entire lithium-ion battery pack is mainly determined by whether the terminal voltage of the lithium-ion battery cells is balanced.

[0049] When switch S1 is turned on, there is a loop C m1 →D 11 →C 21 →D 21 →Cm2 →C m1 , from the KVL theorem we know that u C21 =u Cm1 +u Cm2 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; Similarly, there is a loop C m2 →D 21 →C 31 →D 31 →C m3 →C m2 , from the KVL theorem we know that u C31 =u Cm2 +u Cm3 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 ; There is a loop C m3 →D 31 →C 41 →D 41 →C m4 →C m3 , from the KVL theorem we know that u C41 =u Cm3 +u Cm4 , there is a loop C 41 →B4→C 41 , from the KVL theorem we know that u C41 =u B4 ;

[0050] When switch S1 is turned off, there is a loop C m1 →D 12 →C 11 →D 22 →C m2 →C m1 , from the KVL theorem we know that u C11 =u Cm1 +u Cm2 , there is a loop C 11 →B1→C 11 , from the KVL theorem we know that u C11 =u B1 ; Similarly, there is a loop C m2 →D 22 →C 21 →D 32 →C m3 →C m2 , from the KVL theorem we know that u C21 =u Cm2 +uCm3 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; There is a loop C m3 →D 32 →C 31 →D 42 →C m4 →C m3 , from the KVL theorem we know that u C31 =u Cm3 +u Cm4 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 In the entire switching cycle, according to the capacitance ampere-second balance principle and the above analysis, it can be known that u C11 =u C21 、u C21 =u C31 and u 31 =u 41 , then u C11 =u C21 =u C31 =u C41 , then u B1 =u B2 =u B3 =u B4 , that is, the voltage of each lithium-ion battery cell is equal, achieving the balance of the lithium-ion battery pack.

[0051] The present invention provides a lithium-ion battery SOC active equalization circuit based on an improved Sepic converter, and the technical effects are as follows:

[0052] 1) The active balancing circuit of the present invention achieves the effect of automatic voltage balancing of the output voltage of the multi-channel output improved Sepic converter by connecting a jumper capacitor to the output of the multi-channel output improved Sepic converter, thereby improving the battery balancing degree.

[0053] 2) The active 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

[0054] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0055] Figure 1 It is the circuit principle diagram of the present invention;

[0056] Figure 2 The circuit schematic diagram of the present invention is to realize SOC balancing of a battery pack with four single cells connected in series.

[0057] 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

[0058] like Figure 3 As shown, the lithium-ion battery SOC active balancing circuit based on the improved Sepic converter includes a 4-way output improved Sepic converter, 4 cross-connected capacitors, and 4 lithium-ion batteries, wherein:

[0059] A 4-way output improved Sepic converter consists of a DC input source V in , 2 input inductors L1 and L2, a power switch S1, 2 input capacitors C1 and C2, the first output diode D 11 and D 12 , output capacitor C 11 , the second output diode D 21 and D 22 , output capacitor C 21 , the third output diode D 31 and D 32 , output capacitor C 31 , the fourth output diode D 41 and D 42 , output capacitor C 41 .

[0060] The connection form of the 4-way output improved Sepic converter is as follows: DC input source V in The positive electrode of the input inductor L1 is connected to the input end of the input inductor L1, the output end of the input inductor L1 is connected to the intersection of the drain of the power switch S1 and the input end of the input capacitor C1, the output end of the input capacitor C1 is connected to one end of the input inductor L2, the other end of the input inductor L2 is connected to one end of the input capacitor C2, and the other end of the input capacitor C2 is connected to the DC input source V in The cathode of the diode D is connected to the intersection of the source of the power switch S1, and the gate of S1 is connected to the controller. 11 The cathode of the diode D 12 The anode of the diode D 12 The cathode and output capacitor C 11 One end of the output capacitor C 11 The other end of the diode D 11 Anode connection of diode D 21 The cathode of the diode D 22 The anode of the diode D 22 The cathode and output capacitor C 21 One end of the output capacitor C 21 The other end of the diode D 21Anode connection of diode D 31 The cathode of the diode D 32 The anode of the diode D 32 The cathode and output capacitor C 31 One end of the output capacitor C 31 The other end of the diode D 31 Anode connection of diode D 41 The cathode of the diode D 42 The anode of the diode D 42 The cathode and output capacitor C 41 One end of the output capacitor C 41 The other end of the diode D 41 The anode of diode D is connected. 41 The anode of is connected to the other end of the input capacitor C2.

[0061] The connection between the jumper capacitor and each output is as follows: Capacitor C m1 One end of the capacitor is connected to the output end of the input capacitor C1. m1 The other end of the diode D 11 The cathode of the diode D 12 The intersection of the anode of m2 One end of the capacitor C m1 One end of the capacitor C m2 The other end of the diode D 21 The cathode of the diode D 22 The intersection of the anode of m3 One end of the capacitor C m2 One end of the capacitor C m3 The other end of the diode D 31 The cathode of the diode D 32 The anode of capacitor C is connected to the intersection of m4 One end of the capacitor C m3 One end of the capacitor C m4 The other end of the diode D 41 The cathode of the diode D 42 The intersection of the anodes is connected.

[0062] The connection form of the multi-output battery unit is as follows: one end of the lithium-ion battery B1 is connected to the diode D 12 The cathode and capacitor C 11 The other end of the lithium-ion battery B1 is connected to the intersection of the diode D 11 The anode and capacitor C 11 The other end of the lithium ion battery B2 is connected to the intersection of the diode D 22 The cathode and capacitor C 21The other end of the lithium-ion battery B2 is connected to the intersection of the diode D 21 The anode and capacitor C 21 The other end of the lithium ion battery B3 is connected to the intersection of the diode D 32 The cathode and capacitor C 31 The other end of the lithium-ion battery B3 is connected to the intersection of the diode D 31 The anode and capacitor C 31 The other end of the lithium ion battery B4 is connected to the intersection of the diode D 42 The cathode and capacitor C 41 The other end of the lithium-ion battery B4 is connected to the intersection of the diode D 41 The anode and capacitor C 41 The other end of lithium ion battery B1 is connected to one end of lithium ion battery B2, the other end of lithium ion battery B2 is connected to one end of lithium ion battery B3, and the other end of lithium ion battery B3 is connected to one end of lithium ion battery B4.

[0063] The gate of the power switch S1 is connected to the controller, and its duty cycle can be changed between 0 and 1. When the power switch S1 is in the on mode, the diode D 11 , D 21 , D 31 , D 41 Conducting, diode D 12 , D 22 , D 32 , D 42 Shutdown. Input voltage source V in , inductor L1 and power switch S1 form a closed loop, inductor L1 is charged. Power switch S1, capacitor C1, capacitor C2 and inductor L2 form a closed loop, capacitor C1 is charged, inductor L2 is discharged, and capacitor C2 is charged. Inductor L2 charges capacitor C m1 , capacitor C m2 , capacitor C m3 and capacitor C m4 Charging, inductor L2 to capacitor C 11 And lithium-ion battery B1, capacitor C 21 And lithium-ion battery B2, capacitor C 31 And lithium-ion battery B3, capacitor C 41 And charge the lithium-ion battery B4.

[0064] When the power switch S1 is in the off mode, the diode D 11 , D 21 , D 31 , D 41 Turn off, diode D 12 , D 22, D 32 , D 42 The input voltage source V in , inductor L1 and capacitor C1, capacitor C2 and inductor L2 form a closed loop, inductor L1 discharges, capacitor C1, capacitor C2 and inductor L2 charge. m1 、Diode D 12 and capacitor C 11 , C 21 , C 31 , C 41 The inductor L2, the capacitor C2, and the capacitor C m2 、Diode D 22 , capacitor C 21 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m2 , C 21 , C 31 , C 41 Charging. Inductor L2, capacitor C2, capacitor C m3 、Diode D 32 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m3 , C 31 , C 41 Charging. Inductor L2, capacitor C2, capacitor C m4 、Diode D 42 , capacitor C 41 The circuit is composed of capacitor C m4 , C 41 Charge.

[0065] The principle of battery balancing is to maintain the various lithium-ion battery cells in a series-connected lithium-ion battery pack in a balanced state. Currently, the balance of the entire lithium-ion battery pack is mainly determined by whether the terminal voltage of the lithium-ion battery cells is balanced.

[0066] When switch S1 is turned on, there is a loop C m1 →D 11 →C 21 →D 21 →C m2 →C m1 , from the KVL theorem we know that u C21 =u Cm1 +u Cm2 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; Similarly, there is a loop C m2 →D21 →C 31 →D 31 →C m3 →C m2 , from the KVL theorem we know that u C31 =u Cm2 +u Cm3 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 ; There is a loop C m3 →D 31 →C 41 →D 41 →C m4 →C m3 , from the KVL theorem we know that u C41 =u Cm3 +u Cm4 , there is a loop C 41 →B4→C 41 , from the KVL theorem we know that u C41 =u B4 ;

[0067] When switch S1 is turned off, there is a loop C m1 →D 12 →C 11 →D 22 →C m2 →C m1 , from the KVL theorem we know that u C11 =u Cm1 +u Cm2 , there is a loop C 11 →B1→C 11 , from the KVL theorem we know that u C11 =u B1 ; Similarly, there is a loop C m2 →D 22 →C 21 →D 32 →C m3 →C m2 , from the KVL theorem we know that u C21 =u Cm2 +u Cm3 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; There is a loop C m3 →D 32 →C 31 →D 42 →C m4 →C m3, from the KVL theorem we know that u C31 =u Cm3 +u Cm4 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 .

[0068] During the entire switching cycle, according to the capacitance ampere-second balance principle and the above analysis, it can be known that u C11 =u C21 、u C21 =u C31 and u 31 =u 41 , then u C11 =u C21 =u C31 =u C41 , then u B1 =u B2 =u B3 =u B4 , that is, the voltage of each lithium-ion battery cell is equal, achieving the balance of the lithium-ion battery pack.

[0069] 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 3 It can be seen that when charging multiple groups of batteries with different initial SOCs (State of Charge), different battery SOCs are constantly balanced and charged to the same SOC, and quickly reach a relatively stable and close SOC value, indicating that the topology has a good balanced charging effect and a fast speed.

[0070] The present invention is based on the lithium-ion battery SOC active equalization circuit of the improved Sepic converter, and achieves output consistency by adding a crossover capacitor between each path. Compared with the traditional multi-path series equalization structure, the present invention realizes automatic voltage equalization between battery cells through the crossover capacitor, without the need for complex sampling and control algorithms, effectively reducing voltage deviation and improving battery equalization accuracy.

Claims

1. A lithium-ion battery SOC active equalization circuit based on an improved Sepic converter, characterized in that: It includes an n-way output improved Sepic converter, n-1 jumper capacitors, and n lithium-ion batteries, where: An n-output improved Sepic converter includes a DC input source V in , 2 input inductors L1 and L2, a power switch S1, 2 input capacitors C1 and C2, and: The first output diode D 11 and D 12 , output capacitor C 11 , The second output diode D 21 and D 22 , output capacitor C 21 , ... and so on; The nth output diode D n1 and D n2 , output capacitor C n1 ; The connection form of the n-way output improved Sepic converter is as follows: DC input source V in The positive electrode of the input inductor L1 is connected to the input end of the input inductor L1, the output end of the input inductor L1 is connected to the intersection of the drain of the power switch S1 and the input end of the input capacitor C1, the output end of the input capacitor C1 is connected to one end of the input inductor L2, the other end of the input inductor L2 is connected to one end of the input capacitor C2, and the other end of the input capacitor C2 is connected to the DC input source V in The negative electrode of is connected to the intersection of the source of the power switch S1, and the gate of the power switch S1 is connected to the controller; Diode D 11 The cathode of the diode D 12 The anode of the diode D 12 The cathode and output capacitor C 11 One end of the output capacitor C 11 The other end of the diode D 11 Anode connection; Diode D 21 The cathode of the diode D 22 The anode of the diode D is connected 22 The cathode and output capacitor C 21 One end of the output capacitor C 21 The other end of the diode D 21 Anode connection; ... and so on; Diode D n1 The cathode of the diode D n2 The anode of the diode D is connected n2 The cathode and output capacitor C n1 One end of the output capacitor C n1 The other end of the diode D n1 Anode connection; Diode D n1 The anode of is connected to the other end of the input capacitor C2; The connection between the jumper capacitor and each output is as follows: Capacitor C m1 One end of the capacitor is connected to the output end of the input capacitor C1. m1 The other end of the diode D 11 The cathode of the diode D 12 The intersection of the anode is connected; Capacitor C m2 One end of the capacitor C m1 One end of the capacitor C m2 The other end of the diode D 21 The cathode of the diode D 22 The intersection of the anode is connected; ... and so on; Capacitor C mn One end of the capacitor C m(n-1) One end of the capacitor C mn The other end of the diode D n1 The cathode of the diode D n2 The intersection of the anode is connected; The connection form of n lithium-ion batteries and n-output improved Sepic converter is as follows: One end of the lithium-ion battery B1 is connected to the diode D 12 The cathode and capacitor C 11 The other end of the lithium-ion battery B1 is connected to the intersection of the diode D 11 The anode and capacitor C 11 The other end of the intersection is connected; One end of the lithium-ion battery B2 is connected to the diode D 22 The cathode and capacitor C 21 The other end of the lithium-ion battery B2 is connected to the intersection of the diode D 21 The anode and capacitor C 21 The other end of the intersection is connected; ... and so on; Lithium-ion battery B n One end of the diode D n2 The cathode and capacitor C n1 One end of the lithium-ion battery B is connected to the intersection of n The other end of the diode D n1 The anode and capacitor C n1 The other end of the intersection is connected; The connection between n lithium-ion batteries is as follows: The other end of the lithium-ion battery B1 is connected to one end of the lithium-ion battery B2; The other end of the lithium-ion battery B2 is connected to one end of the lithium-ion battery B3; ... and so on; Lithium-ion battery B n-1 The other end of the lithium-ion battery B n one end of the .

2. The lithium-ion battery SOC active equalization circuit based on the improved Sepic converter according to claim 1, characterized in that: The gate of the power switch S1 is connected to a controller, and its duty cycle can be changed between 0 and 1.

3. Lithium-ion battery SOC active equalization circuit based on improved Sepic converter, characterized by: It contains a 4-way output improved Sepic converter, 4 jumper capacitors, and 4 lithium-ion batteries, including: A 4-way output improved Sepic converter consists of a DC input source V in , 2 input inductors L1 and L2, a power switch S1, 2 input capacitors C1 and C2, the first output diode D 11 and D 12 , output capacitor C 11 , the second output diode D 21 and D 22 , output capacitor C 21 , the third output diode D 31 and D 32 , output capacitor C 31 , the fourth output diode D 41 and D 42 , output capacitor C 41 ; The connection form of the 4-way output improved Sepic converter is as follows: DC input source V in The positive electrode of the input inductor L1 is connected to the input end of the input inductor L1, the output end of the input inductor L1 is connected to the intersection of the drain of the power switch S1 and the input end of the input capacitor C1, the output end of the input capacitor C1 is connected to one end of the input inductor L2, the other end of the input inductor L2 is connected to one end of the input capacitor C2, and the other end of the input capacitor C2 is connected to the DC input source V in The cathode of the diode D is connected to the intersection of the source of the power switch S1, and the gate of S1 is connected to the controller; 11 The cathode of the diode D 12 The anode of the diode D 12 The cathode and output capacitor C 11 One end of the output capacitor C 11 The other end of the diode D 11 Anode connection of diode D 21 The cathode of the diode D 22 The anode of the diode D 22 The cathode and output capacitor C 21 One end of the output capacitor C 21 The other end of the diode D 21 Anode connection of diode D 31 The cathode of the diode D 32 The anode of the diode D 32 The cathode and output capacitor C 31 One end of the output capacitor C 31 The other end of the diode D 31 Anode connection of diode D 41 The cathode of the diode D 42 The anode of the diode D 42 The cathode and output capacitor C 41 One end of the output capacitor C 41 The other end of the diode D 41 Anode connection of diode D 41 The anode of is connected to the other end of the input capacitor C2; The connection between the jumper capacitor and each output is as follows: Capacitor C m1 One end of the capacitor is connected to the output end of the input capacitor C1. m1 The other end of the diode D 11 The cathode of the diode D 12 The intersection of the anode of m2 One end of the capacitor C m1 One end of the capacitor C m2 The other end of the diode D 21 The cathode of the diode D 22 The intersection of the anode of m3 One end of the capacitor C m2 One end of the capacitor C m3 The other end of the diode D 31 The cathode of the diode D 32 The intersection of the anode of m4 One end of the capacitor C m3 One end of the capacitor C m4 The other end of the diode D 41 The cathode of the diode D 42 The intersection of the anode is connected; The connection between 4 lithium-ion batteries and the 4-way output improved Sepic converter is as follows: One end of the lithium-ion battery B1 is connected to the diode D 12 The cathode and capacitor C 11 The other end of the lithium-ion battery B1 is connected to the intersection of the diode D 11 The anode and capacitor C 11 The other end of the lithium ion battery B2 is connected to the intersection of the diode D 22 The cathode and capacitor C 21 The other end of the lithium-ion battery B2 is connected to the intersection of the diode D 21 The anode and capacitor C 21 The other end of the lithium ion battery B3 is connected to the intersection of the diode D 32 The cathode and capacitor C 31 The other end of the lithium-ion battery B3 is connected to the intersection of the diode D 31 The anode and capacitor C 31 The other end of the lithium ion battery B4 is connected to the intersection of the diode D 42 The cathode and capacitor C 41 The other end of the lithium-ion battery B4 is connected to the intersection of the diode D 41 The anode and capacitor C 41 The other end of the intersection is connected; The connection between the 4 lithium-ion batteries is as follows: The other end of lithium ion battery B1 is connected to one end of lithium ion battery B2, the other end of lithium ion battery B2 is connected to one end of lithium ion battery B3, and the other end of lithium ion battery B3 is connected to one end of lithium ion battery B4.

4. The lithium-ion battery SOC active equalization circuit based on the improved Sepic converter according to claim 3 is characterized in that: When the power switch S1 is in the on mode, the diode D 11 , D 21 , D 31 , D 41 Conducting, diode D 12 , D 22 , D 32 , D 42 Shutdown; Input voltage source V in , inductor L1 and power switch S1 form a closed loop, inductor L1 is charged; power switch S1, capacitor C1, capacitor C2 and inductor L2 form a closed loop, capacitor C1 is charged, inductor L2 is discharged, capacitor C2 is charged; inductor L2 supplies capacitor C m1 , capacitor C m2 , capacitor C m3 and capacitor C m4 Charging, inductor L2 to capacitor C 11 And lithium-ion battery B1, capacitor C 21 And lithium-ion battery B2, capacitor C 31 And lithium-ion battery B3, capacitor C 41 and charging of lithium-ion battery B4; When the power switch S1 is in the off mode, the diode D 11 , D 21 , D 31 , D 41 Turn off, diode D 12 , D 22 , D 32 , D 42 On; input voltage source V in , inductor L1 and capacitor C1, capacitor C2 and inductor L2 form a closed loop, inductor L1 discharges, capacitor C1, capacitor C2 and inductor L2 charge; inductor L2, capacitor C2, capacitor C m1 、Diode D 12 and capacitor C 11 , C 21 , C 31 , C 41 The circuit is composed of inductor L2, capacitor C2, capacitor C m2 、Diode D 22 , capacitor C 21 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m2 , C 21 , C 31 , C 41 Charging; inductor L2, capacitor C2, capacitor C m3 、Diode D 32 , capacitor C 31 and capacitor C 41 The circuit is composed of capacitor C m3 , C 31 , C 41 Charging; inductor L2, capacitor C2, capacitor C m4 、Diode D 42 , capacitor C 41 The circuit is composed of capacitor C m4 , C 41 Charge.

5. The lithium-ion battery SOC active equalization circuit based on the improved Sepic converter according to claim 3 is characterized in that: When switch S1 is turned on, there is a loop C m1 →D 11 →C 21 →D 21 →C m2 →C m1 , from the KVL theorem we know that u C21 =u Cm1 +u Cm2 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; Similarly, there is a loop C m2 →D 21 →C 31 →D 31 →C m3 →C m2 , from the KVL theorem we know that u C31 =u Cm2 +u Cm3 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 ; There is a loop C m3 →D 31 →C 41 →D 41 →C m4 → C m3 , from the KVL theorem we know that u C41 =u Cm3 +u Cm4 , there is a loop C 41 →B4→C 41 , from the KVL theorem we know in C41 =in B4 ; When switch S1 is turned off, there is a loop C m1 →D 12 →C 11 →D 22 →C m2 →C m1 , from the KVL theorem we know that u C11 =u Cm1 +u Cm2 , there is a loop C 11 →B1→C 11 , from the KVL theorem we know that u C11 =u B1 ; Similarly, there is a loop C m2 →D 22 →C 21 →D 32 →C m3 →C m2 , from the KVL theorem we know that u C21 =u Cm2 +u Cm3 , there is a loop C 21 →B2→C 21 , from the KVL theorem we know that u C21 =u B2 ; There is a loop C m3 →D 32 →C 31 →D 42 →C m4 →C m3 , from the KVL theorem we know that u C31 =u Cm3 +u Cm4 , there is a loop C 31 →B3→C 31 , from the KVL theorem we know that u C31 =u B3 ; During the entire switching cycle, according to the capacitance ampere-second balance principle and the above analysis, it can be known that u C11 =u C21 、u C21 =u C31 and u 31 =u 41 , then u C11 =u C21 =u C31 =u C41 , then u B1 =u B2 =u B3 =u B4 , that is, the voltage of each lithium-ion battery cell is equal, achieving the balance of the lithium-ion battery pack.

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