State of charge (SOC) self-equalization converter of series lithium ion battery pack

Abstract

The invention relates to an SOC (State of Charge) self-equalization converter of a series lithium ion battery pack, which comprises an n-path output isolation type Sepic converter, n-1 bridging capacitors and n lithium ion batteries, the n-path output isolation type Sepic converter comprises a power switch S1, an inductor Lp1, a capacitor Cp1, an excitation inductor Lm, a transformer T, a first-path output diode D1, an output capacitor C1, a second-path output diode D2, an output capacitor C2,..., and the like, and an nth-path output diode Dn and an output capacitor Cn. On the basis of transformer type equalization, the SOC self-equalization converter of the series battery pack is provided, a circuit comprises an n-winding output SEPIC converter, n-1 bridging capacitors and n lithium ion batteries, and the consistency of the secondary side of a transformer is achieved by adding one bridging capacitor between windings. Compared with other transformer equalization structures, a reset circuit or a reset winding does not need to be additionally arranged, 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 SOC self-equalization converter of a series-connected lithium-ion battery pack. Background Art

[0002] Lithium-ion batteries are widely used as power batteries for electric vehicles due to their low self-discharge rate, long cycle life, no memory effect, high energy efficiency and no pollution. However, the voltage and capacity of a single lithium-ion battery are small, which cannot meet the capacity and power required by electric vehicles. Therefore, multiple lithium-ion batteries need to be connected in series and parallel to form a battery pack. However, differences in factors such as the environment, charge and discharge mode, and chemical properties of lithium batteries during manufacturing and use will lead to inconsistencies in the performance of single cells such as capacity, voltage, and internal resistance. These inconsistencies between single cells will cause problems such as durability, reliability, and safety of the battery pack. Therefore, in order to maintain the balance of single cells in a lithium-ion battery pack, researchers have proposed many equalization circuits, devices, and methods.

[0003] The current battery balancing technology is mainly divided into passive balancing and active balancing. Passive balancing is to consume excess energy in the form of heat through resistance, but this method will cause energy loss of the battery pack, and the high temperature environment caused by improper heat dissipation will damage the performance of the battery pack. Active balancing technology is to transfer energy from higher battery cells to lower battery cells. For example, the patent with application publication number CN117525631A discloses an active lithium-ion battery cell balancing control method, which groups the battery cells in the lithium-ion battery in a group of one and / or two adjacent battery cells in a group, and obtains a number of single battery cells and / or double battery cells; first balance the SOC values ​​of the two battery cells of two adjacent single battery cells, or the two battery cells in one of the double battery cells, and then balance them with the adjacent single battery cells or the balanced double battery cells until the SOC values ​​of all battery cells in the lithium-ion battery are balanced. In addition, the invention discloses a control circuit for balancing lithium-ion battery cells, which uses a logic threshold control method to adjust the size of the lithium-ion battery balancing current, reduce the balancing current and balancing time of the battery pack when charging and discharging electrical equipment at high power, and further reduce the heat generated by the battery. Prevent excessive charging and discharging from damaging the battery cells, thereby extending the battery life. However, the balancing circuit used in the control method contains multiple control switches, and the logic 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 SOC self-balancing converter for a series lithium-ion battery pack, which is composed of a multi-winding SEPIC converter and a plurality of jumper capacitors. The converter is based on transformer-type balancing, adopts a multi-winding transformer balancing topology, and realizes self-balancing of series lithium-ion batteries by adding a jumper capacitor between each winding. Compared with the traditional multi-winding transformer balancing structure, the transformer energy storage has a release loop, and does not require a reset circuit or reset winding; and avoids the problem of terminal voltage imbalance caused by the cross-regulation rate of the transformer when the multi-winding output is effective. The voltage deviation is reduced and the balancing accuracy of the lithium-ion battery is improved.

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

[0006] A SOC self-balancing converter for a series lithium-ion battery pack, the converter comprising: an n-way output isolation type Sepic converter, n-1 cross-connected capacitors, and n lithium-ion batteries, wherein;

[0007] The n-way output isolated Sepic converter includes a power switch S1, an inductor L p1 , capacitor C p1 , Excitation inductance L m , transformer T and:

[0008] The first output diode D1, output capacitor C1,

[0009] The second output diode D2, output capacitor C2,

[0010] ... and so on.

[0011] The nth output diode D n , output capacitor C n ;

[0012] In the n-channel output isolated Sepic converter:

[0013] Inductance L p1 The other end is connected to the drain of power switch S1 and capacitor C p1 One end, capacitor C p1 The other end is connected to the excitation inductor L m One end, the primary winding L of the transformer T p Input side, primary winding L of transformer T p The output ends are connected to the excitation inductor L m The other end, the source of the power switch S1;

[0014] The secondary winding L of the transformer T s1One end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the secondary winding L of the transformer T s1 The other end;

[0015] The secondary winding L of the transformer T s2 One end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the secondary winding L of the transformer T. s2 The other end;

[0016] The secondary winding L of the transformer T s3 One end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the secondary winding L of the transformer T. s3 The other end;

[0017] ...and so on;

[0018] The secondary winding L of the transformer T s(n-1) One end is connected to the anode of the n-1 output diode D3, and the n-1 output diode D n-1 Cathode connected output capacitor C n-1 One end, output capacitor C n-1 The other end is connected to the secondary winding L of transformer T s(n-1) The other end;

[0019] The secondary winding L of the transformer T sn One end is connected to the nth output diode D n Anode, nth output diode D n Cathode connected output capacitor C n One end, output capacitor C n The other end is connected to the secondary winding L of transformer T sn The other end;

[0020] Among n-1 jumper capacitors:

[0021] Cross-over capacitor C p1 One end is connected to the anode of the first output diode D1, and the capacitor C p1 The other end is connected to the anode of the second output diode D2;

[0022] Cross-over capacitor C p2 One end is connected to the anode of the second output diode D2, and the capacitor C p2 The other end is connected to the anode of the third output diode D3;

[0023] Cross-over capacitor C p3One end is connected to the anode of the third output diode D3, and the capacitor C p3 The other end is connected to the anode of the fourth output diode D4;

[0024] ...and so on;

[0025] Cross-over capacitor C p(n-2) One end is connected to the n-2 output diode D n-2 Anode, across capacitor C p(n-2) The other end is connected to the n-1th output diode D n-1 anode;

[0026] Cross-over capacitor C p(n-1) One end is connected to the n-1th output diode D n-1 Anode, across capacitor C p(n-1) The other end is connected to the nth output diode D n anode;

[0027] The connection form of n lithium-ion batteries is as follows:

[0028] The positive electrode of the lithium-ion battery B1 is connected to one end of the output capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the output capacitor C1;

[0029] The positive electrode of the lithium-ion battery B2 is connected to one end of the output capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the output capacitor C2;

[0030] The positive electrode of the lithium-ion battery B3 is connected to one end of the output capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the output capacitor C3;

[0031] ...and so on;

[0032] Lithium-ion battery B n-1 The positive terminal is connected to the output capacitor C n-1 One end, lithium-ion battery B n-1 The negative terminal is connected to the output capacitor C n-1 The other end;

[0033] Lithium-ion battery B n The positive terminal is connected to the output capacitor C n One end, lithium-ion battery B n The negative terminal is connected to the output capacitor C n The other end;

[0034] 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;

[0035] Inductance L p1 One end is connected to the positive electrode of lithium-ion battery B1, and the other end is connected to the positive electrode of lithium-ion battery B n The negative electrode is connected to the source of the power switch S1.

[0036] The gate of the power switch S1 is connected to a controller, and its duty cycle can be changed between 0 and 1.

[0037] A SOC self-balancing converter for a series-connected lithium-ion battery pack containing four lithium-ion battery cells, the converter comprising: a 4-way output isolated Sepic converter, three cross-connected capacitors, and four lithium-ion batteries, wherein:

[0038] The 4-way output isolated Sepic converter includes a power switch S1, an inductor L p1 , capacitor C p1 , Excitation inductance L m , transformer T and:

[0039] The first output diode D1, output capacitor C1,

[0040] The second output diode D2, output capacitor C2,

[0041] The third output diode D3, output capacitor C3,

[0042] The fourth output diode D4, output capacitor C4,

[0043] In the 4-way output isolated Sepic converter:

[0044] Inductance L p1 The other end is connected to the drain of power switch S1 and capacitor C p1 One end, capacitor C p1 The other end is connected to the excitation inductor L m One end, the primary winding L of the transformer T p Input side, primary winding L of transformer T p The output ends are connected to the excitation inductor L m The other end, the source of the power switch S1;

[0045] The secondary winding L of the transformer T s1 One end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the secondary winding L of the transformer T s1 The other end;

[0046] The secondary winding L of the transformer T s2One end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the secondary winding L of the transformer T. s2 The other end;

[0047] The secondary winding L of the transformer T s3 One end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the secondary winding L of the transformer T. s3 The other end;

[0048] The secondary winding L of the transformer T s4 One end is connected to the anode of the fourth output diode D4, the cathode of the fourth output diode D4 is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the secondary winding L of the transformer T. s4 The other end;

[0049] Among the 3 jumper capacitors:

[0050] Cross-over capacitor C p1 One end is connected to the anode of the first output diode D1, and the capacitor C p1 The other end is connected to the anode of the second output diode D2;

[0051] Cross-over capacitor C p2 One end is connected to the anode of the second output diode D2, and the capacitor C p2 The other end is connected to the anode of the third output diode D3;

[0052] Cross-over capacitor C p3 One end is connected to the anode of the third output diode D3, and the capacitor C p3 The other end is connected to the anode of the fourth output diode D4;

[0053] The connection of 4 lithium-ion batteries is as follows:

[0054] The positive electrode of the lithium-ion battery B1 is connected to one end of the output capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the output capacitor C1;

[0055] The positive electrode of the lithium-ion battery B2 is connected to one end of the output capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the output capacitor C2;

[0056] The positive electrode of the lithium-ion battery B3 is connected to one end of the output capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the output capacitor C3;

[0057] The positive electrode of the lithium-ion battery B4 is connected to one end of the output capacitor C4, and the negative electrode of the lithium-ion battery B4 is connected to the other end of the output capacitor C4;

[0058] 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;

[0059] Inductance L p1 One end is connected to the positive electrode of the lithium-ion battery B1, and the negative electrode of the lithium-ion battery B4 is connected to the source of the power switch S1.

[0060] When the power switch S1 is turned on, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned off; the battery pack adds energy to the inductor L through the series connection. p1 On, the excitation inductance L m Discharge, while the primary winding L of transformer T p Transfer energy to the secondary winding L of transformer T s1 , L s2 , L s3 and L s4 The first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode are cut off due to the reverse voltage; the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The cross-over capacitor C p1 , C p2 and C p3 The output capacitors C1, C2, C3 and C4 provide energy for the lithium-ion battery pack.

[0061] When the power switch S1 is turned off, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned on; the inductor L p1 Discharge, transformer excitation inductance L m Charging, energy is added to the primary winding L of transformer T p At the same time, the energy is transferred to the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 On, the capacitor C p1 , C p2 and C p3 discharge, and the output capacitors C1, C2, C3, and C4 charge.

[0062] During the entire switching cycle, the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The average voltage is 0, and L s1 →Cp1 →L s2 →C2→L s1 The KVL principle of the loop can be used to obtain the cross-connected capacitance C p1 The voltage U cp1 Equal to the lithium-ion battery B2 voltage U B2 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B3 B3 , the cross-capacitor C p3 The voltage U cp3 Equal to the voltage U of lithium-ion battery B4 B4 ;

[0063] When the power switch S1 is turned off, diodes D1, D2, D3, and D4 are turned on, and the secondary winding L of the transformer T s1 Through the loop L s1 (C p1 )→D1→C1→L s1 (C p1 ) charges capacitor C1; capacitor C p1 Through the diode D1 and the output capacitor C1 in parallel, the capacitor C p1 The voltage U cp1 Equal to the voltage U of the lithium-ion battery B1 B1 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B2 B2 ; Cross-connect capacitor C p3 The voltage U cp3 Equal to the voltage U of the lithium-ion battery B3 B3 ; When the capacitor C p1 , C p2 , C p3 When the voltage is large enough, the voltages of the lithium-ion battery cells are equal. If there are relatively low-voltage lithium-ion battery cells, the power switch is closed first, and part of the energy of the lithium-ion battery pack is stored in the inductor L on the primary side of the transformer. p1 When the power switch is turned off, the energy is transferred to the lithium-ion battery cells with lower voltage, so that part of the energy of the series lithium-ion battery pack can be transferred to the lithium-ion battery cells with lower energy, achieving the balance of the lithium-ion battery pack.

[0064] The present invention discloses a SOC self-balancing converter for a series-connected lithium-ion battery pack, and the technical effects are as follows:

[0065] 1) The present invention realizes the automatic voltage balancing effect of the output voltage of the multi-channel output isolated SPEIC converter by connecting a jumper capacitor between adjacent output windings of the isolated SPEIC converter, thereby improving the battery balance;

[0066] 2) The converter of the present invention avoids the problem of terminal voltage imbalance caused by the cross regulation rate when the transformer has multiple windings output, effectively reduces voltage deviation, and improves battery balancing accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0068] Figure 1 It is the circuit principle diagram of the present invention;

[0069] Figure 2 The circuit schematic diagram of the present invention is to realize the SOC self-balancing of a battery pack with four single batteries connected in series.

[0070] 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

[0071] like Figure 2 As shown, a SOC self-balancing converter for a series-connected lithium-ion battery pack containing four lithium-ion battery cells includes: a 4-way output isolated Sepic converter, three cross-connected capacitors, and four lithium-ion batteries, wherein:

[0072] The 4-way output isolated Sepic converter includes a power switch S1, an inductor L p1 , capacitor C p1 , Excitation inductance L m , transformer T and:

[0073] The first output diode D1, output capacitor C1,

[0074] The second output diode D2, output capacitor C2,

[0075] The third output diode D3, output capacitor C3,

[0076] The fourth output diode D4, output capacitor C4,

[0077] In the 4-way output isolated Sepic converter:

[0078] Inductance L p1 The other end is connected to the drain of power switch S1 and capacitor C p1 One end, capacitor C p1 The other end is connected to the excitation inductor L m One end, the primary winding L of the transformer T p Input side, primary winding L of transformer T p The output ends are connected to the excitation inductor L m The other end, the source of the power switch S1;

[0079] The secondary winding L of the transformer T s1 One end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the secondary winding L of the transformer T s1 The other end;

[0080] The secondary winding L of the transformer T s2 One end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the secondary winding L of the transformer T. s2 The other end;

[0081] The secondary winding L of the transformer T s3 One end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the secondary winding L of the transformer T. s3 The other end;

[0082] The secondary winding L of the transformer T s4 One end is connected to the anode of the fourth output diode D4, the cathode of the fourth output diode D4 is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the secondary winding L of the transformer T. s4 The other end;

[0083] Among the 3 jumper capacitors:

[0084] Cross-over capacitor C p1 One end is connected to the anode of the first output diode D1, and the capacitor C p1 The other end is connected to the anode of the second output diode D2;

[0085] Cross-over capacitor C p2 One end is connected to the anode of the second output diode D2, and the capacitor C p2 The other end is connected to the anode of the third output diode D3;

[0086] Cross-over capacitor C p3 One end is connected to the anode of the third output diode D3, and the capacitor C p3 The other end is connected to the anode of the fourth output diode D4;

[0087] The connection of 4 lithium-ion batteries is as follows:

[0088] The positive electrode of the lithium-ion battery B1 is connected to one end of the output capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the output capacitor C1;

[0089] The positive electrode of the lithium-ion battery B2 is connected to one end of the output capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the output capacitor C2; the positive electrode of the lithium-ion battery B3 is connected to one end of the output capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the output capacitor C3;

[0090] The positive electrode of the lithium-ion battery B4 is connected to one end of the output capacitor C4, and the negative electrode of the lithium-ion battery B4 is connected to the other end of the output capacitor C4;

[0091] 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;

[0092] Inductance L p1 One end is connected to the positive electrode of the lithium-ion battery B1, and the negative electrode of the lithium-ion battery B4 is connected to the source of the power switch S1.

[0093] When the power switch S1 is turned on, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned off; the battery pack adds energy to the inductor L through the series connection. p1 On, the excitation inductance L m Discharge, while the primary winding L of transformer T p Transfer energy to the secondary winding L of transformer T s1 , L s2 , L s3 and L s4 The first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode are cut off when they are subjected to the reverse voltage; the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The cross-over capacitor C p1 , C p2 and C p3 The output capacitors C1, C2, C3 and C4 provide energy for the lithium-ion battery pack.

[0094] When the power switch S1 is turned off, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned on; the inductor L p1 Discharge, transformer excitation inductance L m Charging, energy is added to the primary winding L of transformer T p At the same time, the energy is transferred to the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 On, the capacitor C p1 , Cp2 and C p3 discharge, and the output capacitors C1, C2, C3, and C4 charge.

[0095] During the entire switching cycle, the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The average voltage is 0, and L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the loop can be used to obtain the cross-connected capacitance C p1 The voltage U cp1 Equal to the lithium-ion battery B2 voltage U B2 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B3 B3 , the cross-capacitor C p3 The voltage U cp3 Equal to the voltage U of lithium-ion battery B4 B4 ;

[0096] When the power switch S1 is turned off, diodes D1, D2, D3, and D4 are turned on, and the secondary winding L of the transformer T s1 Through the loop L s1 (C p1 )→D1→C1→L s1 (C p1 ) charges capacitor C1; capacitor C p1 Through the diode D1 and the output capacitor C1 in parallel, the capacitor C p1 The voltage U cp1 Equal to the voltage U of the lithium-ion battery B1 B1 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B2 B2 ; Cross-connect capacitor C p3 The voltage U cp3 Equal to the voltage U of the lithium-ion battery B3 B3 ; When the capacitor C p1 , C p2 , C p3 When the voltage is large enough, the voltages of the lithium-ion battery cells are equal. If there are relatively low-voltage lithium-ion battery cells, the power switch is closed first, and part of the energy of the lithium-ion battery pack is stored in the inductor L on the primary side of the transformer. p1When the power switch is turned off, the energy is transferred to the lithium-ion battery cells with lower voltage, so that part of the energy of the series lithium-ion battery pack can be transferred to the lithium-ion battery cells with lower energy, achieving the balance of the lithium-ion battery pack.

[0097] Figure 3 This is a simulation diagram of the present invention realizing the balancing of a battery pack with four battery cells connected in series. Figure 3 It can be seen that the initial SOCs set for the four battery packs are different, and the other parameters are the same, where battery B1 is 95, battery B2 is 90, battery B3 is 85, and battery B4 is 75. The converter proposed in the present invention can realize the movement of battery cells with higher SOC to battery cells with lower SOC, and the SOC of battery cells with lower SOC gradually increases, and finally the SOC of the four battery cells is balanced.

[0098] The present invention is based on transformer balancing and proposes a series battery pack SOC self-balancing converter. The circuit includes an n-winding output SEPIC converter, n-1 cross-over capacitors and n lithium-ion batteries. The consistency of the transformer secondary side is achieved by adding a cross-over capacitor between each winding. Compared with other transformer balancing structures, there is no need to set up a reset circuit or reset winding, which reduces the control difficulty and cost of the circuit.

Claims

1. A SOC self-balancing converter for a series-connected lithium-ion battery pack, characterized in that: The converter includes: an n-way output isolated Sepic converter, n-1 cross-connected capacitors, and n lithium-ion batteries, wherein; The n-way output isolated Sepic converter includes a power switch S1, an inductor L p1 , capacitor C p1 , Excitation inductance L m , transformer T and: The first output diode D1, output capacitor C1, The second output diode D2, output capacitor C2, ... and so on. The nth output diode D n , output capacitor C n , In the n-channel output isolated Sepic converter: Inductance L p1 The other end is connected to the drain of power switch S1 and capacitor C p1 One end, capacitor C p1 The other end is connected to the excitation inductor L m One end, the primary winding L of the transformer T p Input side, primary winding L of transformer T p The output ends are connected to the excitation inductor L m The other end, the source of power switch S1; The secondary winding L of the transformer T s1 One end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the secondary winding L of the transformer T s1 The other end; The secondary winding L of the transformer T s2 One end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the secondary winding L of the transformer T. s2 The other end; The secondary winding L of the transformer T s3 One end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the secondary winding L of the transformer T. s3 The other end; ...and so on; The secondary winding L of the transformer T s(n-1) One end is connected to the anode of the n-1 output diode D3, and the n-1 output diode D n-1 Cathode connected output capacitor C n-1 One end, output capacitor C n-1 The other end is connected to the secondary winding L of transformer T s(n-1) The other end; The secondary winding L of the transformer T sn One end is connected to the nth output diode D n Anode, nth output diode D n Cathode connected output capacitor C n One end, output capacitor C n The other end is connected to the secondary winding L of transformer T sn The other end; Among n-1 jumper capacitors: Cross-over capacitor C p1 One end is connected to the anode of the first output diode D1, and the capacitor C p1 The other end is connected to the anode of the second output diode D2; Cross-over capacitor C p2 One end is connected to the anode of the second output diode D2, and the capacitor C p2 The other end is connected to the anode of the third output diode D3; Cross-over capacitor C p3 One end is connected to the anode of the third output diode D3, and the capacitor C p3 The other end is connected to the anode of the fourth output diode D4; ...and so on; Cross-over capacitor C p(n-2) One end is connected to the n-2 output diode D n-2 Anode, across capacitor C p(n-2) The other end is connected to the n-1th output diode D n-1 anode; Cross-over capacitor C p(n-1) One end is connected to the n-1th output diode D n-1 Anode, across capacitor C p(n-1) The other end is connected to the nth output diode D n anode; The connection form of n lithium-ion batteries is as follows: The positive electrode of the lithium-ion battery B1 is connected to one end of the output capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the output capacitor C1; The positive electrode of the lithium-ion battery B2 is connected to one end of the output capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the output capacitor C2; The positive electrode of the lithium-ion battery B3 is connected to one end of the output capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the output capacitor C3; ...and so on; Lithium-ion battery B n-1 The positive terminal is connected to the output capacitor C n-1 One end, lithium-ion battery B n-1 The negative terminal is connected to the output capacitor C n-1 The other end; Lithium-ion battery B n The positive terminal is connected to the output capacitor C n One end, lithium-ion battery B n The negative terminal is connected to the output capacitor C n The other end; 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; Inductance L p1 One end is connected to the positive electrode of lithium-ion battery B1, and the other end is connected to the positive electrode of lithium-ion battery B n The negative electrode is connected to the source of the power switch S1.

2. The SOC self-balancing converter for a series-connected lithium-ion battery pack 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. A SOC self-balancing converter for a lithium-ion battery pack having four lithium-ion battery cells connected in series, characterized in that: The converter includes: a 4-way output isolated Sepic converter, 3 jumper capacitors, and 4 lithium-ion batteries, among which: The 4-way output isolated Sepic converter includes a power switch S1, an inductor L p1 , capacitor C p1 , Excitation inductance L m , transformer T and: The first output diode D1, output capacitor C1, The second output diode D2, output capacitor C2, The third output diode D3, output capacitor C3, The fourth output diode D4, output capacitor C4, In the 4-way output isolated Sepic converter: Inductance L p1 The other end is connected to the drain of power switch S1 and capacitor C p1 One end, capacitor C p1 The other end is connected to the excitation inductor L m One end, the primary winding L of the transformer T p Input side, primary winding L of transformer T p The output ends are connected to the excitation inductor L m The other end, the source of power switch S1; The secondary winding L of the transformer T s1 One end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the secondary winding L of the transformer T s1 The other end; The secondary winding L of the transformer T s2 One end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the secondary winding L of the transformer T. s2 The other end; The secondary winding L of the transformer T s3 One end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the secondary winding L of the transformer T. s3 The other end; The secondary winding L of the transformer T s4 One end is connected to the anode of the fourth output diode D4, the cathode of the fourth output diode D4 is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the secondary winding L of the transformer T. s4 The other end; Among the 3 jumper capacitors: Cross-over capacitor C p1 One end is connected to the anode of the first output diode D1, and the capacitor C p1 The other end is connected to the anode of the second output diode D2; Cross-over capacitor C p2 One end is connected to the anode of the second output diode D2, and the capacitor C p2 The other end is connected to the anode of the third output diode D3; Cross-over capacitor C p3 One end is connected to the anode of the third output diode D3, and the capacitor C p3 The other end is connected to the anode of the fourth output diode D4; The connection of 4 lithium-ion batteries is as follows: The positive electrode of the lithium-ion battery B1 is connected to one end of the output capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the output capacitor C1; the positive electrode of the lithium-ion battery B2 is connected to one end of the output capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the output capacitor C2; The positive electrode of the lithium-ion battery B3 is connected to one end of the output capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the output capacitor C3; The positive electrode of the lithium-ion battery B4 is connected to one end of the output capacitor C4, and the negative electrode of the lithium-ion battery B4 is connected to the other end of the output capacitor C4; 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; Inductance L p1 One end is connected to the positive electrode of the lithium-ion battery B1, and the negative electrode of the lithium-ion battery B4 is connected to the source of the power switch S1.

4. The SOC self-balancing converter of a series-connected lithium-ion battery pack containing four lithium-ion battery cells according to claim 3, characterized in that: When the power switch S1 is turned on, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned off; the battery pack adds energy to the inductor L through the series connection. p1 On, the excitation inductance L m Discharge, while the primary winding L of transformer T p Transfer energy to the secondary winding L of transformer T s1 , L s2 , L s3 and L s4 The first output diode D1, the second output diode D2, the third output diode D3, and the fourth output diode are cut off due to the reverse voltage; the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The cross-over capacitor C p1 , C p2 and C p3 Charging, output capacitors C1, C2, C3 and C4 provide energy for the lithium-ion battery pack; When the power switch S1 is turned off, the first output diode D1, the second output diode D2, the third output diode D3 and the fourth output diode D4 are turned on; the inductor L p1 Discharge, transformer excitation inductance L m Charging, energy is added to the primary winding L of transformer T p At the same time, the energy is transferred to the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 On, the capacitor C p1 , C p2 and C p3 discharge, and the output capacitors C1, C2, C3, and C4 charge.

5. The SOC self-balancing converter of a series-connected lithium-ion battery pack containing four lithium-ion battery cells according to claim 3, characterized in that: During the entire switching cycle, the secondary winding L of the transformer T s1 , L s2 , L s3 and L s4 The average voltage is 0, and L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the loop can be used to obtain the cross-connected capacitance C p1 The voltage U cp1 Equal to the lithium-ion battery B2 voltage U B2 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B3 B3 , the cross-capacitor C p3 The voltage U cp3 Equal to the voltage U of lithium-ion battery B4 B4 ; When the power switch S1 is turned off, diodes D1, D2, D3, and D4 are turned on, and the secondary winding L of the transformer T s1 Through the loop L s1 (C p1 )→D1→C1→L s1 (C p1 ) charges capacitor C1; capacitor C p1 Through the diode D1 and the output capacitor C1 in parallel, the capacitor C p1 The voltage U cp1 Equal to the voltage U of the lithium-ion battery B1 B1 Similarly, the cross-connect capacitor C p2 The voltage U cp2 Equal to the voltage U of the lithium-ion battery B2 B2 ; Cross-connect capacitor C p3 The voltage U cp3 Equal to the voltage U of the lithium-ion battery B3 B3 ; When the capacitor C p1 , C p2 , C p3 When the voltage is large enough, the voltages of the lithium-ion battery cells are equal. If there are relatively low-voltage lithium-ion battery cells, the power switch is closed first, and part of the energy of the lithium-ion battery pack is stored in the inductor L on the primary side of the transformer. p1 When the power switch is turned off, the energy is transferred to the lithium-ion battery cells with lower voltage, so that part of the energy of the series lithium-ion battery pack can be transferred to the lithium-ion battery cells with lower energy, achieving the balance of the lithium-ion battery pack.

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