Multi-lithium battery SOC equalization circuit with isolated Zeta structure

Abstract

The invention relates to a multi-lithium battery SOC equalization circuit with an isolation type Zeta structure. The circuit comprises a Zeta type isolation converter with n paths of outputs, n-1 bridging capacitors and n lithium battery units. The Zeta-type isolation converter with the n-path output comprises a power switch S1, an excitation inductor Lm, a transformer T, a reset winding Ls, a diode D, a first-path output capacitor C1, a first-path output capacitor Cp1, a diode D1 and a filter inductor L1. The second output circuit comprises a capacitor C2, a capacitor Cp2, a diode D2 and a filter inductor L2; ,...; and the nth output circuit comprises capacitors Cn and Cpn, a diode Dn and a filter inductor Ln. The equalization circuit is based on transformer type equalization, a multi-winding transformer equalization topological structure is adopted, and SOC equalization of the series lithium battery pack is realized by adding a bridging capacitor between windings. Compared with a traditional multi-winding transformer equalization topological structure, the isolation type Zeta structure is adopted, the input and output capacity can be guaranteed, certain voltage gain capacity is provided, and the control difficulty and cost of the circuit are greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery balancing, and in particular to an isolated Zeta structure multi-lithium battery SOC balancing circuit. Background Art

[0002] Lithium batteries have the advantages of high energy density, long life, high efficiency, small size, and no pollution. Considering their safety, practicality, and cost, they play a vital role in power and energy storage. Single-cell lithium batteries often require multiple batteries to be connected in series due to their low voltage and small capacity. However, due to different manufacturing processes and the influence of the environment, charging and discharging mode, and chemical factors during use, the battery pack will have differences in charge state, voltage, internal resistance, and capacity. These differences will cause problems such as durability, reliability, and safety of the battery pack. Therefore, in order to maintain the balance of cells in the lithium battery pack, researchers have proposed many balancing circuits, devices, and methods.

[0003] The current equalization technology used in lithium battery packs is mainly divided into active equalization and passive equalization. The idea of ​​passive equalization is to dissipate excess energy in the form of heat through parallel resistors, but this method will cause a large amount of energy loss in the lithium battery pack, and the high temperature environment caused by improper heat dissipation will damage the performance of the lithium battery pack. Active equalization technology is a method of transferring the energy of a higher single cell in a lithium battery pack to a lower single cell. For example, the patent document with application publication number CN113489083A discloses a hierarchical equalization control method for lithium-ion battery packs based on a buck-boost converter. The method adds multiple energy storage inductor elements, diodes, and equalization control switches on the basis of lithium-ion battery packs. By controlling the switch to close, the single cell with higher energy storage stores excess energy in the corresponding inductor, and then controls the switch to turn off, and transfers the energy in the inductor to the single cell with lower energy storage, forming a balanced control of a series lithium-ion battery pack. In addition, two adjacent single cells 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 balanced control. The balancing control method proposed in this patent can not only achieve balancing between two adjacent single cells, but also indirectly achieve balancing between two non-adjacent single cells 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 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 battery pack balancing technology, the present invention proposes an isolated Zeta structure multi-lithium battery SOC balancing circuit. The balancing circuit is based on transformer-type balancing, adopts a multi-winding transformer balancing topology, and realizes SOC balancing of the series lithium battery pack by adding a cross-over capacitor between each winding. Compared with the traditional multi-winding transformer balancing topology, the isolated Zeta structure can ensure input and output capabilities, provide a certain voltage gain capability, and only use one switch to achieve battery pack balancing, which greatly reduces the control difficulty and cost of the circuit, and avoids the problem of output voltage imbalance caused by cross-regulation rate when the traditional multi-winding transformer outputs multiple windings, effectively reducing voltage deviation and improving battery balancing accuracy.

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

[0006] An isolated Zeta structure multi-lithium battery SOC balancing circuit includes a Zeta-type isolation converter with n outputs, n-1 cross-connected capacitors and n lithium battery cells, wherein:

[0007] The n-channel output Zeta-type isolation converter includes a power switch S1, an excitation inductor L m , transformer T, reset winding L s , diode D, first output capacitor C1, C p1 , diode D1, filter inductor L1; the second output capacitor C2, C p2 , diode D2, filter inductor L2; ...; the nth output capacitor C n , C pn , diode D n , filter inductor L n ;

[0008] The connection form of the Zeta type isolation converter with n outputs is as follows:

[0009] Excitation inductance L m One end is connected to the reset winding L s Output end, primary winding L of transformer T p Input terminal, excitation inductance L m The other end is connected to the primary winding L of transformer T p Output terminal, drain of power switch S1, source of power switch S1 connected to anode of diode D, cathode of diode D connected to reset winding L s Input terminal;

[0010] The secondary winding L of the transformer T s1 One end is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the cathode of the diode D1 and one end of the inductor L1. The other end of the inductor L1 is connected to the output capacitor Cp1 One end, output capacitor C p1 The other end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The other end;

[0011] The secondary winding L of the transformer T s2 One end is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the cathode of the diode D2 and one end of the inductor L2. The other end of the inductor L2 is connected to the output capacitor C p2 One end, output capacitor C p2 The other end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The other end;

[0012] The secondary winding L of the transformer T s3 One end is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the cathode of the diode D3 and one end of the inductor L3. The other end of the inductor L3 is connected to the output capacitor C p3 One end, output capacitor C p3 The other end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The other end;

[0013] ... and so on;

[0014] The secondary winding L of the transformer T sn One end is connected to the output capacitor C n One end, output capacitor C n The other end is connected to diode D n Cathode, inductor L n One end, inductor L n The other end is connected to the output capacitor C pn One end, output capacitor C pn The other end is connected to diode D n Anode, secondary winding L of transformer T sn The other end.

[0015] Among n-1 jumper capacitors:

[0016] Output capacitor C q1 One end is connected to the other end of the output capacitor C1. q1 The other end is connected to the other end of the output capacitor C2;

[0017] Output capacitor C q2 One end is connected to the other end of the output capacitor C2. q2 The other end is connected to the other end of the output capacitor C3;

[0018] Output capacitor C q3 One end is connected to the other end of the output capacitor C3.q3 The other end is connected to the other end of the output capacitor C4;

[0019] ... and so on;

[0020] Output capacitor C q(n-1) One end is connected to the output capacitor C q(n-1) The other end, output capacitor C q(n-1) The other end is connected to the output capacitor C n The other end.

[0021] The connection form of n lithium battery cells and n-output Zeta-type isolation converter is as follows:

[0022] The positive pole of lithium battery B1 is connected to the output capacitor C p1 At one end, the negative electrode of the lithium battery B1 is connected to the output capacitor C p1 The other end;

[0023] The positive pole of lithium battery B2 is connected to the output capacitor C p2 At one end, the negative electrode of lithium battery B2 is connected to the output capacitor C p2 The other end;

[0024] The positive pole of lithium battery B3 is connected to the output capacitor C p3 At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C p3 The other end;

[0025] ... and so on;

[0026] Lithium battery B n The positive terminal is connected to the output capacitor C pn At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C pn The other end;

[0027] Among n lithium battery cells:

[0028] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2, the negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3, the negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4, and so on; n-1 Negative connection to lithium battery B n positive electrode;

[0029] Excitation inductance L m One end is connected to the output capacitor C p1 One end; the anode of diode D is connected to capacitor C pn The other end.

[0030] The gate of the power switch S1 is connected to a controller, and its duty cycle can be changed between 0 and 1 and in phase.

[0031] A multi-lithium battery SOC balancing circuit with an isolated Zeta structure containing four lithium battery cells, the circuit comprising a 4-way output Zeta-type isolation converter, three cross-connected capacitors and four lithium battery cells, wherein:

[0032] The 4-way output Zeta-type isolation converter includes a power switch S1, an excitation inductor L m , transformer T, reset winding L s , diode D, first output capacitor C1, C p1 , diode D1, filter inductor L1; the second output capacitor C2, C p2 , diode D2, filter inductor L2; the third output capacitor C3, C p3 , diode D3, filter inductor L3; the fourth output capacitor C4, C p4 , diode D4, filter inductor L4;

[0033] The connection form of the 4-way output Zeta isolation converter is as follows:

[0034] Excitation inductance L m One end is connected to the reset winding L s Output end, primary winding L of transformer T p Input terminal, excitation inductance L m The other end is connected to the primary winding L of transformer T p Output terminal, drain of power switch S1, source of power switch S1 connected to anode of diode D, cathode of diode D connected to reset winding L s Input terminal;

[0035] The secondary winding L of the transformer T s1 One end is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the cathode of the diode D1 and one end of the inductor L1. The other end of the inductor L1 is connected to the output capacitor C p1 One end, output capacitor C p1 The other end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The other end;

[0036] The secondary winding L of the transformer T s2 One end is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the cathode of the diode D2 and one end of the inductor L2. The other end of the inductor L2 is connected to the output capacitor C p2 One end, output capacitor C p2 The other end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The other end;

[0037] The secondary winding L of the transformer T s3One end is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the cathode of the diode D3 and one end of the inductor L3. The other end of the inductor L3 is connected to the output capacitor C p3 One end, output capacitor C p3 The other end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The other end;

[0038] The secondary winding L of the transformer T s4 One end is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the cathode of the diode D4 and one end of the inductor L4. The other end of the inductor L4 is connected to the output capacitor C p4 One end, output capacitor C p4 The other end is connected to the anode of diode D4 and the secondary winding L of transformer T. s4 The other end.

[0039] Among the 3 jumper capacitors:

[0040] Output capacitor C q1 One end is connected to the other end of the output capacitor C1. q1 The other end is connected to the other end of the output capacitor C2;

[0041] Output capacitor C q2 One end is connected to the other end of the output capacitor C2. q2 The other end is connected to the other end of the output capacitor C3;

[0042] Output capacitor C q3 One end is connected to the other end of the output capacitor C3. q3 The other end is connected to the other end of the output capacitor C4;

[0043] The connection between 4 lithium battery cells and 4-way output Zeta-type isolation converter is as follows:

[0044] The positive pole of lithium battery B1 is connected to the output capacitor C p1 At one end, the negative electrode of the lithium battery B1 is connected to the output capacitor C p1 The other end;

[0045] The positive pole of lithium battery B2 is connected to the output capacitor C p2 At one end, the negative electrode of lithium battery B2 is connected to the output capacitor C p2 The other end;

[0046] The positive pole of lithium battery B3 is connected to the output capacitor C p3 At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C p3 The other end;

[0047] The positive pole of lithium battery B4 is connected to the output capacitor C p4At one end, the negative electrode of lithium battery B4 is connected to the output capacitor C p4 The other end;

[0048] In 4 lithium battery cells:

[0049] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2, the negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3, and the negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4;

[0050] Excitation inductance L m One end is connected to the output capacitor C p1 One end; the anode of diode D is connected to capacitor C p4 The other end.

[0051] For four lithium batteries B1, B2, B3, and B4 connected in series to form a lithium battery pack, during the entire switching cycle, according to the principles of inductor volt-second balance and capacitor ampere-second balance, the transformer secondary coil L s1 , L s2 , L s3 , L s4 The average voltage of the output capacitors C1, C2, C3, and C4 is 0. s1 →C1→C q1 →C2→L s2 →C p2 →L s1 The KVL principle of the loop gives the output capacitance C q1 The voltage u cq1 Equal to the output voltage u bat2 .

[0052] Similarly, the output capacitor C q2 The voltage u cq2 Equal to the output voltage u bat3 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat4 .

[0053] When the power switch S1 is turned off, the diodes D1, D2, D3, and D4 are turned on, and the energy of the lithium battery pack is transferred to the primary winding of the transformer through the inductor L and the output capacitor C. p As the current increases, the transformer's energy storage increases and the energy is transferred to the secondary winding L s1 , L s2 , L s3 , L s4 The diodes D1, D2, D3, and D4 are turned on by the forward voltage. The output capacitor C p2 By C p2 →D1→C q1 →C2→L s2 →C p2Loop to output capacitor C q1 Charging, output capacitor C p1 , C p2 , C p3 , C p4 Provide power to the load.

[0054] When the power switch S1 is closed, the diodes D1, D2, D3, and D4 are turned off, and the output capacitor C q1 Through loop C q1 →L1→C p1 →C p2 →L s2 →C2 to output capacitor C p1 Charge. Output capacitor C q1 Through inductors L1, L2 and output capacitor C p1 In parallel, the output capacitor C q1 The voltage u cq1 Equal to the output voltage u bat1 Similarly, the output capacitor C q2 The voltage u cq2 Equal to the output voltage u bat2 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat3 When the output capacitor C q1 , C q2 , C q3 When it is large enough, the voltage of each lithium battery cell is equal.

[0055] Assume that the SOC of the single lithium battery B1 in the lithium battery pack is higher than the average value. When the power switch S1 is turned off, the lithium battery B1 is connected in series with the lithium batteries B2, B3, and B4 to transfer the excess energy to the primary winding of the transformer. When the switch is turned off again, the secondary winding L s2 , L s3 , L s4 They are connected in parallel with lithium batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transmitted to lithium batteries B2, B3, and B4, so that part of the energy of the series-connected lithium battery pack can be transmitted to the lithium battery cells with lower energy, thus achieving SOC balance of the lithium battery pack.

[0056] By adopting the above technical solution, the present invention provides an isolated Zeta structure multi-lithium battery SOC equalization circuit, and the technical effects are as follows:

[0057] 1) The present invention achieves the effect of automatic voltage balancing of the output voltages of the multi-channel output ZETA isolation converter by connecting a jumper capacitor between adjacent output windings of the isolation ZETA converter, thereby improving the battery balance;

[0058] 2) The circuit topology of the present invention is simple and only one switch is used, which reduces the difficulty of control system design.

[0059] 3) The circuit of the present invention has continuous output current and certain voltage-boosting and voltage-reducing capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0061] Figure 1 It is a circuit schematic diagram of the present invention.

[0062] 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.

[0063] 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

[0064] like Figure 2 As shown, a multi-lithium battery SOC balancing circuit with an isolated Zeta structure containing 4 lithium battery cells, the circuit includes a 4-way output Zeta-type isolation converter, 3 cross-connected capacitors and 4 lithium battery cells, wherein:

[0065] The 4-way output Zeta-type isolation converter includes a power switch S1, an excitation inductor L m , transformer T, reset winding L s , diode D, first output capacitor C1, C p1 , diode D1, filter inductor L1; the second output capacitor C2, C p2 , diode D2, filter inductor L2; the third output capacitor C3, C p3 , diode D3, filter inductor L3; the fourth output capacitor C4, C p4 , diode D4, filter inductor L4;

[0066] The connection form of the 4-way output Zeta isolation converter is as follows:

[0067] Excitation inductance L m One end is connected to the reset winding L s Output end, primary winding L of transformer T p Input terminal, excitation inductance L m The other end is connected to the primary winding L of transformer T p Output terminal, drain of power switch S1, source of power switch S1 connected to anode of diode D, cathode of diode D connected to reset winding L s Input terminal;

[0068] The secondary winding L of the transformer T s1 One end is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the cathode of the diode D1 and one end of the inductor L1. The other end of the inductor L1 is connected to the output capacitor C p1 One end, output capacitor C p1 The other end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The other end;

[0069] The secondary winding L of the transformer T s2 One end is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the cathode of the diode D2 and one end of the inductor L2. The other end of the inductor L2 is connected to the output capacitor C p2 One end, output capacitor C p2 The other end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The other end;

[0070] The secondary winding L of the transformer T s3 One end is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the cathode of the diode D3 and one end of the inductor L3. The other end of the inductor L3 is connected to the output capacitor C p3 One end, output capacitor C p3 The other end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The other end;

[0071] The secondary winding L of the transformer T s4 One end is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the cathode of the diode D4 and one end of the inductor L4. The other end of the inductor L4 is connected to the output capacitor C p4 One end, output capacitor C p4 The other end is connected to the anode of diode D4 and the secondary winding L of transformer T. s4 The other end.

[0072] Among the 3 jumper capacitors:

[0073] Output capacitor C q1 One end is connected to the other end of the output capacitor C1. q1 The other end is connected to the other end of the output capacitor C2;

[0074] Output capacitor C q2 One end is connected to the other end of the output capacitor C2. q2 The other end is connected to the other end of the output capacitor C3;

[0075] Output capacitor C q3 One end is connected to the other end of the output capacitor C3. q3 The other end is connected to the other end of the output capacitor C4;

[0076] The connection between 4 lithium battery cells and 4-way output Zeta-type isolation converter is as follows:

[0077] The positive pole of lithium battery B1 is connected to the output capacitor C p1 At one end, the negative electrode of the lithium battery B1 is connected to the output capacitor C p1 The other end;

[0078] The positive pole of lithium battery B2 is connected to the output capacitor C p2 At one end, the negative electrode of lithium battery B2 is connected to the output capacitor C p2 The other end;

[0079] The positive pole of lithium battery B3 is connected to the output capacitor C p3 At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C p3 The other end;

[0080] The positive pole of lithium battery B4 is connected to the output capacitor C p4 At one end, the negative electrode of lithium battery B4 is connected to the output capacitor C p4 The other end;

[0081] In 4 lithium battery cells:

[0082] The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2, the negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3, and the negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4;

[0083] Excitation inductance L m One end is connected to the output capacitor C p1 One end; the anode of diode D is connected to capacitor C p4 The other end.

[0084] For four lithium batteries B1, B2, B3, and B4 connected in series to form a lithium battery pack, during the entire switching cycle, according to the principles of inductor volt-second balance and capacitor ampere-second balance, the transformer secondary coil L s1 , L s2 , L s3 , L s4 The average voltage of the output capacitors C1, C2, C3, and C4 is 0. s1 →C1→C q1 →C2→L s2 →C p2 →L s1 The KVL principle of the loop gives the output capacitance C q1 The voltage u cq1 Equal to the output voltage u bat2 .

[0085] Similarly, the output capacitor C q2 The voltage u cq2Equal to the output voltage u bat3 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat4 .

[0086] When the power switch S1 is turned off, the diodes D1, D2, D3, and D4 are turned on, and the energy of the lithium battery pack is transferred to the primary winding of the transformer through the inductor L and the output capacitor C. p As the current increases, the transformer's energy storage increases and the energy is transferred to the secondary winding L s1 , L s2 , L s3 , L s4 The diodes D1, D2, D3, and D4 are turned on by the forward voltage. The output capacitor C p2 By C p2 →D1→C q1 →C2→L s2 →C p2 Loop to output capacitor C q1 Charging, output capacitor C p1 , C p2 , C p3 , C p4 Provide power to the load.

[0087] When the power switch S1 is closed, the diodes D1, D2, D3, and D4 are turned off, and the output capacitor C q1 Through loop C q1 →L1→C p1 →C p2 →L s2 →C2 to output capacitor C p1 Charge. Output capacitor C q1 Through inductors L1, L2 and output capacitor C p1 In parallel, the output capacitor C q1 The voltage u cq1 Equal to the output voltage u bat1 Similarly, the output capacitor C q2 The voltage u cq2 Equal to the output voltage u bat2 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat3 When the output capacitor C q1 , C q2 , C q3 When it is large enough, the voltage of each lithium battery cell is equal.

[0088] Assume that the SOC of the single lithium battery B1 in the lithium battery pack is higher than the average value. When the power switch S1 is turned off, the lithium battery B1 is connected in series with the lithium batteries B2, B3, and B4 to transfer the excess energy to the primary winding of the transformer. When the switch is turned off again, the secondary winding L s2 , L s3 , L s4 They are connected in parallel with lithium batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transmitted to lithium batteries B2, B3, and B4, so that part of the energy of the series-connected lithium battery pack can be transmitted to the lithium battery cells with lower energy, thus achieving SOC balance of the lithium battery pack.

[0089] Figure 3 This is a simulation diagram of the present invention realizing the balancing of a lithium battery pack with four battery cells in series. Figure 3 It can be seen that the initial SOC values ​​of the four batteries are 72%, 79%, 82% and 86% respectively. After a period of simulation, the SOC standard deviation does not exceed 1%, achieving the balance requirement.

Claims

1. An isolated Zeta structure multi-lithium battery SOC equalization circuit, characterized in that: The circuit includes a Zeta-type isolation converter with n outputs, n-1 cross-connected capacitors and n lithium battery cells, where: The n-channel output Zeta-type isolation converter includes a power switch S1, an excitation inductor L m , transformer T, reset winding L s , diode D, first output capacitor C1, C p1 , diode D1, filter inductor L1; the second output capacitor C2, C p2 , diode D2, filter inductor L2; ...; the nth output capacitor C n , C pn , diode D n , filter inductor L n ; The connection form of the Zeta type isolation converter with n outputs is as follows: Excitation inductance L m One end is connected to the reset winding L s Output end, primary winding L of transformer T p Input terminal, excitation inductance L m The other end is connected to the primary winding L of transformer T p Output terminal, drain of power switch S1, source of power switch S1 connected to anode of diode D, cathode of diode D connected to reset winding L s Input terminal; The secondary winding L of the transformer T s1 One end is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the cathode of the diode D1 and one end of the inductor L1. The other end of the inductor L1 is connected to the output capacitor C p1 One end, output capacitor C p1 The other end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The other end; The secondary winding L of the transformer T s2 One end is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the cathode of the diode D2 and one end of the inductor L2. The other end of the inductor L2 is connected to the output capacitor C p2 One end, output capacitor C p2 The other end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The other end; The secondary winding L of the transformer T s3 One end is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the cathode of the diode D3 and one end of the inductor L3. The other end of the inductor L3 is connected to the output capacitor C p3 One end, output capacitor C p3 The other end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The other end; ... and so on; The secondary winding L of the transformer T sn One end is connected to the output capacitor C n One end, output capacitor C n The other end is connected to diode D n Cathode, inductor L n One end, inductor L n The other end is connected to the output capacitor C pn One end, output capacitor C pn The other end is connected to diode D n Anode, secondary winding L of transformer T sn The other end; Among n-1 jumper capacitors: Output capacitor C q1 One end is connected to the other end of the output capacitor C1. q1 The other end is connected to the other end of the output capacitor C2; Output capacitor C q2 One end is connected to the other end of the output capacitor C2. q2 The other end is connected to the other end of the output capacitor C3; Output capacitor C q3 One end is connected to the other end of the output capacitor C3. q3 The other end is connected to the other end of the output capacitor C4; ... and so on; Output capacitor C q(n-1) One end is connected to the output capacitor C q(n-1) The other end, output capacitor C q(n-1) The other end is connected to the output capacitor C n The other end; The connection form of n lithium battery cells and n-output Zeta-type isolation converter is as follows: The positive pole of lithium battery B1 is connected to the output capacitor C p1 At one end, the negative electrode of the lithium battery B1 is connected to the output capacitor C p1 The other end; The positive pole of lithium battery B2 is connected to the output capacitor C p2 At one end, the negative electrode of lithium battery B2 is connected to the output capacitor C p2 The other end; The positive pole of lithium battery B3 is connected to the output capacitor C p3 At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C p3 The other end; ... and so on; Lithium battery B n The positive terminal is connected to the output capacitor C pn At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C pn The other end; Among n lithium battery cells: The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2, the negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3, the negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4, and so on; n-1 Negative connection to lithium battery B n positive electrode; Excitation inductance L m One end is connected to the output capacitor C p1 One end; the anode of diode D is connected to capacitor C pn The other end.

2. According to claim 1, the isolated Zeta structure multi-lithium battery SOC equalization circuit is 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 and in phase.

3. A multi-lithium battery SOC equalization circuit with four lithium battery cells and an isolated Zeta structure, characterized in that: The circuit includes a 4-way output Zeta-type isolation converter, 3 jumper capacitors and 4 lithium battery cells, among which: The 4-way output Zeta-type isolation converter includes a power switch S1, an excitation inductor L m , transformer T, reset winding L s , diode D, first output capacitor C1, C p1 , diode D1, filter inductor L1; the second output capacitor C2, C p2 , diode D2, filter inductor L2; the third output capacitor C3, C p3 , diode D3, filter inductor L3; the fourth output capacitor C4, C p4 , diode D4, filter inductor L4; The connection form of the 4-way output Zeta isolation converter is as follows: Excitation inductance L m One end is connected to the reset winding L s Output end, primary winding L of transformer T p Input terminal, excitation inductance L m The other end is connected to the primary winding L of transformer T p Output terminal, drain of power switch S1, source of power switch S1 connected to anode of diode D, cathode of diode D connected to reset winding L s Input terminal; The secondary winding L of the transformer T s1 One end is connected to one end of the output capacitor C1, and the other end of the output capacitor C1 is connected to the cathode of the diode D1 and one end of the inductor L1. The other end of the inductor L1 is connected to the output capacitor C p1 One end, output capacitor C p1 The other end is connected to the anode of diode D1 and the secondary winding L of transformer T. s1 The other end; The secondary winding L of the transformer T s2 One end is connected to one end of the output capacitor C2, and the other end of the output capacitor C2 is connected to the cathode of the diode D2 and one end of the inductor L2. The other end of the inductor L2 is connected to the output capacitor C p2 One end, output capacitor C p2 The other end is connected to the anode of diode D2 and the secondary winding L of transformer T. s2 The other end; The secondary winding L of the transformer T s3 One end is connected to one end of the output capacitor C3, and the other end of the output capacitor C3 is connected to the cathode of the diode D3 and one end of the inductor L3. The other end of the inductor L3 is connected to the output capacitor C p3 One end, output capacitor C p3 The other end is connected to the anode of diode D3 and the secondary winding L of transformer T. s3 The other end; The secondary winding L of the transformer T s4 One end is connected to one end of the output capacitor C4, and the other end of the output capacitor C4 is connected to the cathode of the diode D4 and one end of the inductor L4. The other end of the inductor L4 is connected to the output capacitor C p4 One end, output capacitor C p4 The other end is connected to the anode of diode D4 and the secondary winding L of transformer T. s4 The other end; Among the 3 jumper capacitors: Output capacitor C q1 One end is connected to the other end of the output capacitor C1. q1 The other end is connected to the other end of the output capacitor C2; Output capacitor C q2 One end is connected to the other end of the output capacitor C2. q2 The other end is connected to the other end of the output capacitor C3; Output capacitor C q3 One end is connected to the other end of the output capacitor C3. q3 The other end is connected to the other end of the output capacitor C4; The connection between 4 lithium battery cells and 4-way output Zeta-type isolation converter is as follows: The positive pole of lithium battery B1 is connected to the output capacitor C p1 At one end, the negative electrode of the lithium battery B1 is connected to the output capacitor C p1 The other end; The positive pole of lithium battery B2 is connected to the output capacitor C p2 At one end, the negative electrode of lithium battery B2 is connected to the output capacitor C p2 The other end; The positive pole of lithium battery B3 is connected to the output capacitor C p3 At one end, the negative electrode of lithium battery B3 is connected to the output capacitor C p3 The other end; The positive pole of lithium battery B4 is connected to the output capacitor C p4 At one end, the negative electrode of lithium battery B4 is connected to the output capacitor C p4 The other end; In 4 lithium battery cells: The negative electrode of lithium battery B1 is connected to the positive electrode of lithium battery B2, the negative electrode of lithium battery B2 is connected to the positive electrode of lithium battery B3, and the negative electrode of lithium battery B3 is connected to the positive electrode of lithium battery B4; Excitation inductance L m One end is connected to the output capacitor C p1 One end; the anode of diode D is connected to capacitor C p4 The other end.

4. According to claim 3, a multi-lithium battery SOC equalization circuit with four lithium battery cells in an isolated Zeta structure is characterized in that: For four lithium batteries B1, B2, B3, and B4 connected in series to form a lithium battery pack, during the entire switching cycle, the transformer secondary coil L s1 , L s2 , L s3 , L s4 The average voltage of the output capacitors C1, C2, C3, and C4 is 0. s1 →C1→C q1 →C2→L s2 →C p2 →L s1 The KVL principle of the loop gives the output capacitance C q1 The voltage u cq1 Equal to the output voltage u bat2 ; Similarly, the output capacitor C q2 The voltage u cq2 Equal to the output voltage u bat3 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat4 ; When the power switch S1 is turned off, the diodes D1, D2, D3, and D4 are turned on, and the energy of the lithium battery pack is transferred to the primary winding of the transformer through the inductor L and the output capacitor C. p As the current increases, the transformer's energy storage increases and the energy is transferred to the secondary winding L s1 , L s2 , L s3 , L s4 ; Diodes D1, D2, D3, and D4 are turned on by the forward voltage; Output capacitor C p2 By C p2 →D1→C q1 →C2→L s2 →C p2 Loop to output capacitor C q1 Charging, output capacitor C p1 , C p2 , C p3 , C p4 Provide power to the load; When the power switch S1 is closed, the diodes D1, D2, D3, and D4 are turned off, and the output capacitor C q1 Through loop C q1 →L1→C p1 →C p2 →L s2 →C2 to output capacitor C p1 Charging; output capacitor C q1 Through inductors L1, L2 and output capacitor C p1 In parallel, the output capacitor C q1 The voltage u cq1 Equal to the output voltage u bat1 Similarly, the output capacitor C q2 The voltage u cq2 Equal to the output voltage u bat2 , output capacitor C q3 The voltage u cq3 Equal to the output voltage u bat3 ; When the output capacitor C q1 , C q2 , C q3 When it is large enough, the voltage of each lithium battery cell is equal.

5. The multi-lithium battery SOC equalization circuit with four lithium battery cells and isolated Zeta structure according to claim 3, characterized in that: Assume that the SOC of the single lithium battery B1 in the lithium battery pack is higher than the average value. When the power switch S1 is turned off, Lithium battery B1 is connected in series with lithium batteries B2, B3, and B4 to transfer excess energy to the primary winding of the transformer. When the switch is turned off again, the secondary winding L s2 , L s3 , L s4 They are connected in parallel with lithium batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transmitted to lithium batteries B2, B3, and B4, so that part of the energy of the series-connected lithium battery pack can be transmitted to the lithium battery cells with lower energy, thus achieving SOC balance of the lithium battery pack.

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