Lithium ion battery pack soc active balancing circuit based on half bridge

Abstract

The application discloses a lithium ion battery pack SOC active equalization circuit based on a half-bridge, which comprises an n-winding output half-bridge converter, n-1 cross-connection capacitors and n lithium ion batteries. in1 in2 m n n Compared with a traditional multi-winding transformer equalization structure, the active equalization circuit only uses two switches to realize the equalization of the lithium ion battery pack, reduces the control difficulty and cost of the circuit, avoids the end voltage imbalance problem caused by the cross regulation rate of the transformer in the multi-winding output, effectively reduces the voltage deviation and improves the battery equalization precision.​​​​

Description

Technical Field

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

[0002] To meet the performance requirements of energy storage systems, lithium-ion batteries are typically used in groups. However, individual battery cells can exhibit inconsistencies, such as variations in capacity, internal resistance, and voltage. These variations reduce the battery pack's capacity utilization, can also lead to overcharging and over-discharging, accelerate battery aging, and compromise battery system safety. Current battery balancing technologies are most effective in mitigating these inconsistencies. These technologies are primarily categorized as passive and active. Passive balancing, also known as energy-consuming balancing, dissipates excess energy within each battery cell as heat. However, this method results in significant energy loss, and high temperatures caused by improper heat dissipation can damage battery performance. Active balancing, a non-energy-consuming balancing method, transfers energy through energy storage elements, thereby minimizing battery pack inconsistencies and achieving balanced energy distribution. Active balancing, due to its high energy utilization and flexible energy transfer, is a hot topic in battery balancing technology.

[0003] For example, patent application publication number CN116247925A discloses a battery-balancing bidirectional DC-DC converter control method. This method adds multiple balancing control switches to a lithium-ion battery pack and integrates multiple operating modes. By controlling the switch closure, the circuit topology is reconfigured, thereby changing the operating mode, including charging mode, external power supply mode, battery pack function mode, battery pack voltage balancing mode, and energy recovery mode. It can achieve both bidirectional energy flow and boost and buck functions, and the energy supply mode can be combined in multiple different ways to increase backup and improve fault tolerance. The battery pack achieves voltage balancing through the energy storage inductor and switch tubes of the bidirectional DC-DC converter, thereby improving device utilization. However, the balancing circuit adopted by this control method uses fourteen switch tubes for only three battery packs, making the logic control very complex. Summary of the Invention

[0004] To address the shortcomings of existing battery pack balancing technology, this invention proposes a half-bridge-based active SOC balancing circuit for lithium-ion battery packs. This active balancing circuit, based on transformer-based balancing, employs a multi-winding transformer balancing topology. By adding a crossover capacitor between each winding, it achieves SOC balancing for series-connected lithium-ion battery packs. Compared to traditional multi-winding transformer balancing structures, this circuit achieves SOC balancing for lithium-ion battery packs using only two switches, reducing circuit control difficulty and cost. It also avoids the terminal voltage imbalance caused by cross-regulation of the transformer's multi-winding output, effectively reducing voltage deviation and improving battery balancing accuracy.

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

[0006] A half-bridge-based lithium-ion battery pack SOC active balancing circuit includes an n-winding output half-bridge converter, n-1 cross-capacitors, and n lithium-ion batteries, wherein:

[0007] The n-winding output half-bridge converter includes power switches S1, S2, input capacitor C in1 、C in2 , excitation inductance L m , transformer T, first output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, ..., nth output diode D n , the nth output capacitor C n ;

[0008] The connection form of the n-winding output half-bridge converter is as follows:

[0009] Excitation inductance L m One end is connected to the primary winding L of the transformer T p Input terminal, source of power switch S1, drain of power switch S2, magnetizing inductor L m The other end is connected to the primary winding L of transformer T p Output terminal, input capacitor C in1 The other end, input capacitor C in2 one end;

[0010] Transformer T secondary winding L s1 One end is connected to the anode of diode D1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the secondary winding L of transformer T. s1 the other end;

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

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

[0013] ...and so on;

[0014] Transformer T secondary winding L sn One end is connected to diode D n Anode, diode D nCathode connection capacitor C n One end, capacitor C n The other end is connected to the secondary winding L of the transformer T sn the other end;

[0015] Among n-1 jumper capacitors:

[0016] Capacitor C p1 One end is connected to the anode of diode D1 and capacitor C p1 The other end is connected to the anode of diode D2;

[0017] Capacitor C p2 One end is connected to the anode of diode D2 and the capacitor C p2 The other end is connected to the anode of diode D3;

[0018] Capacitor C p3 One end is connected to the anode of diode D3 and capacitor C p3 The other end is connected to the anode of diode D4;

[0019] ...and so on;

[0020] Capacitor C p(n-1) One end is connected to diode D n-1 Anode, capacitor C p(n-1) The other end is connected to diode D n anode.

[0021] The connection form of n lithium-ion batteries is as follows:

[0022] The positive electrode of the lithium-ion battery B1 is connected to one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1;

[0023] The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2;

[0024] The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3;

[0025] ...and so on;

[0026] Lithium-ion battery B n The positive terminal is connected to the capacitor C n One end, lithium-ion battery B n Negative connection capacitor C n The other end.

[0027] The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in1 One end, drain of power switch S1;

[0028] 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; lithium-ion battery B (n-1) Negative electrode connected to lithium-ion battery B n positive electrode;

[0029] Lithium-ion battery B n The negative poles are connected to the input capacitor C in2 The other end is the source of the power switch S2.

[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 is in phase.

[0031] A half-bridge-based SOC active balancing circuit for a lithium-ion battery pack containing four battery cells includes a four-winding output half-bridge converter, three cross-capacitors, and four lithium-ion batteries, wherein:

[0032] The 4-winding output half-bridge converter includes power switches S1, S2, input capacitor C in1 、C in2 , excitation inductance L m , transformer T, first output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, third output diode D3, third output capacitor C3, fourth output diode D4, fourth output capacitor C4;

[0033] The connection form of the 4-winding output half-bridge converter is as follows:

[0034] Excitation inductance L m One end is connected to the primary winding L of the transformer T p Input terminal, source of power switch S1, drain of power switch S2, magnetizing inductor L m The other end is connected to the primary winding L of transformer T p Output terminal, input capacitor C in1 The other end, input capacitor C in2 one end;

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

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

[0037] Transformer T secondary winding L s3 One end is connected to the anode of diode D3, the cathode of diode D3 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary winding L of transformer T. s3 the other end;

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

[0039] Among the 3 jumper capacitors:

[0040] Capacitor C p1 One end is connected to the anode of diode D1 and capacitor C p1 The other end is connected to the anode of diode D2;

[0041] Capacitor C p2 One end is connected to the anode of diode D2 and the capacitor C p2 The other end is connected to the anode of diode D3;

[0042] Capacitor C p3 One end is connected to the anode of diode D3 and capacitor C p3 The other end is connected to the anode of diode D4.

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

[0044] The positive electrode of the lithium-ion battery B1 is connected to one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1;

[0045] The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2;

[0046] The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3;

[0047] The positive electrode of lithium-ion battery B4 is connected to one end of capacitor C4, and the positive electrode of lithium-ion battery B n The negative electrode is connected to the other end of capacitor C4.

[0048] The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in1 One end, drain of power switch S1;

[0049] 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;

[0050] The negative electrode of the lithium-ion battery B4 is connected to the input capacitor C in2 The other end is the source of the power switch S2.

[0051] When the power switch S1 is turned on and the power switch S2 is turned off, the diodes D1, D2, D3, and D4 are turned off, and the battery pack transfers energy to the primary winding of the transformer through series connection. The primary coil L 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 withstand reverse voltage and are cut off, and the secondary winding L s1 、L s2 、L s3 、L s4 is the capacitance C p1 、C p2 、C p3 When the power switch S1 is turned off and the power switch S2 is turned on, the diodes D1, D2, D3 and D4 are turned on, and the secondary winding L of the transformer T is turned on. s1 、L s2 、L s3 、L s4 The current drops, the capacitor C p1 、C p2 、C p3 Discharge, capacitors C1, C2, C3, and C4 charge.

[0052] The principle of battery balancing is to keep each battery cell in a series battery pack in a balanced state. Currently, the balance of the entire battery pack is mainly judged by whether the terminal voltage of the battery cell is balanced (same). During the entire switching cycle, according to the inductor volt-second balance principle, the secondary coil L s1 、L s2 、L s3 and L s4 The average voltage is 0, and the L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the circuit shows that the capacitor C p1 The voltage u Cp1 Equal to the output voltage u B2 Similarly, the capacitor C p2 The voltage u Cp2 Equal to the output voltage u B3 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u B4When the power switch S1 is turned off and the power switch S2 is turned on, the 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 output voltage u of the transformer secondary winding B1 .

[0053] Similarly, the capacitor C p2 The voltage u Cp2 Equal to the output voltage u of the transformer secondary winding B2 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u of the transformer secondary winding B3 When the capacitor C p1 、C p2 、C p3 When it is large enough, the voltages of the lithium-ion battery cells are equal.

[0054] Assume that the SOC of the single cell B1 in the lithium-ion battery pack is higher than the average value. When the power switch S1 is turned on, the lithium-ion battery B1 is connected in series with the lithium-ion batteries B2, B3, and B4, transferring the excess energy to the primary winding of the transformer. After the switch is turned off again, the secondary winding L s2 、L s3 、L s4 They are connected in parallel with lithium-ion batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transferred to lithium-ion batteries B2, B3, and B4. As a result, part of the energy of the series lithium-ion battery pack can be transferred to the battery cells with lower energy, achieving SOC balance of the lithium-ion battery pack.

[0055] The present invention provides a half-bridge based lithium-ion battery pack SOC active balancing circuit, which has the following technical effects:

[0056] 1) The present invention achieves the effect of automatic voltage balancing of the output voltages of a multi-output half-bridge converter by connecting a jumper capacitor between adjacent output windings of the half-bridge converter, thereby improving battery balancing.

[0057] 2) The circuit topology of the present invention is simple and only two switches are used, which reduces the difficulty of control system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0059] Figure 1 It is a circuit principle diagram of the present invention.

[0060] Figure 2 This is a circuit schematic diagram of the present invention for achieving SOC balancing of a lithium-ion battery pack with four single cells connected in series.

[0061] Figure 3 This is a simulation diagram of the present invention achieving balancing of a battery pack with four lithium-ion battery cells connected in series. DETAILED DESCRIPTION

[0062] like Figure 2 As shown, a half-bridge-based lithium-ion battery pack SOC active balancing circuit containing four battery cells includes a four-winding output half-bridge converter, three cross-capacitors, and four lithium-ion batteries, wherein:

[0063] The 4-winding output half-bridge converter includes power switches S1, S2, input capacitor C in1 、C in2 , excitation inductance L m , transformer T, first output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, third output diode D3, third output capacitor C3, fourth output diode D4, fourth output capacitor C4;

[0064] The connection form of the 4-winding output half-bridge converter is as follows:

[0065] Excitation inductance L m One end is connected to the primary winding L of the transformer T p Input terminal, source of power switch S1, drain of power switch S2, magnetizing inductor L m The other end is connected to the primary winding L of transformer T p Output terminal, input capacitor C in1 The other end, input capacitor C in2 one end;

[0066] Transformer T secondary winding L s1 One end is connected to the anode of diode D1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the secondary winding L of transformer T. s1 the other end;

[0067] Transformer T secondary winding L s2 One end is connected to the anode of diode D2, the cathode of diode D2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the secondary winding L of transformer T. s2 the other end;

[0068] Transformer T secondary winding L s3 One end is connected to the anode of diode D3, the cathode of diode D3 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary winding L of transformer T. s3 the other end;

[0069] Transformer T secondary winding L s4One end is connected to the anode of diode D4, the cathode of diode D4 is connected to one end of capacitor C4, and the other end of capacitor C4 is connected to the secondary winding L of transformer T. s4 The other end.

[0070] Among the 3 jumper capacitors:

[0071] Capacitor C p1 One end is connected to the anode of diode D1 and capacitor C p1 The other end is connected to the anode of diode D2;

[0072] Capacitor C p2 One end is connected to the anode of diode D2 and the capacitor C p2 The other end is connected to the anode of diode D3;

[0073] Capacitor C p3 One end is connected to the anode of diode D3 and capacitor C p3 The other end is connected to the anode of diode D4.

[0074] The connection of 4 lithium-ion batteries is as follows:

[0075] The positive electrode of the lithium-ion battery B1 is connected to one end of the capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1;

[0076] The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2;

[0077] The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3;

[0078] The positive electrode of lithium-ion battery B4 is connected to one end of capacitor C4, and the positive electrode of lithium-ion battery B n The negative electrode is connected to the other end of capacitor C4. The lithium-ion battery packs B1, B2, B3, and B4 also serve as the input source of the full-bridge converter.

[0079] The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in1 One end, drain of power switch S1;

[0080] 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;

[0081] The negative electrode of the lithium-ion battery B4 is connected to the input capacitor C in2 The other end is the source of the power switch S2.

[0082] When the power switch S1 is turned on and the power switch S2 is turned off, the diodes D1, D2, D3, and D4 are turned off, and the battery pack transfers energy to the primary winding of the transformer through series connection. The primary coil L 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 withstand reverse voltage and are cut off, and the secondary winding L s1 、L s2 、L s3 、L s4 is the capacitance C p1 、C p2 、C p3 When the power switch S1 is turned off and the power switch S2 is turned on, the diodes D1, D2, D3 and D4 are turned on, and the secondary winding L of the transformer T is turned on. s1 、L s2 、L s3 、L s4 The current drops, the capacitor C p1 、C p2 、C p3 Discharge, capacitors C1, C2, C3, and C4 charge;

[0083] The principle of battery balancing is to keep each battery cell in a series battery pack in a balanced state. Currently, the balance of the entire battery pack is mainly judged by whether the terminal voltage of the battery cell is balanced (same). During the entire switching cycle, according to the inductor volt-second balance principle, the secondary coil L s1 、L s2 、L s3 and L s4 The average voltage is 0, and the L s1 →C p1 →L s2 →C2→L s1 The capacitance C can be obtained by the KVL principle of the circuit p1 The voltage u Cp1 Equal to the output voltage u B2 Similarly, the capacitor C p2 The voltage u Cp2 Equal to the output voltage u B3 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u B4 When the power switch S1 is turned off and the power switch S2 is turned on, the capacitor C p1 Through the diode D1 and the output capacitor C1 in parallel, the capacitor C p1 The voltage uCp1 Equal to the output voltage u of the transformer secondary winding B1 Similarly, the capacitor C p2 The voltage u Cp2 Equal to the output voltage u of the transformer secondary winding B2 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u of the transformer secondary winding B3 When the capacitor C p1 、C p2 、C p3 When it is large enough, the voltages of the individual battery cells are equal.

[0084] Assume that the SOC of the single lithium-ion battery B1 in the battery pack is higher than the average value. When the power switch S1 is turned on, the lithium-ion battery B1 is connected in series with the lithium-ion batteries B2, B3, and B4, transferring the excess energy to the primary winding of the transformer. After the switch is turned off again, the secondary winding L s2 、L s3 、L s4 They are connected in parallel with lithium-ion batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transferred to lithium-ion batteries B2, B3, and B4. As a result, part of the energy of the series battery pack can be transferred to the battery cells with lower energy, achieving SOC balance of the lithium-ion battery pack.

[0085] Depend on Figure 3 It can be seen that the SOCs of the four batteries in the series-connected lithium-ion battery pack are different, while the other parameters are the same. The SOCs of lithium-ion battery B1, lithium-ion battery B2, lithium-ion battery B3, and lithium-ion battery B4 are 0.65. The converter proposed in the present invention can realize the transfer of lithium-ion battery cells with higher SOCs to lithium-ion battery cells with lower SOCs, and finally the SOCs of the four lithium-ion battery cells are balanced.

Claims

1. A half-bridge based lithium-ion battery pack SOC active balancing circuit, characterized by: It includes an n-winding output half-bridge converter, n-1 cross-capacitors, and n lithium-ion batteries, where: The n-winding output half-bridge converter includes power switches S1, S2, input capacitor C in1 、C in2 , excitation inductance L m , transformer T, first output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, ..., nth output diode D n , the nth output capacitor C n ; The connection form of the n-winding output half-bridge converter is as follows: Excitation inductance L m One end is connected to the primary winding L of the transformer T p Input terminal, source of power switch S1, drain of power switch S2, magnetizing inductor L m The other end is connected to the primary winding L of transformer T p Output terminal, input capacitor C in1 The other end, input capacitor C in2 one end; Transformer T secondary winding L s1 One end is connected to the anode of diode D1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the secondary winding L of transformer T. s1 the other end; Transformer T secondary winding L s2 One end is connected to the anode of diode D2, the cathode of diode D2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the secondary winding L of transformer T. s2 the other end; Transformer T secondary winding L s3 One end is connected to the anode of diode D3, the cathode of diode D3 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary winding L of transformer T. s3 the other end; ...and so on; Transformer T secondary winding L sn One end is connected to diode D n Anode, diode D n Cathode connection capacitor C n One end, capacitor C n The other end is connected to the secondary winding L of the transformer T sn the other end; Among n-1 jumper capacitors: Capacitor C p1 One end is connected to the anode of diode D1 and capacitor C p1 The other end is connected to the anode of diode D2; Capacitor C p2 One end is connected to the anode of diode D2 and the capacitor C p2 The other end is connected to the anode of diode D3; Capacitor C p3 One end is connected to the anode of diode D3 and capacitor C p3 The other end is connected to the anode of diode D4; ...and so on; Capacitor C p(n-1) One end is connected to diode D n-1 Anode, capacitor C p(n-1) The other end is connected to 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 capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1; The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2; The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3; ...and so on; Lithium-ion battery B n The positive electrode is connected to the capacitor C n One end, lithium-ion battery B n Negative connection capacitor C n the other end; The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in1 One end, drain of power switch S1; 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; lithium-ion battery B (n-1) Negative electrode connected to lithium-ion battery B n positive electrode; Lithium-ion battery B n The negative poles are connected to the input capacitor C in2 The other end is the source of the power switch S2.

2. The half-bridge based lithium-ion battery pack SOC active balancing circuit 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 and is in phase.

3. A half-bridge-based SOC active balancing circuit for a lithium-ion battery pack containing four battery cells, characterized by: The circuit includes a 4-winding output half-bridge converter, 3 cross-capacitors, and 4 lithium-ion batteries, among which: The 4-winding output half-bridge converter includes power switches S1, S2, input capacitor C in1 、C in2 , excitation inductance L m , transformer T, first output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, third output diode D3, third output capacitor C3, fourth output diode D4, fourth output capacitor C4; The connection form of the 4-winding output half-bridge converter is as follows: Excitation inductance L m One end is connected to the primary winding L of the transformer T p Input terminal, source of power switch S1, drain of power switch S2, magnetizing inductor L m The other end is connected to the primary winding L of transformer T p Output terminal, input capacitor C in1 The other end, input capacitor C in2 one end; Transformer T secondary winding L s1 One end is connected to the anode of diode D1, the cathode of diode D1 is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the secondary winding L of transformer T. s1 the other end; Transformer T secondary winding L s2 One end is connected to the anode of diode D2, the cathode of diode D2 is connected to one end of capacitor C2, and the other end of capacitor C2 is connected to the secondary winding L of transformer T. s2 the other end; Transformer T secondary winding L s3 One end is connected to the anode of diode D3, the cathode of diode D3 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the secondary winding L of transformer T. s3 the other end; Transformer T secondary winding L s4 One end is connected to the anode of diode D4, the cathode of diode D4 is connected to one end of capacitor C4, and the other end of capacitor C4 is connected to the secondary winding L of transformer T. s4 the other end; Among the 3 jumper capacitors: Capacitor C p1 One end is connected to the anode of diode D1 and capacitor C p1 The other end is connected to the anode of diode D2; Capacitor C p2 One end is connected to the anode of diode D2 and the capacitor C p2 The other end is connected to the anode of diode D3; Capacitor C p3 One end is connected to the anode of diode D3 and capacitor C p3 The other end is connected to the anode of 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 capacitor C1, and the negative electrode of the lithium-ion battery B1 is connected to the other end of the capacitor C1; The positive electrode of the lithium-ion battery B2 is connected to one end of the capacitor C2, and the negative electrode of the lithium-ion battery B2 is connected to the other end of the capacitor C2; The positive electrode of the lithium-ion battery B3 is connected to one end of the capacitor C3, and the negative electrode of the lithium-ion battery B3 is connected to the other end of the capacitor C3; The positive electrode of lithium-ion battery B4 is connected to one end of capacitor C4, and the positive electrode of lithium-ion battery B n The negative electrode is connected to the other end of capacitor C4; The positive electrode of the lithium-ion battery B1 is connected to the input capacitor C in1 One end, drain of power switch S1; 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; The negative electrode of the lithium-ion battery B4 is connected to the input capacitor C in2 The other end is the source of the power switch S2.

4. The half-bridge based lithium-ion battery pack SOC active balancing circuit according to claim 3, characterized in that: When the power switch S1 is turned on and the power switch S2 is turned off, the diodes D1, D2, D3, and D4 are turned off, and the battery pack transfers energy to the primary winding of the transformer through series connection. The primary coil L 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 withstand reverse voltage and are cut off, and the secondary winding L s1 、L s2 、L s3 、L s4 is the capacitance C p1 、C p2 、C p3 When the power switch S1 is turned off and the power switch S2 is turned on, the diodes D1, D2, D3 and D4 are turned on, and the secondary winding L of the transformer T is turned on. s1 、L s2 、L s3 、L s4 The current drops, the capacitor C p1 、C p2 、C p3 Discharge, capacitors C1, C2, C3, and C4 charge.

5. The half-bridge based lithium-ion battery pack SOC active balancing circuit according to claim 3, characterized in that: During the entire switching cycle, the transformer secondary coil L s1 、L s2 、L s3 and L s4 The average voltage is 0, and the L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the circuit shows that the capacitor C p1 The voltage u Cp1 Equal to the output voltage u B2 Similarly, capacitor C p2 The voltage u Cp2 Equal to the output voltage u B3 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u B4 When the power switch S1 is turned off and the power switch S2 is turned on, the 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 output voltage u of the transformer secondary winding B1 ; Similarly, the capacitor C p2 The voltage u Cp2 Equal to the output voltage u of the transformer secondary winding B2 , capacitor C p3 The voltage u Cp3 Equal to the output voltage u of the transformer secondary winding B3 ; When the capacitor C p1 、C p2 、C p3 When it is large enough, the voltages of the lithium-ion battery cells are equal.

6. The half-bridge based lithium-ion battery pack SOC active balancing circuit according to claim 3 is characterized in that: The SOC of the single cell B1 in the lithium-ion battery pack is higher than the average value. When the power switch S1 is turned on, the lithium-ion battery B1 is connected in series with the lithium-ion batteries B2, B3, and B4, transferring the excess energy to the primary winding of the transformer. After the switch is turned off again, the secondary winding L s2 、L s3 、L s4 They are connected in parallel with lithium-ion batteries B2, B3, and B4 respectively, and the energy stored in the transformer is transferred to lithium-ion batteries B2, B3, and B4, so that part of the energy of the series lithium-ion battery pack is transferred to the battery cells with lower energy, achieving SOC balance of the lithium-ion battery pack.

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