Battery soc active balancing circuit

Abstract

A battery SOC active balancing circuit contains an n-winding output flyback converter, n-1 cross-over capacitors, and n lithium ion batteries, wherein: the n-winding output flyback converter comprises a power switch S1, an excitation inductor L m , a transformer T, a first output diode D1, an output capacitor C1, a second output diode D2, an output capacitor C2, …, an n-th output diode D n , and an output capacitor C n . The n-1 cross-over capacitors are: cross-over capacitors C p1 , C p2 , …, and C p(n‑1) ; and the batteries are B1, B2, …, and B n . Compared with the conventional multi-winding transformer balancing structure, the battery SOC active balancing circuit only uses one switch to realize the balancing of the battery pack, thereby reducing the control difficulty and cost of the circuit.

Description

Technical Field

[0001] This invention relates to the field of battery balancing for series-connected single-cell batteries, and more specifically to a battery SOC active balancing circuit. Background Technology

[0002] Lithium-ion batteries are widely used as power batteries for electric vehicles due to their advantages such as high energy density, long cycle life, no memory effect, and high energy efficiency and zero pollution. However, the voltage and capacity of a single lithium-ion battery are small and cannot meet the capacity and power requirements of electric vehicles, so multiple lithium-ion batteries need to be connected in series and parallel to form a battery pack. However, differences in the environment, charging and discharging modes, and chemical characteristics of lithium batteries during manufacturing and use will lead to inconsistencies in the capacity, voltage, internal resistance, and other performance characteristics of individual cells. These inconsistencies between individual cells will cause problems with the durability, reliability, and safety of the battery pack. Therefore, in order to maintain the balance of individual cells in a lithium-ion battery pack, researchers have proposed many balancing circuits, devices, and methods. Current battery balancing technologies are mainly divided into passive balancing and active balancing. Passive balancing dissipates excess energy as heat through resistors, but this method will cause energy loss in the battery pack, and the high temperature environment caused by improper heat dissipation can damage the performance of the battery pack.

[0003] Active balancing technology transfers energy from higher-energy-density battery cells to lower-energy-density battery cells. For example, patent document CN113489083A discloses "A hierarchical balancing control method for lithium-ion battery packs based on a buck-boost converter." This method adds multiple energy storage inductors, diodes, and balancing control switches to the lithium-ion battery pack. By closing the control switches, the higher-energy-density cells store excess energy in the corresponding inductors. Then, by closing the control switches, the energy in the inductors is transferred to the lower-energy-density cells, forming a balancing control for the series-connected lithium-ion battery pack. Furthermore, two adjacent cells are grouped into small modules, and then adjacent small modules are grouped into a large module. Logic control achieves balancing at each level, realizing three-level balancing control. The balancing control method proposed in this patent can not only achieve balancing between two adjacent cells but also indirectly achieve balancing between two non-adjacent cells through balancing control between adjacent modules, shortening the energy transfer path and improving the efficiency of the battery pack balancing system. However, the balancing circuit used in this control method contains multiple control switches, making the logic control very complex. Summary of the Invention

[0004] To address the shortcomings of existing battery pack balancing technologies, this invention proposes an active battery SOC balancing circuit. This converter consists of a multi-winding flyback converter and multiple bridging capacitors. Based on transformer-type balancing, this circuit employs a multi-winding transformer balancing topology and achieves SOC balancing of the series-connected battery pack by adding a bridging capacitor between each winding. Compared to traditional multi-winding transformer balancing structures, this circuit uses only a single switch to achieve battery pack balancing, reducing the control complexity and cost.

[0005] The technical solution adopted in this invention is as follows:

[0006] A battery SOC active balancing circuit includes an n-winding output flyback converter, n-1 bridging capacitors, and n lithium-ion batteries, wherein:

[0007] An n-winding output flyback converter includes a power switch S1 and a magnetizing inductor L. m Transformer T, first output diode D1, output capacitor C1, second output diode D2, output capacitor C2, ..., nth output diode D n Output capacitor C n ;

[0008] The connection configuration of the n-winding output flyback converter is as follows:

[0009] Magnetizing inductance L m The upper end is connected to the primary winding L of transformer T. p Input terminal, magnetizing inductor L m The lower ends are respectively connected to the primary winding L of transformer T. p Output terminal, drain of power switch S1;

[0010] The secondary winding L of transformer T S1 The upper end of the capacitor is connected to the anode of diode D1, the cathode of diode D1 is connected to the upper end of capacitor C1, and the lower end of capacitor C1 is connected to the secondary winding L of transformer T. S1 The lower end;

[0011] The secondary winding L of transformer T S2 The upper end of the capacitor is connected to the anode of diode D2, the cathode of diode D2 is connected to the upper end of capacitor C2, and the lower end of capacitor C2 is connected to the secondary winding L of transformer T. S2 The lower end.

[0012] The secondary winding L of transformer T Sn-1 The upper end of the diode D n-1 Anode connection, diode D n-1 Cathode connection capacitor C n-1 At the upper end, capacitor C n-1The lower end is connected to the secondary winding L of transformer T. Sn-1 The lower end.

[0013] ...and so on,

[0014] The secondary winding L of transformer T Sn The upper end of the diode D n Anode connection, diode D n Cathode connection capacitor C n At the upper end, capacitor C n The lower end is connected to the secondary winding L of transformer T. Sn The lower end.

[0015] The connection configuration between the bridging capacitor and each output winding is as follows:

[0016] Cross capacitor C p1 The upper end is connected to the anode of diode D1, and a capacitor C is connected across it. p1 The lower end of the diode is connected to the anode of the diode D2;

[0017] Cross capacitor C p2 The upper end is connected to the anode of diode D2, and a capacitor C is connected across it. p2 The lower end is connected to the anode of diode D3;

[0018] Cross capacitor C p(n-2) The upper end of the diode D n-2 The anode connection is bridged by capacitor C. p(n-2) The lower end of the diode D n-1 Anode connection;

[0019] ...and so on,

[0020] Cross capacitor C p(n-1) The upper end of the diode D n-1 The anode connection, capacitor C p(n-1) The lower end of the diode D n Anode connection;

[0021] The positive terminal of battery B1 is connected to the cathode of diode D1 and the upper end of capacitor C1, respectively; the negative terminal of battery B1 is connected to the secondary winding L of transformer. S1 The lower end of capacitor C1;

[0022] The positive terminal of battery B2 is connected to the cathode of diode D2 and the upper end of capacitor C2, respectively; the negative terminal of battery B2 is connected to the secondary winding L of transformer. S2 The lower end of capacitor C2;

[0023] Battery B n-1 The positive terminals are respectively connected to diode D. n-1 cathode, capacitor Cn-1 The upper end; battery B n-1 The negative terminals are respectively connected to the secondary winding L of the transformer. Sn-1 The lower end, capacitor C n-1 The lower end;

[0024] ...and so on,

[0025] Battery B n The positive terminals are respectively connected to diode D. n cathode, capacitor C n The upper end; battery B n The negative terminals are respectively connected to the secondary winding L of the transformer. Sn The lower end, capacitor C n The lower end;

[0026] Battery packs B1, B2, ..., B n Simultaneously, it serves as the input source for the n-winding output flyback converter, with the positive terminal of battery B1 connected to the magnetizing inductor L. m The upper end of the transformer T, the primary winding L p Input terminal; Battery B n The negative terminal is connected to the source terminal of power switch S1.

[0027] The gate of the power switch S1 is connected to a controller, and its duty cycle can vary between 0 and 1 and is in phase.

[0028] Taking a battery pack composed of three individual cells B1, B2, and B3 connected in series as an example:

[0029] A battery SOC active balancing circuit includes a 3-winding output flyback converter, 2 bridging capacitors, and 3 lithium-ion batteries, wherein:

[0030] A 3-winding output flyback converter includes a power switch S1 and a magnetizing inductor L. m An ideal transformer T has a first-path output diode D1 and an output capacitor C1, a second-path output diode D2 and an output capacitor C2, and a third-path output diode D3 and an output capacitor C3.

[0031] The connection configuration of the 3-winding output flyback converter is as follows:

[0032] Magnetizing inductance L m The upper end is connected to the primary winding L of transformer T. p Input terminal, magnetizing inductor L m The lower ends are respectively connected to the primary winding L of transformer T. p Output terminal, drain of power switch S1;

[0033] The secondary winding L of transformer T S1The upper end of the capacitor is connected to the anode of diode D1, the cathode of diode D1 is connected to the upper end of capacitor C1, and the lower end of capacitor C1 is connected to the secondary winding L of transformer T. S1 The lower end;

[0034] The secondary winding L of transformer T S2 The upper end of the capacitor is connected to the anode of diode D2, the cathode of diode D2 is connected to the upper end of capacitor C2, and the lower end of capacitor C2 is connected to the secondary winding L of transformer T. S2 The lower end.

[0035] The secondary winding L of transformer T S3 The upper end of the capacitor is connected to the anode of diode D3, the cathode of diode D3 is connected to the upper end of capacitor C3, and the lower end of capacitor C3 is connected to the secondary winding L of transformer T. S3 The lower end.

[0036] The connection configuration between the bridging capacitor and each output winding is as follows:

[0037] Cross capacitor C p1 The upper end is connected to the anode of diode D1, and a capacitor C is connected across it. p1 The lower end of the diode is connected to the anode of the diode D2;

[0038] Cross capacitor C p2 The upper end is connected to the anode of diode D2, and a capacitor C is connected across it. p2 The lower end is connected to the anode of diode D3;

[0039] The positive terminal of battery B1 is connected to the cathode of diode D1 and the upper end of capacitor C1, respectively; the negative terminal of battery B1 is connected to the secondary winding L of transformer. S1 The lower end of capacitor C1;

[0040] The positive terminal of battery B2 is connected to the cathode of diode D2 and the upper end of capacitor C2, respectively; the negative terminal of battery B2 is connected to the secondary winding L of transformer. S2 The lower end of capacitor C2;

[0041] The positive terminal of battery B3 is connected to the cathode of diode D3 and the upper end of capacitor C3, respectively; the negative terminal of battery B3 is connected to the secondary winding L of transformer. S3 The lower end of capacitor C3;

[0042] Battery packs B1, B2, and B3 also serve as the input source for a 3-winding flyback converter. The positive terminal of battery B1 is connected to the magnetizing inductor L. m The upper end of the transformer T, the primary winding L p Input terminal: The negative terminal of battery B3 is connected to the source terminal of power switch S1.

[0043] When power switch S1 is turned on, diodes D1, D2, and D3 are turned off. The battery pack transfers energy to the primary winding of the transformer through series connection. p As the current increases, the transformer's energy storage increases, and the energy is simultaneously transferred to the secondary winding L. S1 L S2 L S3 Diodes D1, D2, and D3 are cut off under reverse voltage. Secondary winding L S1 L S2 L S3 For capacitor C p1 C p2 During charging, capacitors C1, C2, and C3 supply power to the load. Based on the inductor volt-second balance principle, the transformer secondary coil L... S1 L S2 and L S3 The average voltage is 0, due to L S1 →C p1 →L S2 →C2→L S1 The capacitance C can be obtained from the KVL principle of the circuit. p1 voltage u cp1 Equal to output voltage u B2 Similarly, capacitor C p2 voltage u cp1 Equal to output voltage u B3 When power switch S1 is turned off, diodes D1, D2, and D3 are turned on, and the secondary winding L... S1 Through loop L S1 (C p1 →D1→C1→L S1 (C p1 Charging capacitor C1; capacitor C p1 Since diode D1 and output capacitor C1 are connected in parallel, capacitor C... p1 voltage u cp1 Equal to the output voltage u of the transformer secondary winding B1 Similarly, capacitor C p2 voltage u cp2 Equal to the output voltage u of the transformer secondary winding B2 When capacitor C p1 C p2 When the capacity is large enough, the voltage of each battery cell is equal.

[0044] Assuming the state of charge (SOC) of individual cell B1 in the battery pack is higher than the average, when power switch S1 is turned on, cell B1 is connected in series with cells B2 and B3, transferring excess energy to the primary winding of the transformer. After the switch is turned off again, the secondary winding L of the transformer... S2 L S3Connected in parallel with batteries B2 and B3 respectively, the energy stored in the transformer is transferred to batteries B2 and B3, so that part of the energy of the series battery pack can be transferred to the lower energy individual battery cells, thus realizing the SOC balance of the battery pack.

[0045] This invention discloses a battery SOC active balancing circuit, the technical effects of which are as follows:

[0046] 1) The equalization circuit of this invention achieves automatic voltage equalization of the output voltage of a multi-output flyback converter by connecting a bridging capacitor between adjacent output windings of the flyback converter, thereby improving battery balance.

[0047] 2) The equalization circuit of this invention has a simple circuit topology and uses only one switch, which reduces the difficulty of the control system design.

[0048] 3) The equalization circuit of this invention avoids the problem of unbalanced terminal voltage caused by cross-regulation when the transformer has multiple windings, effectively reducing voltage deviation and improving battery equalization accuracy. Attached Figure Description

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

[0050] Figure 1 This is the circuit schematic diagram of the present invention;

[0051] Figure 2 This is a circuit diagram illustrating the SOC balancing mechanism of a battery pack consisting of three single-cell batteries connected in series, as described in this invention.

[0052] Figure 3 This is a simulation diagram illustrating the balanced operation of a battery pack consisting of three connected battery cells, as described in this invention. Detailed Implementation

[0053] Example:

[0054] like Figure 2 As shown, a battery SOC active balancing circuit includes a 3-winding output flyback converter, 2 bridging capacitors, and 3 lithium-ion batteries, wherein:

[0055] A 3-winding output flyback converter includes a power switch S1 and a magnetizing inductor L. m An ideal transformer T has a first-path output diode D1 and an output capacitor C1, a second-path output diode D2 and an output capacitor C2, and a third-path output diode D3 and an output capacitor C3.

[0056] The basic dual-winding output flyback converter connection is as follows: Magnet inductor L m The upper end and the primary winding L of the ideal transformer T p Input connection, magnetizing inductor L mThe lower end and the primary winding L of the ideal transformer T p The output terminals are connected to the drain of power switch S1, the gate of S1 is connected to the controller, and the secondary winding L of the ideal transformer T is connected to the controller. S1 The upper end is connected to the anode of diode D1, the cathode of diode D1 is connected to the upper end of capacitor C1, and the lower end of capacitor C1 is connected to the secondary winding L of ideal transformer T. S1 The lower end. The secondary winding L of an ideal transformer T. S2 The upper end is connected to the anode of diode D2, the cathode of diode D2 is connected to the upper end of capacitor C2, and the lower end of capacitor C2 is connected to the secondary winding L of ideal transformer T. S2 The lower end. The secondary winding L of an ideal transformer T. S3 The upper end is connected to the anode of diode D3, the cathode of diode D3 is connected to the upper end of capacitor C3, and the lower end of capacitor C3 is connected to the secondary winding L of ideal transformer T. S3 The lower end.

[0057] The connection configuration between the bridging capacitor and each output winding is as follows:

[0058] Cross capacitor C p1 The upper end is connected to the anode of diode D1, and a capacitor C is connected across it. p1 The lower end of the capacitor is connected to the anode of diode D2. A capacitor C is connected across it. p2 The upper end is connected to the anode of diode D2, and a capacitor C is connected across it. p2 The lower end is connected to the anode of diode D3.

[0059] The positive terminal of battery B1 is connected to the intersection of the cathode of diode D1 and the upper end of capacitor C1. The negative terminal of battery B1 is connected to the secondary winding L of the ideal transformer. S1 The lower end of battery B2 is connected to the lower end of capacitor C1 at the intersection; the positive terminal of battery B2 is connected to the intersection of the cathode of diode D2 and the upper end of capacitor C2 at the intersection; the negative terminal of battery B2 is connected to the secondary winding L of the ideal transformer. S2 The lower end of battery B3 is connected to the intersection of the lower end of capacitor C2; the positive terminal of battery B3 is connected to the intersection of the cathode of diode D3 and the upper end of capacitor C3; the negative terminal of battery B3 is connected to the intersection of the lower end of the ideal transformer secondary winding L. S3 The lower end of the capacitor C1 is connected to the lower end of capacitor C3 at the intersection. Battery packs B1, B2, and B3 also serve as the input source for the flyback converter. The positive terminal of battery B1 is connected to the magnetizing inductor L. m The upper end and the primary winding L of the ideal transformer T p The input terminals are connected at the intersection, and the negative terminal of battery B3 is connected to the source terminal of power switch S1.

[0060] When power switch S1 is turned on, diodes D1, D2, and D3 are turned off. The battery pack transfers energy to the primary winding of the transformer through series connection. p As the current increases, the transformer's energy storage increases, and the energy is simultaneously transferred to the secondary winding L. S1 L S2 L S3 Diodes D1, D2, and D3 are cut off under reverse voltage. Secondary winding L S1 L S2 L S3 For capacitor C p1 C p2 During charging, capacitors C1, C2, and C3 supply power to the load. Based on the inductor volt-second balance principle, the transformer secondary coil L... S1 L S2 and L S3 The average voltage is 0, due to L S1 →C p1 →L S2 →C2→L S1 The capacitance C can be obtained from the KVL principle of the circuit. p1 voltage u cp1 Equal to output voltage u B2 Similarly, capacitor C p2 voltage u cp1 Equal to output voltage u B3 When power switch S1 is turned off, diodes D1, D2, and D3 are turned on, and the secondary winding L... S1 Through loop L S1 (C p1 →D1→C1→L S1 (C p1 Charging capacitor C1; capacitor C p1 Since diode D1 and output capacitor C1 are connected in parallel, capacitor C... p1 voltage u cp1 Equal to the output voltage u of the transformer secondary winding B1 Similarly, capacitor C p2 voltage u cp2 Equal to the output voltage u of the transformer secondary winding B2 When capacitor C p1 C p2 When the voltage is large enough, the output voltages of the transformer's secondary windings are equal, achieving consistency on the transformer's secondary side.

[0061] Assuming the state of charge (SOC) of individual cell B1 in the battery pack is higher than the average, when power switch S1 is turned on, cell B1 is connected in series with cells B2 and B3, transferring excess energy to the primary winding of the transformer. After switch S1 is turned off, the secondary winding L of the transformer... S2 L S3Connected in parallel with batteries B2 and B3 respectively, the energy stored in the transformer is transferred to batteries B2 and B3, so that part of the energy of the series battery pack can be transferred to the lower energy individual battery cells, thus realizing the SOC balance of the battery pack.

[0062] Depend on Figure 3 It can be seen that the three battery packs are actually set with different SOCs, while other parameters are the same. Battery B1 is set to 90, battery B2 to 80, and battery B3 to 70. The converter proposed in this invention can transfer the SOC of the battery cells with higher SOCs to the battery cells with lower SOCs, and finally the SOCs of the three battery cells are balanced.

Claims

1. A battery SOC active balancing circuit, characterized in that: It includes an n-winding flyback converter, n-1 bridging capacitors, and n lithium-ion batteries, wherein: An n-winding output flyback converter includes a power switch. Magnetizing inductor Transformer T, first output diode Output capacitor Second output diode Output capacitor ..., nth output diode Output capacitor ; The connection configuration of the n-winding output flyback converter is as follows: Magnetizing inductor The upper end is connected to the primary winding of transformer T. Input terminal, magnetizing inductor The lower ends are respectively connected to the primary winding of transformer T. Output terminal, power switch The drain electrode; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; ...and so on, The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The connection configuration between the bridging capacitor and each secondary winding is as follows: bridging capacitor The upper end of the diode Anode connection, bridging capacitor The lower end of the diode Anode connection; bridging capacitor The upper end of the diode Anode connection, bridging capacitor The lower end of the diode Anode connection; ...and so on, bridging capacitor The upper end of the diode Anode connection, bridging capacitor The lower end of the diode Anode connection; bridging capacitor The upper end of the diode anode connection, capacitor The lower end of the diode Anode connection; Battery The positive terminals are connected to diodes respectively. cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end of the capacitor The lower end; Battery The positive terminals are connected to diodes respectively. cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end, capacitor The lower end; ...and so on, Battery The positive terminals are connected to diodes respectively. cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end, capacitor The lower end; Battery The positive terminals are connected to diodes respectively. cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end, capacitor The lower end; Battery The positive terminals are respectively connected to the magnetizing inductor The upper end of the primary winding of transformer T Input terminal; battery The negative terminal is connected to the power switch. The source pole.

2. The battery SOC active balancing circuit according to claim 1, characterized in that: The power switch The gate-connected controller has a duty cycle that can vary between 0 and 1 and is in phase.

3. A battery SOC active balancing circuit, characterized in that: It includes a 3-winding output flyback converter, 2 bridging capacitors, and 3 lithium-ion batteries, wherein: A 3-winding output flyback converter includes a power switch. Magnetizing inductor Ideal transformer T, first output diode Output capacitor Second output diode Output capacitor Third output diode Output capacitor ; The connection configuration of the 3-winding output flyback converter is as follows: Magnetizing inductor The upper end is connected to the primary winding of transformer T. Input terminal, magnetizing inductor The lower ends are respectively connected to the primary winding of transformer T. Output terminal, power switch The drain electrode; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The secondary winding of transformer T The upper end of the diode Anode connection, diode Cathode connection capacitor At the top, the capacitor The lower end is connected to the secondary winding of transformer T. The lower end; The connection configuration between the bridging capacitor and each secondary winding is as follows: bridging capacitor The upper end of the diode Anode connection, bridging capacitor The lower end of the diode Anode connection; bridging capacitor The upper end of the diode Anode connection, bridging capacitor The lower end of the diode Anode connection; Battery The positive terminals are connected to diodes respectively. cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end of the capacitor The lower end; Battery The positive terminals are respectively connected to diodes cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end of the capacitor The lower end; Battery The positive terminals are respectively connected to diodes cathode, capacitor The upper part; battery The negative terminals are respectively connected to the secondary winding of the transformer. The lower end of the capacitor The lower end; battery pack , , Simultaneously, it serves as the input source for a 3-winding output flyback converter; the battery... The positive terminals are respectively connected to the magnetizing inductor The upper end of the primary winding of transformer T Input terminal; battery The negative terminal is connected to the power switch. The source pole.

4. The battery SOC active balancing circuit according to claim 3, characterized in that: When the power switch When the diode is turned on, , , When switched off, the battery pack transfers energy to the primary winding of the transformer via series connection. As the current increases, the transformer's energy storage increases, and the energy is transferred to the secondary winding. , , ,diode , , Reverse voltage cutoff; secondary winding , , For capacitor , Charging, capacitor , , To supply power to the load, based on the inductor volt-second balance principle, the transformer secondary winding... , and The average voltage is 0, from → → → → The capacitance can be obtained from the KVL principle of the circuit. voltage equal to output voltage Similarly, capacitors voltage equal to output voltage ; When the power switch When turned off, the diode , , Conduction, secondary winding Through the loop → → → To capacitor Charging; capacitor Through diode and output capacitor Parallel connection, therefore capacitor voltage Equal to the output voltage of the transformer secondary winding Similarly, capacitors voltage Equal to the output voltage of the transformer secondary winding When the capacitor , When the capacity is large enough, the voltage of each battery cell is equal.

5. The battery pack SOC balancing method of the balancing circuit as described in claim 3 or 4, characterized in that: Assume a single cell in the battery pack The SOC is higher than average in power switches. Battery when conducting With battery , In series connection, excess energy is transferred to the primary winding of the transformer. After the switch is opened again, the secondary winding of the transformer... , With batteries respectively , Parallel connection transfers the energy stored in the transformer to the battery. , This allows some of the energy in the series-connected battery pack to be transferred to the lower-energy individual battery cells, thus achieving SOC balancing of the battery pack.

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