A series battery pack active equalization circuit

Abstract

A series battery pack active balancing circuit, comprising n-way output double-tube flyback converter, n-1 cross-over capacitor, n lithium ion battery; n-way output double-tube flyback converter comprises: a power switch S1, power switch S2, excitation inductance L m , n-way output transformer T, clamping diode D 1p , clamping diode D 2p ; first output diode D1, second output diode D2,..., n-way output diode D n ; first output capacitor C 1, second output capacitor C 2,..., n-way output capacitor C n Compared with the traditional multi-winding transformer balancing structure, the present application realizes the automatic voltage balancing between battery units through the cross-over capacitor, without the need for complex sampling and control algorithm, and avoids the end voltage imbalance problem caused by the cross regulation ratio of the transformer in the multi-winding output, effectively reduces the voltage deviation, and improves the battery balancing accuracy.

Description

Technical Field

[0001] This invention relates to the field of battery pack balancing technology, specifically to an active balancing circuit for a series battery pack. 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 no 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. Therefore, multiple lithium-ion batteries need to be connected in series and parallel to form a battery pack.

[0003] However, differences in the environment, charging and discharging modes, and chemical characteristics during the manufacturing and use of lithium batteries can lead to inconsistencies in the capacity, voltage, and internal resistance of individual cells. These inconsistencies can cause problems with the durability, reliability, and safety of the battery pack. Therefore, 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 causes energy loss in the battery pack, and the high-temperature environment caused by improper heat dissipation can damage the performance of the battery pack.

[0004] 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. This patent's balancing control method not only achieves balancing between two adjacent cells but also indirectly achieves 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 method contains multiple control switches, making the logic control very complex. Summary of the Invention

[0005] This invention provides an active balancing circuit for series battery packs. Based on a centralized transformer balancing circuit, it employs a multi-winding transformer balancing topology. By adding a bridging capacitor between each winding, it achieves equal terminal voltage across the battery cells within the pack. Compared to traditional multi-winding transformer balancing structures, this invention achieves automatic voltage equalization between battery cells through the bridging capacitor, eliminating the need for complex sampling and control algorithms. Furthermore, it avoids the terminal voltage imbalance caused by cross-regulation when the transformer operates with multiple windings, effectively reducing voltage deviation and improving battery balancing accuracy.

[0006] The technical solution adopted in this invention is as follows:

[0007] An active balancing circuit for a series battery pack includes an n-channel output dual-transistor flyback converter, n-1 bridging capacitors, and n lithium-ion batteries.

[0008] The n-channel output dual-transistor flyback converter includes: a power switch S1, a power switch S2, and a magnetizing inductor L. m n-channel output transformer T, clamping diode D 1p Clamping diode D 2p The first output diode is D1, the second output diode is D2, ..., the nth output diode is D... n The first output capacitor is C1, the second output capacitor is C2, ..., the nth output capacitor is C... n The n-channel output dual-transistor flyback converter is connected as follows:

[0009] Clamping diode D 1p The cathode is connected to the drain of the power switch S1;

[0010] The source of power switch S1 is connected to clamping diode D. 2p Cathode, magnetizing inductor L m The upper end of the n-channel output transformer T, the primary winding L p The upper end;

[0011] Energy storage inductor L m The lower ends are respectively connected to clamping diodes D 1p The anode of the power switch S2, the drain of the power switch S2, and the primary winding L of the n-channel output transformer T. p The lower end;

[0012] The source of power switch S2 is connected to clamping diode D. 2p anode;

[0013] The secondary winding L of the n-channel output transformer T s1The upper end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to the upper end of the first output capacitor C1, and the lower end of the first output capacitor C1 is connected to the secondary winding L of the n-channel output transformer T. s1 The lower end;

[0014] The secondary winding L of the n-channel output transformer T s2 The upper end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to the upper end of the second output capacitor C2, and the lower end of the second output capacitor C2 is connected to the secondary winding L of the n-channel output transformer T. s2 The lower end;

[0015] The secondary winding L of the n-channel output transformer T s2 The upper end is connected to the (n-1)th diode D n-1 The anode, the (n-1)th output diode D n-1 The cathode is connected to the (n-1)th output capacitor C. n-1 At the top, the (n-1)th output capacitor C n-1 The lower end is connected to the secondary winding L of the n-channel output transformer T. s2 The lower end;

[0016] ...and so on,

[0017] The secondary winding L of the n-channel output transformer T sn The upper end is connected to the nth output diode D n The anode connection, the nth output diode D n The cathode is connected to the nth output capacitor C. n At the top, the nth output capacitor C n The lower end is connected to the secondary winding L of the n-channel output transformer T. sn The lower end;

[0018] The connection configuration between the bridging capacitor and each output winding is as follows:

[0019] Cross capacitor C p1 The upper end is connected to the anode of the first output diode D1, and a capacitor C is connected across it. p1 The lower end is connected to the anode of the second output diode D2; a capacitor C is connected across it. p2 The upper end is connected to the anode of the second output diode D2, and a capacitor C is connected across it. p2 The lower end is connected to the anode of the third output diode D3; ... and so on, with capacitor C connected across it. p(n-1) The upper end is connected to the (n-1)th output diode D n-1 The anode connection is bridged by capacitor C. p(n-1) The lower end is connected to the nth output diode D n Anode connection;

[0020] The upper end of battery B1 is connected to the intersection of the cathode of the first output diode D1 and the upper end of the first output capacitor C1. The lower end of battery B1 is connected to the secondary winding L of the n-channel output transformer T. s1 Connect the lower end of the capacitor to the intersection of the lower end of the first output capacitor C1;

[0021] The upper end of battery B2 is connected to the intersection of the cathode of the second output diode D2 and the upper end of the second output capacitor C2. The lower end of battery B2 is connected to the secondary winding L of the n-channel output transformer T. s2 Connect the lower end of the capacitor to the intersection of the lower end of the second output capacitor C2;

[0022] ...and so on,

[0023] Battery B n-1 The upper end is connected to the (n-1)th output diode D n-1 The cathode and the (n-1)th output capacitor C n-1 The upper end of the intersection is connected; battery B n-1 The lower end is connected to the secondary winding L of the n-1 output transformer T. sn-1 The lower end and the (n-1)th output capacitor C n-1 Connect the lower ends of the intersection;

[0024] Battery B n The upper end is connected to the nth output diode D n The cathode and the nth output capacitor C n The upper end of the intersection is connected; battery B n The lower end is connected to the secondary winding L of the n-channel output transformer T. sn The lower end and the nth output capacitor C n Connect the lower ends of the intersection;

[0025] The upper end of battery B1 is connected to clamping diode D 1p Cathode connection, battery B n The lower end is connected to the clamping diode D 2p Anode connection.

[0026] The gates of power switch S1 and power switch S2 are respectively connected to their respective controllers.

[0027] The batteries B1, B2, ..., B n As the input source of an n-output dual-transistor flyback converter, its duty cycle can vary between 0 and 0.5 and is in phase.

[0028] Taking a battery pack consisting of three single cells B1, B2, and B3 connected in series as an example, when the upper power switch S1 and the lower power switch S2 are turned on, the clamping diode D... 1pClamping diode D 2p With the first output diode D1, the second output diode D2, and the third output diode D3 turned off, the battery pack applies energy to the primary winding L of transformer T through series connection. p Above, magnetizing inductor L m As the current increases, the energy stored in the transformer increases, and simultaneously, the primary winding L of transformer T... p Energy is transferred to the secondary winding L of transformer T. s1 L s2 and L s3 The first output diode D1, the second output diode D2, and the third output diode D3 are cut off under reverse voltage. The secondary winding L of transformer T... s1 L s2 and L s3 For the bridging capacitor C p1 and C p2 During charging, output capacitors C1, C2, and C3 provide energy to the battery pack.

[0029] Taking a battery pack consisting of three individual cells B1, B2, and B3 connected in series as an example, when the upper power switch S1 and the lower power switch S2 are turned off, the clamping diode D... 1p Clamping diode D 2p The circuit is turned on, clamping the voltage on the power switch to the battery pack voltage. After clamping, the clamping diode D... 1p Clamping diode D 2p Turn off. Simultaneously, the first output diode D1, the second output diode D2, and the third output diode D3 remain conducting during the power switch turn-off phase, and the secondary winding L of transformer T... s1 L s2 and L s3 The current decreases, and the capacitor C is connected across it. p1 and C p2 Discharges the capacitors C1, C2, and C3, which in turn charge them.

[0030] The principle of battery balancing is to maintain all battery cells in a series-connected battery pack in a balanced state. Currently, the balance of the entire battery pack is mainly judged by whether the terminal voltages of the battery cells are balanced (identical). Throughout the entire switching cycle, according to the inductor volt-second balance principle, the secondary winding L of transformer T... s1 L s2 and L s3 The average voltage is 0, due to L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the loop can be used to obtain the bridging capacitor C. p1 voltage u cp1equal to the battery B2 voltage u B2 Similarly, the bridging capacitor C p2 voltage u cp2 Equal to battery B3 voltage u B3 When power switches S1 and S2 are off, diodes D1, D2, and D3 are on, and the secondary winding L of transformer T is turned on. 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 battery B1 voltage u B1 Similarly, the bridging capacitor C p2 voltage u cp2 equal to the battery B2 voltage u B2 When capacitor C p1 C p2 When the voltage is large enough, the voltage of each battery cell is equal. If there is a battery cell with a relatively low voltage, the power switch is closed first, and part of the energy of the battery pack is stored in the magnetizing inductance of the transformer. When the power switch is opened, this energy is transferred to the battery cell with the lower voltage. Thus, part of the energy of the series battery pack can be transferred to the battery cell with the lower energy, achieving the balance of the battery pack.

[0031] The present invention discloses an active balancing circuit for a series battery pack, the technical effects of which are as follows:

[0032] 1) This invention can effectively reduce the problem of unbalanced terminal voltage caused by cross-regulation rate when the transformer has multiple windings, reduce voltage deviation, and improve battery balancing accuracy.

[0033] 2) The circuit control of this invention is simple. Automatic voltage equalization between battery cells is achieved by bridging capacitors, without the need for complex sampling and control algorithms.

[0034] 3) Compared with the traditional multi-winding transformer equalization structure, the present invention achieves automatic voltage equalization between battery cells by bridging capacitors, without the need for complex sampling and control algorithms, and avoids the problem of unbalanced terminal voltage caused by cross-regulation rate when the transformer outputs multiple windings, effectively reducing voltage deviation and improving battery equalization accuracy. Attached Figure Description

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0036] Figure 1 This is the circuit schematic diagram of the present invention.

[0037] Figure 2 This is a circuit diagram illustrating the balanced operation of a battery pack consisting of three connected battery cells, as described in this invention.

[0038] 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

[0039] like Figure 2 As shown, this invention provides an active balancing circuit for a battery pack containing three battery cells. The circuit includes a three-output dual-transistor flyback converter, two bridging capacitors, and three lithium-ion batteries, wherein:

[0040] A 3-output dual-transistor flyback converter includes an upper power switch S1, a lower power switch S2, and a magnetizing inductor L. m 3-channel output transformer T, clamping diode D 1p Clamping diode D 2p First output diode D1, first output capacitor C1, second output diode D2, second output capacitor C2, third output diode D3, third output capacitor C3.

[0041] The connection configuration of the 3-output dual-transistor flyback converter is as follows:

[0042] Clamping diode D 1p The cathode is connected to the drain of the upper power switch S1. The magnetizing inductor L... m The upper end and the primary winding L of the 3-way output transformer T p The upper end and the source of the upper power switch S1 are simultaneously connected to the input clamping diode D. 2p The cathode. Magnetizing inductance L m The lower end and the primary winding L of the 3-way output transformer T p The lower end and the drain of the lower power switch S2 are respectively connected to clamping diode D. 1p The anode. Clamping diode D 2p The anode of the upper power switch S1 is connected to the source of the lower power switch S2. The gates of the upper power switch S1 and the lower power switch S2 are respectively connected to their respective controllers. The secondary winding L of the 3-channel output transformer T... s1 The upper end is connected to the anode of the first output diode D1, the cathode of the first output diode D1 is connected to the upper end of the first output capacitor C1, and the lower end of the first output capacitor C1 is connected to the secondary winding L of the 3-channel output transformer T. s1 The lower end; the secondary winding L of the 3-way output transformer T. s2 The upper end is connected to the anode of the second output diode D2, the cathode of the second output diode D2 is connected to the upper end of the second output capacitor C2, and the lower end of the second output capacitor C2 is connected to the secondary winding L of the three-output transformer T.s2 The lower end; the secondary winding L of the 3-way output transformer T. s3 The upper end is connected to the anode of the third output diode D3, the cathode of the third output diode D3 is connected to the upper end of the third output capacitor C3, and the lower end of the third output capacitor C3 is connected to the secondary winding L of the three-output transformer T. s3 The lower end.

[0043] The connection between the bridging capacitor and each output winding is as follows: Bridging capacitor C p1 The upper end is connected to the anode of the first output diode D1, and a capacitor C is connected across it. p1 The lower end is connected to the anode of the second output diode D2; a bridging capacitor C is connected. p2 The upper end is connected to the anode of the second output diode D2, and a capacitor C is connected across it. p2 The lower end is connected to the anode of the third output diode D3.

[0044] The upper end of battery B1 is connected to the intersection of the cathode of the first output diode D1 and the upper end of the first output capacitor C1. The lower end of battery B1 is connected to the secondary winding L of the 3-channel output transformer T. s1 The lower end of battery B2 is connected to the intersection of the lower end of the first output capacitor C1; the upper end of battery B2 is connected to the intersection of the cathode of the second output diode D2 and the upper end of the second output capacitor C2; the lower end of battery B2 is connected to the secondary winding L of the 3-channel output transformer T. s2 The lower end of battery B3 is connected to the intersection of the lower end of the second output capacitor C2; the upper end of battery B3 is connected to the intersection of the cathode of the third output diode D3 and the upper end of the third output capacitor C3; the lower end of battery B3 is connected to the secondary winding L of the 3-channel output transformer T. s3 The lower end of the capacitor is connected to the intersection of the lower end of the third output capacitor C3. Batteries B1, B2, and B3 also serve as the input source of the dual-transistor flyback converter. The upper end of battery B1 is connected to the clamping diode D. 1p The cathode is connected, and the lower end of battery B3 is connected to clamping diode D. 2p Anode connection.

[0045] The gates of the upper power switch S1 and the lower power switch S2 are connected to their respective controllers, and their duty cycles can vary between 0 and 0.5 and are in phase.

[0046] When the upper power switch S1 and the lower power switch S2 are turned on, the clamping diode D 1p Clamping diode D 2p With the first output diode D1, the second output diode D2, and the third output diode D3 turned off, the battery pack applies energy to the primary winding L of transformer T through series connection. p Above, excitation inductor L mAs the current increases, the energy stored in the transformer increases, and simultaneously, the primary winding L of transformer T... p Energy is transferred to the secondary winding L of transformer T. s1 L s2 and L s3 The first output diode D1, the second output diode D2, and the third output diode D3 are cut off under reverse voltage. The secondary winding L of transformer T... s1 L s2 and L s3 For the bridging capacitor C p1 and C p2 During charging, output capacitors C1, C2, and C3 provide energy to the battery pack.

[0047] When the upper power switch S1 and the lower power switch S2 are turned off, the clamping diode D... 1p Clamping diode D 2p The circuit is turned on, clamping the voltage on the power switch to the battery pack voltage. After clamping, the clamping diode D... 1p Clamping diode D 2p Turn off. Simultaneously, the first output diode D1, the second output diode D2, and the third output diode D3 remain conducting during the power switch turn-off phase, and the secondary winding L of transformer T... s1 L s2 and L s3 The current decreases, and the capacitor C is connected across it. p1 and C p2 Discharge, and output capacitors C1, C2 and C3 are charged.

[0048] The principle of battery balancing is to maintain all battery cells in a series-connected battery pack in a balanced state. Currently, the balance of the entire battery pack is mainly judged by whether the terminal voltages of the battery cells are balanced (identical). Throughout the entire switching cycle, according to the inductor volt-second balance principle, the secondary winding L of transformer T... s1 L s2 and L s3 The average voltage is 0, due to L s1 →C p1 →L s2 →C2→L s1 The KVL principle of the loop can be used to obtain the bridging capacitor C. p1 voltage u cp1 equal to the battery B2 voltage u B2 Similarly, the bridging capacitor C p2 voltage u cp2 Equal to battery B3 voltage u B3 When power switches S1 and S2 are off, diodes D1, D2, and D3 are on, and the secondary winding L of transformer T is turned on. s1 Through loop Ls1 (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 battery B1 voltage u B1 Similarly, the bridging capacitor C p2 voltage u cp2 equal to the battery B2 voltage u B2 When capacitor C p1 C p2 When the voltage is large enough, the voltage of each battery cell is equal. If there is a battery cell with a relatively low voltage, the power switch is closed first, and part of the energy of the battery pack is stored in the magnetizing inductance of the transformer. When the power switch is opened, this energy is transferred to the battery cell with the lower voltage. Thus, part of the energy of the series battery pack can be transferred to the battery cell with the lower energy, achieving the balance of the battery pack.

[0049] Depend on Figure 3 It can be seen that the initial SOC of the three battery cells are different, with battery B1 at 90, battery B2 at 80, and battery B3 at 70. Through this invention, the power of the battery cell with higher SOC can be transferred to the battery cell with lower SOC, and finally the SOC of the three battery cells is balanced.

Claims

1. An active balancing circuit for a series battery pack, characterized in that: It includes an n-output dual-transistor flyback converter, n-1 bridging capacitors, and n lithium-ion batteries; The n-channel output dual-transistor flyback converter includes: a power switch S1, a power switch S2, and a magnetizing inductor. L m n-channel output transformer T, clamping diode D 1p Clamping diode D 2p The first output diode is D1, the second output diode is D2, ..., the nth output diode is D... n First output capacitor C 1. Second output capacitor C 2, ..., nth output capacitor C n The n-channel output dual-transistor flyback converter is connected as follows: Clamping diode D 1p The cathode is connected to the drain of the power switch S1; The source of power switch S1 is connected to clamping diode D. 2p Cathode, magnetizing inductor L m The upper end of the n-channel output transformer T, the primary winding L p The upper end; Magnetizing inductor L m The lower ends are respectively connected to clamping diodes D 1p The anode of the power switch S2, the drain of the power switch S2, and the primary winding of the n-channel output transformer T. L p The lower end; The source of power switch S2 is connected to clamping diode D. 2p anode; The secondary winding of the n-channel output transformer T L s1 The upper end is connected to the anode of the first output diode D1, and the cathode of the first output diode D1 is connected to the first output capacitor. C At the top of 1, the first output capacitor C The lower end of 1 is connected to the secondary winding of the n-channel output transformer T. L s1 The lower end; The secondary winding of the n-channel output transformer T L s2 The upper end is connected to the anode of the second output diode D2, and the cathode of the second output diode D2 is connected to the second output capacitor. C At the top of 2, the second output capacitor C The lower end of 2 is connected to the secondary winding of the n-channel output transformer T. L s2 The lower end; The secondary winding of the n-channel output transformer T L s2 upper end and the first n -1 diode D n-1 The anode, the first n -1 Output Diode D n-1 Cathode connection n -1 output capacitor C n-1 The upper end, the first n -1 output capacitor C n-1 The lower end is connected to the secondary winding of the n-channel output transformer T. L s2 The lower end; ...and so on, The secondary winding of the n-channel output transformer T L sn upper end and the first n Output diode D n The anode connection, the first n Output diode D n Cathode connection n Output capacitor C n The upper end, the first n Output capacitor C n lower end connection n The secondary winding of the output transformer T L sn The lower end; The connection configuration between the bridging capacitor and each secondary winding is as follows: bridging capacitor C p1 The upper end is connected to the anode of the first output diode D1, and a capacitor is connected across it. C p1 The lower end is connected to the anode of the second output diode D2; a bridging capacitor is connected. C p2 The upper end is connected to the anode of the second output diode D2, and a capacitor is connected across it. C p2 The lower end is connected to the anode of the third output diode D3; ...and so on, with a bridging capacitor. C p(n-1) The upper end and the first n -1 Output Diode D n-1 Anode connection, bridging capacitor C p(n-1) The lower end is connected to the nth output diode D n Anode connection; Battery B The upper end of 1 is connected to the cathode of the first output diode D1 and the first output capacitor. C The upper intersection of 1 is connected to the battery. B The lower end of 1 is connected to the secondary winding of the n-channel output transformer T. L s1 The lower end and the first output capacitor C Connect the lower ends of 1; Battery B The upper end of 2 is connected to the cathode of the second output diode D2 and the second output capacitor. C The upper intersection of 2 is connected to the battery. B The lower end of 2 is connected to the secondary winding of the n-channel output transformer T. L s2 The lower end and the second output capacitor C Connect the lower ends of 2; ...and so on, Battery B n-1 The upper end and the first n -1 Output Diode D n-1 The cathode and the first n -1 output capacitor C n-1 The upper end of the intersection is connected; battery B n-1 The lower end and n -1 output transformer T secondary winding L s n-1 The lower end and the first n -1 output capacitor C n-1 Connect the lower ends of the intersection; Battery B n The upper end is connected to the nth output diode D n The cathode and the nth output capacitor C n The upper end of the intersection is connected; battery B n The lower end is connected to the secondary winding of the n-channel output transformer T. L sn The lower end and the nth output capacitor C n Connect the lower ends of the intersection; Battery B The upper end of 1 is connected to the clamping diode D. 1p Cathode connection, battery B n The lower end is connected to the clamping diode D 2p Anode connection.

2. The active balancing circuit for a series battery pack according to claim 1, characterized in that: The gates of power switch S1 and power switch S2 are respectively connected to their respective controllers, and their duty cycles can vary between 0 and 0.5 and are in phase.

3. The active balancing circuit for a series battery pack according to claim 1, characterized in that: The battery B 1. B 2, ... B n As the input source of an n-output dual-transistor flyback converter.

4. An active balancing circuit for a battery pack containing three battery cells, characterized in that: The circuit includes a 3-output dual-transistor flyback converter, 2 bridging capacitors, and 3 lithium-ion batteries, wherein: A 3-output dual-transistor flyback converter includes a power switch S1, a power switch S2, and a magnetizing inductor. L m 3-channel output transformer T, clamping diode D 1p Clamping diode D 2p First output diode D1, first output capacitor C 1. Second output diode D2, second output capacitor C 2. Third output diode D3, third output capacitor C The connection configuration of the 3-channel output dual-transistor flyback converter is as follows: Clamping diode D 1p The cathode is connected to the drain of the upper power switch S1; Magnetizing inductor L m The upper end and the primary winding of the 3-way output transformer T L p The upper end and the source of the upper power switch S1 are both connected to clamping diode D. 2p The cathode; Magnetizing inductor L m The lower end and the primary winding of the 3-way output transformer T L p The lower end and the drain of the lower power switch S2 are respectively connected to clamping diode D. 1p anode; Clamping diode D 2p The anode of the circuit is connected to the source of the lower power switch S2; The secondary winding of the 3-channel output transformer T L s1 The upper end is connected to the anode of the first output diode D1, and the cathode of the first output diode D1 is connected to the first output capacitor. C At the top of 1, the first output capacitor C The lower end of 1 is connected to the secondary winding of the 3-way output transformer T. L s1 The lower end; the secondary winding of the 3-way output transformer T L s2 The upper end is connected to the anode of the second output diode D2, and the cathode of the second output diode D2 is connected to the second output capacitor. C At the top of 2, the second output capacitor C The lower end of 2 is connected to the secondary winding of the 3-channel output transformer T. L s2 The lower end; the secondary winding of the 3-way output transformer T L s3 The upper end is connected to the anode of the third output diode D3, and the cathode of the third output diode D3 is connected to the third output capacitor. C The upper end of 3, the third output capacitor C The lower end of 3 is connected to the secondary winding of the 3-channel output transformer T. L s3 The lower end; The connection between the bridging capacitor and each secondary winding is as follows: Bridging capacitor C p1 The upper end is connected to the anode of the first output diode D1, and a capacitor is connected across it. C p1 The lower end is connected to the anode of the second output diode D2; a bridging capacitor is connected. C p2 The upper end is connected to the anode of the second output diode D2, and a capacitor is connected across it. C p2 The lower end is connected to the anode of the third output diode D3; Battery B The upper end of 1 is connected to the cathode of the first output diode D1 and the first output capacitor. C The upper intersection of 1 is connected to the battery. B The lower end of 1 is connected to the secondary winding of the 3-way output transformer T. L s1 The lower end and the first output capacitor C Connect the lower ends of 1 at the intersection; battery B The upper end of 2 is connected to the cathode of the second output diode D2 and the second output capacitor. C The upper intersection of 2 is connected to the battery. B The lower end of 2 is connected to the secondary winding of the 3-way output transformer T. L s2 The lower end and the second output capacitor C Connect the lower ends of 2 at the intersection; battery B The upper end of 3 is connected to the cathode of the third output diode D3 and the third output capacitor. C The upper intersection of 3 is connected to the battery. B The lower end of 3 is connected to the secondary winding of the 3-way output transformer T. L s3 The lower end and the third output capacitor C The lower end of 3 is connected at the intersection; battery B The upper end of 1 is connected to the clamping diode D. 1p Cathode connection, battery B The lower end of 3 is connected to the clamping diode D. 2p Anode connection.

5. The battery pack active balancing circuit according to claim 4, characterized in that: When power switches S1 and S2 are turned on, clamping diode D 1p Clamping diode D 2p With the first output diode D1, the second output diode D2, and the third output diode D3 turned off, the battery pack applies energy to the primary winding of transformer T through series connection. L p Above, magnetizing inductor L m As the current increases, the energy stored in the transformer increases, and simultaneously the primary winding of transformer T... L p Energy is transferred to the secondary winding of transformer T. L s1 , L s2 and L s3 The first output diode D1, the second output diode D2, and the third output diode D3 are cut off under reverse voltage; the secondary winding of transformer T L s1 , L s2 and L s3 For bridging capacitor C p1 and C p2 Charging, output capacitor C 1. C 2 and C 3. Provides energy to the battery pack.

6. The battery pack active balancing circuit according to claim 4, characterized in that: When power switches S1 and S2 are off, clamping diode D 1p Clamping diode D 2p The circuit is turned on, clamping the voltage on the power switch to the battery pack voltage. After clamping, the clamping diode D... 1p Clamping diode D 2p Turn off; simultaneously, the first output diode D1, the second output diode D2, and the third output diode D3 remain conducting during the power switch turn-off phase, and the secondary winding of transformer T... L s1 , L s2 and L s3 The current decreases, and the bridging capacitor... C p1 and C p2 Discharge, output capacitor C 1. C 2 and C 3. Charging.

7. A battery pack balancing method based on the active balancing circuit of claim 4, characterized in that: Throughout the entire switching cycle, according to the inductor volt-second balance principle, the secondary winding of transformer T... L s1 , L s2 and L s3 The average voltage is 0, from L s1 → C p1 → L s2 → C 2→ L s1 The KVL principle of the loop can be used to obtain the bridging capacitor. C p1 voltage u cp1 Equal to battery B 2 voltage u B2 ; Similarly, bridging capacitors C p2 voltage u cp2 Equal to battery B 3 voltage u B3 When power switches S1 and S2 are off, diodes D1, D2, and D3 are on, and the secondary winding of transformer T is turned on. L s1 Through the loop L s1 →D1→ C 1→ L s1 To capacitor C 1. Charging; Capacitor C p1 Through diode D1 and output capacitor C 1. Parallel connection, therefore the capacitance C p1 voltage u cp1 Equal to battery B 1 voltage u B1 ; Similarly, bridging capacitors C p2 voltage u cp2 Equal to battery B 2 voltage u B2 When the capacitor C p1 , C p2 When the voltage is large enough, the voltage of each battery cell is equal. If there is a battery cell with a relatively low voltage, the power switch is closed first, and part of the energy of the battery pack is stored in the magnetizing inductance of the transformer. When the power switch is opened, this energy is transferred to the battery cell with the lower voltage. Thus, part of the energy of the series battery pack can be transferred to the battery cell with the lower energy, achieving the balance of the battery pack.

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