Active equalization topological structure and method of battery pack

Abstract

The invention discloses an active equalization topological structure and method of a battery pack, the topological structure comprises two-way switch tube matrixes, two capacitance and inductance charging and discharging circuits and a two-way DC-DC converter, the two-way switch tube matrixes are respectively arranged at the two sides of the series battery pack, two-way switch tubes are respectively arranged at the two sides of each single battery in the series battery pack, and the two-way switch tubes are connected with the two-way DC-DC converter. Each single battery is respectively connected with the capacitance and inductance charging and discharging circuits through the two-way switch tubes on the two sides, and the capacitance and inductance charging and discharging circuits on the two sides of the series battery pack are connected through the two-way DC-DC converter; the specific structure of the capacitance-inductance charging and discharging circuit is that an inductor and a capacitor are connected in series and then are connected with a fly-wheel diode in parallel; one end of the capacitance-inductance charging and discharging circuit is connected with the bidirectional switching tube matrix, and the other end of the capacitance-inductance charging and discharging circuit is connected with the bidirectional DC-DC converter to charge and discharge the single battery; the bidirectional DC-DC converter comprises a transformer. Two sides of the transformer are respectively and symmetrically provided with a bidirectional MOSFET power switch tube and a rectifier diode. And current flow direction control and voltage conversion are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicle batteries, and in particular relates to an active balancing topology structure and method for a battery pack. Background Art

[0002] Lithium-ion battery packs are widely used in new energy vehicle power systems and microgrid energy storage systems. Since the manufacturing process and materials cannot be completely consistent, there are slight differences in the capacity and impedance of the single cells. These differences will increase with the running time of the battery pack, thereby reducing the available capacity and cycle life of the battery pack, and even causing overcharge and overdischarge, bringing safety hazards. In order to improve the energy utilization rate of the battery pack and extend its cycle life, effective battery balancing technology must be used to reduce the inconsistency of the battery pack.

[0003] Battery balancing technology mainly includes balancing strategy and balancing topology. The former controls the circuit through an algorithm, and the latter forms a current path through component connection. The balancing topology provides a path for energy transfer between battery cells. The circuit components and circuit connection methods it contains have a profound impact on the performance of the balancing topology. The basic balancing topology can be mainly divided into two categories: passive balancing and active balancing. Passive balancing, also known as energy-consuming balancing, refers to the consumption of all excess energy of battery cells in the form of heat. Active balancing, as a non-energy-consuming balancing, refers to the transfer of energy through energy storage elements, thereby reducing the inconsistency of the battery pack. According to the different energy transfer elements, active balancing can be divided into four types of balancing topologies: capacitor-based, inductor-based, transformer-based, and converter-based. The capacitor-based balancing topology has a fast balancing speed and high balancing efficiency, but when the capacitor voltage is not much different from the balancing target voltage, the balancing speed drops significantly, making it unsuitable for high-precision balancing. The inductor-based balancing topology has the characteristics of strong controllability of balancing current and high balancing accuracy, but the inrush current of its switching devices is often large, which can easily have an adverse effect on the battery. The balancing topology based on inductor-capacitor energy storage is an improvement on the traditional balancing topology based on switched capacitors. It has the characteristics of fast capacitor balancing speed and high inductor balancing accuracy, and has gradually become a research hotspot for active balancing methods of series battery packs in recent years. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention proposes an active balancing topology structure and method for a battery pack, which can achieve active balancing and avoid excessive energy loss.

[0005] In the first aspect, the present invention proposes an active balancing topology of a battery pack, including a series battery pack, a bidirectional switch tube matrix and a bidirectional DC-DC converter based on a forward converter. Each single battery has a bidirectional switch tube on both sides, which is respectively connected to the bidirectional DC-DC converter. The DC-DC converters on the left and right sides are symmetrical, and the single batteries on both sides are connected to the two sides of the DC-DC converter through the left and right bidirectional switch tubes.

[0006] The specific structure of the capacitor-inductor charging and discharging circuit includes: an inductor (La; Lb) and a capacitor (Ca; Cb) are connected in series and then connected in parallel with a freewheeling diode (D1; D2); one end of the capacitor-inductor charging and discharging circuit is connected to a bidirectional switch tube matrix, and the other end is connected to a bidirectional DC-DC converter to realize charging and discharging of a battery cell.

[0007] The specific structure of the bidirectional DC-DC converter includes a transformer (T), and a bidirectional MOSFET power switch tube (Sa; Sb) and a rectifier diode (Da; Db) are symmetrically arranged on both sides of the transformer to control the current flow direction and voltage conversion.

[0008] In a second aspect, the present invention provides an active balancing method for a battery pack. The method is based on the active balancing topology of the battery pack and includes:

[0009] When a single cell in the battery pack is higher than other single cells, the corresponding bidirectional MOSFET power switch tube and bidirectional DC-DC converter are controlled to release the excess electricity through the capacitor-inductor charge-discharge circuit.

[0010] When a single cell in the battery pack is lower than the other single cells, the corresponding bidirectional MOSFET power switch tube and the bidirectional DC-DC converter are controlled to charge it by utilizing the capacitor-inductor charging and discharging circuit and the inductor-capacitor series circuit.

[0011] Beneficial effects of the invention: The invention designs a novel active balancing topology structure for a series battery pack. This balancing topology not only uses only one bidirectional symmetrical DC-DC converter to complete the energy transfer in the battery pack, reducing the size and complexity of the balancing system, but also has obvious advantages in terms of balancing speed, scalability and volume, so it is suitable for use in new energy vehicle battery balancing systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A schematic diagram of the working principle of the basic topological structure of an embodiment of the present invention;

[0013] Figure 2 The bidirectional switch tube S shown in this specification aSchematic diagram of the principle of charging single battery B1 to single battery B2 when conducting;

[0014] Figure 3 The bidirectional switch tube S shown in this specification a Schematic diagram of the principle of charging single battery B1 to single battery B2 when shut down;

[0015] Figure 4 The bidirectional switch tube S shown in this specification b Schematic diagram of the principle of charging single battery B1 to single battery B2 when conducting;

[0016] Figure 5 The bidirectional switch tube S shown in this specification b Schematic diagram of the principle of charging single battery B1 to single battery B2 when shut down;

[0017] In the accompanying drawings,

[0018] VCC means power supply; GND means ground;

[0019] 1 represents a series battery pack; 2 represents a bidirectional switch tube matrix;

[0020] 3 represents a capacitor and inductor charging and discharging circuit; 4 represents a bidirectional DC-DC converter;

[0021] B 1 Indicates the first single cell in the battery pack; B 2 Indicates the second single cell in the battery pack; B n represents the nth single battery in the battery pack; A, B, a, b represent different connection nodes respectively; Da represents the first rectifier diode; Db represents the second rectifier diode;

[0022] D1 represents the first freewheeling diode; D2 represents the second freewheeling diode;

[0023] C a Represents the first filter capacitor; C b represents the second filter capacitor;

[0024] L a Represents the first filter inductor; L b represents the second filtering inductor;

[0025] T stands for transformer;

[0026] N sa Represents the first transformer winding; N sb represents the second transformer winding;

[0027] N pa Indicates the third transformer winding; N pbrepresents the fourth transformer winding;

[0028] + indicates the positive pole of the transformer winding; - indicates the negative pole of the transformer winding;

[0029] S a , S b , S A1 , S A2 ……S An , S B1 , S B2 ……S Bn Both represent bidirectional switch tubes with the same structure; the red arrows and blue arrows in the attached drawings both indicate the direction of current flow. DETAILED DESCRIPTION

[0030] The terms "first", "second", "third", "fourth", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable under appropriate circumstances. This is just a way of distinguishing objects with the same attributes when describing the embodiments of this application.

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Among them, the drawings are only used for exemplary illustrations, representing only schematic diagrams, not physical diagrams, and cannot be understood as limitations on the present invention; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted. It is known to those of ordinary skill in the art that with the development of technology and the emergence of new scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0032] The embodiment of the present invention provides an active balancing topology structure of a battery pack, referring to Figure 1 As shown, its active balancing topology structure includes: a series battery group 1, a bidirectional switch tube matrix 2, two capacitor and inductor charging and discharging circuits 3 and a bidirectional DC-DC converter 4. The bidirectional switch tube matrix 2 is respectively arranged on both sides of the series battery group 1, and a bidirectional switch tube is arranged on both sides of each single battery in the series battery group 1. Each single battery is connected to the capacitor and inductor charging and discharging circuit 3 through the bidirectional switch tubes on both sides, and the capacitor and inductor charging and discharging circuits 3 on both sides of the series battery group are connected through a bidirectional DC-DC converter.

[0033] The series battery pack 1 is composed of n single cells connected in series, where each single cell is marked as B1 , B 2 , …, B n .

[0034] With each single battery (B 1 , B 2 , …, B n The bidirectional switch tubes connected on both sides are marked as S A1 , S A2 , …, S An and S B1 , S B2 , …, S Bn , which together constitute a bidirectional switch tube matrix 2.

[0035] The bidirectional switch is a bidirectional MOSFET power switch, and its circuit structure is as follows: two N-channel enhancement MOSFET tubes are connected to the common source to achieve reverse connection of the two MOSFET tubes, and the drain of one MOSFET tube is connected to the single battery (B 1 , B 2 , …, B n ) is connected, and the drain of the other MOSFET is connected to the filter capacitor (C a , C b ), filter inductor (L a , L b ). When a positive voltage is applied to the gate of an N-channel enhancement MOSFET in the bidirectional MOSFET power switch, the MOSFET is turned on, allowing current to flow from the source to the drain. Since the two N-channel enhancement MOSFETs are connected in reverse, no matter what the current direction is, there is always an N-channel enhancement MOSFET in the on state, thus achieving bidirectional current control.

[0036] The specific structure of the capacitor-inductor charge-discharge circuit 3 includes: a filter inductor (La, Lb) and a filter capacitor (Ca, Cb) are connected in series and then connected in parallel with a freewheeling diode (D1, D2); one end of the capacitor-inductor charge-discharge circuit 3 is connected to a bidirectional switch tube matrix 2, and the other end is connected to a bidirectional DC-DC converter 4 to realize charging and discharging of the battery cell.

[0037] Reference Figure 1 As shown, the capacitor and inductor charging and discharging circuit 3 is specifically:

[0038] First, the first filter inductor La is connected in series with the first filter capacitor Ca and then connected in parallel with the first rectifier diode Da.

[0039] Secondly, the second filter inductor Lb and the second filter capacitor Cb are connected in series and then connected in parallel with the second rectifier diode Db.

[0040] The bidirectional DC-DC converter (DC-DC Converter) 4 is a device or circuit that converts a fixed DC voltage into a variable DC voltage, also known as a DC chopper or a DC chopper circuit. The specific structure of the bidirectional DC-DC converter includes: a transformer T, two bidirectional MOSFET power switches (Sa, Sb) and two rectifier diodes (Da, Db), and one bidirectional MOSFET power switch (Sa, Sb) and one rectifier diode (Da, Db) are symmetrically arranged on both sides of the transformer T, and the bidirectional charging and discharging current control and voltage conversion of the battery are realized through the bidirectional DC-DC converter.

[0041] The windings of the transformer T are divided into the first transformer winding N sa , the second transformer winding N sb , the third transformer winding N pa and the fourth transformer winding N pb , the first transformer winding N sa , the third transformer winding N pa The second transformer winding N sb , the fourth transformer winding N pb coupling;

[0042] The first transformer winding N sa The positive electrode is connected to the cathode of the first rectifier diode Da, and the anode of the first rectifier diode Da is connected to the bidirectional MOSFET power switch tube S a The drain of the third transformer winding N is connected to the anode of the first freewheeling diode D1 in the capacitor and inductor charging and discharging circuit 3; pa The anode of the capacitor and the inductor are connected to the cathode of the first freewheeling diode D1 in the capacitor and the inductor charging and discharging circuit 3, and the third transformer winding N pa The negative pole of the bidirectional MOSFET power switch tube S is connected a The source of the bidirectional MOSFET power switch tube S a The gate of is grounded;

[0043] The second transformer winding N sb The positive electrode is connected to the anode of the second rectifier diode Db, and the cathode of the second rectifier diode Db is connected to the bidirectional MOSFET power switch tube S b The drain of the fourth transformer winding N is connected to the anode of the second freewheeling diode D2 in the capacitor and inductor charging and discharging circuit 3. pb The positive electrode of the fourth transformer is connected to the cathode of the freewheeling diode D2. pb The negative pole of the bidirectional MOSFET power switch tube S is connected b The source of the bidirectional MOSFET power switch tube S b The gate of is grounded.

[0044] Reference Figure 1 As shown, the positive electrode of each single battery (B1, B2, ..., Bn) in the series battery group 1 is connected to a bidirectional MOSFET power switch tube (S A1 , S A2 , S A3 …, S An ), and connected to the capacitor and inductor charging and discharging circuit 3 through a bidirectional MOSFET power switch tube, and the capacitor and inductor charging and discharging circuit 3 is connected to a bidirectional DC-DC converter; each single battery (B1, B2, ..., Bn) must form a series path through a corresponding bidirectional MOSFET power switch tube; the negative electrode of each single battery (B1, B2, ..., Bn) is connected to the bidirectional MOSFET power switch tube (S B1 , S B2 , S B3 …, S Bn ), and connected to the capacitor and inductor charging and discharging circuit 3 through a bidirectional MOSFET power switch tube, and the capacitor and inductor charging and discharging circuit 3 is connected to a bidirectional DC-DC converter to form a current control channel.

[0045] The embodiment of the present invention proposes an active balancing topology for a series battery pack, controls the current direction through a bidirectional MOSFET power switch tube, realizes voltage conversion through a bidirectional DC-DC converter, and charges or discharges the selected single battery through a capacitor and inductor charging and discharging circuit, which can improve the balancing efficiency of the battery pack and distribute more charging current to low SOC (State of Charge) batteries.

[0046] An embodiment of the present invention provides an active balancing method for a battery pack. The method is based on an active balancing topology structure of the battery pack and includes:

[0047] When a single cell in the battery pack is higher than other single cells, the corresponding bidirectional MOSFET power switch tube and bidirectional DC-DC converter are controlled to discharge it through the capacitor and inductor charging and discharging circuit;

[0048] When a single cell in the battery pack is lower than the other single cells, the corresponding bidirectional MOSFET power switch tube and bidirectional DC-DC converter are controlled to charge it using the capacitor and inductor charging and discharging circuit.

[0049] In one embodiment shown, reference is made to Figure 2-5 As shown, the series battery pack consists of 4 single cells connected in series, and each single cell in the series battery pack is marked as B 1 , B 2 , B 3 , B 4; The bidirectional MOSFET power switch tube (hereinafter referred to as MOS tube) connected to the single battery is marked as S A1 , S A2 , S A3 , S A4 and S B1 , S B2 , S B3 , S B4 .

[0050] The active balancing topology of the series battery pack includes: 10 MOS tubes (Sa, Sb, S A1 , S A2 , S A3 , S A4 and S B1 , S B2 , S B3 , S B4 ), 22 diodes, two inductor and capacitor charging and discharging circuits; the DC-DC conversion circuit is composed of 4 bidirectional MOSFET power switch tubes on both sides of the single battery; the inductor and capacitor charging and discharging circuit includes an inductor (L a , L b ) and capacitance (C a , C b ) are connected in series and then connected in parallel with a freewheeling diode (D1, D2); the 22 diodes include two rectifier diodes D a and D b , two freewheeling diodes D 1 and D 2 .

[0051] Each single cell (B 1 , B 2 , B 3 , B 4 ) are connected to the positive pole of the bidirectional MOSFET power switch tube (S A1 , S A2 , S A3 , S A4 ) are connected to form a current control channel; each single cell (B 1 , B 2 , B 3 , B 4 ) are connected to the negative pole of the bidirectional MOSFET power switch tube (S B1 , S B2 , S B3 , S B4 ) are connected to form a current loop; the capacitor and inductor charging and discharging circuit 3 are connected to a bidirectional DC-DC converter to form a DC-DC conversion circuit. 1 The positive electrode is connected to the bidirectional MOSFET power switch tube SA1 On the left side, single battery B 2 The positive terminal is connected to S A2 The left side of the battery, and so on. 4 The negative electrode is connected to the bidirectional MOSFET power switch tube S B4 The last end of .

[0052] Inductance L a One end is connected to the freewheeling diode D 1 The cathode of the inductor L a The other end is connected to capacitor C a . Diode D 1 The anode and capacitor C a The lower end of capacitor C b and inductor L b After forming a series circuit with the freewheeling diode D 1 Connect in parallel to form a capacitor and inductor charging and discharging circuit, which is connected with the bidirectional MOSFET power switch tube S b Related; Rectifier diode D a The anode of the inductor is connected to a One end of the rectifier diode D a The cathode of the bidirectional MOSFET power switch tube S a The drain terminal of the rectifier diode D b The anode of the bidirectional MOSFET power switch S b The drain terminal of the rectifier diode D b The cathode is connected to the capacitor C b The top of the circuit forms a DC-DC conversion circuit.

[0053] In one embodiment shown, reference is made to Figure 2 As shown, based on the active balancing topology of the battery pack, the active balancing method of the battery pack is: when the power SOC (State of Charge) of the single battery B1 is higher than the power SOC of the single battery B2 nearby and the bidirectional MOSFET power switch tube Sa is turned on, its corresponding switch tube (S A1 ,S A2 ,S B1 ,S B2 ) is turned on, and the remaining switches (S A3 ; S A4 ; S B3 ; S B4 At this time, the single battery B1 supplies power to the filter inductor L a 、Filter capacitor C a and the primary winding N of the bidirectional converter pa Charging, primary winding N pa The current iNpa Gradually increases, at this time the primary winding N pa The induced electromotive force is "positive at the top and negative at the bottom". Under the coupling effect, the primary winding N pa The energy is transferred to the secondary winding N sb On the secondary winding N sb The current i Nsb At this time, the secondary winding N sb The direction of the induced electromotive force and the primary winding N pa The induced electromotive force has the same direction, and the rectifier diode D b Conducting, freewheeling diode D 2 Cut-off, energy passes through the filter inductor L b With filter capacitor C b To single cell B 2 Charge.

[0054] In one embodiment shown, reference is made to Figure 3 As shown, based on the active balancing topology of the battery pack, the balancing method of the battery pack is: when the power SOC (State of Charge) of the single battery B1 is higher than the power SOC of the single battery B2 nearby and the switch tube Sa is turned off, the switch tube S A1 ,S A2 ,S B1 ,S B2 At this time, the primary winding N pa The current is interrupted. According to the principle of electromagnetic induction, the secondary winding N sb and reset winding N sa At the same time, an induced voltage with a polarity of "negative on top and positive on bottom" will be generated. At this time, the diode D a The reset winding N sa The induced current i Nsa Through the filter inductor L a Charge back to single battery B 1 In this way, the energy stored in the magnetizing inductor is released and effectively recovered to battery B. 1 On. Rectifier diode D b After cutoff, due to the inductance L b The current on the diode cannot change suddenly, which will generate an induced voltage of "negative on the left and positive on the right", causing the freewheeling diode D 2 is turned on, and the current stored in the inductor L b The energy on the 2 The circuit formed is back to the battery.

[0055] In one embodiment shown, reference is made to Figure 4 As shown in the figure, based on the active balancing topology of the battery pack, the balancing method of the battery pack is: when the single battery B 2The SOC of the battery is higher than that of the single battery B. 1 When the power SOC is B1 ,S B2 ,S A1 ,S A2 and S b The other switches are turned off. 2 Filter inductor L b , filter capacitor C b and the primary winding N of the bidirectional converter pb Charging, primary winding N pb The current i Npb Gradually increases, at this time the primary winding N pb The induced electromotive force is "negative at the top and positive at the bottom". Under the coupling effect, the primary winding N pb The energy is transferred to the secondary winding N sa On the secondary winding N sa The current i Nsa At this time, the secondary winding N sa The direction of the induced electromotive force and the primary winding N pb The induced electromotive force has the same direction, and the rectifier diode D a Conducting, freewheeling diode D 1 Cut-off, energy passes through the filter inductor L a With filter capacitor C a To battery B 1 Charge.

[0056] In one embodiment shown, reference is made to Figure 5 As shown, based on the active balancing topology of the battery pack, the active balancing method of the battery pack is: when the power SOC of the single battery B2 is higher than the power SOC of the single battery B1, the switch tube S b Turn off, switch tube S B1 ,S B2 ,S A1 ,S A2 Continue to conduct. The primary winding N pb The current is interrupted. According to the principle of electromagnetic induction, the secondary winding N sa and reset winding N sb The induced voltage with the polarity of "positive on top and negative on bottom" will be generated at the same time. b The reset winding N sb The induced current i Nsb Through the filter inductor L b Charge back to single battery B 2 In this way, the energy stored in the magnetizing inductor is released and effectively recovered to battery B. 2 On. Rectifier diode Da After cutoff, due to the inductance L a The current on the diode cannot change suddenly, which will generate an induced voltage of "positive on the left and negative on the right", causing the freewheeling diode D 1 is turned on, and the current stored in the inductor L a The energy on D 1 The circuit formed is to battery B 1 Charging, filter capacitor C a With battery B 1 The circuit is formed to charge the stored energy back to battery B 1 superior.

[0057] A person skilled in the art can understand that all or part of the steps in the various methods of the above embodiments can be completed by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium, which can include: ROM, RAM, disk or CD, etc.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An active balancing topology of a battery pack, wherein the battery pack is a series battery pack (1) consisting of n single cells connected in series, characterized in that: The active balancing topology structure comprises: a bidirectional switch tube matrix (2), two capacitor and inductor charging and discharging circuits (3) and a bidirectional DC-DC converter (4); the bidirectional switch tube matrix (2) is respectively arranged on both sides of the series battery group (1); a bidirectional switch tube is arranged on both sides of each single battery in the series battery group; each single battery is respectively connected to the capacitor and inductor charging and discharging circuit (3) via the bidirectional switch tubes on both sides; and the capacitor and inductor charging and discharging circuits (3) on both sides of the series battery group are connected via the bidirectional DC-DC converter; The specific structure of the capacitor-inductor charging and discharging circuit comprises: an inductor (La; Lb) and a capacitor (Ca; Cb) are connected in series and then connected in parallel with a freewheeling diode (D1; D2); one end of the capacitor-inductor charging and discharging circuit is connected to a bidirectional switch tube matrix, and the other end is connected to a bidirectional DC-DC converter to realize charging and discharging of a battery cell; The specific structure of the bidirectional DC-DC converter includes a transformer (T), and a bidirectional MOSFET power switch tube (Sa; Sb) and a rectifier diode (Da; Db) are symmetrically arranged on both sides of the transformer to achieve current flow control and voltage conversion.

2. The active balancing topology of the battery pack according to claim 1, characterized in that: The bidirectional switch tube is a bidirectional MOSFET power switch tube, and its circuit structure specifically includes: two N-channel enhancement MOSFET tubes are connected with a common source, the drain of one MOSFET tube is connected to a single battery, and the drain of the other MOSFET tube is connected to a capacitor and inductor charging and discharging circuit to achieve bidirectional current control.

3. The active balancing topology of the battery pack according to claim 1 or 2, characterized in that: The transformer winding is divided into a first transformer winding (N sa ), the second transformer winding (N sb ), the third transformer winding (N pa ) and the fourth transformer winding (N pb ), the first transformer winding (N sa ), the third transformer winding (N pa ) are respectively connected to the second transformer winding (N sb )、The fourth transformer winding (N pb )coupling; The first transformer winding (N sa ) is connected to the cathode of the first rectifier diode (Da), and the anode of the first rectifier diode (Da) is connected to the bidirectional MOSFET power switch tube (S a ) is connected to the anode of the first freewheeling diode (D1) in the capacitor and inductor charging and discharging circuit; the third transformer winding (N pa ) is connected to the cathode of the first freewheeling diode (D1) in the capacitor and inductor charging and discharging circuit, and the third transformer winding (N pa ) is connected to the negative pole of the bidirectional MOSFET power switch tube (S a ) source, bidirectional MOSFET power switch tube (S a ) has its gate grounded; The second transformer winding (N sb ) is connected to the anode of the second rectifier diode (Db), and the cathode of the second rectifier diode (Db) is connected to the bidirectional MOSFET power switch tube (S b ) is connected to the anode of the second freewheeling diode (D2) in the capacitor and inductor charging and discharging circuit, and the fourth transformer winding (N pb ) is connected to the cathode of the freewheeling diode (D2), and the fourth transformer winding (N pb ) is connected to the negative pole of the bidirectional MOSFET power switch tube (S b ) source, bidirectional MOSFET power switch tube (S b ) has its gate grounded.

4. An active balancing method for a battery pack, characterized in that: The method is based on the active balancing topology of the battery pack, and includes: When a single cell in the battery pack is higher than other single cells, the corresponding bidirectional MOSFET power switch tube and bidirectional DC-DC converter are controlled to discharge the excess electricity through the capacitor and inductor charging and discharging circuit; When a single cell in the battery pack is lower than the other single cells, the corresponding bidirectional MOSFET power switch tube and the bidirectional DC-DC converter are controlled to charge it by utilizing the capacitor-inductor charging and discharging circuit and the inductor-capacitor series circuit.

5. The active equalization method for a battery pack according to claim 4, wherein the battery pack is a series battery pack composed of four single cells connected in series, characterized in that: The method comprises: when the power of a single cell (B1) is higher than the power of a single cell (B2) nearby and a bidirectional MOSFET power switch tube (Sa) is turned on, the corresponding bidirectional MOSFET power switch tube (S A1 ; S A2 ; S B1 ; S B2 ) is turned on and the remaining bidirectional MOSFET power switches (S A3 ; S A4 ; S B3 ; S B4 ; Sb).

6. The active equalization method for a battery pack according to claim 4, wherein the battery pack is a series battery pack composed of four single cells connected in series, characterized in that: The method comprises: when the power of a single cell (B1) is higher than the power of a single cell (B2) nearby and a bidirectional MOSFET power switch tube (Sa) is turned off, the corresponding bidirectional MOSFET power switch tube (S A1 ; S A2 ; S B1 ; S B2 ; Sa) is turned on.

7. The active equalization method for a battery pack according to claim 4, wherein the battery pack is a series battery pack composed of four single cells connected in series, characterized in that: The method comprises: when the power of a single cell (B2) is higher than the power of a single cell (B1) nearby and a bidirectional MOSFET power switch tube (Sb) is turned on, the corresponding bidirectional MOSFET power switch tube (S B1 ; S B2 ; S A1 ; S A2 ) is turned on and the remaining bidirectional MOSFET power switches (S A3 ; S A4 ; S B3 ; S B4 ; Sa).

8. The active equalization method for a battery pack according to claim 4, wherein the battery pack is a series battery pack consisting of four single cells connected in series, characterized in that: The method comprises: when the power of a single cell (B2) is higher than the power of a single cell (B1) nearby and a bidirectional MOSFET power switch tube (Sb) is turned off, the corresponding bidirectional MOSFET power switch tube (S A1 ; S A2 ; S B1 ; S B2 ) is turned on.

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