Battery pack charging control method based on improved buck-boost equalization circuit

Abstract

The application relates to a battery pack charging control method based on an improved Buck-Boost equalization circuit, a battery pack composed of four single batteries is used as a basic unit of inter-group equalization control, an intra-group equalization circuit is used for electric quantity equalization in the battery pack, and an inter-group equalization circuit and a flyback transformer are used between the battery pack and other arbitrary battery packs to realize equalization and charging between the two battery packs. The application realizes electric quantity equalization between arbitrary battery packs, increases the flexibility of electric quantity equalization of the battery pack, improves the battery equalization efficiency, avoids unnecessary intermediate batteries from participating in the electric quantity equalization process, reduces the switch tube loss and the electric energy loss, reduces the battery equalization time and the battery charging time, realizes concurrent control of inter-group equalization and battery pack charging, and improves the charging and equalization efficiency of the battery pack.

Description

Technical Field

[0001] This invention belongs to the field of battery charging and discharging control, specifically relating to a battery pack charging control method based on an improved Buck-Boost balancing circuit. Background Technology

[0002] With the rapid development of large-scale energy storage systems, battery energy storage is also developing at an increasingly rapid pace. To meet the demands for large capacity and high power, individual batteries are often used in series and parallel combinations. However, due to differences in the internal structure of the batteries and variations in ambient temperature, charge / discharge rate, and self-discharge rate during use, the inherent inconsistencies between individual batteries become increasingly pronounced during operation. These inconsistencies can easily lead to overcharging and over-discharging of the batteries. Prolonged overcharging and over-discharging not only reduce battery life but can also cause serious damage and even explosions. Therefore, to improve battery capacity utilization and efficiency, and to ensure the safe and sustainable operation of battery packs, excellent balancing technology is crucial.

[0003] Battery balancing technology mainly comprises two parts: battery balancing topology and balancing control strategy. Traditional Buck-Boost balancing circuits have several problems. Firstly, because energy must be transferred sequentially between individual cells during the balancing process, the overall balancing efficiency drops significantly when a large number of cells need balancing, severely impacting battery performance. Secondly, because balancing can only be done sequentially between adjacent cells, attempting to balance two non-adjacent cells with significant energy differences results in the unnecessarily charged and discharged cells accumulating charge and discharge, leading to additional power loss.

[0004] To address the shortcomings of existing technologies, a step-by-step balancing topology circuit for intra-group and inter-group operations is proposed. Within a group, a Buck-Boost circuit is used to transfer energy through an inductor, while between groups, a flyback converter is used to charge different battery packs. This balancing topology not only improves the additional power loss caused by repeated charging and discharging of certain batteries, but also significantly reduces the balancing time and switching transistor losses. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a battery pack charging control method based on an improved Buck-Boost balancing circuit. The method uses a battery pack composed of four individual cells as the basic unit for inter-pack balancing control. The battery pack uses an intra-pack balancing circuit for power balancing, and inter-pack balancing circuits and flyback transformers to achieve balancing and charging between any two battery packs, thereby improving battery balancing efficiency and flexibility.

[0006] The technical solution of this invention is a battery pack charging control method based on an improved Buck-Boost balancing circuit. The improved Buck-Boost balancing circuit includes n battery pairs, where the k-th battery pair and the (k+1)-th battery pair constitute an intra-group balancing circuit, k = 1, 2…n-1, n ≥ 2; the intra-group balancing circuit includes the k-th battery pair, i.e., battery B connected in series. 2k-1 B 2k Battery B is connected in series with the (k+1)th battery pair. 2k+1 B 2k+2 and the switching transistor S 2k-1 S 2k S 2k+1 S 2k+2 and inductor L k，1 L k+1，1 Inductor L k,1 One end is connected to battery B 2k-1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k-1 The source and switch S 2k The drain connection, the switching transistor S 2k-1 The drain of the battery B 2k-1 The positive terminal is connected, and the switching transistor S... 2k The source electrode and battery B 2k The negative terminal is connected; inductor L k+1,1 One end is connected to battery B 2k+1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k+1 The source and switch S 2k+2 The drain connection, the switching transistor S 2k+1 The drain of the battery B 2k+1 The positive terminal is connected, and the switching transistor S... 2k+2 The source electrode and battery B 2k+2 The negative terminal connection.

[0007] Battery B 2k-1 The positive electrode is connected to the switching transistor M used for battery charge balancing. k,2 The drain connection of battery B 2k+2 The negative electrode is connected to the switching transistor M used for battery charge balancing. k+1,1 The source connection, inductor L k,2 One end is connected to battery B 2k The negative electrode of battery B 2k+1 The positive terminal is connected, and the inductor L k,2 The other end is connected to the switching transistor M. k,2 The source and switch M k+1,1 The drain connection.

[0008] Furthermore, each switching transistor is connected in anti-parallel to a freewheeling diode;

[0009] When k≥2, the switching transistor M used for battery charge balancing k,1 The drain and switching transistor M k-1,2 The source is connected and connected via inductor L. k-1,2 With battery B 2k-2 The negative terminal connection.

[0010] The k-th battery pair can perform intra-group power balancing with the (k+1)-th or (k-1)-th battery pair as needed for power balancing.

[0011] Furthermore, regarding the intra-group power balancing, taking the intra-group balancing circuit composed of batteries B1, B2, B3, and B4 as an example, without loss of generality, let the state of charge (SOC) of a single battery be... B1 SOC B2 SOC B3 SOC B4 .

[0012] First, the batteries B1 and B2 are balanced. This process includes the discharge phase of battery B1 and the charging phase of battery B2.

[0013] During the discharge phase of battery B1: When t = t0, the PWM signal controls the switching transistor S1 to turn on, and the discharge occurs through battery B1, switching transistor S1, and inductor L. 1,1 The formed circuit transfers electrical energy from battery B1 to inductor L. 1,1 superior;

[0014] B2 Charging stage: When t = t1, switch S1 is turned off, at which time inductor L 1,1 A circuit is formed through battery B2 and the freewheeling diode connected in anti-parallel to switch S2, and inductor L... 1,1 The electrical energy stored in battery B1 during the discharge phase is released to battery B2 to charge battery B2.

[0015] The charge balance of batteries B3 and B4 is similar to that of batteries B1 and B2.

[0016] Then, the battery pairs consisting of batteries B1 and B2 and batteries B3 and B4 are each considered as a unit. The charge balance is performed between batteries B1 and B2 and batteries B3 and B4. The charge balance of adjacent battery pairs is similar to that of batteries B1 and B2.

[0017] Preferably, the improved Buck-Boost balancing circuit further includes an inter-group balancing circuit, which includes switching transistors Q1 and Q2, an inductor L, and multiple multiplexers. The improved Buck-Boost balancing circuit uses adjacent battery pairs (i.e., battery packs consisting of four adjacent batteries) as the basic unit for inter-group power balancing, and performs inter-group power balancing with other battery packs. Taking the inter-group power balancing between the k-th and k+1-th battery pairs and the (n-1)-th and n-th battery pairs as an example, the drain of the switching transistor Q1 used for inter-group power balancing is connected to the battery B of the k-th battery pair via a switch. 2k+1 The positive terminal is connected to the source of the switching transistor Q2, which is used for inter-group charge balancing, and is connected to the battery B of the nth battery pair via the switch. 2n The negative terminal connection; inductor L used for inter-group charge balancing. BG One end of the inductor is connected to the source of switching transistor Q1 and the drain of switching transistor Q2. BG The other end is connected to a switch and a switching transistor M respectively. k+1,1 The source and switch M n-1,1 Drain connection;

[0018] Preferably, the improved Buck-Boost equalization circuit further includes an external charging circuit, which includes a transformer T, a switching transistor Q3, an electrolytic capacitor C, and a diode D. The same-named terminal H of the primary winding of the transformer T is connected to the positive terminal of the external DC power supply, the other end of the primary winding of the transformer T is connected to the drain of the switching transistor Q3, and the source of the switching transistor Q3 is connected to the negative terminal of the external DC power supply. A freewheeling diode is connected in anti-parallel to the switching transistor Q3. The same-named terminal H' of the secondary winding of the transformer T is connected to the negative terminal of the electrolytic capacitor C. The other end of the secondary winding of the transformer T is connected to the anode of the diode D, and the cathode of the diode D is connected to the positive terminal of the electrolytic capacitor C. The negative terminal of the electrolytic capacitor C serves as the negative terminal of the external charging circuit, and the positive terminal of the electrolytic capacitor C serves as the positive terminal of the external charging circuit.

[0019] Preferably, transformer T is a flyback transformer.

[0020] The inter-group power balancing process specifically includes:

[0021] 1) Select the battery packs to be balanced between groups. Let the selected battery packs to be balanced between groups be the p-th battery pack and the q-th battery pack.

[0022] 2) Control the multiple-choice switch separately to connect the p-th and q-th battery packs to the inter-group equalization circuit and the external charging circuit respectively;

[0023] 2.1) Control the multiple-choice switch so that the drain of the switching transistor Q1 used for inter-group power balancing is connected to the positive terminal of the first battery of the p-th battery pack.

[0024] 2.2) Control the multiple-choice switch so that the source of the switching transistor Q2 used for inter-group power balancing is connected to the negative terminal of the fourth battery of the qth battery pack.

[0025] 2.3) Control the multi-select switch so that the end of the inductor L used for inter-group power balancing is away from the switch tube Q1 and connected to the negative terminal of the fourth battery of the p-th battery pack and the positive terminal of the first battery of the q-th battery pack, respectively.

[0026] 2.4) Control the multiple-choice switch to connect the positive terminal of the first battery in the p-th battery pack to the positive terminal of the external charging circuit;

[0027] 2.5) Control the multi-select switch to connect the negative terminal of the fourth battery in the q-th battery pack to the negative terminal of the external charging circuit;

[0028] 3) Control the switching transistors Q1 and Q2, and use the inductor L to balance the power of the p-th and q-th battery packs;

[0029] 4) Control switch Q3 to charge the p-th and q-th battery packs using different programs with the help of an external DC power supply and transformer T until they are fully charged.

[0030] The battery pack charging control method based on the improved Buck-Boost equalization circuit includes the following steps:

[0031] Step 1: Real-time acquisition of individual battery current and voltage;

[0032] Step 2: Estimate the SOC value of each individual cell and the battery pack based on the collected current and voltage;

[0033] Step 3: Calculate the average SOC value ε of the battery pack and the charge difference ΔSOC between adjacent individual cells within the battery pack;

[0034] Step 4: Determine whether ε≥γ holds true, where γ represents the power threshold;

[0035] Step 4.1: If ε≥γ holds true, then perform intra-group equalization on the batteries in the battery pack and execute step 2;

[0036] Step 4.2: If ε≥γ does not hold, then proceed to step 5;

[0037] Step 5: Sample the SOC value of each battery pack;

[0038] Step 6: Compare the SOC values ​​of the battery packs and sort them.

[0039] Step 7: Based on the sorting in Step 6, determine the order of equalization between battery pack groups;

[0040] The order of determining the inter-pack balancing is to sequentially select the battery pack with the highest SOC value and the battery pack with the lowest SOC value from the list of battery packs to be balanced, and then pair them for inter-pack balancing to improve the efficiency and effectiveness of power balancing.

[0041] Step 8: Connect the inter-group equalization circuit and the external charging circuit to perform equalization and charging;

[0042] Step 9: Determine if the battery pack is fully charged. If it is, end the process; otherwise, proceed to step 8.

[0043] Compared with the prior art, the beneficial effects of the present invention include:

[0044] 1) This invention uses a battery pack composed of 4 individual cells as the basic unit for inter-pack equalization control. The battery pack uses an intra-pack equalization circuit for power equalization. The battery pack uses an inter-pack equalization circuit and a flyback transformer to achieve equalization and charging between each other. This realizes power equalization between any battery pack, increases the flexibility of power equalization of the battery pack, improves battery equalization efficiency, avoids unnecessary intermediate cells from participating in the power equalization process, reduces switching transistor losses and energy losses, and reduces battery equalization time and battery charging time.

[0045] 2) This invention realizes concurrent control of inter-group balancing and battery pack charging, thereby improving the efficiency of battery pack charging and balancing;

[0046] 3) This invention enables the pairing of high-capacity battery packs with low-capacity battery packs for inter-pack balancing and charging, further improving power balancing and charging efficiency. Attached Figure Description

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] Figure 1 This is a circuit diagram of the improved Buck-Boost equalization circuit according to an embodiment of the present invention.

[0049] Figure 2 This is a circuit diagram of an improved Buck-Boost equalization circuit containing eight batteries, according to an embodiment of the present invention.

[0050] Figure 3 This is a circuit simulation diagram illustrating the inter-pack balancing of battery packs p and q according to an embodiment of the present invention.

[0051] Figure 4 This is a circuit diagram of an internal balancing circuit containing four batteries, according to an embodiment of the present invention.

[0052] Figure 5 This is a schematic diagram of the inductor current waveform for balancing the charge of batteries B1 and B2 in an embodiment of the present invention.

[0053] Figure 6 This is a flowchart of a battery pack charging control method according to an embodiment of the present invention. Detailed Implementation

[0054] like Figure 1 As shown, the improved Buck-Boost equalization circuit includes n battery pairs, where the k-th battery pair and the (k+1)-th battery pair form an intra-group equalization circuit, k = 1, 2…n-1, n ≥ 2; the intra-group equalization circuit includes the k-th battery pair, i.e., the battery B connected in series. 2k-1 B 2k Battery B is connected in series with the (k+1)th battery pair. 2k+1 B 2k+2 and the switching transistor S 2k-1 S 2k S 2k+1 S 2k+2 and inductor L k,1 L k+1,1 Inductor L k,1 One end is connected to battery B 2k-1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k-1 The source and switch S 2k The drain connection, the switching transistor S 2k-1 The drain of the battery B 2k-1 The positive terminal is connected, and the switching transistor S... 2k The source electrode and battery B 2k The negative terminal is connected; inductor L k+1,1 One end is connected to battery B 2k+1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k+1 The source and switch S 2k+2 The drain connection, the switching transistor S 2k+1 The drain of the battery B 2k+1 The positive terminal is connected, and the switching transistor S... 2k+2 The source electrode and battery B 2k+2 Negative terminal connection; Battery B 2k-1 The positive electrode is connected to the switching transistor M used for battery charge balancing. k,2 The drain connection of battery B 2k+2 The negative electrode is connected to the switching transistor M used for battery charge balancing. k+1,1 The source connection, inductor L k,2 One end is connected to battery B 2k The negative electrode of battery B 2k+1 The positive terminal is connected, and the inductor L k,2 The other end is connected to the switching transistor M. k,2 The source and switch M k+1,1 The drain connection is such that each switch has a freewheeling diode connected in anti-parallel.

[0055] like Figure 2 and Figure 3 As shown, the improved Buck-Boost equalization circuit also includes an inter-group equalization circuit and an external charging circuit. The inter-group equalization circuit includes switching transistors Q1 and Q2, an inductor L, and multiple multiplexers. The external charging circuit includes a transformer T, a switching transistor Q3, an electrolytic capacitor C, and a diode D.

[0056] The improved Buck-Boost balancing circuit uses adjacent battery pairs (i.e., four adjacent batteries) as the basic unit for inter-pack power balancing. It performs inter-pack power balancing with other battery packs. Taking the inter-pack power balancing between the k-th and k+1-th battery pairs and the (n-1)-th and n-th battery pairs as an example, the drain of the switching transistor Q1 used for inter-pack power balancing is connected to the battery B of the k-th battery pair via a switch. 2k+1 The positive terminal is connected to the source of the switching transistor Q2, which is used for inter-group charge balancing, and is connected to the battery B of the nth battery pair via the switch. 2n The negative terminal connection; inductor L used for inter-group charge balancing. BG One end of the inductor is connected to the source of switching transistor Q1 and the drain of switching transistor Q2. BG The other end is connected to a switch and a switching transistor M respectively. k+1,1 The source and switch M n-1,1 The drain connection.

[0057] The primary winding of transformer T is connected to the positive terminal of an external DC power supply. The other end of the primary winding of transformer T is connected to the drain of switching transistor Q3, and the source of switching transistor Q3 is connected to the negative terminal of the external DC power supply. A freewheeling diode is connected in anti-parallel to switching transistor Q3. The secondary winding of transformer T is connected to the negative terminal of electrolytic capacitor C. The other end of the secondary winding of transformer T is connected to the anode of diode D, and the cathode of diode D is connected to the positive terminal of electrolytic capacitor C. The negative terminal of electrolytic capacitor C is connected to switching transistor M via a switch. n,1 The source terminal of the electrolytic capacitor C is connected to the source terminal of the switching transistor M. k,2 The drain connection.

[0058] In this embodiment, transformer T is a flyback transformer.

[0059] In one embodiment, the improved Buck-Boost equalization circuit comprises eight individual battery cells, such as... Figure 2 As shown.

[0060] When k≥2, the switching transistor M used for battery charge balancing k,1 The drain and switching transistor M k-1,2 The source is connected and connected via inductor L. k-1,2 With battery B 2k-2 The negative terminal connection;

[0061] The k-th battery pair can perform intra-group power balancing with the (k+1)-th or (k-1)-th battery pair as needed for power balancing.

[0062] Taking the intra-group equalization circuit composed of batteries B1, B2, B3, and B4 as an example, such as Figure 4 As shown, without loss of generality, let the state of charge (SOC) of a single cell be... B1 >SOC B2 >SOC B3 >SOC B4 ,

[0063] First, the batteries B1 and B2 are balanced. This process includes the discharge phase of battery B1 and the charging phase of battery B2.

[0064] During the discharge phase of battery B1: When t = t0, the PWM signal controls the switching transistor S1 to turn on, transferring electrical energy from battery B1 to inductor L through circuit ①. 1，1 In the absence of internal resistance, the following formula holds true:

[0065]

[0066]

[0067] Where t0 represents the inductance L 1，1 Charging begins; Inductance L 1，1 voltage, This indicates the voltage of battery B1. Indicating inductance L 1，1 The current;

[0068] because Since it is a constant, the inductor current at this time is... The current increases linearly from 0, and reaches its maximum value at t = t1. t1 represents inductance L 1，1 The moment charging ends;

[0069]

[0070] In the formula T on T represents the on-time of switch S1; s D represents the switching period of switch S1; D represents the duty cycle of switch S1.

[0071] During the charging phase of battery B2: When t = t1, switch S1 is turned off, and at this time, inductor L... 1，1 Through the conduction of battery B2 and the freewheeling diode connected in anti-parallel to switch S2, circuit ② is formed, and inductor L 1，1The electrical energy stored in battery B1 during the discharge phase is released to battery B2, charging battery B2. At this time, we have:

[0072]

[0073]

[0074] In the formula, t2 represents the inductance L 1，1 Discharge end time;

[0075] Therefore, the inductor current decreases linearly from its maximum value. When t = t2, the inductor current drops to 0, at which point one cycle ends, and the waveform is as follows. Figure 5 As shown;

[0076] The charge balancing of batteries B3 and B4 is similar to that of batteries B1 and B2.

[0077] Then, the battery pairs consisting of batteries B1 and B2 and batteries B3 and B4 are each considered as a unit. The charge balance is performed between batteries B1 and B2 and batteries B3 and B4. The charge balance of adjacent battery pairs is similar to that of batteries B1 and B2.

[0078] The improved Buck-Boost equalization circuit also achieves inter-group power equalization, specifically through the following process:

[0079] 1) Select the battery packs to be balanced between groups. Let the selected battery packs to be balanced between groups be the p-th battery pack and the q-th battery pack.

[0080] 2) Control the multiple-choice switch separately to connect the p-th and q-th battery packs to the inter-group equalization circuit and the external charging circuit respectively;

[0081] 2.1) Control the multiple-choice switch so that the drain of the switching transistor Q1 used for inter-group power balancing is connected to the positive terminal of the first battery of the p-th battery pack.

[0082] 2.2) Control the multiple-choice switch so that the source of the switching transistor Q2 used for inter-group power balancing is connected to the negative terminal of the fourth battery of the qth battery pack.

[0083] 2.3) Control the multi-select switch so that the end of the inductor L used for inter-group power balancing is away from the switch tube Q1 and connected to the negative terminal of the fourth battery of the p-th battery pack and the positive terminal of the first battery of the q-th battery pack, respectively.

[0084] 2.4) Control the multiple-choice switch to connect the positive terminal of the first battery in the p-th battery pack to the positive terminal of the external charging circuit;

[0085] 2.5) Control the multi-select switch to connect the negative terminal of the fourth battery in the q-th battery pack to the negative terminal of the external charging circuit;

[0086] 3) Control the switching transistors Q1 and Q2, and use the inductor L to balance the power of the p-th and q-th battery packs;

[0087] 4) Control switch Q3 to charge the p-th and q-th battery packs using different programs with the help of an external DC power supply and transformer T until they are fully charged.

[0088] like Figure 6 As shown, the battery pack charging control method based on the improved Buck-Boost equalization circuit includes the following steps:

[0089] Step 1: Real-time acquisition of individual battery current and voltage;

[0090] Step 2: Estimate the SOC value of each individual cell and the battery pack based on the collected current and voltage;

[0091] Step 3: Calculate the average SOC value ε of the battery pack and the charge difference ΔSOC between adjacent individual cells within the battery pack;

[0092] Step 4: Determine if ≥ is true, where represents the power threshold;

[0093] Step 4.1: If ≥ is true, then perform intra-group balancing on the batteries in the battery pack and proceed to step 2;

[0094] Step 4.2: If ≥ is not true, proceed to step 5;

[0095] Step 5: Sample the SOC value of each battery pack;

[0096] Step 6: Compare the SOC values ​​of the battery packs and sort them.

[0097] Step 7: Based on the sorting in Step 6, determine the order of equalization between battery pack groups;

[0098] Step 8: Connect the inter-group equalization circuit and the external charging circuit to perform equalization and charging;

[0099] Step 9: Determine if the battery pack is fully charged. If it is, end the process; otherwise, proceed to step 8.

Claims

1. A battery pack charging control method based on an improved Buck-Boost equalization circuit, characterized in that, The improved Buck-Boost equalization circuit includes n battery pairs, wherein the k-th battery pair and the (k+1)-th battery pair constitute an intra-group equalization circuit, k=1,2…n-1, n≥2; the intra-group equalization circuit includes the k-th battery pair… k A battery pair, i.e., battery B connected in series. 2k-1 B 2k Battery B is connected in series with the (k+1)th battery pair. 2k+1 B 2k+2 and the switching transistor S 2k-1 S 2k S 2k+1 S 2k+2 and inductor L k,1 L k+1,1 Inductor L k,1 One end is connected to battery B 2k-1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k-1 The source and switch S 2k The drain connection, the switching transistor S 2k-1 The drain of the battery B 2k-1 The positive terminal is connected, and the switching transistor S... 2k The source electrode and battery B 2k The negative terminal connection; Inductor L k+1,1 One end is connected to battery B 2k+1 The negative terminal is connected, and the other end is connected to the switching transistor S. 2k+1 The source and switch S 2k+2 The drain connection, the switching transistor S 2k+1 The drain of the battery B 2k+1 The positive terminal is connected, and the switching transistor S... 2k+2 The source electrode and battery B 2k+2 The negative terminal connection; Battery B 2k-1 The positive terminal and the switching transistor M k,2 The drain connection of battery B 2k+2 The negative terminal and the switching transistor M k+1,1 The source connection, inductor L k,2 One end is connected to battery B 2k The negative electrode of battery B 2k+1 The positive terminal is connected, and the inductor L k,2 The other end is connected to the switching transistor M. k,2 The source and switch M k+1,1 Drain connection; When k≥2, the switching transistor M k,1 The drain and switching transistor M k-1,2 The source is connected and connected via inductor L. k-1,2 With battery B 2k-2 The negative terminal connection; Each switching transistor is connected in anti-parallel to a freewheeling diode; The k-th battery pair can perform intra-group power balancing with the (k+1)-th or (k-1)-th battery pair as needed for power balancing. Switch S 2k-1 S 2k S 2k+1 S 2k+2 M k+1,1 M k,2 The gates are respectively connected to the corresponding PWM signals; The improved Buck-Boost equalization circuit also includes an inter-group equalization circuit, which includes switching transistors Q1 and Q2, an inductor L, and multiple multiplexers. The improved Buck-Boost balancing circuit uses adjacent battery pairs (i.e., four adjacent batteries) as the basic unit for inter-pack power balancing. It performs inter-pack power balancing with other battery packs. Taking the inter-pack power balancing between the k-th and k+1-th battery pairs and the (n-1)-th and n-th battery pairs as an example, the drain of the switching transistor Q1 used for inter-pack power balancing is connected to the battery B of the k-th battery pair via a switch. 2k+1 The positive terminal is connected to the source of the switching transistor Q2, which is used for inter-group charge balancing, and is connected to battery B of the nth battery pair via the switch. 2n The negative terminal connection; inductor L used for inter-group charge balancing. BG One end of the inductor is connected to the source of switching transistor Q1 and the drain of switching transistor Q2. BG The other end is connected to a switch and a switching transistor M respectively. k+1,1 The source and switch M n-1,1 The drain connection.

2. The battery pack charging control method according to claim 1, characterized in that, The intra-group power balancing, taking the intra-group balancing circuit composed of batteries B1, B2, B3, and B4 as an example, without loss of generality, assumes that the power of a single battery is... SOC B1 > SOC B2 > SOC B3 > SOC B4 ,in SOC B1 , SOC B2 , SOC B3 , SOC B4 These are the charge levels of batteries B1, B2, B3, and B4, respectively. First, the batteries B1 and B2 are balanced. This process includes the discharge phase of battery B1 and the charging phase of battery B2. Battery B1 discharge stage: when At this time, the PWM signal controls the switching transistor S1 to turn on, and the power flows through the battery B1, the switching transistor S1, and the inductor L. 1,1 The formed circuit transfers electrical energy from battery B1 to inductor L. 1,1 In the absence of internal resistance, the following formula holds true: ；（1） ；（2） in Indicating inductance L 1,1 Charging begins; Inductance L 1,1 voltage, This indicates the voltage of battery B1. Inductance L 1,1 The current; because Since it is a constant, the inductor current at this time is... Starting from 0, it increases linearly. At this time, the inductor current reaches its maximum value. , Indicating inductance L 1,1 The moment charging ends; ；（3） In the formula This indicates the on-time of the switching transistor S1; D represents the switching period of switch S1; D represents the duty cycle of switch S1. Battery B2 charging stage: When When the switching transistor S1 is turned off, the inductor L... 1,1 A circuit is formed through battery B2 and the freewheeling diode connected in anti-parallel to switch S2, and inductor L... 1,1 The electrical energy stored in battery B1 during the discharge phase is released to battery B2, charging battery B2. At this time, we have: ；（4） ；（5） In the formula Indicating inductance L 1,1 Discharge end time; This indicates the voltage of battery B2; At this time, the inductor current decreases linearly from its maximum value. When the inductor current drops to 0, one cycle of balancing between battery groups B1 and B2 ends. The charge balancing of batteries B3 and B4 is similar to that of batteries B1 and B2. Then, the battery pairs consisting of batteries B1 and B2 and batteries B3 and B4 are each considered as a unit. The charge balance is performed between batteries B1 and B2 and batteries B3 and B4. The charge balance of adjacent battery pairs is similar to that of batteries B1 and B2.

3. The battery pack charging control method according to claim 2, characterized in that, The improved Buck-Boost equalization circuit also includes an external charging circuit, which includes a transformer T, a switching transistor Q3, an electrolytic capacitor C, and a diode D. The primary winding of transformer T is connected to the positive terminal of an external DC power supply, and the other end of the primary winding of transformer T is connected to the drain of switching transistor Q3. The source of switching transistor Q3 is connected to the negative terminal of the external DC power supply. A freewheeling diode is connected in anti-parallel to switching transistor Q3. The secondary winding of transformer T is connected to the negative terminal of electrolytic capacitor C. The other end of the secondary winding of transformer T is connected to the anode of diode D. The cathode of diode D is connected to the positive terminal of electrolytic capacitor C. The negative terminal of electrolytic capacitor C serves as the negative terminal of the external charging circuit, and the positive terminal of electrolytic capacitor C serves as the positive terminal of the external charging circuit.

4. The battery pack charging control method according to claim 3, characterized in that, Transformer T is a flyback transformer.

5. The battery pack charging control method according to claim 4, characterized in that, The inter-group power balancing process specifically includes: 1) Select the battery packs to be balanced between groups. Let the selected battery packs to be balanced between groups be the p-th battery pack and the q-th battery pack. 2) Control the multiple-choice switch separately to connect the p-th and q-th battery packs to the inter-group equalization circuit and the external charging circuit respectively; 2.1) Control the multiple-choice switch so that the drain of the switching transistor Q1 used for inter-group power balancing is connected to the positive terminal of the first battery of the p-th battery pack. 2.2) Control the multiple-choice switch so that the source of the switching transistor Q2 used for inter-group power balancing is connected to the negative terminal of the fourth battery of the qth battery pack. 2.3) Control the multi-select switch so that the end of the inductor L used for inter-group power balancing is away from the switch tube Q1 and connected to the negative terminal of the fourth battery of the p-th battery pack and the positive terminal of the first battery of the q-th battery pack, respectively. 2.4) Control the multiple-choice switch to connect the positive terminal of the first battery in the p-th battery pack to the positive terminal of the external charging circuit; 2.5) Control the multiple-choice switch to connect the negative terminal of the fourth battery in the q-th battery pack to the negative terminal of the external charging circuit; 3) Control the switching transistors Q1 and Q2, and use the inductor L to balance the power of the p-th and q-th battery packs; 4) Control switch Q3 to charge the p-th and q-th battery packs using different programs with the help of an external DC power supply and transformer T until they are fully charged.

6. The battery pack charging control method according to claim 5, characterized in that, The method includes the following steps: Step 1: Real-time acquisition of individual battery current and voltage; Step 2: Estimate the SOC value of each individual cell and the battery pack based on the collected current and voltage; Step 3: Calculate the average SOC value ε of the battery pack and the charge difference ΔSOC between adjacent individual cells within the battery pack; Step 4: Determine Whether it is valid, among which ; Step 4.1: If If successful, perform intra-group balancing of the batteries in the battery pack and proceed to step 2; Step 4.2: If If not, proceed to step 5; Step 5: Sample the SOC value of each battery pack; Step 6: Compare the SOC values ​​of the battery packs and sort them. Step 7: Based on the sorting in Step 6, determine the order of equalization between battery pack groups; Step 8: Connect the inter-group equalization circuit and the external charging circuit to perform equalization and charging; Step 9: Determine if the battery pack is fully charged. If it is, end the process; otherwise, proceed to step 8.

7. The battery pack charging control method according to claim 6, characterized in that, In step 7, the order of determining the inter-pack balancing is to sequentially select the battery pack with the highest SOC value and the battery pack with the lowest SOC value from the list of battery packs to be balanced, and then pair them for inter-pack balancing to improve the efficiency and effectiveness of power balancing.

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