Balanced fuzzy control method between groups in battery pack

Abstract

The invention relates to the technical field of battery equalization, in particular to a fuzzy control method for inter-pack equalization in a battery pack, which comprises the following steps of: acquiring voltage, current and SOC (State of Charge) values of each battery; calculating an SOC difference value and a voltage difference value of adjacent batteries in the group; when the SOC difference value is greater than a first SOC threshold value or the voltage difference value is greater than a first voltage threshold value, outputting a control signal through an in-group self-adaptive fuzzy PID controller, and controlling the on and off of an in-group equalization switch tube; and when the SOC difference value is smaller than the first SOC threshold value and the voltage difference value is smaller than the first voltage threshold value, the intra-group equalization is ended. The equalization problem caused by inconsistency of the single batteries in the existing series lithium ion battery pack is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery equalization, and particularly to a fuzzy control method for inter-group equalization within a battery pack. Background Art

[0002] Due to differences in the battery manufacturing process and changes in usage and environmental conditions, inconsistencies will inevitably occur within and between battery packs; when the battery pack is unbalanced, overcharging or over-discharging may occur, affecting performance and service life, and even causing safety problems.

[0003] Active equalization methods have become the mainstream of research because they can achieve efficient energy transfer; GUO X et al. proposed a flyback series battery equalization structure that uses dual-objective thresholds to equalize the battery pack, but the circuit structure is complex, and the equalization efficiency will decrease significantly as the number of battery packs increases;

[0004] The literature "Multi-Winding Transformer Based Cell Balancing System with Cost-Effective Gate Drivers" adopted a multi-winding multi-transformer topology, which can adapt to large-scale series battery packs, but the circuit is complex and the manufacturing cost is high;

[0005] The key to the equalization control strategy lies in selecting appropriate equalization variables and designing an efficient control algorithm; the literature "Adaptive estimation-based hierarchical model predictive control methodology for battery active equalization topologies" proposed an active equalization strategy for MPC; some scholars also proposed applying the particle swarm algorithm to the equalization of series battery packs, using SOC as an input parameter to solve the global optimal solution and the best equalization time; although MPC and the particle swarm algorithm can achieve battery pack equalization, their practical applications are limited due to complex design and high implementation difficulty. Summary of the Invention

[0006] Aiming at the deficiencies of existing methods, the present invention uses an improved Buck-Boost circuit within the group and a single-inductor topology circuit between groups; voltage and SOC are selected as equalization variables, and an adaptive fuzzy control PID algorithm is used to equalize the batteries within and between groups, solving the equalization problem caused by the inconsistency of single cells in existing series lithium-ion battery packs.

[0007] The technical solution adopted by the present invention is: a fuzzy control method for inter-group equalization within a battery pack includes the following steps:

[0008] Step 1: Collect the voltage, current, and SOC values of each battery;

[0009] Step 2: Calculate the SOC difference and voltage difference between adjacent batteries within the group; when the SOC difference is greater than the first SOC threshold or the voltage difference is greater than the first voltage threshold, output a control signal through the in-group adaptive fuzzy PID controller to control the closing and conduction of the in-group equalization switch tubes; until the SOC difference is less than the first SOC threshold and the voltage difference is less than the first voltage threshold, the in-group equalization ends.

[0010] As a preferred embodiment of the present invention, the inter-group equalization based on adjacent batteries within the group includes:

[0011] Calculate the difference in the average SOC and the difference in the average voltage of each battery group; when the difference in the average SOC is greater than the second SOC threshold or the difference in the average voltage is greater than the second voltage threshold, output a control signal through the inter-group adaptive fuzzy PID controller to control the closing and conduction of the inter-group equalization switch tubes; until the difference in the averages is less than the second SOC threshold and the difference in the average voltage is less than the second voltage threshold, the inter-group equalization ends.

[0012] As a preferred embodiment of the present invention, the in-group adaptive fuzzy PID controller includes:

[0013] Perform fuzzyfication, fuzzy inference, and defuzzyfication on SOC dif1 and SOC avg1 to obtain the current i 1 soc ;

[0014] Perform fuzzyfication, fuzzy inference, and defuzzyfication on U dif1 and U avg1 to obtain the current i 1 v ;

[0015] Perform fuzzyfication, fuzzy inference, and defuzzyfication on SOC c and SOC d to obtain the weight α 1 ;

[0016] Add α 1 *i 1 soc to i 1 v *(1 - α 1 ) to perform an addition operation to obtain i 1 ref ; Add i 1 ref to the feedback inductor current i of the in-group equalization circuit 1Perform a subtraction operation, input it into a PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the intra-group equalization circuit.

[0017] As a preferred embodiment of the present invention, the inter-group adaptive fuzzy PID controller includes:

[0018] Perform fuzzyfication, fuzzy inference, and defuzzyfication on SOC dif2 and SOC avg2 to obtain the current i 2 soc ;

[0019] Perform fuzzyfication, fuzzy inference, and defuzzyfication on U dif2 and U avg2 to obtain the current i 2 v ;

[0020] Perform fuzzyfication, fuzzy inference, and defuzzyfication on SOC pamax and SOC pamin to obtain the weight α 2 ;

[0021] Add α 2 *i 2 soc and i 2 v *(1 - α 2 ) to obtain i 2 ref ; Subtract i 2 ref from the feedback inductor current i 2 of the intra-group equalization circuit, input it into a PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the inter-group equalization circuit.

[0022] As a preferred embodiment of the present invention, the intra-group equalization circuit includes: batteries B1 to B3, NMOS transistors S1a, S1b, S2a, S2b, S3a, S3b, inductors L1, L2, L3; the positive pole of B1 is respectively connected to the common drain of S 1a and the source of S 3a , the common negative pole of B1 and the positive pole of B2 are connected to the lower end of L1, the source of S 1a and the common drain of S 1b are connected to the upper end of L1, the source of S 1b is connected to the common negative pole of B2, the positive pole of B3, and the upper end of L2, the drain of S 2a is connected to the lower end of L1 and the common source of S 3b , the source of S 2a is connected to the lower end of L2 and S 2bis connected to the drain common terminal, the upper end of L2 is connected to the negative pole of B2, the positive pole of B3, and S 1b is connected to the source common terminal, the positive pole of B3 is connected to the S 4b source, the negative pole of B3 is connected to the S 2b source, S 4b is connected to the source common terminal, S 4b drain is connected to the lower end of L3 and S 3a is connected to the drain common terminal, the upper end of L3 is connected to S 3b drain, S 4a is connected to the drain common terminal.

[0023] As a preferred embodiment of the present invention, the equalization of B1 to B3 in the intra-group equalization circuit includes:

[0024] S 3a and S 3b are turned on, and L3 is charged within the duty cycle D1;

[0025] S 3a and S 3b are turned off, S 4a and S 4b are turned on; within the duty cycle D2, L3 is used to charge B3.

[0026] As a preferred embodiment of the present invention, the inter-group equalization circuit includes: inductor L m and battery packs B w1 to B w3 , NMOS transistors S1 to S8, S1, S3, S5, S7 are common-source; the common-drain of S2, S4, S6, S8, and L m is connected in series between the common-source and the common-drain. S1, S2, S3, and S4 form the first H-bridge, S3, S4, S5, and S6 form the second H-bridge, and S5, S6, S7, and S8 form the third H-bridge. The three H-bridges are connected in parallel with B w1 , B w2 , B w3 .

[0027] As a preferred embodiment of the present invention, the equalization of B w1 to B w3 includes:

[0028] Turn on S1 and S4, and charge L m within the duty cycle D'1;

[0029] S1 and S4 are turned off, S6 and S7 are turned on, and within the duty cycle D'2, L m is used to charge B w3 .

[0030] As a preferred embodiment of the present invention, an inter-group equalization fuzzy control system within a battery pack includes: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement an inter-group equalization fuzzy control method within the battery pack.

[0031] As a preferred embodiment of the present invention, a computer-readable medium storing computer program code, the computer program code implementing an inter-group equalization fuzzy control method when executed by a processor.

[0032] Advantages of the present invention:

[0033] 1. To solve the equalization problem caused by the inconsistency of individual batteries in a series-connected lithium-ion battery pack, the present invention proposes a novel hierarchical equalization topology structure, which combines an improved Buck-Boost circuit and a single-inductor equalization circuit to achieve coordinated control of intra-group and inter-group equalization;

[0034] 2. Use the improved Buck-Boost circuit as an intra-group equalization unit to achieve efficient energy transfer between individual batteries;

[0035] 3. Utilize a single-inductor circuit to form the second-level topology to achieve rapid equalization between battery packs; this hierarchical design significantly shortens the equalization path and effectively solves the problems of too long equalization paths and slow equalization speed in traditional topologies;

[0036] 4. Experimental results show that the equalization speed of the present invention is about 49.1% higher than that of traditional hierarchical topologies; in the equalization control strategy, SOC and voltage are used as dual equalization variables, and by introducing a weight coefficient to dynamically allocate their influence on the output current, multi-objective coordinated control is achieved; this multi-variable control strategy can more accurately reflect the actual state of each individual battery and avoid the limitations brought by a single equalization variable;

[0037] 5. To verify the superiority of this strategy, comparative simulations were carried out under conditions such as static, charging, and discharging, and compared with the traditional FLC algorithm; the results show that the control strategy of the present invention is significantly superior to the traditional FLC algorithm in terms of shortening the equalization time, improving the consistency of the battery pack, and increasing the energy transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flowchart of the inter-group equalization fuzzy control method of the present invention;

[0039] Figure 2 is a fuzzy control logic block diagram of the present invention;

[0040] Figure 3 is a PWM signal block diagram of the present invention;

[0041] Figure 4It is the membership function diagram of voltage and SOC of the present invention;

[0042] Figure 5 It is the membership function diagram of coefficients of the present invention;

[0043] Figure 6 It is the battery pack balancing circuit of the present invention;

[0044] Figure 7 It is the in-group balancing circuit diagram of the present invention;

[0045] Figure 8 It is the between-group balancing circuit diagram;

[0046] Figure 9 It is the SOC-OCV curve diagram;

[0047] Figure 10 It is the comparison diagram for verifying topological performance;

[0048] Figure 11 It is the comparison diagram for static balancing;

[0049] Figure 12 It is the comparison diagram for charging balancing;

[0050] Figure 13 It is the comparison diagram for discharging balancing. Specific embodiments

[0051] The present invention will be further described below in conjunction with the drawings and embodiments. This figure is a simplified schematic diagram, which only illustrates the basic structure of the present invention in a schematic manner. Therefore, it only shows the components related to the present invention.

[0052] As Figure 1 shown, a method for in-group and between-group balancing fuzzy control of a battery pack includes the following steps:

[0053] Step 1: Collect the voltage, current, and SOC values of each battery;

[0054] Step 2: Calculate the SOC difference SOC dif1 and voltage difference U dif1 between adjacent batteries in the group; when SOC dif1 is greater than the first SOC threshold or U dif1 is greater than the first voltage threshold, output a control signal through the in-group adaptive fuzzy PID controller to control the closing and conduction of the in-group balancing switch tube; until SOC dif1 is less than the first SOC threshold and U dif1 is less than the first voltage threshold, the in-group balancing ends;

[0055] Or

[0056] Step 2: Calculate the difference SOC of the average SOC of each battery packdif2 The difference U from the average voltage dif2 ; When the SOC dif2 is greater than the second SOC threshold or U dif2 is greater than the second voltage threshold, a control signal is output through the inter-group adaptive fuzzy PID controller to control the turn-off and turn-on of the inter-group equalization switch tube; until the SOC dif2 is less than the second SOC threshold and U dif2 is less than the second voltage threshold, the inter-group equalization ends;

[0057] Among them, the first and second SOC thresholds, the first and second voltage thresholds are all user-defined parameters. In this embodiment, the first SOC threshold = 0.06%, the first voltage threshold = 0.02, the second SOC threshold = 0.1%, and the second voltage threshold = 0.04;

[0058] Utilize the adaptive fuzzy PID controller to output a control signal to make the battery or battery pack with the highest energy transfer energy to the battery or battery pack with the lowest energy.

[0059] As Figure 2 shown, the adaptive fuzzy PID controller consists of a fuzzifier, fuzzy inference, a rule base, and a defuzzifier; the fuzzifier first converts the input exact value into a fuzzy value, then transmits it to the fuzzy inference engine, and outputs according to the rules; the output fuzzy quantity is then sent to the defuzzifier, and the final output is obtained through defuzzification.

[0060] The present invention designs three fuzzy controllers based on voltage, SOC, and weight coefficient respectively; the reference current of the equalization circuit consists of two parts: one part is the current i soc output by the SOC fuzzy controller, and the other part is the current i v output by the voltage fuzzy controller; after these two parts of current are adjusted by the weight coefficient α, they are further adjusted by the PID controller to control the actual equalization circuit.

[0061] The intra-group adaptive fuzzy PID controller includes: the SOC fuzzy controller for intra-group equalization, the voltage fuzzy controller for intra-group equalization;

[0062] The inter-group adaptive fuzzy PID controller includes: the SOC fuzzy controller for inter-group equalization, the voltage fuzzy controller for inter-group equalization;

[0063] The output current of the SOC fuzzy controller for intra-group equalization is i 1 soc , and the SOC output current of the SOC fuzzy controller for inter-group equalization is i 2 soc ;

[0064] The output current of the voltage fuzzy controller for intra-group equalization is i1 v The voltage output current of the voltage fuzzy controller with equalization between groups is i 2 v ;

[0065] Among them, the output current of the SOC fuzzy controller with in-group equalization is obtained by calculating the difference SOC of the SOC values of adjacent batteries dif1 and the average value SOC of the SOC values of adjacent batteries avg1 After fuzzification, the fuzzy language variables u(x) and u(y) are obtained; then, through fuzzy inference, the fuzzy inference variable u(z) is obtained, and finally, defuzzification is performed to obtain i 1 soc ;

[0066] Among them, SOC dif1 = SOC c - SOC d , SOC c 、SOC d are the SOC values of adjacent batteries;

[0067] The output current of the voltage fuzzy controller with in-group equalization is obtained by calculating the difference U of the voltage values of adjacent batteries dif1 and the average value U of the voltage values of adjacent batteries avg1 After fuzzification, the fuzzy language variables u(x) and u(y) are obtained; then, through fuzzy inference, the fuzzy inference variable u(z) is obtained, and finally, defuzzification is performed to obtain i 1 v ;

[0068] Among them, U dif1 = U c - U d , U c 、U d are the voltage values of adjacent batteries;

[0069] The in-group equalization weight coefficient α 1 is obtained by fuzzifying the SOC values SOC c 、SOC d of adjacent batteries to obtain the fuzzy language variable Then, through fuzzy inference, the fuzzy inference variable Finally, defuzzification is performed to obtain α 1 ;

[0070] For example Figure 3 is to use α 1 、i 1 soc 、i 1 vThe PWM signal generation process during in-group balancing includes:

[0071] Adding α 1 *i 1 soc to i 1 v *(1 - α 1 ) to obtain i 1 ref ; Subtracting i 1 ref from the inductance current i of the feedback circuit of the in-group balancing circuit, inputting it to the PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the in-group balancing circuit; that is, the PID controller adjusts the duty cycle using the input current difference; 1

[0072] Similarly, calculate the inter-group i 2 soc and i 2 v and α 2 ;

[0073] The output current of the SOC fuzzy controller for inter-group balancing is obtained by calculating the difference in SOC values between groups, SOC dif2 and the average value of the SOC values of the inter-group batteries, SOC avg2 After fuzzification to obtain the fuzzy linguistic variables u(x) and u(y); then through fuzzy inference to obtain the fuzzy inference variable u(z), and finally defuzzification to obtain i 2 soc ;

[0074] The difference in SOC average values, SOC dif2 is obtained by calculating the maximum SOC pamax and the minimum SOC pamin of the average SOC values of each battery group;

[0075] SOC dif2 = SOC pamax - SOC pamin ;

[0076] Among them,

[0077]

[0078] n is the total number of battery groups, and SOC pna is the SOC value of the nth battery group.

[0079] The output current of the voltage fuzzy controller for inter-group balancing is obtained by calculating the difference in voltage values between groups, U dif2and the average voltage value U between groups avg2 After fuzzification, fuzzy linguistic variables u(x) and u(y) are obtained; then through fuzzy inference, a fuzzy inference variable u(z) is obtained, and finally defuzzification is performed to obtain i 2 v ;

[0080] The difference in the average voltage U dif2 By calculating the maximum value U of the average voltage of each battery pack pamax and the minimum value U of the average voltage pamin ;

[0081] where U dif2 = U pmax - U pmin ,

[0082] U pna is the voltage value of the nth battery pack;

[0083]

[0084] The inter-group balance weight coefficient α 2 is obtained through the SOC values SOC pamax 、SOC pamin of adjacent batteries through fuzzification to obtain fuzzy linguistic variables and then through fuzzy inference to obtain a fuzzy inference variable and finally defuzzification is performed to obtain α 2 .

[0085] Adding α 2 * i 2 soc to i 2 v *(1 - α 2 ) performs an addition operation to obtain i 2 ref ; Subtracting i 2 ref from the inductor current i of the feedback circuit of the inter-group balance circuit, inputting it into the PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the inter-group balance circuit. 2

[0086] According to the rule base, the fuzzy variables μ(z) are inferred and output, To ensure that the battery operates within a safe range, the maximum current output by the fuzzy control is limited to (0, 3.5), and μ(x) and μ(y) are each divided into 5 fuzzy subsets, namely VS (very small), S (small), MD (medium), LG (large), and EG (extremely large); SOC dif ​and the SOC avg range from (0%, 40%) and (0%, 100%) respectively, and V dif and V avg range from (0, 0.40) and (2.5, 3.65) respectively; According to the practical experience of the battery equalization process, the fuzzy inference rules shown in Table 1 are established; Using S-shaped, Z-shaped, and triangular membership functions, the membership functions of voltage and SOC are as Figure 4 shown Figure 4 where a of dif is SOC dif or V Figure 4 where b of avg is SOC avg or V Figure 4 where c of soc is i v or i

[0087] Table 1 Fuzzy control rules

[0088]

[0089] As can be seen from Table 1, when SOC dif is extremely large and SOC avg is extremely small, to prevent the battery from over-discharging, the equalization current should be small; When SOC dif and SOC avg are both large, to prevent the battery from over-charging, the equalization current should be large; When SOC dif and SOC avg are both at a moderate level, the equalization current should be moderate.

[0090] As Figure 9 shown, the battery equalization variable directly affects the equalization efficiency. Currently, the commonly used variables include open circuit voltage OCV, SOC, and terminal voltage; Among them, the terminal voltage is the most widely used equalization index because it can be obtained through measurement; However, due to the polarization phenomenon of the battery, the measurement result may be disturbed, making it difficult to achieve the ideal effect of the voltage difference between batteries; Figure 9 shows the relationship between OCV and SOC; When SOC is in the range of 20% - 80%, the change of OCV is small. If OCV is used as the equalization variable, the equalization speed will slow down and it is difficult to eliminate the inconsistency between batteries; When SOC is in the range of 0% - 20% or 90% - 100%, if it is used as the equalization variable, it may cause the battery to overcharge or over-discharge; In summary, single-variable equalization is difficult to achieve the ideal effect.

[0091] Therefore, the present invention adopts a multi-variable coordinated equalization scheme, and within the entire range of SOC from 0% to 100%, both voltage and SOC are used as equalization variables simultaneously.

[0092] Table 2 Fuzzy Control Rules

[0093]

[0094] Weight coefficient α 1 and β 1 affect the output of the voltage and SOC fuzzy controller. According to Figure 9 , the open-circuit voltage changes differently within different SOC intervals; therefore, the fuzzy control rules can be formulated based on this curve. Taking the intra-group balance as an example, as can be seen from Table 2, when SOC c and SOC d are at the minimum and maximum respectively, the balance weights of SOC and OCV should be close, and α 1 should take a moderate value; when SOC c and SOC d are large and moderate respectively, the weight of SOC as the balance variable should be increased, and α 1 should take a large value; when SOC c and SOC d are both small, at this time the weight of OCV as the balance variable should be increased, and α should take a small value. The membership function of the weight coefficient is as Figure 5 shown, Figure 5 where a is the membership function of SOC c or SOC d , and Figure 5 where b is the membership function of the weight coefficient α.

[0095] Since the balance system cannot directly utilize the fuzzy language signal, defuzzification processing must be carried out. The centroid method is used for defuzzification processing, and the defuzzification formula is: where ψ(q) is the fuzzy result of the inference.

[0096] As Figure 6 is the circuit diagram of intra-group balance and inter-group balance; Figure 1 for the left diagram, an improved Buck-Boost topology is adopted to achieve energy transfer between the batteries within the group;

[0097] For a battery pack composed of 3 lithium batteries, only 8 power tubes and 3 inductors are required to form an equalization unit; compared with the traditional Buck-Boost circuit, when there is a large energy difference between the batteries, this scheme avoids the problem of energy transfer step by step. In particular, the present invention realizes the balance between the head and tail batteries; by utilizing the characteristics of the built-in body diode of the power tube, during the discharge process, the energy storage inductor can charge the battery with lower energy through the body diode, thus avoiding the additional use of diodes.

[0098] Figure 6 Taking the left half diagram of

[0099] Batteries B1, B2, B3, NMOS transistors S 1a , S 1b , S 2a , S 2b , S 3a , S 3b , inductors L1, L2, L3; among them, B1, B2, B3 are connected in series, the positive pole of B1 is respectively connected to the common drain of S 1a and the common source of S 3a , the common terminal of the negative pole of B1 and the positive pole of B2 is connected to the lower end of L1, the source of S 1a is connected to the common drain of the source of S 1b and the upper end of L1 is connected, the source of S 1b is connected to the common terminal of the negative pole of B2, the positive pole of B3, and the upper end of L2, the drain of S 2a is connected to the lower end of L1 and the common source of S 3b , the source of S 2a is connected to the lower end of L2 and the common drain of S 2b , the upper end of L2 is connected to the common terminal of the negative pole of B2, the positive pole of B3, and the source of S 1b , the positive pole of B3 is connected to the source of S 4b , the negative pole of B3 is connected to the source of S 2b , the source of S 4b , the source of S 4b , the drain of S 3a is connected to the common drain of the lower end of L3 and the drain of S 3b , the upper end of L3 is connected to the common drain of the drain of S 4a and the drain of S

[0100] For example Figure 7 taking the in-group equalization of the head and tail batteries B1 and B3 by battery B1 as an example, when the SOC or voltage of the adjacent batteries B1 and B3 in the group is lower than the set threshold, the energy transfer between the high-energy battery and the low-energy battery is realized through the inductor; assuming that the energy of battery B1 is higher than that of B3, the energy transfer process can be divided into two stages;

[0101] Stage 1: B1 discharges, L3 starts to work, MOS transistors S 3a , S 3b conduct, and B1 forms a discharge circuit as shown by the red arrow; in this stage, the current of inductor L3 rises from 0 to the maximum value; the current calculation formula on L3 is:

[0102]

[0103] In the formula, R s is the total resistance of the circuit loop when B1 charges inductor L3, V1 is the voltage of battery B1, D1 is the discharge duty ratio of the control signal, T sis the period of the switch.

[0104] When t = D1T s At this time, the current on L3 reaches the maximum value, and the maximum current passing through L3 is:

[0105]

[0106] Stage 2: After the current on L3 reaches the maximum value, S 3a and S 3b turn off, and S 4a and S 4b turn on; the current of inductor L3 forms a discharge loop through S 4a and S 4b and B3; the charging direction of B3 is as shown by the blue arrow; at this time, the calculation method of the current on L3 is:

[0107]

[0108] where R d is the total resistance of the circuit loop when B3 is charging; V3 is the voltage of battery B3, and V d is the conduction voltage drop of the MOS body diode; D2 = 1 - D1;

[0109] When B1 charges B2, in stage 1, S 1a turns on to charge L1; in stage 2, S 1b turns on to charge B1 using L1.

[0110] When B2 charges B3, in stage 1, S 2a turns on to charge L2; in stage 2, S 2b turns on to charge B3 using L2.

[0111] Figure 1 The single-inductor bi-directional topology structure shown on the right consists of n battery packs, 2n + 4 power tubes, 2n + 3 diodes, and an energy storage inductor; each battery pack operates independently without interfering with each other's equalization process; this topology structure can achieve energy transfer between any battery packs, only requiring a pair of complementary PWM-controlled MOS tubes; in addition, the diodes shown in the figure are used to prevent battery short circuits and suppress interference between other battery modules.

[0112] As Figure 8 shown, the inter-group equalization includes: inductor L m , battery packs B w1 , B w2 , B w3, diodes D1, D2, D3, D4, D5, D6, D7, D8, NMOS transistors S1 to S8, with S1, S3, S5, S7 having a common source; the common drain of S2, S4, S6, S8, and an inductor L is connected in series between the common source and the common drain m , S1, S2, S3, S4 form a first H-bridge, S3, S4, S5, S6 form a second H-bridge, S5, S6, S7, S8 form a third H-bridge, and the three H-bridges are connected in parallel with each other in sequence by B w1 , B w2 , B w3 ; Each NMOS transistor is connected in series with a diode.

[0113] Taking the equalization of battery pack B W1 to B W3 as an example, assume that B w1 has the highest energy, while B w3 has the lowest energy; during the energy transfer process between battery packs, within the duty cycle D'1, B w1 first turns on MOS transistors S1 and S4 to form a discharge loop composed of diodes D1 and D4, and transfers the energy to inductor L m ; The current in inductor L m gradually rises until it reaches the peak value; the current direction of B w1 discharging is as shown by the red arrow; subsequently, within the duty cycle D'2, when MOS transistors S1 and S4 are turned off and S6 and S7 are turned on, the circuit completes the switching; at this time, inductor L m forms a charging loop with S6, S7, D6, and D7, and delivers the stored energy to B w3 , thereby charging B w3 ; the current direction of B w3 charging is as shown by the blue arrow.

[0114] That is, turn on S1 and S4 to charge L within the duty cycle D'1 m ; S1 and S4 are turned off, S6 and S7 are turned on, and within the duty cycle D'2, use L m to charge B w3 .

[0115] Simulation experiments and analysis:

[0116] To verify the hierarchical equalization circuit based on the combination of Buck - Boost and single - inductor topology proposed in the present invention, 9 series - connected batteries were selected as the research object and divided into 3 groups. A simulation model was built on the MATLAB / Simulink platform for experiments. Among them, the nominal voltage of each battery is 3.7V, the rated capacity is 2Ah, and the initial SOCs of the 9 batteries are 82%, 75%, 70%, 73%, 69%, 66%, 77%, 61%, and 65% respectively. The internal resistance of the MOS transistor is 0.01Ω, the forward voltage drop of the diode is 0.7V, the value of the inductor L is 0.5H, and the period of the switching transistor is set to 1s.

[0117] To verify the equalization performance of the hierarchical topology proposed in the present invention, it was compared with the traditional Buck - Boost hierarchical topology. The comparative experiment adopted the adaptive fuzzy control algorithm. Figure 10 Show the changes in the SOC of each single battery of the present invention and the traditional hierarchy; under the static state, Figure 10 (a) The traditional Buck - Boost hierarchical topology takes 827 seconds to complete equalization, while Figure 10 (b) The hierarchical topology proposed in the present invention completes equalization within 421.1 seconds. The equalization time is shortened by 405.9 seconds, and the efficiency is increased by 49.1%. In the hierarchical topology proposed in the present invention, an improved buck - boost circuit is adopted within the group, shortening the energy transfer path between the first and last batteries, thus accelerating the equalization speed. A single - inductor topology circuit is adopted between groups to achieve two - way equalization of any battery group. From the perspective of equalization time, the topology performance proposed in the present invention is superior to the traditional hierarchical topology.

[0118] Verification of the adaptive fuzzy control algorithm includes static equalization experiments, charging equalization experiments, and discharging equalization experiments. Among them,

[0119] In the static equalization experiment, under the static state, as Figure 11 shown, Figure 11 (a) It takes 578.3 seconds for the traditional fuzzy control algorithm to achieve energy transfer of the battery pack, while Figure 11 (b) The algorithm of the present invention only needs 421.1 seconds to complete the equalization of the battery pack. Compared with the traditional FLC algorithm, the present invention shortens the equalization time by 27.2%. According to the data analysis in Table 3, before the equalization starts, the range of the SOC of the single battery is 21%, and the standard deviation is 6.547%. After equalization using the traditional FLC algorithm, the range of the SOC drops to 0.177%, and the standard deviation drops to 0.054%. While the algorithm of the present invention further reduces the range of the SOC to 0.046%, and the standard deviation drops to 0.017%. Therefore, the algorithm of the present invention is superior to the traditional FLC algorithm under the static state and reduces the number of energy transfers.

[0120] Table 3 Comparison results of static equalization

[0121]

[0122] In the charging equalization experiment, the battery pack was charged at a constant current of 1.25C. Figure 12 It shows the changes in the SOC of each single battery under the traditional FLC algorithm and the algorithm of the present invention during the charging state; according to the SOC data of each single battery under different algorithms in Table 4, the time required for the traditional FLC algorithm to complete equalization is 555.6 seconds, while the algorithm of the present invention only requires 408.5 seconds; under the same conditions, the algorithm of the present invention shortens the equalization time by 26.5%; after 700 seconds of charging, the SOC range of the battery pack under the traditional FLC algorithm is 0.136%, while the SOC range of the algorithm of the present invention is 0.056%; in summary, the algorithm of the present invention improves the equalization efficiency, reduces the overcharging phenomenon of single batteries, and increases the available capacity of the battery pack during the charging state.

[0123] Table 4 Comparison results of charging equalization

[0124]

[0125] To simulate the actual power supply situation of the battery pack, the present invention adopts a 1.25C rate discharge test; according to the cask effect, the available capacity of the battery pack depends on the single battery with the worst performance; the traditional FLC algorithm and the algorithm of the present invention are compared under the discharge state. Figure 13 (a) The traditional FLC algorithm reaches the equalization state at 595.1 seconds during the discharge process of the battery pack, while the algorithm of the present invention completes equalization at 417.6 seconds, and its time efficiency is improved by 29.8%. As can be seen from Table 5, after 700 seconds of discharge, the standard deviation of each single battery under the traditional FLC algorithm is 0.063%, while that under the algorithm of the present invention is 0.022%; thus, it can be seen that the algorithm of the present invention not only achieves a faster equalization speed but also has a lower final inconsistency of the battery pack under the discharge state, which is superior to the traditional FLC algorithm.

[0126] Table 5 Comparison results of discharge equalization

[0127]

[0128]

[0129] To solve the equalization problem caused by the inconsistency of single batteries in a series lithium-ion battery pack, the present invention proposes a novel hierarchical equalization topology structure, which combines an improved Buck-Boost circuit and a single-inductor equalization circuit to achieve the coordinated control of intra-group and inter-group equalization. The present invention uses the improved Buck-Boost circuit as the intra-group equalization unit to achieve efficient energy transfer between each single battery.

[0130] Meanwhile, a second-stage topology is formed using a single-inductor circuit to achieve fast equalization between battery packs; this hierarchical design significantly shortens the equalization path and effectively solves the problems of overly long paths and slow equalization speed in traditional topologies; experimental results show that the equalization speed of the present invention is about 49.1% higher than that of traditional hierarchical topologies; in terms of the equalization control strategy, the present invention uses SOC and voltage as dual equalization variables and dynamically allocates their influence on the output current by introducing a weight coefficient to achieve multi-objective cooperative control; this multi-variable control strategy can more accurately reflect the actual state of each single cell and avoid the limitations brought by a single equalization variable.

[0131] To verify the superiority of this strategy, the present invention conducts comparative simulations under conditions such as standing, charging, and discharging, and compares with the traditional FLC algorithm; the results show that the control strategy proposed by the present invention is significantly superior to the traditional FLC algorithm in terms of shortening the equalization time, improving the consistency of the battery pack, and increasing the energy transfer efficiency.

[0132] Inspired by the above ideal embodiments according to the present invention, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A fuzzy control method for inter-group balancing within a battery pack, characterized in that, Including the following steps: Step 1, collect the voltage, current, and SOC value of each battery; Step 2: Calculate the SOC difference SOC dif1 and the voltage difference U dif1 ; when the SOC difference is greater than the first SOC threshold or the voltage difference is greater than the first voltage threshold, a control signal is output through the in-group adaptive fuzzy PID controller to control the turning off and on of the in-group equalizing switch tubes; The in-group equalization ends until the SOC difference is less than the first SOC threshold and the voltage difference is less than the first voltage threshold.

2. The inter-group equalization fuzzy control method for the battery pack according to claim 1, characterized in that, The inter-group equalization based on adjacent batteries in the group includes: Calculate the difference in the average SOC, denoted as ΔSOC, of each battery pack dif2 and the difference in the average voltage, denoted as ΔU dif2 ; when the difference in the average SOC is greater than the second SOC threshold or the difference in the average voltage is greater than the second voltage threshold, output a control signal through the inter-group adaptive fuzzy PID controller to control the turning off and on of the inter-group equalization switch tube; the inter-group equalization ends until the difference in the average value is less than the second SOC threshold and the difference in the average voltage is less than the second voltage threshold.

3. The method for fuzzy control of intra-group and inter-group balancing in a battery pack according to claim 1, characterized in that The in-group adaptive fuzzy PID controller includes: For the SOC dif1 and the SOC avg1 perform fuzzification, fuzzy inference, and defuzzification to obtain the current i 1 soc ; Perform fuzzification, fuzzy inference, and defuzzification on U dif1 and U avg1 to obtain the current i 1 v ; For the SOC c and the SOC d perform fuzzification, fuzzy inference, and defuzzification to obtain the weight α 1 ; Add α 1 *i 1 soc to i 1 v *(1 - α 1 ) to obtain i 1 ref ; Subtract i 1 ref from the inductor current i 1 fed back by the intra-group balancing circuit, input it to the PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the intra-group balancing circuit.

4. The battery pack internal and between-group equalization fuzzy control method according to claim 2, characterized in that The inter-group adaptive fuzzy PID controller includes: For the SOC dif2 and the SOC avg2 perform fuzzification, fuzzy inference, and defuzzification to obtain the current i 2 soc ; Perform fuzzification, fuzzy inference, and defuzzification on U dif2 and U avg2 to obtain the current i 2 v ; For the SOC pamax and the SOC pamin perform fuzzification, fuzzy inference, and defuzzification to obtain the weight α 2 ; Add α 2 *i 2 soc to i 2 v *(1 - α 2 ) to obtain i 2 ref ; Subtract i 2 ref from the inductor current i 2 fed back by the intra-group balancing circuit, input it to the PID controller, and the signal generator adjusts the duty cycle according to the PID controller to control the inter-group balancing circuit.

5. The battery pack internal and inter-group balancing fuzzy control method according to claim 3, characterized in that The in-group balancing circuit includes: batteries B1 to B3, NMOS transistors S1a, S1b, S2a, S2b, S3a, S3b, inductors L1, L2, L3; the positive electrode of B1 is respectively connected to the common drain of S 1a and the common source of S 3a . The common negative electrode of B1 and the positive electrode of B2 are connected to the lower end of L1. The source of S 1a and the common drain of S 1b are connected to the upper end of L1. The source of S 1b is connected to the common negative electrode of B2, the positive electrode of B3, and the upper end of L2. The drain of S 2a is connected to the common source of the lower end of L1 and S 3b . The source of S 2a is connected to the common drain of the lower end of L2 and S 2b . The upper end of L2 is connected to the common source of the negative electrode of B2, the positive electrode of B3, and S 1b . The positive electrode of B3 is connected to the source of S 4b . The negative electrode of B3 is connected to the common source of the source of S 2b and the source of S 4b . The drain of S 4b is connected to the common source of the lower end of L3 and S 3a . The upper end of L3 is connected to the common source of the drain of S 3b and the drain of S 4a .

6. The fuzzy control method for intra-group and inter-group balancing in the battery pack according to claim 5, wherein In the in-group equalization circuit, B1 equalizes B3 Including: S 3a and S 3b conduct, and charge L3 within the duty cycle D1; S 3a and S 3b turn off, S 4a and S 4b turn on; within the duty cycle D2, charge B3 using L3.

7. The method for fuzzy control of intra-group and inter-group equalization in a battery pack according to claim 4, wherein The inter-group balancing circuit includes: inductor L m , battery packs B w1 to B w3 , NMOS transistors S1 to S8, the common source of S1, S3, S5, S7; the common drain of S2, S4, S6, S8, and L is connected in series between the common source and the common drain m , S1, S2, S3, S4 form the first H-bridge, S3, S4, S5, S6 form the second H-bridge, S5, S6, S7, S8 form the third H-bridge, and B w1 , B w2 , B w3 are connected in parallel in sequence between the three H-bridges 8. The method for fuzzy control of intra-group and inter-group equalization in a battery pack according to claim 7, characterized in that, B in the inter-group equalization circuit w1 For B w3 The equalization includes: Turn on S1 and S4, and charge L within the duty cycle D’1 m ; S1 and S4 are turned off, S6 and S7 are turned on, and within the duty cycle D’2, L m charges B w3 .

9. Battery pack internal and inter-group balancing fuzzy control system, characterized in that, Including: A memory for storing instructions executable by a processor; A processor for executing the instructions to implement the in-group and inter-group equalization fuzzy control method of the battery pack as described in any one of claims 1-8.

10. A computer-readable medium storing computer program code, characterized in that, The computer program code implements the in-group and inter-group equalization fuzzy control method of the battery pack as described in any one of claims 1-8 when executed by the processor.

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