Multi-battery pack equalization control circuit and control method thereof
By combining a multi-battery pack balancing control circuit and a fuzzy logic controller, the balancing current is dynamically adjusted, solving the problem of low energy transfer efficiency in traditional battery packs and achieving efficient energy balancing within the battery pack and extending battery life.
Patent Information
- Application Number
- CN202511808312.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-03
- Publication Date
- 2026-03-06
AI Technical Summary
Traditional battery pack equalization control suffers from low energy transfer efficiency and the equalization current cannot be dynamically adjusted, leading to severe inconsistencies within the battery pack and affecting its performance and lifespan.
A multi-battery pack equalization control circuit is adopted, including intra-pack equalization circuit, inter-pack equalization circuit, and intra-pack start-end connection circuit. The equalization current is dynamically adjusted by a fuzzy logic controller, and combined with the SOC and voltage value judgment, to achieve efficient energy transfer and equalization.
It improves the energy transfer efficiency within the battery pack, prevents overcharging and over-discharging of the battery, and enhances the energy utilization rate and lifespan of the battery pack.
Smart Images
Figure CN121618668A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of active battery pack balancing control technology, and in particular to a multi-battery pack balancing control circuit and its control method. Background Technology
[0002] Inconsistency between batteries is a common problem. Due to factors such as battery production, usage, and environment, the performance parameters of individual battery cells vary, leading to differences in current, voltage, and capacity among the cells within a battery pack. For large-scale energy storage power stations, where numerous battery cells are connected in series and parallel, this inconsistency causes circulating current losses and a bottleneck effect, thus affecting the performance of the entire battery cluster. For example, it can lead to reduced cluster capacity, decreased safety, and shortened cycle life. To address this inconsistency, battery balancing technology is needed to maintain a balance in energy and state of charge (SOC) among series- or parallel-connected batteries as much as possible.
[0003] The selection of the balancing object affects the balancing effect and efficiency of battery balancing. The balancing objects include the following: (1) Battery voltage equalization: The measurement of battery voltage is relatively simple and has good research value in the range of high and low SOC. However, it is easily affected by the internal parameters of the battery and the external environment, which leads to the generation of prediction error and makes the equalization control less stable.
[0004] (2) Battery capacity balancing: Battery capacity refers to the maximum usable capacity of each individual cell in the battery pack. The inconsistency in capacity between individual cells in the battery pack can reflect the actual differences between individual cells, but capacity cannot be estimated online and can only be obtained under static conditions. Therefore, using battery capacity as a balancing variable is not suitable for online balancing schemes.
[0005] (3) Battery SOC balancing: SOC represents the ratio between the current remaining capacity of the battery and the total capacity. It is a comprehensive representation of the battery's internal parameters such as voltage and resistance. Using SOC as a balancing variable, it can fundamentally improve the inconsistency between battery packs. Therefore, SOC-based balancing control can effectively improve the energy utilization rate of the battery pack. However, the battery's SOC cannot be directly measured and needs to be predicted based on data such as battery voltage, current, and temperature.
[0006] In traditional equalization circuits, energy can only be transferred stage by stage, resulting in low efficiency. The equalization control strategy used employs a fixed duty cycle, which cannot dynamically adjust the equalization current, leading to overcharging and over-discharging problems. Summary of the Invention
[0007] Based on the shortcomings of the existing technology, the present invention provides a multi-battery pack equalization control circuit and its control method, which solves the problem that the energy of traditional double-layer inductors can only be transferred step by step.
[0008] The present invention adopts the following technical solution: In a first aspect, the present invention provides a multi-battery pack equalization control circuit, wherein each battery pack consists of m batteries connected in series, and the multiple battery packs are connected in series. The equalization control circuit includes an intra-pack equalization circuit, an inter-pack equalization circuit, and an intra-pack end-to-end connection circuit. The group's end-to-end connection circuit includes a first parallel branch, a first parallel unit, a second parallel unit, a third parallel unit, and a fourth parallel unit. The first parallel branch includes parallel resistors and inductors. Each parallel unit consists of parallel switching transistors and diodes, with one end being the common connection point of the source of the switching transistor and the cathode of the diode, and the other end being the common connection point of the drain of the switching transistor and the anode of the diode. In each battery pack, the positive terminal of the first battery is connected to one end of the first parallel unit, the other end of the first parallel unit is connected to one end of the first parallel branch and one end of the second parallel unit, and the other end of the second parallel unit is connected to the negative terminal of the last battery; the negative terminal of the first battery is connected to one end of the third parallel unit, the other end of the third parallel unit is connected to the other end of the first parallel branch and one end of the fourth parallel unit, and the other end of the fourth parallel unit is connected to the positive terminal of the last battery.
[0009] Preferably, the group equalization circuit includes multiple second parallel branches, multiple fifth parallel units, and multiple sixth parallel units. The second parallel branches have the same structure as the first parallel branches, and the fifth and sixth parallel units have the same structure as the first parallel units. In each battery pack, for the i-th battery cell B i , Its positive terminal is connected to one end of a fifth parallel unit, the other end of the fifth parallel unit is connected to one end of the second parallel branch and one end of the sixth parallel unit, and the other end of the sixth parallel unit is connected to B. i+1 The negative terminal is connected, and the other end of the second parallel branch is connected to B. i Negative electrode and B i+1 On the line connecting the positive and negative electrodes.
[0010] Preferably, the inter-group equalization circuit includes a third parallel branch, a seventh parallel unit, and an eighth parallel unit. The third parallel branch has the same structure as the first parallel branch, and the seventh and eighth parallel units have the same structure as the first parallel unit. In each battery pack, the positive terminal of the first battery is connected to one end of the seventh parallel unit, the other end of the seventh parallel unit is connected to one end of the third parallel branch and one end of the eighth parallel unit, the other end of the eighth parallel unit is connected to the negative terminal of the last battery in the next battery pack connected in series with the current battery pack, and the other end of the third parallel branch is connected to the line between the negative terminal of the last battery in the current battery pack and the positive terminal of the first battery in the next battery pack.
[0011] A control method for a multi-battery pack equalization control circuit, characterized by comprising the following steps: Obtain the SOC value of all individual cells in each battery pack; When the SOC value is between 10% and 90%, the first SOC variance of all battery cells in each battery pack and the second SOC variance of all battery packs are obtained based on the SOC value of each battery cell. The first SOC variance and the second SOC variance are judged relative to the first set threshold. Based on the judgment result, the corresponding SOC input variable is input to the fuzzy logic controller with preset fuzzy rules to obtain the corresponding SOC control duty cycle. The intra-group balancing, inter-group balancing, or simultaneous intra-group and inter-group balancing are started by the SOC control duty cycle. When the SOC value is between 0-10% or 90%-100%, the first voltage variance of all battery cells in each battery pack and the second voltage variance of all battery packs are obtained based on the voltage value of each battery cell. The magnitudes of the first voltage variance, the second voltage variance, and the second set threshold are judged respectively. Based on the judgment result, the corresponding voltage input variable is input to the fuzzy logic controller with preset fuzzy rules to obtain the corresponding voltage control duty cycle. The intra-group equalization, inter-group equalization, or simultaneous intra-group and inter-group equalization are started by the voltage control duty cycle.
[0012] Preferably, the first set threshold is 0.02%, and the second set threshold is 10%. -5 V.
[0013] Preferably, the SOC input variables include the average SOC of all individual cells in the battery pack, the maximum SOC difference between individual cells in the battery pack, the average SOC between two adjacent battery packs, and the SOC difference between two adjacent battery packs; the step of judging the magnitudes of the first SOC variance and the second SOC variance relative to the first set threshold, and inputting the corresponding SOC input variables to the fuzzy logic controller with preset fuzzy rules according to the judgment results, specifically includes the following steps: If the first SOC variance is greater than the first set threshold and the second SOC variance is less than the first set threshold, then the average SOC between two adjacent battery packs and the SOC difference between two adjacent battery packs are input to the fuzzy logic controller. If the first SOC variance is less than the first set threshold and the second SOC variance is greater than the first set threshold, then the average SOC of all battery cells in the battery pack and the maximum SOC difference of battery cells in the battery pack are input to the fuzzy logic controller. If the first SOC variance is greater than the first set threshold and the second SOC variance is greater than the first set threshold, then the fuzzy logic controller is input with the average SOC of all battery cells in the battery pack, the maximum SOC difference of battery cells in the battery pack, the average SOC between two adjacent battery packs, and the SOC difference between two adjacent battery packs. If both the first SOC variance and the second SOC variance are less than the first set threshold, then balancing will not be initiated.
[0014] Preferably, the voltage input variables include the average voltage of all individual cells in the battery pack, the maximum voltage difference between individual cells in the battery pack, the average voltage between two adjacent battery packs, and the voltage difference between two adjacent battery packs. The step of judging the magnitudes of the first voltage variance, the second voltage variance, and the second preset threshold, and inputting the corresponding voltage input variables to a fuzzy logic controller with preset fuzzy rules based on the judgment results, specifically includes the following steps: If the first voltage variance is greater than the second set threshold and the second voltage variance is less than the second set threshold, then the average voltage between two adjacent battery packs and the voltage difference between two adjacent battery packs are input to the fuzzy logic controller. If the first voltage variance is less than the second set threshold and the second voltage variance is greater than the second set threshold, then the average voltage of all battery cells in the battery pack and the maximum voltage difference of the battery cells in the battery pack are input to the fuzzy logic controller. If the first voltage variance is greater than the second set threshold and the second voltage variance is greater than the second set threshold, then the average voltage of all battery cells in the battery pack, the maximum voltage difference of battery cells in the battery pack, the average voltage between two adjacent battery packs, and the voltage difference between two adjacent battery packs are input to the fuzzy logic controller. If both the first voltage variance and the second voltage variance are less than the second set threshold, then equalization will not be initiated.
[0015] Preferably, during equalization within a starting group, the SOC or voltage values of two connected batteries within the battery pack are compared, and the energy of the battery with the higher SOC or voltage value is transferred to the battery with the lower SOC or voltage value; during equalization between starting groups, the SOC or voltage values of two connected battery packs are compared, and the energy of the battery pack with the higher SOC or voltage value is transferred to the battery pack with the lower SOC or voltage value.
[0016] Preferably, when the energy of the first cell in each battery pack is higher than that of the last cell, The energy of the first battery is transferred to the last battery through multiple batteries connected in series. Alternatively, the energy of the first battery can charge the inductor of the first parallel branch through a circuit formed by the first battery, the switch of the first parallel unit, the inductor of the first parallel branch, and the diode of the third parallel unit. The energy of the inductor of the first parallel branch can charge the last battery through a circuit formed by the inductor of the first parallel branch, the switch of the fourth parallel unit, the last battery, and the diode of the second parallel unit.
[0017] Secondly, the present invention provides a control method for a multi-battery pack equalization control circuit, comprising: Compared with the prior art, the above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects: This invention first proposes a multi-battery pack balancing control circuit. Compared to existing structures, it adds an in-pack end-to-end connection circuit, including a first parallel branch, a first parallel unit, a second parallel unit, a third parallel unit, and a fourth parallel unit. Compared to traditional two-layer balancing circuits, energy can be transferred not only step-by-step within the battery pack but also directly through the in-pack end-to-end connection circuit, improving energy transfer efficiency. This invention also proposes a control method for the multi-battery pack balancing control circuit. In this method, different balancing objects are transformed by different SOC values. Simultaneously, each balancing object is input with a corresponding control duty cycle through different fuzzy rules, dynamically adjusting the balancing current. This effectively prevents overcharging when the battery has high energy and over-discharging when the energy is low. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 The flowchart shows an improved dual-layer inductor active balancing control method for lithium iron phosphate battery packs according to the present invention. Figure 2 Diagram of a traditional double-layer inductor equalization circuit within / between groups; Figure 3 This is a schematic diagram of the improved double-layer inductor active balancing circuit structure within / between the lithium iron phosphate battery pack of the present invention; Figure 4 This is a graph showing the OCV-SOC curve of a lithium iron phosphate battery. Figure 5 Membership input function for this invention and A schematic diagram; in, Figure 5 (a): Membership input A schematic diagram, Figure 5 (b): Membership input A schematic diagram; Figure 6 Membership input function for this invention and A schematic diagram; in, Figure 6 (a): Membership input A schematic diagram, Figure 6 (b): Membership input A schematic diagram; Figure 7 This invention uses the membership input function eSOC / eU to control the duty cycle diagram. Figure 8 A static balancing diagram of a traditional double-layer inductor balancing circuit; Figure 9 This is a static balancing diagram of the improved double-layer inductor active balancing circuit of the present invention. Detailed Implementation
[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Example 1 To address the aforementioned problems, this invention provides a multi-battery pack equalization control circuit, wherein each battery pack consists of m batteries connected in series, and the equalization control circuit includes an intra-pack equalization circuit, an inter-pack equalization circuit, and an intra-pack end-to-end connection circuit.
[0022] The circuit connecting the beginning and end of the group includes a first parallel branch, a first parallel unit, a second parallel unit, a third parallel unit, and a fourth parallel unit. The first parallel branch includes parallel resistors and inductors. Each parallel unit consists of a parallel switch and a diode. One end of the unit is the common connection point of the source of the switch and the cathode of the diode, and the other end is the common connection point of the drain of the switch and the anode of the diode.
[0023] In each battery pack, the positive terminal of the first battery is connected to one end of the first parallel unit, the other end of the first parallel unit is connected to one end of the first parallel branch and one end of the second parallel unit, and the other end of the second parallel unit is connected to the negative terminal of the last battery; the negative terminal of the first battery is connected to one end of the third parallel unit, the other end of the third parallel unit is connected to the other end of the first parallel branch and one end of the fourth parallel unit, and the other end of the fourth parallel unit is connected to the positive terminal of the last battery.
[0024] This embodiment uses the first and last battery cells as an example for illustration. Furthermore, this invention can also connect any two non-adjacent batteries via an internal head-to-tail connection circuit, allowing direct energy transfer between these two batteries.
[0025] The group-wide equalization circuit includes multiple second parallel branches, multiple fifth parallel units, and multiple sixth parallel units. The second parallel branches have the same structure as the first parallel branches, and the fifth and sixth parallel units have the same structure as the first parallel units. In each battery pack, for the i-th battery cell B... i , Its positive terminal is connected to one end of a fifth parallel unit, the other end of the fifth parallel unit is connected to one end of the second parallel branch and one end of the sixth parallel unit, and the other end of the sixth parallel unit is connected to B. i+1 The negative terminal is connected, and the other end of the second parallel branch is connected to B. i Negative electrode and B i+1 On the line connecting the positive and negative electrodes.
[0026] The inter-group balancing circuit includes a third parallel branch, a seventh parallel unit, and an eighth parallel unit. The third parallel branch has the same structure as the first parallel branch, and the seventh and eighth parallel units have the same structure as the first parallel unit. In each battery pack, the positive terminal of the first battery is connected to one end of the seventh parallel unit, the other end of the seventh parallel unit is connected to one end of the third parallel branch and one end of the eighth parallel unit, the other end of the eighth parallel unit is connected to the negative terminal of the last battery in the next battery pack connected in series with the current battery pack, and the other end of the third parallel branch is connected to the line between the negative terminal of the last battery in the current battery pack and the positive terminal of the first battery in the next battery pack.
[0027] Reference Figure 2 and Figure 3 Compared to traditional double-layer inductor balancing circuits, this invention adds an end-to-end connection circuit within the group. Taking two series-connected battery packs as an example, B1-B... m Group B is the first group. m+1 -B 2m This is the second group, and the two groups have the same number of batteries.
[0028] The first parallel branch includes resistors R connected in parallel.22 and inductor L 22 The first parallel unit includes a switching transistor M. 21 and diode D 21 The second parallel unit includes a switching transistor M. 22 and diode D 22 The third parallel unit includes the switching transistor M. 23 and diode D 23 The fourth parallel unit includes the switching transistor M. 24 and diode D 24 .
[0029] The third parallel branch includes parallel resistors R. 11 and inductor L 11 The seventh parallel unit includes the switching transistor M. 11 and diode D 11 The eighth parallel unit includes the switching transistor M. 12 and diode D 12 .
[0030] The intra-group equalization circuit structure is as follows: Circuit connection structure between two adjacent battery cells within the group: For the i-th battery cell (B i (i from 1 to m-1), its positive terminal is connected to the common junction of a MOSFET switch and a diode parallel unit (MOSFET source / diode cathode), and the other end of this parallel unit (MOSFET drain / diode anode) is connected to an inductor L. i With resistance R i One end in parallel; B i+1 The negative terminal is connected to the common junction of a MOSFET switch and a diode in parallel (MOSFET drain / diode anode); the other end of this parallel unit (MOSFET anode / diode cathode) is connected to an inductor L. i With resistance R i One end connected in parallel, inductor L i and resistance R i The other end of the parallel connection is connected to B. i Negative electrode and B i+1 On the line connecting the positive and negative electrodes.
[0031] Connection structure of the first and last connection circuit within the group: For the first battery (B1), its positive terminal is also connected to the common junction of a MOSFET switch and a diode parallel unit (MOSFET source / diode cathode). The other end of this parallel unit (MOSFET drain / diode anode) is connected to a set of inductors L. 22 and resistance R 22 One end of the parallel branch; B mThe negative terminal is connected to the common junction of a MOSFET switch and a diode in parallel (MOSFET drain / diode anode), and the other end of this parallel unit (MOSFET anode / diode cathode) is connected to a set of inductors L. 22 With resistance R 22 One end of the parallel branch, inductor L 22 and resistance R 22 The other end of the parallel connection is simultaneously connected to two additional MOSFET switching and diode parallel connection units: the common junction (MOSFET drain / diode anode) of one unit (called unit A), and the common junction (MOSFET source / diode cathode) of the other unit (called unit B). The other end of unit A (MOSFET source / diode cathode) is connected to the negative terminal of B1, and the other end of unit B (MOSFET drain / diode anode) is connected to B1. m The positive pole.
[0032] The inter-group equalization circuit structure is as follows: The positive terminal of the single unit B1 is connected to the common junction of a MOSFET switch and a diode parallel unit (MOSFET source / diode cathode), and the other end of the parallel unit (MOSFET drain / diode anode) is connected to an inductor L. 11 With resistance R 11 One end connected in parallel; the monomer B 2m The negative terminal is connected to the common junction of a MOSFET switch and a diode in parallel (MOSFET drain / diode anode), and the other end of this parallel unit (MOSFET source / diode cathode) is connected to an inductor L. 11 With resistance R 11 One end connected in parallel, inductor L 11 With resistance R 11 The other end of the parallel connection is connected to battery cell B. m negative electrode and B m+1 On the positive terminal connection.
[0033] Example 2 OCV-SOC curves describe the nonlinear relationship between the battery's terminal voltage and its state of charge / discharge under no-load conditions. The potential response of the electrochemical reaction varies in different SOC ranges and is affected by factors such as temperature, historical charge / discharge history, aging, and charge / discharge rate. In battery management systems, static / quasi-static OCV is used to calibrate and initialize SOC, improving the accuracy of SOC estimation and health assessment. (Refer to...) Figure 4 It can be observed that the slope is smaller when the SOC is between 10% and 90%, while the slope is relatively larger when the SOC is between 0% and 10% or between 90% and 100%.
[0034] Therefore, considering the relationship between the open-circuit voltage (OCV) and state of charge (SOC) of a lithium iron phosphate battery cell, this invention employs a dual-threshold trigger-based equalization control strategy. In short, both battery voltage (U) and SOC are used as equalization indicators to control the on / off state of equalization. When the SOC is between 10% and 90%, SOC equalization is used; when the SOC is between 0% and 10% or between 90% and 100%, battery voltage equalization is used. The battery voltage can be directly measured using a multimeter, and the SOC of each battery is estimated using an algorithm.
[0035] Reference Figure 1 The present invention also provides a control method for a multi-battery pack equalization control circuit, comprising the following specific steps: Step 1: Divide the 2m battery cells into two battery packs, each containing m battery cells, where m is a positive integer greater than 1. Estimate the SOC value of each battery cell using SOC estimation and measure the battery voltage using a multimeter.
[0036] Step 2: When the SOC value is between 10% and 90%, obtain the first SOC variance of all battery cells in each battery pack and the second SOC variance of all battery packs based on the SOC value of each individual battery cell. When the SOC is between 0% and 10% or between 90% and 100%, obtain the first voltage variance of all battery cells in each battery pack and the second voltage variance of all battery packs based on the voltage value of each individual battery cell.
[0037] The first SOC variance of all individual cells in the battery pack is calculated using formulas (2) and (4). The second SOC variance of all battery packs The first voltage variance of all individual cells in the battery pack and the second voltage variance of the entire battery pack are calculated according to formulas (6) and (8).
[0038] (1); (2); (3); (4); (5); (6); (7); (8); in, This represents the average SOC of all individual battery cells within the group. This represents the variance of the SOC of all individual battery cells within the group. This represents the average SOC of all battery packs. This represents the SOC variance of all battery packs. This represents the average voltage of all individual battery cells within the group. This represents the variance of the voltage of all individual battery cells within the group. This represents the average voltage of all battery packs. This represents the voltage variance of all battery packs. N Configure according to the actual situation.
[0039] Step 3: Judge the magnitudes of the first SOC variance and the second SOC variance relative to the first set threshold. Based on the judgment results, input the corresponding SOC input variable into the fuzzy logic controller with preset fuzzy rules to obtain the corresponding SOC control duty cycle. Start intra-group balancing, inter-group balancing, or simultaneous intra-group and inter-group balancing through the SOC control duty cycle.
[0040] If the first SOC variance is greater than the first set threshold and the second SOC variance is less than the first set threshold, then SOC group equalization is initiated. A fuzzy logic controller dynamically adjusts the control variables to transfer energy from battery cells with higher SOC values to those with lower SOC values. The SOC values of two connected batteries within the battery pack are compared, and energy from the battery with the higher SOC value is transferred to the battery with the lower SOC value.
[0041] If the first SOC variance is less than a first preset threshold and the second SOC variance is greater than a first preset threshold, then SOC inter-group equalization is initiated. A fuzzy logic controller dynamically adjusts the control variables to transfer energy from battery packs with higher SOC values to battery packs with lower SOC values. The SOC values of two connected battery packs are compared, and energy from the battery pack with the higher SOC value is transferred to the battery pack with the lower SOC value.
[0042] If the variance of the first SOC is greater than the first set threshold and the variance of the second SOC is greater than the first set threshold, then both intra-group SOC balancing and inter-group SOC balancing are initiated simultaneously.
[0043] If both the first SOC variance and the second SOC variance are less than the first set threshold, then balancing will not be initiated.
[0044] Step 4: Judge the magnitudes of the first voltage variance and the second voltage variance with the second set threshold respectively. Based on the judgment results, input the corresponding voltage input variable into the fuzzy logic controller with preset fuzzy rules to obtain the corresponding voltage control duty cycle. Start intra-group equalization, inter-group equalization, or simultaneous intra-group and inter-group equalization through the voltage control duty cycle.
[0045] If the first voltage variance is greater than the second set threshold and the second voltage variance is less than the second set threshold, then voltage equalization within the battery pack is initiated. A fuzzy logic controller dynamically adjusts the control variables to transfer energy from battery cells with higher voltage values to those with lower voltage values. Specifically, the voltage values of two connected batteries within the battery pack are compared, and energy from the battery with the higher voltage value is transferred to the battery with the lower voltage value.
[0046] If the first voltage variance is less than the second set threshold and the second voltage variance is greater than the second set threshold, then voltage group equalization is initiated. A fuzzy logic controller dynamically adjusts the control variables to transfer energy from the battery group with the higher voltage to the battery group with the lower voltage. The voltage values of two connected battery groups are compared, and energy from the battery group with the higher voltage is transferred to the battery group with the lower voltage.
[0047] If the first voltage variance is greater than the second set threshold and the second voltage variance is greater than the second set threshold, then both intra-group voltage equalization and inter-group voltage equalization are initiated simultaneously.
[0048] If both the first voltage variance and the second voltage variance are less than the second set threshold, then equalization will not be initiated.
[0049] The first set threshold is 0.02%, and the second set threshold is 10%. -5 V. For some high-performance lithium iron phosphate battery packs, setting it to 0.02% is primarily to pursue better battery pack consistency and lifespan within the accuracy limits of current battery management system hardware. This is a comprehensive decision based on system capability, safety redundancy, and experimental verification. The second threshold is set based on the limitations of actual circuit component parameters and continuous experimental testing; at this threshold, the balancing effect is better.
[0050] Steps 3 and 4 involve inputs to the fuzzy logic controller, including the average SOC / U of all individual cells within the battery pack, the maximum SOC / U difference between individual cells, and the average and difference in SOC / U between adjacent battery packs. The fuzzy logic controller uses these values to determine the output control variable, which is then used to regulate the switching transistor's frequency. If SOC equalization is used, this output controls the duty cycle based on SOC. If voltage equalization is used, this output controls the duty cycle based on voltage. Since there are two input variables and one output variable, three universes of discourse are generated.
[0051] (9); (10); (11); (12); (13); (14); (15); (16); in, This represents the average SOC of all individual battery cells within the group. This represents the maximum SOC difference between individual cells within the battery pack. The average SOC of two adjacent battery packs in the representative group. The difference in SOC between two adjacent battery packs represents the difference in SOC between the two groups. This represents the average voltage of all individual battery cells within the group. This represents the maximum voltage difference between individual cells within the battery pack. The average voltage of two adjacent battery packs represents the average voltage between the two groups. This represents the voltage difference between two adjacent battery packs.
[0052] The universe of discourse for the average SOC between two connected battery cells within the battery pack is set to [0,1], and the universe of discourse for the SOC difference is set to [0,0.5]. The SOC control duty cycle is set to [0.35,0.75]. The universe of discourse for the average voltage between two adjacent battery packs is set to [0.26,0.42], the universe of discourse for the voltage difference is set to [0,0.2], and the universe of discourse for the voltage control duty cycle is set to [0.35,0.75]. The input variables are described using fuzzy language, with the fuzzy language variables set as negative large (NB), negative small (NS), zero (ZO), positive small (PS), and positive large (PB). The membership function is as follows: Figures 5-7 As shown.
[0053] The improved dual-layer inductor active balancing circuit within / between lithium iron phosphate battery packs achieves specific control through a fuzzy controller that controls the duty cycle. A fuzzy logic controller is a control system based on fuzzy logic theory. It does not rely on traditional precise models but instead controls the system through fuzzy rules and fuzzy inference. The fuzzy logic controller consists of three main steps: fuzzification, inference, and defuzzification. Fuzzification refers to the fuzzer converting precise inputs into fuzzy variables; inference, within the inference engine, processes these fuzzy variables using a pre-defined rule base based on experience and knowledge; and defuzzification converts the fuzzy results of the inference into accurate output values using a defuzzer.
[0054] This embodiment uses SOC as an example. By analyzing the relationship between the average SOC and SOC difference between two connected battery cells within and between battery packs, and the control duty cycle of the control variable SOC, 25 fuzzy control rules can be obtained. These rules cover all cases of average SOC and SOC difference between battery cells and between battery packs, as well as the corresponding SOC control duty cycles, as shown in Table 1 below.
[0055] If means "if", and means "and", then means "then". The fuzzy linguistic variables corresponding to NB, NS, ZO, PS, and PB are negative large, negative small, zero, positive small, and positive large, respectively. The control variable SOC controls the duty cycle of increasing from negative large to positive large.
[0056] As can be seen from the above fuzzy rule control table, the SOC control duty cycle (eSOC) is jointly determined by the average SOC and SOC difference between two connected battery cells within the battery pack, and also by the average SOC and SOC difference between two adjacent battery packs. When the SOC... avg Large, and SOC dif When the SOC is low, the eSOC is low to prevent overcharging; when the SOC is low... avg Small, and SOC dif If the battery is discharged for a short period of time, the eSOC will be low, in order to prevent the battery from being over-discharged.
[0057] Steps 3 and 4, which utilize a fuzzy logic controller to adjust the energy transfer path between individual cells within the battery pack, include the following specific steps: When the energy of B1 is higher than that of B m When the energy of B1 is such that the variance of all cells in the battery pack is greater than a threshold, the energy of B1 can be transferred to B through B2, B3, etc. m Energy can also be obtained through B1 and the switching transistor M. 21 Inductor L 22 diode D 23 Form a loop for inductor L 22 Charging, then inductor L 22 Energy is transmitted through the switching transistor M 24 Battery B m Diode D 22 Form a circuit for battery B m Charge it.
[0058] When B m When the energy of B1 is higher than that of B1, and the variance of all individual cells is greater than the threshold, B m Energy can not only be obtained through B m-1 B m-2…B3 and B2 are transferred step by step to B1, and energy can also be transferred through B… m Switching transistor M 24 Inductor L 22 Diode D 22 Form a loop for inductor L 22 Charging, then inductor L 22 Energy is transmitted through diode D 21 Battery B1, Switching transistor M 23 A circuit is formed to charge battery B1.
[0059] The method of adjusting the energy transfer path between battery packs using a fuzzy controller includes the following specific steps: When the energy of the first battery pack is higher than that of the second battery pack, and the variance between the two is greater than a threshold, the energy of battery pack 1 flows from its positive terminal to the switch M. 11 to inductor L 11 Then, to the negative terminal of battery pack 1, a closed loop is formed, supplying power to inductor L. 11 Charge, then inductor L 11 Energy is supplied through battery pack 2 and diode D. 12 This forms a closed loop, thereby charging battery pack 2.
[0060] When the energy of the second battery pack is higher than that of the first battery pack, and the variance between the two is greater than a threshold, the energy of battery pack 2 flows from the positive terminal of battery pack 2 to inductor L. 11 To the switching transistor M 12 Then, to the negative terminal of battery pack 2, a closed loop is formed, supplying power to inductor L. 11 Charge, then inductor L 11 Energy is transmitted through diode D 11 The battery pack 1 forms a closed loop, thereby charging the battery pack 1.
[0061] Example 2 Static equilibrium experiment In the static equilibration experiment, equilibration was performed simultaneously within / between groups, referring to... Figure 8 and Figure 9 B1-B8 represent eight individual battery cells. B1-B4 form the first group of batteries, and B5-B8 form the second group. The initial SOCs of the first group of batteries are 80%, 69%, 78%, and 75%, respectively. The initial SOCs of the second group of batteries are 74%, 82%, 77%, and 70%, respectively. According to simulation results, traditional intra-group / inter-group double-layer inductor balancing completes balancing in 1484 seconds, while the improved intra-group / inter-group double-layer inductor active balancing completes balancing in 1167 seconds. It can be seen that the improved double-layer inductor active balancing circuit can shorten the balancing time.
[0062] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.
[0063] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A multi-battery pack equalization control circuit, comprising: Each battery pack is composed of m batteries in series, and a plurality of battery packs are connected in series, the equalization control circuit comprises an intra-pack equalization circuit, an inter-pack equalization circuit and an intra-pack head-tail connection circuit; The intra-pack head-tail connection circuit comprises a first parallel branch, a first parallel unit, a second parallel unit, a third parallel unit and a fourth parallel unit, wherein the first parallel branch comprises a resistor and an inductor in parallel, and each parallel unit is composed of a switch tube and a diode in parallel, one end of which is a common junction of the switch tube source and the diode cathode, and the other end of which is a common junction of the switch tube drain and the diode anode; In each battery pack, the positive electrode of the first battery is connected to one end of the first parallel unit, the other end of the first parallel unit is connected to one end of the first parallel branch and one end of the second parallel unit, and the other end of the second parallel unit is connected to the negative electrode of the last battery; the negative electrode of the first battery is connected to one end of the third parallel unit, the other end of the third parallel unit is connected to the other end of the first parallel branch and one end of the fourth parallel unit, and the other end of the fourth parallel unit is connected to the positive electrode of the last battery.
2. A multi-bank equalization control circuit as claimed in claim 1, wherein, The intra-pack equalization circuit comprises a plurality of second parallel branches, a plurality of fifth parallel units and a plurality of sixth parallel units, the second parallel branches have the same structure as the first parallel branch, and the fifth parallel units and the sixth parallel units have the same structure as the first parallel unit; In each battery pack, for the i-th battery cell B i , its positive electrode is connected to one end of a fifth parallel unit, the other end of the fifth parallel unit is connected to one end of a second parallel branch and one end of a sixth parallel unit, the other end of the sixth parallel unit is connected to the negative electrode of B i+1 , the other end of the second parallel branch is connected to the line between the negative electrode of B i and the positive electrode of B i+1 .
3. A multi-bank equalization control circuit as recited in claim 1, wherein, The inter-pack equalization circuit comprises a third parallel branch, a seventh parallel unit and an eighth parallel unit, the third parallel branch has the same structure as the first parallel branch, and the seventh parallel unit and the eighth parallel unit have the same structure as the first parallel unit; In each battery pack, the positive electrode of the first battery is connected to one end of the seventh parallel unit, the other end of the seventh parallel unit is connected to one end of the third parallel branch and one end of the eighth parallel unit, the other end of the eighth parallel unit is connected to the negative electrode of the last battery of the next battery pack connected in series with the current battery pack, and the other end of the third parallel branch is connected to a wire between the negative electrode of the last battery of the current battery pack and the positive electrode of the first battery of the next battery pack.
4. A control method of the multi-battery pack equalization control circuit according to any one of claims 1 to 3, characterized by The method comprises the following steps: Obtaining the SOC values of all battery monomers in each battery pack; When the SOC value is between 10% and 90%, obtaining the first SOC variance of all battery monomers in each battery pack and the second SOC variance of all battery packs based on the SOC value of each battery monomer; Judging the size of the first SOC variance and the second SOC variance and the first set threshold value respectively, inputting the corresponding SOC input variable to the fuzzy logic controller with preset fuzzy rules according to the judgment result, obtaining the corresponding SOC control duty ratio, and starting the intra-pack equalization, the inter-pack equalization or the intra-pack and inter-pack equalization simultaneously through the SOC control duty ratio; When the SOC value is between 0 and 10% or between 90% and 100%, obtaining the first voltage variance of all battery monomers in each battery pack and the second voltage variance of all battery packs based on the voltage value of each battery monomer; The size of the first voltage variance and the second voltage variance is respectively compared with the second set threshold value, and corresponding voltage input variables are input to a fuzzy logic controller with preset fuzzy rules according to the comparison result, so as to obtain corresponding voltage control duty cycles, and the voltage control duty cycles are used to start the intra-group balancing, the inter-group balancing or the intra-group and inter-group balancing.
5. The control method of the multi-battery-pack equalization control circuit according to claim 4, characterized by, The first set threshold is 0.02%, and the second set threshold is 10 -5 V.
6. The control method of the multi-battery-pack equalization control circuit according to claim 4, characterized by, The SOC input variables include the average SOC of all battery cells in a battery group, the maximum SOC difference of the battery cells in the battery group, the average SOC between two adjacent battery groups and the SOC difference between the two adjacent battery groups; the size of the first SOC variance and the second SOC variance is respectively compared with the first set threshold value, and corresponding SOC input variables are input to the fuzzy logic controller with preset fuzzy rules according to the comparison result, and the method specifically includes the following steps: If the first SOC variance is greater than the first set threshold value and the second SOC variance is less than the first set threshold value, the average SOC between two adjacent battery groups and the SOC difference between the two adjacent battery groups are input to the fuzzy logic controller; If the first SOC variance is less than the first set threshold value and the second SOC variance is greater than the first set threshold value, the average SOC of all battery cells in a battery group and the maximum SOC difference of the battery cells in the battery group are input to the fuzzy logic controller; If the first SOC variance is greater than the first set threshold value and the second SOC variance is greater than the first set threshold value, the average SOC of all battery cells in a battery group, the maximum SOC difference of the battery cells in the battery group, the average SOC between two adjacent battery groups and the SOC difference between the two adjacent battery groups are input to the fuzzy logic controller; If the first SOC variance and the second SOC variance are both less than the first set threshold value, the balancing is not started.
7. The control method of the multi-battery-pack equalization control circuit according to claim 4, characterized by, The voltage input variables include the average voltage of all battery cells in a battery group, the maximum voltage difference of the battery cells in the battery group, the average voltage between two adjacent battery groups and the voltage difference between the two adjacent battery groups; the size of the first voltage variance and the second voltage variance is respectively compared with the second set threshold value, and corresponding voltage input variables are input to the fuzzy logic controller with preset fuzzy rules according to the comparison result, and the method specifically includes the following steps: If the first voltage variance is greater than the second set threshold value and the second voltage variance is less than the second set threshold value, the average voltage between two adjacent battery groups and the voltage difference between the two adjacent battery groups are input to the fuzzy logic controller; If the first voltage variance is less than the second set threshold value and the second voltage variance is greater than the second set threshold value, the average voltage of all battery cells in a battery group and the maximum voltage difference of the battery cells in the battery group are input to the fuzzy logic controller; If the first voltage variance is greater than the second set threshold value and the second voltage variance is greater than the second set threshold value, the average voltage of all battery cells in a battery group, the maximum voltage difference of the battery cells in the battery group, the average voltage between two adjacent battery groups and the voltage difference between the two adjacent battery groups are input to the fuzzy logic controller; If the first voltage variance and the second voltage variance are both less than the second set threshold value, the balancing is not started.
8. The control method of a multi-battery-pack equalization control circuit according to claim 4, characterized by, In the start-up of the intra-battery group balancing, the SOC value or voltage value of the two connected batteries in the battery group is compared, and the energy of the battery with higher SOC value or voltage value is transferred to the battery with lower SOC value or voltage value; In the start-up of the inter-battery group balancing, the SOC value or voltage value of the two connected battery groups is compared, and the energy of the battery group with higher SOC value or voltage value is transferred to the battery group with lower SOC value or voltage value.
9. The control method of the multi-battery-pack equalization control circuit according to claim 5, characterized by, When the energy of the first battery of each battery group is higher than that of the last battery, The energy of the first battery is transferred to the last battery through multiple batteries in series; Or the energy of the first battery charges the inductor of the first parallel branch through a loop formed by the first battery, the switch tube of the first parallel unit, the inductor of the first parallel branch, and the diode of the third parallel unit, and the energy of the inductor of the first parallel branch charges the last battery through a loop formed by the inductor of the first parallel branch, the switch tube of the fourth parallel unit, the last battery, and the diode of the second parallel unit.