A battery pack equalization topology and its control method

Abstract

The present invention discloses a battery pack equalization topology structure and its control method, which relates to the field of power electronics control technology and includes: a battery pack, a transformer, a switch array, a monitoring circuit, and a control unit. A group of switch tube components are shared between adjacent battery cells. After collecting the voltages of the battery cells, clustering and cluster division are performed to obtain a cluster - number of individuals - mean matrix. For the cluster - number of individuals - mean matrix, the first voltage number in the cluster with the maximum voltage mean and the second voltage number in the cluster with the minimum voltage mean are determined. According to the number of clusters and the comparison result between the first voltage number and the second voltage number, the discharge equalization, charge equalization, and automatic equalization working modes are adaptively switched, which improves the equalization efficiency while significantly reducing costs.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic control, and particularly relates to a battery pack equalization topology and a control method thereof. Background Art

[0002] Due to the fact that the quality of lithium batteries is difficult to control during mass production, there will inevitably be inconsistencies among battery cells when leaving the factory. Especially when battery cells are connected in series for use, the inconsistencies will be further amplified, resulting in a decrease in the available capacity of the battery pack, an accelerated attenuation of the lifespan, and a reduction in safety, seriously affecting the safe and efficient utilization of battery energy. Therefore, implementing battery pack equalization is an important means to improve such inconsistencies.

[0003] Currently, battery management systems generally adopt passive equalization methods, that is, discharging battery cells through equalization resistors, which have problems such as energy waste and slow speed. Adopting active equalization methods can solve the above problems.

[0004] In related prior arts, Patent CN2019105611377 discloses an equalization circuit based on a flyback converter, but there are a large number of switching tubes in the circuit, and each battery cell needs to be equipped with a transformer winding, resulting in problems such as a complex structure, high cost, and difficult control.

[0005] Patent CN2020112091331 realizes battery equalization based on a half-bridge structure and a notch filter, significantly reducing the number of switching tubes, but there are still transformer windings corresponding to each battery cell one by one, and its volume, cost, and equalization efficiency need to be considered.

[0006] In addition, most of the existing active equalizations have a single equalization mode and cannot adjust the equalization mode according to the voltage distribution of the battery pack, resulting in poor flexibility and slow speed. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a battery pack equalization topology and a control method thereof. Battery cells share a switch array, and the adjacent battery cells realize bidirectional excitation of the transformer core during the charging and discharging processes, significantly reducing the cost while improving the equalization efficiency. At the same time, it automatically identifies the voltage distribution of the battery pack and adaptively switches the working modes of discharging equalization, charging equalization, and automatic equalization, thereby improving the equalization speed and flexibility.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a battery pack equalization topology, including:

[0010] A battery pack, including n battery cells, where n is a positive integer greater than 1;

[0011] A transformer, the primary side of the transformer is sequentially connected to each battery cell through a first switching tube assembly and a switching array, and the secondary side is connected to the battery pack through a second switching tube assembly;

[0012] The switching array includes n + 1 groups of switching tube assemblies. The positive and negative electrodes of each battery cell are respectively connected to the primary side of the transformer through a switching tube assembly, and a group of switching tube assemblies is shared between adjacent battery cells;

[0013] The monitoring circuit is used to collect the voltage of the battery cell;

[0014] The control unit obtains the voltage of the battery cell and is configured as:

[0015] Cluster the voltages of the battery cells. Take the voltages of the battery cells in the same class as a cluster. Obtain a cluster - number of individuals - mean matrix based on the number of voltages and the mean voltage in each cluster. Determine the first voltage number in the cluster with the maximum voltage mean and the second voltage number in the cluster with the minimum voltage mean in the cluster - number of individuals - mean matrix;

[0016] If the number of clusters is 1 or the first voltage number is equal to the second voltage number, perform cyclic charging and discharging on the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage;

[0017] Otherwise, if the first voltage number is greater than the second voltage number, charge the battery cell corresponding to the minimum battery cell voltage. If the first voltage number is less than the second voltage number, discharge the battery cell corresponding to the maximum battery cell voltage.

[0018] As an alternative implementation, each group of switching tube assemblies in the switching array includes two switching tubes connected in reverse series;

[0019] The first switching tube assembly includes two switching tubes connected in reverse series. The first switching tube is connected to the positive electrode of the odd - numbered battery cells and the negative electrode of the even - numbered battery cells;

[0020] The second switching tube assembly includes four groups of switching tube assemblies. Both ends of the secondary side of the transformer are connected to the positive electrode of the battery pack through a group of switching tube assemblies, and both ends of the secondary side of the transformer are connected to the negative electrode of the battery pack through a group of switching tube assemblies.

[0021] As an alternative implementation, the process of clustering the voltages of the battery cells includes: setting a voltage distance, and clustering the battery cells with a voltage difference less than or equal to the voltage distance into one class.

[0022] As an alternative implementation, the battery cell discharging process includes three modes, specifically:

[0023] Mode I: Turn on the switching tube assembly and the first switching tube assembly that connect the battery cell to the primary side of the transformer, and turn off the second switching tube assembly; when the odd-numbered battery cells discharge, the odd-numbered battery cells charge the primary side coil of the transformer, the magnetic flux increases in the positive direction, and a positive electromotive force is generated in the primary side coil; when the even-numbered battery cells discharge, the even-numbered battery cells charge the primary side coil, the magnetic flux increases in the negative direction, and a negative electromotive force is generated in the primary side coil; the discharge current of the battery cell increases from zero;

[0024] Mode II: Turn on a group of switching tubes in the second switching tube assembly whose two ends of the secondary side are respectively connected to the positive and negative poles of the battery pack, and turn off the other switching tubes; an instant positive electromotive force is generated in the secondary side coil when switching from Mode I to Mode II, the current in the primary side coil continues to flow through the secondary side coil, the current flows from the secondary side coil to the battery pack, and the maximum value of the charging current of the battery pack begins to decrease and decreases to zero after a time interval;

[0025] Mode III: The state of the switching tubes is the same as that in Mode II until the charging current of the battery pack drops to zero and then enters a static state.

[0026] As an alternative implementation, the time interval is:

[0027] ;

[0028] wherein, L S is the exciting inductance of the secondary side coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance on the secondary side coil side, i S is the initial current of the primary side coil refracted to the secondary side coil;

[0029] Within an equalization period, the conduction time range on the secondary side coil side of the transformer is set to 1.05 -1.25 .

[0030] As an alternative implementation, in Mode I, the discharge current of the battery cell at time t is:

[0031] ;

[0032] In Mode II, the charging current of the battery pack at time t is:

[0033] ;

[0034] wherein, V B1is the voltage across the battery cell, R P is the equivalent resistance on the primary coil side; L P is the exciting inductance of the primary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance on the secondary coil side, i S is the initial current refracted from the primary coil to the secondary coil; L S is the exciting inductance of the secondary coil.

[0035] As an alternative embodiment, the charging process of the battery cell includes three modes, specifically:

[0036] Mode I: Turn on a group of switching tubes in the second switching tube assembly where the two ends of the secondary side are respectively connected to the positive and negative poles of the battery pack, and turn off the remaining switching tubes; when the odd-numbered battery cells are charged, the battery pack charges the secondary coil of the transformer, the magnetic flux increases positively, and a positive electromotive force is generated in the secondary coil; when the even-numbered battery cells are charged, the magnetic flux of the secondary coil is negative; the discharge current of the battery pack increases from zero;

[0037] Mode II: Turn on the switching tube assembly connecting the battery cell to the primary side of the transformer and the first switching tube assembly, and turn off the remaining switching tubes; at the moment of switching from Mode I to Mode II, a positive electromotive force is generated in the primary coil, the current in the secondary coil continues to flow through the primary coil, the current flows from the primary coil to the battery cell, and the maximum value of the charging current of the battery cell begins to decrease and decreases to zero after a time interval;

[0038] Mode III: The state of the switching tubes is the same as that in Mode II until the charging current of the battery cell drops to zero and then enters a static state.

[0039] As an alternative embodiment, the time interval is:

[0040] ;

[0041] wherein, i P is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance on the primary coil side, L P is the exciting inductance of the primary coil, V B1 is the voltage across the battery cell;

[0042] Within an equalization period, the conduction time range on the secondary coil side of the transformer is set to 1.05 -1.25 。

[0043] As an alternative embodiment, in Mode I, the discharge current of the battery pack at time t is:

[0044] ;

[0045] In Mode II, the charging current of the battery cell at time t is:

[0046] ;

[0047] wherein, V Pack is the voltage across the battery pack, R S is the equivalent resistance on the secondary coil side; L S is the exciting inductance of the secondary coil; i P is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance on the primary coil side, L P is the exciting inductance of the primary coil, V B1 is the voltage across the battery cell.

[0048] In a second aspect, the present invention provides a control method for the battery pack equalization topology structure as described in the first aspect, including:

[0049] Collect the battery cell voltages;

[0050] Cluster the battery cell voltages, take the battery cell voltages of the same class as a cluster, and obtain a cluster - number of individuals - mean matrix according to the number of voltages and the voltage mean values in each cluster;

[0051] Determine the first number of voltages in the cluster with the maximum voltage mean value and the second number of voltages in the cluster with the minimum voltage mean value in the cluster - number of individuals - mean matrix;

[0052] If the number of clusters is 1 or the first number of voltages is equal to the second number of voltages, perform cyclic charging and discharging on the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage;

[0053] Otherwise, if the first number of voltages is greater than the second number of voltages, charge the battery cell corresponding to the minimum battery cell voltage, and if the first number of voltages is less than the second number of voltages, discharge the battery cell corresponding to the maximum battery cell voltage.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] The present invention provides a battery pack equalization topology structure and a control method thereof. Battery cells share a switch array, and the battery cells are connected to the transformer through the switch array. Then, when the number of battery cells in the battery pack increases, there is no need to increase additional transformer windings. At the same time, a group of anti-series connected switch tubes are shared between adjacent battery cells to achieve switch sharing, reducing the number of switch devices in the traditional bi-directional flyback conversion by about 50%. For a battery pack composed of n battery cells, the battery pack equalization topology only requires (2 n +12) switch tubes and one transformer winding, significantly reducing the number of devices, not only reducing the volume of the equalization topology and improving the equalization efficiency, but also greatly reducing the total failure probability of the devices, thereby improving the topology stability and reliability.

[0056] The present invention provides a battery pack equalization topology structure and a control method thereof. When odd-numbered battery cells discharge, the magnetic flux on the primary side of the transformer is positive, and when even-numbered battery cells discharge, the magnetic flux on the primary side of the transformer is negative; when odd-numbered battery cells are charged, the magnetic flux on the primary side of the transformer is positive, and when even-numbered battery cells are charged, the magnetic flux on the primary side of the transformer is negative. Thus, the bi-directional excitation of the transformer core is realized during the discharge process and the charging process of adjacent battery cells. For any scale of battery pack, only a single-winding flyback transformer is required to complete the discharge and charging of all battery cells, significantly reducing the cost while improving the equalization efficiency.

[0057] The present invention provides a battery pack equalization topology structure and a control method thereof. By clustering and dividing the battery cell voltages, a cluster-individual number-mean matrix is obtained, and the first voltage number in the cluster with the maximum voltage mean and the second voltage number in the cluster with the minimum voltage mean in the cluster-individual number-mean matrix are determined; according to the number of clusters and the comparison result of the first voltage number and the second voltage number, the voltage distribution of the battery pack is automatically identified, and then the three working modes of discharge equalization, charge equalization, and automatic equalization are adaptively switched, thereby improving the equalization speed and flexibility.

[0058] Advantages of additional aspects of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0060] Figure 1 Schematic diagram of the battery pack equalization topology provided in Embodiment 1 of the present invention;

[0061] Figure 2 Adaptive equalization flowchart provided in Embodiment 1 of the present invention;

[0062] Figure 3 Equalization result of the voltage waveform of Experiment #1 provided in Embodiment 1 of the present invention;

[0063] Figure 4 Equalization result of the consistency statistics of Experiment #1 provided in Embodiment 1 of the present invention;

[0064] Figure 5 Equalization result of the voltage waveform of Experiment #2 provided in Embodiment 1 of the present invention;

[0065] Figure 6 Equalization result of the consistency statistics of Experiment #2 provided in Embodiment 1 of the present invention;

[0066] Figure 7 Equalization result of the voltage waveform of Experiment #3 provided in Embodiment 1 of the present invention;

[0067] Figure 8 Equalization result of the consistency statistics of Experiment #3 provided in Embodiment 1 of the present invention. Detailed implementation manners

[0068] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0069] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0070] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that the terms "comprising" and "including" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0071] In the case of no conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0072] Embodiment 1

[0073] This embodiment provides an efficient and compact battery pack equalization topology structure, and the schematic diagram is as Figure 1 shown, including: a battery pack, a transformer, a switch array, a monitoring circuit, and a control unit.

[0074] Among them, the battery pack includes n battery cells B1, B2,..., B n ; and the battery cells B1, B3, B5,......, B n-1 are odd-numbered battery cells, and the battery cells B2, B4, B6,......, B n are even-numbered battery cells, and n is a positive integer greater than 1;

[0075] The primary side of the transformer is sequentially connected to each battery cell through a first switch tube assembly and a switch array, and the secondary side is connected to the battery pack through a second switch tube assembly;

[0076] The switch array includes n + 1 groups of switch tube assemblies. The positive and negative electrodes of each battery cell are respectively connected to the primary side of the transformer through a switch tube assembly, and a group of switch tube assemblies is shared between adjacent battery cells;

[0077] A monitoring circuit for collecting the voltage of the battery cells;

[0078] A control unit that obtains the voltage of the battery cells and is configured to:

[0079] Cluster all the battery cell voltages, take the battery cell voltages in the same class as a cluster, and obtain a cluster - number of individuals - mean matrix according to the number of voltages and the voltage mean values in each cluster;

[0080] For the cluster - number of individuals - mean matrix, determine the first voltage number in the cluster with the maximum voltage mean and the second voltage number in the cluster with the minimum voltage mean;

[0081] If the number of clusters is 1 or the first voltage number is equal to the second voltage number, perform cyclic charging and discharging on the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage;

[0082] If the first voltage number is greater than the second voltage number, charge the battery cell corresponding to the minimum battery cell voltage, otherwise discharge the battery cell corresponding to the maximum battery cell voltage.

[0083] As an alternative embodiment, in the switch array, each group of switch tube assemblies includes two switch tubes connected in reverse series, a total of 2 n +2 switch tubes Q c1 、Q c2 、…、Q c(2n+2) ; The switch array is used to select the battery cells connected to the transformer T and the connection direction.

[0084] As an alternative embodiment, the first switching tube assembly connected to the primary side of the transformer includes two switching tubes Q1 and Q2 connected in reverse series. The first switching tube is connected to the positive electrode of the odd battery cells and the negative electrode of the even battery cells.

[0085] For example, taking battery cells B1, B2, B3, and B4 as an example, switching tube Q1 and switching tube Q2 are connected in reverse series. Switching tube Q2 is connected to the primary side of the transformer, and switching tube Q1 is connected to the positive electrodes of battery cells B1 and B3 and the negative electrodes of battery cells B2 and B4.

[0086] As an alternative embodiment, the second switching tube assembly connected to the secondary side of the transformer includes four groups of switching tube assemblies. Both ends of the secondary side of the transformer are connected to the positive electrode of the battery pack, i.e., the positive electrode of battery cell B1, through a group of switching tube assemblies. Both ends of the secondary side of the transformer are connected to the negative electrode of the battery pack, i.e., the negative electrode of battery cell B n of the battery pack.

[0087] More specifically, each group of switching tube assemblies includes two switching tubes connected in reverse series, i.e., switching tube Q3 and switching tube Q4 are connected in reverse series to form the first group of switching tube assemblies, switching tube Q5 and switching tube Q6 are connected in reverse series to form the second group of switching tube assemblies, switching tube Q7 and switching tube Q8 are connected in reverse series to form the third group of switching tube assemblies, and switching tube Q9 and switching tube Q 10 are connected in reverse series to form the fourth group of switching tube assemblies;

[0088] One end of the secondary side of the transformer is connected to the positive electrode of the battery pack through the first group of switching tube assemblies, i.e., switching tube Q3 is connected to one end of the secondary side of the transformer, and switching tube Q4 is connected to the positive electrode of battery cell B1; it is connected to the negative electrode of the battery pack through the second group of switching tube assemblies, i.e., switching tube Q5 is connected to one end of the secondary side of the transformer, and switching tube Q6 is connected to the negative electrode of battery cell B n of the battery pack;

[0089] The other end of the secondary side of the transformer is connected to the positive electrode of the battery pack through the third group of switching tube assemblies, i.e., switching tube Q7 is connected to the other end of the secondary side of the transformer, and switching tube Q8 is connected to the positive electrode of battery cell B1; it is connected to the negative electrode of the battery pack through the fourth group of switching tube assemblies, i.e., switching tube Q9 is connected to the other end of the secondary side of the transformer, and switching tube Q 10 is connected to the negative electrode of battery cell B n of the battery pack.

[0090] It can be understood that switching tubes Q1, Q2, …, Q 10 are all MOSFET switching tubes, which are used to control the connection of transformer T to the battery pack and the connection direction.

[0091] It is understandable that the switching transistors in the switch array are all MOSFETs, and the switch array is used to select the battery cells connected to the transformer T and the connection directions.

[0092] As an alternative embodiment, an equalization strategy and a PWM (Pulse Width Modulation) control unit are integrated in the control unit. Usually, a microcontroller unit (MCU) or a digital signal processor (DSP) is selected. The control unit is connected to each switching transistor, determines the equalization mode according to the voltage distribution of the battery pack, and thus controls the conduction and cut-off of the switching transistors through PWM control signals, thereby forming different energy paths to implement equalization. As shown in Figure 1 FIG., the parts connected by the dotted lines indicate that the PWM control signals issued by the control unit are connected to each switching transistor. For the sake of simplicity, Figure 1 only shows the connection of switching transistor Q c2 , switching transistor Q2, and switching transistor Q3.

[0093] It can be seen from the battery pack equalization topology structure proposed in this embodiment that there is only one set of MOSFET switching transistors connected in reverse series between adjacent battery cells, realizing the sharing of switching transistors, thus reducing the number of switching transistors; at the same time, the battery cells and the transformer are connected through the switch array, and when the number of battery cells in the battery pack increases, there is no need to add additional transformer windings.

[0094] In short, for a n battery pack composed of battery cells, the battery pack equalization topology only requires (2 n +12) MOSFET switching transistors and one transformer winding, significantly reducing the number of components, not only reducing the volume of the equalization topology and improving the equalization efficiency, but also greatly reducing the total failure probability of the components, thereby improving the stability and reliability of the topology.

[0095] It is understandable that the monitoring circuit usually selects an analog front end (AFE) chip; other chips can also be used as long as they can collect the voltages of the battery cells and send them to the control unit, and no specific limitations are made.

[0096] It is understandable that the transformer uses a single-winding flyback transformer.

[0097] To better illustrate the working process, the following assumptions are made:

[0098] (1) The side of the transformer connected to the battery cell is the primary side (i.e., the primary coil), and the side connected to the battery pack is the secondary side (i.e., the secondary coil).

[0099] (2) On the primary side of the transformer, the direction in which the current flows out of the battery cell is positive; on the secondary side of the transformer, the direction in which the current flows into the battery pack is positive.

[0100] (3) When the electric potential on the primary side of the transformer is "positive on the upper side and negative on the lower side", it is a positive electric potential; when the electric potential on the secondary side is "negative on the upper side and positive on the lower side", it is a negative electric potential.

[0101] (4) When the current on the primary side of the transformer is "from top to bottom", the magnetic flux is positive; when the current on the secondary side of the transformer is "from bottom to top", the magnetic flux is negative.

[0102] (5) Battery cells B1, B3, B5,......, B n-1 are odd-numbered battery cells; battery cells B2, B4, B6,......, B n are even-numbered battery cells.

[0103] In this embodiment, in order to improve the flexibility and speed of balancing, three balancing modes are designed: discharge balancing, charge balancing, and automatic balancing. The clustering average extreme value statistical algorithm based on DBSCAN (Density-Based Spatial Clustering of Applications with Noise) is used to intelligently identify the voltage distribution, and then the balancing mode is adaptively switched according to different voltage distributions, hoping to complete the balancing in the most reasonable way at the fastest speed.

[0104] As Figure 2 shown in the adaptive balancing flow chart, the following steps are given in combination with Figure 2 :

[0105] (1) Collect the voltages of the battery cells, denoted as the vector Vol = V Bi | i = 1, 2, 3,..., n ], V Bi being the voltage of the i-th battery cell.

[0106] (2) Determine the maximum battery cell voltage V max and the minimum battery cell voltage V min . When the difference between the maximum battery cell voltage and the minimum battery cell voltage is greater than or equal to the set threshold voltage V th , that is, V max - V min ≥ V th , then go to step (3), otherwise end the balancing.

[0107] (3) Use the DBSCAN algorithm to cluster all the battery cell voltages in the vector Vol, and set the distance metric eps as the set voltage distance V dis , that is, cluster the battery cells with a voltage difference less than or equal to V dis into one category; the clustering category is denoted as the vector Lab = L Bi | i = 1, 2, 3, …, n , L Bi ∈ [0, n , representing the i-th category; vertically splice the vectors Lab and Vol to label each battery cell voltage with a category label to form a category-voltage matrix M = [Lab; Vol].

[0108] (4) In the category-voltage matrix M, group the columns with the same category L Bi into one cluster, that is, regard the battery cell voltages of the same category as one cluster, and count the number of voltages and the voltage mean in each cluster to form a cluster-number-mean matrix:

[0109] (1);

[0110] Among them, m is the number of clusters, at least 1 and at most the number of voltages n ; the first row Cluster i | i = 1, 2, 3, …, m is the i -th cluster; the second row Cnt i | i = 1, 2, 3, …, m is the number of voltages in the i -th cluster; the third row V avg_i | i = 1, 2, 3, …, m is the voltage mean in the i -th cluster.

[0111] (5) Conduct average extreme value statistics in the cluster-number-mean matrix M C , that is, respectively count the first voltage number Cnt avg_max in the cluster with the largest voltage mean, Cnt avg_min and the second voltage number in the cluster with the smallest voltage mean.

[0112] (6) If m = 1, or Cnt avg_max = Cnt avg_min , that is, all the battery cell voltages are grouped into one cluster or the first voltage number is the same as the second voltage number, then switch to the automatic equalization mode; in the automatic equalization mode, perform time - slice round - robin charging and discharging on the battery cells corresponding to V min , V max .

[0113] (7) Otherwise, if Cnt avg_max > Cnt avg_min , then switch to the charging equalization mode.

[0114] (8) Otherwise, if Cnt avg_max < Cnt avg_min , then switch to the discharging equalization mode.

[0115] (9) Perform equalization; in the charging mode, continuously charge the battery cell corresponding to the minimum battery cell voltage V min ; in the discharging mode, continuously discharge the battery cell corresponding to the maximum battery cell voltage V max ; in the automatic equalization mode, perform time - slice round - robin charging and discharging on the battery cells corresponding to the minimum battery cell voltage V min and the maximum battery cell voltage V max .

[0116] (10) Repeat steps (1) to (9) until the determination in step (2) that V max - V min < V th when the equalization ends.

[0117] It can be seen that in the discharge equalization mode, the equalization topology always selects the battery cell with the highest voltage for discharging, which is applicable to the situation where the voltages of a small number of battery cells are significantly higher; in the charging equalization mode, the equalization topology continuously charges the battery cell with the lowest voltage, which is applicable to the situation where the voltages of a small number of battery cells are significantly lower; in the automatic equalization mode, the battery cells charge and discharge alternately, which is applicable to the situation with a uniform voltage distribution. Therefore, the clustering average extreme value statistical algorithm based on DBSCAN in this embodiment can flexibly select an appropriate equalization method according to different voltage distributions to achieve fast equalization.

[0118] The charging process and discharging process of the battery cell will be described below.

[0119] There are two states during the operation of the circuit, namely battery cell discharging and battery cell charging. During the battery cell discharging process, the energy flow path is from the battery cell to the battery pack, and during the battery cell charging process, the energy flow path is from the battery pack to the battery cell.

[0120] A. Discharging state:

[0121] The analysis of the discharging processes of odd-numbered battery cells and even-numbered battery cells is basically the same, except for the conduction or cut-off of the switch array. Taking battery cell B1 as an example, in one switching period, battery cell B1 has three operating modes.

[0122] Mode I:

[0123] Switching transistor Q C1 、switching transistor Q C2 、switching transistor Q C3 、switching transistor Q C4 、switching transistor Q1 and switching transistor Q2 are conducting, and switching transistors Q3 to Q 10 are cut off; at this time, the odd-numbered battery cell B1 charges the primary side of the transformer, the magnetic flux increases in the positive direction, a positive potential is generated on the primary side of the transformer, and a negative potential is generated on the secondary side. Since the secondary side is open-circuited, no current flows through the secondary side.

[0124] The voltage across the inductor coil at the primary side of the transformer is:

[0125] (2);

[0126] Wherein, V L1 is the voltage across the inductor coil at the primary side of the transformer, L P is the magnetizing inductance at the primary side of the transformer, i 1 is the current at the primary side of the transformer.

[0127] According to Kirchhoff's law and by solving the differential equation, the discharge current of a single battery cell is obtained. i 1:

[0128] (3);

[0129] Wherein, is the charging current of the battery pack at time t, V B1 is the voltage across the single battery cell B1, R P is the equivalent resistance of the primary side circuit of the transformer.

[0130] As can be seen from Equation (3), the discharge current of the single battery cell i 1 (i.e., the primary side current of the transformer) gradually increases from zero.

[0131] Mode II:

[0132] The switching transistor Q3, the switching transistor Q9, the switching transistor Q 10 are turned on, and the rest of the switching transistors are turned off. According to the law of electromagnetic induction, a positive electromotive force will be generated on the secondary side of the transformer at the moment of switching from Mode I to Mode II. At this time, the current on the primary side of the transformer will flow through the secondary side for freewheeling, and the current flows from the inductor coil on the secondary side of the transformer to the battery pack.

[0133] The voltage across the inductor coil on the secondary side of the transformer is:

[0134] (4);

[0135] Wherein, V L2 is the voltage across the inductor coil on the secondary side of the transformer, L S is the magnetizing inductance on the secondary side of the transformer, i 2 is the current on the secondary side of the transformer.

[0136] According to Kirchhoff's law and by solving the differential equation, the charging current of the battery pack can be solved as i 2:

[0137] (5);

[0138] Wherein, is the charging current of the battery pack at time t, V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary side circuit of the transformer, i S is the initial current refracted from the primary side of the transformer to the secondary side.

[0139] As can be seen from Equation (5), i 2 gradually decreases from the maximum value i S and decreases to zero after a time interval of (6).

[0140] (6).

[0141] Mode III:

[0142] The state of the switching tube in this stage is the same as that in Mode II. When the current on the secondary side of the transformer (i.e., the charging current of the battery pack) drops to zero, the equalization topology will naturally be in a static state. During an equalization cycle, it is necessary to reasonably allocate the conduction time of the primary side and the secondary side of the transformer so that the conduction time of the secondary side of the transformer is greater than that in Equation (6) to ensure that the circuit operates in the discontinuous mode, so that the transformer can be completely demagnetized after an equalization cycle; at the same time, if the conduction time of the secondary side of the transformer is too large, it will lead to a low equalization efficiency because it is equivalent to increasing the time of the equalization static state. Therefore, in this embodiment, the conduction time range of the secondary side of the transformer is preferably set to be between 1.05 times and 1.25 times of.

[0143] Similarly, when the even battery cell, such as battery cell B2, discharges, in Mode I, the switching tubes Q C3 , switching tube Q C4 , switching tube Q C5 , switching tube Q C6 , switching tube Q1 and switching tube Q2 are conducting, and switching tubes Q3 to Q 10 are turned off; in Mode II, switching tubes Q5, Q6, and Q7 are conducting, and the rest of the switches are turned off; the switch states in Mode III are the same as those in Mode II.

[0144] It can be seen that when the odd battery cell discharges, the magnetic flux on the primary side of the transformer is positive, and when the even battery cell discharges, the magnetic flux on the primary side of the transformer is negative. The discharge processes of adjacent battery cells realize the bidirectional excitation of the transformer core, so that only a single-winding flyback transformer is required to complete the discharge of all battery cells.

[0145] B. Charging state:

[0146] The analysis of the charging processes of odd and even battery cells is basically the same, only the conduction or turn-off of the switch array is different. Taking battery cell B1 as an example, in a switching cycle, battery cell B1 has three operating modes.

[0147] Mode I:

[0148] Switching tubes Q3, Q4, Q9, Q 10Conduct, and the rest of the switching tubes are turned off. At this time, the battery pack charges the secondary side of the transformer, and the magnetic flux increases positively. A positive electromotive force is generated on the secondary side of the transformer, and a negative electromotive force is generated on the primary side. Since the primary side is open, no current flows through the primary side.

[0149] From this, the discharge current of the battery pack is solved i 3:

[0150] (7);

[0151] It can be seen from Equation (7) that i 3 gradually increases from zero.

[0152] Mode II:

[0153] Switching tube Q C1 , switching tube Q C2 , switching tube Q C3 , switching tube Q C4 and switching tube Q2 are conducting, and the rest of the switches are turned off. According to the law of electromagnetic induction, a positive electromotive force will be generated on the primary side of the transformer at the moment of switching from Mode I to Mode II. At this time, the current on the secondary side of the transformer will flow through the primary side for freewheeling, and the current flows from the inductor coil of the transformer to the battery cell B1.

[0154] From this, the charging current of the battery cell B1 is solved i 4:

[0155] (8);

[0156] Among them, i P is the initial current refracted from the secondary side of the transformer to the primary side.

[0157] It can be seen from Equation (8) that i 4 gradually decreases from the maximum value i P and decreases to zero after a time interval ;

[0158] (9).

[0159] Mode III:

[0160] In this stage, the switching tube state is the same as that in Mode II. When the current on the primary side of the transformer drops to zero, the equalization topology will naturally be in a static state. Within an equalization period, it is necessary to reasonably allocate the conduction time of the primary side and the secondary side of the transformer so that the conduction time of the secondary side of the transformer is greater than , ensuring that the circuit operates in the discontinuous mode, enabling the transformer to be fully demagnetized after an equalization period; meanwhile, if the conduction time on the secondary side of the transformer is too large, it will lead to a low equalization efficiency because it is equivalent to increasing the time of the equalization static state. Therefore, in this embodiment, the conduction time range on the secondary side of the transformer is preferably set to be between 1.05 times and 1.25 times of

[0161] Similarly, when charging the even battery cells, such as battery cell B2, in Mode I, switches Q5, Q6, Q7, and Q8 are turned on, and the rest of the switches are turned off; in Mode II, switches Q C1 , Q C2 , Q C3 , Q C4 and Q1 are turned on, and the rest of the switches are turned off; the switch states in Mode III are the same as those in Mode II.

[0162] It can be seen that when charging the odd battery cells, the magnetic flux on the primary side of the transformer is negative, and when charging the even battery cells, the magnetic flux on the primary side of the transformer is positive. The charging processes of adjacent battery cells achieve the bidirectional excitation of the transformer core, enabling all battery cells to be charged with only a single-winding flyback transformer.

[0163] In this embodiment, a battery pack equalization experimental platform is built. The battery pack is composed of 12 battery cells connected in series. In the experiment, V th and V dis are set to 5 mV and 10 mV respectively. Three groups of equalization experiments are set up, numbered Experiment #1, Experiment #2, and Experiment #3 respectively, and the initial voltage distribution is shown in Table 1.

[0164] Table 1 Initial voltage distribution of the battery pack;

[0165] .

[0166] The equalization result of Experiment #1 is as shown in Figure 3 - Figure 4 , where the battery voltages in Figure 3 are the voltages of each battery cell in Table 1. It can be seen that in this voltage distribution, the adaptive equalization mode is mainly based on discharge equalization. As the equalization progresses, the voltage difference of the battery pack gradually decreases, and the maximum voltage difference and standard deviation decrease from 60 mV and 16.7 mV to 5 mV and 2.1 mV respectively, and it only takes 25 minutes to complete the equalization.

[0167] The equalization result of Experiment #2 is as shown in Figure 5 - Figure 6 , where Figure 5The battery voltage in [it] is the voltage of each battery cell in Table 1. It can be seen that under this voltage distribution, the adaptive equalization mode is mainly charging equalization. As the equalization progresses, the voltage difference of the battery pack gradually decreases, and the maximum voltage difference and standard deviation decrease from 59 mV and 22 mV to 5 mV and 1.6 mV respectively, and it only takes 27 minutes to complete the equalization.

[0168] The equalization result of Experiment #3 is as Figure 7 - Figure 8 shown, where Figure 7 the battery voltage in [it] is the voltage of each battery cell in Table 1. It can be seen that under this voltage distribution, the adaptive equalization mode is mainly automatic equalization. As the equalization progresses, the voltage difference of the battery pack gradually decreases, and the maximum voltage difference and standard deviation decrease from 50 mV and 10.7 mV to 5 mV and 1.4 mV respectively, and it only takes 10 minutes to complete the equalization.

[0169] In summary, the equalization topology structure proposed in this embodiment is compact, low-cost, and high-efficiency. For n a battery pack composed of [number] battery cells, the battery pack equalization topology only requires (2 n +12) MOSFET switches and a transformer winding, which not only reduces the volume of the equalization topology and improves the equalization efficiency, but also greatly reduces the total failure probability of the devices, thereby improving the topology stability and reliability. The clustering average extreme value statistical algorithm based on DBSCAN proposed in this embodiment can automatically identify the voltage distribution of the battery pack, and then adaptively switch among the three working modes of discharge equalization, charging equalization, and automatic equalization, so as to improve the equalization speed and flexibility.

[0170] Embodiment 2

[0171] This embodiment proposes a control method for the battery pack equalization topology structure described in Embodiment 1, including:

[0172] Collect the battery cell voltage;

[0173] Cluster the battery cell voltages, take the battery cell voltages of the same class as a cluster, and obtain a cluster-number-mean matrix according to the number of voltages and voltage means in each cluster;

[0174] Determine the first number of voltages in the cluster with the maximum voltage mean and the second number of voltages in the cluster with the minimum voltage mean in the cluster-number-mean matrix;

[0175] If the number of clusters is 1 or the first number of voltages is equal to the second number of voltages, then perform cyclic charging and discharging on the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage;

[0176] Otherwise, if the first number of voltages is greater than the second number of voltages, charge the battery cell corresponding to the minimum battery cell voltage, and if the first number of voltages is less than the second number of voltages, discharge the battery cell corresponding to the maximum battery cell voltage.

[0177] Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made without creative efforts on the basis of the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A battery pack equalization topology, characterized in that, Comprising: A battery pack including n battery cells, where n is a positive integer greater than 1; A transformer, the primary side of which is sequentially connected to each battery cell through a first switch tube assembly and a switch array, and the secondary side is connected to the battery pack through a second switch tube assembly; A switch array including n + 1 groups of switch tube assemblies, the positive and negative electrodes of each battery cell are respectively connected to the primary side of the transformer through a switch tube assembly, and a group of switch tube assemblies is shared between adjacent battery cells; A monitoring circuit for collecting the voltage of the battery cell; A control unit that obtains the voltage of the battery cell and is configured to: Cluster the voltages of the battery cells, take the voltages of the battery cells in the same class as a cluster, obtain a cluster - individual number - mean matrix based on the number of voltages and the voltage mean values in each cluster, and determine the first voltage number in the cluster with the maximum voltage mean value and the second voltage number in the cluster with the minimum voltage mean value in the cluster - individual number - mean matrix; If the number of clusters is 1 or the first voltage number is equal to the second voltage number, then cyclically charge and discharge the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage; Otherwise, if the first voltage number is greater than the second voltage number, charge the battery cell corresponding to the minimum battery cell voltage, and if the first voltage number is less than the second voltage number, discharge the battery cell corresponding to the maximum battery cell voltage; Wherein, the battery cell discharging process includes three modes, specifically: Mode I: Turn on the switch tube assembly connecting the battery cell to the primary side of the transformer and the first switch tube assembly, and turn off the second switch tube assembly; when an odd - numbered battery cell discharges, the odd - numbered battery cell charges the primary side coil of the transformer, the magnetic flux increases positively, and a positive electromotive force is generated in the primary side coil; when an even - numbered battery cell discharges, the even - numbered battery cell charges the primary side coil, the magnetic flux increases negatively, and a negative electromotive force is generated in the primary side coil; the discharging current of the battery cell starts to increase from zero; Mode II: Turn on a group of switch tubes in the second switch tube assembly where the two ends of the secondary side are respectively connected to the positive and negative electrodes of the battery pack, and turn off the other switch tubes; at the moment of switching from Mode I to Mode II, a positive electromotive force is generated in the secondary side coil, the current in the primary side coil continues to flow through the secondary side coil, the current flows from the secondary side coil to the battery pack, and the maximum value of the charging current of the battery pack starts to decrease and decreases to zero after a time interval; Mode III: The state of the switch tubes is the same as that in Mode II until the charging current of the battery pack drops to zero and then enters a static state.

2. A battery pack equalization topology structure as claimed in claim 1, wherein Each group of switch tube assemblies in the switch array includes two switch tubes connected in reverse series; The first switch tube assembly includes two switch tubes connected in reverse series, the first switch tube is connected to the positive electrode of the odd - numbered battery cell and the negative electrode of the even - numbered battery cell; The second switch tube assembly includes four groups of switch tube assemblies, both ends of the secondary side of the transformer are connected to the positive electrode of the battery pack through a group of switch tube assemblies, and both ends of the secondary side of the transformer are connected to the negative electrode of the battery pack through a group of switch tube assemblies.

3. The battery pack equalization topology structure according to claim 1, wherein, The process of clustering the voltages of the battery cells includes: setting a voltage distance, and clustering the battery cells with a voltage difference less than or equal to the voltage distance into one class.

4. The battery pack equalization topology structure according to claim 1, wherein Time interval is as follows: ； Among them, L S is the exciting inductance of the secondary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance on the secondary coil side, i S is the initial current refracted from the primary coil to the secondary coil; During an equilibrium period, the conduction time range on the secondary coil side of the transformer is set to 1.05 -1.25 .

5. A battery pack equalization topology structure as claimed in claim 1, wherein In Mode I, the discharge current of the battery cell at time t is: ； In Mode II, the battery pack charging current at time t is as follows: ； Among them, V B1 is the voltage across the battery cell; R P is the equivalent resistance on the primary coil side; L P is the exciting inductance of the primary coil; V Pack is the voltage across the battery pack; R S is the equivalent resistance on the secondary coil side; i S is the initial current refracted from the primary coil to the secondary coil; L S is the exciting inductance of the secondary coil.

6. The battery pack equalization topology structure according to claim 1, wherein, the charging process of the battery cells includes three modes, specifically: Mode I: Turn on a group of switching tubes in the second switching tube assembly, where the two ends of the secondary side are respectively connected to the positive and negative electrodes of the battery pack, and the remaining switching tubes are turned off; when the odd-numbered battery cells are charged, the battery pack charges the secondary side coil of the transformer, the magnetic flux increases in the positive direction, and a positive electromotive force is generated in the secondary side coil; when the even-numbered battery cells are charged, the magnetic flux of the secondary side coil is negative; the discharge current of the battery pack starts to increase from zero. Mode II: Turn on the switching tube assembly connecting the battery cell to the primary side of the transformer and the first switching tube assembly, and turn off the remaining switching tubes; at the moment of switching from Mode I to Mode II, a positive electromotive force is generated in the primary side coil, and the current in the secondary side coil continues to flow through the primary side coil, and the current flows from the primary side coil to the battery cell, and the maximum value of the charging current of the battery cell starts to decrease and decreases to zero after a time interval. Mode III: The state of the switching tubes is the same as that in Mode II until the charging current of the battery cell drops to zero and then enters a static state.

7. The battery pack equalization topology structure according to claim 6, characterized in that Time interval is as follows: ； Among them, i P is the initial current refracted from the secondary side coil to the primary side coil, R P is the equivalent resistance on the primary side coil, L P is the exciting inductance of the primary side coil, V B1 is the voltage across the battery cell; During an equilibrium period, the conduction time range on the secondary coil side of the transformer is set to 1.05 -1.25 .

8. A battery pack equalization topology structure as claimed in claim 6, wherein In Mode I, the battery pack discharge current at time t is as follows: ； In Mode II, the charging current of the battery cell at time t is as follows: ； Among them, V Pack is the voltage across the battery pack, R S is the equivalent resistance on the secondary coil side; L S is the magnetizing inductance of the secondary coil; i P is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance on the primary coil side, L P is the magnetizing inductance of the primary coil, V B1 is the voltage across the battery cell.

9. A control method for the battery pack equalization topology structure according to any one of claims 1-8, characterized in that, it includes: Collect the voltage of the battery cells; Cluster the voltages of the battery cells, take the voltages of the battery cells in the same class as a cluster, and obtain a cluster-number-mean matrix according to the number of voltages and the voltage mean value in each cluster; Determine the first voltage number in the cluster with the maximum voltage mean value and the second voltage number in the cluster with the minimum voltage mean value in the cluster-number-mean matrix; If the number of clusters is 1 or the first voltage number is equal to the second voltage number, then cycle charge and discharge the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage; Otherwise, if the first voltage number is greater than the second voltage number, charge the battery cell corresponding to the minimum battery cell voltage, and if the first voltage number is less than the second voltage number, discharge the battery cell corresponding to the maximum battery cell voltage.

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