Battery pack equalization topological structure and control method thereof

Abstract

The invention discloses a battery pack equalization topological structure and a control method thereof, and relates to the technical field of power electronic control, the battery pack equalization topological structure comprises a battery pack, a transformer, a switch array, a monitoring circuit and a control unit, adjacent battery monomers share a group of switch tube assemblies, and clustering and cluster division are carried out after the voltage of the battery monomers is collected; and determining a first voltage number in the cluster where the maximum voltage mean value is located and a second voltage number in the cluster where the minimum voltage mean value is located according to the cluster number and a comparison result of the first voltage number and the second voltage number, and the working modes of discharging equalization, charging equalization and automatic equalization are adaptively switched, so that the equalization efficiency is improved while the cost is remarkably reduced.

Description

Technical Field

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

[0002] Since the quality of lithium batteries is difficult to control during mass production, there will inevitably be inconsistencies between battery cells when they leave the factory. Especially when battery cells are connected in series and used in groups, the inconsistency will be further amplified, resulting in a decrease in the available capacity of the battery pack, accelerated attenuation of life, and reduced safety, which seriously affects the safe and efficient use of battery energy. Therefore, implementing battery pack balancing is an important means to improve this inconsistency.

[0003] At present, the battery management system generally adopts the passive balancing method, that is, the battery cells are discharged through the balancing resistor, which has problems such as energy waste and slow speed. The active balancing method can solve the above problems.

[0004] In the relevant prior art, 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 needs to be equipped with a transformer winding, which has problems such as complex structure, high cost, and difficult control.

[0005] Patent CN2020112091331 achieves battery balancing based on a half-bridge structure and a trap filter, significantly reducing the number of switching tubes, but there are still transformer windings that correspond one-to-one to the battery cells, and their volume, cost, and balancing efficiency need to be considered.

[0006] In addition, most existing active balancing methods have a single balancing mode and are unable to adjust the balancing 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 balancing topology structure and a control method thereof. The battery cells share a switch array, and the charging and discharging processes of adjacent battery cells realize bidirectional excitation of the transformer core, thereby significantly reducing costs while improving the balancing efficiency. At the same time, the battery pack voltage distribution is automatically identified, and the discharge balancing, charging balancing and automatic balancing working modes are adaptively switched, thereby improving the balancing speed and flexibility.

[0008] In order to achieve the above object, the present invention adopts the following technical solution: In a first aspect, the present invention provides a battery pack balancing topology structure, comprising: A battery pack, comprising n battery cells, where n is a positive integer greater than 1; A transformer, wherein the primary side of the transformer is connected to each battery cell through a first switch tube assembly and a switch array in sequence, 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, wherein the positive and negative electrodes of each battery cell are connected to the primary side of the transformer through a switch tube assembly respectively, and adjacent battery cells share one group of switch tube assemblies; Monitoring circuit, used to collect battery cell voltage; The control unit obtains the battery cell voltage and is configured as follows: The battery cell voltages are clustered, and the battery cell voltages of the same type are clustered. A cluster-individual number-mean matrix is ​​obtained according to the voltage number and voltage mean in each cluster. The cluster-individual number-mean matrix is ​​used to determine the first voltage number in the cluster where the maximum voltage mean value is located and the second voltage number in the cluster where the minimum voltage mean value is located; If the number of clusters is 1 or the first voltage number is equal to the second voltage number, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; Otherwise, if the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, and if the first voltage value is less than the second voltage value, the battery cell corresponding to the maximum battery cell voltage is discharged.

[0009] As an optional implementation, each group of switch tube components 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, and the first switch tube is connected to the positive electrodes of the odd-numbered battery cells and the negative electrodes of the even-numbered battery cells; 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.

[0010] As an optional implementation, the process of clustering the battery cell voltages includes: setting a voltage distance, and clustering the battery cells whose voltage differences are less than or equal to the voltage distance into one category.

[0011] As an optional implementation, the battery cell discharge process includes three modes, specifically: Mode I: Turn on the switch tube assembly and the first switch tube assembly that connect the battery cell to the primary side of the transformer, and turn off the second switch tube assembly; when the odd-numbered battery cells are discharged, the odd-numbered battery cells charge the primary coil of the transformer, the magnetic flux increases in a positive direction, and the primary coil generates a positive potential; when the even-numbered battery cells are discharged, the even-numbered battery cells charge the primary coil, the magnetic flux increases in a negative direction, and the primary coil generates a negative potential; the battery cell discharge current increases from zero; Mode II: In the second switch tube assembly, a group of switch tubes are turned on, with the two ends of the secondary side connected to the positive and negative electrodes of the battery pack respectively, and the other switch tubes are turned off; when mode I switches to mode II, a positive electromotive force is generated in the secondary coil, and the current of the primary coil continues to flow through the secondary coil, and the current flows from the secondary coil to the battery pack. The maximum value of the battery pack charging current begins to decrease and decreases to zero after a time interval; Mode III: The switch tube state is the same as Mode II, until the battery pack charging current drops to zero and then it is in a static state.

[0012] As an alternative embodiment, the time interval for: ; in, L S is the magnetizing inductance of the secondary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary coil side, i S It is the initial current refracted from the primary coil to the secondary coil; In one balancing cycle, the conduction time range of the secondary coil side of the transformer is set to 1.05 -1.25 .

[0013] As an optional implementation, in mode I, the battery cell discharge current at time t is for: ; In mode II, the battery pack charging current at time t is for: ; in, V B1 is the voltage across the battery cell, R P is the equivalent resistance on the primary coil side; L P is the magnetizing inductance of the primary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary coil side, i S It is the initial current refracted from the primary coil to the secondary coil; L S is the magnetizing inductance of the secondary coil.

[0014] As an optional implementation, the battery cell charging process includes three modes, specifically: Mode I: In the second switch tube assembly, a group of switch tubes are turned on, with the two ends of the secondary side connected to the positive and negative poles of the battery pack respectively, and the other switch tubes are turned off; when the odd-numbered battery cells are charged, the battery pack charges the secondary coil of the transformer, the magnetic flux increases in a positive direction, and the secondary coil generates a positive electromotive force; 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; Mode II: The switch tube assembly and the first switch tube assembly connected to the primary side of the transformer and the battery cell are turned on, and the other switch tubes are turned off; when mode I is switched to mode II, a positive electromotive force is generated in the primary coil, and the current of the secondary coil flows through the primary coil. The current flows from the primary coil to the battery cell, and the maximum value of the battery cell charging current begins to decrease, and decreases to zero after a time interval; Mode III: The switch tube state is the same as Mode II, until the battery cell charging current drops to zero and then it is in a static state.

[0015] As an alternative embodiment, the time interval for: ; in, i P is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance of the primary coil side, L P is the magnetizing inductance of the primary coil, V B1 is the voltage across the battery cell; In one balancing cycle, the conduction time range of the secondary coil side of the transformer is set to 1.05 -1.25 .

[0016] As an optional implementation, in mode I, the battery pack discharge current at time t is for: ; In mode II, the battery cell charging current at time t is for: ; in, V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary coil side; L S is the magnetizing inductance of the secondary coil; iP is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance of the primary coil side, L P is the magnetizing inductance of the primary coil, V B1 is the voltage across the battery cell.

[0017] In a second aspect, the present invention provides a method for controlling a battery pack balancing topology structure as described in the first aspect, comprising: Collect battery cell voltage; The battery cell voltages are clustered, and the battery cell voltages of the same type are clustered. The cluster-individual number-mean matrix is ​​obtained according to the voltage number and voltage mean in each cluster. Determine the first voltage number in the cluster where the maximum voltage mean is located and the second voltage number in the cluster where the minimum voltage mean is located for 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, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; Otherwise, if the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, and if the first voltage value is less than the second voltage value, the battery cell corresponding to the maximum battery cell voltage is discharged.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a battery pack balancing topology structure and a control method thereof. The battery cells share a switch array, and the battery cells and the transformer are connected through the switch array. Therefore, when the number of battery pack cells increases, there is no need to add additional transformer windings; at the same time, adjacent battery cells share a group of reverse series switch tubes to achieve switch tube sharing, reducing the number of switch devices in the traditional bidirectional flyback conversion by about 50%; n The battery pack consists of a battery cell, and the battery pack balancing topology only needs (2 n +12) switching tubes and a transformer winding, significantly reducing the number of components, not only reducing the volume of the balanced topology and improving the balancing efficiency, but also greatly reducing the total failure probability of the components, thereby improving the topology stability and reliability.

[0019] The present invention proposes a battery pack balancing topology structure and a control method thereof. When odd-numbered battery cells are discharged, the primary side magnetic flux of the transformer is positive, and when even-numbered battery cells are discharged, the primary side magnetic flux of the transformer is negative; when odd-numbered battery cells are charged, the primary side magnetic flux of the transformer is positive, and when even-numbered battery cells are charged, the primary side magnetic flux of the transformer is negative. Thus, the discharge and charging processes of adjacent battery cells realize bidirectional excitation of the transformer core. For battery packs of any size, only a single-winding flyback transformer is needed to complete the discharge and charging of all battery cells, which significantly reduces the cost while improving the balancing efficiency.

[0020] The present invention proposes a battery pack balancing topology structure and a control method thereof. The battery cell voltages are clustered and divided into clusters to obtain a cluster-individual number-mean matrix. The cluster-individual number-mean matrix determines the first voltage number in the cluster where the maximum voltage mean is located and the second voltage number in the cluster where the minimum voltage mean is located. According to the number of clusters and the comparison result between the first voltage number and the second voltage number, the battery pack voltage distribution is automatically identified, and then the three working modes of discharge balancing, charge balancing and automatic balancing are adaptively switched, thereby improving the balancing speed and flexibility.

[0021] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0023] Figure 1 A schematic diagram of a battery pack balancing topology structure provided in Embodiment 1 of the present invention; Figure 2 The adaptive equalization flow chart provided in Embodiment 1 of the present invention; Figure 3 The equalization result of the voltage waveform of Experiment #1 provided in Example 1 of the present invention; Figure 4 The balanced results of the consistency statistics of Experiment #1 provided in Example 1 of the present invention; Figure 5 The equalization result of the voltage waveform of Experiment #2 provided in Example 1 of the present invention; Figure 6 The balanced results of the consistency statistics of Experiment #2 provided in Example 1 of the present invention; Figure 7The equalization result of the voltage waveform of Experiment #3 provided in Example 1 of the present invention; Figure 8 This is the balanced result of the consistency statistics of Experiment #3 provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that the terms "include" and "comprise" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0027] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0028] Example 1 This embodiment provides an efficient and compact battery pack balancing topology structure, the schematic diagram is as follows: Figure 1 As shown, it includes: a battery pack, a transformer, a switch array, a monitoring circuit and a control unit.

[0029] The battery pack includes n battery cells B1, B2, ..., B n ; and battery cells B1, B3, B5, ..., B n-1 Odd-numbered battery cells, battery cells B2, B4, B6, ..., B n is an even number of battery cells, and n is a positive integer greater than 1; The primary side of the transformer is connected to each battery cell through the first switch tube assembly and the switch array in sequence, and the secondary side is connected to the battery pack through the second switch tube assembly; The switch array includes n+1 groups of switch tube assemblies, the positive and negative electrodes of each battery cell are connected to the primary side of the transformer through a switch tube assembly respectively, and adjacent battery cells share a group of switch tube assemblies; Monitoring circuit, used to collect battery cell voltage; The control unit obtains the battery cell voltage and is configured as follows: Cluster all battery cell voltages, and take the battery cell voltages of the same type as a cluster. According to the number of voltages and the voltage mean in each cluster, the cluster-individual number-mean matrix is ​​obtained; For the cluster-individual number-mean matrix, determine the first voltage number in the cluster where the maximum voltage mean is located and the second voltage number in the cluster where the minimum voltage mean is located; If the number of clusters is 1 or the first voltage number is equal to the second voltage number, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; If the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, otherwise the battery cell corresponding to the maximum battery cell voltage is discharged.

[0030] As an optional implementation, in the switch array, each switch tube assembly 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.

[0031] As an optional implementation, the first switch tube assembly connected to the primary side of the transformer includes two switch tubes Q1 and Q2 connected in reverse series, and the first switch tube is connected to the positive electrodes of the odd-numbered battery cells and the negative electrodes of the even-numbered battery cells; For example, taking battery cells B1, B2, B3 and B4 as an example, switch tube Q1 and switch tube Q2 are connected in reverse series, switch tube Q2 is connected to the primary side of the transformer, and switch tube Q1 is connected to the positive electrodes of battery cells B1 and B3, and the negative electrodes of battery cells B2 and B4.

[0032] As an optional implementation, the second switch tube assembly connected to the secondary side of the transformer 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, that is, the positive electrode of the battery cell B1, 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, that is, the positive electrode of the battery cell B n of the negative electrode.

[0033] More specifically, each group of switch tube assemblies includes two switch tubes connected in reverse series, that is, switch tubes Q3 and switch tubes Q4 are connected in reverse series to form a first group of switch tube assemblies, switch tubes Q5 and switch tubes Q6 are connected in reverse series to form a second group of switch tube assemblies, switch tubes Q7 and switch tubes Q8 are connected in reverse series to form a third group of switch tube assemblies, and switch tubes Q9 and Q10 are connected in reverse series to form a third group of switch tube assemblies. 10 Reverse series connection forms a fourth group of switch tube components; One end of the secondary side of the transformer is connected to the positive electrode of the battery pack through the first group of switch tube components, that is, the switch tube Q3 is connected to one end of the secondary side of the transformer, and the switch tube Q4 is connected to the positive electrode of the battery cell B1; it is connected to the negative electrode of the battery pack through the second group of switch tube components, that is, the switch tube Q5 is connected to one end of the secondary side of the transformer, and the switch tube Q6 is connected to the positive electrode of the battery cell B1. n The negative electrode; 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 switch tube components, that is, the switch tube Q7 is connected to the other end of the secondary side of the transformer, and the switch tube Q8 is connected to the positive electrode of the battery cell B1; it is connected to the negative electrode of the battery pack through the fourth group of switch tube components, that is, the switch tube Q9 is connected to the other end of the secondary side of the transformer, and the switch tube Q 10 Connect battery cell B n of the negative electrode.

[0034] It can be understood that the switch tubes Q1, Q2, ..., Q 10 They are all MOSFET switch tubes, which are used to control the connection of transformer T to the battery pack and the connection direction.

[0035] It can be understood that the switch tubes in the switch array are all MOSFET switch tubes, and the switch array is used to select the battery cells connected to the transformer T and the connection direction.

[0036] As an optional implementation, the control unit integrates the balancing strategy and PWM (Pulse Width Modulation) control unit, usually a microcontroller unit (MCU) or a digital signal processor (DSP). The control unit is connected to each switch tube and determines the balancing mode according to the voltage distribution of the battery pack, thereby controlling the on and off of the switch tube through the PWM control signal, thereby forming different energy paths to implement balancing. Figure 1 In the figure, the dotted line indicates that the PWM control signal sent by the control unit is connected to each switch tube. Figure 1 Only the connection switch Q is shown c2 , switch tube Q2 and switch tube Q3.

[0037] It can be seen from the battery pack balancing topology proposed in this embodiment that there is only one set of reverse-series MOSFET switch tubes between adjacent battery cells, which realizes switch tube sharing and reduces the number of switch tubes; at the same time, the battery cells and the transformer are connected through a switch array, and when the number of battery pack cells increases, there is no need to add additional transformer windings.

[0038] In short, for n The battery pack consists of a battery cell, and the battery pack balancing topology only needs (2n +12) MOSFET switch tubes and a transformer winding, significantly reducing the number of devices, not only reducing the volume of the balanced topology and improving the balancing efficiency, but also greatly reducing the total failure probability of the device, thereby improving the topology stability and reliability.

[0039] It is understandable that the monitoring circuit usually uses an analog front end (AFE) chip; other chips can also be used as long as they can collect the battery cell voltage and send it to the control unit without specific limitation.

[0040] As can be understood, the transformer adopts a single-winding flyback transformer.

[0041] In order to better illustrate the working process, the following assumptions are made: (1) The side of the transformer connected to the battery cell is the primary side (also known as the primary coil), and the side connected to the battery pack is the secondary side (also known as the secondary coil).

[0042] (2) On the primary side of the transformer, the current flows out of the battery cell in the positive direction; on the secondary side of the transformer, the current flows into the battery pack in the positive direction.

[0043] (3) The potential on the primary side of the transformer is positive when the top is positive and the bottom is negative; the potential on the secondary side is negative when the bottom is positive and the top is negative.

[0044] (4) When the current on the primary side of the transformer flows from top to bottom, the magnetic flux is positive; when the current on the secondary side of the transformer flows from bottom to top, the magnetic flux is negative.

[0045] (5) Battery cells B1, B3, B5, ..., B n-1 Odd-numbered battery cells; battery cells B2, B4, B6, ..., B n Even number of battery cells.

[0046] 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 cluster 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 adaptively switch the balancing mode according to different voltage distributions, hoping to complete the balancing in the most reasonable way and at the fastest speed.

[0047] like Figure 2 The figure shows the adaptive equalization flow chart, combined with Figure 2 Given the following steps: (1) Collect the battery cell voltage, recorded as vector Vol = [ V Bi | i =1,2,3,…, n ], V Bi is the voltage of the ith battery cell.

[0048] (2) Determine the maximum battery cell voltage V max and 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 When V max - V min ≥ V th , then go to step (3), otherwise end the equilibrium.

[0049] (3) Use the DBSCAN algorithm to cluster all battery cell voltages in the vector Vol, and set the distance metric eps to the set voltage distance V dis , that is, the voltage difference is less than or equal to V dis The battery cells are clustered into one category; the cluster category is recorded as vector Lab=[ L Bi | i =1,2,3,…, n ], L Bi ∈[0, n ], indicating the i-th category; vertically concatenate the vectors Lab and Vol, label each battery cell voltage with a category label, and form a category-voltage matrix M=[Lab;Vol].

[0050] (4) In the category-voltage matrix M, the same category L Bi The columns of are grouped into one cluster, that is, the battery cell voltages of the same type are grouped into one cluster, and the number of voltages and the voltage mean in each cluster are counted to form a cluster-individual number-mean matrix: (1); in, m is the number of clusters, at least 1 and at most the number of voltages n ; First line [ Cluster i | i =1,2,3,…, m ] is the firsti clusters; the second row [ Cnt i | i =1,2,3,…, m ] is the first i The number of voltages in the cluster; the third row [ V avg_i | i =1,2,3,…, m ] is the first i The mean voltage in each cluster.

[0051] (5) In the cluster-individual number-mean matrix M C The average extreme value statistics are performed in the cluster, that is, the first voltage number in the cluster where the maximum voltage mean is located is counted respectively. Cnt avg_max , and the second voltage number in the cluster with the minimum voltage mean Cnt avg_min .

[0052] (6) If m =1, or Cnt avg_max = Cnt avg_min , that is, all battery cell voltages are grouped into one cluster or the first voltage number is consistent with the second voltage number, then switch to automatic balancing mode; in automatic balancing mode, V min , V max The corresponding battery cells are charged and discharged in a time-slice cycle.

[0053] (7) Otherwise, if Cnt avg_max > Cnt avg_min , it switches to charge balancing mode.

[0054] (8) Otherwise, if Cnt avg_max < Cnt avg_min , it switches to discharge balance mode.

[0055] (9) Perform balancing; in charging mode, continuously balance the minimum battery cell voltage V min The corresponding battery cell is charged; in the discharge mode, the maximum battery cell voltage is continuously V max The corresponding battery cell discharges; in the automatic balancing mode, the minimum battery cell voltage V min and maximum battery cell voltage V maxThe corresponding battery cells are charged and discharged in a time-slice cycle.

[0056] (10) Repeat steps (1) to (9) until the result in step (2) is V max - V min < V th End of equilibrium.

[0057] It can be seen that in the discharge balancing mode, the balancing topology always selects the battery cell with the highest battery cell voltage for discharge, which is suitable for the case where the voltage of a few battery cells is obviously too high; in the charge balancing mode, the balancing topology continuously charges the battery cell with the lowest battery cell voltage, which is suitable for the case where the voltage of a few battery cells is obviously too low; in the automatic balancing mode, the battery cells are charged and discharged alternately, which is suitable for the case where the voltage distribution is uniform. Therefore, the cluster average extreme value statistical algorithm based on DBSCAN in this embodiment can flexibly select the appropriate balancing method according to different voltage distributions to achieve fast balancing.

[0058] The battery cell charging and battery cell discharging processes are described below.

[0059] There are two states in the circuit operation process, namely, battery cell discharge and battery cell charging. In the battery cell discharge process, the energy flow path is from the battery cell to the battery pack, and in the battery cell charging process, the energy flow path is from the battery pack to the battery cell.

[0060] A.Discharge status: The discharge process analysis of odd-numbered battery cells and even-numbered battery cells is basically the same, except that the switch array is turned on or off differently. Taking battery cell B1 as an example, in one switching cycle, battery cell B1 has three working modes.

[0061] Mode I: Switching tube Q C1 , switch tube Q C2 , switch tube Q C3 , switch tube Q C4 , switch tube Q1 and switch tube Q2 are turned on, switch tube Q3 to switch tube Q 10 Turn 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.

[0062] The voltage across the primary inductor of the transformer is: (2); in, VL1 is the voltage across the primary inductor of the transformer, L P is the transformer primary side magnetizing inductance, i 1 is the transformer primary current.

[0063] According to Kirchhoff's law and solving the differential equation, the battery monomer discharge current is obtained i 1: (3); in, is the battery pack charging current at time t, V B1 is the voltage across the battery cell B1, R P is the equivalent resistance of the primary side line of the transformer.

[0064] It can be seen from formula (3) that the battery cell discharge current i 1 (that is, the primary current of the transformer) gradually increases from zero.

[0065] Modality II: Switching tube Q3, switching tube Q9, switching tube Q 10 The switch tubes are turned on, and the other switch tubes 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 when mode I switches to mode II. At this time, the current on the primary side of the transformer will flow through the secondary side, and the current will flow from the inductor coil on the secondary side of the transformer to the battery pack.

[0066] The voltage across the inductor on the secondary side of the transformer is: (4); in, V L2 is the voltage across the inductor on the secondary side of the transformer, L S is the transformer secondary side magnetizing inductance, i 2 is the transformer secondary current.

[0067] According to Kirchhoff's law and solving the differential equation, the battery pack charging current can be obtained i 2: (5); in, is the battery pack charging current at time t, V Pack is the voltage across the battery pack, R S is the equivalent resistance of the transformer secondary side line, i S It is the initial current refracted from the primary side of the transformer to the secondary side.

[0068] From formula (5), we can see that i 2 from the maximum i S Starts to decrease gradually, after a time interval Decrease to zero.

[0069] (6).

[0070] Mode III: The state of the switch tube in this stage is the same as that in mode II. When the current on the secondary side of the transformer (that is, the charging current of the battery pack) drops to zero, the balancing topology will naturally be in a static state. In a balancing cycle, it is necessary to reasonably allocate the conduction time of the primary and secondary sides of the transformer so that the conduction time of the secondary side of the transformer is greater than the conduction time in formula (6). , ensuring that the circuit works in discontinuous mode, so that the transformer can be completely demagnetized after one balancing cycle; at the same time, if the transformer secondary side conduction time is too long, the balancing efficiency will be low, because it is equivalent to increasing the time of the balancing static state. Therefore, in this embodiment, the transformer secondary side conduction time range is preferably set to between 1.05 and 1.25 times of.

[0071] Similarly, when an even-numbered battery cell, such as battery cell B2, is discharged, the switch tube Q is C3 , switch tube Q C4 , switch tube Q C5 , switch tube Q C6 , switch tube Q1 and switch tube Q2 are turned on, switch tube Q3 to switch tube Q 10 Turn off; in mode II, switch tubes Q5, Q6, and Q7 are turned on, and the remaining switches are turned off; the switching state of mode III is consistent with that of mode II.

[0072] It can be seen that when odd-numbered battery cells are discharged, the magnetic flux on the primary side of the transformer is positive, and when even-numbered battery cells are discharged, the magnetic flux on the primary side of the transformer is negative. The discharge process of adjacent battery cells realizes the bidirectional excitation of the transformer core, so that only a single-winding flyback transformer is needed to complete the discharge of all battery cells.

[0073] B.Charging status: The charging process analysis of odd-numbered battery cells and even-numbered battery cells is basically the same, except that the switch array is turned on or off differently. Taking battery cell B1 as an example, in one switching cycle, battery cell B1 has three working modes.

[0074] Mode I: Switching tube Q3, switching tube Q4, switching tube Q9, switching tube Q 10The secondary side of the transformer is turned on, and the other switches are turned off. At this time, the battery pack charges the secondary side of the transformer, and the magnetic flux increases in the positive direction. 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 circuit, no current flows on the primary side.

[0075] Therefore, the battery pack discharge current is solved i 3: (7); From formula (7), we can see that i 3 gradually increases from zero.

[0076] Modality II: Switching tube Q C1 , switch tube Q C2 , switch tube Q C3 , switch tube Q C4 The switch tube Q2 is turned on, and the other 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 when mode I switches to mode II. At this time, the current on the secondary side of the transformer will flow through the primary side, and the current will flow from the transformer inductor to the battery cell B1.

[0077] Therefore, the charging current of battery cell B1 is obtained i 4: (8); in, i P It is the initial current refracted from the secondary side of the transformer to the primary side.

[0078] From formula (8), we can see that i 4 from the maximum i P Starts to decrease gradually, after a time interval Reduce to zero; (9).

[0079] Mode III: The state of the switch tube in this stage is the same as that in mode II. When the current on the primary side of the transformer drops to zero, the balanced topology will naturally be in a static state. In a balanced 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 the conduction time in formula (8). , ensuring that the circuit works in discontinuous mode, so that the transformer can be completely demagnetized after one balancing cycle; at the same time, if the transformer secondary side conduction time is too long, the balancing efficiency will be low, because it is equivalent to increasing the time of the balancing static state. Therefore, in this embodiment, the transformer secondary side conduction time range is preferably set to between 1.05 and 1.25 times of.

[0080] Similarly, when an even-numbered battery cell, such as battery cell B2, is charged, in mode I, switch tubes Q5, Q6, Q7, and Q8 are turned on, and the remaining switch tubes are turned off; in mode II, switch tube Q C1 , switch tube Q C2 , switch tube Q C3 , switch tube Q C4 The switch tube Q1 is turned on, and the other switch tubes are turned off; the switch tube states of mode III and mode II are consistent.

[0081] It can be seen that when odd-numbered battery cells are charged, the magnetic flux on the primary side of the transformer is negative, and when even-numbered battery cells are charged, the magnetic flux on the primary side of the transformer is positive. The charging process of adjacent battery cells realizes the bidirectional excitation of the transformer core, so that only a single-winding flyback transformer is needed to complete the charging of all battery cells.

[0082] In this embodiment, a battery pack balancing experimental platform is built. The battery pack is composed of 12 battery cells connected in series. V th and V dis 5mV and 10mV respectively. Three groups of equalization experiments were set up, numbered as experiment #1, experiment #2 and experiment #3, and the initial voltage distribution is shown in Table 1.

[0083] Table 1 Initial voltage distribution of battery pack; .

[0084] The results of experiment #1 are as follows Figure 3-Figure 4 As shown, Figure 3 The battery voltage in is the voltage of each battery cell in Table 1. It can be seen that the adaptive balancing mode under this voltage distribution is mainly based on discharge balancing. As the balancing progresses, the battery pack voltage difference gradually decreases, and the maximum voltage difference and standard deviation decrease from 60mV and 16.7mV to 5mV and 2.1mV respectively. It only takes 25 minutes to complete the balancing.

[0085] The equilibrium results of Experiment #2 are as follows Figure 5-Figure 6 As shown, Figure 5 The battery voltage in is the voltage of each battery cell in Table 1. It can be seen that the adaptive balancing mode under this voltage distribution is mainly based on charging balancing. As the balancing progresses, the battery pack voltage difference gradually decreases, and the maximum voltage difference and standard deviation decrease from 59mV and 22mV to 5mV and 1.6mV respectively. It only takes 27 minutes to complete the balancing.

[0086] The results of experiment #3 are as follows Figure 7-Figure 8 As shown, Figure 7The battery voltage in is the voltage of each battery cell in Table 1. It can be seen that the adaptive balancing mode under this voltage distribution is mainly automatic balancing. As the balancing progresses, the battery pack voltage difference gradually decreases, and the maximum voltage difference and standard deviation decrease from 50mV and 10.7mV to 5mV and 1.4mV respectively. It only takes 10 minutes to complete the balancing.

[0087] In summary, the balanced topology proposed in this embodiment is compact, low-cost and highly efficient. n The battery pack consists of a battery cell, and the battery pack balancing topology only needs (2 n +12) MOSFET switch tubes and a transformer winding, which not only reduces the volume of the balancing topology and improves the balancing efficiency, but also greatly reduces the total failure probability of the device, thereby improving the topology stability and reliability. The cluster 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 between the three working modes of discharge balancing, charge balancing and automatic balancing, thereby improving the balancing speed and flexibility.

[0088] Example 2 This embodiment provides a control method for the battery pack balancing topology structure described in Embodiment 1, including: Collect battery cell voltage; The battery cell voltages are clustered, and the battery cell voltages of the same type are clustered. The cluster-individual number-mean matrix is ​​obtained according to the voltage number and voltage mean in each cluster. Determine the first voltage number in the cluster where the maximum voltage mean is located and the second voltage number in the cluster where the minimum voltage mean is located for 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, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; Otherwise, if the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, and if the first voltage value is less than the second voltage value, the battery cell corresponding to the maximum battery cell voltage is discharged.

[0089] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is 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 by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A battery pack balancing topology structure, characterized in that: include: A battery pack, comprising n battery cells, where n is a positive integer greater than 1; A transformer, wherein the primary side of the transformer is connected to each battery cell through a first switch tube assembly and a switch array in sequence, 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, wherein the positive and negative electrodes of each battery cell are connected to the primary side of the transformer through a switch tube assembly respectively, and adjacent battery cells share one group of switch tube assemblies; Monitoring circuit, used to collect battery cell voltage; The control unit obtains the battery cell voltage and is configured as follows: The battery cell voltages are clustered, and the battery cell voltages of the same type are clustered. A cluster-individual number-mean matrix is ​​obtained according to the voltage number and voltage mean in each cluster. The cluster-individual number-mean matrix is ​​used to determine the first voltage number in the cluster where the maximum voltage mean value is located and the second voltage number in the cluster where the minimum voltage mean value is located; If the number of clusters is 1 or the first voltage number is equal to the second voltage number, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; Otherwise, if the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, and if the first voltage value is less than the second voltage value, the battery cell corresponding to the maximum battery cell voltage is discharged.

2. A battery pack balancing topology structure as claimed in claim 1, characterized in that: Each group of switch tube components 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, and the first switch tube is connected to the positive electrodes of the odd-numbered battery cells and the negative electrodes of the even-numbered battery cells; 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. A battery pack balancing topology structure as claimed in claim 1, characterized in that: The process of clustering the battery cell voltages includes: setting a voltage distance, and clustering the battery cells whose voltage differences are less than or equal to the voltage distance into one category.

4. A battery pack balancing topology structure as claimed in claim 1, characterized in that: The battery cell discharge process includes three modes, specifically: Mode I: Turn on the switch tube assembly and the first switch tube assembly that connect the battery cell to the primary side of the transformer, and turn off the second switch tube assembly; when the odd-numbered battery cells are discharged, the odd-numbered battery cells charge the primary coil of the transformer, the magnetic flux increases in a positive direction, and the primary coil generates a positive potential; when the even-numbered battery cells are discharged, the even-numbered battery cells charge the primary coil, the magnetic flux increases in a negative direction, and the primary coil generates a negative potential; the battery cell discharge current increases from zero; Mode II: In the second switch tube assembly, a group of switch tubes are turned on, with the two ends of the secondary side connected to the positive and negative electrodes of the battery pack respectively, and the other switch tubes are turned off; when mode I switches to mode II, a positive electromotive force is generated in the secondary coil, and the current of the primary coil continues to flow through the secondary coil, and the current flows from the secondary coil to the battery pack. The maximum value of the battery pack charging current begins to decrease and decreases to zero after a time interval; Mode III: The switch tube state is the same as Mode II, until the battery pack charging current drops to zero and then it is in a static state.

5. A battery pack balancing topology structure as claimed in claim 4, characterized in that: Time interval for: ； in, L S is the magnetizing inductance of the secondary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary coil side, i S It is the initial current refracted from the primary coil to the secondary coil; In one balancing cycle, the conduction time range of the secondary coil side of the transformer is set to 1.05 -1.25 .

6. A battery pack balancing topology structure as claimed in claim 4, characterized in that: In mode I, the battery cell discharge current at time t for: ； In mode II, the battery pack charging current at time t is for: ； in, V B1 is the voltage across the battery cell, R P is the equivalent resistance on the primary coil side; L P is the magnetizing inductance of the primary coil; V Pack is the voltage across the battery pack, R S is the equivalent resistance of the secondary coil side, i S It is the initial current refracted from the primary coil to the secondary coil; L S is the magnetizing inductance of the secondary coil.

7. A battery pack balancing topology structure as claimed in claim 1, characterized in that: The battery cell charging process includes three modes, specifically: Mode I: In the second switch tube assembly, a group of switch tubes are turned on, with the two ends of the secondary side connected to the positive and negative poles of the battery pack respectively, and the other switch tubes are turned off; when the odd-numbered battery cells are charged, the battery pack charges the secondary coil of the transformer, the magnetic flux increases in a positive direction, and the secondary coil generates a positive electromotive force; 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; Mode II: The switch tube assembly and the first switch tube assembly connected to the primary side of the transformer and the battery cell are turned on, and the other switch tubes are turned off; when mode I is switched to mode II, a positive electromotive force is generated in the primary coil, and the current of the secondary coil flows through the primary coil. The current flows from the primary coil to the battery cell, and the maximum value of the battery cell charging current begins to decrease, and decreases to zero after a time interval; Mode III: The switch tube state is the same as Mode II, until the battery cell charging current drops to zero and then it is in a static state.

8. A battery pack balancing topology structure as claimed in claim 7, characterized in that: Time interval for: ； in, i P is the initial current refracted from the secondary coil to the primary coil, R P is the equivalent resistance of the primary coil side, L P is the magnetizing inductance of the primary coil, V B1 is the voltage across the battery cell; In one balancing cycle, the conduction time range of the secondary coil side of the transformer is set to 1.05 -1.25 .

9. A battery pack balancing topology structure as claimed in claim 7, characterized in that: In mode I, the battery pack discharge current at time t for: ； In mode II, the battery cell charging current at time t is for: ； in, 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 of the primary coil side, L P is the magnetizing inductance of the primary coil, V B1 is the voltage across the battery cell.

10. A method for controlling a battery pack balancing topology structure according to any one of claims 1 to 9, characterized in that: include: Collect battery cell voltage; The battery cell voltages are clustered, and the battery cell voltages of the same type are clustered. The cluster-individual number-mean matrix is ​​obtained according to the voltage number and voltage mean in each cluster. Determine the first voltage number in the cluster where the maximum voltage mean is located and the second voltage number in the cluster where the minimum voltage mean is located for 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, the battery cells corresponding to the minimum battery cell voltage and the maximum battery cell voltage are charged and discharged in a cycle; Otherwise, if the first voltage value is greater than the second voltage value, the battery cell corresponding to the minimum battery cell voltage is charged, and if the first voltage value is less than the second voltage value, the battery cell corresponding to the maximum battery cell voltage is discharged.

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