Passive equalization control method and device for battery system

Abstract

The invention provides a battery system passive equalization control method and device, and relates to the technical field of energy storage system power management. The method comprises the following steps: acquiring the voltage of each single cell and identifying the highest single voltage of each battery module, wherein the highest single voltage is the maximum value of the voltage of the single cell in the corresponding battery module; when the highest monomer voltage of one of the plurality of battery modules reaches the charging cut-off voltage, performing stepping passive equalization on the battery module of which the highest monomer voltage reaches the charging cut-off voltage; obtaining the minimum value of the plurality of highest monomer voltages; whether the minimum value is larger than a preset value or not is judged, if yes, the stepping type passive equalization is completed and stopped, and if not, the stepping type passive equalization is not completed, and passive equalization continues until the minimum value is larger than the preset value. According to the invention, it is ensured that the short-plate capacity batteries in each battery module are fully charged, so that the available capacity of the system is maximized, the battery modules are balanced, and the overall performance and safety of the system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management of energy storage systems, and in particular to a method and device for passive balancing control of a battery system. Background Art

[0002] The battery pack in the energy storage system is usually composed of multiple battery modules connected in series, and each battery module is composed of multiple single cells connected in series. In the energy storage system, for the single cells of different manufacturers, the voltage points corresponding to 100% power and 0% power are generally defined. The common ones are 3.65V corresponding to 100% power and 2.5V corresponding to 0% power. Due to the inconsistency of the factory capacity, aging degree and self-discharge rate of the single cells, the available capacity and voltage points of each single cell are different. Under the premise that the power cannot be transferred between the single cells in series, the total available capacity of the energy storage system is limited by the single cells with short capacity.

[0003] In the battery module, the single cell with the short capacity is connected in series with other single cells. Therefore, it is impossible to accurately identify which single cell is the short capacity cell. However, when the single cell with the short capacity is discharged in series with other single cells at the same full charge voltage, it reaches the discharge cut-off voltage first. Therefore, the single cell with the short capacity determines the theoretical maximum available capacity that can be released by the battery module. In other words, the single cell with the short capacity determines the theoretical maximum available capacity that can be released by the energy storage system.

[0004] In order to ensure that the power of single cells with capacity shortcomings can be fully utilized and the battery pack reaches the theoretical maximum available capacity, the industry urgently needs to develop a passive balancing control method and control device that can align the voltage tops of single cells with capacity shortcomings in each battery module, so as to maximize the available capacity of the battery pack. Summary of the invention

[0005] In response to the above-mentioned problem that the single cells with capacity shortcomings in the battery module cannot be accurately identified, the theoretical maximum available capacity that can be released by the energy storage system is limited.

[0006] The present application proposes a passive balancing control method for a battery system, wherein the battery system comprises a plurality of battery modules, each of which comprises a plurality of single cells, and the control method comprises the following steps: Acquire the voltage of each of the single cells and identify the highest single cell voltage of each of the battery modules, wherein the highest single cell voltage is the maximum value of the voltage of the single cells in the corresponding battery module; When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, performing step-by-step passive balancing on the battery module whose highest cell voltage reaches the charge cut-off voltage; Obtaining a minimum value of the plurality of highest cell voltages; and Determine whether the minimum value is greater than a preset value. If so, the step-by-step passive balancing is completed and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed and the step-by-step passive balancing is continued until the minimum value is greater than the preset value.

[0007] Optionally, when the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, performing step-by-step passive balancing on the battery module whose highest cell voltage reaches the charge cut-off voltage specifically includes: When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, the battery module whose highest cell voltage reaches the charge cut-off voltage is controlled to discharge with a preset power as a step length.

[0008] Optionally, the preset power level is the product of a preset percentage and a nominal capacity.

[0009] Optionally, when the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the battery module with the highest single-cell voltage reaching the charging cut-off voltage is discharged in steps of preset power, specifically including: when the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, controlling the switch unit connected to the battery module with the highest single-cell voltage reaching the charging cut-off voltage to close, so that the battery module with the highest single-cell voltage reaching the charging cut-off voltage releases the preset power through the energy consumption unit connected to it.

[0010] Optionally, the preset value is a difference between the charging cut-off voltage and the convergence voltage.

[0011] Optionally, obtaining the minimum value of the multiple highest single-cell voltages specifically includes: According to the highest cell voltage of each of the battery modules, a highest cell voltage sequence sorted from large to small is formed to obtain the minimum value of the plurality of highest cell voltages.

[0012] The present application also proposes a battery system passive balancing control device, wherein the battery system includes multiple battery modules, each battery module includes multiple single cells, and the device includes: a controller, wherein the controller is used to obtain the voltage of each single cell and identify the highest single cell voltage of each battery module, wherein the highest single cell voltage is the maximum value of the voltage of the single cell in the corresponding battery module; when the highest single cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, performing step-by-step passive balancing on the battery module whose highest single cell voltage reaches the charging cut-off voltage; obtaining the minimum value of the multiple highest single cell voltages; and determining whether the minimum value is greater than a preset value. If so, the step-by-step passive balancing is completed and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed and the step-by-step passive balancing is continued until the minimum value is greater than the preset value.

[0013] Optionally, when the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, the controller controls the battery module whose highest cell voltage reaches the charge cut-off voltage to discharge with a preset power as a step size.

[0014] Optionally, the preset power level is the product of a preset percentage and a nominal capacity.

[0015] Optionally, the passive balancing control device further comprises: a plurality of battery management units; The number of the battery management units is equal to that of the battery modules and they correspond one to one; each of the battery management units is connected to the corresponding battery module, and is used to collect the voltage of each single cell in the battery module, and transmit the voltage of each single cell to the controller.

[0016] Optionally, the passive balancing control device further includes: a plurality of switch units and a plurality of energy consumption units; The number of the switch units and the energy consumption units is equal to and corresponds one to one with the battery modules; when the highest single cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the controller provides a control signal to the battery management unit connected to the battery module whose highest single cell voltage reaches the charging cut-off voltage, and the battery management unit controls the corresponding switch unit to close according to the control signal, so that the battery module releases the preset power through the corresponding energy consumption unit.

[0017] Optionally, the preset value is a difference between the charging cut-off voltage and the convergence voltage.

[0018] Optionally, the controller is used to form a highest cell voltage sequence sorted from large to small according to the highest cell voltage of each of the battery modules, so as to obtain a minimum value of the multiple highest cell voltages.

[0019] The present application can achieve at least one of the following beneficial effects: The passive equalization method of the battery system of the present application includes the following steps: obtaining the voltage of each of the single cells and identifying the highest single cell voltage of each of the battery modules, wherein the highest single cell voltage is the maximum value of the voltage of the single cells in the corresponding battery module. When the highest single cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the battery module whose highest single cell voltage reaches the charging cut-off voltage is subjected to step-by-step passive equalization. Obtain the minimum value of the multiple highest single cell voltages. Determine whether the minimum value is greater than the preset value. If so, the step-by-step passive equalization is completed and the step-by-step passive equalization is stopped. If not, the step-by-step passive equalization is not completed and the passive equalization is continued until the minimum value is greater than the preset value. The passive equalization method of the present application can ensure that each battery module reaches an ideal state during the charging and discharging process. By aligning the top of the capacity short board single cell of each battery module, the available capacity of the battery module can be maximized, so that the battery system can output more energy, and the overall performance is significantly improved compared to before equalization. In addition, by setting a reasonable preset value, the charging process of the battery system is accurately controlled to avoid overcharging, effectively protect the health of the battery system, and extend its service life. The passive balancing method of the present application is used in a passive balancing device, which makes the passive balancing device simple in structure, reduces failure rate, reduces maintenance cost, ensures long-term stable and orderly operation of the battery system, and reduces the failure rate of the battery and battery management system. The present application can be applied to battery modules of different manufacturers, different aging degrees, and different states of charge (S0C), meeting a variety of application scenarios.

[0020] The above is a fairly broad overview of the features and technical advantages of the present application, so that the following detailed description of the present application can be better understood. The additional features and advantages of the present application will be described below, and they form the subject matter of the claims of the present application. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments can be easily utilized as the basis for modifying or designing other structures or processes for realizing the same purpose of the present application. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present application as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more fully understand the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which: Figure 1 A flow chart showing a passive balancing control method for a battery system according to an embodiment of the present application is shown; Figure 2 A schematic structural diagram of a passive balancing control device for a battery system according to an embodiment of the present application is shown.

[0022] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0023] Various exemplary embodiments, features and aspects of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0024] The word "exemplary" is used herein to mean "serving as an example, embodiment or illustration". Any embodiment described herein as "exemplary" is not necessarily to be interpreted as being superior or better than other embodiments. The terms "first", "second", "third", etc. (if any) in the specification and claims of the present invention and the drawings are used to distinguish similar objects, and are not necessarily used to describe a particular order or sequence.

[0025] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "coupled", "connected", and "connected" should be understood in a broad sense. For example, it can be an electrical connection or mutual communication, it can be a direct connection, it can also be an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] In addition, in order to better illustrate the present invention, numerous specific details are provided in the following specific embodiments. It should be understood by those skilled in the art that the present invention can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present invention.

[0027] The passive balancing control device of the present invention is simple and reliable, and the control method is also simple and reliable. It is not restricted by the environment, can adapt to the initial capacity differences of different manufacturers, and can adapt to the aging trends of batteries of different manufacturers. The application scenarios are flexible. The specific application scenario analysis is shown in the following table.

[0028] Table 1 Analysis of different application scenarios

[0029] In different practical application scenarios, the key goal of achieving passive balancing is to fully charge the short-board capacity battery to maximize the available capacity of the battery pack.

[0030] In the use scenario of multiple battery modules, the key goal of achieving passive balancing is to make the highest single cell voltage of each battery module reach the charging cut-off voltage at the same time, that is, to align the top of the highest single cell voltage between each battery module.

[0031] Figure 1 A flow chart of a passive balancing control method for a battery system according to an embodiment of the present application is shown. Figure 2 The structure diagram of the passive balancing control device for a battery system according to an embodiment of the present application is shown. Figure 2 As shown, the battery system includes a plurality of battery modules 213, 223, ..., 2n3, each battery module includes a plurality of single cells, wherein the plurality of single cells are connected in series, and the plurality of battery modules are also connected in series with each other.

[0032] The battery system passive balancing control device includes a controller 20, a plurality of battery management units 214, 224, ..., 2n4, a plurality of switch units 211, 221, ..., 2n1 and a plurality of energy consumption units 212, 222, ..., 2n2, wherein n is a natural number greater than 1. In this embodiment, the number of the battery management units is equal to and corresponds to the number of the battery modules, and the number of the switch units and the energy consumption units is equal to and corresponds to the number of the battery modules. Each switch unit is connected in series with the corresponding energy consumption unit and then connected in parallel with the corresponding battery module, and each battery management unit is connected to the corresponding battery module and the controller 20.

[0033] Specifically, the switch unit 211 and the energy consumption unit 212 are connected in series and then connected in parallel with the battery module 213, and the battery management unit 214 is connected to the battery module 213 to collect the voltage of each single cell in the battery module 213; the switch unit 221 and the energy consumption unit 222 are connected in series and then connected in parallel with the battery module 223, and the battery management unit 224 is connected to the battery module 223 to collect the voltage of each single cell in the battery module 223; and so on, the switch unit 2n1 and the energy consumption unit 2n2 are connected in series and then connected in parallel with the battery module 2n3, and the battery management unit 2n4 is connected to the battery module 2n3 to collect the voltage of each single cell in the battery module 2n3. In this embodiment, the voltage of the single cell is directly collected by the battery management unit, and the collection accuracy and temperature are reliable, the error is small, and the mis-balancing can be effectively avoided. In this embodiment, the energy consumption units 212, 222, ..., 2n2 can be elements with impedance such as resistors, inductors, or capacitors. In other embodiments, the energy consumption units 212, 222, ..., 2n2 may also be impedance circuits composed of resistors, inductors, or capacitors connected in series or in parallel. In an embodiment, the switch unit may be a controllable switch, such as MOS or JFET, but is not limited thereto. In this embodiment, the battery module whose highest single cell voltage reaches the charging cut-off voltage consumes power through the corresponding energy consumption unit, so that the top ends of each battery module can be aligned, the amount of calculation can be reduced, and the system operation efficiency can be improved.

[0034] The battery management unit 214, the battery management unit 224 and the battery management unit 2n4 are connected to the controller 20, for example, they can be connected via a CAN bus. The battery management units 214, 224, ..., 2n4 transmit the voltages of the collected single cells to the controller 20, that is, the controller 20 can obtain the voltage of each single cell and identify the highest single cell voltage of each battery module, wherein the highest single cell voltage is the maximum value of the voltage of the single cell in the battery module, such as the highest single cell voltage of the battery module 213, the highest single cell voltage of the battery module 223, and the highest single cell voltage of the battery module 2n3. When one of the highest single cell voltage of the battery module 213, the highest single cell voltage of the battery module 223, and the highest single cell voltage of the battery module 2n3 reaches the charging cut-off voltage, the controller 20 controls the battery module whose highest single cell voltage reaches the charging cut-off voltage to perform step-by-step passive balancing, that is, the controller controls the battery module whose highest single cell voltage reaches the charging cut-off voltage to discharge with a preset power as the step length, and the discharge amplitude is small, thereby avoiding the over-balancing phenomenon caused by excessive single discharge. The controller 20 obtains the minimum value according to the highest cell voltage of each battery module identified, and determines whether the minimum value is greater than the preset value. If so, the step-by-step passive balancing is completed and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed, and the step-by-step passive balancing is continued until the minimum value is greater than the preset value. In this embodiment, the minimum value is greater than the preset value, indicating that the passive balancing has reached convergence, the top alignment effect of each battery module has been achieved, and the step-by-step passive balancing is completed. This embodiment can maximize the available capacity of the battery module by controlling the top alignment of the highest cell voltage of each battery module, so that the entire battery system can output more energy, and the overall performance is significantly improved compared to before passive balancing. By performing step-by-step balancing on the battery module whose highest cell voltage reaches the charging cut-off voltage, the charging time of other battery modules can be slightly extended, so that the highest cell voltage of each battery module is closer to the top 100% power.

[0035] During the charging process of the battery system of this embodiment, the highest cell voltages in each battery module are different. When the highest cell voltage in any battery module reaches the charging cut-off voltage, the charging process of the entire battery system will be forced to be interrupted. For the battery system to maximize the available capacity, the goal is to control the highest cell voltage of each battery module to reach the charging cut-off voltage at the same time, that is, to control the top of the highest cell voltage of each battery module to align.

[0036] In this embodiment, the preset value is the difference between the charge cut-off voltage and the convergence voltage. In this embodiment, the convergence voltage can be a small voltage range below the charge cut-off voltage. When the minimum value of the multiple highest single cell voltages is greater than the preset value, it is considered that the balance has reached convergence, and the "top alignment" effect has been achieved. By setting a reasonable preset value, the battery charging process is accurately controlled to avoid overcharging, effectively protect the health of the battery module, and perform the battery module service life.

[0037] In this embodiment, the preset power is the product of the preset percentage and the nominal capacity. The preset percentage may be 0.5%, but is not limited thereto in this embodiment, as long as the product of the preset percentage and the nominal capacity satisfies a small discharge amount.

[0038] In this embodiment, when the highest cell voltage of the battery module 213, the highest cell voltage of the battery module 223, and the highest cell voltage of the battery module 2n3 reach the charging cut-off voltage, the controller 20 generates a corresponding control signal to the battery management unit connected to the battery module whose highest cell voltage reaches the charging cut-off voltage, and controls the corresponding switch unit to close, so that the battery module, the corresponding switch unit and the corresponding energy consumption unit form a loop, and the battery module releases the preset power through the corresponding energy consumption unit. Assume that when the highest cell voltage of the battery module 213 reaches the charging cut-off voltage first, the controller transmits the generated control signal to the battery management unit 214. The battery management unit 214 controls the switch unit 211 to close according to the control signal, and the battery module 213, the switch unit 211 and the energy consumption unit 212 form a loop, and the battery module 213 releases the preset power through the energy consumption unit 212. This embodiment only needs to add a switch unit and an energy consumption unit, and the structure is simple, which reduces the difficulty and cost of the passive balancing control device.

[0039] During the charge and discharge process of this embodiment, the highest cell voltages of each battery module in the battery system are inconsistent, resulting in different times for each highest cell voltage to reach the charge cut-off voltage. In the short term, this time difference does not change with the charge and discharge cycle. Therefore, it is necessary to use an energy-consuming unit to realize the power consumption of the battery module whose highest cell voltage reaches the charge cut-off voltage, thereby slowing down the time it takes to reach the charge cut-off voltage and shortening the time difference between it and other battery modules to reach the charge cut-off voltage. In order to better control the time when the highest cell voltage of each battery module reaches the charge cut-off voltage, it is necessary to perform additional discharge processing on the battery module that reaches the charge cut-off voltage first, such as releasing a preset amount of power, slowing down the time it takes to reach the full charge point, and shortening the time difference with the latest full charge point.

[0040] In this embodiment, the controller 20 forms a sequence of highest cell voltages arranged from large to small according to the highest cell voltage of each battery module, so as to obtain the minimum value of the plurality of highest cell voltages.

[0041] The battery system passive balancing device of the present application is compatible with battery modules of different manufacturers, different aging degrees, and different states of charge (SOC), meeting a variety of application scenarios, and showing strong versatility and adaptability. The battery system passive balancing device of the present application has a simple structure, low failure rate, and reduced maintenance costs. In addition, effective passive balancing can ensure the long-term stable and orderly operation of the battery system and reduce the failure rate of the battery system and battery management system.

[0042] Combination Figure 1 and Figure 2 A passive balancing control method for a battery system, wherein the battery system comprises a plurality of battery modules 213, 223, ..., 2n3, each battery module comprises a plurality of single cells, each battery module comprises a plurality of single cells, wherein the plurality of single cells are connected in series, and the plurality of battery modules are also connected in series with each other.

[0043] The control method comprises the following steps: Step 11: Obtain the voltage of each single cell and identify the highest single cell voltage of each battery module, wherein the highest single cell voltage is the maximum value of the voltage of the single cells in the corresponding battery module.

[0044] Specifically, the battery management unit 214 is connected to the battery module 213, and is used to collect the voltage of each single cell in the battery module 213; the battery management unit 224 is connected to the battery module 223, and is used to collect the voltage of each single cell in the battery module 223; and so on, the battery management unit 2n4 is connected to the battery module 2n3, and is used to collect the voltage of each single cell in the battery module 2n3. In this embodiment, the voltage of the single cell is directly collected by the battery management unit, and the collection accuracy and temperature are reliable, the error is small, and the mis-balancing can be effectively avoided.

[0045] The battery management unit 214, the battery management unit 224 and the battery management unit 2n4 are connected to the controller 20, for example, they can be connected via a CAN bus. The battery management units 214, 224, ..., 2n4 transmit the voltages of the collected single cells to the controller 20, that is, the controller 20 can obtain the voltage of each single cell and identify the highest single cell voltage of each battery module, wherein the highest single cell voltage is the maximum value of the voltage of the single cell in the battery module, such as the highest single cell voltage of the battery module 213, the highest single cell voltage of the battery module 223, and the highest single cell voltage of the battery module 2n3.

[0046] Step 12: When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, performing step-by-step passive balancing on the battery module whose highest cell voltage reaches the charge cut-off voltage.

[0047] Specifically, when one of the highest single cell voltage of battery module 213, the highest single cell voltage of battery module 223, and the highest single cell voltage of battery module 2n3 reaches the charging cut-off voltage, the controller 20 controls the battery module whose highest single cell voltage reaches the charging cut-off voltage to perform step-by-step passive balancing, that is, the controller controls the battery module whose highest single cell voltage reaches the charging cut-off voltage to discharge with a preset power as the step size, and the discharge amplitude is small, thereby avoiding over-balancing caused by excessive single discharge.

[0048] Step 13: Obtain the minimum value of the plurality of highest cell voltages.

[0049] Specifically, the controller 20 obtains the minimum value according to the highest cell voltage of each identified battery module.

[0050] Step 14: Determine whether the minimum value is greater than a preset value. If so, the step-by-step passive equalization is completed and the step-by-step passive equalization is stopped. If not, the step-by-step passive equalization is not completed and the step-by-step passive equalization is continued until the minimum value is greater than the preset value.

[0051] Specifically, the controller 20 determines whether the minimum value is greater than the preset value. If so, the step-by-step passive balancing is completed by executing step 15, and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed, and the step-by-step passive balancing continues, and step 11 continues until the minimum value is greater than the preset value. In this embodiment, the minimum value is greater than the preset value, indicating that the passive balancing has reached convergence, the top alignment effect of each battery module has been achieved, and the step-by-step passive balancing is completed. This embodiment can maximize the available capacity of the battery module by controlling the top alignment of the highest single cell voltage of each battery module, so that the entire battery system can output more energy, and the overall performance is significantly improved compared to before passive balancing. By performing step-by-step balancing on the battery module whose highest single cell voltage reaches the charging cut-off voltage, the charging time of other battery modules can be slightly extended, so that the highest single cell voltage of each battery module is closer to the top 100% power.

[0052] In this embodiment, the preset power is the product of the preset percentage and the nominal capacity. The preset percentage may be 0.5%, but is not limited thereto in this embodiment, as long as the product of the preset percentage and the nominal capacity satisfies a small discharge amount.

[0053] In this embodiment, when the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the battery module with the highest single-cell voltage reaching the charging cut-off voltage is controlled to discharge with a preset power as a step size, specifically including: when the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the switch unit connected to the battery module with the highest single-cell voltage reaching the charging cut-off voltage is controlled to be closed, so that the battery module with the highest single-cell voltage reaching the charging cut-off voltage releases the preset power through the energy consumption unit connected to it.

[0054] Specifically, the switch unit 211 and the energy consumption unit 212 are connected in series and then connected in parallel with the battery module 213, the switch unit 221 and the energy consumption unit 222 are connected in series and then connected in parallel with the battery module 223, and the switch unit 2n1 and the energy consumption unit 2n2 are connected in series and then connected in parallel with the battery module 2n3. When the highest cell voltage of the battery module 213, the highest cell voltage of the battery module 223, and the highest cell voltage of the battery module 2n3 reach the charging cut-off voltage, the controller 20 generates a corresponding control signal to the battery management unit connected to the battery module whose highest cell voltage reaches the charging cut-off voltage, and controls the corresponding switch unit to close, so that the battery module, the corresponding switch unit and the corresponding energy consumption unit form a loop, and the battery module releases the preset power through the corresponding energy consumption unit. This embodiment only needs to add a switch unit and an energy consumption unit, and the structure is simple, which reduces the difficulty and cost of the passive balancing control device.

[0055] During the charge and discharge process of this embodiment, the highest cell voltages of each battery module in the battery system are inconsistent, resulting in different times for each highest cell voltage to reach the charge cut-off voltage. In the short term, this time difference does not change with the charge and discharge cycle. Therefore, it is necessary to use an energy-consuming unit to realize the power consumption of the battery module whose highest cell voltage reaches the charge cut-off voltage, thereby slowing down the time it takes to reach the charge cut-off voltage and shortening the time difference between it and other battery modules to reach the charge cut-off voltage. In order to better control the time when the highest cell voltage of each battery module reaches the charge cut-off voltage, it is necessary to perform additional discharge processing on the battery module that reaches the charge cut-off voltage first, such as releasing a preset amount of power, slowing down the time it takes to reach the full charge point, and shortening the time difference with the latest full charge point.

[0056] In this embodiment, the preset value is the difference between the charge cut-off voltage and the convergence voltage. In this embodiment, the convergence voltage can be a small voltage range below the charge cut-off voltage. When the minimum value of the multiple highest single cell voltages is greater than the preset value, it is considered that the balance has reached convergence, and the "top alignment" effect has been achieved. By setting a reasonable preset value, the battery charging process is accurately controlled to avoid overcharging, effectively protect the health of the battery module, and perform the battery module service life.

[0057] In this embodiment, obtaining the minimum value of the multiple highest single cell voltages specifically includes: forming a highest single cell voltage sequence sorted from large to small according to the highest single cell voltage of each of the battery modules to obtain the minimum value of the multiple highest single cell voltages.

[0058] The battery system passive balancing method of the present application is compatible with battery modules of different manufacturers, different aging degrees, and different states of charge (SOC), meeting a variety of application scenarios, and showing strong versatility and adaptability. The battery system passive balancing device of the present application has a simple structure, low failure rate, and reduced maintenance costs. In addition, effective passive balancing can ensure the long-term stable and orderly operation of the battery system and reduce the failure rate of the battery system and battery management system.

[0059] The passive balancing control method of the battery system is described by a specific embodiment: In this embodiment, the battery system is composed of battery modules of three different manufacturers, A, B, and C, connected in series, with a nominal capacity of 50Ah. Due to the difference in initial power consistency, when the battery system reaches the charging cutoff for the first time: the highest single cell voltage of the battery module of manufacturer A reaches the charging cutoff voltage first, that is, fully charged, with an available capacity of 50Ah; the highest single cell voltage of the battery module of manufacturer B is second, with an available capacity of 49Ah; the highest single cell voltage of the battery module of manufacturer C is the lowest, with an available capacity of 48Ah.

[0060] At this time, since the battery module of manufacturer A is fully charged first, a step-by-step passive balancing is performed to release the product of the preset power discharge percentage (for example, 0.5%) and the nominal capacity, for example, 0.5%*50Ah = 0.25Ah; at this time, the capacity difference between the battery module of manufacturer A and the battery module of manufacturer B drops from 1Ah to 0.75Ah; the capacity difference between the battery module of manufacturer A and the battery module of manufacturer C drops from 2Ah to 1.75Ah.

[0061] During the second round of charging of the battery system, due to a step-by-step passive balancing operation of the battery module of manufacturer A, when the battery system was fully charged, the highest single-cell voltage of the battery module of manufacturer A reached the charging cut-off voltage first, and the available capacity remained at 50Ah; the highest single-cell voltage of the battery module of manufacturer B was second, but its available capacity was increased to 49.25Ah; the highest single-cell voltage of the battery module of manufacturer C was the lowest, and its available capacity was increased to 48.25Ah.

[0062] Since the highest single cell voltage of the battery module of manufacturer A still reaches the charging cut-off voltage first, a step-by-step passive balancing operation is performed again, which releases 0.5%*50Ah=0.25Ah of electricity again; at this time, the capacity difference between the battery module of manufacturer A and the battery modules of manufacturers B and C is reduced again.

[0063] The battery system is charged for the third time. When the system is fully charged, the difference in the maximum single-cell voltage of the battery modules of the three manufacturers A, B, and C will be further narrowed, and the available capacity of each battery module will be more consistent.

[0064] By repeatedly performing step-by-step passive balancing on the battery module whose highest single cell voltage reaches the charging cut-off voltage first, the capacity differences between the battery modules of manufacturers A, B, and C will gradually narrow, and when the battery system charging is cut off, the highest single cell voltage of each battery module will gradually align at the top.

[0065] As the battery module whose highest single cell voltage reaches the charge cut-off voltage first is subjected to step-by-step passive balancing each time, the battery module whose highest single cell voltage reaches the charge cut-off voltage first may change alternately, and the highest single cell voltage of each battery module is closer to the "top". As the number of passive balancing increases, the difference between the highest single cell voltages of each battery module will gradually converge. In order to avoid invalid passive balancing, it is necessary to set the judgment conditions for terminating passive balancing.

[0066] According to the characteristic that the voltage of the battery at the end of charging will rise rapidly as the power increases, a small voltage range below the charging cut-off voltage is selected as the judgment condition for reaching the "top" alignment. Assuming that the charging cut-off voltage is Volcutoff and the voltage difference range for judging convergence is detaV, the condition for judging that the balance has reached convergence is: When the highest cell voltage of a battery module reaches the charging cut-off voltage, the controller 20 reads the highest cell voltage of each battery module to form a highest cell voltage sequence. If the minimum value in the sequence is greater than a preset value (for example, preset value = Volcutoff - detaV), it is considered that passive balancing has reached convergence, the "top alignment" effect has been achieved, the step-by-step passive balancing is completed, and the step-by-step passive balancing is stopped.

[0067] The battery system passive balancing device and control method of the present application are compatible with battery modules of different manufacturers, different aging degrees, and different states of charge (SOC), meeting a variety of application scenarios, and showing strong versatility and adaptability. The battery system passive balancing device of the present application has a simple structure, low failure rate, and reduced maintenance costs. In addition, effective passive balancing can ensure the long-term stable and orderly operation of the battery system and reduce the failure rate of the battery system and battery management system.

[0068] Although the embodiments of the present application and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

[0069] In addition, the scope of the present application is not limited to the specific embodiments of the processes, machines, manufactures, material compositions, modes, methods, and steps described in this specification. Those skilled in the art will readily understand from the disclosure of the present application that, according to the present application, currently existing or later to be developed processes, machines, manufactures, material compositions, modes, methods, or steps that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein may be utilized. Therefore, it is intended that the appended claims include such processes, machines, manufactures, material compositions, modes, methods, or steps within their scope.

Claims

1. A passive balancing control method for a battery system, wherein the battery system comprises a plurality of battery modules, each battery module comprises a plurality of single cells, characterized in that: The control method comprises the following steps: Obtaining the voltage of each of the single cells and identifying the highest single cell voltage of each of the battery modules, wherein the highest single cell voltage is the maximum value of the voltages of the single cells in the corresponding battery module; When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, performing step-by-step passive balancing on the battery module whose highest cell voltage reaches the charge cut-off voltage; Obtaining a minimum value of the plurality of highest cell voltages; and Determine whether the minimum value is greater than a preset value. If so, the step-by-step passive balancing is completed and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed and the step-by-step passive balancing is continued until the minimum value is greater than the preset value.

2. The battery system passive balancing control method according to claim 1, characterized in that: When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, step-by-step passive balancing is performed on the battery module whose highest cell voltage reaches the charge cut-off voltage, specifically including: When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, the battery module whose highest cell voltage reaches the charge cut-off voltage is controlled to discharge with a preset power as a step length.

3. The battery system passive balancing control method according to claim 2, characterized in that: The preset power is the product of the preset percentage and the nominal capacity.

4. The battery system passive balancing control method according to claim 3, characterized in that: When the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the battery module whose highest single-cell voltage reaches the charging cut-off voltage is controlled to discharge with a preset power as a step size, specifically including: when the highest single-cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the switch unit connected to the battery module whose highest single-cell voltage reaches the charging cut-off voltage is controlled to be closed, so that the battery module whose highest single-cell voltage reaches the charging cut-off voltage releases the preset power through the energy consumption unit connected to it.

5. The battery system passive balancing control method according to claim 1, characterized in that: The preset value is the difference between the charging cut-off voltage and the convergence voltage.

6. The battery system passive balancing control method according to claim 1, characterized in that: Obtaining the minimum value of the plurality of highest cell voltages specifically includes: According to the highest cell voltage of each of the battery modules, a highest cell voltage sequence sorted from large to small is formed to obtain the minimum value of the plurality of highest cell voltages.

7. A battery system passive balancing control device, characterized in that: The battery system includes a plurality of battery modules, each of which includes a plurality of single cells. The device includes: a controller, the controller is used to obtain the voltage of each single cell and identify the highest single cell voltage of each battery module, wherein the highest single cell voltage is the maximum value of the voltage of the single cell in the corresponding battery module; when the highest single cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, performing step-by-step passive balancing on the battery module whose highest single cell voltage reaches the charge cut-off voltage; obtaining the minimum value of the plurality of highest single cell voltages; and determining whether the minimum value is greater than a preset value. If so, the step-by-step passive balancing is completed and the step-by-step passive balancing is stopped. If not, the step-by-step passive balancing is not completed and the step-by-step passive balancing is continued until the minimum value is greater than the preset value.

8. The battery system passive balancing control device according to claim 7, characterized in that: When the highest cell voltage of one of the plurality of battery modules reaches the charge cut-off voltage, the controller is used to control the battery module whose highest cell voltage reaches the charge cut-off voltage to discharge with a preset power as a step size.

9. The battery system passive balancing control device according to claim 8, characterized in that: The preset power is the product of the preset percentage and the nominal capacity.

10. The battery system passive balancing control device according to claim 8, characterized in that: The passive balancing control device further includes: a plurality of battery management units; The number of the battery management units is equal to that of the battery modules and they correspond one to one; each of the battery management units is connected to the corresponding battery module, and is used to collect the voltage of each single cell in the battery module, and transmit the voltage of each single cell to the controller.

11. The battery system passive balancing control device according to claim 10, characterized in that: The passive balancing control device further includes: a plurality of switch units and a plurality of energy consumption units; The number of the switch units and the energy consumption units is equal to and corresponds one to one with the battery modules; when the highest single cell voltage of one of the multiple battery modules reaches the charging cut-off voltage, the controller provides a control signal to the battery management unit connected to the battery module whose highest single cell voltage reaches the charging cut-off voltage, and the battery management unit controls the corresponding switch unit to close according to the control signal, so that the battery module releases the preset power through the corresponding energy consumption unit.

12. The battery system passive balancing control device according to claim 7, characterized in that: The preset value is the difference between the charging cut-off voltage and the convergence voltage.

13. The battery system passive balancing control device according to claim 7, characterized in that: The controller is used for forming a sequence of highest cell voltages arranged from large to small according to the highest cell voltage of each of the battery modules, so as to obtain a minimum value of the plurality of highest cell voltages.

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