Active balancing control method for battery system

Abstract

A method for active balancing control of a battery system is proposed, relating to the technical field of battery management for energy storage systems. The method includes: receiving the system current and balancing compensation current of a lower battery module; receiving multiple real-time available capacities; calculating the average available capacity; and calculating the difference between the average available capacity and the minimum of the multiple real-time available capacities in real time. When the difference is greater than a first preset value, active balancing is initiated to control the operation of a DC / DC balancing module, thereby actively balancing the capacities of multiple battery modules. Embodiments of the present invention can effectively balance the capacities of each battery module in a battery system, ensuring efficient operation and long-term stability of the battery system.

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 for active balancing control of a battery system. Background Art

[0002] The core operating mechanism of an electrochemical energy storage system involves connecting numerous battery cells in series and parallel configurations. The series connection boosts the system's output voltage, while the parallel connection increases the system's energy storage capacity to accommodate diverse power applications and load demands. This storage configuration optimizes power management efficiency and enhances the flexibility and reliability of energy utilization.

[0003] However, in energy storage battery packs composed of multiple battery modules, the individual cells within each module may come from different manufacturers and may experience varying degrees of aging and different State of Charge (SOC) levels. Failure to properly balance the battery capacity between these modules can negatively impact the battery system's charge and discharge efficiency and shorten its service life. In extreme cases, this imbalance can even trigger safety hazards.

[0004] Therefore, the industry urgently needs to develop a battery system active balancing control method that can effectively balance the capacity of each battery module in the battery system to ensure the efficient operation and long-term stability of the battery system. Summary of the Invention

[0005] Regarding the above-mentioned problem that the capacity between each battery module in the battery pack cannot be balanced in a timely manner, it will have a negative impact on the charging and discharging efficiency of the battery system.

[0006] The present application proposes a method for active balancing control of a battery system, wherein the battery system includes a plurality of battery modules, each of which includes at least one battery cell string; the control method is characterized in that the control method comprises the following steps:

[0007] S11: Sending the system current and balancing compensation current of each battery module;

[0008] S12: receiving multiple real-time available capacities;

[0009] S13: Calculate and obtain the average available capacity; and

[0010] S14: calculating in real time the difference between the average available capacity and the minimum of the multiple real-time available capacities, and when the difference is greater than a first preset value, starting active balancing to control the operation of the DC / DC balancing module so that the capacities of the multiple battery modules are actively balanced;

[0011] The multiple real-time available capacities are provided by multiple battery management units, each of which corresponds to each battery module one-to-one. Each battery management unit estimates the SOC (state of charge) of each cell string in the battery module and the SOH (state of health) of the battery module based on the voltage, temperature and preset information of each cell string in the corresponding battery module, the system current and the balancing compensation current of the battery module, and estimates the real-time available capacity of the battery module based on the minimum value of the multiple SOCs and the SOH.

[0012] Optionally, the control method further comprises the steps of:

[0013] S15: Evaluate the current theoretically allowed maximum balancing power according to the system current and battery state of power (SOP) table of the multiple battery modules.

[0014] Optionally, step S15 specifically includes:

[0015] S151: Calculating in real time the current theoretical maximum balancing current of the multiple battery modules according to the current maximum allowable charging current and the current maximum allowable discharging current obtained from the battery state of power (SOP) table of the multiple battery modules and the system current of the multiple battery modules;

[0016] S152: Calculate the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum module voltage of the multiple battery modules.

[0017] Optionally, the current theoretical maximum balancing current is the smaller value of the first current value of the multiple battery modules and the second current value of the multiple battery modules, wherein the first current value is the difference between the maximum allowable charging current of each battery module and the system current, and the second current value is the difference between the maximum allowable discharge current of each battery module and the system current.

[0018] Optionally, the control method further comprises the steps of:

[0019] S16: Determine whether the minimum power level of the DC / DC balancing module is less than the current theoretical maximum allowable balancing power. If so, execute step 12; if not, disable active balancing.

[0020] Optionally, after executing step S12, the control method further includes the steps of:

[0021] S121: Refresh the first battery module number and the second battery module number in real time, wherein the first battery module number is the module number of the battery module with the maximum value among the multiple real-time available capacities, and the second battery module number is the module number of the battery module with the minimum value among the multiple real-time available capacities.

[0022] Optionally, after executing step S14, the control method further includes the steps of:

[0023] S18: Send a request for balancing command and the current theoretically allowed maximum balancing power to the control unit of the DC / DC balancing module, and the control unit controls the DC / DC balancing module connected to the battery module with the first battery module number and the DC / DC balancing module connected to the battery module with the second battery module number to operate with the current theoretically allowed maximum balancing power, so that the battery module with the first battery module number transfers a preset amount of power to the battery module with the second battery module number.

[0024] Optionally, when the minimum value of the single cell voltages of the multiple battery cell strings in the battery module with the first battery module number is less than or equal to the first voltage value or the maximum value of the single cell voltages of the multiple battery cell strings in the battery module with the second battery module number is greater than or equal to the second voltage value, active balancing is turned off.

[0025] Optionally, step S18 specifically includes:

[0026] S181: accumulating the transferred power according to the balanced compensation current fed back by the controlled DC / DC balancing module, and when the accumulated value of the transferred power reaches the preset power, executing steps S12, S121, S13, and S14; and

[0027] S182: Clear the accumulated value of the transferred power and repeat step S18.

[0028] Optionally, if the balancing compensation current fed back by the controlled DC / DC balancing module exceeds a preset range, active balancing is turned off.

[0029] Optionally, when the difference is smaller than a second preset value, or a BMS (battery management system) of the battery system fails, active balancing is turned off.

[0030] The present application can achieve at least one of the following beneficial effects:

[0031] 1. This application estimates the real-time available capacity through a battery management unit, and then uses a battery controller to calculate the average available capacity based on multiple real-time available capacities. The difference between the average available capacity and the minimum of the multiple real-time available capacities is calculated in real time. When the difference is greater than a first preset value, active balancing is initiated, and power is transferred through a DC / DC balancing module to achieve capacity balancing between battery modules. This has greater practical application value, does not require additional energy storage components, and does not require additional hardware circuits. The balancing efficiency is higher, the system cost is lower, and problems such as over-balancing or under-balancing can be avoided, thereby improving the safety of the battery system and extending the battery life.

[0032] 2. Accumulate the transferred power according to the balanced compensation current fed back by the DC / DC balancing module. When the accumulated value of the transferred power reaches the preset power, refresh the first battery module number and the second battery module number. Use a step-by-step method to refresh the paired module number to ensure the efficiency of active balancing.

[0033] 3. The parameters used in the active balancing control of this application can be obtained from the battery management unit and the battery controller. The battery management unit is responsible for SOC estimation at the battery module level, and the battery controller is responsible for SOC estimation and balancing strategy control at the system level, thereby improving the scalability and flexibility of the system. Each battery management system performs SOC and SOH estimation independently to avoid mutual interference between different battery modules and improve estimation accuracy.

[0034] 4. Comprehensively consider multiple factors such as battery management system failure, DC / DC balancing module failure, balancing overcurrent, module capacity difference, and over-balancing protection at the end of charge and discharge to ensure the safety of the active balancing process; monitor the operating status of the DC / DC balancing module in real time, discover and handle faults in a timely manner, and provide overall system reliability; use constant power to transfer power, limit the charge and discharge current, and ensure the stability and safety of the active balancing process; end-of-charge protection, that is, if the minimum value of the single cell voltage of the multiple cell strings in the battery module with the first battery module number is less than the first voltage value or the maximum value of the single cell voltage of the multiple cell strings in the battery module with the second battery module number is greater than the second voltage value, turn off active balancing to avoid active balancing overvoltage or over-discharge, and protect the safety of the battery system;

[0035] 5. The active balancing control method of this application is compatible with battery modules from different manufacturers, providing system flexibility.

[0036] The above has generally summarized the features and technical advantages of the present application so that the following detailed description of the application can be better understood. The additional features and advantages of the present application will be described below, which form the subject matter of the claims of the present application. It will be understood 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 achieving 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

[0037] For a more complete understanding of the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0038] Figure 1 A schematic structural diagram of a battery system according to an embodiment of the present application is shown;

[0039] Figure 2 Shown Figure 1 Circuit diagram of the connection between the battery module and the DC / DC balancing module;

[0040] Figure 3 A flow chart showing a method for active balancing control of a battery system according to an embodiment of the present application is shown;

[0041] Figure 4 A more specific flow chart of the active balancing control method for a battery system according to an embodiment of the present application is shown.

[0042] 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

[0043] 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 indicated.

[0044] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. The terms "first," "second," "third," and so on (if any) in the description and claims of the present invention and in the drawings are used to distinguish similar items and are not necessarily used to describe a particular order or sequential sequence.

[0045] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the terms "coupled," "connected," and "connected" should be understood broadly. For example, they can refer to electrical connection or mutual communication, direct connection or indirect connection through an intermediary, internal communication between two components, or interaction between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on specific circumstances.

[0046] In addition, numerous specific details are provided in the following detailed description to better illustrate the present invention. Those skilled in the art will appreciate that the present invention can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main points of the present invention.

[0047] The active balancing control method of the present invention utilizes a relatively low amount of computation, is compatible with battery packs from different manufacturers, and has flexible application scenarios. Specific application scenario analysis is shown in the following table.

[0048] Table 1 Analysis of different application scenarios

[0049]

[0050] Based on the analysis of different application scenarios, the key to achieving active balancing is to accurately calculate the real-time available capacity of each battery module, and through the corresponding DC / DC balancing module, transfer power from battery modules with high available capacity to battery modules with low capacity.

[0051] Figure 1 A schematic structural diagram of a battery system according to an embodiment of the present application is shown. Figure 2 Shown Figure 1 The circuit diagram of the battery module connected to the DC / DC balancing module. Figure 1 and Figure 2As shown, the battery system includes multiple battery modules 11, 12, ..., 1n connected in series, each of which includes multiple strings of battery cells connected in series (not shown). The active balancing control device includes multiple battery management units (BMUs) 21, 22, ..., 2n, a DC / DC optimization module 20, and a battery control unit (BCU) 10. Each BMU 21, 22, ..., 2n corresponds one-to-one with each battery module 11, 12, ..., 1n. That is, one BMU connects to and manages one battery module. For example, BMU 21 connects to and manages battery module 11, BMU 22 connects to and manages battery module 12, and so on, with BMU 2n connecting to and managing battery module 1n. Multiple BMUs are connected to the BCU and communicate with each other. The DC / DC optimization module 20 includes multiple DC / DC balancing modules 201, 202, ..., 20n, each DC / DC balancing module corresponding to each battery module one-to-one. That is, one end of a DC / DC balancing module is connected in parallel to both ends of a battery module, and the other end of the DC / DC balancing module is connected between the DC bus DC BUS+ and DC BUS-. For example, one end of the DC / DC balancing module 201 is connected in parallel to both ends of a battery module 11, and the other end of the DC / DC balancing module 201 is connected between the DC bus DC BUS+ and DC BUS-. One end of the DC / DC balancing module 202 is connected in parallel to both ends of a battery module 12, and the other end of the DC / DC balancing module 202 is connected between the DC bus DC BUS+ and DC BUS-. Similarly, one end of the DC / DC balancing module 20n is connected in parallel to both ends of a battery module 1n, and the other end of the DC / DC balancing module 20n is connected between the DC bus DC BUS+ and DC BUS-.

[0052] In this embodiment, the BMU is the core component of the Battery Management System (BMS), responsible for monitoring and managing the status of the connected battery modules. The BMU comes with manufacturer-matched single-cell parameters, making it compatible with mixed battery module usage. When each battery module leaves the factory, preset single-cell information from the corresponding manufacturer, such as factory capacity, open-circuit voltage (OCV), direct current resistance (DCR), and aging curves, is imported into the BMU. This allows for individual battery module state-of-charge (SOX) estimation, which can include state-of-charge (SOC) and state-of-health (SOH), allowing for the mixing of battery modules from different manufacturers within the same battery system.

[0053] Figure 3A flow chart of a battery system active balancing control method according to an embodiment of the present application is shown. Figure 4 FIG. 1 shows a more specific flow chart of the active balancing control method for a battery system according to an embodiment of the present application. Figure 3 As shown, the battery system active balancing control method of the present application includes the following steps:

[0054] S11: Sending the system current and the balancing compensation current of each battery module.

[0055] Specifically, the BCU collects the system current on the main circuit of each battery module connected in series, as well as the balancing compensation current fed back by the DC / DC balancing module, and transmits the system current and balancing compensation current to each BMU. It should be noted that when battery modules are connected in series, the system current on the main circuit can be considered the system current of each battery module. The current used to calculate the State of Charge (SOC) of each cell string in the battery module (i.e., the total current of the battery module) is the sum of the system current and balancing compensation current of the battery module.

[0056] S12: Receive multiple real-time available capacities RemCapi,i>1.

[0057] Specifically, multiple BMUs report multiple real-time available capacities RemCapi to the BCU. That is, each BMU calculates the real-time available capacity of the corresponding battery module in real time and reports the real-time available capacity to the BCU.

[0058] S13: Calculate and obtain the available capacity mean RemCap_mean.

[0059] Specifically, the BCU averages multiple real-time available capacities to obtain the available capacity mean RemCap_mean, which is used as the active balancing target.

[0060] S14: Calculate in real time the difference between the available capacity mean RemCap_mean and the minimum value RemCap_min among the multiple real-time available capacities RemCapi. When the difference is greater than a first preset value, start active balancing to control the action of the DC / DC balancing module so that the capacities of the multiple battery modules are actively balanced.

[0061] Specifically, the BCU calculates in real time the difference between the available capacity mean RemCap_mean and the minimum value of the multiple real-time available capacities RemCapi. When the difference is greater than a first preset value, active balancing is started to control the action of the DC / DC balancing module so that the capacities of the multiple battery modules are actively balanced.

[0062] The multiple real-time available capacities RemCapi are provided by multiple battery management units, each of which corresponds to each battery module one-to-one. Each battery management unit estimates the SOC (state of charge) of each cell string in the battery module and the SOH (state of health) of the battery module based on the voltage, temperature and preset information of each cell string in the corresponding battery module, the system current and the balancing compensation current of the battery module, and estimates the real-time available capacity RemCap of the battery module based on the minimum value of the multiple SOCs and the SOH.

[0063] Specifically, each BMU is used to estimate the state of charge (SOC) and state of health (SOH) of each cell string in the battery module based on the voltage, temperature and preset information of each cell string in the corresponding battery module (which can be the parameters of the cell string provided by the manufacturer, such as factory capacity, OCV, DCR, aging curve and other SOX algorithm parameters), the system current and balanced compensation current of the battery module, and estimate the real-time available capacity RemCap of the battery module based on the minimum value SOCmin and the SOH among the multiple SOCs, where RemCap = factory capacity * SOH * SOCmin. It should be noted that the voltage of each cell string in the same battery module can be different, and thus the SOC corresponding to each cell string can also be different, where the minimum value SOCmin can be the SOC corresponding to the cell string with the lowest voltage in the battery module. Specifically, taking the battery management unit 21 as an example, the BMU 21 estimates the state of charge (SOC) of each cell string in the battery module 11 and the state of health (SOH) of the battery module 11 based on the voltage, temperature, and preset information of each cell string in the battery module 11, the system current of the battery module 11, and the balancing compensation current. Furthermore, the BMU 21 estimates the real-time available capacity RemCap1 of the battery module 11 based on the minimum value SOCmin among the multiple SOCs and the SOH. In this embodiment, the BMU is responsible for module-level SOC estimation, and the BCU is responsible for system-level SOC estimation and active balancing strategy control, providing scalability and flexibility for the battery system. Each BMU performs SOX estimation independently, avoiding mutual interference between different battery modules and improving estimation accuracy.

[0064] In this embodiment, the BMU collects the temperature and voltage of each battery cell string in the battery module connected thereto.

[0065] The active balancing method of this embodiment can promptly detect issues such as capacity inconsistencies between battery modules, achieving balancing between the modules. This method has practical application value, reduces battery system failure rates, and reduces maintenance costs. Furthermore, the structure is relatively simple, primarily relying on the BMU and BCU for SOC estimation, eliminating the need for additional hardware circuitry. This reduces complexity, simplifies maintenance, extends battery life, and reduces maintenance costs. Furthermore, the active balancing control method of this embodiment is compatible with battery modules from different manufacturers, enhancing the flexibility of the battery system.

[0066] In this embodiment, the parameters used for active balancing, such as system current, balancing compensation current, cell string voltage, temperature, and preset information, can all be obtained through the BMU and BCU, without increasing computational complexity or hardware.

[0067] Furthermore, the BCU 10 is configured to evaluate the current theoretically allowed maximum balancing power based on the system current and battery state of power (SOP) table of the plurality of battery modules. In this embodiment, the SOP table can generally be represented by a short-term peak power value.

[0068] Furthermore, the control method further comprises the steps of:

[0069] S15: Evaluate the current theoretically allowed maximum balancing power according to the system current and battery state of power (SOP) table of the multiple battery modules.

[0070] Specifically, the BCU 10 is configured to estimate in real time the current theoretically allowed maximum balancing power according to the maximum allowed charging current and the maximum allowed discharging current obtained from the SOP tables of the multiple battery modules and the system current BMSCur of the multiple battery modules.

[0071] Furthermore, the step S15 specifically includes:

[0072] S151: Calculating the current theoretical maximum balancing current of the multiple battery modules in real time according to the current maximum allowable charging current and the current maximum allowable discharging current obtained from the battery state of power (SOP) table of the multiple battery modules and the system current of the multiple battery modules.

[0073] Specifically, the BCU 10 is used to estimate the current theoretical maximum balancing current MaxBalCur in real time based on the maximum allowable charging current and maximum allowable discharging current obtained from the SOP tables of the multiple battery modules and the system current BMSCur of the multiple battery modules. The current theoretical maximum balancing current MaxBalCur is the difference between the SOP allowable current MaxSOPCur and the system current BMSCur of the battery module, that is, MaxBalCur = MaxSOPCur - BMSCur. In order to control the accuracy error, some balancing current error can be reserved so that the current theoretical maximum balancing current MaxBalCur is equal to the SOP allowable current MaxSOPCur minus the system current BMSCur of the battery module minus the balancing current error BalCurSplError, that is, MaxBalCur = MaxSOPCur - BMSCur - BalCurSplError. It should be noted that the SOP table is included with the battery module when it leaves the factory. The BMU can obtain the maximum allowable charging current and the maximum allowable discharging current by looking up the SOP table. The maximum allowable charging current and the maximum allowable discharging current may be related to parameters such as the temperature of the battery string, the current SOC of the battery string, and the voltage of the battery string.

[0074] S152: Calculate the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum module voltage of the multiple battery modules.

[0075] Specifically, the BCU 10 is used to calculate the current theoretical maximum allowable balancing power MaxBalPower based on the current theoretical maximum balancing current MaxBalCur and the minimum total voltage value MinModuleVol among the module voltages of the multiple battery modules, that is, MaxBalPower=MaxBalCur*MinModuleVol, where the minimum total voltage value MinModuleVol can be the minimum value of the multiple battery module voltages.

[0076] Furthermore, the current theoretical maximum balancing current MaxBalCur is the smaller value of the first current value of the multiple battery modules and the second current value of the multiple battery modules, wherein the first current value is the difference between the maximum allowable charging current of each battery module and the system current, and the second current value is the difference between the maximum allowable discharge current of each battery module and the system current. It should be noted that the maximum allowable charging current and the maximum allowable discharge current obtained by looking up the SOP table are the boundaries of the SOP table, and the system current and the balancing compensation current of the battery module cannot exceed the boundaries of the SOP table after superposition, that is, the system current and the balancing compensation current of the battery module cannot exceed the maximum allowable charging current after superposition, or the system current and the balancing compensation current of the battery module cannot exceed the maximum allowable discharge current after superposition.

[0077] In this embodiment, when the current theoretical maximum balancing current MaxBalCur is 0, active balancing is not started. For example, the balancing start flag bit can be set to 0.

[0078] Furthermore, the control method further comprises the steps of:

[0079] S16: Determine whether the minimum power level of the DC / DC balancing module is less than the current theoretical maximum allowable balancing power. If so, execute step 12; if not, disable active balancing.

[0080] Specifically, the BCU 10 determines whether the minimum power level of the DC / DC balancing module is less than the current theoretically allowed maximum balancing power MaxBalPower. If so, the balancing overcurrent flag is set to 0 and step S12 is executed. If not, the balancing overcurrent flag is set to 1, disabling active balancing. In other words, if the balancing power corresponding to the minimum balancing power level of the DC / DC balancing module is greater than or equal to the current theoretically allowed maximum balancing power MaxBalPower, a balancing failure is determined to have occurred, the balancing overcurrent flag is set to 1, and active balancing is disabled. If the balancing power corresponding to the minimum balancing power level of the DC / DC balancing module is less than the current theoretically allowed maximum balancing power MaxBalPower, a balancing overcurrent failure is determined not to have occurred, the balancing overcurrent flag is set to 0, and subsequent active balancing steps are continued. In this embodiment, the BCU 10 provides the current theoretically allowed maximum balancing power to control the operation of the corresponding DC / DC balancing module. By determining whether the balancing power corresponding to the balancing power level is greater than the current theoretically allowed maximum balancing power MaxBalPower, and if so, setting the balancing overcurrent flag, the safety of the active balancing process is ensured.

[0081] Furthermore, after executing step S12, the control method further includes the steps of:

[0082] S121: Refresh the first battery module number and the second battery module number in real time, wherein the first battery module number is the module number of the battery module with the maximum value among the multiple real-time available capacities, and the second battery module number is the module number of the battery module with the minimum value among the multiple real-time available capacities.

[0083] Specifically, if the balancing overcurrent flag is 0, i.e., if there is no balancing overcurrent fault, the BCU 10 determines whether to initiate active balancing based on the real-time available capacity of the battery modules. Specifically, the BCU 10 is configured to refresh the first battery module number and the second battery module number in real time, wherein the first battery module number is the module number of the battery module with the maximum value among the multiple real-time available capacities, and the second battery module number is the module number of the battery module with the minimum value among the multiple real-time available capacities. It should be noted that the first battery module number and the second battery module number serve as the module numbers for active balancing pairing.

[0084] Furthermore, the BCU 10 refreshes the first battery module number and the second battery module number in real time as active balancing paired module numbers. Calculate the difference BalDifCap between the available capacity mean RemCap_mean and the minimum value RemCap_min among the multiple real-time available capacities. Wherein BalDifCap=RemCap_mean-RemCap_min. When the difference BalDifCap is greater than the first preset value, active balancing is started, and the balancing start flag is set to 1. Specifically, when the balancing overcurrent flag is 0 and the difference BalDifCap is greater than the first preset value, the balancing start flag is set to 1, wherein the first preset value can be the product of the nominal capacity and the first preset ratio, wherein the first preset ratio can be 5%, but is not limited thereto, and any value that can meet the requirements is acceptable.

[0085] Furthermore, the step S14 specifically further includes: outputting the first battery module number and the second battery module number.

[0086] Specifically, the BCU 10 sets the balancing start flag to 1 and outputs the balancing paired module numbers, namely, the first battery module number and the second battery module number.

[0087] Furthermore, if the difference BalDifCap is less than a second preset value, the BCU 10 disables active balancing and sets the balancing enable flag to 0. The second preset value may be the product of the nominal capacity and a second preset ratio. The second preset ratio may be 2%, but is not limited to this value and may be any value that meets the requirements. By comparing the difference BalDifCap with the second preset value, the security of the active balancing process is ensured.

[0088] Furthermore, active balancing is performed according to the paired module number, and the paired module number is refreshed step by step. Specifically, after executing the step S14, the control method further includes the steps of:

[0089] S18: Send a request for balancing command and the current theoretically allowed maximum balancing power to the control unit of the DC / DC balancing module, and the control unit controls the DC / DC balancing module connected to the battery module with the first battery module number and the DC / DC balancing module connected to the battery module with the second battery module number to operate with the current theoretically allowed maximum balancing power, so that the battery module with the first battery module number transfers a preset amount of power to the battery module with the second battery module number.

[0090] Specifically, when active balancing is initiated, the BCU 10 is configured to send a balancing request command and the current theoretically allowed maximum balancing power to the control unit of the DC / DC balancing module, thereby controlling the DC / DC balancing module connected to the battery module with the first battery module number and the DC / DC balancing module connected to the battery module with the second battery module number to operate at the current theoretically allowed maximum balancing power, causing the battery module with the first battery module number to transfer a preset amount of power to the battery module with the second battery module number. In this embodiment, multiple DC / DC balancing modules are connected to the same control unit. In other embodiments, each DC / DC balancing module can be connected to its own control unit, that is, each DC / DC balancing module has a one-to-one correspondence with each control unit. In this embodiment, the DC / DC balancing module calculates the duty cycle of the control signal based on the current theoretically allowed maximum balancing power to control the opening or closing of the power switches within the DC / DC balancing module.

[0091] Further, when the minimum value of the voltages of the multiple single cells in the battery module with the first battery module number is less than the first voltage value or the maximum value of the voltages of the multiple single cells in the battery module with the second battery module number is greater than the second voltage value, the balancing start flag is set to 0, and BCU 10 is used to turn off active balancing.

[0092] Specifically, when the minimum voltage of the multiple single cells in the battery module with the first battery module number is less than or equal to the first voltage value, for example, 3.05V, the balancing start flag is set to 0, and the BCU 10 is used to turn off active balancing to avoid overdischarge. When the maximum voltage of the multiple single cells in the battery module with the second battery module number is greater than or equal to the second voltage value, for example, 3.45V, the balancing start flag is set to 0, and the BCU 10 is used to turn off active balancing to avoid overcharging. This end-of-charge and discharge protection can prevent active balancing from overvoltage or overdischarge. The BCU 10 will turn off active balancing to protect the safety of the battery system.

[0093] The step S18 specifically includes:

[0094] S181: Accumulate the transferred power according to the balanced compensation current fed back by the controlled DC / DC balancing module. When the accumulated value of the transferred power reaches the preset power, execute steps S12, S121, S13, and S14.

[0095] Specifically, the BCU 10 is configured to accumulate transferred power based on the balancing compensation current fed back by the controlled DC / DC balancing module, where the accumulated value of the transferred power can be the product of the balancing compensation current and the duration t of the balancing compensation current. When the accumulated value of the transferred power reaches the preset power level, steps S12, S121, S13, and S14 are executed. That is, when the transferred power reaches the preset power level, the BCU 10 re-receives the real-time available capacities reported by multiple BMUs and refreshes the first and second battery module numbers in real time as new balancing paired module numbers. The average available capacity is recalculated, and the difference between the average available capacity and the minimum of the multiple real-time available capacities is calculated. When the difference is greater than a first preset value, the balancing start flag is set to 1, initiating active balancing, and outputting the balancing paired module numbers, namely, the first and second battery module numbers.

[0096] S182: Clear the accumulated value of the transferred power and repeat step S18.

[0097] Specifically, after obtaining the new balancing paired module number, the BCU 10 clears the accumulated transferred power value and then executes step S18. That is, after clearing the accumulated transferred power value, the BCU 10 sends a balancing request command and the current theoretically allowed maximum balancing power to the control unit of the DC / DC balancing module, thereby controlling the DC / DC balancing module connected to the battery module with the first battery module number and the DC / DC balancing module connected to the battery module with the second battery module number to operate at the current theoretically allowed maximum balancing power, causing the battery module with the first battery module number to transfer a preset power value to the battery module with the second battery module number. When the accumulated transferred power value based on the balancing compensation current feedback from the DC / DC balancing module reaches the preset power value, steps S12, S121, S13, and S14 are executed. This step-by-step refresh of the paired module numbers ensures active balancing efficiency. Furthermore, the constant power mode for power transfer limits the charge and discharge currents, ensuring the stability and safety of the active balancing process.

[0098] Furthermore, if the balancing compensation current fed back by the controlled DC / DC balancing module exceeds a preset range, active balancing is turned off.

[0099] Specifically, the controlled DC / DC balancing module will feedback a balancing compensation current. The BCU 10 determines in real time whether the balancing compensation current feedback from each DC / DC converter matches the current theoretical maximum allowable balancing power (reserving time for active balancing). When the balancing compensation current exceeds a preset range, it indicates a possible balancing compensation current overshoot or undershoot. If this mismatch persists for longer than a predetermined time, the DC / DC balancing module is deemed faulty, the balancing fault flag is set to 1, active balancing is disabled, and the balancing enable flag is set to 0. It should be noted that the balancing fault flag is initially set to 0. When a fault occurs, it is set to 1 and remains so, preserving the fault clear instruction and ensuring the safety of the active balancing process.

[0100] Furthermore, when a serious fault occurs in the BMS, such as overvoltage, undervoltage, overcurrent or overtemperature, the battery controller 10 sets the balancing start flag to 0 to turn off active balancing to ensure the safety of the active balancing process.

[0101] The active balancing control method of the present application is compatible with battery modules of different manufacturers, different aging degrees and different SOC states. By step-by-step refreshing of paired module numbers, the balanced paired modules are dynamically adjusted to ensure balancing efficiency. By calculating the actual balancing power, over-balancing or under-balancing is avoided, and the capacity balancing between battery modules is well achieved, which has more practical application value. It comprehensively considers various factors such as BSM failure, DC / DC balancing module failure, balancing overcurrent, over-balancing at the end of charge and discharge, and other balancing protection factors to ensure the safety of the active balancing process. By estimating SOX separately for each BMU, mutual interference between different battery modules is avoided, thereby improving the estimation accuracy. By directly controlling the DC / DC balancing module for power transfer, no additional energy storage unit is required, and no additional hardware circuit is required. The active balancing efficiency is higher and the battery system cost is lower.

[0102] 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.

[0103] Furthermore, the scope of this application is not limited to the particular embodiments of the processes, machines, manufactures, compositions of matter, means, methods, and steps described in this specification. Those skilled in the art will readily appreciate from the disclosure of this application that, in accordance with this application, currently existing or later developed processes, machines, manufactures, compositions of matter, means, methods, or steps may be utilized that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein. Accordingly, it is intended that the appended claims include within their scope such processes, machines, manufactures, compositions of matter, means, methods, or steps.

Claims

1. A method for active balancing control of a battery system, wherein the battery system comprises a plurality of battery modules, each of which comprises at least one battery cell string; The control method comprises the following steps: S11: Sending the system current and balancing compensation current of each battery module; S12: receiving multiple real-time available capacities; S13: Calculate and obtain the average available capacity; and S14: calculating in real time the difference between the average available capacity and the minimum of the multiple real-time available capacities, and when the difference is greater than a first preset value, starting active balancing to control the operation of the DC / DC balancing module so that the capacities of the multiple battery modules are actively balanced; The multiple real-time available capacities are provided by multiple battery management units, each of which corresponds to each battery module on a one-to-one basis. Each battery management unit estimates the SOC of each cell string in the battery module and the SOH of the battery module based on the voltage, temperature, and preset information of each cell string in the corresponding battery module, the system current, and the balancing compensation current of the battery module, and estimates the real-time available capacity of the battery module based on the minimum value of the multiple SOCs and the SOH. The control method further comprises the steps of: S151: Calculating in real time the current theoretical maximum balancing current of the multiple battery modules according to the current maximum allowable charging current and the current maximum allowable discharging current obtained from the battery power status tables of the multiple battery modules and the system currents of the multiple battery modules; S152: Calculating the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum module voltage of the multiple battery modules; The current theoretical maximum balancing current is the smaller value of the first current value of the multiple battery modules and the second current value of the multiple battery modules, wherein the first current value is the difference between the maximum allowable charging current of each battery module and the system current, and the second current value is the difference between the maximum allowable discharge current of each battery module and the system current.

2. The battery system active balancing control method according to claim 1, characterized in that: The control method further comprises the steps of: S16: Determine whether the minimum power level of the DC / DC balancing module is less than the current theoretical maximum allowable balancing power. If so, execute step 12; if not, disable active balancing.

3. The battery system active balancing control method according to claim 2, characterized in that: After executing step S12, the control method further includes the steps of: S121: Refresh the first battery module number and the second battery module number in real time, wherein the first battery module number is the module number of the battery module with the maximum value among the multiple real-time available capacities, and the second battery module number is the module number of the battery module with the minimum value among the multiple real-time available capacities.

4. The battery system active balancing control method according to claim 3, characterized in that: After executing step S14, the control method further includes the steps of: S18: Send a request for balancing command and the current theoretically allowed maximum balancing power to the control unit of the DC / DC balancing module, and the control unit controls the DC / DC balancing module connected to the battery module with the first battery module number and the DC / DC balancing module connected to the battery module with the second battery module number to operate with the current theoretically allowed maximum balancing power, so that the battery module with the first battery module number transfers a preset amount of power to the battery module with the second battery module number.

5. The battery system active balancing control method according to claim 3, characterized in that: When the minimum value of the single cell voltages of the multiple battery cell strings in the battery module with the first battery module number is less than or equal to the first voltage value or the maximum value of the single cell voltages of the multiple battery cell strings in the battery module with the second battery module number is greater than or equal to the second voltage value, active balancing is turned off.

6. The battery system active balancing control method according to claim 4, wherein: The step S18 specifically includes: S181: accumulating the transferred power according to the balanced compensation current fed back by the controlled DC / DC balancing module, and when the accumulated value of the transferred power reaches the preset power, executing steps S12, S121, S13, and S14; and S182: Clear the accumulated value of the transferred power and repeat step S18.

7. The battery system active balancing control method according to claim 6, characterized in that: If the balancing compensation current fed back by the controlled DC / DC balancing module exceeds a preset range, active balancing is turned off.

8. The battery system active balancing control method according to claim 1, characterized in that: When the difference is less than a second preset value, or a BMS of the battery system fails, active balancing is turned off.

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