Active equalization control method for battery system

Abstract

The invention provides a battery system active equalization control method, and relates to the technical field of energy storage system battery management. The active equalization control method of the battery system comprises system current and equalization compensation current of a lower battery module; receiving a plurality of real-time available capacities; calculating to obtain an available capacity mean value; and calculating the difference value between the average value of the available capacities and the minimum value in the plurality of real-time available capacities in real time, and when the difference value is greater than a first preset value, starting active equalization to control the DC / DC equalization module to act, so that the capacities of the plurality of battery modules are actively equalized. According to the embodiment of the invention, the capacity of each battery module in the battery system can be effectively balanced, and the efficient operation and long-term stability of the battery system are ensured.

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 the electrochemical energy storage system involves configuring many battery cells in series and parallel, increasing the system's output voltage through series connection, and increasing the system's energy storage capacity through parallel connection to adapt to diverse power application scenarios and load requirements. This energy storage configuration optimizes power management efficiency and improves the flexibility and reliability of energy utilization.

[0003] However, in an energy storage battery pack composed of multiple battery modules, since the cells in each battery module may come from different manufacturers and have different degrees of aging and different state of charge (SOC) levels, if the battery capacity between these modules is not balanced in time, it will have a negative impact on the charging and discharging efficiency of the battery system and shorten the service life of the battery system. In extreme cases, this imbalance may also 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 the battery modules 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 includes the following steps: S11: Sending the system current and the balancing compensation current of each battery module; S12: receiving multiple real-time available capacities; S13: Calculate and obtain the average value of available capacity; and S14: calculating in real time the difference between the average value of the available capacity and the minimum value 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 one-to-one, and each of the battery management units estimates the SOC (state of charge) of each battery 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 battery 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.

[0007] Optionally, the control method further comprises the steps of: S15: Evaluate the current theoretically allowed maximum balancing power according to the system currents of the plurality of battery modules and a battery state of power (SOP) table.

[0008] Optionally, the step S15 specifically includes: 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 state (SOP) table of the multiple battery modules and the system current of the multiple battery modules; S152: Calculate the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum value of the module voltage among the multiple battery modules.

[0009] Optionally, the current theoretical maximum balancing current is a smaller value between a first current value of the multiple battery modules and a 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.

[0010] Optionally, 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 theoretically allowed maximum balancing power. If so, execute step 12; if not, turn off active balancing.

[0011] Optionally, 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 where the maximum value of the multiple real-time available capacities is located, and the second battery module number is the module number of the battery module where the minimum value of the multiple real-time available capacities is located.

[0012] Optionally, after executing step S14, the control method further includes the steps of: S18: Send a request for balancing command and the current theoretical maximum balancing power allowed to the control unit of the DC / DC balancing module, 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 theoretical maximum balancing power allowed, 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.

[0013] 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.

[0014] Optionally, the step S18 specifically includes: S181: accumulating the transferred power according to the balanced compensation current fed back by the DC / DC balanced module under control, and when the accumulated value of the transferred power reaches the preset power, executing the steps S12, S121, S13, and S14; and S182: Clear the accumulated value of the transferred power and repeat step S18.

[0015] Optionally, if the balancing compensation current fed back by the DC / DC balancing module in the controlled action exceeds a preset range, active balancing is turned off.

[0016] Optionally, when the difference is smaller than a second preset value, or a battery management system (BMS) of the battery system fails, active balancing is turned off.

[0017] The present application can achieve at least one of the following beneficial effects: 1. This application estimates the real-time available capacity through a battery management unit, and then obtains the average available capacity through a battery controller according to multiple real-time available capacities, and calculates the difference between the average available capacity and the minimum of multiple real-time available capacities in real time. When the difference is greater than a first preset value, active balancing is started, and power is transferred through a DC / DC balancing module to achieve capacity balancing between battery modules. It has more practical application value, does not require additional energy storage elements, does not require additional hardware circuits, has higher balancing efficiency, and lower system cost. It can also avoid problems such as over-balancing or under-balancing, thereby improving the safety of the battery system and extending the battery life. 2. Accumulate the transferred power according to the balanced compensation current fed back by the DC / DC balanced module, and when the accumulated value of the transferred power reaches the preset power, refresh the first battery module number and the second battery module number, and use a step-by-step method to refresh the paired module number to ensure the efficiency of active balancing; 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 the SOC estimation at the battery module level, and the battery controller is responsible for the SOC estimation and balancing strategy control at the system level, which improves the scalability and flexibility of the system. Each battery management system performs SOC and SOH estimation separately to avoid mutual interference between different battery modules and improve estimation accuracy. 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 time, and provide overall system reliability; use constant power to transfer power, limit the size of the charge and discharge current, and ensure the stability and safety of the active balancing process; end-of-charge and discharge protection, that is, 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, avoid active balancing overvoltage or over-discharge, and protect the safety of the battery system; 5. The active balancing control method of the present application is compatible with battery modules from different manufacturers, providing system flexibility.

[0018] 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

[0019] 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 schematic diagram showing the structure of a battery system according to an embodiment of the present application is shown; Figure 2 Shows Figure 1 The circuit diagram of the battery module connected to the DC / DC balancing module; Figure 3A flow chart showing a method for active balancing control of a battery system according to an embodiment of the present application is shown; 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.

[0020] 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

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The active balancing control method of the present invention utilizes a relatively low amount of calculation, is compatible with battery packs from different manufacturers, and has flexible application scenarios. The specific application scenario analysis is shown in the following table.

[0026] Table 1 Analysis of different application scenarios

[0027] According to 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.

[0028] Figure 1 A schematic structural diagram of a battery system according to an embodiment of the present application is shown. Figure 2 Shows Figure 1 The circuit diagram of the battery module connected to the DC / DC balancing module. Figure 1 and Figure 2 As shown, the battery system includes a plurality of battery modules 11, 12, ..., 1n connected in series, and each battery module includes a plurality of battery cell strings connected in series (not shown in the figure). The active balancing control device includes a plurality of battery management units (BMU) 21, 22, ..., 2n, a DC / DC optimization module 20, and a battery controller (BCU) 10. Each BMU 21, 22, ..., 2n corresponds to each battery module 11, 12, ..., 1n one by one, that is, one BMU connects to and manages one battery module, for example, BMU21 connects to and manages battery module 11, BMU 22 connects to and manages battery module 12, and so on, BMU 2n connects to and manages 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 corresponds to each battery module one by one, that is, one end of a DC / DC balancing module is connected in parallel to the two 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 the two 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 the two 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 the two 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-.

[0029] In this embodiment, the BMU is the core part of the battery management system (BMS), which is responsible for monitoring and managing the status of the battery modules connected to it. The BMU comes with single cell parameters that match the manufacturer and is compatible with mixed use of battery modules. When each battery module leaves the factory, the preset information of the single cell of the corresponding manufacturer will be imported into the BMU, such as factory capacity, open circuit voltage (OCV), DC internal resistance (DCR), and aging curve parameters, so that each battery module can perform battery state (SOX) estimation separately, where SOX can include state of charge (SOC) and state of health (SOH), etc., which is compatible with mixed use of battery modules from different manufacturers in the same battery system.

[0030] Figure 3 A flow chart of a battery system active balancing control method according to an embodiment of the present application is shown. Figure 4 FIG. 2 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: S11: Sending the system current and the balancing compensation current of each battery module.

[0031] Specifically, the BCU collects the system current on the main circuit of each battery module in series and the balanced compensation current fed back by the DC / DC balancing module, and sends the system current and balanced compensation current to each BMU. It should be noted that the battery modules are connected in series, and the system current on the main circuit can be considered as 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 (that is, the total current of the battery module) is the sum of the system current and the balanced compensation current of the battery module.

[0032] S12: Receive multiple real-time available capacities RemCapi,i>1.

[0033] 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.

[0034] S13: Calculate and obtain the available capacity mean RemCap_mean.

[0035] Specifically, the BCU averages multiple real-time available capacities to obtain the available capacity mean RemCap_mean as an active balancing target.

[0036] 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, and 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.

[0037] 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.

[0038] 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, and each of the battery management units estimates the SOC (state of charge) of each battery 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 battery 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.

[0039] 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 according to the voltage, temperature and preset information of each cell string in the corresponding battery module (which may 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 to estimate the real-time available capacity RemCap of the battery module according to 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 may be different, so the SOC corresponding to each cell string may also be different, where the minimum value SOCmin may 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, 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 according to the voltage, temperature and preset information of each cell string in the battery module 11, the system current and the balancing compensation current of the battery module 11, and estimates the real-time available capacity RemCap1 of the battery module 11 according to 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, which provides scalability and flexibility of the battery system. Each BMU performs SOX estimation separately, avoiding mutual interference between different battery modules and providing estimation accuracy.

[0040] In this embodiment, the BMU collects the temperature and voltage of each battery cell string in the battery module connected thereto.

[0041] The active balancing method in this embodiment can timely discover problems such as inconsistent capacity between battery modules, achieve balancing between various battery modules, have more practical application value, reduce the failure rate of the battery system, reduce maintenance costs, and have a relatively simple structure. It mainly relies on BMU and BCU to estimate SOC, does not require additional hardware circuits, has low complexity, is easy to maintain, extends battery life and reduces maintenance costs. In addition, the active balancing control method in this embodiment is compatible with battery modules produced by different manufacturers, improving the flexibility of the battery system.

[0042] In this embodiment, the parameters used for active balancing, such as system current, balancing compensation current, cell string voltage, temperature and preset information, etc., can all be obtained through the BMU and BCU, without increasing the computational complexity or hardware.

[0043] Furthermore, the BCU 10 is used to evaluate the current theoretically allowed maximum balancing power according to the system current and battery power state (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.

[0044] Furthermore, the control method further comprises the steps of: S15: Evaluate the current theoretically allowed maximum balancing power according to the system currents of the plurality of battery modules and a battery state of power (SOP) table.

[0045] Specifically, the BCU 10 is used 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.

[0046] Further, the step S15 specifically includes: S151: Calculate 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 state (SOP) table of the multiple battery modules and the system current of the multiple battery modules.

[0047] Specifically, BCU 10 is used to estimate the current theoretical maximum balancing current MaxBalCur in real time based on the maximum allowable charging current and the maximum allowable discharging current obtained from the SOP table 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 allowed current MaxSOPCur and the system current BMSCur of the battery module, that is, MaxBalCur=MaxSOPCur-BMSCur. In order to control the accuracy error, part of the balancing current error can be reserved so that the current theoretical maximum balancing current MaxBalCur is equal to the SOP allowed 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 built into 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.

[0048] S152: Calculate the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum value of the module voltage among the multiple battery modules.

[0049] Specifically, 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.

[0050] Further, 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 checking 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.

[0051] 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.

[0052] Furthermore, 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 theoretically allowed maximum balancing power. If so, execute step 12; if not, turn off active balancing.

[0053] Specifically, the BCU 10 determines whether the minimum power level of the DC / DC balancing module is less than the current theoretical 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 and active balancing is turned off. That is to say, 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 theoretical maximum balancing power MaxBalPower, it is determined that a balancing fault has occurred, then the balancing overcurrent flag is set to 1 and active balancing is turned off; if the balancing power corresponding to the minimum balancing power level of the DC / DC balancing module is less than the current theoretical maximum balancing power MaxBalPower, it is determined that no balancing overcurrent fault has occurred, then the balancing overcurrent flag is set to 0 and the subsequent active balancing steps are continued. In this embodiment, the BCU 10 provides the current theoretical maximum balancing power to control the corresponding DC / DC balancing module action. By determining whether the balancing power corresponding to the balancing power level is greater than the current theoretical maximum balancing power MaxBalPower, if so, the balancing overcurrent flag is set to ensure the safety of the active balancing process.

[0054] Further, 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 where the maximum value of the multiple real-time available capacities is located, and the second battery module number is the module number of the battery module where the minimum value of the multiple real-time available capacities is located.

[0055] Specifically, under the premise that the balancing overcurrent flag is 0, that is, there is no balancing overcurrent fault, the BCU 10 determines whether to start active balancing according to the real-time available capacity of the battery module. Specifically, the BCU 10 is used 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 where the maximum value of the multiple real-time available capacities is located, and the second battery module number is the module number of the battery module where the minimum value of the multiple real-time available capacities is located. It should be noted that the first battery module number and the second battery module number are paired as module numbers for active balancing.

[0056] Further, 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.

[0057] Furthermore, the step S14 specifically includes: outputting the first battery module number and the second battery module number.

[0058] Specifically, the BCU 10 sets the balancing start flag bit to 1 and outputs the balancing paired module numbers, namely, the first battery module number and the second battery module number.

[0059] Further, if the difference BalDifCap is less than a second preset value, the BCU 10 turns off active balancing and sets the balancing start flag to 0, wherein the second preset value may be the product of the nominal capacity and the second preset ratio, wherein the second preset ratio may be 2%, but is not limited thereto, and any value that can meet the requirements may be used. By comparing the difference BalDifCap with the second preset value, the safety of the active balancing process is ensured.

[0060] Further, 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: S18: Send a request for balancing command and the current theoretical maximum balancing power allowed to the control unit of the DC / DC balancing module, 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 theoretical maximum balancing power allowed, 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.

[0061] Specifically, when active balancing is started, the BCU 10 is used to send a request balancing command and the current theoretical maximum allowed balancing power to the control unit of the DC / DC balancing module to control 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 act with the current theoretical maximum allowed balancing power, so that the battery module with the first battery module number transfers a preset amount of electricity 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 corresponds to each control unit one by one. In this embodiment, the DC / DC balancing module calculates the duty cycle of the control signal according to the current theoretical maximum allowed balancing power to control the power switch in the DC / DC balancing module to be turned on or off.

[0062] 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.

[0063] Specifically, when the minimum voltage value 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 BCU 10 is used to turn off active balancing to avoid over-discharge. When the maximum voltage value 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 BCU 10 is used to turn off active balancing to avoid overcharging. Through this end-of-charge and discharge protection, active balancing overvoltage or over-discharge can be avoided, and BCU 10 will turn off active balancing to protect the safety of the battery system.

[0064] The step S18 specifically includes: S181: Accumulate the transferred power according to the balanced compensation current fed back by the DC / DC balanced module under control, and when the accumulated value of the transferred power reaches the preset power, execute the steps S12, S121, S13, and S14.

[0065] Specifically, the BCU 10 is used to accumulate the transfer amount according to the balanced compensation current fed back by the DC / DC balancing module of the controlled action, wherein the accumulated value of the transfer amount can be the product of the balanced compensation current and the duration t of the balanced compensation current. When the accumulated value of the transfer amount reaches the preset amount, the steps S12, S121, S13, and S14 are executed. That is, when the transfer amount reaches the preset amount, the BCU 10 re-receives the real-time available capacity reported by multiple BMUs, and refreshes the first battery module number and the second battery module number in real time as new balanced paired module numbers. The average available capacity is recalculated, and the difference between the average available capacity and the minimum value of the multiple real-time available capacities is calculated. When the difference is greater than the first preset value, the balancing start flag is set to 1, active balancing is started, and the balancing paired module number, i.e., the first battery module number and the second battery module number, is output.

[0066] S182: Clear the accumulated value of the transferred power and repeat step S18.

[0067] Specifically, after the BCU 10 obtains the new balancing paired module number, it clears the accumulated value of the transferred power, and then executes step S18. That is, after clearing the accumulated value of the transferred power, the BCU 10 sends a request for balancing command and the current theoretical maximum allowed balancing power to the control unit of the DC / DC balancing module to control 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 act with the current theoretical maximum allowed balancing power, so that the battery module with the first battery module number transfers the preset power to the battery module with the second battery module number, and when the accumulated transferred power according to the balanced compensation current fed back by the DC / DC balancing module reaches the preset power, the steps S12, S121, S13, and S14 are executed. By refreshing the paired module number in this step-by-step manner, the active balancing efficiency is guaranteed, and the power transfer is performed in a constant power manner, which limits the size of the charge and discharge current and ensures the stability and safety of the active balancing process.

[0068] Furthermore, the balancing compensation current fed back by the DC / DC balancing module under control exceeds a preset range, and active balancing is turned off.

[0069] Specifically, the DC / DC balancing module of the controlled action will feedback the balancing compensation current. BCU 10 determines in real time whether the balancing compensation current fed back by each DC / DC converter matches the current theoretical maximum allowable balancing power (reserve the corresponding time for active balancing). When the balancing compensation current exceeds the preset range, it indicates that there may be a fault in which the balancing compensation current is too large or too small. If this mismatch lasts for more than a predetermined time, it is considered that the DC / DC balancing module has a fault, and the balancing fault flag is set to 1, active balancing is turned off, and the balancing start flag is set to 0. It should be noted that the initial value of the balancing fault flag is 0. When a fault occurs, it is set to 1 and maintained, and the fault clearing instruction is retained to ensure the safety of the active balancing process.

[0070] 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.

[0071] The active balancing control method of the present application is compatible with battery modules of different manufacturers, different degrees of aging and different SOC states. By step-by-step refreshing of paired module numbers, the balancing 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 can be well achieved, which has more practical application value. 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 are comprehensively considered to ensure the safety of the active balancing process. SOX is estimated separately by each BMU to avoid mutual interference between different battery modules and improve the estimation accuracy. By directly controlling the DC / DC balancing module to transfer power, no additional energy storage unit or additional hardware circuit is required, and the active balancing efficiency is higher and the battery system cost is lower.

[0072] 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.

[0073] 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 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; characterized in that: The control method comprises the following steps: S11: Sending the system current and the balancing compensation current of each battery module; S12: receiving multiple real-time available capacities; S13: Calculate and obtain the average value of available capacity; and S14: calculating in real time the difference between the average value of the available capacity and the minimum value 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 the battery management units corresponds one-to-one to each of the battery modules, and each of the battery management units estimates the SOC of each of the battery cell strings in the battery module and the SOH of the battery module based on the voltage, temperature and preset information of each of the battery cell strings 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.

2. The battery system active balancing control method according to claim 1, characterized in that: The control method further comprises the steps of: S15: Evaluate the current theoretically allowed maximum balancing power according to the system current and battery power status table of the multiple battery modules.

3. The battery system active balancing control method according to claim 2, characterized in that: The step S15 specifically includes: 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 power state table of the multiple battery modules and the system current of the multiple battery modules; S152: Calculate the current theoretical maximum allowable balancing power according to the current theoretical maximum balancing current and the minimum value of the module voltage among the multiple battery modules.

4. The battery system active balancing control method according to claim 3, characterized in that: 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.

5. The battery system active balancing control method according to claim 2, 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 theoretically allowed maximum balancing power. If so, execute step 12; if not, turn off active balancing.

6. The battery system active balancing control method according to claim 5, 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 where the maximum value of the multiple real-time available capacities is located, and the second battery module number is the module number of the battery module where the minimum value of the multiple real-time available capacities is located.

7. The battery system active balancing control method according to claim 6, characterized in that: After executing step S14, the control method further comprises the steps of: S18: Send a request for balancing command and the current theoretical maximum balancing power allowed to the control unit of the DC / DC balancing module, 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 theoretical maximum balancing power allowed, 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.

8. The battery system active balancing control method according to claim 6, 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.

9. The battery system active balancing control method according to claim 7, characterized in that: The step S18 specifically includes: S181: accumulating the transferred power according to the balanced compensation current fed back by the DC / DC balanced module under control, and when the accumulated value of the transferred power reaches the preset power, executing the steps S12, S121, S13, and S14; and S182: Clear the accumulated value of the transferred power and repeat step S18.

10. The battery system active balancing control method according to claim 9, characterized in that: The balanced compensation current fed back by the controlled DC / DC balanced module exceeds a preset range, and active balanced operation is turned off.

11. 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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