Control circuit and method capable of outputting battery pack with balance in gradient mode

Abstract

The embodiment of the invention provides a control circuit and method capable of outputting a battery pack with equalization in a gradient mode, and belongs to the technical field of power electronics and battery management systems. The control circuit comprises a first switch, a second switch, a first diode, a second diode, an inductor, a third diode, a third switch and a fourth diode, the other ends of the third switches of all the subunits are connected with one another, and the positive electrode of one single battery connected with the subunit is connected with one end of the inductor of the previous subunit; the positive electrode of the single battery connected with the first subunit is connected with the other end of the third switch; and the controller is connected with each switch. According to the control circuit and method, alternating current output and active equalization can be realized at the same time on the premise of saving the volume and cost required by the inverter and the equalization module, and the working efficiency of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics and battery management systems, and in particular to a control circuit and method for a gradient output balanced battery pack. Background Art

[0002] In traditional battery pack systems (such as electric vehicles and energy storage devices), after the batteries are connected in series, independent inverters are required to convert DC power into AC power for load use. At the same time, active balancing circuits are required to solve the problem of uneven state of charge (SOC) between the series battery cells.

[0003] The inverter and active balancing circuits in this system are independent of each other, and both the software and hardware are relatively complex, increasing the size and cost of the power battery system. Energy undergoes multiple conversions during the inversion (DC-AC) and balancing (DC-DC) processes, resulting in reduced efficiency. Inversion and balancing require time-sharing control, making algorithm coordination difficult and making it difficult to meet high-frequency dynamic requirements (such as electric vehicle fast charging or regenerative braking). Although some studies have attempted to achieve partial functional integration through multiplexing switches or improved topologies (such as multi-level inverters), there are still problems such as difficulty in synchronous operation of inverter and balancing, resulting in balancing speed lag or output waveform distortion. In addition, in traditional solutions, the inductor is only used for filtering or single-function energy transfer, and its energy storage characteristics are not fully utilized to achieve multi-functional coordination. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a control circuit and method for a gradient output battery pack with balancing, which can simultaneously achieve AC output and active balancing while saving the volume and cost required for the inverter and balancing module, thereby improving system operating efficiency.

[0005] To achieve the above objectives, an embodiment of the present invention provides a control circuit capable of gradient output and balanced battery pack, comprising:

[0006] A first switch, one end of which is connected to the negative electrode of a connected single battery;

[0007] A second switch, one end of which is connected to the positive electrode of another connected single battery;

[0008] a first diode, having an anode connected to one end of the first switch and a cathode connected to the other end of the first switch;

[0009] a second diode, having an anode connected to one end of the second switch and a cathode connected to the other end of the second switch;

[0010] An inductor, one end of which is connected to the negative terminal of another single battery;

[0011] A third diode has its anode connected to one end of the inductor and its cathode connected to the other end of the inductor;

[0012] a third switch, one end of which is connected to the other end of the inductor;

[0013] a fourth diode, having an anode connected to one end of the third switch and a cathode connected to the other end of the third switch;

[0014] The other end of the third switch of each subunit is connected to each other, the positive electrode of a corresponding single battery is connected to one end of the inductor of the previous subunit, and the positive electrode of a single battery connected to the first subunit is connected to the other end of the third switch;

[0015] A controller is connected to each switch.

[0016] Optionally, the controller is configured to:

[0017] Get the required output level;

[0018] determining a discharge sub-unit to be used for discharge according to the output level;

[0019] Determine the discharge cycle;

[0020] The discharge sub-unit is controlled to discharge according to the discharge period.

[0021] Optionally, the controller is configured to:

[0022] Get the required output level;

[0023] Determine an equalizing subunit to be used as equalizer according to the output level;

[0024] Determine the discharge cycle;

[0025] The balancing subunit is controlled to perform balancing according to the discharge cycle.

[0026] On the other hand, the present invention also provides a control method for a battery pack with gradient output and balancing, which is used to control the control circuit as described above, comprising:

[0027] Get the required output level;

[0028] Determine a discharge sub-unit for discharging and a balance sub-unit for balancing according to the output level;

[0029] Determine the discharge cycle;

[0030] The discharge sub-unit is controlled to discharge according to the discharge cycle, and the equalization sub-unit is controlled to perform an equalization operation on the discharge sub-unit.

[0031] Optionally, controlling the discharge sub-unit to discharge according to the discharge cycle, and controlling the equalization sub-unit to perform an equalization operation on the discharge sub-unit, includes:

[0032] Determine the discharge voltage;

[0033] Determining whether the discharge voltage is greater than or equal to a preset first threshold;

[0034] When it is determined that the discharge voltage is greater than or equal to a preset first threshold, turning off balancing;

[0035] If it is determined that the discharge voltage is less than the preset first threshold, determining whether the discharge voltage is less than or equal to a preset second threshold;

[0036] When it is determined that the discharge voltage is less than or equal to the preset second threshold, balancing is turned off.

[0037] Optionally, the number of the subunits is 4, and the control method includes:

[0038] When the output level is 8 unit voltages, the first switches of the four subunits are all controlled to be turned on, and the third switch of the first subunit is controlled to be turned on;

[0039] When the output level is 6 unit voltages, the first switch of the first subunit is controlled to be off, the first switches of the second, third and fourth subunits are controlled to be on, the second switches of the second, third and fourth subunits are controlled to be on, and the third switch of the second subunit is controlled to be on.

[0040] Optionally, the control method further includes:

[0041] When the output level is 4 unit voltages, the first switches of the first and second subunits are controlled to be off, the first switches of the third and fourth subunits are controlled to be on, the second switches of the third and fourth subunits are controlled to be on, and the third switch of the third subunit is controlled to be on;

[0042] When the output level is 2 unit voltages, the first switches of the first, second and third subunits are controlled to be off, the first switch of the fourth subunit is controlled to be on, and the second switch of the fourth subunit is controlled to be on;

[0043] When the output level is 0 unit voltage, the first switches of the first, second, third and fourth subunits are controlled to be off.

[0044] Optionally, the control method further includes:

[0045] When the output level is 6 unit voltages, the total reduction in power after equalization of the first sub-unit is calculated according to the discharge level using formula (1):

[0046]

[0047] Among them, SOC down1 is the total amount of power reduction, L1 is the inductance of the first subunit, Q is the capacity of the single battery, u1 and u2 are the voltages of the two single batteries connected to the first subunit, t2 is the end time point of balancing of the first subunit, and t1 is the start time point of balancing of the first subunit;

[0048] According to the discharge level, the total power reduction after the second, third and fourth sub-units supply power to the load resistor is calculated according to formula (2):

[0049]

[0050] Among them, SOC down2 is the total power reduction, u i is the voltage of the i-th single cell, and R is the resistance value of the load resistor;

[0051] According to the total power reduction and the total power drop, the inductance of the first subunit is determined according to formula (3):

[0052]

[0053] Wherein, L1 is the inductance of the inductor of the first subunit.

[0054] Optionally, the control method further includes:

[0055] The inductance of the second subunit is calculated according to formula (4):

[0056]

[0057] Wherein, L2 is the inductance of the second subunit, u j is the voltage of the jth single cell;

[0058] The inductance of the third subunit is calculated according to formula (5):

[0059]

[0060] Wherein, L3 is the inductance of the inductor of the third subunit.

[0061] Through the above technical solution, the control circuit and method for a battery pack with gradient output and balancing provided by the present invention achieves the series connection and disconnection of the connected individual batteries within the subunits by opening and closing multiple switches within the subunits, thereby achieving a stepped voltage output. Simultaneously, the opening and closing of the multiple switches, combined with the inductors within the subunits, achieves balancing of the individual batteries within the subunits. This allows for both AC output and active balancing while reducing the size and cost of the inverter and balancing modules, thereby improving system efficiency.

[0062] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0064] Figure 1 is a circuit diagram of a control circuit capable of gradient output with a balanced battery pack according to one embodiment of the present invention;

[0065] Figure 2 is a flow chart of a method for controlling discharge of a controller of a control circuit capable of gradient output with a balanced battery pack according to one embodiment of the present invention;

[0066] Figure 3 is a flow chart of a method for controlling balancing of a controller of a control circuit capable of gradient outputting a balanced battery pack according to one embodiment of the present invention;

[0067] Figure 4 is a flow chart of a control method for a battery pack with gradient output and balancing according to an embodiment of the present invention;

[0068] Figure 5 is a flow chart of a method for controlling balancing and discharging of a control method for a battery pack with gradient output and balancing according to an embodiment of the present invention;

[0069] Figure 6 It is the switching timing diagram for achieving AC output.

[0070] Description of Reference Numerals

[0071] A. Subunit S1, first switch

[0072] S2, second switch S3, third switch

[0073] D1, first diode D2, second diode

[0074] D3, third diode D4, fourth diode

[0075] L, inductance DETAILED DESCRIPTION

[0076] The following describes the specific implementation of the embodiment of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiment of the present invention and is not used to limit the embodiment of the present invention.

[0077] like Figure 1 The figure shows a circuit diagram of a control circuit capable of gradient output with balanced battery pack according to an embodiment of the present invention. Figure 1 In the embodiment, the control circuit may include multiple subunits A, each of which may include a first switch S1, a second switch S2, a first diode D1, a second diode D2, an inductor L, a third diode D3, a third switch S3, a fourth diode D4, and a controller. One end of the first switch S1 is connected to the negative electrode of a connected single battery, and one end of the second switch S2 is connected to the positive electrode of another connected single battery. The anode of the first diode D1 is connected to one end of the first switch S1, and the cathode is connected to the other end of the first switch S1. The anode of the second diode D2 is connected to one end of the second switch S2, and the cathode is connected to the other end of the second switch S2. One end of the inductor L is connected to the negative electrode of another connected single battery, the anode of the third diode D3 is connected to one end of the inductor L, and the cathode is connected to the other end of the inductor L. One end of the third switch S3 is connected to the other end of the inductor L, and the anode of the fourth diode D4 is connected to one end of the third switch S3, and the cathode is connected to the other end of the third switch S3. The other end of the third switch S3 of each subunit A is connected to each other, the positive electrode of a single battery connected to the subunit A is connected to one end of the inductor L of the previous subunit A, the positive electrode of a single battery connected to the first subunit A is connected to the other end of the third switch S3, and the controller is connected to each switch.

[0078] In order to output the required level, the controller can be used to control the circuit to discharge. In this embodiment, the method for the controller to control the circuit to discharge can be various forms known to those skilled in the art. In a preferred example of the present invention, the method for the controller to control the circuit to discharge can include: Figure 2 The steps shown. Figure 2 In the method in which the controller controls the circuit to discharge, the method may include the following steps:

[0079] In step S10, the required output level is obtained;

[0080] In step S11, a discharge sub-unit is determined as a discharge unit according to the output level;

[0081] In step S12, a discharge period is determined;

[0082] In step S13 , the discharge sub-cell is controlled to discharge according to a discharge cycle.

[0083] In order to balance the single cells connected to the sub-unit A, the controller can be used to control the circuit to balance. In this embodiment, the method for the controller to control the circuit to balance can be various forms known to those skilled in the art. In a preferred example of the present invention, the method for the controller to control the circuit to balance can include: Figure 3 The steps shown. Figure 3 In the method of controlling the circuit to perform balancing, the controller may include the following steps:

[0084] In step S20, the required output level is obtained;

[0085] In step S21, the equalization subunit to be used for equalization is determined according to the output level;

[0086] In step S22, a discharge period is determined;

[0087] In step S23 , the balancing subunit is controlled to perform balancing according to the discharge cycle.

[0088] like Figure 4 The flowchart of the control method of the battery pack with gradient output and equalization according to one embodiment of the present invention is shown. In the figure, the control method may include the following steps:

[0089] In step S30, the required output level is obtained;

[0090] In step S31, a discharge sub-unit for discharging and a balance sub-unit for balancing are determined according to the output level;

[0091] In step S32, a discharge period is determined;

[0092] In step S33 , the discharge sub-unit is controlled to discharge according to the discharge cycle, and the equalization sub-unit is controlled to perform an equalization operation on the discharge sub-unit.

[0093] In this Figure 4 In the method shown, step S33 can be used to control the discharge of the discharge sub-unit according to the discharge cycle, and control the equalization sub-unit to perform an equalization operation on the discharge sub-unit. In this embodiment, the method of controlling the discharge of the discharge sub-unit according to the discharge cycle and controlling the equalization sub-unit to perform an equalization operation on the discharge sub-unit can be various forms known to those skilled in the art. In a preferred example of the present invention, the method of controlling the discharge of the discharge sub-unit according to the discharge cycle and controlling the equalization sub-unit to perform an equalization operation on the discharge sub-unit can include the following: Figure 5The steps shown. Figure 5 In the method, the discharge sub-unit is controlled to discharge according to the discharge cycle, and the equalization sub-unit is controlled to perform an equalization operation on the discharge sub-unit, which may include the following steps:

[0094] In step S330, the discharge voltage is determined;

[0095] In step S331, it is determined whether the discharge voltage is greater than or equal to a preset first threshold;

[0096] In step S332, when it is determined that the discharge voltage is greater than or equal to a preset first threshold, balancing is turned off;

[0097] In step S333, when it is determined that the discharge voltage is less than the preset first threshold, it is determined whether the discharge voltage is less than or equal to the preset second threshold;

[0098] When it is determined that the discharge voltage is less than or equal to the preset second threshold, the balancing operation is turned off, that is, step S332 is executed.

[0099] In this embodiment, the number of subunits A can be multiple values ​​known to those skilled in the art. In a preferred example of the present invention, the number of subunits A can be four. Each subunit A connects to two single cells, so the maximum voltage that the circuit can provide is 8 unit voltages, and the minimum voltage that can be provided is 0 unit voltage. When the output level is 8 unit voltages, the first switches S1 of all four subunits A are controlled to be turned on, and all the single cells in the four subunits A participate in discharge. The third switch S3 of the first subunit is controlled to be turned on to charge the inductor L of the first subunit. When the output level is 6 unit voltages, the first switch S1 of the first subunit is controlled to be turned off, and the first switches S1 of the second, third, and third subunits are controlled to be turned on, and the single cells in the second, third, and third subunits participate in discharge. The second switches S2 of the second, third, and third subunits are controlled to be turned on, and the inductor L of the first subunit is discharged to balance the single cells in the second, third, and third subunits. The third switch S3 of the second subunit is controlled to be turned on to charge the inductor L of the second subunit. When the output level is 4 unit voltages, the first switches S1 of the first and second subunits are controlled to be off, and the first switches S1 of the third and third subunits are controlled to be on. The single cells of the third and third subunits participate in discharge. The second switches S2 of the third and third subunits are controlled to be on. The inductor L of the second subunit discharges and balances the single cells of the third and third subunits. The third switch S3 of the third subunit is controlled to be on to charge the inductor L of the third subunit. When the output level is 2 unit voltages, the first switches S1 of the first, second, and third subunits are controlled to be off, and the first switch S1 of the third subunit is controlled to be on. Only the single cells of the third subunit participate in discharge. The second switch S2 of the third subunit is controlled to be on. The inductor L of the third subunit balances the single cells of the third subunit. When the output level is 0 unit voltage, the first switches S1 of the first, second, third, and third subunits are controlled to be off. At this time, no single cells of subunit A participate in discharge.

[0100] like Figure 6 The figure shows the switching timing diagram for achieving AC output. Waveform 1 is the actual output level value, and waveform 2 is the equivalent AC voltage. Figure 6 As shown, outputting a specific step voltage in a continuous time can be equivalent to outputting an AC voltage.

[0101] The inductors L of the first, second, and third subunits need to be designed for specific inductances, while the inductor L of the third subunit is only used to prevent short circuits, and its value is not required. The values ​​of the inductors L of the first, second, and third subunits can be various values ​​known to those skilled in the art. In a preferred embodiment of the present invention, the design of the inductor L of the first subunit may include the following steps:

[0102] When the output level is 6 unit voltages, the total reduction in power after equalization of the first sub-unit is calculated according to the discharge level using formula (1):

[0103]

[0104] Among them, SOC down1 is the total power reduction, L1 is the inductance of the inductor L of the first subunit, Q is the capacity of the single battery, u1 and u2 are the voltages of the two single batteries connected to the first subunit, t2 is the end time point of the balancing of the first subunit, and t1 is the start time point of the balancing of the first subunit;

[0105] According to the discharge level, the total power reduction after the second, third and third sub-units supply power to the load resistor is calculated according to formula (2):

[0106]

[0107] Among them, SOC down2 is the total power reduction, u i is the voltage of the i-th single cell, R is the resistance value of the load resistor;

[0108] According to the total power reduction and the total power drop, the inductance of the inductor L of the first subunit is determined according to formula (3):

[0109]

[0110] Wherein, L1 is the inductance of the inductor L of the first subunit.

[0111] The design of the inductance L of the second and third subunits can be determined by the following formula:

[0112] The inductance of the second subunit L is calculated according to formula (4):

[0113]

[0114] Wherein, L2 is the inductance of the second subunit L, u j is the voltage of the jth single cell;

[0115] The inductance of the third subunit L is calculated according to formula (5):

[0116]

[0117] Wherein, L3 is the inductance of the inductor L of the third subunit.

[0118] Through the above technical solution, the control circuit and method for a battery pack with gradient output and balancing provided by the present invention achieves the series connection and disconnection of the connected individual batteries within the subunits by opening and closing multiple switches within the subunits, thereby achieving a stepped voltage output. Simultaneously, the opening and closing of the multiple switches, combined with the inductors within the subunits, achieves balancing of the individual batteries within the subunits. This allows for both AC output and active balancing while reducing the size and cost of the inverter and balancing modules, thereby improving system efficiency.

[0119] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0120] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0121] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0122] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0123] In a typical configuration, a computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0124] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0125] Computer-readable media includes permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include transitory computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0126] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0127] The above are merely embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A control circuit capable of gradient output with balanced battery pack, characterized in that: It includes multiple subunits, each of which includes: A first switch, one end of which is connected to the negative electrode of a connected single battery; A second switch, one end of which is connected to the positive electrode of another connected single battery; a first diode, having an anode connected to one end of the first switch and a cathode connected to the other end of the first switch; a second diode, having an anode connected to one end of the second switch and a cathode connected to the other end of the second switch; An inductor, one end of which is connected to the negative terminal of another single battery; A third diode has its anode connected to one end of the inductor and its cathode connected to the other end of the inductor; a third switch, one end of which is connected to the other end of the inductor; a fourth diode, having an anode connected to one end of the third switch and a cathode connected to the other end of the third switch; The other end of the third switch of each subunit is connected to each other, the positive electrode of a corresponding single battery is connected to one end of the inductor of the previous subunit, and the positive electrode of a single battery connected to the first subunit is connected to the other end of the third switch; A controller is connected to each switch.

2. The control circuit according to claim 1, wherein: The controller is used to: Get the required output level; determining a discharge sub-unit to be used for discharge according to the output level; Determine the discharge cycle; The discharge sub-unit is controlled to discharge according to the discharge period.

3. The control circuit according to claim 1, wherein: The controller is used to: Get the required output level; Determine an equalizing subunit to be used as equalizer according to the output level; Determine the discharge cycle; The balancing subunit is controlled to perform balancing according to the discharge cycle.

4. A control method for a battery pack with gradient output and equalization, used to control the control circuit according to claim 1, characterized in that: include: Get the required output level; Determine a discharge sub-unit for discharging and a balance sub-unit for balancing according to the output level; Determine the discharge cycle; The discharge sub-unit is controlled to discharge according to the discharge cycle, and the equalization sub-unit is controlled to perform an equalization operation on the discharge sub-unit.

5. The control method according to claim 4, characterized in that: Controlling the discharge sub-unit to discharge according to the discharge cycle, and controlling the equalization sub-unit to perform an equalization operation on the discharge sub-unit, including: Determine the discharge voltage; Determining whether the discharge voltage is greater than or equal to a preset first threshold; When it is determined that the discharge voltage is greater than or equal to a preset first threshold, turning off balancing; If it is determined that the discharge voltage is less than the preset first threshold, determining whether the discharge voltage is less than or equal to a preset second threshold; When it is determined that the discharge voltage is less than or equal to the preset second threshold, balancing is turned off.

6. The control method according to claim 4, characterized in that: The number of the subunits is 4, and the control method includes: When the output level is 8 unit voltages, the first switches of the four subunits are all controlled to be turned on, and the third switch of the first subunit is controlled to be turned on; When the output level is 6 unit voltages, the first switch of the first subunit is controlled to be off, the first switches of the second, third and fourth subunits are controlled to be on, the second switches of the second, third and fourth subunits are controlled to be on, and the third switch of the second subunit is controlled to be on.

7. The control method according to claim 6, characterized in that: The control method further includes: When the output level is 4 unit voltages, the first switches of the first and second subunits are controlled to be off, the first switches of the third and fourth subunits are controlled to be on, the second switches of the third and fourth subunits are controlled to be on, and the third switch of the third subunit is controlled to be on; When the output level is 2 unit voltages, the first switches of the first, second and third subunits are controlled to be off, the first switch of the fourth subunit is controlled to be on, and the second switch of the fourth subunit is controlled to be on; When the output level is 0 unit voltage, the first switches of the first, second, third and fourth subunits are controlled to be off.

8. The control method according to claim 7, characterized in that: The control method further includes: When the output level is 6 unit voltages, the total reduction in power after equalization of the first sub-unit is calculated according to the discharge level using formula (1): Among them, SOC down1 is the total amount of power reduction, L1 is the inductance of the first subunit, Q is the capacity of the single battery, u1 and u2 are the voltages of the two single batteries connected to the first subunit, t2 is the end time point of balancing of the first subunit, and t1 is the start time point of balancing of the first subunit; According to the discharge level, the total power reduction after the second, third and fourth sub-units supply power to the load resistor is calculated according to formula (2): Among them, SOC down2 is the total power reduction, u i is the voltage of the i-th single cell, and R is the resistance value of the load resistor; According to the total power reduction and the total power drop, the inductance of the first subunit is determined according to formula (3): Wherein, L1 is the inductance of the inductor of the first subunit.

9. The control method according to claim 8, characterized in that: The control method further includes: The inductance of the second subunit is calculated according to formula (4): Wherein, L2 is the inductance of the second subunit, u j is the voltage of the jth single cell; The inductance of the third subunit is calculated according to formula (5): Wherein, L3 is the inductance of the inductor of the third subunit.

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