A discontinuous pulse width modulation method and device for a cascade battery energy storage system

Abstract

The present invention relates to the field of electric energy storage technology, and in particular to a discontinuous pulse width modulation method and device for a cascaded battery energy storage system. The method comprises the following steps: obtaining a voltage modulation reference value and calculating the minimum number of submodules to be put into operation; dividing the submodules of each phase of the cascaded battery energy storage system into two groups; selecting multiple submodules from the two groups of submodules as clamping submodules; clamping the modulation voltage reference of the clamping submodule to obtain a switching signal of the clamping submodule, calculating the modulation reference value of the non-clamping submodule, and obtaining a switching signal of the non-clamping submodule; and applying the switching signals of the clamping submodule and the non-clamping submodule to the corresponding power devices. The method and device provided by the present invention improve the charge state balancing capability and balancing rate between modules within a phase, reduce the number of system switching operations, reduce the power loss of the system, and have good harmonic performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy storage, and in particular to a discontinuous pulse width modulation method and device for a cascade battery energy storage system. Background Art

[0002] The cascaded battery energy storage system achieves scale by distributing battery groups directly to the cascaded H-bridge converter submodules. It has high control flexibility and strong battery management capabilities, can effectively reduce the circulation current between battery groups, and improve the charging and discharging efficiency of the battery energy storage system. It has broad prospects in large-scale battery energy storage systems.

[0003] However, due to the parameter differences between the battery groups in the cascaded battery energy storage system, it is easy to cause uneven state of charge between the battery groups, resulting in a reduction in the capacity utilization of the system. In order to improve the capacity utilization of the cascaded battery energy storage system, it is necessary to balance the state of charge between phases and within phases. Traditional state of charge balancing control introduces the state of charge deviation into the PI control link to generate an additional voltage acting on the modulation signal. It has a certain state of charge balancing ability, but has disadvantages such as slow balancing speed and difficulty in parameter setting. In addition, traditional cascaded battery energy storage systems use multi-carrier phase-shift modulation technology to produce better voltage harmonic performance, but there is high power loss, which leads to a reduction in the power conversion efficiency of the system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a discontinuous pulse width modulation method and device for a cascade battery energy storage system, which can greatly improve the charge state balancing capability and speed within the phase of the cascade battery energy storage system and can greatly reduce the power loss of the system.

[0005] The present invention is achieved through the following technical solutions:

[0006] A discontinuous pulse width modulation method for a cascade battery energy storage system comprises the following steps:

[0007] S1: Use the output current control link to obtain the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system and calculate the minimum number of submodules to be put into use in the cascaded battery energy storage system;

[0008] S2: Obtaining the state of charge (SOC) of each phase submodule of the cascaded battery energy storage system in real time, dividing the submodules of each phase of the cascaded battery energy storage system into two groups based on the relationship between the SOC of each phase submodule and the average SOC of each phase of the cascaded battery energy storage system, and sorting the submodules of the two groups according to the SOC;

[0009] S3: Based on the minimum number of submodules put into operation in the cascaded battery energy storage system, multiple submodules are selected from the two groups of submodules in the cascaded battery energy storage system as clamped submodules, and the remaining submodules are non-clamped submodules;

[0010] S4: Clamp the modulation voltage reference of the clamping submodule to obtain a clamped modulation reference value, and query the switch state table according to the clamped modulation reference value to obtain the clamping submodule switching signal, calculate the modulation reference value of the non-clamping submodule, and apply the modulation reference value of the non-clamping submodule to the carrier phase shift modulation module to obtain the non-clamping submodule switching signal;

[0011] S5: applying the clamping submodule switching signal and the non-clamping submodule switching signal to corresponding power devices respectively to control the on and off of the corresponding power devices.

[0012] Furthermore, in step S1, the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system is obtained according to formula (1):

[0013] (1);

[0014] in: Indicates the initial voltage modulation reference value of each phase bridge arm of the cascaded battery energy storage system, The phase number of the bridge arm , Indicates the actual reference value of each phase bridge arm voltage of the cascaded battery energy storage system. Indicates the number of sub-modules in each phase of the cascaded battery energy storage system, Indicates the DC side voltage of each phase submodule of the cascaded battery energy storage system.

[0015] Furthermore, step S1 calculates the minimum number of submodules to be put into operation in the cascaded battery energy storage system according to formula (2):

[0016] (2);

[0017] in: Indicates the minimum number of submodules to be put into use in the cascade battery energy storage system. Indicates rounding down. It means that the value is 1 when the independent variable is greater than 0 and 0 when it is less than 0.

[0018] Furthermore, in step S2, the average state of charge of each phase of the cascaded battery energy storage system is calculated according to formula (3):

[0019] (3);

[0020] in: Represents a cascade battery energy storage system The average value of the phase state of charge, Represents a cascade battery energy storage system Xiangdi The state of charge of each submodule, Indicates the serial number of the cascaded battery energy storage system submodule, .

[0021] Furthermore, in step S2, the submodules whose states of charge of the submodules of each phase of the cascaded battery energy storage system are higher than or equal to the average state of charge of the submodules of each phase of the cascaded battery energy storage system are taken as the first group of submodules, and the submodules whose states of charge of the submodules of each phase of the cascaded battery energy storage system are lower than the average state of charge of the submodules of each phase of the cascaded battery energy storage system are taken as the second group of submodules.

[0022] Furthermore, in step S3, multiple submodules are selected from the two groups of submodules in the cascaded battery energy storage system as clamping submodules according to the following method:

[0023] When the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, multiple submodules are selected from the first group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of submodules input in the cascaded battery energy storage system. Multiple submodules are selected from the second group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascaded battery energy storage system and the minimum number of submodules input in the cascaded battery energy storage system minus 1.

[0024] When the instantaneous power of the cascade battery energy storage system is less than 0, multiple submodules are selected from the second group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of input submodules of the cascade battery energy storage system. Multiple submodules are selected from the first group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascade battery energy storage system and the minimum number of submodules in the cascade battery energy storage system minus 1.

[0025] Furthermore, the number of selected submodules is calculated according to formula (4):

[0026] (4);

[0027] in: Represents a cascade battery energy storage system Phase input clamping submodule number, Represents a cascade battery energy storage system The number of submodules in the first group, Represents a cascade battery energy storage system Phase instantaneous power, Represents a cascade battery energy storage system The number of submodules in the second group, Indicates taking the minimum value, Represents a cascade battery energy storage system Number of phase bypass clamp submodules.

[0028] Furthermore, in step S4, when the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, multiple submodules are selected from the first group of submodules as the input clamped submodules, and the voltage reference clamping is modulated according to formula (5). When the instantaneous power of the cascaded battery energy storage system is less than 0, multiple submodules are selected from the second group of submodules as the input clamped submodules, and the voltage reference clamping is modulated according to formula (6). The modulation reference value of the non-clamped submodule is calculated according to formula (7):

[0029] (5);

[0030] (6);

[0031] (7);

[0032] in: Indicates the first module selected from the first group of submodules Each submodule modulates the voltage reference clamp, Indicates the first module selected from the second group of submodules Each submodule modulates the voltage reference clamp, Indicates the modulation reference value of the non-clamped submodule, Indicates the number of submodules selected from the first group of submodules, Indicates the number of submodules selected from the second group of submodules.

[0033] A discontinuous pulse width modulation device for a cascaded battery energy storage system, used to perform a discontinuous pulse width modulation method for a cascaded battery energy storage system as described in any one of the above, comprising a modulation reference processing module, a grouping and sorting module, a clamping submodule selection module, a voltage clamping module, a modulation signal correction module, and a carrier phase shift modulation module;

[0034] The modulation reference processing module is used to input a modulation reference value and calculate the minimum number of sub-modules to be invested;

[0035] The grouping and sorting module is used to divide the submodules in the phase into two groups according to the state of charge, and sort the two groups of submodules respectively;

[0036] The clamping submodule selection module is used to calculate the number of two clamping submodules, and select the number of clamping submodules of each of the two groups of submodules and determine the clamping type, and the remaining submodules are used as non-clamping submodules;

[0037] The voltage clamping module is used to obtain a clamping modulation reference value and obtain a switching signal of the clamping submodule;

[0038] The modulation signal correction module is used to correct the modulation reference value of the non-clamped submodule;

[0039] The carrier phase-shift modulation module is used to modulate the modulation reference value of the non-clamped sub-module into a non-clamped sub-module switching signal.

[0040] Beneficial effects of the invention:

[0041] The present invention provides a discontinuous pulse width modulation method and device for a cascaded battery energy storage system. This method can significantly improve the charge state balancing capability and balancing rate between modules within a phase through voltage clamping, while ensuring that the battery power is consistent with the system's charge and discharge instructions. It also reduces the number of switching actions in the system as a whole, significantly reducing the system's power loss. Furthermore, by retaining a single or multiple pulse width modulation links, the system exhibits good harmonic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic flow chart of the present invention.

[0043] Figure 2 It is a schematic diagram of the device of the present invention.

[0044] In the figure: 1. Modulation reference processing module; 2. Grouping and sorting module; 3. Clamping sub-module selection module; 4. Voltage clamping module; 5. Modulation signal correction module; 6. Carrier phase shift modulation module. DETAILED DESCRIPTION

[0045] A discontinuous pulse width modulation method for a cascade battery energy storage system, the flow diagram is as follows Figure 1 As shown, the specific steps include:

[0046] S1: Use the output current control link to obtain the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system and calculate the minimum number of submodules to be put into use in the cascaded battery energy storage system;

[0047] Specifically, the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system can be obtained according to formula (1):

[0048] (1);

[0049] in: Indicates the initial voltage modulation reference value of each phase bridge arm of the cascaded battery energy storage system, The phase number of the bridge arm , Indicates the actual reference value of each phase bridge arm voltage of the cascaded battery energy storage system. Indicates the number of sub-modules in each phase of the cascaded battery energy storage system, Indicates the DC side voltage of each phase submodule of the cascaded battery energy storage system.

[0050] In order to meet the modulation requirements of the overall bridge arm voltage, the minimum number of submodules in the cascaded battery energy storage system can be calculated according to formula (2):

[0051] (2);

[0052] in: Indicates the minimum number of submodules to be put into use in the cascade battery energy storage system. Indicates rounding down. It means that the value is 1 when the independent variable is greater than 0 and 0 when it is less than 0.

[0053] S2: Obtaining the state of charge (SOC) of each phase submodule of the cascaded battery energy storage system in real time, dividing the submodules of each phase of the cascaded battery energy storage system into two groups based on the relationship between the SOC of each phase submodule and the average SOC of each phase of the cascaded battery energy storage system, and sorting the submodules of the two groups according to the SOC;

[0054] Specifically, the average state of charge of each phase of the cascaded battery energy storage system can be calculated according to formula (3):

[0055] (3);

[0056] in: Represents a cascade battery energy storage system The average value of the phase state of charge, Represents a cascade battery energy storage system Xiangdi The state of charge of each submodule, Indicates the serial number of the cascaded battery energy storage system submodule, .

[0057] Specifically, the submodules of each phase of the cascaded battery energy storage system can be divided into two groups according to the following principles:

[0058] The submodules whose state of charge of each phase submodule of the cascaded battery energy storage system is higher than or equal to the average state of charge of each phase of the cascaded battery energy storage system are taken as the first group of submodules, and the submodules whose state of charge of each phase submodule of the cascaded battery energy storage system is lower than the average state of charge of each phase of the cascaded battery energy storage system are taken as the second group of submodules.

[0059] When the two groups of submodules are sorted respectively according to the state of charge, they can be sorted in descending order.

[0060] S3: Based on the minimum number of submodules put into operation in the cascaded battery energy storage system, multiple submodules are selected from the two groups of submodules in the cascaded battery energy storage system as clamped submodules, and the remaining submodules are non-clamped submodules;

[0061] The switching states of the submodules can be divided into forward input, reverse input, and bypass. When the system power command remains unchanged, the battery charge and discharge power is the same in both forward input and reverse input switching states. Therefore, only two submodule voltage clamping modes can be defined: one is input clamping, which clamps the modulation signal of the submodule to 1 or -1, and the other is bypass clamping, which clamps the modulation signal of the submodule to 0.

[0062] Furthermore, multiple submodules can be selected from the two groups of submodules of the cascaded battery energy storage system as clamping submodules according to the following method:

[0063] When the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, it can be defined as discharging. Then, multiple submodules are selected from the first group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of submodules input in the cascaded battery energy storage system. Multiple submodules are selected from the second group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascaded battery energy storage system and the minimum number of submodules input in the cascaded battery energy storage system minus 1.

[0064] When the instantaneous power of the cascade battery energy storage system is less than 0, multiple submodules are selected from the second group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of input submodules of the cascade battery energy storage system. Multiple submodules are selected from the first group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascade battery energy storage system and the minimum number of submodules in the cascade battery energy storage system minus 1.

[0065] The above-mentioned submodule clamping method can ensure that the charge and discharge state of each battery is the same as that of the system, and reverse charging does not occur. It also meets the bridge arm voltage modulation constraint and at least one submodule performs pulse width modulation, and has good harmonic performance.

[0066] Furthermore, the number of selected submodules can be calculated according to formula (4):

[0067] (4);

[0068] in: Represents a cascade battery energy storage system Phase input clamping submodule number, Represents a cascade battery energy storage system The number of submodules in the first group, Represents a cascade battery energy storage system Phase instantaneous power, Represents a cascade battery energy storage system The number of submodules in the second group, Indicates taking the minimum value, Represents a cascade battery energy storage system Number of phase bypass clamp submodules.

[0069] The calculation formulas for the submodule selected from the first group of submodules and the submodule selected from the second group of submodules as the clamping submodule are as follows:

[0070] ;

[0071] ;

[0072] in: Represents a cascade battery energy storage system The submodule selected from the first group of submodules as the clamping submodule, Represents a cascade battery energy storage system A submodule selected from the second group of submodules as a clamping submodule.

[0073] S4: Clamp the modulation voltage reference of the clamping submodule to obtain a clamped modulation reference value, and query the switch state table according to the clamped modulation reference value to obtain the clamping submodule switching signal, calculate the modulation reference value of the non-clamping submodule, and apply the modulation reference value of the non-clamping submodule to the carrier phase shift modulation module to obtain the non-clamping submodule switching signal;

[0074] Specifically, when the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, and multiple submodules are selected from the first group of submodules as the input clamped submodules, the voltage reference clamp can be modulated according to formula (5). When the instantaneous power of the cascaded battery energy storage system is less than 0, and multiple submodules are selected from the second group of submodules as the input clamped submodules, the voltage reference clamp can be modulated according to formula (6). The modulation reference value of the non-clamped submodule can be calculated according to formula (7):

[0075] (5);

[0076] (6);

[0077] (7);

[0078] in: Indicates the first module selected from the first group of submodules Each submodule modulates the voltage reference clamp, Indicates the first module selected from the second group of submodules Each submodule modulates the voltage reference clamp, Indicates the modulation reference value of the non-clamped submodule, Indicates the number of submodules selected from the first group of submodules, Indicates the number of submodules selected from the second group of submodules.

[0079] S5: applying the clamping submodule switching signal and the non-clamping submodule switching signal to corresponding power devices respectively to control the on and off of the corresponding power devices.

[0080] By modulating the clamp submodule into a voltage reference clamp using the above method and distributing the switching signal of the clamp submodule according to the instantaneous power, the charge state within the phase can be balanced, which greatly improves the charge state balancing capability and balancing rate between modules within the phase, reduces the number of switching actions of the entire system, and significantly reduces the power loss of the system.

[0081] Specifically, taking a three-phase cascade battery energy storage system with 5 submodules as an example, assuming that there are 3 submodule battery packs with a state of charge higher than the average value, and 2 submodule battery packs with a state of charge lower than the average value, the system is in a discharging state, and the submodule numbers are arranged in descending order according to the state of charge, that is, the submodules a 1 has the highest state of charge of the battery pack, submodule a The battery pack 2 has the lowest state of charge. The submodules with a high state of charge are in the clamped state, and the submodules with a low state of charge are in the bypass state.

[0082] Based on the modulation signal of the clamp submodule, the switching signals of each switch in the submodule can be directly obtained by looking up Table 1. Any switch has only two switching states: switch state 1 indicates the switch is on, and switch state 0 indicates the switch is off. When the modulation signal of the submodule is 1, the switch states of switches S1 and S3 are 1 and 0, respectively. When the modulation signal of the submodule is 0, the switch states of switches S1 and S3 are 0 and 0, respectively. When the modulation signal of the submodule is -1, the switch states of switches S1 and S3 are 0 and 1, respectively. The state of switch S2 is the opposite of that of switch S1, and the state of switch S4 is the opposite of that of switch S3.

[0083] Table 1 Switch status

[0084]

[0085] A discontinuous pulse width modulation device for a cascade battery energy storage system, used to perform a discontinuous pulse width modulation method for a cascade battery energy storage system as described in any one of the above, the structural diagram of which is as shown in FIG. Figure 2As shown, it includes a modulation reference processing module 1, a grouping and sorting module 2, a clamping submodule selection module 3, a voltage clamping module 4, a modulation signal correction module 5 and a carrier phase shift modulation module 6;

[0086] The modulation reference processing module is used to input a modulation reference value and calculate the minimum number of sub-modules to be invested;

[0087] The grouping and sorting module is used to divide the submodules in the phase into two groups according to the state of charge, and sort the two groups of submodules respectively;

[0088] The clamping submodule selection module is used to calculate the number of two clamping submodules, and select the number of clamping submodules of each of the two groups of submodules and determine the clamping type, and the remaining submodules are used as non-clamping submodules;

[0089] The voltage clamping module is used to obtain a clamping modulation reference value and obtain a switching signal of the clamping submodule;

[0090] The modulation signal correction module is used to correct the modulation reference value of the non-clamped submodule;

[0091] The carrier phase-shift modulation module is used to modulate the modulation reference value of the non-clamped sub-module into a non-clamped sub-module switching signal.

[0092] The execution entities of the above modules can be devices with computing functions such as computers, single-chip microcomputers, and microcontrollers. In specific implementation, the embodiments of the present invention do not limit the execution entities and they can be selected according to the needs of actual applications.

[0093] In summary, the present invention provides a discontinuous pulse width modulation method and device for a cascaded battery energy storage system. While ensuring that battery power is consistent with system charge and discharge instructions, this method significantly improves the charge state balancing capability and balancing rate between modules within a phase, reduces the number of switching operations in the system as a whole, and significantly reduces system power loss. Furthermore, by retaining single or multiple pulse width modulation links, the system exhibits good harmonic performance.

[0094] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A discontinuous pulse width modulation method for a cascade battery energy storage system, characterized by: The steps include: S1: Use the output current control link to obtain the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system and calculate the minimum number of submodules to be put into use in the cascaded battery energy storage system; S2: Obtaining the state of charge (SOC) of each phase submodule of the cascaded battery energy storage system in real time, dividing the submodules of each phase of the cascaded battery energy storage system into two groups based on the relationship between the SOC of each phase submodule and the average SOC of each phase of the cascaded battery energy storage system, and sorting the submodules of the two groups according to the SOC; S3: Based on the minimum number of submodules put into operation in the cascaded battery energy storage system, multiple submodules are selected from the two groups of submodules in the cascaded battery energy storage system as clamped submodules, and the remaining submodules are non-clamped submodules; S4: Clamp the modulation voltage reference of the clamping submodule to obtain a clamped modulation reference value, and query the switch state table according to the clamped modulation reference value to obtain the clamping submodule switching signal, calculate the modulation reference value of the non-clamping submodule, and apply the modulation reference value of the non-clamping submodule to the carrier phase shift modulation module to obtain the non-clamping submodule switching signal; When the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, multiple submodules are selected from the first group of submodules as the input clamped submodules, and the voltage reference clamp is modulated according to formula (5). When the instantaneous power of the cascaded battery energy storage system is less than 0, multiple submodules are selected from the second group of submodules as the input clamped submodules, and the voltage reference clamp is modulated according to formula (6). The modulation reference value of the non-clamped submodule is calculated according to formula (7): （5）； （6）； （7）； in: Indicates the first module selected from the first group of submodules Each submodule modulates the voltage reference clamp, Indicates the first module selected from the second group of submodules Each submodule modulates the voltage reference clamp, Indicates the modulation reference value of the non-clamped submodule, Indicates the number of submodules selected from the first group of submodules, Indicates the number of submodules selected from the second group of submodules; S5: applying the clamping submodule switching signal and the non-clamping submodule switching signal to corresponding power devices respectively to control the on and off of the corresponding power devices.

2. A discontinuous pulse width modulation method for a cascade battery energy storage system according to claim 1, characterized in that: In step S1, the initial bridge arm voltage modulation reference value of the cascaded battery energy storage system is obtained according to formula (1): （1）； in: Indicates the initial voltage modulation reference value of each phase bridge arm of the cascaded battery energy storage system, The phase number of the bridge arm , Indicates the actual reference value of each phase bridge arm voltage of the cascaded battery energy storage system. Indicates the number of sub-modules in each phase of the cascaded battery energy storage system, Indicates the DC side voltage of each phase submodule of the cascaded battery energy storage system.

3. A discontinuous pulse width modulation method for a cascade battery energy storage system according to claim 2, characterized in that: Step S1 calculates the minimum number of submodules to be put into operation in the cascaded battery energy storage system according to formula (2): （2）； in: Indicates the minimum number of submodules to be put into use in the cascade battery energy storage system. Indicates rounding down. It means that the value is 1 when the independent variable is greater than 0 and 0 when it is less than 0.

4. A discontinuous pulse width modulation method for a cascade battery energy storage system according to claim 1, characterized in that: In step S2, the average state of charge of each phase of the cascaded battery energy storage system is calculated according to formula (3): （3）； in: Represents a cascade battery energy storage system The average value of the phase state of charge, Represents a cascade battery energy storage system Xiangdi The state of charge of each submodule, Indicates the serial number of the cascaded battery energy storage system submodule, .

5. The discontinuous pulse width modulation method of a cascade battery energy storage system according to claim 1, characterized in that: In step S2, the submodules whose states of charge of the submodules of each phase of the cascaded battery energy storage system are higher than or equal to the average state of charge of the submodules of each phase of the cascaded battery energy storage system are taken as the first group of submodules, and the submodules whose states of charge of the submodules of each phase of the cascaded battery energy storage system are lower than the average state of charge of the submodules of each phase of the cascaded battery energy storage system are taken as the second group of submodules.

6. A discontinuous pulse width modulation method for a cascade battery energy storage system according to claim 5, characterized in that: In step S3, multiple submodules are selected from two groups of submodules in the cascaded battery energy storage system as clamping submodules according to the following method: When the instantaneous power of the cascaded battery energy storage system is greater than or equal to 0, multiple submodules are selected from the first group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of submodules input in the cascaded battery energy storage system. Multiple submodules are selected from the second group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascaded battery energy storage system and the minimum number of submodules input in the cascaded battery energy storage system minus 1. When the instantaneous power of the cascade battery energy storage system is less than 0, multiple submodules are selected from the second group of submodules as input clamping submodules, and the number of submodules selected as input clamping submodules is less than the minimum number of input submodules of the cascade battery energy storage system. Multiple submodules are selected from the first group of submodules as bypass clamping submodules, and the number of submodules selected as bypass clamping submodules is less than the difference between the number of submodules in each phase of the cascade battery energy storage system and the minimum number of submodules in the cascade battery energy storage system minus 1.

7. A discontinuous pulse width modulation method for a cascade battery energy storage system according to claim 6, characterized in that: The number of selected submodules is calculated according to formula (4): （4）； in: Represents a cascade battery energy storage system Phase input clamping submodule number, Represents a cascade battery energy storage system The number of submodules in the first group, Represents a cascade battery energy storage system Phase instantaneous power, Represents a cascade battery energy storage system The number of submodules in the second group, Indicates taking the minimum value, Represents a cascade battery energy storage system Number of phase bypass clamp submodules.

8. A discontinuous pulse width modulation device for a cascade battery energy storage system, characterized in that: Used to execute a discontinuous pulse width modulation method for a cascade battery energy storage system according to any one of claims 1 to 7, comprising a modulation reference processing module, a grouping and sorting module, a clamping submodule selection module, a voltage clamping module, a modulation signal correction module and a carrier phase shift modulation module; The modulation reference processing module is used to input a modulation reference value and calculate the minimum number of sub-modules to be invested; The grouping and sorting module is used to divide the submodules in the phase into two groups according to the state of charge, and sort the two groups of submodules respectively; The clamping submodule selection module is used to calculate the number of two clamping submodules, and select the number of clamping submodules of each of the two groups of submodules and determine the clamping type, and the remaining submodules are used as non-clamping submodules; The voltage clamping module is used to obtain a clamping modulation reference value and obtain a switching signal of the clamping submodule; The modulation signal correction module is used to correct the modulation reference value of the non-clamped submodule; The carrier phase-shift modulation module is used to modulate the modulation reference value of the non-clamped sub-module into a non-clamped sub-module switching signal.

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