Control period determination method and modulation method of modular cascade battery energy storage system

Abstract

The invention provides a control period determination method and a modulation method for a modularized cascade battery energy storage system, and the method comprises the steps: determining the sum of the minimum voltages of the DC sides of all phases of corresponding modules, the sum of the maximum voltages of the DC sides of all phases of corresponding modules, and the maximum value of the effective values of grid-connected phase voltages; according to the sum of the minimum voltages of the direct current sides of the corresponding modules and the maximum value of the effective values of the grid-connected phase voltages, the preset maximum modulation ratio of the modularized cascade battery energy storage system is determined; determining a control period according to the maximum modulation ratio, the maximum value of the sum of the maximum voltages of the direct current side of each corresponding module, a preset modulation wave amplitude and a preset modulation wave period; and according to the instantaneous value of the modulation wave and a sequence operation result of the direct current side voltage cut off to each module according to the charging and discharging priorities of the modules, determining the input number of the modules. According to the invention, the module utilization rate of the modularized cascade battery energy storage system is improved, and the accuracy of the output voltage and the quality of the output electric energy of the modularized cascade battery energy storage system are improved.

Description

Technical Field

[0001] The present disclosure relates to the field of power electronics and energy storage control technology, and in particular to a control period determination method and a modulation method for a modular cascade battery energy storage system. Background Art

[0002] Modular converter technology can achieve efficient high-voltage and large-capacity power conversion and is widely used in motor drive, grid reactive power compensation, DC transmission, medium-voltage direct-mounted energy storage and other fields. Cascaded H-bridge and modular multi-level are two typical modular converter technologies. Modulation technology converts the modulation wave output by the control algorithm into switching instructions for the converter power devices, which directly affects the efficiency and response speed of the converter and is one of the core technologies of modular converters.

[0003] With the large-scale application of battery energy storage in independent energy storage of power grids and new energy stations, the demand for indicators such as efficiency, single-unit capacity and dynamic response speed is getting higher and higher. Therefore, battery energy storage systems based on modular converter technology have received more and more attention and application. In order to obtain better output voltage and current harmonic characteristics, the modular battery energy storage system requires a large number of modules per phase, usually no less than 8 for 6kV systems, no less than 12 for 10kV systems, and no less than 40 for 35kV systems.

[0004] Balanced control of batteries is an essential function of battery energy storage systems. The modulation technology of modular converters directly affects the implementation method of balanced control of modular battery energy storage systems. The modulation technologies for modular converters mainly include carrier stacked PWM modulation (LS-PWM), carrier phase shifted PWM modulation (PS-PWM) and nearest level modulation. Carrier stacked PWM modulation will cause unbalanced power distribution between modules, which requires carrier rotation between different modules, which is more complicated. Nearest level modulation is mainly used in situations where the number of modules per phase ranges from dozens to hundreds, such as high-voltage flexible direct current transmission. In high-voltage flexible direct current transmission, the capacitor voltage of each module is kept basically equal through capacitor voltage balance control. The number of modules to be put into use is determined according to the ratio of modulation voltage to capacitor voltage.

[0005] The common advantages of carrier stacking PWM modulation and carrier phase shift PWM modulation are high equivalent switching frequency and good output voltage and current waveforms. They can obtain excellent output voltage and current waveforms when the number of sub-modules is not small, the output filtering pressure is small, and it is easy to meet the relevant requirements of the grid connection standard.

[0006] The basic carrier stacking PWM modulation uses a triangular carrier with different amplitude average values ​​but the same waveform to compare with the modulation wave to generate the switching signal of the corresponding module power device. This leads to inconsistent conduction time of each module power device within an industrial frequency cycle, resulting in unbalanced power distribution between modules and inconsistent heat generation of module power devices. To overcome the above problems, it is necessary to rotate the carrier between different modules, which is more complicated to implement. In addition, if module battery balancing is to be achieved, the differences between the batteries of each module need to be considered when rotating the carrier. There are many influencing factors and they are coupled with each other, making the control more complicated.

[0007] The number of triangular carrier waves required for carrier stacking PWM modulation is the same as the number of modules. The basic carrier stacking PWM modulation uses a triangular carrier wave with equal amplitude and phase division to compare with the modulation wave to generate the switching signal of the module power device. Therefore, the on-time of each module power device during operation is exactly the same, and the power and heat generation of each module are consistent. If you want to achieve module battery balancing, adjust the carrier size corresponding to each module to change the on-time of each module power device, so as to achieve the purpose of changing the module power. Battery balancing control has few influencing factors and is simple to implement.

[0008] The number of triangular carriers required for carrier phase-shift PWM modulation is also consistent with the number of modules. Therefore, in situations where the battery energy storage system has a high voltage level and a large number of modules, the requirements for control resources are high. In situations where the number of modules is large, the quality of the output voltage and current waveforms can also be easily met through the nearest level modulation, and its equivalent switching frequency is higher than the nearest level modulation in terms of loss.

[0009] Recently, level modulation has the advantages of better output waveform quality and lower switching loss in situations where the number of modules per phase ranges from dozens to hundreds. It is widely used in situations where a large number of modules are required to achieve high-voltage flexible DC transmission and in high-voltage dynamic reactive generators. In view of the differences in parameters and losses between different modules, in order to maintain the capacitor voltage balance of each module, a capacitor voltage sorting algorithm is generally used. Under the premise of ensuring that the total number of modules invested remains unchanged, the modules are selectively switched according to the direction of the current. The balance of capacitor voltage can be completed on a time scale of 10ms, so at the power control level, it can be considered that the capacitor voltage of each module is always the same, that is, equal to the average voltage. At this time, the number of modules invested can be calculated based on the ratio of the modulation voltage to the average capacitor voltage.

[0010] However, even if the number of modules is large, the above-mentioned level modulation cannot be directly applied to modular battery energy storage systems. The reasons are:

[0011] 1) The energy of the DC side battery in the modular battery energy storage system is much greater than the capacitor on the DC side of the flexible DC transmission system and the dynamic reactive generator module. The battery voltage will not change significantly within a time scale of several minutes or even tens of minutes. When the module batteries of the modular battery energy storage system are unbalanced, the voltages of the modules will be quite different. Directly using the average voltage of the module batteries to calculate the number of modules that need to be invested will cause large errors and affect the output voltage and current quality.

[0012] 2) The selection of control frequency during the nearest level modulation is related to the DC side voltage of the module. For modular battery energy storage systems, the DC side voltages of each module are different. Selecting the control frequency based on the average voltage of the module battery cannot fully utilize the advantages of the multi-level topology. Summary of the invention

[0013] In view of the defects in the prior art, the purpose of the present invention is to provide a control period determination method and a modulation method for a modular cascade battery energy storage system.

[0014] To achieve the above objective, according to one aspect of the present disclosure, a control period determination method and a modulation method of a modular cascade battery energy storage system are provided, comprising:

[0015] According to the preset design parameters of the modular cascade battery energy storage system, determine the sum of the minimum voltage on the DC side of each corresponding module and the sum of the maximum voltage on the DC side of each corresponding module;

[0016] Determining the maximum value of the effective value of the grid-connected phase voltage according to the preset design parameters of the modular cascade battery energy storage system;

[0017] Determine the maximum modulation ratio of the preset modular cascade battery energy storage system according to the sum of the minimum voltages of the DC sides of the modules corresponding to each phase and the maximum value of the effective value of the grid-connected phase voltage;

[0018] Determine a control period according to the preset maximum modulation ratio of the modular cascade battery energy storage system, the maximum value of the sum of the maximum voltages of the DC sides of each corresponding module, the preset modulation wave amplitude, and the preset modulation wave period;

[0019] Acquire the instantaneous value of the modulation wave and the module charging and discharging priority of the preset modular cascade battery energy storage system;

[0020] Determine the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the result of the series operation of the DC side voltage of each module according to the module charging and discharging priority;

[0021] According to the preset maximum modulation ratio of the modular cascade battery energy storage system and the number of modules put into operation according to the module charging and discharging priority, the preset modular cascade battery energy storage system is controlled to perform nearest level modulation.

[0022] Optionally, the determining the sum of the minimum DC side voltages of each corresponding module and the sum of the maximum DC side voltages of each corresponding module according to the preset design parameters of the modular cascade battery energy storage system includes:

[0023] Determine the DC side voltage operating range of each module of the preset modular cascade battery energy storage system according to the design parameters of the preset modular cascade battery energy storage system;

[0024] Determining the maximum value of the DC side voltage of all modules according to the DC side voltage operation range of each module;

[0025] According to the DC side voltage operating range of each module, the minimum DC voltages of each corresponding module are summed, and the maximum DC side voltages of each corresponding module are summed to determine the sum of the minimum DC side voltages of each corresponding module and the sum of the maximum DC side voltages of each corresponding module.

[0026] Optionally, the maximum value of the DC side voltage of all the modules is the same as the preset modulation wave amplitude.

[0027] Optionally, the acquiring the instantaneous value of the modulation wave and the module charging and discharging priority of the preset modular cascade battery energy storage system includes:

[0028] Obtaining the instantaneous value of the modulation wave from the control strategy based on a preset first time interval through a modulation function;

[0029] The module charging and discharging priority of the preset modular cascade battery energy storage system is obtained from the balancing algorithm based on the preset second time interval through the modulation function.

[0030] Optionally, the method further comprises:

[0031] According to the DC side voltage of each priority module and the module charge and discharge priority, the numerical calculation results of the DC side voltage ending at each priority module according to the module charge and discharge priority are determined in sequence.

[0032] Optionally, the step of determining the number of modules put into operation according to the module charging and discharging priority based on the instantaneous value of the modulation wave and the result of a series operation of the DC side voltage of each module according to the module charging and discharging priority includes:

[0033] If the result of the series operation of the DC side voltage up to the current priority module according to the module charging and discharging priority is greater than the instantaneous value of the modulation wave, the number of modules put into operation is the previous priority module from the first priority module to the current priority module according to the module charging and discharging priority.

[0034] Optionally, the determining the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the result of the series operation of the DC side voltage of each module according to the module charging and discharging priority, further includes:

[0035] If the result of the series calculation of the DC side voltage up to the current priority module according to the module charging and discharging priority is not greater than the instantaneous value of the modulation wave, the next priority module of the current priority module is used as the new current priority module, and the result of the series calculation of the DC side voltage up to the new current priority module according to the module charging and discharging priority is compared with the instantaneous value of the modulation wave, until the result of the series calculation of the DC side voltage up to the new current priority module is greater than the instantaneous value of the modulation wave, and the number of modules put into operation is determined to be the previous priority module from the first priority module to the new current priority module according to the module charging and discharging priority.

[0036] Compared with the prior art, the embodiments of the present disclosure have at least one of the following beneficial effects:

[0037] Through the above technical scheme, based on the preset design parameters of the modular cascade battery energy storage system, the control cycle is determined, so as to obtain the preset optimal control cycle of the modular cascade battery energy storage system, and provide design indicators for the design of the controller of the modular cascade battery energy storage system. Under this control cycle, the modular cascade battery energy storage system generates the largest number of levels of output voltage and the best output voltage waveform quality; the modular cascade battery energy storage system is modulated by the nearest level modulation method to improve the utilization rate of the module, reduce the influence of inconsistent module voltage on the output voltage waveform, improve the accuracy of the output voltage and the quality of the output electric energy, and improve the output efficiency of electric energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present disclosure will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0039] Figure 1 The present invention is a flowchart of a control period determination method and a modulation method of a modular cascade battery energy storage system according to an exemplary embodiment. DETAILED DESCRIPTION

[0040] The present disclosure is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present disclosure, but are not intended to limit the present disclosure in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present disclosure. These all fall within the scope of protection of the present disclosure.

[0041] Figure 1 The present invention is a flowchart of a control period determination method and a modulation method of a modular cascade battery energy storage system according to an exemplary embodiment.

[0042] like Figure 1 As shown, the present disclosure provides a control period determination method and a modulation method for a modular cascade battery energy storage system, including S11 to S17.

[0043] S11, according to the preset design parameters of the modular cascade battery energy storage system, determine the sum of the minimum voltage on the DC side of each corresponding module and the sum of the maximum voltage on the DC side of each corresponding module.

[0044] Among them, the design parameters of the preset modular cascade battery energy storage system can refer to the design parameters of the DC side voltage of each module of the preset modular cascade battery energy storage system, such as the number of DC side batteries of the module, the maximum operating voltage of the single battery, and the minimum operating voltage of the single battery.

[0045] Maximum voltage on the DC side of the module = the highest voltage of the single battery * the number of battery cells on the DC side of the module;

[0046] The minimum voltage on the DC side of the module = the lowest voltage of the single battery * the number of battery cells on the DC side of the module.

[0047] The sum of the minimum DC side voltages of each corresponding module represents the sum of the minimum DC side voltages of each corresponding module, which is expressed as Among them, U dcmin_j,x Indicates the minimum DC side voltage of the xth module corresponding to j, U dc_min_sum_j It represents the sum of the minimum DC side voltages of the modules corresponding to j, N represents the number of modules corresponding to each other, a represents phase a, b represents phase b, and c represents phase c.

[0048] The sum of the maximum DC side voltages of each corresponding module represents the sum of the maximum DC side voltages of each corresponding module, which is expressed as Among them, U dcmax_j,x Indicates the maximum DC side voltage of the xth module corresponding to j, U dc_max_sum_j It represents the sum of the maximum voltages on the DC side of the modules corresponding to j, N represents the number of modules corresponding to each other, a represents phase a, b represents phase b, and c represents phase c.

[0049] S12, determining the maximum value of the effective value of the grid-connected phase voltage according to the preset design parameters of the modular cascade battery energy storage system.

[0050] Among them, the design parameters of the preset modular cascade battery energy storage system may include the grid rated voltage and its fluctuation range, grid-connected inductance, and maximum grid-connected current.

[0051] The maximum effective value of the grid-connected phase voltage of the modular cascade battery energy storage system is expressed as U acmax .

[0052] S13, determining a preset maximum modulation ratio of the modular cascade battery energy storage system according to the sum of the minimum voltages on the DC sides of the modules corresponding to each phase and the maximum effective value of the grid-connected phase voltage.

[0053] Among them, the sum of the minimum voltages on the DC side of each phase of the corresponding module is: the sum of the minimum voltages on the DC side of the a phase module is U dc_min_sum_a , the sum of the minimum voltages on the DC side of the b-phase modules is U dc_min_sum_b , the sum of the minimum voltages of the DC side of the c-phase modules U dc_min_sum_c .

[0054] The preset maximum modulation ratio of the modular cascade battery energy storage system is M max .

[0055] S14, determining a control period according to a preset maximum modulation ratio of the modular cascade battery energy storage system, a maximum value of the sum of the maximum voltages on the DC sides of each corresponding module, a preset modulation wave amplitude, and a preset modulation wave period.

[0056] Among them, the preset maximum modulation ratio of the modular cascade battery energy storage system is M max The maximum value of the sum of the maximum voltages on the DC side of each corresponding module is: max[U dc_max_sum_a ,U dc_max_sum_b ,U dc_max_sum_c ]. The preset modulation wave amplitude is U dcmax The preset modulation wave period is T m , in the grid-connected system, T m It also represents the power frequency period.

[0057] The preset modulation wave adopts a sinusoidal modulation wave.

[0058] The control period is T c .

[0059] According to a control cycle T c The amplitude of the sinusoidal modulation wave is U dcmax , to design the control period T c .

[0060] S15, obtaining the instantaneous value of the modulation wave and the module charging and discharging priority of the preset modular cascade battery energy storage system.

[0061] Among them, the module charging and discharging priority of the preset modular cascade battery energy storage system is represented by the first priority module, the second priority module, ..., the nth priority module in descending order of charging and discharging priority, and the corresponding module DC side voltages are U(1), U(2), U(3), ..., U(n) in sequence.

[0062] S16, determining the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the numerical calculation result of the DC side voltage ending at each module according to the module charging and discharging priority.

[0063] S17, according to the preset maximum modulation ratio of the modular cascade battery energy storage system and the number of modules put into use according to the module charging and discharging priority, control the preset modular cascade battery energy storage system to perform the nearest level modulation.

[0064] Through the above technical scheme, based on the preset design parameters of the modular cascade battery energy storage system, the control cycle is determined, so as to obtain the preset optimal control cycle of the modular cascade battery energy storage system, and provide design indicators for the design of the controller of the modular cascade battery energy storage system. Under this control cycle, the modular cascade battery energy storage system generates the largest number of levels of output voltage and the best output voltage waveform quality; the modular cascade battery energy storage system is modulated by the nearest level modulation method to improve the utilization rate of the module, reduce the influence of inconsistent module voltage on the output voltage waveform, improve the accuracy of the output voltage and the quality of the output electric energy, and improve the output efficiency of electric energy.

[0065] In a possible embodiment, S11 may include S21 to S23.

[0066] S21, determining a DC side voltage operating range of each module of a preset modular cascade battery energy storage system according to a preset design parameter of the modular cascade battery energy storage system.

[0067] Among them, the DC side voltage operating range of each module is expressed as [U dcmin_j,x ,U dcmax_j,x ], in a three-phase system, j = a, b, c, x = 1, 2, .., N, N represents the number of modules corresponding to each phase. dcmin_j,x Indicates the minimum operating voltage of the DC side of the xth module of phase j, U dcmax_j,x Indicates the maximum operating voltage on the DC side of the xth module of phase j.

[0068] S22, determining the maximum DC side voltage of all modules according to the DC side voltage operation range of each module.

[0069] Among them, the maximum DC side voltage of all modules is U dcmax :U dcmax =max[U dcmax_j,x ].

[0070] S23, according to the DC side voltage operating range of each module, sum the minimum DC voltage of each corresponding module, and sum the maximum DC side voltage of each corresponding module, to determine the sum of the minimum DC side voltage of each corresponding module and the sum of the maximum DC side voltage of each corresponding module.

[0071] Among them, the sum of the minimum DC voltage measured for each corresponding module is:

[0072]

[0073] Among them, U dc_min_sum_j Indicates the sum of the minimum DC side voltages of the modules corresponding to j, U dcmin_j,x Represents the sum of the minimum DC side voltages of the xth module in phase j.

[0074] Sum the maximum DC side voltage of each corresponding module:

[0075]

[0076] Among them, U dc_max_sum_j Indicates the sum of the maximum voltages on the DC side of the module corresponding to j, U dcmax_j,x Represents the sum of the maximum DC side voltages of the xth module in phase j.

[0077] In a possible embodiment, in the present disclosure, all the maximum values ​​of the DC side voltages are the same as the preset modulation wave amplitude, that is, they are all U dcmax .

[0078] In a possible embodiment, S13 may include:

[0079]

[0080] Among them, M max represents the maximum modulation ratio of the preset modular cascade battery energy storage system, U acmax Indicates the maximum effective value of the grid-connected phase voltage, U dc_min_sum_a Indicates the sum of the minimum voltages on the DC side of the a-phase module, U dc_min_sum_b Indicates the sum of the minimum voltages on the DC side of the b-phase module, U dc_min_sum_c Indicates the sum of the minimum voltages on the DC side of the c-phase module. min[] indicates the minimum value operation.

[0081] In a possible embodiment, S14 may include:

[0082]

[0083] Among them, T c represents the control period, U dcmax Indicates the preset modulation wave amplitude, M max represents the maximum modulation ratio of the preset modular cascade battery energy storage system, U dc_max_sum_a Indicates the sum of the maximum voltages on the DC side of the a-phase module, U dc_max_sum_b Indicates the sum of the maximum voltages on the DC side of the b-phase modules, U dc_max_sum_c Indicates the sum of the maximum voltages on the DC side of the c-phase module. max[] indicates the maximum value operation. max[U dc_max_sum_a ,U dc_max_sum_b ,U dc_max_sum_c ] indicates the maximum value of the sum of the maximum voltages on the DC sides of each corresponding module.

[0084] Based on the control cycle, the preferred control frequency can be determined to provide design indicators for the controller of the preset modular cascade battery energy storage system, thereby improving the output voltage and current quality of the preset modular cascade battery energy storage system.

[0085] The preset modular cascade battery energy storage system disclosed in the present invention adopts the nearest level modulation method. The controller of the preset modular cascade battery energy storage system adopts a timing control method, and the power control period is Tp.

[0086] In a possible embodiment, S15 may include S31 to S32.

[0087] S31, obtaining an instantaneous value of a modulation wave from a control strategy based on a preset first time interval through a modulation function.

[0088] The modulation function can be implemented in the form of software algorithm or hardware module, and the instantaneous value U of the modulation wave is obtained in the control strategy based on the preset first time interval by the latest level modulation. x .

[0089] S32, obtaining a preset module charging and discharging priority of the modular cascade battery energy storage system from a balancing algorithm based on a preset second time interval through a modulation function.

[0090] The module charging and discharging priority ranking is obtained from the balancing algorithm based on the preset second time interval by the latest level modulation.

[0091] In a possible embodiment, a method for controlling the nearest level of a modular cascade battery energy storage system may further include S18.

[0092] S18, according to the DC side voltage of each priority module and the module charge and discharge priority, sequentially determine the result of the series operation of the DC side voltage up to each priority module according to the module charge and discharge priority.

[0093] According to the module charging and discharging priority, determine the series operation result of the DC side voltage ending at each priority module:

[0094] ...

[0096]

[0097] Wherein, U(1) represents the DC side voltage of the first priority module, represents the result of the series operation according to the module charging and discharging priority until the DC side voltage of the first priority module, U(2) represents the DC side voltage of the second priority module, represents the result of the series operation of the DC side voltage up to the second priority module according to the module charging and discharging priority, U(k-1) represents the DC side voltage of the k-1 priority module, and U(k) represents the DC side voltage of the k priority module. It represents the result of the series calculation of the DC side voltage up to the kth module according to the module charging and discharging priority.

[0098] In a possible embodiment, S16 may include S41.

[0099] S41, if the result of the series operation of the DC side voltage up to the current priority module according to the module charging and discharging priority is greater than the instantaneous value of the modulation wave, the number of modules put into use is the previous priority module from the first priority module to the current priority module according to the module charging and discharging priority.

[0100] In a possible embodiment, S16 may further include S42.

[0101] If the result of the series calculation of the DC side voltage up to the current priority module according to the module charging and discharging priority is not greater than the instantaneous value of the modulation wave, the next priority module of the current priority module is used as the new current priority module, and the result of the series calculation of the DC side voltage up to the new current priority module according to the module charging and discharging priority is compared with the instantaneous value of the modulation wave until the result of the series calculation of the DC side voltage up to the new current priority module is greater than the instantaneous value of the modulation wave, and the number of modules put into operation is determined to be the previous priority module from the first priority module to the new current priority module according to the module charging and discharging priority.

[0102] For example, if Then invest in the first priority module;

[0103] like Then invest in the first priority module and the second priority module;

[0104] If Then invest in the first priority module, the second priority module and the third priority module;

[0105] By analogy, if Then the first priority module, the second priority module, ..., the k-1th priority module and the kth priority module are invested.

[0106] Until Stop comparing the numerical calculation result of the DC side voltage up to the new current priority module with the instantaneous value of the modulation wave. The k+1th priority module, the k+2th priority module, ..., the nth priority module are not put into operation. Then the modules to be put into operation currently are from the first priority module to the kth priority module according to the module charging and discharging priority. The number of modules put into operation according to the module charging and discharging priority is k.

[0107] By determining the modules to be put into use and the number of modules to be put into use according to the module charging and discharging priority and the actual DC side voltage of each priority module, the impact of the voltage differences between each module is reduced, the module utilization rate is improved, and the nearest level modulation method is used to achieve the output voltage of the preset modular cascade battery energy storage system to be as close to the modulation wave as possible.

[0108] The above describes the specific embodiments of the present disclosure. It should be understood that the present disclosure is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present disclosure. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A control period determination method and modulation method for a modular cascade battery energy storage system, characterized in that: include: According to the preset design parameters of the modular cascade battery energy storage system, determine the sum of the minimum voltage on the DC side of each corresponding module and the sum of the maximum voltage on the DC side of each corresponding module; Determining the maximum value of the effective value of the grid-connected phase voltage according to the preset design parameters of the modular cascade battery energy storage system; Determine the maximum modulation ratio of the preset modular cascade battery energy storage system according to the sum of the minimum voltages of the DC sides of the modules corresponding to each phase and the maximum value of the effective value of the grid-connected phase voltage; Determine a control period according to the preset maximum modulation ratio of the modular cascade battery energy storage system, the maximum value of the sum of the maximum voltages of the DC sides of each corresponding module, the preset modulation wave amplitude, and the preset modulation wave period; Acquire the instantaneous value of the modulation wave and the module charging and discharging priority of the preset modular cascade battery energy storage system; Determine the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the result of the series operation of the DC side voltage of each module according to the module charging and discharging priority; According to the preset maximum modulation ratio of the modular cascade battery energy storage system and the number of modules put into operation according to the module charging and discharging priority, the preset modular cascade battery energy storage system is controlled to perform nearest level modulation.

2. The method according to claim 1, characterized in that The step of determining the sum of the minimum voltage on the DC side of each corresponding module and the sum of the maximum voltage on the DC side of each corresponding module according to the preset design parameters of the modular cascade battery energy storage system includes: Determine the DC side voltage operating range of each module of the preset modular cascade battery energy storage system according to the design parameters of the preset modular cascade battery energy storage system; Determining the maximum DC side voltage of all modules according to the DC side voltage operation range of each module; According to the DC side voltage operating range of each module, the minimum DC voltages of each corresponding module are summed, and the maximum DC side voltages of each corresponding module are summed to determine the sum of the minimum DC side voltages of each corresponding module and the sum of the maximum DC side voltages of each corresponding module.

3. The method according to claim 2, characterized in that The maximum value of the DC side voltage of all the modules is the same as the preset modulation wave amplitude.

4. The method according to claim 1, characterized in that The method of determining the maximum modulation ratio of the preset modular cascade battery energy storage system according to the sum of the minimum voltages of the DC sides of the modules corresponding to each phase and the maximum value of the effective value of the grid-connected phase voltage comprises: Among them, M max represents the maximum modulation ratio of the preset modular cascade battery energy storage system, U acmax Indicates the maximum effective value of the grid-connected phase voltage, U dc_min_sum_a Indicates the sum of the minimum voltages on the DC side of the a-phase module, U dc_min_sum_b Indicates the sum of the minimum voltages on the DC side of the b-phase module, U dc_min_sum_c Indicates the sum of the minimum voltages on the DC side of the c-phase module. min[] indicates the minimum value operation.

5. The method according to claim 1, characterized in that Determining a control period according to the preset maximum modulation ratio of the modular cascade battery energy storage system, the maximum value of the sum of the maximum voltages of the DC sides of each corresponding module, the preset modulation wave amplitude, and the preset modulation wave period, including: Among them, T c represents the control period, U dcmax Indicates the preset modulation wave amplitude, M max represents the maximum modulation ratio of the preset modular cascade battery energy storage system, U dc_max_sum_a Indicates the sum of the maximum voltages on the DC side of the a-phase module, U dc_max_sum_b Indicates the sum of the maximum voltages on the DC side of the b-phase modules, U dc_max_sum_c Indicates the sum of the maximum voltages on the DC side of the c-phase module. max[] indicates the maximum value operation. max[U dc_max_sum_a ,U dc_max_sum_b ,U dc_max_sum_c ] represents the maximum value of the sum of the maximum voltages on the DC sides of each corresponding module.

6. The method according to claim 1, characterized in that The step of acquiring the instantaneous value of the modulation wave and the module charging and discharging priority of the preset modular cascade battery energy storage system includes: Obtaining the instantaneous value of the modulation wave from the control strategy based on a preset first time interval through a modulation function; The module charging and discharging priority of the preset modular cascade battery energy storage system is obtained from the balancing algorithm based on the preset second time interval through the modulation function.

7. The method according to claim 1, characterized in that The method further comprises: According to the DC side voltage of each priority module and the module charge and discharge priority, the numerical calculation results of the DC side voltage ending at each priority module according to the module charge and discharge priority are determined in sequence.

8. The method according to claim 7, characterized in that According to the DC side voltage of each priority module and the module charge and discharge priority, sequentially determine the result of the series operation of the DC side voltage of each priority module according to the module charge and discharge priority, including: ... Wherein, U(1) represents the DC side voltage of the first priority module, represents the result of the series operation according to the module charging and discharging priority until the DC side voltage of the first priority module, U(2) represents the DC side voltage of the second priority module, represents the result of the series operation of the DC side voltage up to the second priority module according to the module charging and discharging priority, U(k-1) represents the DC side voltage of the k-1th priority module, and U(k) represents the DC side voltage of the kth priority module. It represents the result of the series operation of the DC side voltage up to the kth module according to the module charging and discharging priority.

9. The method according to claim 1, characterized in that: The step of determining the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the result of the series operation of the DC side voltage of each module according to the module charging and discharging priority includes: If the result of the series operation of the DC side voltage up to the current priority module according to the module charging and discharging priority is greater than the instantaneous value of the modulation wave, the number of modules put into operation is the previous priority module from the first priority module to the current priority module according to the module charging and discharging priority.

10. The method according to claim 9, characterized in that The method of determining the number of modules put into operation according to the module charging and discharging priority according to the instantaneous value of the modulation wave and the result of the series operation of the DC side voltage of each module according to the module charging and discharging priority, further includes: If the result of the series calculation of the DC side voltage up to the current priority module according to the module charging and discharging priority is not greater than the instantaneous value of the modulation wave, the next priority module of the current priority module is used as the new current priority module, and the result of the series calculation of the DC side voltage up to the new current priority module according to the module charging and discharging priority is compared with the instantaneous value of the modulation wave, until the result of the series calculation of the DC side voltage up to the new current priority module is greater than the instantaneous value of the modulation wave, and the number of modules put into operation is determined to be the previous priority module from the first priority module to the new current priority module according to the module charging and discharging priority.

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