NLM-based in-phase equalization method and system for modular cascaded battery energy storage system

Abstract

The invention provides an NLM-based in-phase equalization method and system for a modular cascaded battery energy storage system, and the method comprises the steps: S1, obtaining a DC side battery SOCj, x and (1-SOC) j, x, the maximum rechargeable current MAXCHGj, x and the maximum dischargeable current MAXDCHGj, x of each module at regular time through a battery management system according to an equalization control period Tequ; s2, selecting a proper balance index according to engineering requirements; s3, calculating an input counter CTj, x of each module according to the power control period Tp and the balance control period Tequ, and generating an input counter queue; and S4, in each power control period, the number K of modules needing to be input is determined according to a nearest level modulation algorithm or other control algorithms, and charging and discharging operation is carried out. According to the method, the input time is allocated to different modules in proportion according to the SOC and the maximum chargeable and dischargeable current of the sub-modules in each phase, regulation and control are carried out from the time dimension, the control period of the balance control strategy is larger than the power control period, and the requirement for controller resources is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of battery balancing control, and in particular, to a method and system for intra-phase balancing of a modular cascade battery energy storage system based on NLM. 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, etc. 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 converter efficiency and response speed and is one of the core technologies of modular converters.

[0003] With the large-scale application of battery energy storage in independent energy storage and new energy stations in the power grid, the demand for 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 good output voltage and current harmonic characteristics, the modular battery energy storage system needs 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 is closely related to 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, so carrier rotation is required between different modules, which is more complicated.

[0005] Carrier phase-shift PWM modulation does not have this problem. The intra-phase balance based on carrier phase-shift PWM modulation adjusts the modulation wave size of each module, changes the power distribution size between modules without changing the power direction, thereby achieving the purpose of online balance.

[0006] Recently, level modulation is mainly used in situations where the number of modules per phase ranges from dozens to hundreds, such as high-voltage flexible DC transmission. In high-voltage flexible DC transmission, the capacitor voltage balance control is used to keep the capacitor voltages of each module basically equal. The number of modules to be invested is determined by rounding off the ratio of the modulation voltage to the capacitor voltage.

[0007] Recently, level modulation has the advantages of good output waveform quality and low 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 remains unchanged, the modules are selectively switched according to the direction of the current. Therefore, the balancing control strategy needs to monitor the current direction in real time and make judgments. Therefore, the control cycle of the balancing control strategy is short, which occupies a large amount of controller resources, and also causes the module switching frequency to increase and the loss to increase.

[0008] On the other hand, the parameters that reflect energy, such as battery voltage and SOC of the energy storage system, change slowly and will not change significantly within a few minutes or even tens of minutes. When the modular battery of the modular battery energy storage system is unbalanced, if the battery voltage or SOC is used as the basis for sorting in the nearest level modulation, it is still necessary to monitor the direction of the current in real time and make a judgment. Therefore, the control cycle of the balancing control strategy is short, and the controller resources are still relatively large.

[0009] Based on the characteristics and application of the above modulation technologies, carrier phase-shift PWM modulation is the most convenient modulation technology to achieve balanced control side, and is most widely used in 6-10kV modular cascade grid-connected energy storage systems. The recent level modulation technology has the advantages of less controller resource requirements and less loss in 35kV modular cascade grid-connected energy storage systems, but there is room for optimization of the corresponding balanced control method.

[0010] The higher the voltage level of the battery energy storage system and the more modules it has, the higher the resource requirements for the control system. Different modulation methods have different resource requirements for the control system. Relatively speaking, the nearest level modulation requires less controller resources than carrier phase shift modulation and carrier stacking modulation, and has lower losses; carrier phase shift modulation and carrier stacking modulation can achieve good output voltage and current quality with fewer modules than the nearest level modulation, but the losses are higher.

[0011] In situations where there are a large number of modules, it is easy to meet the standard requirements for output voltage and current waveform quality through the nearest level modulation, and its low controller resource requirements have a more significant advantage.

[0012] However, if the above capacitor voltage sequencing method is directly applied to a modular cascade battery energy storage system using nearest level modulation, it will cause problems. The reasons are:

[0013] The energy of the DC-side battery in the modular battery energy storage system is much greater than the capacitance on the DC side of the flexible DC transmission system and the dynamic VAR generator module, and the battery voltage will not change significantly within a time scale of several minutes or even tens of minutes.

[0014] When the modular battery energy storage system has imbalanced modules, if the battery voltage or SOC is used as the basis for sorting in the latest level modulation, it is still necessary to monitor the current direction in real time and make judgments. Therefore, the control cycle of the balancing control strategy is short, and the controller resources are still occupied.

[0015] In view of this, the present invention is proposed. Summary of the invention

[0016] In view of the defects in the prior art, the purpose of this application is to provide a modular cascade battery energy storage system based on NLM intra-phase balancing method and system, according to the SOC of each phase sub-module, the maximum charge and discharge current, the investment time is allocated to different modules in proportion, that is, the intra-phase balance is achieved by regulating from the time dimension.

[0017] In one aspect of the present application, a method for balancing phases in a modular cascade battery energy storage system based on NLM is provided, the method comprising:

[0018] S1. According to the balancing control cycle Tequ, the battery management system regularly obtains the SOC of the DC side battery of each module j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x ;

[0019] S2. Select appropriate balancing indicators according to project requirements; the balancing indicators include charging balancing indicators and discharging balancing indicators;

[0020] S3, calculate the input counter CT of each module according to the power control period Tp and the balance control period Tequ j,x , generate an input counter queue;

[0021] S4. In each power control cycle, the number of modules K required to be put into use is determined according to the latest level modulation algorithm or other control algorithms, and charging and discharging operations are performed.

[0022] Furthermore, in S2, it specifically includes:

[0023] Set the charge balance index and discharge balance index to EQU_CHG respectively. j,x ,EQU_DCHG j,x ;

[0024] Select SOC j,x and (1-SOC) j,x , as a balance indicator, or the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x As an indicator of equilibrium;

[0025] All charging and discharging balancing indicators of the same-phase or same-bridge-arm modules are normalized to generate normalized charging and discharging balancing indicators.

[0026] Furthermore, it is characterized in that, when selecting SOC j,x and (1-SOC) j,x , when used as a balance indicator, EQU_CHG j,x , = (1-SOC) j,x ;EQU_DCHG j,x =SOC j,x ;

[0027] Select the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x When used as a balance indicator, EQU_CHG j,x ,=MAX_CHG j,x ;EQU_DCHG j,x =MAX_DCHG j,x .

[0028] Furthermore, the normalized charging balance index and discharging balance index are respectively:

[0029]

[0030] Among them, equ_chg j,x Represents the normalized charge equalization index; equ_dchg j,x Represents the normalized discharge balance index.

[0031] Furthermore, S3 specifically includes:

[0032] Obtain the power control period Tp and the balancing control period Tequ, and calculate the ratio of the two M=Tequ / Tp;

[0033] Set a input counter CT for each module j,x ;

[0034] The normalized charge and discharge balance index is obtained, the input counter value of each module is calculated, and the calculated input counter is used to generate an input counter column.

[0035] Furthermore, the step of calculating the input counter value of each module and generating an input counter column from the calculated input counter includes:

[0036] Obtain the ratio M between the normalized charging equalization index and the power control period Tp and the equalization control period Tequ, and calculate the input calculator value during charging;

[0037] Obtain the ratio M between the normalized discharge balance index and the power control period Tp and the balance control period Tequ, and calculate the input calculator value during discharge;

[0038] Set the input counter value CT of all modules j,x Combined into a [CT j,1 ,CT j,2 ,…,CT j,N ] queue.

[0039] Furthermore, the input calculator value during charging is:

[0040] CT j,x =equ_chg j,x ×M;

[0041] The input calculator value during the discharge is:

[0042] CT j,x =equ_dchg j,x ×M;

[0043] Among them, if the calculated CT j,x If it is a decimal, it will be rounded up according to the rules.

[0044] Furthermore, in S4, it specifically includes:

[0045] S41, at the beginning of each power control cycle, the controller calculates the number of modules K that currently need to be put into use through the nearest level modulation algorithm;

[0046] S42, according to the set reading rules, from the input counter queue [CT j,1 ,CT j,2 ,…,CT j,N ] starts reading from the starting position and selects the input module according to the reading rules;

[0047] S43, obtaining the number of modules selected for input, and determining whether the number of modules input reaches the number of modules K currently required for calculation, and if so, stopping the selection.

[0048] Furthermore, in S42, it specifically includes:

[0049] S421, setting the module selected for input in the yth power control cycle;

[0050] S422, from the queue [CT j,1 ,CT j,2 ,…,CT j,N ] reads the Yth element CT j,y ; In CT j,y = 0, the yth module is not put into use; j,y >0, then CT j,(y+1) Subtract 1, and select the yth module as the input module;

[0051] S423, Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+1)th element CT j,(y+1) CT j,(y+1) =0, the (y+1)th module is not put into use; if CT j,(y+1) >0, then CT j,(y+1) Subtract 1, and select the (y+1)th as the input module;

[0052] S424, read queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+x)th element CT j,(y+x) CT j,(y+x) =0, the (y+x)th module is not put into use; if CT j,(y+x) >0, then CT j,(y+x) Subtract 1, and select the (y+x)th module as the input module;

[0053] If (y+x)>N, then read the (y+xN)th element CT from the head of the queue j,(y+x-N) As the basis for calculation and judgment in the above process.

[0054] A second aspect of the present invention provides a modular cascade battery energy storage system with a phase-balanced system under the nearest level modulation, comprising:

[0055] The acquisition module is used to obtain the SOC of the DC side battery of each module through the battery management system according to the balancing control cycle Tequ j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x ;

[0056] A selection module is used to select appropriate balancing indicators according to engineering needs; the balancing indicators include charging balancing indicators and discharging balancing indicators;

[0057] The calculation module is used to calculate the input counter CT of each module according to the power control period Tp and the balance control period Tequ j,x , generate an input counter queue;

[0058] The determination module is used to determine the number of modules K that need to be put into use in each power control cycle according to the latest level modulation algorithm or other control algorithms to perform charging and discharging operations.

[0059] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0060] The present invention allocates input time to different modules in proportion according to the SOC and the maximum chargeable and discharge current of the sub-modules in each phase, that is, it achieves intra-phase balance through regulation from the time dimension, so as to solve the problem that the traditional balancing control allocates different powers to different modules at the same time and achieves intra-phase balance through regulation from the power dimension, which occupies a large number of resources, and avoids real-time monitoring of the direction of the current flowing into the module. The control period of the balancing control strategy can be much longer than the power control period, and the demand for controller resources is greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0062] Figure 1 This is an intra-phase balancing method based on NLM for a modular cascade battery energy storage system in one embodiment of the present application.

[0063] Figure 2 This is a flowchart of step S4 in one embodiment of the present application.

[0064] Figure 3 Flow chart of step S42 in one embodiment of the present application. DETAILED DESCRIPTION

[0065] The present application 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 application, but do not limit the present application in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0066] This application allocates the input time to different modules in proportion according to the SOC and maximum charge and discharge current of each sub-module in each phase; it avoids real-time monitoring of the direction of the current flowing into the module, and the control cycle of the balancing control strategy can be much longer than the power control cycle. For example, if the power control cycle is 50-100us, the balancing control cycle can reach more than 10ms, or even seconds, which greatly reduces the demand for controller resources.

[0067] Reference Figure 1 As shown, a method for balancing phases in a modular cascade battery energy storage system based on NLM is provided in accordance with an embodiment of the present application, and the method includes:

[0068] S1. According to the balancing control cycle Tequ, the battery management system regularly obtains the SOC of the DC side battery of each module j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x .

[0069] Among them, j=abc, indicating the phase where the module is located; x=1, 2, ..., N, indicating the serial number of the module in the phase or bridge arm.

[0070] Among them, SOC j,x State of charge, which represents the ratio of the current remaining charge of the battery to the rated capacity of the battery; (1-SOC) j,x It is the ratio of the battery's charge capacity to the battery's rated capacity.

[0071] S2. According to the project requirements, select appropriate balancing indicators; the balancing indicators include charging balancing indicators and discharging balancing indicators.

[0072] S3, calculate the input counter CT of each module according to the power control period Tp and the balance control period Tequ j,x , generate an input counter queue.

[0073] S4. In each power control cycle, the number of modules K required to be put into use is determined according to the latest level modulation algorithm or other control algorithms, and charging and discharging operations are performed.

[0074] The present application allocates relative usage time or number of times to each module by calculating the input counter, and actually performs charging and discharging operations in each power control cycle according to these allocation results to achieve time dimension regulation. Compared with the traditional method of regulation from the power dimension, this method may be more flexible and efficient, improve the overall reliability and stability of the system, and enable the system to adapt to different application scenarios and needs.

[0075] Among them, NLM (Nearest Level Modulation, NLM) is the SOC balancing strategy based on the nearest level modulation; S0C (State of Charge, SOC) is the charge state of the sub-module within the phase.

[0076] Specifically, assuming that the number of modules per phase of the modular cascade H-bridge battery energy storage system or the number of modules per bridge arm of the modular multi-level battery energy storage system is N, the balancing control period Tequ is first set. At the end of each Tequ period, the battery management system (BMS) reads the SOC (SOC j,x ) and (1-SOC j,x ), maximum chargeable current (MAX_CHG j,x ) and the maximum discharge current (MAX_DCHGj,x), and then select SOC or maximum charge and discharge current as the balancing indicator according to engineering requirements, and set the charge balancing indicator EQU_CHG j,x and discharge balance indicator EQU_DCHG j,x . The ratio M = Tequ / Tp is calculated according to the power control period Tp and the balancing control period Tequ, and then the input counter CTj,x is calculated for each module, and the input counters of all modules are combined into an input counter queue. In each power control period Tp, the number of modules K to be put into operation is determined according to NLM or other control algorithms, and finally the modules are selected in turn for charging and discharging operations according to the order of the input counter queue until K modules are reached or the queue ends.

[0077] In some possible embodiments, S2 specifically includes:

[0078] Set the charge balance index and discharge balance index to EQU_CHG respectively. j,x ,EQU_DCHG j,x .

[0079] Select SOC j,x and (1-SOC) j,x , as a balance indicator, or the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x as an indicator of equilibrium.

[0080] Among them, when selecting the balance index, it is selected according to the needs of the user. At present, most of them are based on SOC as the balance index. Taking SOC as the balance index mainly considers the balance within a charge and discharge cycle, and taking the maximum charge and discharge current as the main consideration is that the short-term heating of the battery is within a safe range.

[0081] All charging and discharging balancing indicators of the same-phase or same-bridge-arm modules are normalized to generate normalized charging and discharging balancing indicators.

[0082] In this application, the balancing indicators (SOC or maximum charge and discharge current) are obtained from the battery management system (BMS) and are continuously updated during operation, and the update cycle is generally within 1 second.

[0083] The purpose of using the SOC balance indicator is to allow the modules with more power to discharge faster during discharge, and to allow the modules with less power to charge faster during charge.

[0084] The purpose of using the maximum charge and discharge current as the balancing indicator is to allow the modules with strong discharge capabilities to discharge faster during discharge, and to allow the modules with strong charging capabilities to charge faster during charge.

[0085] In the above embodiment, one specific implementation method is: when selecting SOC j,x and (1-SOC) j,x , when used as a balance indicator, EQU_CHG j,x , = (1-SOC) j,x ;EQU_DCHG j,x =SOC j,x .

[0086] Another specific implementation is: select the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x When used as a balance indicator, EQU_CHG j,x ,=MAX_CHG j,x ;EQU_DCHG j,x =MAX_DCHG j,x .

[0087] In some possible implementation examples, the normalized charging balance index and discharging balance index are respectively:

[0088]

[0089] Among them, equ_chg j,x Represents the normalized charge equalization index; equ_dchg j,x Represents the normalized discharge balance index.

[0090] First, according to the engineering requirements or system operating status, decide whether to select SOC (and its corresponding charging demand and discharge capacity) as the balancing indicator or to select the maximum chargeable and dischargeable current as the balancing indicator.

[0091] If SOC is selected as the balancing indicator, then for each module j, x, its charging balancing indicator EQU_CHG j,x =(1-SOC) j,x , indicating the charging demand of the module; discharge balance indicator EQU_DCHG j,x Equal to SOC j,x , indicating the discharge capacity of the module. If the maximum charge and discharge current is selected as the balancing indicator, MAX_CHG is used directly. j,x and MAX_DCHG j,x As the charge and discharge balance index. Finally, all the charge and discharge balance indexes of the same phase or same bridge arm modules are normalized. In this way, the system can more accurately evaluate the balance requirements and capabilities of each module, and make more reasonable charge and discharge decisions accordingly, thereby realizing the balance management within the battery pack.

[0092] By allowing the selection of a balancing indicator between SOC and the maximum charge and discharge current, the system can adapt to different application scenarios and requirements, ensuring that the system can achieve the optimal balancing effect under different operating conditions. By normalizing the balancing indicator and reducing the performance differences between modules, the energy of the battery pack can be more effectively utilized, thereby improving the overall efficiency of the system.

[0093] In some possible embodiments, S3 specifically includes:

[0094] The power control period Tp and the balancing control period Tequ are obtained, and a ratio M=Tequ / Tp between the two is calculated.

[0095] The power control period Tp refers to the time interval for the operation of the active and reactive power control algorithm of the energy storage system, which is related to the computing power of the processor and the size of the inertial components of the main circuit (such as the inductance value), and is generally 50-100us.

[0096] The balancing control period Tequ refers to the time interval between two adjustments to balance the power of each module. This time interval depends on the duration of the energy storage system, and the balancing control period can be no more than 1% of its energy storage duration. For example, for an energy storage system with a storage duration of 30 minutes, its balancing control period can be no less than 18 seconds.

[0097] Set a input counter CT for each module j,x .

[0098] The input counter is used to store how many control cycles each module can be put into operation (charging or discharging) in one balancing cycle. The larger the count value, the greater the charging or discharging amount in one balancing control cycle.

[0099] The normalized charge and discharge balance index is obtained, the input counter value of each module is calculated, and the calculated input counter is used to generate an input counter column.

[0100] In S3, the processing mainly revolves around calculating the input counter value of each module and generating an input counter queue. The following are the detailed steps:

[0101] In the above embodiment, the input counter value of each module is calculated, and the calculated input counter is used to generate an input counter sequence, including:

[0102] The normalized charging balance index and the ratio M between the power control period Tp and the balance control period Tequ are obtained, and the input calculator value during charging is calculated.

[0103] The normalized discharge balance index and the ratio M between the power control period Tp and the balance control period Tequ are obtained, and the input calculator value during discharge is calculated.

[0104] Set the input counter value CT of all modules j,x Combined into a [CT j,1 ,CT j,2 ,…,CT j,N ] queue.

[0105] The present application first obtains the power control period Tp and the balancing control period Tequ. The ratio M = Tequ / Tp between the two is calculated to allocate the balancing demand within the balancing control period to each power control period; then an input counter CT is set for each module j, x respectively j,x , the initial value can be 0, and the normalized charge equalization index equ_chg is used j,x and discharge balance indicator equ_dchg j,x , and the ratio M, to calculate the input counter value of each module during charging and discharging.

[0106] In the above embodiment, the input calculator value during charging is:

[0107] CT j,x =equ_chg j,x ×M.

[0108] The input calculator value during discharge is:

[0109] CT j,x =equ_dchg j,x ×M.

[0110] Among them, if the calculated CT j,x If it is a decimal, it will be rounded up according to the rules.

[0111] Set the input counter value CT of all modules j,x Combine into a queue according to the module number (or other logical order), such as [CT j,1 ,CT j,2 ,…,CT j,N ], where N is the total number of modules in that phase or leg.

[0112] By calculating the input counter value of each module, the system can more accurately control the degree of participation of each module in the charging and discharging process and achieve more refined balancing management; the input counter is calculated based on the normalized balancing index to ensure that all modules can be selected fairly during the balancing process, which can more effectively utilize the energy of the battery pack, reduce unnecessary energy loss, and improve the overall efficiency of the system.

[0113] For example: assuming that only the charging mode is considered currently, there are 10 modules (a1, a2, …, a10) in the same phase, the power control period Tp is 100us, the balancing control period Tequ is 1s, and the normalized charging balancing indicators are equ_chg_a1=0.1, equ_chg_a2=0.11, equ_chg_a3=0.12, equ_chg_a4=0.08, equ_chg_a5=0.09, equ_chg_a6=0.1, equ_chg_a7=0.1, equ_chg_a8=0.1, equ_chg_a9=0.1, equ_chg_a10=0.1.

[0114] The calculated ratio is M=Tequ / Tp=1s / 100us=10000.

[0115] Calculate the input counter value for each module:

[0116] equ_chg_a1×M=0.1×10000=1000.

[0117] equ_chg_a2×M=0.11×10000=1100.

[0118] equ_chg_a3×M=0.12×10000=1200.

[0119] equ_chg_a4×M=0.08×10000=800.

[0120] equ_chg_a5×M=0.09×10000=900.

[0121] equ_chg_a6×M=0.1×10000=1000.

[0122] equ_chg_a7×M=0.1×10000=1000.

[0123] equ_chg_a8×M=0.1×10000=1000.

[0124] equ_chg_a9×M=0.1×10000=1000.

[0125] equ_chg_a10×M=0.1×10000=1000.

[0126] Generate an input counter queue: [CT_a1, CT_a2, CT_a3, CT_a4, CT_a5, CT_a6, CT_a7, CT_a8, CT_a9, CT_a10] = [1000, 1100,, 1200, 800, 900, 1000, 1000, 1000, 1000, 1000].

[0127] Reference Figure 2 As shown, in some possible embodiments, in S4, specifically including:

[0128] S41. At the beginning of each power control cycle, the controller calculates the number of modules K that currently need to be put into use through a nearest level modulation algorithm.

[0129] S42, according to the set reading rules, from the input counter queue [CT j,1 ,CT j,2 ,…,CT j,N ] starts reading from the starting position and selects the input module according to the reading rules.

[0130] S43, obtaining the number of modules selected for input, and determining whether the number of modules input reaches the number of modules K currently required for input. If so, stop the selection.

[0131] Specifically, the controller uses the nearest level modulation algorithm (NLM) to calculate the number of modules K that need to be put into use according to the current system voltage; wherein the number K changes dynamically and depends on the real-time operating status of the system; then, according to the selection rules set by the system, the modules to be put into use are selected from the generated input counter queue, and in the process of selecting modules, the number of selected modules is counted in real time. Once the number of selected modules reaches or exceeds K, the selection process is stopped and these modules are used in the current power control cycle.

[0132] The present application realizes precise control of the system state and improves the stability and response speed of the system by dynamically calculating the number of modules that need to be invested, assigning the number of counts to different modules, and selecting modules in combination with the investment counter queue. In the selection process, the investment counter queue is read cyclically and the selection is stopped immediately when the required number of modules is reached, thus reducing unnecessary calculation and judgment processes and improving the operation efficiency of the system.

[0133] Reference Figure 3 As shown, in the above embodiment, in S42, specifically includes:

[0134] S421, setting the module selected for input in the yth power control cycle;

[0135] S422, from the queue [CT j,1 ,CT j,2 ,…,CT j,N ] reads the yth element CT j,y ; In CT j,y = 0, the yth module is not put into use; j,y >0, then CT j,y Subtract 1 and select the yth module as the input module.

[0136] S423, Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+1)th element CT j,(y+1) CT j,(y+1) =0, the (y+1)th module is not put into use; if CT j,(y+1) >0, then CT j,(y+1) Subtract 1 and select the (y+1)th as the input module.

[0137] S424, read queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+x)th element CT j,(y+x) CT j,(y+x) =0, the (y+x)th module is not put into use; if CT j,(y+x) >0, then CT j,(y+x) Subtract 1 and select the (y+x)th module as the input module.

[0138] If (y+x)>N, then read the (y+xN)th element CT from the head of the queue j,(y+x-N) As the basis for calculation and judgment in the above process.

[0139] Specifically, from the input counter queue [CTj,1 ,CT j,2 ,…,CT j,N ] starts reading from the starting position (i.e. the first element); reads the input counter value CT at the current position j,y (where y is the current read position index, initially 1); if CT j,y If it is greater than 0, it means that the module should be put into use in the current power control cycle; at this time, CT j,y Subtract 1 (indicating that the module has been selected once), and mark the module as in the engaged state; then, increase the read position index y by 1, and continue to read the input counter value of the next position; if CT j,y If it is equal to 0, it means that the module should not be put into use in the current power control cycle, and the module is skipped directly. Repeat the above steps until the total number of selected modules reaches K, or the entire queue has been traversed.

[0140] Finally, if the read position index y exceeds the queue length N (ie, y>N), rereading starts from the head of the queue (ie, y=y-N) until the total number of selected modules reaches K.

[0141] For example: Assume that each phase of the energy storage system has 10 modules, and take the intra-phase balancing control of phase A as an example. Assume that after the battery energy storage system has run for 8 power control cycles, the total number of modules that need to be put into use in phase A given by the power control strategy in the 9th power control cycle is 8. Assume that at this time, the counter queue [CT j,1 ,CT j,2 ,…,CT j,10 ]=[994,1094,1194,794,894,994,994,993,994,995]. The module to be put into use is selected in the 9th power control cycle.

[0142] From the queue [CT j,1 ,CT j,2 ,…,CT j,10 ] reads the ninth element CT j,9 ; Due to CT j,9 =994>0, the 9th module is selected as the input module, and CT j,9 Subtract 1 and update to CT j,9 =993.

[0143] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] reads the 10th element CT j,10 ; Due to CT j,10 =995>0, then select the (y+1)th module as the input module, and set CT j,10Subtract 1 and update to CT j,10 =994.

[0144] The previous step has read to the end of the queue, so loop back to the head of the queue and read the queue [CT j,1 ,CT j,2 ,…,CT j,10 ] reads the first element CT j,1 ; Due to CT j,1 =994>0, then the (y+x)th module is selected as the input module, and CTj,(y+x) is reduced by 1 and updated to CT j,1 =993.

[0145] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] read the second element CT j,2 ; Due to CT j,2 =1094>0, then select the second module as the input module, and set CT j,2 Subtract 1 and update to CT j,2 =1093.

[0146] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] read the third element CT j,3 ; Due to CT j,2 =1194>0, then select the third module as the input module, and set CT j,3 Subtract 1 and update to CT j,3 =1193.

[0147] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] reads the fourth element CT j,4 ; Due to CT j,4 =794>0, then select the 4th module as the input module, and set CT j,4 Subtract 1 and update to CT j,4 =793.

[0148] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] read the fifth element CT j,5 ; Due to CT j,5 =894>0, then select the 5th module as the input module, and set CT j,5 Subtract 1 and update to CT j,5 =893.

[0149] Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,10 ] read the sixth element CT j,6 ; Due to CT j,6 =994>0, then select the 6th module as the input module, and set CT j,6 Subtract 1 and update to CT j,6 =993.

[0150] A second aspect of the present invention provides a phase balancing system based on NLM for a modular cascade battery energy storage system, comprising:

[0151] The acquisition module is used to obtain the SOC of the DC side battery of each module through the battery management system according to the balancing control cycle Tequ j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x .

[0152] The selection module is used to select appropriate balancing indicators according to engineering needs; the balancing indicators include charging balancing indicators and discharging balancing indicators.

[0153] The calculation module is used to calculate the input counter CT of each module according to the power control period Tp and the balance control period Tequ j,x , generate an input counter queue.

[0154] The determination module is used to determine the number of modules K that need to be put into use in each power control cycle according to the latest level modulation algorithm or other control algorithms to perform charging and discharging operations.

[0155] This application obtains the SOC of the DC side battery of each module according to the balancing control cycle Tequ through the battery management system at regular intervals. j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x Then, by selecting the module, according to the project needs, select the appropriate balance index; normalize all the charge balance and discharge balance indexes of the same phase or same bridge arm modules to generate the normalized charge balance index and discharge balance index equ_chg j,x , equ_dchg j,x Then, the calculation module calculates the input counter CT of each module according to the power control period Tp and the balance control period Tequ. j,x, generate the input counter queue [CT j,1 ,CT j,2 ,…,CT j,N ], finally, according to the determined module, in each power control cycle, the number of modules K that need to be put into use is determined according to the nearest level modulation algorithm or other control algorithms, and the charging and discharging operations are performed. Compared with the traditional balancing control that allocates different powers to different modules at the same time, which is regulated from the power dimension, the intra-phase balancing is realized according to the SOC and the maximum chargeable and dischargeable current of each sub-module in each phase, and the investment time is allocated to different modules in proportion, that is, the intra-phase balancing is achieved by regulating from the time dimension, avoiding real-time monitoring of the direction of the current flowing into the module, and the control cycle of the balancing control strategy can be much longer than the power control cycle. For example, if the power control cycle is 50-100us, the balancing control cycle can reach more than 10ms, or even seconds, which greatly reduces the demand for controller resources.

[0156] The above describes the specific embodiments of the present application. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the substantive content of the present application. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A phase balancing method based on NLM for a modular cascade battery energy storage system, characterized in that: The method comprises: S1. According to the balancing control cycle Tequ, the battery management system regularly obtains the SOC of the DC side battery of each module j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x ; S2. Select appropriate balancing indicators according to project requirements; the balancing indicators include charging balancing indicators and discharging balancing indicators; S3, calculating the input counter CTj,x of each module according to the power control period Tp and the balance control period Tequ, and generating an input counter queue; S4. In each power control cycle, the number of modules K required to be put into use is determined according to the latest level modulation algorithm or other control algorithms, and charging and discharging operations are performed.

2. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 1, characterized in that: In S2, it specifically includes: Set the charge balance index and discharge balance index to EQU_CHG respectively. j,x ,EQU_DCHG j,x ; Select SOC j,x and (1-SOC) j,x , as a balance indicator, or the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x As an indicator of equilibrium; All charging and discharging balancing indicators of the same-phase or same-bridge-arm modules are normalized to generate normalized charging and discharging balancing indicators.

3. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 2, characterized in that: When selecting SOC j,x and (1-SOC) j,x , when used as a balance indicator, EQU_CHG j,x , = (1-SOC) j,x ;EQU_DCHG j,x =SOC j,x ; Select the maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x When used as a balance indicator, EQU_CHG j,x ,=MAX_CHG j,x ;EQU_DCHG j,x =MAX_DCHG j,x .

4. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 2, characterized in that: The normalized charge balance index and discharge balance index are respectively: Among them, equ_chg j,x Represents the normalized charge equalization index; equ_dchg j,x Represents the normalized discharge balance index.

5. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 2, characterized in that: In S3, it specifically includes: Obtain the power control period Tp and the balancing control period Tequ, and calculate the ratio of the two M=Tequ / Tp; Set a input counter CT for each module j,x ; The normalized charge and discharge balance index is obtained, the input counter value of each module is calculated, and the calculated input counter is used to generate an input counter column.

6. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 5, characterized in that: The step of calculating the input counter value of each module and generating an input counter sequence from the calculated input counter includes: Obtain the ratio M between the normalized charging equalization index and the power control period Tp and the equalization control period Tequ, and calculate the input calculator value during charging; Obtain the ratio M between the normalized discharge balance index and the power control period Tp and the balance control period Tequ, and calculate the input calculator value during discharge; Set the input counter value CT of all modules j,x Combined into a [CT j,1 ,CT j,2 ,…,CT j,N ] queue.

7. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 6, characterized in that: The input calculator value for charging is: CT j,x =equ_chg j,x ×M; The input calculator value during the discharge is: CT j,x =equ_dchg j,x ×M; Among them, if the calculated CT j,x If it is a decimal, it will be rounded up according to the rules.

8. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 1, characterized in that: In S4, it specifically includes: S41, at the beginning of each power control cycle, the controller calculates the number of modules K that currently need to be put into use through the nearest level modulation algorithm; S42, according to the set reading rules, from the input counter queue [CT j,1 ,CT j,2 ,…,CT j,N ] starts reading from the starting position and selects the input module according to the reading rules; S43, obtaining the number of modules selected for input, and determining whether the number of modules input reaches the number of modules K currently required for calculation, and if so, stopping the selection.

9. The NLM-based intra-phase balancing method for a modular cascade battery energy storage system according to claim 8, characterized in that: In S42, specifically including: S421, setting the module selected for input in the yth power control cycle; S422, from the queue [CT j,1 ,CT j,2 ,…,CT j,N ] reads the yth element CT j,y ; In CT j,y = 0, the yth module is not put into use; j,y >0, then CT j,(y+1) Subtract 1, and select the yth module as the input module; S423, Sequential Read Queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+1)th element CT j,(y+1) CT j,(y+1) =0, the (y+1)th module is not put into use; if CT j,(y+1) >0, then CT j,(y+1) Subtract 1, and select the (y+1)th as the input module; S424, read queue [CT j,1 ,CT j,2 ,…,CT j,N ] read the (y+x)th element CT j,(y+x) CT j,(y+x) =0, the (y+x)th module is not put into use; if CT j,(y+x) >0, then CT j,(y+x) Subtract 1, and select the (y+x)th module as the input module; If (y+x)>N, then read the (y+xN)th element CT from the head of the queue j,(y+x-N) As the basis for calculation and judgment in the above process.

10. A modular cascade battery energy storage system based on NLM phase balancing system, characterized in that: include: The acquisition module is used to obtain the SOC of the DC side battery of each module through the battery management system according to the balancing control cycle Tequ j,x and (1-SOC) j,x , Maximum chargeable current MAX_CHG j,x and the maximum discharge current MAX_DCHG j,x ; A selection module is used to select appropriate balancing indicators according to engineering needs; the balancing indicators include charging balancing indicators and discharging balancing indicators; The calculation module is used to calculate the input counter CT of each module according to the power control period Tp and the balance control period Tequ j,x , generate an input counter queue; The determination module is used to determine the number of modules K that need to be put into use in each power control cycle according to the latest level modulation algorithm or other control algorithms to perform charging and discharging operations.

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