A multi-AC feed type converter station simulation method, device, terminal equipment, storage medium and multi-AC feed type converter station

Abstract

The present invention discloses a multi-AC feeder converter station simulation method, device, terminal equipment, storage medium and multi-AC feeder converter station. The method first obtains preset power flow parameters, and determines the DC side voltage of the MMC in the multi-AC feeder converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC and the capacitance value of the half-bridge submodules in the MMC, the number of full-bridge submodules in the eACPFC and the capacitance value of the full-bridge submodules, based on the power flow parameters. Then, when the determined key parameters and the power flow parameters are input into preset simulation software, the generated simulation results can more accurately evaluate the performance of the multi-AC feeder converter station system and reduce the initial investment and operating costs of the system.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a multi-AC feed-type converter station simulation method, device, terminal equipment, storage medium, and multi-AC feed-type converter station. Background Art

[0002] Currently, multi-terminal flexible DC transmission projects often use a back-to-back modular multi-level converter (BTB-MMC) solution, where multiple lines are interconnected with the HVDC line via full-power MMCs. While this existing solution combines the advantages of flexible interconnection and DC transmission, its high cost and large footprint make it difficult to implement on a large scale.

[0003] In response to the above problems, some researchers have proposed a multi-AC-fed converter station at the receiving end of a sea breeze flexible DC system. The multi-AC-fed converter station at the receiving end of a sea breeze flexible DC system consists of an MMC and an AC power flow controller (eACPFC) embedded in the MMC. The eACPFC can interconnect multiple AC lines and has the ability to independently decouple and control the active and reactive power of each line, thereby realizing the joint absorption of DC-transmitted sea wind power by multiple lines. By adjusting the DC component and interacting with the MMC DC circulation, the embedded eACPFC power balance can be achieved. Compared with the traditional BTB-MMC solution, the proposed multi-AC-fed converter station at the receiving end of a sea breeze flexible DC system has the advantages of compactness, low cost, and easy expansion. However, when simulating the multi-AC-fed converter station system at the receiving end of the offshore wind flexible direct current system, if reasonable main circuit parameters are lacking, there may be a large deviation between the simulation results and the actual operating conditions. This not only makes it impossible to accurately evaluate the dynamic and steady-state performance of the system, but may also mislead design decisions and increase the initial investment and operating costs of the system. Summary of the Invention

[0004] The present invention provides a multi-AC feed type converter station simulation method, apparatus, terminal equipment, storage medium and multi-AC feed type converter station. The simulation results generated by the multi-AC feed type converter station simulation method can more accurately evaluate the performance of the multi-AC feed type converter station system and reduce the initial investment and operating costs of the system.

[0005] An embodiment of the present invention provides a multi-AC feed-type converter station simulation method, comprising:

[0006] Get the preset power flow parameters;

[0007] Determining, based on the power flow parameters, the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC, and the capacitance value of the half-bridge submodule in the MMC;

[0008] Determining the number of full-bridge submodules and the capacitance values ​​of the full-bridge submodules in the eACPFC according to the power flow parameters; wherein the eACPFC is embedded in the MMC;

[0009] The power flow parameters, the DC side voltage, the number of half-bridge sub-modules in the MMC, the bridge arm inductance, the capacitance value of the half-bridge sub-module in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance value of the full-bridge sub-module are input into the preset simulation software to generate the simulation results of the multi-AC feed-type converter station.

[0010] Furthermore, the power flow parameters include: the rated line voltage of the AC line, the rated capacity of the feeder, the effective value of the AC port output voltage, the compensated DC common-mode voltage, the DC side rated current, the preset operating voltage of the switching device, the grid angular frequency, the preset maximum fluctuation rate of the sub-module capacitor voltage, the rated capacitor voltage of the full-bridge sub-module in the eACPFC, the MMC modulation index, the preset equivalent reactance capacity range, the preset bridge arm current rise rate, the double frequency current, the phase voltage rated value, the maximum DC common-mode voltage, the bridge arm fundamental frequency differential mode output voltage, the AC line current value and the DC circulating current of the full-bridge sub-module.

[0011] Furthermore, the determining, based on the power flow parameters, the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the arm inductance of the MMC, and the capacitance of the half-bridge submodule in the MMC includes:

[0012] Determining the DC side voltage of the MMC in the multi-AC feeder converter station according to the effective value of the AC port output voltage and the compensated DC common mode voltage;

[0013] Determining the rated capacitance voltage of the MMC submodule according to the preset operating voltage of the switching device;

[0014] Determining the number of half-bridge submodules in the MMC according to the rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feed-type converter station;

[0015] Determining the capacitance value of the half-bridge submodule in the MMC according to the feeder rated capacity, the grid angular frequency, the preset submodule capacitor voltage maximum fluctuation rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the MMC modulation index, and the number of half-bridge submodules in the MMC;

[0016] The bridge arm inductance of the MMC is determined according to the preset equivalent reactance capacity interval, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the double frequency current and the feeder rated capacity.

[0017] Furthermore, determining the bridge arm inductance of the MMC according to the preset equivalent reactance capacity interval, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the doubled frequency current, and the feeder rated capacity includes:

[0018] Determining a first candidate interval of the bridge arm inductance in the MMC according to the preset equivalent reactance capacity interval;

[0019] Determine a first lower limit of the bridge arm inductance in the MMC according to the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the doubled frequency current, the feeder rated capacity, and the DC side voltage of the MMC in the multi-AC feeder converter station;

[0020] Determining a second lower limit value of the bridge arm inductance in the MMC according to the bridge arm current rising rate and the DC side voltage of the MMC in the multi-AC feed-type converter station;

[0021] The bridge arm inductance of the MMC is determined according to the first candidate interval, the first lower limit value, and the second lower limit value.

[0022] Furthermore, determining the number of full-bridge submodules in the eACPFC and the capacitance values ​​of the full-bridge submodules according to the power flow parameters includes:

[0023] Determining the number of full-bridge submodules in the eACPFC according to the rated capacitor voltage of the MMC submodule, the phase voltage rating, and the maximum DC common mode voltage;

[0024] The capacitance value of the full-bridge submodule is determined based on the preset maximum fluctuation rate of the submodule capacitor voltage, the grid angular frequency, the number of full-bridge submodules in the eACPFC, the compensated DC common-mode voltage, the rated capacitor voltage of the full-bridge submodule in the eACPFC, the bridge arm fundamental frequency differential-mode output voltage, the AC line current value, and the DC circulating current of the full-bridge submodule.

[0025] Furthermore, the multi-AC feed-type converter station simulation method further includes:

[0026] Determining a feeder rated current according to the rated line voltage and the feeder rated capacity;

[0027] determining an operating current of the switching device according to the feeder rated current and the DC side rated current;

[0028] The model information of the switching device in the half-bridge submodule in the MMC is determined according to the operating current of the switching device and the preset operating voltage of the switching device.

[0029] An embodiment of the present invention further provides a multi-AC feed-in converter station simulation device, comprising: a data acquisition module, an MMC parameter determination module, an eACPFC parameter determination module, and a simulation module;

[0030] The data acquisition module is used to obtain preset power flow parameters;

[0031] The MMC parameter determination module is used to determine the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC, and the capacitance value of the half-bridge submodule in the MMC according to the power flow parameters;

[0032] The eACPFC parameter determination module is used to determine the number of full-bridge submodules in the eACPFC and the capacitance value of the full-bridge submodules according to the power flow parameters; wherein the eACPFC is embedded in the MMC;

[0033] The simulation module is used to input the power flow parameters, the DC side voltage, the number of half-bridge sub-modules in the MMC, the bridge arm inductance, the capacitance of the half-bridge sub-modules in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance of the full-bridge sub-modules into the preset simulation software to generate simulation results of the multi-AC feed-type converter station.

[0034] The present application also provides a terminal device, including:

[0035] one or more processors;

[0036] a memory, coupled to the processor, for storing one or more programs;

[0037] When the one or more programs are executed by the one or more processors, the one or more processors implement the multi-AC feed-type converter station simulation method as described in the above-mentioned embodiment of the invention.

[0038] The present application also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the multi-AC feed-type converter station simulation method as described in the above-mentioned embodiment of the invention is implemented.

[0039] An embodiment of the present invention further provides a multi-AC feed-in converter station, characterized by comprising: an MMC and an eACPFC embedded in the MMC;

[0040] The MMC is composed of three phase units connected in parallel, each phase unit includes two bridge arms, and each bridge arm is composed of a plurality of half-bridge sub-modules connected in cascade;

[0041] The eACPFC comprises a plurality of eACPFC subunits, each of which is composed of a plurality of full-bridge submodules;

[0042] Among them, the DC side voltage of the MMC in the multi-AC fed converter station, the number of half-bridge sub-modules in the MMC, the bridge arm inductance of the MMC, the capacitance value of the half-bridge sub-module in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance value of the full-bridge sub-module are determined according to the preset power flow parameters.

[0043] The following beneficial effects are achieved by implementing the present invention:

[0044] The present invention provides a multi-AC feeder converter station simulation method, device, terminal equipment, storage medium and multi-AC feeder converter station. The method obtains preset power flow parameters and determines the key parameters of the main circuit according to the power flow parameters, wherein the key parameters of the main circuit include the DC side voltage of the MMC in the multi-AC feeder converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC and the capacitance value of the half-bridge submodule in the MMC, the number of full-bridge submodules in the eACPFC and the capacitance value of the full-bridge submodule; wherein the eACPFC is embedded in the MMC, thereby, when the key parameters of the main circuit and the preset power flow parameters are input into the preset simulation software, the generated simulation results can more accurately evaluate the performance of the multi-AC feeder converter station system, thereby facilitating engineering design and reducing the initial investment and operating costs of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0046] Figure 1 This is a flow chart of a multi-AC feed-type converter station simulation method provided in one embodiment of the present application;

[0047] Figure 2 This is the capacitor voltage waveform of some submodules of the multi-AC feed-in converter station MMC provided by one embodiment of the present application;

[0048] Figure 3 This is the capacitor voltage waveform of some submodules of the eACPFC multi-AC feed-in converter station provided by an embodiment of the present application;

[0049] Figure 4 This is the current waveform of line 1 connected to a multi-AC feeder converter station provided in one embodiment of the present application;

[0050] Figure 5 This is the current waveform of line 2 connected to a multi-AC feeder converter station provided in one embodiment of the present application;

[0051] Figure 6 This is the current waveform of line 3 connected to a multi-AC feeder converter station provided in one embodiment of the present application;

[0052] Figure 7 The voltage and current waveforms of the DC lines connected to the multi-AC feeder converter station provided in one embodiment of the present application are as follows;

[0053] Figure 8 This is the active power waveform of each line connected to the multi-AC feed-out converter station provided in one embodiment of the present application;

[0054] Figure 9 This is the reactive power waveform of each line connected to the multi-AC feed-type converter station provided in one embodiment of the present application;

[0055] Figure 10 This is a schematic diagram of the topological structure of a multi-AC feed-type converter station provided in one embodiment of the present application;

[0056] Figure 11 This is a structural diagram of a multi-AC feed-type converter station simulation device provided in one embodiment of the present application;

[0057] Figure 12 This is a schematic diagram of the structure of a terminal device provided in a certain embodiment of the present application. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions in this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0059] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0060] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0061] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0062] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0063] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0064] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0065] See also Figure 1 , is a flow chart of a multi-AC feed-in converter station simulation method provided by one embodiment of the present invention, comprising:

[0066] S1. Obtain preset power flow parameters;

[0067] In a preferred embodiment, the power flow parameters include: the rated line voltage of the AC line, the rated capacity of the feeder, the effective value of the AC port output voltage, the compensated DC common mode voltage, the DC side rated current, the preset operating voltage of the switching device, the grid angular frequency, the preset maximum fluctuation rate of the sub-module capacitor voltage, the rated capacitor voltage of the full-bridge sub-module in the eACPFC, the MMC modulation index, the preset equivalent reactance capacity range, the preset bridge arm current rise rate, the double frequency current, the phase voltage rated value, the maximum DC common mode voltage, the bridge arm fundamental frequency differential mode output voltage, the AC line current value and the DC circulating current of the full-bridge sub-module.

[0068] S2. Determine, based on the power flow parameters, the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the arm inductance of the MMC, and the capacitance of the half-bridge submodules in the MMC;

[0069] In a preferred embodiment, determining the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC, and the capacitance value of the half-bridge submodule in the MMC based on the power flow parameters includes:

[0070] Determining the DC side voltage of the MMC in the multi-AC feeder converter station according to the effective value of the AC port output voltage and the compensated DC common mode voltage;

[0071] Determining the rated capacitance voltage of the MMC submodule according to the preset operating voltage of the switching device;

[0072] Determining the number of half-bridge submodules in the MMC according to the rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feed-type converter station;

[0073] Determining the capacitance value of the half-bridge submodule in the MMC according to the feeder rated capacity, the grid angular frequency, the preset submodule capacitor voltage maximum fluctuation rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the MMC modulation index, and the number of half-bridge submodules in the MMC;

[0074] Determine the bridge arm inductance of the MMC according to the preset equivalent reactance capacity range, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the double frequency current, and the feeder rated capacity;

[0075] Specifically, according to the actual application scenario requirements, select the rated line voltage V of the AC line line , feeder rated capacity S N_line , then the feeder rated current is recorded as I N ,MMC rated capacity S N Same as the feeder rated capacity, i.e. S N =S N_line .

[0076] Specifically, in order to ensure the required voltage output by the MMC bridge arm, it is necessary to first analyze the components of the MMC bridge arm voltage. The components of the upper and lower bridge arm voltages of the MMC can be expressed as

[0077]

[0078] Where, v p is the voltage modulation wave of the upper bridge arm of MMC; v n is the voltage modulation wave of the lower bridge arm of MMC; V dc V is the DC side voltage of the MMC in the multi-AC feeder converter station; diff is the effective value of the AC port output voltage; V c_dc To compensate for the DC common-mode voltage, compensation is performed in the MMC bridge arm, thereby preventing the introduction of additional circulating current in the MMC.

[0079] It should be noted that the DC side voltage is the voltage of the DC line to which the multi-AC feeder converter station MMC part is connected;

[0080] In order to ensure that the MMC bridge arm can modulate the above voltage components, the DC side voltage of the MMC must meet

[0081]

[0082] Among them, V diff is the effective value of the AC port output voltage; V c_dcTo compensate for DC common-mode voltage.

[0083] Therefore, according to formula (3), according to the obtained AC port output voltage effective value V diff and compensated DC common mode voltage V c_dc , calculate and obtain the DC side voltage of the MMC in the multi-AC feeder converter station.

[0084] Schematically, the bridge arms of an MMC are cascaded half-bridge structures. The number of half-bridge submodules in an MMC directly depends on the selected submodule capacitor voltage and the DC side voltage. To ensure device reliability, a certain margin is usually retained when selecting the number of half-bridge submodules. When the selected half-bridge submodule capacitor voltage value is too large, a higher-voltage-withstand switching device is required, and the corresponding manufacturing cost will increase sharply. A smaller number of half-bridge submodules will result in a lower output voltage level and poorer harmonic characteristics. If the selected half-bridge submodule capacitor voltage value is too low, the manufacturing cost of the required switching devices will be significantly reduced, but the excessive number of half-bridge submodules will complicate control and increase the overall size of the device. Based on engineering experience, the operating voltage of an IGBT is generally suitable to be between 50% and 70% of its rated voltage. When the operating voltage is too high, the device loss will increase significantly, while when the operating voltage is too low, the device utilization rate will be insufficient.

[0085] Specifically, after determining the preset operating voltage V corresponding to the selected switching device type, IGBT Then, according to the preset working voltage V IGBT , determine the rated capacitance voltage of the MMC submodule, as shown in the following formula:

[0086] 0.5 V IGBT ≤V c ≤0.7·V IGBT ; (4)

[0087] Where V c is the rated capacitance voltage of the MMC submodule;

[0088] Then, the number of half-bridge submodules in the MMC is determined according to the rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feed-out converter station. The number N of half-bridge submodules in the MMC is determined by the following formula: MMC :

[0089]

[0090] Therefore, the number of half-bridge submodules in the MMC is determined according to the determined rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feeder converter station.

[0091] Schematically, the capacitance value of the half-bridge submodule in the MMC is determined mainly based on the capacitor's suppression effect on DC voltage ripple, and its capacitor voltage fluctuation is constrained within a specified range to limit the voltage stress of the device;

[0092] The bridge arm voltage of MMC is shown in formula (1), and the bridge arm current can be expressed as

[0093]

[0094] Where, I dc is the DC side current, i diff is the MMC differential mode AC output current, where the instantaneous expression of the AC component is

[0095]

[0096] Where V diff is the effective value of the AC port output voltage; δ diff is the AC port output voltage phase; I diff is the effective value of the AC port output current; ρ diff is the AC port output current phase. The MMC modulation index is

[0097]

[0098] Combining equations (1), (5) and (6), the current flowing into the MMC submodule capacitor can be expressed as

[0099]

[0100] Due to the power balance constraint, the DC component of the capacitor current of the half-bridge submodule is 0, and the capacitor voltage fluctuation of the half-bridge submodule can be expressed as

[0101]

[0102] The capacitor voltage fluctuation of the half-bridge submodule in the MMC includes the fundamental frequency component and the double frequency component, and their fluctuation rates can be expressed as

[0103]

[0104] From Equation 10), we can see that when cosφ = 0, the fundamental frequency fluctuation reaches its maximum value. Considering the fundamental frequency component and the double frequency component of the capacitor voltage fluctuation, the maximum fluctuation rate is set to ε. Then the capacitance value of the MMC half-bridge submodule satisfies the following equation:

[0105]

[0106] Where N MMC is the number of half-bridge submodules in the MMC;N is the rated capacity of the MMC; ω is the grid angular frequency; ε is the maximum fluctuation rate of the preset submodule capacitor voltage; V dc is the DC side voltage of the MMC in the multi-AC feeder converter station; m' is the MMC modulation index.

[0107] Specifically, the capacitance value of the half-bridge submodule in the MMC is determined based on the obtained MMC modulation index, grid angular frequency, preset submodule capacitor voltage maximum fluctuation rate, the number of half-bridge submodules in the MMC, the DC side voltage of the MMC in the multi-AC feeder converter station, and the MMC rated capacity;

[0108] Schematically, the bridge arm inductor acts as the link for power transmission between the MMC and the AC grid, regulating power transmission and suppressing output current fluctuations. The bridge arm inductor forms part of the MMC's internal circulating current loop and effectively suppresses internal circulating currents. The design of the bridge arm inductor is crucial to the stable operation of the MMC and system performance. Therefore, parameter design must be comprehensively considered from multiple perspectives, including meeting system power requirements, circulating current suppression, and fault current suppression.

[0109] In a preferred embodiment, determining the bridge arm inductance of the MMC according to the preset equivalent reactance capacity interval, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the double frequency current, and the feeder rated capacity includes:

[0110] Determining a first candidate interval of the bridge arm inductance in the MMC according to the preset equivalent reactance capacity interval;

[0111] Determine a first lower limit of the bridge arm inductance in the MMC according to the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the doubled frequency current, the feeder rated capacity, and the DC side voltage of the MMC in the multi-AC feeder converter station;

[0112] Determining a second lower limit value of the bridge arm inductance in the MMC according to the bridge arm current rising rate and the DC side voltage of the MMC in the multi-AC feed-type converter station;

[0113] determining the bridge arm inductance of the MMC according to the first candidate interval, the first lower limit, and the second lower limit;

[0114] Specifically, first, the bridge arm inductance of the MMC must meet the system power operation requirements. N Based on this capacity, the unit value of the equivalent reactance is

[0115]

[0116] Where S LN is the per-unit value of equivalent reactance capacity; S L is the equivalent reactance capacity; I N is the rated phase current effective value; U ON is the effective value of the MMC output phase voltage; I ON is the effective value of the MMC output phase current; X is the bridge arm reactance. The capacity of the equivalent reactance is related to the phase difference δ between the grid voltage and the MMC output voltage. In the steady state, δ is between 6 and 19. Therefore, the preset equivalent reactance capacity interval S LN (pu) takes 0.1 to 0.3;

[0117] Specifically, according to formula (12) and the preset equivalent reactance capacity interval, a first candidate interval of the bridge arm inductance in the MMC is obtained;

[0118] Secondly, the bridge arm inductance of the MMC should meet the requirements of circulating current suppression, mainly considering the suppression effect of the double frequency circulating current. In order to accurately calculate the size of the double frequency circulating current, the double frequency voltage fluctuation and the double frequency circulating current should be added to the bridge arm voltage and bridge arm current respectively, and the total energy of the upper and lower bridge arms should be recalculated. The calculated bridge arm energy is

[0119]

[0120] Where, I 2f is the double frequency current; θ 2f is the phase of the double frequency circulating current; U 2f In addition, considering the double frequency fluctuation of the capacitor voltage of the half-bridge submodule, it is assumed that the double frequency voltage fluctuation is evenly distributed to the 2N half-bridge submodules of each phase unit, then the energy stored in the phase unit is W c Expressed as:

[0121]

[0122] The bridge arm energy generated by the double frequency circulating current should be equal to the energy stored in the phase capacitance, that is, the double frequency components in equations (13) and (14) should be equal, so

[0123]

[0124] The amplitude of the double frequency circulating current can be calculated from this formula, and the inductance value under the specified circulating current suppression effect can be obtained from it, as shown in the following formula:

[0125]

[0126] Where, I2f is the double frequency current; U 2f is the double frequency voltage; ω is the grid angular frequency; L is the MMC bridge arm inductance; S N is the rated capacity of MMC; C MMC is the capacitance value of the half-bridge submodule in the MMC; V c is the rated capacitance voltage of the MMC submodule; V dc is the DC side voltage of the MMC in the multi-AC feeder converter station;

[0127] Specifically, according to formula (16), the obtained grid angular frequency ω and double frequency current I 2f , and the determined MMC submodule rated capacitance voltage V c , the DC side voltage V of the MMC in the multi-AC feeder converter station dc , the capacitance value C of the half-bridge submodule in MMC MMC 、MMC rated capacity S N , determining a first lower limit value of the bridge arm inductance in the MMC;

[0128] In addition, the bridge arm inductance of the MMC should also be able to limit the surge current in the event of a system fault. Considering the most serious DC side positive and negative busbar short circuit fault, the short circuit current can form a loop through the same phase unit. Based on Kirchhoff's voltage theorem, the bridge arm current rise rate is

[0129]

[0130] Under the condition of limiting transient, when the bridge arm current rise rate is α at most, the bridge arm inductance should satisfy

[0131]

[0132] Where, α is the bridge arm current rising rate; V dc is the DC side voltage of the MMC in the multi-AC feeder converter station;

[0133] Therefore, according to formula (18), the bridge arm current rising rate and the DC side voltage of the MMC in the multi-AC feeder type converter station, the second lower limit value of the bridge arm inductance in the MMC is determined;

[0134] Based on the first candidate interval calculated by formula (12), the first lower limit value calculated by formula (16), and the second lower limit value calculated by formula (18), the bridge arm inductance L of the MMC is determined.

[0135] S3. Determine the number of full-bridge submodules and the capacitance values ​​of the full-bridge submodules in the eACPFC according to the power flow parameters; wherein the eACPFC is embedded in the MMC;

[0136] In a preferred embodiment, determining the number of full-bridge submodules in the eACPFC and the capacitance values ​​of the full-bridge submodules according to the power flow parameters includes:

[0137] Determining the number of full-bridge submodules in the eACPFC according to the rated capacitor voltage of the MMC submodule, the phase voltage rating, and the maximum DC common mode voltage;

[0138] Determine the capacitance value of the full-bridge submodule according to the preset maximum fluctuation rate of the submodule capacitor voltage, the grid angular frequency, the number of full-bridge submodules in the eACPFC, the compensated DC common-mode voltage, the rated capacitance voltage of the full-bridge submodule in the eACPFC, the bridge arm fundamental frequency differential-mode output voltage, the AC line current value, and the DC circulating current of the full-bridge submodule;

[0139] Schematically, the submodules of the eACPFC adopt a full-bridge structure. The number of full-bridge submodules in the eACPFC directly depends on the selection of the full-bridge submodule capacitor voltage and the bridge arm output voltage amplitude. Since the bridge arm current rating of the eACPFC is the same as the bridge arm current rating of the MMC, the capacitor voltage of the full-bridge submodule of the eACPFC is set to be the same as the capacitor voltage of the half-bridge submodule of the MMC, which is V c * ;

[0140] It should be noted that the switching device parameters of the eACPFC are also the same as those of the MMC, ensuring the consistency of the device. Next, the bridge arm output voltage amplitude is analyzed. The eACPFC bridge arm voltage contains the following components:

[0141]

[0142] Where, v cpk is the output voltage of the upper bridge arm of the kth cluster of eACPFC; v cnk is the output voltage of the lower bridge arm of the kth cluster of eACPFC; V c_dc To compensate for the DC common mode voltage; V ck_diff is the fundamental frequency differential mode output voltage of the eACPFC bridge arm, is the equivalent series voltage between lines, and is used to regulate the power between lines.

[0143] Since the eACPFC regulates the line power flow by controlling the differential mode output voltage, its regulation principle is similar to that of the series part of the traditional UPFC. The AC component amplitude of the series voltage is selected to be 0.1 times the phase voltage amplitude, that is:

[0144]

[0145] Where V ck_diff_maxis the maximum differential mode output voltage of the eACPFC bridge arm, V phase is the phase voltage rating, all of which are effective values. Considering the typical application scenario constraints of the multi-port flexible DC converter, the maximum DC common mode voltage injected into the eACPFC is V c_dc_max .

[0146] The number of eACPFC submodules satisfies the following formula:

[0147]

[0148] Specifically, since the full-bridge submodule capacitor voltage of eACPFC is V c * Same as the rated capacitance voltage of the MMC submodule, i.e. V c * =V c Thus, the number of full-bridge submodules in the eACPFC is determined by obtaining the phase voltage rated value, the maximum DC common-mode voltage, the MMC submodule rated capacitor voltage, the phase voltage rated value, and the maximum DC common-mode voltage.

[0149] The determination of the capacitor value of the eACPFC full-bridge sub-module is mainly based on the capacitor's suppression effect on voltage ripple, and its capacitor voltage fluctuation is constrained within a specified range to limit the voltage stress of the device.

[0150] The bridge arm voltage of eACPFC is shown in Equation (22), and the bridge arm current can be expressed as

[0151]

[0152] Where i pk is the upper arm current of the kth cluster of eACPFC; i nk is the lower arm current of the kth cluster of eACPFC; I dc is the DC side current; n line is the number of AC lines connected to the eACPFC; i k is the current of the kth line, so the instantaneous value expressions of the eACPFC bridge arm differential mode output voltage and feeder current are:

[0153]

[0154] Where V ck_diff is the effective value of the fundamental frequency differential mode output voltage of the eACPFC bridge arm; δ ck_diff is the fundamental frequency differential mode output phase of the eACPFC bridge arm; I k is the effective value of the current in the kth line; ρ k is the phase of the kth line current.

[0155] Combining equations (19), (22) and (23), the current flowing into the capacitor of the eACPFC full-bridge submodule can be expressed as

[0156]

[0157] Due to power balance constraints, the DC component of the full-bridge submodule capacitor current is 0. Taking the upper bridge arm of the kth cluster of eACPFC as an example, the full-bridge submodule capacitor voltage fluctuation can be expressed as:

[0158]

[0159] The voltage fluctuation of the full-bridge submodule capacitor contains fundamental frequency and double frequency components. When the following relationship is satisfied

[0160] δ ck_diff =ρ k ; (26)

[0161] The fundamental frequency fluctuation reaches its maximum value, which can be expressed as:

[0162]

[0163] Considering the superposition of the fundamental frequency fluctuation and the double frequency fluctuation amplitude, given the preset submodule capacitor voltage maximum fluctuation rate is ε, the eACPFC submodule capacitor capacitance satisfies

[0164]

[0165] Where V c_dc To compensate for DC common mode voltage; I k is the AC line current value; V ck_diff is the bridge arm fundamental frequency differential mode output voltage; I ck is the DC circulating current of the full-bridge submodule; ω is the grid angular frequency; ε is the maximum fluctuation rate of the capacitor voltage of the preset submodule; N eMMC is the number of full-bridge submodules in eACPFC; V c_ref is the rated capacitor voltage of the full-bridge submodule in eACPFC.

[0166] Specifically, the capacitance value of the eACPFC submodule is determined based on the obtained compensated DC common-mode voltage, the bridge arm fundamental frequency differential-mode output voltage, the AC line current value, the DC circulating current of the full-bridge submodule, the grid angular frequency, the preset maximum fluctuation rate of the submodule capacitor voltage, and the determined number of full-bridge submodules in the eACPFC.

[0167] S4. Input the power flow parameters, the DC side voltage, the number of half-bridge submodules in the MMC, the bridge arm inductance, the capacitance of the half-bridge submodules in the MMC, the number of full-bridge submodules in the eACPFC, and the capacitance of the full-bridge submodules into a preset simulation software to generate simulation results of the multi-AC feed-type converter station;

[0168] Specifically, for the determination of MMC parameters, the DC side voltage of the MMC in the multi-AC feed-out converter station is selected as 500kV, the rated capacitance voltage of the MMC submodule is determined to be 2300V, the number of half-bridge submodules in the MMC is determined to be 220, and the capacitance value of the half-bridge submodule in the MMC is 20mF.

[0169] Then, considering the system power operation requirements, since the preset equivalent reactance capacity range is 0.1~0.3pu, considering that the design of the inductance needs to satisfy formula (16) when suppressing the double frequency circulating current, when the fault current rise rate is not greater than 0.1kA / μs, the inductance value should be greater than 2.5mF, and the bridge arm inductance of the MMC is 7mH.

[0170] Similarly, for the design of some eACPFC parameters, the first step is to design the number of eACPFC submodules. Since the bridge arm current rating of the eACPFC is the same as that of the MMC, the rated capacitor voltage of the eACPFC submodule is set to the same as the rated capacitor voltage of the MMC submodule, which is 2300V. At this time, the switching device parameters of the eACPFC are also the same as those of the MMC, ensuring the consistency of the device and facilitating early manufacturing and later maintenance. The number of full-bridge submodules in the eACPFC is 15. The design of the submodule capacitor takes into account the suppression of the fundamental frequency, double frequency, and triple frequency ripple by the capacitor voltage. When the ripple is suppressed to within 10%, the capacitance value of the full-bridge submodule is designed to be 21mF.

[0171] Then, simulation is performed. Figure 2 is the capacitor voltage of the MMC half-bridge submodule, and its capacitor voltage fluctuation is about 8.66%, which meets the design requirements. Figure 3 is the capacitor voltage of the eACPFC full-bridge sub-module. Its maximum capacitor voltage fluctuation is about 9.29%, which is less than the design value of 10%, so it also meets the requirements. In addition, the capacitor voltage fluctuations of the eACPFC full-bridge sub-modules connected to different feeders have significant differences, which is consistent with the theoretical analysis. Figures 4 to 6 They are the current waveforms of each AC line respectively. Figure 7 is the DC line voltage and current waveform. Figure 8 and Figure 9The waveforms for active power and reactive power, respectively, are shown for each line. The voltage and current waveforms for each line meet the requirements. Simulation results demonstrate that this application can achieve efficient and stable device operation, and the effectiveness of the proposed design approach is verified in the results.

[0172] In a preferred embodiment, the multi-AC feed-type converter station simulation method further includes:

[0173] Determining a feeder rated current according to the rated line voltage and the feeder rated capacity;

[0174] determining an operating current of the switching device according to the feeder rated current and the DC side rated current;

[0175] Determining model information of a switching device in a half-bridge submodule in the MMC according to an operating current of the switching device and a preset operating voltage of the switching device;

[0176] Specifically, the operating current of the switching device in the MMC is consistent with the bridge arm current, which mainly includes base frequency AC and DC, that is,

[0177]

[0178] Where, I dc is the DC side current; I N is the feeder rated current;

[0179] Therefore, the operating current of the switching device can be determined according to the feeder rated current and the DC side rated current, and a switching device that meets the requirements can be selected according to the operating current of the switching device and the preset operating voltage of the switching device.

[0180] See Figure 10 , is a multi-AC feed-type converter station provided by one embodiment of the present invention, comprising: an MMC and an eACPFC embedded in the MMC;

[0181] The MMC is composed of three phase units connected in parallel, each phase unit includes two bridge arms, and each bridge arm is composed of a plurality of half-bridge sub-modules FBSM connected in cascade;

[0182] The eACPFC comprises a plurality of eACPFC subunits, each of which is composed of a plurality of full-bridge submodules HBSM;

[0183] The DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules FBSM in the MMC, the bridge arm inductance of the MMC, the capacitance value of the half-bridge submodule FBSM in the MMC, the number of full-bridge submodules HBSM in the eACPFC, and the capacitance value of the full-bridge submodule HBSM are determined according to the preset power flow parameters.

[0184] It should be noted that the specific calculation method of the DC side voltage of the MMC in the above-mentioned multi-AC fed converter station, the number of half-bridge sub-modules FBSM in the MMC, the bridge arm inductance of the MMC, the capacitance value of the half-bridge sub-module FBSM in the MMC, the number of full-bridge sub-modules HBSM in the eACPFC, and the capacitance value of the full-bridge sub-module HBSM are consistent with the calculation method mentioned in the above-mentioned method embodiment of the present invention, and will not be repeated here.

[0185] See Figure 11 , is a multi-AC feed-type converter station simulation device provided by one embodiment of the present invention, comprising: a data acquisition module, an MMC parameter determination module, an eACPFC parameter determination module and a simulation module;

[0186] The data acquisition module is used to obtain preset power flow parameters;

[0187] The MMC parameter determination module is used to determine the DC side voltage of the MMC in the multi-AC feed-type converter station, the number of half-bridge submodules in the MMC, the bridge arm inductance of the MMC, and the capacitance value of the half-bridge submodule in the MMC according to the power flow parameters;

[0188] The eACPFC parameter determination module is used to determine the number of full-bridge submodules in the eACPFC and the capacitance value of the full-bridge submodules according to the power flow parameters; wherein the eACPFC is embedded in the MMC;

[0189] The simulation module is used to input the power flow parameters, the DC side voltage, the number of half-bridge sub-modules in the MMC, the bridge arm inductance, the capacitance of the half-bridge sub-modules in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance of the full-bridge sub-modules into the preset simulation software to generate simulation results of the multi-AC feed-type converter station.

[0190] See also Figure 12 , an embodiment of the present application further provides a terminal device, including:

[0191] one or more processors;

[0192] a memory, coupled to the processor, for storing one or more programs;

[0193] When the one or more programs are executed by the one or more processors, the one or more processors implement the multi-AC feed-type converter station simulation method as described above.

[0194] The processor is used to control the overall operation of the terminal device to complete all or part of the steps of the multi-AC feed-type converter station simulation method described above. The memory is used to store various types of data to support the operation of the terminal device. For example, these data may include instructions for any application or method used to operate on the terminal device, as well as application-related data. The memory can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk.

[0195] In an exemplary embodiment, the terminal device can be implemented by one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components, and is used to execute the multi-AC feed-type converter station simulation method described in any of the above embodiments, and achieve the same technical effect as the above method.

[0196] In another exemplary embodiment, a computer-readable storage medium including a computer program is further provided. When executed by a processor, the computer program implements the steps of the multi-AC feed converter station simulation method described in any of the aforementioned embodiments. For example, the computer-readable storage medium may be the aforementioned memory including the computer program. The computer program may be executed by a processor of a terminal device to perform the multi-AC feed converter station simulation method described in any of the aforementioned embodiments, thereby achieving the same technical effects as those described in the aforementioned methods.

[0197] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A simulation method for a multi-AC feed-in converter station, characterized in that: include: Obtaining preset power flow parameters; wherein the power flow parameters include: the rated line voltage of the AC line, the rated capacity of the feeder, the effective value of the AC port output voltage, the compensated DC common-mode voltage, the DC side rated current, the preset operating voltage of the switching device, the grid angular frequency, the preset maximum fluctuation rate of the submodule capacitor voltage, the rated capacitor voltage of the full-bridge submodule in the eACPFC, the MMC modulation index, the preset equivalent reactance capacity range, the preset bridge arm current rise rate, the double frequency current, the phase voltage rating, the maximum DC common-mode voltage, the bridge arm fundamental frequency differential mode output voltage, the AC line current value, and the DC circulating current of the full-bridge submodule; Determining the DC side voltage of the MMC in the multi-AC feeder converter station according to the effective value of the AC port output voltage and the compensated DC common mode voltage; Determining the rated capacitance voltage of the MMC submodule according to the preset operating voltage of the switching device; Determining the number of half-bridge submodules in the MMC according to the rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feed-type converter station; Determining the capacitance value of the half-bridge submodule in the MMC according to the feeder rated capacity, the grid angular frequency, the preset submodule capacitor voltage maximum fluctuation rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the MMC modulation index, and the number of half-bridge submodules in the MMC; Determine the bridge arm inductance of the MMC according to the preset equivalent reactance capacity range, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the double frequency current, and the feeder rated capacity; Determining the number of full-bridge submodules and the capacitance values ​​of the full-bridge submodules in the eACPFC according to the power flow parameters; wherein the eACPFC is embedded in the MMC; The power flow parameters, the DC side voltage, the number of half-bridge sub-modules in the MMC, the bridge arm inductance, the capacitance value of the half-bridge sub-module in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance value of the full-bridge sub-module are input into the preset simulation software to generate the simulation results of the multi-AC feed-type converter station.

2. The multi-AC feed-type converter station simulation method according to claim 1, characterized in that: The determining of the bridge arm inductance of the MMC according to the preset equivalent reactance capacity interval, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the doubled frequency current, and the feeder rated capacity includes: Determining a first candidate interval of the bridge arm inductance in the MMC according to the preset equivalent reactance capacity interval; Determine a first lower limit of the bridge arm inductance in the MMC according to the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the doubled frequency current, the feeder rated capacity, and the DC side voltage of the MMC in the multi-AC feeder converter station; Determining a second lower limit value of the bridge arm inductance in the MMC according to the bridge arm current rising rate and the DC side voltage of the MMC in the multi-AC feed-type converter station; The bridge arm inductance of the MMC is determined according to the first candidate interval, the first lower limit value, and the second lower limit value.

3. The multi-AC feed-type converter station simulation method according to claim 1, characterized in that: The determining, based on the power flow parameters, the number of full-bridge submodules in the eACPFC and the capacitance values ​​of the full-bridge submodules includes: Determining the number of full-bridge submodules in the eACPFC according to the rated capacitance voltage of the MMC submodule, the phase voltage rating, and the maximum DC common mode voltage; The capacitance value of the full-bridge submodule is determined based on the preset maximum fluctuation rate of the submodule capacitor voltage, the grid angular frequency, the number of full-bridge submodules in the eACPFC, the compensated DC common-mode voltage, the rated capacitor voltage of the full-bridge submodule in the eACPFC, the bridge arm fundamental frequency differential-mode output voltage, the AC line current value, and the DC circulating current of the full-bridge submodule.

4. The multi-AC feed-type converter station simulation method according to claim 1, characterized in that: Also includes: Determining a feeder rated current according to the rated line voltage and the feeder rated capacity; determining an operating current of the switching device according to the feeder rated current and the DC side rated current; The model information of the switching device in the half-bridge submodule in the MMC is determined according to the operating current of the switching device and the preset operating voltage of the switching device.

5. A multi-AC feed-in converter station simulation device, characterized in that: include: Data acquisition module, MMC parameter determination module, eACPFC parameter determination module and simulation module; The data acquisition module is used to obtain preset power flow parameters; wherein the power flow parameters include: the rated line voltage of the AC line, the rated capacity of the feeder, the effective value of the output voltage of the AC port, the compensated DC common mode voltage, the rated current of the DC side, the preset operating voltage of the switching device, the grid angular frequency, the preset maximum fluctuation rate of the submodule capacitor voltage, the rated capacitor voltage of the full-bridge submodule in the eACPFC, the MMC modulation index, the preset equivalent reactance capacity range, the preset bridge arm current rise rate, the double frequency current, the phase voltage rated value, the maximum DC common mode voltage, the bridge arm fundamental frequency differential mode output voltage, the AC line current value, and the DC circulating current of the full-bridge submodule; The MMC parameter determination module is configured to determine the DC side voltage of the MMC in the multi-AC feeder converter station according to the effective value of the AC port output voltage and the compensated DC common mode voltage; Determining the rated capacitance voltage of the MMC submodule according to the preset operating voltage of the switching device; Determining the number of half-bridge submodules in the MMC according to the rated capacitance voltage of the MMC submodule and the DC side voltage of the MMC in the multi-AC feed-type converter station; Determining the capacitance value of the half-bridge submodule in the MMC according to the feeder rated capacity, the grid angular frequency, the preset submodule capacitor voltage maximum fluctuation rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the MMC modulation index, and the number of half-bridge submodules in the MMC; Determine the bridge arm inductance of the MMC according to the preset equivalent reactance capacity range, the bridge arm current rise rate, the DC side voltage of the MMC in the multi-AC feeder converter station, the grid angular frequency, the capacitance value of the half-bridge submodule in the MMC, the rated capacitance voltage of the MMC submodule, the double frequency current, and the feeder rated capacity; The eACPFC parameter determination module is used to determine the number of full-bridge submodules in the eACPFC and the capacitance value of the full-bridge submodules according to the power flow parameters; wherein the eACPFC is embedded in the MMC; The simulation module is used to input the power flow parameters, the DC side voltage, the number of half-bridge sub-modules in the MMC, the bridge arm inductance, the capacitance of the half-bridge sub-modules in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance of the full-bridge sub-modules into the preset simulation software to generate simulation results of the multi-AC feed-type converter station.

6. A terminal device, characterized in that: include: one or more processors; a memory, coupled to the processor, for storing one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the multi-AC feed-type converter station simulation method according to any one of claims 1 to 4.

7. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the multi-AC feed-type converter station simulation method according to any one of claims 1 to 4 is implemented.

8. A multi-AC feed-out converter station, characterized in that: A multi-AC feed-type converter station simulation method applicable to any one of claims 1 to 4, comprising: an MMC and an eACPFC embedded in the MMC; The MMC is composed of three phase units connected in parallel, each phase unit includes two bridge arms, and each bridge arm is composed of a plurality of half-bridge sub-modules connected in cascade; The eACPFC comprises a plurality of eACPFC subunits, each of which is composed of a plurality of full-bridge submodules; Among them, the DC side voltage of the MMC in the multi-AC fed converter station, the number of half-bridge sub-modules in the MMC, the bridge arm inductance of the MMC, the capacitance value of the half-bridge sub-module in the MMC, the number of full-bridge sub-modules in the eACPFC, and the capacitance value of the full-bridge sub-module are determined according to the preset power flow parameters.

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