MMC AC-DC admittance model establishment method considering AC frequency and related equipment

Abstract

The invention discloses an MMC AC-DC admittance model establishment method considering AC frequency and related equipment, and the method comprises the steps: obtaining a main circuit small signal model, a voltage loop small signal model and a current loop small signal model of a modular multilevel converter, and carrying out the rewriting of the models through a harmonic state space method, according to the method, the working condition of alternating-current side rated operation frequency change is considered, the method is suitable for stability analysis of a flexible direct-current transmission sending-out system considering frequency change of a new energy collection system, then unknown numbers in a rewritten model are obtained based on a steady-state theory solving method, and finally a modular multilevel converter mixed admittance model is established. The method is not influenced by AC side and DC side power grid admittance, is only determined by a steady state working point, a control structure and converter parameters of the modular multilevel converter, and better meets the requirements of fully protecting user privacy and commercial confidentiality during system stability analysis.

Description

Technical Field

[0001] The invention belongs to the field of flexible direct current power transmission, and specifically relates to a method for establishing an MMC alternating current and direct current admittance model taking into account alternating current frequency and related equipment. Background Art

[0002] High-voltage direct current transmission is suitable for long-distance transmission of electric energy. Flexible high-voltage direct current transmission (modular multilevel converter-high voltage DC, MMC-HVDC) is currently one of the main ways to connect new energy to the grid over long distances. The transmission of new energy through a flexible direct current transmission system is the development trend and future presentation of power electronics systems. It has richer and more flexible frequency levels and electric energy forms, and can provide support for more efficient and reliable energy development and utilization. The concept of a multi-frequency power system is novel.

[0003] In the flexible direct current transmission system for new energy, the collection technology is also one of the key technologies that affect the development of new power systems. At present, the mainstream collection technologies are industrial frequency AC collection and DC collection. Among them, DC collection faces problems such as multi-pole DC conversion, complex voltage transformation, difficulty in networking, low reliability, and high cost. As a new transmission method, low-frequency transmission technology can effectively reduce line impedance, shorten electrical distance, and thus greatly improve line transmission capacity. In recent years, the development of low-frequency transmission systems has been booming, and low-frequency transmission technology also has great development potential in the collection field. Taking into account the economic cost, reliability, and stability of the system, the optimal frequency of the collection system is related to the specific parameters of the flexible direct current transmission system for new energy. Although some scholars have paid attention to the issue of flexible direct current transmission of new energy, there is little research on the flexible direct current transmission system for new energy taking into account the frequency change of the collection system, and breakthroughs in basic theories and key technologies are urgently needed.

[0004] The frequency-variable flexible DC transmission and delivery system for new energy and collection systems contains large-scale power electronic devices, many control links, mutual influence between the AC and DC sides, and complex internal dynamic characteristics, which also brings new stability problems. Impedance analysis is a simple and effective method for analyzing the stability of complex power electronic systems, and impedance modeling is a key link. The traditional modular multilevel converter impedance / admittance modeling is to fix the rated operating frequency of the AC side system to 50Hz or 60Hz. The applicable working conditions have certain limitations and cannot study the broadband oscillation problem of the frequency-variable flexible DC transmission and delivery system for new energy and collection systems. Summary of the invention

[0005] The present invention provides a method for establishing an MMC AC / DC admittance model taking into account AC frequency and related equipment, which solves the problem of being unable to study the broadband oscillation of a flexible DC transmission system taking into account frequency changes of new energy and aggregating systems.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for establishing an MMC AC / DC admittance model taking into account AC frequency comprises:

[0008] Obtaining a main circuit small signal model, a voltage loop small signal model, and a current loop small signal model of a modular multilevel converter;

[0009] The main circuit small signal model, voltage loop small signal model and current loop small signal model are rewritten using the harmonic state space method;

[0010] Obtain unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on the steady-state theory solution method;

[0011] A modular multilevel converter hybrid admittance model is established based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

[0012] Preferably, the harmonic state space method converts any continuous periodic signal into a frequency domain form, and the conversion formula is:

[0013]

[0014] In the formula, X h is the Fourier coefficient, T is the fundamental period of the system, x(t) is any continuous periodic signal, e is the natural base, j is the imaginary unit, h is the harmonic order, and t is time.

[0015] Preferably, the step of obtaining the small signal model of the main circuit of the modular multilevel converter is specifically as follows:

[0016] First, the average value model of the modular multi-level converter is obtained.

[0017] Based on the average value model and harmonic state space method of modular multi-level converter, the sum of sub-module capacitor voltage and circulating current disturbance are obtained;

[0018] The main circuit small signal model of the modular multilevel converter is obtained according to the sum of the sub-module capacitor voltages and the disturbance of the circulating current.

[0019] Preferably, the main circuit small signal model rewritten using the harmonic state space method is:

[0020] Y acdcT v p -Y acdc1T e p =i p

[0021] Where Y acdcT is the main circuit admittance matrix in the harmonic state space, v p is the small signal component of AC and DC voltage in the harmonic state space, Y acdc1T is the AC / DC main circuit admittance matrix in the harmonic state space, e p is the small signal component of the internal potential difference in the harmonic state space, i p is the small signal component of current in the harmonic state space.

[0022] Preferably, the voltage loop small signal model rewritten using the harmonic state space method is:

[0023]

[0024] In the formula, is the reference value of the current small signal component in the harmonic state space, G cvT is the voltage loop transfer function matrix in the harmonic state space, is the voltage small signal component reference value in the harmonic state space, v p is the voltage small signal component in the harmonic state space.

[0025] Preferably, the current loop small signal model rewritten using the harmonic state space method is:

[0026]

[0027] In the formula, e p is the small signal component of the internal potential difference in the harmonic state space, G ciT is the current loop transfer function matrix in the harmonic state space, is the circuit small signal component reference value in the harmonic state space, i p is the circuit small signal component in the harmonic state space, G deiT is the current loop decoupling matrix in the harmonic state space.

[0028] Preferably, the steady-state value theoretical solution is:

[0029] Analyze the single-phase state of the modular multilevel converter during steady-state operation, obtain the upper and lower arm currents and switching functions, and solve the unknowns based on the upper and lower arm currents and switching functions;

[0030] The upper and lower bridge arm currents are expressed as:

[0031]

[0032] In the formula, i au is the upper arm current, I a is the one-fold frequency amplitude of the AC side current, I ad is the DC current, Iaz is the circulation amplitude, i al is the lower arm current, ω 1 is the fundamental angular frequency of the AC system, t is the time, and θ is the circulating current phase angle;

[0033] The switch function is expressed as:

[0034]

[0035] Where M is the modulation ratio, α is the switching function phase angle, and d k is the k-phase switching function.

[0036] A system for establishing an MMC AC / DC admittance model taking into account AC frequency, comprising:

[0037] Model acquisition module: used to obtain the main circuit small signal model, voltage loop small signal model and current loop small signal model of the modular multi-level converter;

[0038] Rewriting module: used to rewrite the main circuit small signal model, voltage loop small signal model and current loop small signal model using the harmonic state space method;

[0039] Solution module: used to obtain unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on the steady-state theory solution method;

[0040] Modeling module: used to establish a modular multi-level converter hybrid admittance model based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

[0041] A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a method for establishing an MMC AC / DC admittance model taking into account AC frequency are implemented.

[0042] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the computer program implements the steps of a method for establishing an MMC AC / DC admittance model taking into account AC frequency.

[0043] Compared with the prior art, the present invention has the following beneficial effects: the present invention provides a method for establishing an MMC AC / DC admittance model taking into account AC frequency, obtains a main circuit small signal model, a voltage loop small signal model and a current loop small signal model of a modular multilevel converter, and rewrites the above model using the harmonic state space method, taking into account the working conditions of the rated operating frequency change on the AC side, which is suitable for the stability analysis of the flexible DC transmission and sending system with frequency change of the new energy meter and the collection system, and then obtains the unknowns in the rewritten model based on the steady-state theory solution method, and finally establishes a hybrid admittance model of the modular multilevel converter, which is not affected by the admittance of the AC side and the DC side power grid, and is only determined by the steady-state operating point, control structure and converter parameters of the modular multilevel converter itself, which is more in line with the requirements of fully protecting user privacy and commercial secrets during system stability analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of a method for establishing an MMC AC / DC admittance model taking into account AC frequency according to an embodiment of the present invention;

[0045] Figure 2 This is a single-phase equivalent schematic diagram of a modular multilevel converter according to an embodiment of the present invention;

[0046] Figure 3 This is a small signal model diagram of a modular multilevel converter according to an embodiment of the present invention;

[0047] Figure 4 The present invention provides a system block diagram for establishing an MMC AC / DC admittance model taking into account AC frequency according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0049] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0051] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] like Figure 1 As shown, the present invention provides a method for establishing an MMC AC / DC admittance model taking into account AC frequency:

[0053] S101 obtains a main circuit small signal model, a voltage loop small signal model, and a current loop small signal model of a modular multilevel converter;

[0054] S102 uses the harmonic state space method to rewrite the main circuit small signal model, voltage loop small signal model and current loop small signal model;

[0055] S103 obtains unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on a steady-state theory solution method;

[0056] S104 establishes a modular multilevel converter hybrid admittance model based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

[0057] The harmonic state space method is specifically:

[0058] The modular multilevel converter is a periodic time-varying system with no fixed DC steady-state operating point. The harmonic state space method can be used to achieve the conversion from time domain to frequency domain. The Fourier transform can convert any continuous periodic signal x(t) into a frequency domain form:

[0059]

[0060] Among them, ω 1 =2π / T, T is the fundamental period of the system, x(t) is any continuous periodic signal, e is the natural base, j is the imaginary unit, j is the harmonic order, and t is time. h is the Fourier coefficient, which can be calculated as follows:

[0061]

[0062] For the expression of the system in the time domain:

[0063]

[0064] It can be written in the frequency domain:

[0065] sX=(AQ)X+BU (4)

[0066] in,

[0067] X=[X-h ,...,X -1 ,X 0 ,X 1 ,...,X h ] T (5)

[0068] U=[U -h ,...,U -1 ,U 0 ,U 1 ,...,U h ] T (6)

[0069]

[0070]

[0071] Q=diag(-jhω 1 ·I … 0·I … jhω 1 ·I) (9)

[0072] Where I is the identity matrix whose order is equal to the number of state variables.

[0073] The specific steps for small signal modeling of the main circuit of the system are:

[0074] The present invention establishes an AC / DC hybrid admittance model of a modular multilevel converter in a voltage control mode. The following figure is a schematic diagram of the topological structure of the modular multilevel converter in the present invention, where a single-phase equivalent circuit is used as an example (k = a, b, c). Figure 2 As shown:

[0075] From the average value model of modular multilevel converter:

[0076]

[0077]

[0078] Among them, d k is the switching function, u uk and u lk is the equivalent submodule voltage of the upper and lower bridge arms, and is the sum of the submodule capacitor voltages of the upper and lower bridge arms, i uk and i lk is the bridge arm current of the upper and lower bridge arms, C arm is the capacitance of the equivalent submodule.

[0079] Get the internal potential difference, the expression is:

[0080]

[0081] Get the equivalent resistance and equivalent inductance of the AC side:

[0082]

[0083]

[0084] Among them, R 0 is the bridge arm resistance, L 0 is the bridge arm inductance.

[0085] Get the circulation:

[0086]

[0087] Here, the subscript s is introduced to represent the steady-state quantity, and the subscript p is introduced to represent the disturbance quantity.

[0088] The disturbances of circulating current and DC current satisfy the relationship:

[0089] i dcp =i cap +i cbp +i ccp (16)

[0090] The expression of the bridge arm equivalent submodule voltage in the system synchronous rotating coordinate system is:

[0091]

[0092] Where P is the Parker transformation matrix, P -1 is the Parker inverse transformation matrix, which is defined as follows:

[0093]

[0094]

[0095] The internal potential difference is expressed by the bridge arm equivalent submodule voltage as follows:

[0096]

[0097] The sum of the submodule capacitor voltages and the disturbance of the circulating current can be solved by combining the following equations using the harmonic state space method:

[0098]

[0099] definition:

[0100]

[0101]

[0102]

[0103] The main circuit small signal model of the modular multilevel converter in the dq coordinate system is:

[0104]

[0105] By rewriting the small signal model of the main circuit using the harmonic state space method, the small signal model of the main circuit of the modular multilevel converter can be obtained as follows:

[0106] Y acdcT v p -Y acac1T e p =i p (26)

[0107] Where Y acdcT is the main circuit admittance matrix in the harmonic state space, v p is the small signal component of AC and DC voltage in the harmonic state space, Y acdc1T is the AC / DC main circuit admittance matrix in the harmonic state space, e p is the small signal component of the internal potential difference in the harmonic state space, i p is the small signal component of current in the harmonic state space.

[0108] in,

[0109] Y acdcT =diag(Y acdcT-3 ,…,Y acdcT0 ,…,Y acdcT3 )(27)

[0110] Y acdc1T =diag(Y acdc1T-3 ,…,Y acdc1T0 ,…,Y acdc1T3 )(28)

[0111] v p =[… v dp0 v qp0 v dcp0 …] T (29)

[0112] e p =[… e dp0 e qp0 i dcp0 …] T (30)

[0113] i p =[… i dp0 i qp0i dcp0 …] T (31)

[0114] The steps for small signal modeling of voltage loop and current loop are as follows:

[0115] In the control module, a PI voltage loop is used to control the d-axis and q-axis voltages. The small signal model of the voltage loop controller is:

[0116]

[0117] G cv represents the voltage loop transfer function matrix, which is defined as follows:

[0118]

[0119] Among them, k pv and k iv Represents the proportional gain and integral gain of the voltage loop controller.

[0120] In the control module, a PI current loop is used to control the d-axis and q-axis currents. The small signal model of the current loop controller is:

[0121]

[0122] G ci represents the current loop transfer function matrix, which is defined as follows:

[0123]

[0124] Among them, k pi and k ii Represents the proportional gain and integral gain of the current loop controller.

[0125] G dei The decoupling matrix of the current loop is defined as follows:

[0126]

[0127] The small signal model of equations (32)-(36) can be rewritten by the harmonic state space method:

[0128]

[0129] In the formula, is the reference value of the current small signal component in the harmonic state space, G cvT is the voltage loop transfer function matrix in the harmonic state space, is the voltage small signal component reference value in the harmonic state space, v p is the voltage small signal component in the harmonic state space.

[0130] G cvT =diag(G cv-3 ,...,G cv0 ,...,G cv3 ) (38)

[0131]

[0132] In the formula, e p is the small signal component of the internal potential difference in the harmonic state space, G ciT is the current loop transfer function matrix in the harmonic state space, is the reference value of the circuit small signal component in the harmonic state space, i p is the circuit small signal component in the harmonic state space, G deiT is the current loop decoupling matrix in the harmonic state space.

[0133] G ciT =diag(G ci-3 ,...,G ci0 ,...,G ci3 ) (40)

[0134] G deiT =diag(G dei-3 ,...,G dei0 ,...G dei3 ) (41)

[0135] The specific solution of the steady-state value theory is:

[0136] When the MMC is in steady-state operation, the three phases are symmetrical, so only a single phase needs to be analyzed. Taking phase a as an example, the currents of the upper and lower bridge arms are expressed as:

[0137]

[0138] In the formula, i au is the upper arm current, I a is the one-fold frequency amplitude of the AC side current, I ad is the DC current, I az is the circulation amplitude, i al is the lower arm current, ω 1 is the fundamental angular frequency of the AC system, t is the time, and θ is the circulating current phase angle;

[0139] The switching function can be expressed as:

[0140]

[0141] Where M is the modulation ratio, θ is the switching function phase angle, and d k is the k-phase switching function.

[0142] have:

[0143]

[0144]

[0145] in.

[0146]

[0147]

[0148]

[0149]

[0150] The frequency components of the submodule capacitor voltage can be expressed as:

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157] in, and They represent the first, second and third harmonic components of the capacitor voltage of the upper bridge arm submodule respectively; and They represent the first, second and third harmonic components of the capacitor voltage of the lower bridge arm submodule respectively.

[0158] The specific method of obtaining unknown numbers using the steady-state solution is:

[0159] For example, when solving formula (20), it is necessary to know Then from formula (50) we can get The expression can be obtained by using formula (2)

[0160]

[0161] The process of solving other steady-state values ​​is similar.

[0162] The small signal model of the modular multilevel converter is obtained as follows:

[0163] Based on the above small signal modeling of the main circuit, voltage loop and current loop of the system, the small signal model of the modular multilevel converter in the voltage control mode is obtained. Figure 3 As shown:

[0164] AC / DC hybrid admittance of modular multilevel converter It can be calculated as follows:

[0165]

[0166] in,

[0167]

[0168] Y dd , Y qq , Y dcdc Y represents the d-axis self-admittance, q-axis self-admittance and DC side self-admittance. dq , Y qd , Y ddc , Y qdc , Y dcd , Y dcq It represents the mutual admittance between the d-axis, q-axis and DC side.

[0169] like Figure 4 As shown, the present invention provides a system for establishing an MMC AC / DC admittance model taking into account AC frequency, comprising:

[0170] Model acquisition module: used to obtain the main circuit small signal model, voltage loop small signal model and current loop small signal model of the modular multi-level converter;

[0171] Rewriting module: used to rewrite the main circuit small signal model, voltage loop small signal model and current loop small signal model using the harmonic state space method;

[0172] Solution module: used to obtain unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on the steady-state theory solution method;

[0173] Modeling module: used to establish a modular multi-level converter hybrid admittance model based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

[0174] A terminal device is provided in one embodiment of the present invention. The terminal device of this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of the modules / units in the above-mentioned device embodiments are implemented.

[0175] The computer program may be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to accomplish the present invention.

[0176] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0177] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0178] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0179] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0180] Although the embodiments of the present invention are described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments and application fields, and the above-mentioned specific embodiments are only illustrative and instructive, rather than restrictive. Under the guidance of the specification, a person skilled in the art can make many forms without departing from the scope of protection of the claims of the present invention, all of which belong to the scope of protection of the present invention.

Claims

1. A method for establishing an MMC AC / DC admittance model taking into account AC frequency, characterized in that: include: Obtaining a main circuit small signal model, a voltage loop small signal model, and a current loop small signal model of a modular multilevel converter; The main circuit small signal model, voltage loop small signal model and current loop small signal model are rewritten using the harmonic state space method; Obtain unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on the steady-state theory solution method; A modular multilevel converter hybrid admittance model is established based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

2. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The harmonic state space method converts any continuous periodic signal into frequency domain form. The conversion formula is: Where, X h is the Fourier coefficient, T is the fundamental period of the system, x(t) is any continuous periodic signal, e is the natural base, j is the imaginary unit, h is the harmonic order, and t is time.

3. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The specific steps of obtaining the small signal model of the main circuit of the modular multilevel converter are: First, the average value model of the modular multi-level converter is obtained. Based on the average value model and harmonic state space method of modular multi-level converter, the sum of sub-module capacitor voltage and circulating current disturbance are obtained; The main circuit small signal model of the modular multilevel converter is obtained according to the sum of the sub-module capacitor voltages and the disturbance of the circulating current.

4. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The small signal model of the main circuit rewritten using the harmonic state space method is: AND acdcT v p -AND acdc1T and p =i p Where Y acdcT is the main circuit admittance matrix in the harmonic state space, v p is the small signal component of AC and DC voltage in the harmonic state space, Y acdc1T is the AC and DC main circuit admittance matrix in the harmonic state space, e p is the small signal component of the internal potential difference in the harmonic state space, i p is the small signal component of current in the harmonic state space.

5. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The voltage loop small signal model rewritten using the harmonic state space method is: In the formula, is the reference value of the current small signal component in the harmonic state space, G cvT is the voltage loop transfer function matrix in the harmonic state space, is the voltage small signal component reference value in the harmonic state space, v p is the voltage small signal component in the harmonic state space.

6. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The current loop small signal model rewritten using the harmonic state space method is: In the formula, e p is the small signal component of the internal potential difference in the harmonic state space, G ciT is the current loop transfer function matrix in the harmonic state space, is the circuit small signal component reference value in the harmonic state space, i p is the circuit small signal component in the harmonic state space, G deiT is the current loop decoupling matrix in the harmonic state space.

7. The method for establishing an MMC AC / DC admittance model taking into account AC frequency according to claim 1, characterized in that: The steady-state value theory solution is: Analyze the single-phase state of the modular multilevel converter during steady-state operation, obtain the upper and lower arm currents and switching functions, and solve the unknowns based on the upper and lower arm currents and switching functions; The upper and lower bridge arm currents are expressed as: In the formula, i au is the upper arm current, I a is the one-fold frequency amplitude of the AC side current, I ad is the DC current, I az is the circulation amplitude, i al is the lower arm current, ω1 is the fundamental angular frequency of the AC system, t is the time, and θ is the circulating current phase angle; The switch function is expressed as: Where M is the modulation ratio, α is the switching function phase angle, and d k is the k-phase switching function.

8. A system for establishing an MMC AC / DC admittance model taking into account AC frequency, characterized in that: include: Model acquisition module: used to obtain the main circuit small signal model, voltage loop small signal model and current loop small signal model of the modular multi-level converter; Rewriting module: used to rewrite the main circuit small signal model, voltage loop small signal model and current loop small signal model using the harmonic state space method; Solution module: used to obtain unknowns in the rewritten main circuit small signal model, voltage loop small signal model and current loop small signal model based on the steady-state theory solution method; Modeling module: used to establish a modular multi-level converter hybrid admittance model based on the main circuit small signal model, voltage loop small signal model and current loop small signal model after obtaining the unknowns.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method for establishing an MMC AC / DC admittance model taking into account AC frequency as described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method for establishing an MMC AC / DC admittance model taking into account AC frequency are implemented as described in any one of claims 1 to 7.

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