MMC-MTDC structural impedance modeling method and related devices

Abstract

The present invention belongs to the field of high-voltage direct current (HVDC) impedance modeling and stability analysis, and discloses a MMC-MTDC structured impedance modeling method and related devices. The method comprises: establishing a small-signal model of the MMC main circuit at each end of the MMC-MTDC system; establishing a structured small-signal model of the MMC modulation signal at each end based on modular modeling of the control link; calculating the MMC positive and negative sequence control structured AC and DC port impedances based on the established small-signal model of the MMC main circuit at each end and the structured small-signal model of the MMC modulation signal at each end; establishing an impedance model of any node in the DC transmission grid based on network aggregation; and establishing structured impedance models of different MMC ports at each end of the MMC-MTDC. The present invention can accurately establish impedance models for different application scenarios, different control modes, and different AC and DC ports of the system, providing key technical support for arbitrary section oscillation analysis and stability improvement of the MMC-MTDC system.

Description

Technical Field

[0001] The present invention belongs to the field of high-voltage direct current transmission impedance modeling and stability analysis, and in particular relates to an MMC-MTDC structured impedance modeling method and related devices. Background Art

[0002] Modular multilevel converters (MMC-MTDC) are widely used in high-voltage direct current (HVDC) transmission applications due to their modular design, strong scalability, and excellent harmonic performance. Multi-terminal flexible direct current (HVDC) (MMC-MTDC) enables multi-terminal power transmission, multi-point power reception, and cross-domain grid interconnection. This unique advantage in long-distance, high-capacity transmission of renewable energy has made it a key method for large-scale centralized renewable energy transmission.

[0003] With the widespread adoption of power electronics in renewable energy generation and flexible direct current transmission (HVDC), power systems with a high proportion of renewable energy and power electronics are gradually emerging. Wideband oscillations are becoming a frequent problem, seriously impacting the safe and stable operation of the system and the efficient absorption of renewable energy. In recent years, impedance analysis has become an effective method for analyzing and resolving oscillation issues in flexible direct current transmission systems connected to renewable energy.

[0004] Modeling the impedance of the MMC AC and DC ports at each end of an MMC-MTDC is a fundamental prerequisite for analyzing and resolving oscillation issues across different sections of the system. Existing MMC impedance modeling primarily focuses on specific control structures for specific scenarios and currently only considers flexible direct current transmission at both ends. Existing MMC impedance modeling methods have the following limitations:

[0005] (1) Impedance modeling methods based on specific control structures for specific scenarios are not suitable for MMC-MTDC impedance modeling. With the large-scale development and utilization of new energy and the interconnection of regional power grids, MMC-MTDC has become an important trend in the development of future high-voltage direct current grids. Due to the diversity and complexity of application scenarios at each end of MMC-MTDC, the MMC control methods at each end are flexible and changeable. Establishing an independent MMC impedance model for each end is repetitive, tedious, and inefficient.

[0006] (2) Existing methods are difficult to apply to impedance modeling of complex multi-terminal DC transmission grids. With the rapid development of MMC-MTDC, multi-terminal DC grids have gradually taken shape. The number of MMC-MTDC transmission terminals is highly uncertain and random, resulting in a DC transmission grid with a mesh-like, complex, and randomly diverse characteristics. This makes impedance modeling that takes into account the effects of multi-terminal interaction coupling difficult.

[0007] Therefore, in order to solve the above technical difficulties, it is urgent to propose a new method to carry out structural impedance modeling of the MMC AC and DC ports at each end of the MMC-MTDC system. Summary of the Invention

[0008] The purpose of the present invention is to provide an MMC-MTDC structured impedance modeling method and related devices to solve the technical problems of impedance modeling difficulties, time-consuming and labor-intensive due to the flexible and diverse control of MMC at each end of MMC-MTDC. The present invention proposes a modular modeling method for common and unique control links to flexibly establish a structured model of the diversified control system of MMC at each end. In response to the impedance modeling difficulties of complex multi-terminal DC transmission grids, the present invention proposes a DC transmission grid aggregation network modeling method to establish an impedance model of any node in the DC transmission grid. The MMC-MTDC structured impedance modeling method proposed in the present invention can accurately establish impedance models for different application scenarios, different control modes, and different AC and DC ports of the system, providing key technical support for arbitrary section oscillation analysis and stability improvement of the MMC-MTDC system.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a MMC-MTDC structural impedance modeling method, comprising:

[0011] Establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system;

[0012] Based on modular modeling of the control link, a structured small signal model of the MMC modulation signal at each end is established;

[0013] Based on the established small signal model of the MMC main circuit at each end and the structured small signal model of the MMC modulation signal at each end, the AC and DC port impedances of the MMC positive and negative sequence control structure are calculated;

[0014] Based on network aggregation, an impedance model of any node in the DC transmission grid is established;

[0015] Establish the structural impedance model of different MMC ports at each end of MMC-MTDC.

[0016] In a second aspect, the present invention provides an MMC-MTDC structured impedance modeling device, comprising:

[0017] The first module is used to establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system;

[0018] The second module is used to establish a structured small signal model of the MMC modulation signal at each end based on modular modeling of the control link;

[0019] The third module is used to calculate the MMC positive and negative sequence control structured AC and DC port impedances based on the established MMC main circuit small signal model at each end and the structured small signal model of the MMC modulation signal at each end;

[0020] The fourth module is used to establish an impedance model of any node in the DC transmission grid based on network aggregation;

[0021] The fifth module is used to establish the structural impedance model of different MMC ports at each end of the MMC-MTDC.

[0022] In a third aspect, the present invention provides an electronic device comprising a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement the MMC-MTDC structural impedance modeling method.

[0023] In a fourth aspect, the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the MMC-MTDC structural impedance modeling method is implemented.

[0024] Compared with the prior art, the present invention has the following unexpected beneficial effects:

[0025] The present invention provides a method and related devices for MMC-MTDC structured impedance modeling. Addressing the impedance modeling challenges caused by the flexible and diverse MMC control at each end of an MMC-MTDC, a modular modeling method for common and unique control links is proposed. This method flexibly establishes structured models of the MMC control systems at each end of the MMC-MTDC system, taking into account the VF control mode, VDC control mode, and PQ control mode, effectively resolving the issues of repetitive, tedious, and inefficient impedance modeling for specific control structures in specific scenarios.

[0026] To address the impedance modeling challenges of complex multi-terminal DC transmission grids, this paper proposes a DC transmission grid aggregation network modeling method to establish an impedance model for any node in the DC transmission grid, effectively supporting the modeling challenges brought about by the rapid development of MMC-MTDC multi-terminal DC transmission networks.

[0027] The MMC-MTDC structural impedance modeling method proposed in this invention can accurately establish impedance models for different application scenarios, different control modes, and different AC and DC ports of the system, providing key technical support for arbitrary cross-section oscillation analysis and stability improvement of the MMC-MTDC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 Schematic diagram of the topology of the MMC-MTDC system;

[0030] Figure 2 It is a schematic diagram of the MMC average model;

[0031] Figure 3 This is the positive and negative sequence separation control block diagram;

[0032] Figure 4 This is a block diagram for obtaining the synchronous rotation angle; Figure 4 (a) is self-generated, Figure 4 (b) is a phase-locked loop;

[0033] Figure 5 is the AC voltage control block diagram; where, Figure 5 (a) is the positive sequence control block diagram, Figure 4 (b) is the negative sequence control block diagram;

[0034] Figure 6 It is the block diagram of DC voltage control;

[0035] Figure 7 It is the power control block diagram;

[0036] Figure 8 is the AC current control block diagram; where, Figure 8 (a) is the positive sequence control block diagram, Figure 8 (b) is the negative sequence control block diagram;

[0037] Figure 9 is the circulation control block diagram; among them, Figure 9 (a) is the positive sequence control block diagram, Figure 9 (b) is the negative sequence control block diagram;

[0038] Figure 10 is a schematic diagram of a node admittance network;

[0039] Figure 11 Schematic diagram of a flow chart of an MMC-MTDC structured impedance modeling method of the present invention;

[0040] Figure 12 Schematic diagram of a three-terminal MMC-MTDC system;

[0041] Figure 13 The following is a schematic diagram of the impedance verification of the MMC DC ports at each end of the MMC-MTDC system; Figure 13 (a) is the schematic diagram of RVF-MMC DC port impedance calibration. Figure 13 (b) is the schematic diagram of the VDC-MMC DC port impedance calibration. Figure 13 (c) Schematic diagram of GPQ-MMC DC port impedance calibration;

[0042] Figure 14 The following is a schematic diagram of the impedance verification of the MMC AC ports at each end of the MMC-MTDC system; Figure 14 (a) is the schematic diagram of RVF-MMC AC port impedance calibration. Figure 14 (b) is the schematic diagram of VDC-MMC AC port impedance calibration. Figure 14 (c) is the schematic diagram of GPQ-MMC AC port impedance calibration;

[0043] Figure 15 This is a structural schematic diagram of an MMC-MTDC structured impedance modeling device of the present invention;

[0044] Figure 16 This is a structural block diagram of an electronic device of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0046] The following detailed description is an exemplary description and is intended to provide further detailed description of the present invention. Unless otherwise indicated, all technical terms used in the present invention have the same meaning as those generally understood by those skilled in the art to which the present invention belongs. The terms used in the present invention are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention.

[0047] The present invention proposes an MMC-MTDC structured impedance modeling method. The MMC-MTDC system topology using the method of the present invention includes an isolated new energy system 1, an RVF-MMC2 (voltage and frequency control based MMC for renewable energy connection, a voltage and frequency control MMC converter station connected to new energy), a DC transmission grid 3, a networked new energy system 4, an RPQ-MMC5 (active and reactive power control based MMC for renewable energy connection, an active and reactive power control MMC converter station connected to new energy), a VDC-MMC6 (DC voltage control based MMC, a DC voltage control MMC converter station), a first AC power grid 7, a GPQ-MMC8 (active and reactive power control based MMC for grid connection, an active and reactive power control MMC converter station connected to the grid), a second AC power grid 9, an LVF-MMC10 (voltage and frequency controlbased MMC for loading connection, a voltage and frequency control MMC converter station connected to the load) and a load system 11.

[0048] The isolated new energy system 1 is connected to the AC side of RVF-MMC2 via an AC collection line. RVF-MMC2 establishes AC voltage and frequency for the isolated new energy system 1. The DC side of RVF-MMC2 is connected to the DC transmission grid 3 via node A. The networked new energy system 4 is connected to the AC side of RPQ-MMC5 via an AC collection line. RPQ-MMC5 transmits the power generated by the networked new energy system 4 to the DC transmission system. The DC side of RPQ-MMC5 is connected to the multi-terminal DC transmission grid 3 via node B. The DC side of VDC-MMC6 is connected to node C of the multi-terminal DC transmission grid 3. The AC side of VDC-MMC6 is grid-connected to the first AC grid 7. VDC-MMC6 establishes a stable DC voltage for the multi-terminal DC transmission grid 3. The DC side of GPQ-MMC8 is connected to node D of the multi-terminal DC transmission grid 3. The AC side of GPQ-MMC8 is grid-connected to the second AC grid 9. GPQ-MMC8 facilitates power transmission between the multi-terminal DC transmission grid 3 and the second AC grid 9. The DC side of the LVF-MMC 10 is connected to the node E of the multi-terminal DC transmission grid 3 , and the AC side of the LVF-MMC 10 is connected to the load system 11 . The LVF-MMC 10 establishes AC voltage and frequency for the load system 11 .

[0049] Example 1

[0050] The present invention proposes a MMC-MTDC structural impedance modeling method, which specifically includes the following steps:

[0051] Step 1: Establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system; Since the main circuit topology of the MMC at each end of the MMC-MTDC (RVF-MMC2, RPQ-MMC5, VDC-MMC6, GPQ-MMC8, LVF-MMC10) is the same, based on Figure 2 The MMC average value model shown can establish analytical expressions for the MMC bridge arm current small signal, AC current small signal, circulating current small signal, and DC current small signal at each end.

[0052] After the MMC-MTDC system is running stably, the frequency f is injected into the system. p Positive sequence voltage disturbance The frequency range of the positive-sequence voltage disturbance is 1 to 1000 Hz, and the amplitude is within 10% of the fundamental frequency voltage V1. After superimposing the disturbance, a small signal is obtained by subtracting the steady-state signal from the superimposed disturbance signal. The amplitude of the small signal is within 10% of the steady-state signal. Except for the steady-state signal explicitly stated in the present invention, all other signals are small signals.

[0053] Step 1.1: Based on the MMC average value model, calculate the MMC a-phase upper arm current small signal The analytical expression is

[0054]

[0055] Where, is the MMC AC voltage small signal, is the MMC DC voltage small signal, is the small signal of the MMC a-phase upper bridge arm modulation signal, calculated by step 2; Z Larm is the MMC bridge arm inductance impedance matrix; M au is the Toeplitz matrix of the modulation signal of the upper bridge arm of the MMC steady-state phase a; Y Ceq is the MMC bridge arm capacitance admittance matrix; V Cau is the Toeplitz matrix of the upper bridge arm capacitor voltage of phase a in the MMC steady state; I au is the Toeplitz matrix of the upper arm current of phase a in the MMC steady state;

[0056] I au is the Toeplitz matrix of the upper arm current of phase a of the MMC in steady state. Considering that the maximum frequency of the internal harmonics is g during steady-state operation of the MMC, the matrix order is (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (2), and the remaining columns are obtained according to the Toeplitz matrix principle.

[0057] I au_g+1 =[{I auk}| k＝-g～g ] T (2)

[0058] Among them, I auk is the steady-state component of the upper arm current of phase a of the MMC at frequency kf1; f1 is the fundamental frequency;

[0059] V Cau is the Toeplitz matrix of the upper bridge arm capacitor voltage of phase a of the MMC steady state, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in (3), and the remaining columns are obtained according to the Toeplitz matrix principle.

[0060] V Cau_g+1 =[{V Cauk}| k＝-g～g ] T (3)

[0061] Among them, V Cauk is the steady-state component of the upper bridge arm capacitor voltage of phase a of the MMC at frequency kf1;

[0062] M au is the Toeplitz matrix of the MMC steady-state a-phase upper bridge arm modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in (4), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0063] M au_g+1 =[{M auk}| k＝-g～g ] T (4)

[0064] Among them, M auk is the steady-state component of the MMC steady-state a-phase upper bridge arm modulation signal at frequency kf1;

[0065] Y Ceq is the MMC bridge arm capacitance admittance matrix, and its expression is:

[0066]

[0067] Where diag[·] represents diagonal matrix operation, C sm is the MMC submodule capacitance, N is the number of MMC bridge arm submodules; f p is the disturbance frequency;

[0068] Z Larm is the MMC bridge arm inductance impedance matrix, and its expression is:

[0069] ZLarm =R arm U+j2πL arm ·diag[{f p +kf1}| k＝-g～g ] (6)

[0070] Among them, R arm is the MMC bridge arm resistance, L arm is the MMC bridge arm inductance, U is the (2g+1)×(2g+1) unit matrix;

[0071] Step 1.2: Since the differential mode component of the MMC bridge arm current constitutes the MMC AC current, the MMC AC current small signal is calculated. The analytical expression is:

[0072]

[0073] Where A d is the MMC bridge arm current differential mode matrix, and its expression is:

[0074]

[0075] Step 1.3: Since the common mode component of the MMC bridge arm current constitutes the MMC circulating current, the MMC circulating current small signal is calculated. The analytical expression is:

[0076]

[0077] Where A c is the MMC bridge arm current differential mode matrix, and its expression is:

[0078]

[0079] Step 1.4: Since the common-mode zero-sequence component of the MMC bridge arm current constitutes the MMC DC current, the MMC DC current is calculated as The small signal analytical expression is:

[0080]

[0081] Where A c0 is the common mode zero sequence matrix of the MMC bridge arm current, and its expression is:

[0082]

[0083] Among them, mod(k+1,3) represents the modulo function with 3 as the divisor, and its expression is:

[0084]

[0085] Step 2: Based on modular modeling of the control link, a structured small signal model of the modulation signal of each MMC at each end is established based on the diverse operating functions and control modes of the MMC at each end of the MMC-MTDC system. The modules in the control link of the MMC-MTDC system include the common positive and negative sequence separation module, the inner loop control module, and the synchronization module and outer loop control module unique to each MMC at each end.

[0086] Step 2.1, establish the small signal model of the positive and negative sequence separation module; considering the stable operation function requirements of the MMC at each end under steady state, symmetrical fault, and asymmetrical fault conditions, the MMC at each end adopts positive and negative sequence control. Positive and negative sequence separation is the basis of positive and negative sequence control; the positive and negative sequence separation control block diagram is as follows Figure 3 As shown, v abc is the MMC AC three-phase voltage, T is the fundamental wave period, ω1t is the given rotation angle, ω1 is the fundamental wave angular frequency, t is time, is the MMC AC three-phase positive sequence voltage, is the MMC AC three-phase negative sequence voltage;

[0087] according to Figure 3 , the analytical expression of the small signal model of the positive and negative sequence separation module is calculated as:

[0088]

[0089] Where, is the MMC AC a phase voltage small signal, is the MMC AC a phase positive sequence voltage small signal, is the MMC AC a phase negative sequence voltage small signal; is the small signal of the MMC AC a-phase current, is the small positive sequence current signal of MMC AC phase a, is the MMC AC a phase negative sequence current small signal;

[0090] In formula (14), Ts p 、T sn The transfer function matrices are extracted for the positive sequence component and the negative sequence component respectively, and the expressions are:

[0091]

[0092] Among them, G adp is the positive sequence Park transform d-axis coefficient matrix; G aqp is the positive sequence Park transform q-axis coefficient matrix; G adn is the negative sequence Park transform d-axis coefficient matrix; G aqn is the negative sequence Park transform q-axis coefficient matrix; G dais the Park inverse transform d-axis (24g+3)×(24g+3) coefficient matrix; G qa is the Park inverse transform q-axis (24g+3)×(24g+3) coefficient matrix; G DSC is the delay signal elimination transfer function matrix, which is expressed as:

[0093]

[0094] G adp is the positive-sequence Park transform d-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0, k = -g to g;

[0095]

[0096] G aqp is the positive-sequence Park transform q-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0097]

[0098] G adn is the negative-sequence Park transform d-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0099]

[0100] G aqn is the negative-sequence Park transform q-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0101]

[0102] G da is the Park inverse transform d-axis (24g+3)×(24g+3) coefficient matrix, except for the following elements, all other elements are 0;

[0103]

[0104] G qa This is the Park inverse transform q-axis (24g+3)×(24g+3) coefficient matrix. All elements except the following are 0.

[0105]

[0106] Step 2.2: Establish a small signal model for the synchronization module. Considering the island and network operation modes of each MMC, the synchronization module includes two types: self-generation of synchronous rotation angle and phase-locked loop, providing synchronous rotation angle for the outer loop control module and the inner loop control block.

[0107] Step 2.2.1: For RVF-MMC2 and LVF-MMC10, each MMC adopts VF control mode, the fundamental frequency f1 is given, and the synchronous rotation angle is generated automatically, such as Figure 4 As shown in (a), the synchronous rotation angle small signal

[0108] Step 2.2.2: For RPQ-MMC5, VDC-MMC6 and GPQ-MMC8, each MMC uses a phase-locked loop to track the grid voltage phase. The phase-locked loop control block diagram is as follows: Figure 4 As shown in (b), the analytical expression of the small signal model of the synchronization module is:

[0109]

[0110] Where, T PLL is the closed-loop transfer function matrix of the phase-locked loop, and its expression is:

[0111] T PLL =H PLL (U+V1H PLL ) -1 G pqp (twenty four)

[0112] Among them, V1 is the fundamental frequency positive sequence voltage amplitude, H PLL is the open-loop transfer function matrix of the phase-locked loop, and its expression is:

[0113] Among them, k pp 、k pi are the proportional coefficient and integral coefficient of the phase-locked loop PI controller respectively;

[0114] G pqp is the q-axis coefficient matrix of the positive sequence voltage Park transformation, with an order of (2g+1)×(2g+1). Except for the following elements, all other elements are 0;

[0115]

[0116] in, is the fundamental frequency positive sequence voltage phase;

[0117] Step 2.3: Establish a small signal model for the outer loop control module. Based on the functional requirements of each MMC, the outer loop control module includes three functions: AC voltage control, DC voltage control, and active and reactive power control, providing reference instructions for the inner loop control module.

[0118] Step 2.3.1, for RVF-MMC2 and LVF-MMC10, each end MMC adopts VF control mode, and the outer loop control module adopts AC voltage control. The control block diagram is as follows Figure 5 As shown in the figure, the outer loop control module generates positive sequence and negative sequence dq axis current reference instructions by inputting the MMC AC three-phase positive sequence and negative sequence voltages as the input of the inner loop control module.

[0119] The analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is calculated as follows:

[0120]

[0121] Where, They are respectively the positive sequence current d and q axis reference command small signals; are the d-axis and q-axis transfer functions of the positive sequence voltage control, respectively, and their expressions are:

[0122]

[0123] Among them, G pdp is the positive sequence voltage Park transform d-axis coefficient matrix, with an order of (2g+1)×(2g+1), and all elements except the following are 0;

[0124]

[0125] H vacp is the transfer function matrix of the positive sequence voltage PI controller, and its expression is

[0126]

[0127] Among them, k vacpp 、k vacpi are the proportional coefficient and integral coefficient of the positive sequence voltage PI controller respectively;

[0128] The analytical expression of the negative sequence current dq axis reference instruction small signal model in the outer loop control module is calculated as follows:

[0129]

[0130] Where, They are respectively the negative sequence current d and q axis reference command small signals; are the negative sequence voltage control d and q axis transfer functions respectively, and the expressions are

[0131]

[0132] Among them, G ndn is the negative sequence voltage Park transform d-axis coefficient matrix, with an order of (2g+1)×(2g+1), and all elements except the following are 0;

[0133]

[0134] G nqn is the negative sequence voltage Park transformation q-axis coefficient matrix, with an order of (2g+1)×(2g+1), and all elements except the following are 0;

[0135]

[0136] H vacn is the negative sequence voltage PI controller transfer function matrix, expressed as:

[0137]

[0138] Among them, k vacnp 、k vacni are the proportional coefficient and integral coefficient of the negative sequence voltage PI controller respectively;

[0139] Step 2.3.2, for VDC-MMC6, MMC adopts VDC control mode, the outer loop control module is DC voltage control and supporting reactive power control, the control block diagram is as follows Figure 6 and Figure 7 As shown; the outer loop control module generates a positive sequence dq axis current reference instruction by inputting the MMC DC voltage and reactive power instructions as the input of the inner loop control module. The negative sequence dq axis current reference instruction is

[0140] The analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is calculated as follows:

[0141]

[0142] Where, are the DC voltage control d-axis and q-axis transfer functions, respectively, and their expressions are:

[0143]

[0144] Among them, k Q is the reactive power coefficient, and its expression is:

[0145]

[0146] Among them, Q refis the reactive power instruction; V1 is the fundamental frequency voltage amplitude;

[0147] H vdc is the transfer function matrix of the DC voltage PI controller, and its expression is:

[0148]

[0149] Among them, k vdcp 、k vdci are the proportional coefficient and integral coefficient of the DC voltage PI controller respectively;

[0150] Step 2.3.3, for RPQ-MMC5 and GPQ-MMC8, each end MMC adopts PQ control mode, and the outer loop control module is power control. The control block diagram is as follows Figure 8 As shown; the outer loop control module generates the positive sequence dq axis current reference instruction by inputting the MMC active and reactive power instructions as the input of the inner loop control module, and the negative sequence dq axis current reference instruction is

[0151] The analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is calculated as follows:

[0152]

[0153] Where, are the power control d-axis and q-axis transfer functions, respectively, and their expressions are:

[0154]

[0155] Among them, k P is the active coefficient, and the expression is

[0156]

[0157] Among them, P ref is the active power instruction;

[0158] Step 2.4: Establish a small signal model for the outer loop control module. The inner loop control module is a common link for the MMCs at each end of the MMC-MTDC system. It uses the output of the outer loop control module as an input reference instruction to generate a modulation signal, including AC current control and circulating current control.

[0159] Step 2.4.1, establish the AC current control small signal model; the AC current control block diagram is as follows Figure 8 As shown in the figure, the analytical expression of the small signal model of the positive sequence AC modulation signal is calculated as:

[0160]

[0161] Where G da is the Park inverse transform d-axis coefficient matrix; G qa H is the Park inverse transform q-axis coefficient matrix; iacp is the transfer function matrix of the positive sequence AC current PI controller; k d is the AC current control decoupling coefficient; is the steady-state positive-sequence d-axis current Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (44), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0162]

[0163] in, is the steady-state component of the positive-sequence d-axis current at frequency kf1;

[0164] is the steady-state positive-sequence q-axis current Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (45), and the remaining columns are obtained according to the Toeplitz matrix principle.

[0165]

[0166] in, is the steady-state component of the positive-sequence q-axis current at frequency kf1;

[0167] is the Toeplitz matrix of the steady-state positive-sequence d-axis modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (46), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0168]

[0169] in, is the steady-state component of the positive-sequence d-axis modulation signal at frequency kf1;

[0170] is the Toeplitz matrix of the steady-state positive-sequence q-axis modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (47), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0171]

[0172] in, is the steady-state component of the positive-sequence q-axis modulation signal at frequency kf1;

[0173] H iacpis the transfer function matrix of the positive sequence AC current PI controller, and its expression is

[0174]

[0175] Among them, k iacpp 、k iacpi are the proportional coefficient and integral coefficient of the positive sequence AC current PI controller respectively;

[0176] G da is the Park inverse transform d-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0177]

[0178] G qa is the Park inverse transform q-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0179]

[0180] The analytical expression of the small signal model of the negative sequence AC modulation signal is calculated as follows:

[0181]

[0182] Where, is the steady-state negative-sequence d-axis current Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (52), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0183]

[0184] in, is the steady-state component of the negative-sequence d-axis current at frequency kf1;

[0185] is the steady-state negative-sequence q-axis current Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (53), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0186]

[0187] in, is the steady-state component of the negative-sequence q-axis current at frequency kf1;

[0188] is the steady-state negative-sequence d-axis voltage Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (54), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0189]

[0190] in, is the steady-state component of the negative-sequence d-axis voltage at frequency kf1;

[0191] is the steady-state negative-sequence q-axis voltage Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (55), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0192]

[0193] in, is the steady-state component of the negative-sequence q-axis voltage at frequency kf1;

[0194] is the Toeplitz matrix of the steady-state negative-sequence d-axis modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (56), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0195]

[0196] in, is the steady-state component of the negative-sequence d-axis modulation signal at frequency kf1;

[0197] is the Toeplitz matrix of the steady-state negative-sequence q-axis modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (57), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0198]

[0199] in, is the steady-state component of the negative-sequence q-axis modulation signal at frequency kf1;

[0200] H iacn is the negative sequence AC current PI controller transfer function matrix, the expression is

[0201]

[0202] Among them, k iacnp 、k iacni are the proportional coefficient and integral coefficient of the negative sequence AC current PI controller respectively;

[0203] Step 2.4.2, establish the small signal model of the loop current control; the loop current control block diagram is as follows Figure 9 As shown in the figure, the analytical expression of the small signal model of the positive sequence circulating current modulation signal is calculated as:

[0204]

[0205] Where G 2da is the double frequency Park inverse transform d-axis coefficient matrix; G 2qa is the double frequency Park inverse transform q-axis coefficient matrix; G 2adp is the double frequency positive sequence Park transform d-axis coefficient matrix; G 2aqp is the q-axis coefficient matrix of the double frequency positive sequence Park transform; H icp is the transfer function matrix of the positive sequence circulating PI controller; k c is the decoupling coefficient of circulating control; is the steady-state positive-sequence d-axis annular flow Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (60), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0206]

[0207] in, is the steady-state component of the positive-sequence d-axis circulating current at frequency kf1;

[0208] is the steady-state positive-sequence q-axis circulation Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (61), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0209]

[0210] in, is the steady-state component of the positive-sequence q-axis circulating current at frequency kf1;

[0211] is the Toeplitz matrix of the steady-state positive-sequence d-axis circulating current modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (62), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0212]

[0213] in, is the steady-state component of the positive-sequence d-axis circulating current modulation signal at frequency kf1;

[0214] is the Toeplitz matrix of the steady-state positive-sequence q-axis circulating current modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (63), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0215]

[0216] in, is the steady-state component of the positive-sequence q-axis circulating current modulation signal at frequency kf1;

[0217] H icp is the transfer function matrix of the positive sequence circulating PI controller, and its expression is:

[0218]

[0219] Among them, k icpp 、k icpi are the proportional coefficient and integral coefficient of the positive sequence circulating current PI controller respectively;

[0220] G 2adp is the double frequency positive sequence Park transform d-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0221]

[0222] G 2aqp is the q-axis coefficient matrix of the double frequency positive sequence Park transform, with an order of (2g+1)×(2g+1). Except for the following elements, all other elements are 0;

[0223]

[0224] G 2da is the d-axis coefficient matrix of the double-frequency inverse Park transform, with an order of (2g+1)×(2g+1). Except for the following elements, all other elements are 0;

[0225]

[0226] G 2qa is the q-axis coefficient matrix of the double-frequency Park inverse transform, with an order of (2g+1)×(2g+1). Except for the following elements, all other elements are 0;

[0227]

[0228] The analytical expression of the small signal model of the negative sequence circulating current modulation signal is calculated as follows:

[0229]

[0230] Where, is the steady-state negative-sequence d-axis circulation Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (70), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0231]

[0232] in, is the steady-state component of the negative-sequence d-axis circulating current at frequency kf1;

[0233] is the steady-state negative-sequence q-axis circulation Toeplitz matrix, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (71), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0234]

[0235] in, is the steady-state component of the negative-sequence q-axis circulating current at frequency kf1;

[0236] is the Toeplitz matrix of the steady-state negative-sequence d-axis circulating current modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (72), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0237]

[0238] in, is the steady-state component of the negative-sequence d-axis circulating current modulation signal at frequency kf1;

[0239] is the Toeplitz matrix of the steady-state negative-sequence q-axis circulating current modulation signal, with an order of (2g+1)×(2g+1). The analytical expression of the middle column is shown in Equation (73), and the remaining columns are obtained according to the Toeplitz matrix principle;

[0240]

[0241] in, is the steady-state component of the negative-sequence q-axis circulating current modulation signal at frequency kf1;

[0242] H icn is the negative sequence circulating current PI controller transfer function matrix, and its expression is

[0243]

[0244] Among them, k icnp 、k icni are the proportional coefficient and integral coefficient of the negative sequence circulating current PI controller respectively;

[0245] G 2adn is the double frequency positive sequence Park transform d-axis coefficient matrix, with order (2g+1)×(2g+1), and all elements except the following are 0;

[0246]

[0247] G 2aqn is the q-axis coefficient matrix of the double frequency positive sequence Park transform, with an order of (2g+1)×(2g+1). Except for the following elements, all other elements are 0;

[0248]

[0249] In step 2.5, according to steps 2.1 to 2.4, the analytical expression of the structured small signal model of the modulation signal of the MMC a-phase upper bridge arm at each end of the MMC-MTDC system is calculated as follows:

[0250]

[0251] Where G i is the AC current control transfer function matrix; G ic is the circulation control transfer function matrix; G v is the voltage coefficient matrix; G VF is the VF control mode matrix; G PQ is the PQ control mode matrix; G cc is the current coefficient matrix; G VDC1 , G VDC2 They are VDC control mode matrix 1 and matrix 2 respectively; K VF , K PQ , K VDC They are VF control flag, PQ control flag, and VDC control flag respectively;

[0252] Based on the structured small signal model, by flexibly selecting the flag bit, the small signal model of the MMC modulated signal at each end of the MMC-MTDC can be obtained:

[0253] (a) For RVF-MMC2 and LVF-MMC10, K VF =1, K PQ =0, K VDC =0;

[0254] (b) For RPQ-MMC5 and GPQ-MMC8, K VF =0, K PQ =1, K VDC =0;

[0255] (c) For VDC-MMC6, KVF =0, K PQ =0, K VDC =1;

[0256] In formula (77), G i is the AC current control transfer function matrix, which is expressed as:

[0257] G i =[(G da H iacp +k d G qa )G pdp -(G qa H iacp -k d G da )G pqp ]T sp +[(G da H iacn +k d G qa )G ndn +(G qa H iacn -k d G da )G nqn ]T sn (78)

[0258] G ic is the circulation control transfer function matrix, which is expressed as:

[0259] G ic =(G 2da H icp +G 2qa k c )G 2adp -(G 2qa H icp -G 2da k c )G 2aqp +(G 2da H icn +k c G 2qa )G 2adn +(G 2qa H icn -k c G 2da )G 2aqn (79)

[0260] G v is the voltage coefficient matrix, and its expression is:

[0261] G v =-G da Gpdp T sp -(G da G ndn +G qa G nqn )T sn (80)

[0262] G VF is the VF control mode matrix, and its expression is:

[0263] G VF =(G da H iacp H vacp G pdp -G qa H iacp H vacp G pqp +G qa G pqp )T sp +(G da H iacn H vacn G ndn +G qa H iacn H vacn G nqn )T sn (81)

[0264] G PQ is the PQ control mode matrix, and its expression is:

[0265]

[0266] Among them, G cc is the current coefficient matrix, and its expression is:

[0267]

[0268] G VDC1 , G VDC2 They are VDC control mode matrix 1 and matrix 2 respectively, and the expressions are:

[0269]

[0270] Step 3: According to Step 1 and Step 2, the AC and DC port impedances of the MMC positive and negative sequence control structure are calculated;

[0271] Step 3.1: According to equations (1), (7), and (77), the analytical expression of the DC port admittance of each MMC is calculated as:

[0272]

[0273] Where Y dc Refers to the admittance from the MMC DC port to the MMC;

[0274] The AC system impedance connected to the AC side of each MMC is the impedance viewed from the MMC AC port to the AC system. Specifically:

[0275] (a) For RVF-MMC2, is the AC port impedance of the island new energy system 1;

[0276] (b) For RPQ-MMC5, The impedance of the 4 AC ports of the networked new energy system;

[0277] (c) For VDC-MMC6, is the AC port impedance of the first AC grid 7;

[0278] (d) For GPQ-MMC8, is the AC port impedance of the second AC grid 9;

[0279] (c) For LVF-MMC10, is the AC port impedance of the load system 11;

[0280] In step 3.2, according to equations (1), (11), and (77), the analytical expression of the AC port admittance of each MMC is calculated as:

[0281]

[0282] Where Y ac Refers to the admittance from the MMC AC port to the MMC;

[0283] is the impedance of the DC transmission grid connected to the DC side of each MMC, that is, the impedance viewed from the MMC DC port to the DC transmission grid. Specifically:

[0284] (a) For RVF-MMC2, is the impedance from node A to the DC transmission grid 3;

[0285] (b) For RPQ-MMC5, is the impedance from node B to the DC transmission grid 3;

[0286] (c) For VDC-MMC6, is the impedance from node C to the DC transmission grid 3;

[0287] (d) For GPQ-MMC8, is the impedance from node D to the DC transmission grid 3;

[0288] (c) For LVF-MMC10, is the impedance from node E to the DC transmission grid 3;

[0289] Step 4: Based on network aggregation, establish the impedance model of any node in the DC transmission grid; without loss of generality, we can use Figure 10 The N-node admittance network shown represents the DC transmission grid. Taking any MMC at one end as an example, the target MMC is designated as node 0, and the remaining MMCs are numbered sequentially. The admittance of node h (h = 0 to N) to the ground branch is expressed as Y hG Indicates that the branch admittance between node h and node i (i=0~N, i≠h) is expressed as Y hi express;

[0290] The voltage equation of the N-node aggregate network is established as:

[0291]

[0292] Where, are the voltage and current small signals of the target converter station respectively, is the voltage matrix of all nodes except node 0; Y 0m is the admittance matrix between node 0 and other nodes; Y net is the admittance matrix of other nodes;

[0293] Admittance matrix Y between node 0 and other nodes 0m The expression is:

[0294] Y 0m =[-Y 01 ,-Y 02 ,…,-Y 0(N-1) ] T (88)

[0295] Y net is the admittance matrix of other nodes, and its expression is:

[0296]

[0297] In the formula, the main diagonal element Y hh is the sum of the admittances of all branches of node h, and its expression is:

[0298]

[0299] The analytical expression of the admittance matrix of the target MMC DC port looking toward the DC transmission grid is calculated as follows:

[0300]

[0301] Step 5: Establishing the structural impedance model of different MMC ports at each end of the MMC-MTDC;

[0302] Step 5.1: For the target MMC DC port impedance, connect the target MMC AC side to the system impedance. Substitute into equation (85) and calculate the target MMC DC port impedance Z dc The analytical expression is:

[0303]

[0304] Step 5.2: For the target MMC AC port impedance, connect the AC side of the remaining MMCs except the target MMC to the system impedance. Substitute them into equation (85) to calculate the DC admittance Y of each other MMC end dc Then, combined with the DC transmission grid impedance model, the DC transmission grid impedance of the target MMC DC side is calculated according to formula (91): Finally, it is substituted into equation (86) to calculate the target MMC AC port positive sequence impedance Negative sequence impedance The analytical expression is:

[0305]

[0306] The process of applying the method of obtaining DC impedance of diode rectification and MMC hybrid considering multi-harmonic interaction is as follows: Figure 11 shown.

[0307] In this specific application example, Figure 12 Electromagnetic transient simulation verification was performed on the three-terminal MMC-HVDC ring network system shown. The DC voltage was ±320kV, the RVF-MMC capacity was 1000MVA, the VDC-MMC capacity was 400MVA, the connected first AC grid had an SCR of 5, the GPQ-MMC capacity was 600MVA, and the connected second AC grid had an SCR of 2.5.

[0308] According to steps 1 to 5, the DC port impedances of the RVF-MMC, VDC-MMC, and GPQ-MMC of the MMC-MTDC system are established, and the impedance sweep frequency is simulated by MATLAB / SIMULINK to obtain the DC port impedance of each MMC. The impedance calibration results are as follows: Figure 13 (a), 13(b), and 13(c). Figure 13 The solid line in the middle is the impedance analysis result, and the discrete points are the simulation results. The two are basically consistent, verifying the accuracy of the structural impedance modeling of the MMC-MTDC DC port described in the present invention.

[0309] According to steps 1 to 5, the AC port impedances of RVF-MMC, VDC-MMC and GPQ-MMC of the MMC-MTDC system are established, and the impedance sweep simulation of MATLAB / SIMULINK is used to obtain the AC port impedance of each MMC. The impedance calibration results are as follows: Figure 14 (a), 14(b), and 14(c). Figure 14 The solid line in the middle represents the analytical result for the positive-sequence impedance of the AC port, while the dots represent the corresponding simulation results. The dashed line represents the analytical result for the negative-sequence impedance of the AC port, while the crosses represent the corresponding simulation results. The impedance analytical results are largely consistent with the simulation results, verifying the accuracy of the structural impedance modeling of the AC port of the MMC-MTDC described in this invention.

[0310] This paper proposes a method for modeling the positive and negative sequence control of MMCs at each end of an MMC-MTDC system, as well as the structured impedance of different AC and DC ports. It also proposes a modular modeling method for common and unique control links, enabling flexible establishment of small-signal models for the diversified control systems of MMCs at each end of an MMC-MTDC system. It also proposes a method for modeling the aggregated network of a DC transmission grid, enabling the establishment of impedance models for any node in a complex multi-terminal flexible DC transmission system.

[0311] In the present invention, step 1 is to model the MMC main circuit. The main circuit requires the MMC control system to provide control instructions (obtained in step 2). At the same time, the main circuit is connected to the DC transmission grid, so there is a KVL relationship between the MMC and the DC transmission grid (obtained in step 4).

[0312] Step 2: Establish an MMC control system model. The input of this model is the AC and DC side voltages, currents and other electrical quantities in step 1.

[0313] Step 3: Combine the main circuit of step 1 and the control system of step 2 to establish the MMC impedance model at each end. However, the impedance model is related to the DC transmission grid.

[0314] Step 4: Establish a DC transmission grid model and connect the MMC impedances at each end;

[0315] Step 5: Substitute step 4 into step 3 to establish the structural impedance model of different sections on the AC and DC sides of each end of the MMC.

[0316] Example 2

[0317] See also Figure 15 As shown, the present invention provides an MMC-MTDC structured impedance modeling device, comprising:

[0318] The first module is used to establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system;

[0319] The second module is used to establish a structured small signal model of the MMC modulation signal at each end based on modular modeling of the control link;

[0320] The third module is used to calculate the MMC positive and negative sequence control structured AC and DC port impedances based on the established MMC main circuit small signal model at each end and the structured small signal model of the MMC modulation signal at each end;

[0321] The fourth module is used to establish an impedance model of any node in the DC transmission grid based on network aggregation;

[0322] The fifth module is used to establish the structural impedance model of different MMC ports at each end of the MMC-MTDC.

[0323] Example 3

[0324] See also Figure 16 As shown, the present invention also provides an electronic device 100 for implementing the MMC-MTDC structural impedance modeling method; the electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on the at least one processor 102, and at least one communication bus 104.

[0325] The memory 101 may be used to store the computer program 103 , and the processor 102 implements the steps of the MMC-MTDC structural impedance modeling method described in Example 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101 .

[0326] The memory 101 in the electronic device 100 stores a plurality of instructions to implement an MMC-MTDC structural impedance modeling method, and the processor 102 can execute the plurality of instructions to implement:

[0327] Establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system;

[0328] Based on modular modeling of the control link, a structured small signal model of the MMC modulation signal at each end is established;

[0329] Based on the established small signal model of the MMC main circuit at each end and the structured small signal model of the MMC modulation signal at each end, the AC and DC port impedances of the MMC positive and negative sequence control structure are calculated;

[0330] Based on network aggregation, an impedance model of any node in the DC transmission grid is established;

[0331] Establish the structural impedance model of different MMC ports at each end of MMC-MTDC.

[0332] Example 4

[0333] If the module / unit integrated in the electronic device 100 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 process 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 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, etc. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory and read-only memory (ROM, Read-Only Memory).

[0334] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. MMC-MTDC structural impedance modeling method, characterized by: include: Establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system; Based on modular modeling of the control link, a structured small signal model of the MMC modulation signal at each end is established; Based on the established small signal model of the MMC main circuit at each end and the structured small signal model of the MMC modulation signal at each end, the AC and DC port impedances of the MMC positive and negative sequence control structure are calculated; Based on network aggregation, an impedance model of any node in the DC transmission grid is established; Establish the structural impedance model of different MMC ports at each end of MMC-MTDC; In the step of establishing a structured small signal model of the MMC modulated signal at each end based on modular modeling of the control link, the structured small signal model of the MMC modulated signal at each end includes: Small signal model of positive and negative sequence separation module, small signal model of synchronization module, small signal model of outer loop control module, small signal model of inner loop control module; The small signal model of the outer loop control module includes: an analytical expression of a small signal model of a positive sequence current dq axis reference instruction in the outer loop control module, and an analytical expression of a small signal model of a negative sequence current dq axis reference instruction in the outer loop control module; The small signal models of the inner loop control module include: positive sequence AC modulation signal small signal model, negative sequence AC modulation signal small signal model, positive sequence circulating current modulation signal small signal model, and negative sequence circulating current modulation signal small signal model; In the step of establishing a structured small signal model of the MMC modulation signal at each end based on the modular modeling of the control link, the analytical expression of the structured small signal model of the bridge arm modulation signal of the MMCa phase at each end is: Where G i is the AC current control transfer function matrix; G ic is the circulation control transfer function matrix; G v is the voltage coefficient matrix; G VF is the VF control mode matrix; G PQ is the PQ control mode matrix; G VDC1 , G VDC2 They are VDC control mode matrix 1 and matrix 2 respectively; K VF , K PQ , K VDC They are VF control flag, PQ control flag, and VDC control flag respectively; is the MMC AC a phase voltage small signal; It is the structured small signal of the bridge arm modulation signal of the MMCa phase; is the small signal of the MMC AC a-phase current, is the MMC circulating current small signal, is the small DC voltage signal of MMC; In the step of establishing an impedance model of any node in the DC transmission grid based on network aggregation: The voltage equation of the N-node aggregate network is established as: Where, are the voltage and current small signals of the target converter station respectively, is the voltage matrix of all nodes except node 0; Y 0m is the admittance matrix between node 0 and other nodes; is the admittance matrix Y between node 0 and other nodes 0m The transpose of Y net is the admittance matrix of other nodes; is the admittance matrix Y of other nodes net The inverse matrix of Calculate the admittance matrix of the target MMC DC port looking towards the DC transmission grid The analytical expression is:

2. The MMC-MTDC structured impedance modeling method according to claim 1, wherein: In the step of establishing the small signal model of the MMC main circuit at each end of the MMC-MTDC system, the small signal model of the MMC main circuit at each end of the MMC-MTDC system includes: Small signal of MMCa phase upper arm current Parsing expression: Where Z Larm is the MMC bridge arm inductance impedance matrix; M au is the Toeplitz matrix of the modulation signal of the upper bridge arm of the MMC steady-state phase a; Y Ceq is the MMC bridge arm capacitance admittance matrix; V Cau is the Toeplitz matrix of the upper bridge arm capacitor voltage of phase a in the MMC steady state; I au is the Toeplitz matrix of the upper arm current of phase a in the MMC steady state; MMC AC a-phase current small signal Parsing expression: Where A d is the MMC bridge arm current differential mode matrix; MMC circulating current small signal Parsing expression: MMC DC current Small signal analytical expression: Where A c0 is the common-mode zero-sequence matrix of the MMC bridge arm current.

3. The MMC-MTDC structural impedance modeling method according to claim 1, wherein: In the step of establishing a structured small signal model of the MMC modulation signal at each end based on modular modeling of the control link: The analytical expression of the small signal model of the positive and negative sequence separation module is: Where, is the MMC AC a phase positive sequence voltage small signal, is the MMC AC a phase negative sequence voltage small signal; is the small positive sequence current signal of MMC AC phase a, is the MMC AC a phase negative sequence current small signal; T sp 、T sn Extract transfer function matrices for positive-sequence components and negative-sequence components respectively; In the synchronous rotation angle self-generation mode, the synchronous module small signal The analytical expression of the model is: When the phase-locked loop tracks the grid voltage phase, the synchronization module small signal The analytical expression of the model is: Where, T PLL is the closed-loop transfer function matrix of the phase-locked loop; In the AC voltage control mode, the analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is: Where, They are respectively the positive sequence current d and q axis reference command small signals; are the d-axis and q-axis transfer functions of positive sequence voltage control, respectively; In the AC voltage control mode, the analytical expression of the negative sequence current dq axis reference instruction small signal model in the outer loop control module is: Where, They are respectively the negative sequence current d and q axis reference command small signals; are the d-axis and q-axis transfer functions of negative sequence voltage control, respectively; In the DC voltage control mode, the analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is: Where, are the DC voltage control d-axis and q-axis transfer functions, respectively; In the DC voltage control mode, the analytical expression of the negative sequence current dq axis reference instruction small signal model in the outer loop control module is: In the power control mode, the analytical expression of the small signal model of the positive sequence current dq axis reference instruction in the outer loop control module is: Where, are the power control d-axis and q-axis transfer functions respectively; In the power control mode, the analytical expression of the negative sequence current dq axis reference instruction small signal model in the outer loop control module is: The analytical expression of the small signal model of the positive sequence AC modulation signal is: Where G da is the Park inverse transform d-axis coefficient matrix; G qa H is the Park inverse transform q-axis coefficient matrix; iacp is the transfer function matrix of the positive sequence AC current PI controller; k d is the AC current control decoupling coefficient; is the steady-state positive-sequence d-axis current Toeplitz matrix; G pdp is the positive sequence voltage Park transformation d-axis coefficient matrix; G pqp is the q-axis coefficient matrix of the positive sequence voltage Park transformation; is the steady-state positive-sequence q-axis current Toeplitz matrix; is the Toeplitz matrix of the steady-state positive-sequence d-axis modulation signal; is the Toeplitz matrix of the steady-state positive-sequence q-axis modulation signal; is the inverse matrix of the open-loop transfer function of the phase-locked loop; The analytical expression of the small signal model of the negative sequence AC modulation signal is: Where, is the steady-state negative-sequence d-axis current Toeplitz matrix; is the steady-state negative-sequence q-axis current Toeplitz matrix; is the steady-state negative-sequence d-axis voltage Toeplitz matrix; is the steady-state negative-sequence q-axis voltage Toeplitz matrix; is the Toeplitz matrix of the steady-state negative-sequence d-axis modulation signal; is the Toeplitz matrix of the steady-state negative-sequence q-axis modulation signal; H iacn is the negative sequence AC current PI controller transfer function matrix; G ndn is the negative sequence voltage Park transformation d-axis coefficient matrix; G nqn is the negative sequence voltage Park transformation q-axis coefficient matrix; The analytical expression of the small signal model of the positive sequence circulating current modulation signal is: Where G 2da is the double frequency Park inverse transform d-axis coefficient matrix; G 2qa is the double frequency Park inverse transform q-axis coefficient matrix; G 2adp is the double frequency positive sequence Park transform d-axis coefficient matrix; G 2aqp is the q-axis coefficient matrix of the double frequency positive sequence Park transform; H icp is the transfer function matrix of the positive sequence circulating PI controller; k c is the decoupling coefficient of circulating control; is the steady-state positive-sequence d-axis circulation Toeplitz matrix; is the steady-state positive-sequence q-axis circulation Toeplitz matrix; is the Toeplitz matrix of the steady-state positive-sequence d-axis circulating current modulation signal; is the Toeplitz matrix of the steady-state positive-sequence q-axis circulating current modulation signal; The analytical expression of the small signal model of the negative sequence circulating current modulation signal is: Where, is the steady-state negative-sequence d-axis circulation Toeplitz matrix; is the Toeplitz matrix of the steady-state negative-sequence q-axis circulation; is the Toeplitz matrix of the steady-state negative-sequence d-axis circulating current modulation signal; is the Toeplitz matrix of the steady-state negative-sequence q-axis circulating current modulation signal; H icn is the negative sequence circulating current PI controller transfer function matrix; G 2adn is the double frequency negative sequence Park transform d-axis coefficient matrix; G 2aqn is the q-axis coefficient matrix of the double-frequency negative-sequence Park transform.

4. The MMC-MTDC structural impedance modeling method according to claim 2, characterized in that: In the step of calculating the MMC positive and negative sequence control structured AC and DC port impedances based on the established MMC main circuit small signal model at each end and the structured small signal model of the MMC modulation signal at each end: The analytical expression of the DC port admittance of each MMC is: Where Y dc Refers to the admittance from the MMC DC port to the MMC; The AC system impedance connected to the AC side of each MMC; The analytical expression of the AC port admittance of each MMC is: Where Y ac Refers to the admittance from the MMC AC port to the MMC; is the DC transmission grid impedance connected to the DC side of each MMC.

5. The MMC-MTDC structural impedance modeling method according to claim 1, characterized in that: In the step of establishing the MMC-MTDC different port structured impedance model, the target MMC DC port impedance Z dc The analytical expression is: Target MMC AC port positive sequence impedance Negative sequence impedance The analytical expression is: 6.MMC-MTDC structured impedance modeling device, characterized by: include: The first module is used to establish the small signal model of the MMC main circuit at each end of the MMC-MTDC system; The second module is used to establish a structured small signal model of the MMC modulation signal at each end based on modular modeling of the control link; The third module is used to calculate the MMC positive and negative sequence control structured AC and DC port impedances based on the established MMC main circuit small signal model at each end and the structured small signal model of the MMC modulation signal at each end; The fourth module is used to establish an impedance model of any node in the DC transmission grid based on network aggregation; The fifth module is used to establish the structural impedance model of different MMC ports at each end of the MMC-MTDC; In the step of establishing a structured small signal model of the MMC modulated signal at each end based on modular modeling of the control link, the structured small signal model of the MMC modulated signal at each end includes: Small signal model of positive and negative sequence separation module, small signal model of synchronization module, small signal model of outer loop control module, small signal model of inner loop control module; The small signal model of the outer loop control module includes: an analytical expression of a small signal model of a positive sequence current dq axis reference instruction in the outer loop control module, and an analytical expression of a small signal model of a negative sequence current dq axis reference instruction in the outer loop control module; The small signal models of the inner loop control module include: positive sequence AC modulation signal small signal model, negative sequence AC modulation signal small signal model, positive sequence circulating current modulation signal small signal model, and negative sequence circulating current modulation signal small signal model; In the step of establishing a structured small signal model of the MMC modulation signal at each end based on the modular modeling of the control link, the analytical expression of the structured small signal model of the bridge arm modulation signal of the MMCa phase at each end is: Where G i is the AC current control transfer function matrix; G ic is the circulation control transfer function matrix; G v is the voltage coefficient matrix; G VF is the VF control mode matrix; G PQ is the PQ control mode matrix; G VDC1 , G VDC2 are VDC control mode matrix 1 and matrix 2 respectively; K VF , K PQ , K VDC They are VF control flag, PQ control flag, and VDC control flag respectively; is the MMC AC a phase voltage small signal; It is the structured small signal of the bridge arm modulation signal of the MMCa phase; is the small signal of the MMC AC a-phase current, is the MMC circulating current small signal, is the MMC DC voltage small signal; In the step of establishing an impedance model of any node in the DC transmission grid based on network aggregation: The voltage equation of the N-node aggregate network is established as: Where, are the voltage and current small signals of the target converter station respectively, is the voltage matrix of all nodes except node 0; Y 0m is the admittance matrix between node 0 and other nodes; is the admittance matrix Y between node 0 and other nodes 0m The transpose of Y net is the admittance matrix of other nodes; is the admittance matrix Y of other nodes net The inverse matrix of Calculate the admittance matrix of the target MMC DC port looking towards the DC transmission grid The analytical expression is:

7. An electronic device, characterized in that: The method comprises a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement the MMC-MTDC structural impedance modeling method according to any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that The computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the MMC-MTDC structural impedance modeling method according to any one of claims 1 to 5 is implemented.

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