Modular multilevel converter multi-frequency coupling transfer function matrix model construction method

Abstract

The application relates to the technical field of power system analysis and control, in particular to a modular multilevel converter multi-frequency coupling transfer function matrix model construction method. The method comprises the following steps: acquiring circuit parameters, control parameters and steady-state operation parameters of a modular multilevel converter; determining a three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters; determining a multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix; and performing stability analysis on the modular multilevel converter according to the multi-frequency coupling transfer function matrix model. The multi-frequency coupling transfer function matrix model constructed by the application can accurately analyze the stability of the wide-frequency oscillation of the modular multilevel converter HVDC system under multiple scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system analysis and control, and in particular to a modular multilevel converter multi-frequency coupling transfer function matrix model construction method. BACKGROUND

[0002] In recent years, with the development of power electronic technology, the application of modular multilevel converters in power systems is becoming more and more widespread, and the flexible DC transmission technology based on modular multilevel converters is developing rapidly. However, the system stability problem caused by modular multilevel converters is becoming increasingly prominent, and multiple wide-frequency oscillation events have occurred in the flexible DC transmission system based on modular multilevel converters, causing serious power accidents.

[0003] At present, the impedance analysis method has been widely used in the stability analysis of the high-frequency oscillation problem of the flexible DC system. However, the model construction method of the traditional two-level voltage source converter is often used in the research of the impedance model construction of the modular multilevel converter, and the impedance model of the modular multilevel converter obtained based on this model construction method cannot accurately analyze the stability of the wide-frequency oscillation of the flexible DC system. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art to some extent.

[0005] To this end, the first object of the present application is to propose a modular multilevel converter multi-frequency coupling transfer function matrix model construction method to solve the technical problem that the impedance model of the modular multilevel converter obtained by following the model construction method of the traditional two-level voltage source converter cannot accurately analyze the stability of the wide-frequency oscillation of the flexible DC system.

[0006] The second object of the present application is to propose a modular multilevel converter multi-frequency coupling transfer function matrix model construction device.

[0007] To achieve the above-mentioned objects, the modular multilevel converter multi-frequency coupling transfer function matrix model construction method proposed by the first aspect of the present application comprises:

[0008] Obtaining the circuit parameters, control parameters and steady-state operation parameters of the modular multilevel converter;

[0009] Determining the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters;

[0010] According to the three-dimensional transfer function matrix, a multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter is determined to complete stability analysis of the modular multilevel converter.

[0011] Optionally, in an embodiment of the present application, the circuit parameters include: winding self-inductance of primary winding of the converter transformer, winding self-inductance of secondary winding of the converter transformer, mutual inductance between the two windings of the converter transformer, resistance of the bridge arm, electric reactance of the bridge arm, capacitance of the bridge arm sub-module, and number of the bridge arm sub-modules.

[0012] Optionally, in an embodiment of the present application, the control parameters include: modulation ratio, sampling delay, delay time of the control link, simulation step length of the electromagnetic transient simulation software, phase angle compensation of the inverse Park transformation link, transfer function of the phase-locked loop link, transfer function of the active outer loop control PI link, transfer function of the reactive outer loop control PI link, transfer function of the d-axis PI link in the positive sequence current inner loop control, transfer function of the q-axis PI link in the positive sequence current inner loop control, transfer function of the d-axis PI link in the negative sequence current inner loop control, transfer function of the q-axis PI link in the negative sequence current inner loop control, decoupling coefficient in the current inner loop control, transfer function of the elimination of the out-of-sequence fundamental component link, transfer function of the simulation step length delay link, reference value of the transformer grid-side voltage, reference value of the transformer valve-side current, rated capacity of the converter.

[0013] Optionally, in an embodiment of the present application, the steady-state operation parameters include: steady-state voltage on the DC side, steady-state current on the DC side, amplitude of the transformer grid-side fundamental voltage under steady state, transformer grid-side current fundamental phasor under steady state, transformer valve-side current fundamental phasor, dq-axis voltage reference value of the positive sequence current inner loop under steady state, fundamental phasor of the reference voltage, amplitude of the reference voltage fundamental component, and phasor of the double-frequency negative sequence circulating current.

[0014] Optionally, in an embodiment of the present application, the three-dimensional transfer function matrix includes: three-dimensional transfer function matrix of the AC / DC port external characteristics of the modular multilevel converter, three-dimensional transfer function matrix of the internal bridge arm dynamics of the modular multilevel converter, three-dimensional transfer function matrix of the positive sequence current inner loop control, three-dimensional transfer function matrix of the negative sequence current inner loop control, three-dimensional transfer function matrix of the modulation link containing the controller delay, and three-dimensional transfer function matrix of the relationship between the transformer valve-side electrical quantity and the grid-side electrical quantity.

[0015] Optionally, in an embodiment of the present application, the three-dimensional transfer function matrix of the internal bridge arm dynamics of the modular multilevel converter includes a three-dimensional transfer function matrix of the circulating current dynamics of the modular multilevel converter.

[0016] Optionally, in an embodiment of the present application, the determining the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters comprises:

[0017] Obtaining a control mode of the modular multilevel converter;

[0018] According to the control mode, the matrix parameters of the node voltage matrix and the matrix parameters of the node current matrix in the three-dimensional transfer function matrix of the positive sequence current inner loop control are corrected.

[0019] Optionally, in an embodiment of the present application, the control mode comprises active control, reactive control, DC voltage control and AC voltage control.

[0020] Optionally, in an embodiment of the present application, the determining the multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix comprises:

[0021] According to the three-dimensional transfer function matrix, a coefficient matrix of a voltage harmonic disturbance component and a coefficient matrix of a current harmonic component are determined;

[0022] According to the coefficient matrix of the voltage harmonic disturbance component and the coefficient matrix of the current harmonic component, the multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter is determined.

[0023] In summary, the method proposed by the first aspect embodiment of the present application obtains the circuit parameters, the control parameters and the steady-state operation parameters of the modular multilevel converter; determines the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters; determines the multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix, and performs stability analysis on the modular multilevel converter according to the multi-frequency coupled transfer function matrix model. The multi-frequency coupled transfer function matrix model constructed by the present application can accurately analyze the stability of the wide-frequency oscillation of the flexible DC system in multiple scenarios.

[0024] To achieve the above-mentioned purpose, the second aspect embodiment of the present application proposes a modular multilevel converter multi-frequency coupled transfer function matrix model construction device, comprising:

[0025] A parameter acquisition module is configured to obtain the circuit parameters, the control parameters and the steady-state operation parameters of the modular multilevel converter;

[0026] A matrix determination module is configured to determine the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters;

[0027] a model determining module configured to determine a multi-frequency coupling transfer function matrix corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix.

[0028] To sum up, the device provided by the second aspect of the present application obtains the circuit parameters, control parameters and steady-state operation parameters of the modular multilevel converter through the parameter obtaining module; the three-dimensional matrix determining module determines the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters; the multi-frequency matrix determining module determines the multi-frequency coupling transfer function matrix corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix, and performs stability analysis on the modular multilevel converter according to the multi-frequency coupling transfer function matrix model. The multi-frequency coupling transfer function matrix model constructed by the present application can accurately analyze the stability of the wide-frequency oscillation of the modular multilevel converter HVDC system in multiple scenarios.

[0029] Additional aspects and advantages of the present application will be made apparent by the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the accompanying drawings, wherein:

[0031] Figure 1 A flowchart of a modular multilevel converter multi-frequency coupling transfer function matrix model construction method provided by an embodiment of the present application;

[0032] Figure 2 A structural schematic diagram of a modular multilevel converter grid-connected system provided by an embodiment of the present application;

[0033] Figure 3 A structural schematic diagram of a modular multilevel converter multi-frequency coupling transfer function matrix model construction device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0034] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents falling within the spirit and scope of the appended claims.

[0035] According to some embodiments, the research on the model construction of the modular multilevel converter (MMC) impedance model follows the model construction method of the traditional two-level voltage source converter, without considering the internal bridge arm dynamics specific to the modular multilevel converter, and without considering the influence of various delays in the model construction. On the other hand, the flexible DC system itself is a kind of AC-DC-AC conversion system, and the current impedance model usually considers the DC side to be constant, and only establishes the impedance model from the AC side; this ignores the dynamics of the DC side and the dynamics of the converter and AC system on the other side, cannot consider the influence of the AC system or the DC system on the other side on the impedance characteristics of itself, and is difficult to be used for stability analysis of the flexible DC system in multiple scenarios.

[0036] It is easy to understand that the current impedance model of the modular multilevel converter still has certain defects and deficiencies in the stability analysis of the wide frequency oscillation of the flexible DC system. In order to more accurately study the stability of the wide frequency oscillation of the flexible DC system, the frequency coupling effect of the AC side and the coupling relationship between the AC and DC ports, the internal bridge arm dynamics of the MMC and the influence of various delays need to be considered.

[0037] The application will be described in detail below with reference to specific embodiments.

[0038] Figure 1 A flowchart of a modular multilevel converter multi-frequency coupled transfer function matrix model construction method provided by an embodiment of the application.

[0039] As shown in Figure 1 A modular multilevel converter multi-frequency coupled transfer function matrix model construction method provided by an embodiment of the application includes the following steps:

[0040] Step 110, obtaining circuit parameters, control parameters and steady-state operation parameters of the modular multilevel converter;

[0041] Step 120, determining a three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters;

[0042] Step 130, determining a multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix, and performing stability analysis on the modular multilevel converter according to the multi-frequency coupled transfer function matrix model.

[0043] According to some embodiments, the multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter is equivalent to an impedance or admittance model in physical meaning, and is a three-dimensional matrix containing self-impedance (admittance) and mutual impedance (admittance) in form.

[0044] In some embodiments, the multi-frequency coupling transfer function matrix model in impedance form and the multi-frequency coupling transfer function matrix model in admittance form are inverse matrices of each other, and the admittance model can be obtained by inverting the impedance model according to the following formula:

[0045] Y = Z -1

[0046] Wherein, Z represents the multi-frequency coupling transfer function matrix model in impedance form, namely the impedance model, and Y represents the multi-frequency coupling transfer function matrix model in admittance form, namely the admittance model.

[0047] In the embodiments of the present application, the circuit parameters include: the self-inductance L of the primary winding of the converter transformer 11 , the self-inductance L of the secondary winding of the converter transformer 22 , the mutual inductance L between the two windings of the converter transformer 12 , the resistance R0 of the bridge arm, the reactance L0 of the bridge arm, the capacitance C0 of the bridge arm sub-module, and the number N of the bridge arm sub-modules.

[0048] In the embodiments of the present application, the control parameters include: the modulation ratio K PWM , the sampling delay T1, the delay time T2 of the control link, the simulation step T of the electromagnetic transient simulation software d , the phase angle compensation Pha of the Park inverse transformation link, the transfer function G of the phase-locked loop link PLL , the transfer function G of the active outer loop control PI link PI1 , the transfer function G of the reactive outer loop control PI link PI2 , the transfer function G of the d-axis PI link in the positive sequence current inner loop control PI4 , the transfer function G of the q-axis PI link in the positive sequence current inner loop control PI5 , the transfer function G of the d-axis PI link in the negative sequence current inner loop control PI6 , the transfer function G of the q-axis PI link in the negative sequence current inner loop control PI7 , the decoupling coefficient ωL in the current inner loop control, the transfer function G of the elimination of the hetero-sequence fundamental component link PN , the transfer function G of the simulation step delay link dT , the reference value V of the transformer grid-side voltage base , the reference value I of the transformer valve-side current base , the rated capacity S of the converter base .

[0049] In the embodiments of the present application, the steady-state operating parameters include: the steady-state voltage V dc0 , the steady-state current I of the DC side dc0, the amplitude of the fundamental voltage of the transformer grid side in steady state V1, the fundamental current phasor of the converter transformer grid side I1, the fundamental current phasor of the converter transformer valve side I'1, the dq axis voltage reference value of the positive sequence current inner loop in steady state the fundamental phasor of the reference voltage the amplitude of the fundamental component of the reference voltage the phasor I of the double-frequency negative sequence circulating current cir .

[0050] According to some embodiments, the steady-state operation parameters refer to relevant electrical quantities and control quantities measured when the modular multilevel converter grid-connected system is running to a steady state

[0051] In the embodiments of the present application, the three-dimensional transfer function matrix includes: a three-dimensional transfer function matrix of the external characteristics of the AC / DC port of the modular multilevel converter, a three-dimensional transfer function matrix of the internal bridge arm dynamics of the modular multilevel converter, a three-dimensional transfer function matrix of the positive sequence current inner loop control, a three-dimensional transfer function matrix of the negative sequence current inner loop control, a three-dimensional transfer function matrix of the modulation link containing the delay of the controller, and a three-dimensional transfer function matrix of the relationship between the valve side electrical quantity and the grid side electrical quantity of the converter transformer.

[0052] According to some embodiments, the modular multilevel converter grid-connected system includes a DC end, a converter and its control strategy, a converter transformer, and an AC power grid, as shown in Figure 2 The control strategy of the modular multilevel converter adopts a typical double-loop control strategy, the inner loop adopts positive and negative sequence current inner loop control, and the outer loop control includes different control modes such as active power control, reactive power control, DC voltage control, and AC voltage control.

[0053] In some embodiments, when the control strategy of the modular multilevel converter is a constant active power and constant reactive power mode, the obtained three-dimensional transfer function matrix is as follows:

[0054] The three-dimensional transfer function matrix of the external characteristics of the AC / DC port of the modular multilevel converter is determined according to the following formula:

[0055]

[0056]

[0057] wherein, is the three-dimensional transfer function matrix of the external characteristics of the AC / DC port of the modular multilevel converter; s p =jω p , j is an imaginary unit, ω p is the angular frequency under the harmonic frequency f p ; s p2 =jω p2 , ω p2for coupling the angular frequency under the frequency f p2

[0058] In some embodiments, the three-dimensional transfer function matrix of the converter transformer valve side electrical quantities and grid side electrical quantities relationship is determined according to the following formula:

[0059]

[0060]

[0061] wherein, is the three-dimensional transfer function matrix of the converter transformer valve side electrical quantities and grid side electrical quantities relationship; s1=jω1, ω1 is the fundamental angular frequency.

[0062] In some embodiments, the three-dimensional transfer function matrix of the modular multilevel converter internal bridge arm dynamics is determined according to the following formula:

[0063]

[0064]

[0065] wherein, is the three-dimensional transfer function matrix of the modular multilevel converter internal bridge arm dynamics;

[0066] wherein the values of the matrix elements in are determined according to the following formula:

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073] wherein,

[0074]

[0075]

[0076]

[0077] wherein,

[0078] ​

[0079]

[0080] wherein,

[0081]

[0082]

[0083]

[0084]

[0085] wherein the values of the elements of the matrix are determined according to

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095] wherein,

[0096]

[0097]

[0098] In some embodiments, the three-dimensional transfer function matrix of the modulation section including the controller delay is determined according to:

[0099]

[0100]

[0101] wherein, ​A three-dimensional transfer function matrix for a three-phase power system including a controller time delay modulation link.

[0102] In some embodiments, a three-dimensional transfer function matrix for positive sequence current inner loop control is determined according to:

[0103]

[0104] wherein, is a three-dimensional transfer function matrix for positive sequence current inner loop control.

[0105] wherein,

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] wherein, T = T1 - T d T1 is a sampling time delay,

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] In some embodiments, a three-dimensional transfer function matrix for negative sequence current inner loop control is determined according to:

[0118]

[0119] wherein, is a three-dimensional transfer function matrix for negative sequence current inner loop control.

[0120] wherein,

[0121]

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130] In the embodiment of the present application, the three-dimensional transfer function matrix of the internal bridge arm dynamics of the modular multilevel converter includes the three-dimensional transfer function matrix of the circulating current dynamics of the modular multilevel converter.

[0131] In the embodiment of the present application, the three-dimensional transfer function matrix corresponding to the modular multilevel converter is determined according to the circuit parameters, the control parameters and the steady-state operation parameters, and includes:

[0132] The control mode of the modular multilevel converter is obtained.

[0133] The matrix parameters of the node voltage matrix and the matrix parameters of the node current matrix in the three-dimensional transfer function matrix of the positive sequence current inner loop control are corrected according to the control mode.

[0134] In the embodiment of the present application, the control mode includes active control, reactive control, DC voltage control and AC voltage control.

[0135] In some embodiments, if the outer ring of the modular multilevel converter adopts the constant DC voltage and constant AC voltage control mode, the form of the impedance model obtained is consistent with that in the constant active power and constant reactive power mode, and only the matrix elements of the node voltage matrix and the node current matrix of the three-dimensional transfer function matrix of the positive sequence current inner loop control need to be corrected, without the need to re-derive the three-dimensional transfer function matrix of the positive sequence current inner loop control of the entire control link, and the complexity of the method proposed in the present application is not increased.

[0136] As can be easily understood, the multi-frequency coupling transfer function matrix model obtained by the method proposed in the embodiment of the present application is also applicable to the case where the outer ring adopts DC voltage and AC voltage control.

[0137] In the embodiment of the present application, the multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter is determined according to the three-dimensional transfer function matrix, and includes:

[0138] The coefficient matrix of the voltage harmonic disturbance component and the coefficient matrix of the current harmonic component are determined according to the three-dimensional transfer function matrix;

[0139] The multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter is determined according to the coefficient matrix of the voltage harmonic disturbance component and the coefficient matrix of the current harmonic component.

[0140] According to some embodiments, the multi-frequency coupling transfer function matrix model in the form of impedance is analyzed in view of the conversion relationship between the impedance model and the admittance model, wherein the admittance model can be calculated from the impedance model. The multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter is determined according to the following formula:

[0141]

[0142] Wherein, Z 11 , Z 22 , Z 33 are self-impedances, Z 11 , Z 22 are impedances under two coupling frequencies on the alternating current side, Z 33 is an impedance under a direct current harmonic frequency, and the remaining matrix elements are mutual impedances, i.e., impedances between different frequencies on the alternating current side or between the alternating current and the direct current; V p , V p2 are harmonic voltage disturbance components under two frequency couplings on the alternating current side, and the frequency coupling represents that the sum of the frequencies of the two harmonic voltages is 2 times the power frequency, i.e., f p +f p2 =2f1, f1 is the frequency of the fundamental component; ΔV dc is a harmonic voltage disturbance component on the direct current side, and the frequency of ΔV dc should be f p -f1 according to the power conservation principle; I p and I p2 are harmonic current components under two frequency couplings on the alternating current side, and ΔI dc is a harmonic current component on the direct current side; the superscript “*” represents taking a conjugate.

[0143] In some embodiments, the multi-frequency coupling transfer function matrix model corresponding to the modular multilevel converter can be further written as:

[0144]

[0145] Wherein, T is the coefficient matrix of the voltage harmonic disturbance component, and A is the coefficient matrix of the current harmonic component.

[0146] Wherein, the expression of the coefficient matrix of the voltage harmonic disturbance component and the coefficient matrix of the current harmonic component is:

[0147]

[0148] wherein, is a three-dimensional transfer function matrix of the MMC AC / DC port external characteristics; is a three-dimensional transfer function matrix of the MMC internal bridge arm dynamics; is a three-dimensional transfer function matrix of the positive sequence current inner loop control; is a three-dimensional transfer function matrix of the negative sequence current inner loop control; is a three-dimensional transfer function matrix of the modulation link containing the controller delay; is a three-dimensional transfer function matrix of the relationship between the valve side electrical quantity and the network side electrical quantity of the converter transformer.

[0149] In some embodiments, the multi-frequency coupling transfer function matrix model of the modular multilevel converter corresponding to the three-dimensional transfer function matrix is an expression about the harmonic frequency. With the change of the harmonic frequency, the multi-frequency coupling transfer function matrix model of the modular multilevel converter in a wide frequency range can be obtained.

[0150] To sum up, the method provided in the embodiments of the present application acquires the circuit parameters, the control parameters and the steady-state operation parameters of the modular multilevel converter; determines the three-dimensional transfer function matrix of the modular multilevel converter corresponding to the circuit parameters, the control parameters and the steady-state operation parameters; determines the multi-frequency coupling transfer function matrix model of the modular multilevel converter corresponding to the three-dimensional transfer function matrix, and performs stability analysis on the modular multilevel converter according to the multi-frequency coupling transfer function matrix model. The multi-frequency coupling transfer function matrix model constructed in the present application considers the frequency coupling effect of the AC side and the coupling relationship between the AC / DC ports, and also considers the influence of the internal bridge arm dynamics of the MMC and various delays. It is of great significance for the stability analysis of the wide frequency oscillation stability of the modular multilevel converter HVDC system in multiple scenarios, and the wide frequency oscillation stability of the modular multilevel converter HVDC system in multiple scenarios can be accurately analyzed.

[0151] In order to realize the above-mentioned embodiments, the present application further provides a modular multilevel converter multi-frequency coupling transfer function matrix model construction device.

[0152] Figure 3 A structural schematic diagram of a modular multilevel converter multi-frequency coupling transfer function matrix model construction device provided by the embodiments of the present application.

[0153] As Figure 3 shown, a modular multilevel converter multi-frequency coupling transfer function matrix model construction device, the device 300 comprises:

[0154] The parameter acquisition module 310 is configured to acquire the circuit parameters, the control parameters and the steady-state operation parameters of the modular multilevel converter.

[0155] The matrix determination module 320 is configured to determine the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters.

[0156] The model determination module 330 is configured to determine a multi-frequency coupled transfer function matrix corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix, and perform stability analysis on the modular multilevel converter according to the multi-frequency coupled transfer function matrix model.

[0157] To sum up, the device provided in the embodiments of the present application acquires the circuit parameters, the control parameters and the steady-state operation parameters of the modular multilevel converter through the parameter acquisition module; determines the three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters through the three-dimensional matrix determination module; determines the multi-frequency coupled transfer function matrix corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix through the multi-frequency matrix determination module, and performs stability analysis on the modular multilevel converter according to the multi-frequency coupled transfer function matrix model. The multi-frequency coupled transfer function matrix model constructed in the present application can accurately perform stability analysis on the wide-frequency oscillation of the modular multilevel converter flexible direct current system in multiple scenarios.

[0158] It should be noted that, in the description of the present application, the terms “first”, “second” and the like are only used for descriptive purposes and should not be construed as indicating or implying relative importance. In addition, in the description of the present application, unless otherwise specified, the meaning of “multiple” is two or more.

[0159] Any process or method descriptions in flow charts or described elsewhere herein can be understood as representing code modules, segments, or portions of code which include one or more executable instructions for performing specific logic functions or steps in the process. The various embodiments of the present application can include additional or fewer steps or processes in addition to or other than those of the process described in this specification as a result of, for example, the performance of functions described as occurring in a particular sequence. These descriptions and representations are used by those skilled in the art of software manufacturing to describe the software that is used in performing one or more functions or steps in the process with the understanding that the software described can be implemented with software of one or more types as previously described, even if the particular type of software is not explicitly described herein.

[0160] It should be understood that various parts of the present application can be realized in hardware, software, firmware or a combination thereof. In the above-described embodiments, a plurality of steps or methods can be realized by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if realized in hardware, and as in another embodiment, it can be realized by any one or a combination of the following technologies known in the art: discrete logic circuit with logic gate circuit for implementing logic functions on data signals, application specific integrated circuit with suitable combination logic gate circuit, programmable gate array (PGA), field programmable gate array (FPGA) and the like.

[0161] Those skilled in the art can understand that all or part of the steps of the method carried out by the above-mentioned embodiments can be instructed by a program to complete the relevant hardware, and the program can be stored in a computer readable storage medium. When the program is executed, it includes one of the steps of the method embodiment or a combination thereof.

[0162] In addition, each functional unit in each embodiment of the present application can be integrated into one processing module, or each unit can exist physically alone, or two or more units can be integrated into one module. The integrated module can be realized in the form of hardware or in the form of a software functional module. When the integrated module is realized in the form of a software functional module and sold or used as an independent product, it can also be stored in a computer readable storage medium.

[0163] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc.

[0164] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0165] Although the embodiments of the present application have been shown and described above, it can be understood that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application. Those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A modular multilevel converter multi-frequency coupling transfer function matrix model construction method, characterized in that, The method comprises: obtaining circuit parameters, control parameters and steady-state operation parameters of a modular multilevel converter; determining a three-dimensional transfer function matrix corresponding to the modular multilevel converter according to the circuit parameters, the control parameters and the steady-state operation parameters, wherein the three-dimensional transfer function matrix comprises a three-dimensional transfer function matrix of external characteristics of AC / DC ports of the modular multilevel converter, a three-dimensional transfer function matrix of internal bridge arm dynamics of the modular multilevel converter, a three-dimensional transfer function matrix of positive sequence current inner loop control, a three-dimensional transfer function matrix of negative sequence current inner loop control, a three-dimensional transfer function matrix of a modulation link containing controller delay, a three-dimensional transfer function matrix of a relationship between electrical quantities on a valve side of a converter transformer and electrical quantities on a network side, obtaining a control mode of the modular multilevel converter, and correcting matrix parameters of a node voltage matrix and matrix parameters of a node current matrix in the three-dimensional transfer function matrix of the positive sequence current inner loop control according to the control mode; determining a multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter according to the three-dimensional transfer function matrix, and performing stability analysis on the modular multilevel converter according to the multi-frequency coupled transfer function matrix model, wherein a coefficient matrix of a voltage harmonic disturbance component and a coefficient matrix of a current harmonic component are determined according to the three-dimensional transfer function matrix, and the multi-frequency coupled transfer function matrix model corresponding to the modular multilevel converter is determined according to the coefficient matrix of the voltage harmonic disturbance component and the coefficient matrix of the current harmonic component.

2. The method of claim 1, wherein, The circuit parameters comprise primary winding self-inductance of a converter transformer, secondary winding self-inductance of the converter transformer, mutual inductance between the two windings of the converter transformer, bridge arm resistance, bridge arm reactance, capacitance value of a bridge arm sub-module, and number of bridge arm sub-modules.

3. The method of claim 1, wherein, The control parameters comprise a modulation ratio, a sampling delay, a control link delay time, a simulation step length of electromagnetic transient simulation software, a phase angle compensation of a Park inverse transformation link, a transfer function of a phase-locked loop link, a transfer function of an active outer loop control PI link, a transfer function of a reactive outer loop control PI link, a transfer function of a d-axis PI link in positive sequence current inner loop control, a transfer function of a q-axis PI link in positive sequence current inner loop control, a transfer function of a d-axis PI link in negative sequence current inner loop control, a transfer function of a q-axis PI link in negative sequence current inner loop control, a decoupling coefficient in current inner loop control, a transfer function of a component for eliminating an alien sequence fundamental component, a transfer function of a simulation step length delay link, a reference value of a transformer network side voltage, a reference value of a transformer valve side current, and a rated capacity of the converter.

4. The method of claim 1, wherein, The steady-state operation parameters comprise a steady-state voltage on a DC side, a steady-state current on the DC side, an amplitude of a transformer network side fundamental voltage under steady state, a transformer network side current fundamental phasor under steady state, a converter transformer valve side current fundamental phasor, a dq-axis voltage reference value of a positive sequence current inner loop under steady state, a fundamental phasor of a reference voltage, an amplitude of a reference voltage fundamental component, and a phasor of a two-frequency negative sequence circulating current.

5. The method of claim 1, wherein, The three-dimensional transfer function matrix of internal bridge arm dynamics of the modular multilevel converter comprises a three-dimensional transfer function matrix of circulating current dynamics of the modular multilevel converter.

6. The method of claim 1, wherein, The control modes include active control, reactive control, direct current voltage control and alternating current voltage control. 7.A modular multilevel converter multi-frequency coupling transfer function matrix model construction device, characterized in that, The device comprises: a parameter acquisition module configured to acquire circuit parameters, control parameters and steady-state operation parameters of the MMC; a matrix determination module configured to determine a three-dimensional transfer function matrix corresponding to the MMC according to the circuit parameters, the control parameters and the steady-state operation parameters, wherein the three-dimensional transfer function matrix comprises a three-dimensional transfer function matrix of external characteristics of AC / DC ports of the MMC, a three-dimensional transfer function matrix of internal bridge arm dynamics of the MMC, a three-dimensional transfer function matrix of positive sequence current inner loop control, a three-dimensional transfer function matrix of negative sequence current inner loop control, a three-dimensional transfer function matrix of a modulation link containing controller delay, a three-dimensional transfer function matrix of a relationship between valve side electrical quantities and network side electrical quantities of a converter transformer, and matrix parameters and matrix parameters of node voltage matrix and node current matrix in the three-dimensional transfer function matrix of the positive sequence current inner loop control are corrected according to a control mode of the MMC; a model determination module configured to determine a multi-frequency coupled transfer function matrix model corresponding to the MMC according to the three-dimensional transfer function matrix, and perform stability analysis on the MMC according to the multi-frequency coupled transfer function matrix model, wherein a coefficient matrix of voltage harmonic disturbance components and a coefficient matrix of current harmonic components are determined according to the three-dimensional transfer function matrix, and the multi-frequency coupled transfer function matrix model corresponding to the MMC is determined according to the coefficient matrix of voltage harmonic disturbance components and the coefficient matrix of current harmonic components.

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