Electromechanical transient modeling method and topology of modular multilevel matrix converter

Abstract

The present invention discloses an electromechanical transient modeling method and a topological structure of a modular multi-level matrix converter, and belongs to the field of simulation of power systems. Existing simulation modeling schemes mainly focus on the direction of electromagnetic transient modeling, and lack electromechanical transient simulation models that can be actually applied. The electromechanical transient modeling method of the modular multi-level matrix converter of the present invention constructs a simplified model of the converter transient, which is used for an equivalent modular multi-level matrix converter, and then a simplified model that can be used for an electromechanical transient simulation program can be obtained. The scheme is simple, practical, and feasible, and can effectively improve the engineering calculation accuracy and engineering calculation efficiency of the electromechanical transient modeling method, fill the gap in the electromechanical transient model of the modular multi-level matrix converter, can be used for the planning and safe and stable calculation of large power grids, and provides an important method for the research of low-frequency power transmission systems, while being easy to program and implement.

Description

Technical Field

[0001] The invention relates to an electromechanical transient modeling method and a topological structure of a modular multi-level matrix converter, and belongs to the field of simulation of power systems. Background Art

[0002] Low-frequency transmission technology reduces the electrical distance by reducing the transmission frequency, thereby increasing the transmission capacity. Compared with traditional high-voltage AC and DC transmission, it has great advantages in transmission distance and transmission cost. Among them, Modular Multilevel Matrix Converter (M3C), as one of the key devices of low-frequency transmission technology, has received extensive attention and has important research significance.

[0003] Furthermore, a Chinese patent (publication number: CN109428340B) discloses a simulation method and topological structure of a flexible direct current transmission device, including: obtaining a bridge arm reactance voltage, a submodule capacitance, and the number of submodules in the bridge arm; simulating the flexible direct current transmission device based on the bridge arm reactance, the submodule capacitance, the number of submodules in the bridge arm, and a pre-established modular multi-level converter model to obtain electromechanical transient operating characteristics under different operating conditions of the flexible direct current and direct current grids; the pre-established modular multi-level converter model is constructed through main circuit parameters, an equivalent voltage source control quantity on the AC side, and a controllable current source control quantity on the DC side.

[0004] However, the simulation modeling schemes of the above schemes and other existing technologies mainly focus on electromagnetic transient modeling, and lack electromechanical transient simulation models that can be used in practice.

[0005] Furthermore, since the flexible low-frequency power transmission system contains a large number of power electronic devices and controllers, and the low-frequency side and the AC side need to be coupled through a converter, the existing electromechanical transient simulation model of the flexible low-frequency power transmission system is very complex, which in turn affects the engineering calculation accuracy and engineering calculation efficiency of the electromechanical transient modeling method.

[0006] Furthermore, in the commercial power system analysis software widely used in my country, such as the Power System Analysis Comprehensive Program (PSASP) and PSD-BPA, there are no corresponding multi-level modular matrix converter electromechanical transient models, making it difficult to carry out relevant research on the impact of flexible low-frequency transmission systems on grid stability. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide an electromechanical transient modeling method and topological structure of a modular multilevel matrix converter by constructing a simplified transient model of a converter for equivalent modular multilevel matrix converter, so as to realize electromechanical transient simulation of the modular multilevel matrix converter. The scheme is simple, practical and feasible, and can effectively improve the engineering calculation accuracy and engineering calculation efficiency of the electromechanical transient modeling method.

[0008] To achieve the above object, the first technical solution of the present invention is:

[0009] A method for electromechanical transient modeling of modular multilevel matrix converters.

[0010] Construct a simplified transient model of the converter for equivalent modular multi-level matrix converter;

[0011] The simplified transient model of the converter includes an AC power injection model on the power frequency side, an AC power injection model on the low frequency side, and an equivalent model of the bridge arm matrix, so as to realize the electromechanical transient simulation of the modular multi-level matrix converter;

[0012] The power frequency side AC power injection model is a power frequency side equivalent mathematical model, which is used to determine the relationship between the power frequency side AC system and the equivalent DC side;

[0013] The low-frequency side AC power injection model is a low-frequency side equivalent mathematical model, which is used to determine the relationship between the low-frequency side AC system and the equivalent DC side;

[0014] The bridge arm matrix equivalent model is an equivalent DC side model, which is used to determine the connection relationship between the power frequency side model and the low frequency side model.

[0015] After continuous exploration and experiments, the present invention constructs a simplified transient model of the converter for an equivalent modular multi-level matrix converter; the simplified transient model of the converter includes an AC power injection model on the power frequency side, an AC power injection model on the low frequency side, and an equivalent model of the bridge arm matrix, so as to realize the electromechanical transient simulation of the modular multi-level matrix converter, and then effectively simplify the modeling of the modular multi-level matrix converter, and obtain a simplified model that can be used for an electromechanical transient simulation program. The scheme is simple, practical, and feasible, and can effectively improve the engineering calculation accuracy and engineering calculation efficiency of the electromechanical transient modeling method.

[0016] Furthermore, the present invention simplifies the modeling of the modular multilevel matrix converter and obtains a simplified transient model of the converter that can be used in an electromechanical transient simulation program, filling the gap in the electromechanical transient model of the modular multilevel matrix converter. It can be used for the planning and safe and stable calculation of large power grids, provides an important method for the research of low-frequency transmission systems, and is easy to program.

[0017] As the preferred technical measures:

[0018] The method for constructing the AC power injection model on the power frequency side specifically includes the following steps:

[0019] The first step is to obtain the outer loop current control instruction I sdref ,I sqref ;

[0020] In the second step, according to the outer loop current control instruction I sdref ,I sqref Generate power frequency grid-side current I sd ,I sq ;

[0021] The third step is to use the power frequency grid side current I in the second step sd ,I sq , calculate the power on the industrial frequency AC side, the calculation formula is as follows:

[0022] P s =|U s |*I sd

[0023] Q s =|U s |*I sq ;

[0024] Among them, U s is the AC voltage on the power frequency side;

[0025] P s , Q s Inject active power and reactive power of modular multi-level matrix converter into the AC system on the power frequency side;

[0026] The fourth step is to calculate the AC side power of the power frequency system injected into the AC system of the power frequency side through the AC side power of the power frequency system in the third step. The calculation formula is as follows:

[0027]

[0028] Among them, U sx is the X-axis component of the AC voltage on the power frequency grid side;

[0029] U sy It is the Y-axis component of the AC voltage on the power frequency grid side;

[0030] Step 5: Convert the AC power I sx ,I sy , injected into the AC system on the power frequency side.

[0031] As the preferred technical measures:

[0032] The power frequency side equivalent mathematical model is based on the principle that the active power injected into the converter on the power frequency AC side is equal to the equivalent DC side power, and the calculation formula of the power frequency side equivalent DC power is obtained:

[0033]

[0034]

[0035] Where P dcs is the equivalent DC power on the power frequency side, P s is the active power injected into the converter by the AC system on the power frequency side, Q s is the reactive power injected into the converter by the AC system on the power frequency side, P sloss is the equivalent power loss on the power frequency side, and n% is the total loss coefficient of the modular multilevel matrix converter.

[0036] As the preferred technical measures:

[0037] The voltage phasor at the injection node on the power frequency side is U s , taking the direction of injection into the converter as the positive direction of power, the active and reactive power injected into the node satisfy the following formulas respectively:

[0038]

[0039] Among them, P s , Q s Inject active power and reactive power of multi-level modular matrix converter into the AC system on the power frequency side;

[0040] I sd ,I sq U is the AC current on the power frequency side s The D-axis component and Q-axis component of the AC current are determined after DQ decomposition of the reference phase.

[0041] As the preferred technical measures:

[0042] The method for constructing the low-frequency side AC power injection model specifically includes the following steps:

[0043] The first step is to obtain the outer loop current control instruction I ldref ,I lqref ;

[0044] In the second step, according to the outer loop current control instruction I ldref ,I lqref Generate low-frequency grid-side current I ld ,I lq ;

[0045] The third step is to use the low-frequency grid-side current I in the second step. ld ,Ilq , calculate the low-frequency AC side power, the calculation formula is as follows:

[0046] P l =|U l |*I ld

[0047] Q l =|U l |*I lq ;

[0048] Among them, U l is the AC voltage on the low frequency side;

[0049] P l , Q l Inject active power and reactive power of modular multi-level matrix converter into low-frequency side AC system;

[0050] The fourth step is to calculate the low-frequency system AC side power injected into the low-frequency side AC system through the low-frequency AC side power in the third step. The calculation formula is as follows:

[0051]

[0052] Among them, U lx is the X-axis component of the low-frequency grid-side AC voltage;

[0053] U ly is the Y-axis component of the low-frequency grid-side AC voltage;

[0054] Step 5: Convert the low-frequency system AC side power I lx ,I ly , injected into the low-frequency side AC system.

[0055] As the preferred technical measures:

[0056] The mathematical model of the low-frequency side equivalent value is based on the principle that the active power injected into the converter on the low-frequency AC side is equal to the equivalent DC side power. The calculation formula of the equivalent DC power on the low-frequency side is obtained as follows:

[0057]

[0058]

[0059] Where P dcl is the equivalent DC power on the low frequency side, P l is the active power injected into the converter by the low-frequency AC system, Q l is the reactive power injected into the converter by the low-frequency AC system, P lloss is the equivalent power loss on the low frequency side, and n% is the total loss coefficient of the modular multilevel matrix converter.

[0060] As the preferred technical measures:

[0061] The voltage phasor at the injection node on the low-frequency side is U l , taking the direction of injection into the converter as the positive direction of power, the active and reactive power injected into the node satisfy the following formulas respectively:

[0062]

[0063] Among them, P l , Q l Inject active power and reactive power of multi-level modular matrix converter into the low-frequency side AC system;

[0064] I ld ,I lq U is the low-frequency side AC current l The D-axis component and Q-axis component of the AC current are determined after DQ decomposition of the reference phase.

[0065] As the preferred technical measures:

[0066] The equivalent DC side model includes loss coefficient calculation, equivalent capacitance C req Calculation, controlled current source I on the power frequency side dcs Calculation, low frequency side controlled current source I dcl Calculation, equivalent DC voltage calculation;

[0067] The loss coefficient calculation includes the following contents:

[0068] When considering the converter loss, according to the power P injected into the power frequency side s and the power P injected into the power frequency side l , the loss coefficient calculation formula of the converter is obtained, namely:

[0069]

[0070] Among them, n% is the converter power loss coefficient;

[0071] When the converter loss is not considered, n% = 0, and the power injected on both sides is equal;

[0072] The equivalent capacitance calculation includes the following:

[0073] Since each bridge arm in the modular multi-level matrix converter is composed of multiple sub-modules in series, each sub-module is connected in parallel with a DC capacitor. According to the topological connection relationship, the capacitance of each sub-module is connected in series and parallel to obtain the total equivalent capacitance value C req , the specific calculation formula is as follows:

[0074]

[0075] Among them, C req is the equivalent capacitance value, C i is the parallel capacitance of each submodule, n1 is the number of submodules connected in series on a single bridge arm, and n2 is the number of bridge arms of the multi-level modular matrix converter;

[0076] The calculation of the equivalent DC controlled current on the industrial and low frequency sides includes the following:

[0077] According to the power exchange law between the power frequency side and the low frequency side, the controlled current source I is obtained. dcs ,I dcl , controlled current source I dcs ,I dcl The calculation formula is as follows:

[0078]

[0079] The equivalent DC voltage calculation includes the following contents:

[0080] According to the circuit structure and equivalent capacitance of the DC side, the circuit calculation of the equivalent DC side is performed to obtain the equivalent DC voltage U dc , and its calculation formula is as follows:

[0081]

[0082] To achieve the above object, the second technical solution of the present invention is:

[0083] A multi-level modular matrix converter main circuit topology structure,

[0084] Applying the above-mentioned electromechanical transient modeling method of a modular multi-level matrix converter, which includes an AC system on the power frequency side and an AC system on the low frequency side;

[0085] The power frequency side AC system and the low frequency side AC system are electrically connected via a matrix connection structure;

[0086] The matrix connection structure is provided with at least 9 bridge arms;

[0087] The bridge arm is composed of a plurality of submodules connected in series.

[0088] As the preferred technical measures:

[0089] There are also neutral point O on the power frequency side and neutral point N on the low frequency side.

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] After continuous exploration and experiments, the present invention constructs a simplified transient model of the converter for an equivalent modular multi-level matrix converter; the simplified transient model of the converter includes an AC power injection model on the power frequency side, an AC power injection model on the low frequency side, and an equivalent model of the bridge arm matrix, so as to realize the electromechanical transient simulation of the modular multi-level matrix converter, and then effectively simplify the modeling of the modular multi-level matrix converter, and obtain a simplified model that can be used for an electromechanical transient simulation program. The scheme is simple, practical, and feasible, and can effectively improve the engineering calculation accuracy and engineering calculation efficiency of the electromechanical transient modeling method.

[0092] Furthermore, the present invention simplifies the modeling of the modular multilevel matrix converter and obtains a simplified transient model of the converter that can be used in an electromechanical transient simulation program, filling the gap in the electromechanical transient model of the modular multilevel matrix converter. It can be used for the planning and safe and stable calculation of large power grids, provides an important method for the research of low-frequency transmission systems, and is easy to program. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 It is a schematic diagram of the process flow of the simplified electromechanical transient modeling method of the present invention.

[0094] Figure 2 It is a schematic diagram of the simplified transient model of the converter of the present invention.

[0095] Figure 3 It is a schematic diagram of the topological structure of the present invention. DETAILED DESCRIPTION

[0096] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0097] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0098] like Figure 1As shown, a method for electromechanical transient modeling of a modular multi-level matrix converter is used to convert the modular multi-level matrix converter into an industrial frequency side model, a low frequency side model, and an equivalent DC model connecting the two parts, and the above models are respectively subjected to corresponding equivalent modeling, including an industrial frequency side AC power injection model, a low frequency side AC power injection model, and a bridge arm matrix equivalent model, to form a simplified transient model of the converter. The bridge arm matrix equivalent modeling includes loss coefficient calculation, equivalent capacitance calculation, establishment of controlled current sources on the industrial frequency side and the low frequency side, and equivalent DC voltage calculation.

[0099] The present invention simplifies the modeling of a modular multilevel matrix converter (M3C) to obtain a simplified model that can be used in an electromechanical transient simulation program, filling the gap in the electromechanical transient model of a modular multilevel matrix converter, which can be used for the planning and safe and stable calculation of large power grids, and provides an important method for the research of low-frequency transmission systems.

[0100] like Figure 2 As shown, a specific embodiment of the simplified transient model of the converter of the present invention is:

[0101] The simplified transient model of the converter consists of an AC power injection model on the power frequency side, an AC power injection model on the low frequency side, and an equivalent model of a bridge arm matrix, so as to realize the electromechanical transient simulation of a modular multi-level matrix converter.

[0102] Among them: U s , U l are the AC voltages on the power frequency side and the low frequency side respectively;

[0103] P s , Q s Inject active power and reactive power of M3C converter into the AC system on the power frequency side;

[0104] P l , Q l Inject active power and reactive power of M3C converter into low-frequency AC system;

[0105] I sd ,I sq The D-axis component and Q-axis component of the AC current at the power frequency side are determined by performing DQ decomposition with Us as the reference phase;

[0106] I ld ,I lq The D-axis component and Q-axis component of the AC current are determined by DQ decomposition of the AC current on the low-frequency side with Ul as the reference phase;

[0107] X ts is the reactance value of the converter transformer on the power frequency side, X tl is the reactance value of the converter transformer on the low-frequency side.

[0108] P dcs , P dcl The DC power injected into the M3C converter is respectively on the power frequency side and the low frequency side;

[0109] I dcs ,I dcl The equivalent DC current injected into the M3C converter is injected into the power frequency side and the low frequency side respectively;

[0110] C req is the equivalent capacitance of all bridge arms of M3C;

[0111] U dc is the DC voltage across the equivalent capacitor C of M3C.

[0112] A specific embodiment of the power frequency side AC power injection model of the present invention:

[0113] The AC power injection model on the power frequency side is actually an equivalent mathematical model on the power frequency side, which is used to describe the relationship between the AC system on the power frequency side and the equivalent DC side. Typically, according to the principle that the active power injected into the converter on the power frequency AC side is equal to the equivalent DC side power, the following power exchange model on the power frequency side can be obtained:

[0114]

[0115]

[0116] Where P s is the active power injected into the converter by the AC system on the power frequency side, Q s is the reactive power injected into the converter by the AC system on the power frequency side, P sloss is the equivalent power loss on the power frequency side, P dcs is the equivalent DC power on the power frequency side, and n% is the total loss coefficient of the modular multilevel matrix converter.

[0117] The voltage phasor at the power frequency side injection node of the M3C circuit topology is Us. The direction of injection into the converter is the positive direction of power. The active and reactive power of the injection node satisfy:

[0118]

[0119] A specific embodiment of the low-frequency side AC power injection model of the present invention:

[0120] The low-frequency side AC power injection model is actually a low-frequency side equivalent mathematical model, which is used to describe the relationship between the low-frequency side AC system and the equivalent DC side. Typically, according to the principle that the active power injected into the converter on the low-frequency AC side is equal to the equivalent DC side power, the following low-frequency side power exchange model can be obtained:

[0121]

[0122]

[0123] Where P l is the active power injected into the converter by the low-frequency AC system, Q l is the reactive power injected into the converter by the low-frequency AC system, P lloss is the equivalent power loss on the low frequency side, P dcl is the equivalent DC power on the low-frequency side, n% is the total loss coefficient of the modular multilevel matrix converter, and the voltage phasor at the injection node on the low-frequency side is U l , taking the direction of injection into the converter as the positive direction of power, the active and reactive power injected into the node satisfy:

[0124]

[0125] A specific embodiment of the bridge arm matrix equivalent model of the present invention:

[0126] The bridge arm matrix equivalent model is an equivalent DC side model, which describes the connection relationship between the power frequency side model and the low frequency side model. The bridge arm matrix equivalent model includes loss coefficient calculation, equivalent capacitance C req Calculate and establish the controlled current source I on the power frequency side dcs , low frequency side controlled current source I dcl , equivalent DC voltage calculation.

[0127] The method for constructing an equivalent DC side model of the present invention comprises the following steps:

[0128] Step 301: Loss coefficient calculation

[0129] The equivalent model of the modular multilevel matrix converter can be divided into two cases: one without considering the converter loss and the other considering the converter loss. s and the power P injected into the power frequency side l , the loss coefficient of the converter can be obtained, that is:

[0130]

[0131] Wherein, n% is the converter power loss coefficient. Typically, when the converter loss is not considered, n%=0, and the power injected on both sides is equal.

[0132] Step 302: Equivalent capacitance calculation

[0133] Each bridge arm in the modular multi-level matrix converter is composed of multiple sub-modules connected in series, in which each sub-module is connected in parallel with a DC capacitor. According to the topological connection relationship, the capacitance of each sub-module is connected in series and parallel to obtain the total equivalent capacitance value C.req , as shown below:

[0134]

[0135] Among them, C req is the equivalent capacitance value, C i is the parallel capacitance of each submodule, n1 is the number of submodules connected in series on a single bridge arm, and n2 is the number of M3C bridge arms.

[0136] Step 303: Calculate the equivalent DC controlled current on the power and low frequency sides.

[0137] According to the power exchange model of the power frequency side and the low frequency side, the controlled current source I can be obtained. dcs ,I dcl , controlled current source I dcs ,I dcl The expression is as follows:

[0138]

[0139] Step 304: Calculate the equivalent DC voltage

[0140] According to the circuit structure and equivalent capacitance of the DC side, the circuit calculation of the equivalent DC side is performed to obtain the equivalent DC voltage U dc .

[0141]

[0142] like Figure 3 As shown, a specific embodiment of a main circuit topology structure of a multi-level modular matrix converter of the present invention is as follows:

[0143] A multi-level modular matrix converter main circuit topology structure, a matrix consisting of 9 bridge arms connecting an AC system on the power frequency side and an AC system on the low frequency side, each bridge arm being composed of a plurality of submodules connected in series.

[0144] Among them: U su , U sv , U sw is the AC voltage on the power frequency side;

[0145] i u 、i v 、i w is the AC current on the power frequency side;

[0146] O is the neutral point on the power frequency side;

[0147] U la , U lb , U lc is the AC voltage on the low-frequency side;

[0148] ia 、i b 、i c is the AC current on the low-frequency side;

[0149] N is the neutral point of low-frequency measurement;

[0150] U ua , U va , U wa , U ub , U vb , U wb , U uc , U vc , U wc is the voltage difference of each bridge arm;

[0151] U cua1 , U cua2 ...U cuan is the voltage difference on each submodule in a single bridge arm;

[0152] i ua 、i va 、i wa 、i ub 、i vb 、i wb 、i uc 、i vc 、i wc is the current flowing through each bridge arm;

[0153] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0154] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant 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 within the scope of protection of the claims of the present invention.

Claims

1. A method for electromechanical transient modeling of a modular multi-level matrix converter, characterized in that: Construct a simplified transient model of the converter for equivalent modular multi-level matrix converter; The simplified transient model of the converter includes an AC power injection model on the power frequency side, an AC power injection model on the low frequency side, and an equivalent model of the bridge arm matrix, so as to realize the electromechanical transient simulation of the modular multi-level matrix converter; The power frequency side AC power injection model is a power frequency side equivalent mathematical model, which is used to determine the relationship between the power frequency side AC system and the equivalent DC side; The method for constructing the AC power injection model on the power frequency side specifically includes the following steps: The first step is to obtain the outer loop current control instruction I sdref ,I sqref ; In the second step, according to the outer loop current control instruction I sdref ,I sqref Generate power frequency grid-side current I sd ,I sq ; The third step is to use the power frequency grid side current I in the second step sd ,I sq , calculate the power on the industrial frequency AC side, the calculation formula is as follows: P s =|U s |*I sd Q s =|U s |*I sq ; Among them, U s is the AC voltage on the power frequency side; P s , Q s Inject active power and reactive power of modular multi-level matrix converter into the AC system on the power frequency side; The fourth step is to calculate the AC side power of the power frequency system injected into the AC system of the power frequency side through the AC side power of the power frequency system in the third step. The calculation formula is as follows: Among them, U sx is the X-axis component of the AC voltage on the power frequency grid side; U sy It is the Y-axis component of the AC voltage on the power frequency grid side; Step 5: Convert the AC power I sx ,I sy , injected into the AC system on the power frequency side; The low-frequency side AC power injection model is a low-frequency side equivalent mathematical model, which is used to determine the relationship between the low-frequency side AC system and the equivalent DC side; The method for constructing the low-frequency side AC power injection model specifically includes the following steps: The first step is to obtain the outer loop current control instruction I ldref ,I lqref ; In the second step, according to the outer loop current control instruction I ldref ,I lqref Generate low-frequency grid-side current I ld ,I lq ; The third step is to use the low-frequency grid-side current I in the second step. ld ,I lq , calculate the low-frequency AC side power, the calculation formula is as follows: P l =|U l |*I ld Q l =|U l |*I lq ; Among them, U l is the AC voltage on the low frequency side; P l , Q l Inject active power and reactive power of modular multi-level matrix converter into low-frequency side AC system; The fourth step is to calculate the low-frequency system AC side power injected into the low-frequency side AC system through the low-frequency AC side power in the third step. The calculation formula is as follows: Among them, U lx is the X-axis component of the low-frequency grid-side AC voltage; U ly is the Y-axis component of the low-frequency grid-side AC voltage; Step 5: Convert the low-frequency system AC side power I lx ,I ly , injected into the low-frequency side AC system; The bridge arm matrix equivalent model is an equivalent DC side model, which is used to determine the connection relationship between the power frequency side model and the low frequency side model; The equivalent DC side model includes loss coefficient calculation, equivalent capacitance C req Calculation, controlled current source I on the power frequency side dcs Calculation, low frequency side controlled current source I dcl Calculation, equivalent DC voltage calculation; The loss coefficient calculation includes the following contents: When considering the converter loss, according to the power P injected into the power frequency side s and the power P injected into the power frequency side l , the loss coefficient calculation formula of the converter is obtained, namely: Among them, n% is the converter power loss coefficient; When the converter loss is not considered, n% = 0, and the power injected on both sides is equal; The equivalent capacitance calculation includes the following: According to the topological connection relationship, the capacitance of each submodule is connected in series and parallel to obtain the total equivalent capacitance value C req , the specific calculation formula is as follows: Among them, C req is the equivalent capacitance value, C i is the parallel capacitance of each submodule, n1 is the number of submodules connected in series on a single bridge arm, and n2 is the number of bridge arms of the multi-level modular matrix converter; The calculation of the equivalent DC controlled current on the industrial and low frequency sides includes the following: According to the power exchange law between the power frequency side and the low frequency side, the controlled current source I is obtained. dcs ,I dcl , controlled current source I dcs ,I dcl The calculation formula is as follows: The equivalent DC voltage calculation includes the following contents: According to the circuit structure and equivalent capacitance of the DC side, the circuit calculation of the equivalent DC side is performed to obtain the equivalent DC voltage U dc , and its calculation formula is as follows:

2. The electromechanical transient modeling method of a modular multi-level matrix converter according to claim 1, characterized in that: The power frequency side equivalent mathematical model is based on the principle that the active power injected into the converter on the power frequency AC side is equal to the equivalent DC side power, and the calculation formula of the power frequency side equivalent DC power is obtained: Where P dcs is the equivalent DC power on the power frequency side, P s is the active power injected into the converter by the AC system on the power frequency side, Q s is the reactive power injected into the converter by the AC system on the power frequency side, P sloss is the equivalent power loss on the power frequency side, and n% is the total loss coefficient of the modular multilevel matrix converter.

3. The electromechanical transient modeling method of a modular multi-level matrix converter according to claim 1, characterized in that: The voltage phasor at the injection node on the power frequency side is U s , taking the direction of injection into the converter as the positive direction of power, the active and reactive power injected into the node satisfy the following formulas respectively: Among them, P s , Q s Inject active power and reactive power of multi-level modular matrix converter into the AC system on the power frequency side; I sd ,I sq U is the AC current on the power frequency side s The D-axis component and Q-axis component of the AC current are determined after DQ decomposition of the reference phase.

4. The electromechanical transient modeling method of a modular multi-level matrix converter according to claim 3, characterized in that: The mathematical model of the low-frequency side equivalent value is based on the principle that the active power injected into the converter on the low-frequency AC side is equal to the equivalent DC side power. The calculation formula of the equivalent DC power on the low-frequency side is obtained as follows: Where P dcl is the equivalent DC power on the low frequency side, P l is the active power injected into the converter by the low-frequency AC system, Q l is the reactive power injected into the converter by the low-frequency AC system, P lloss is the equivalent power loss on the low frequency side, and n% is the total loss coefficient of the modular multilevel matrix converter.

5. The electromechanical transient modeling method of a modular multi-level matrix converter according to claim 4, characterized in that: The voltage phasor at the injection node on the low-frequency side is U l , taking the direction of injection into the converter as the positive direction of power, the active and reactive power injected into the node satisfy the following formulas respectively: Among them, P l , Q l Inject active power and reactive power of multi-level modular matrix converter into the low-frequency side AC system; I ld ,I lq U is the low-frequency side AC current l The D-axis component and Q-axis component of the AC current are determined after DQ decomposition of the reference phase.

6. A multi-level modular matrix converter main circuit topology structure, characterized in that: A method for electromechanical transient modeling of a modular multi-level matrix converter as claimed in any one of claims 1 to 5 is applied, comprising an AC system on the power frequency side and an AC system on the low frequency side; The power frequency side AC system and the low frequency side AC system are electrically connected via a matrix connection structure; The matrix connection structure is provided with at least 9 bridge arms; The bridge arm is composed of a plurality of submodules connected in series.

7. A multi-level modular matrix converter main circuit topology structure as claimed in claim 6, characterized in that: There are also neutral point O on the power frequency side and neutral point N on the low frequency side.

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