A method and system for electromagnetic transient simulation of grid-following converter

Abstract

The present invention relates to the technical field of electronic device simulation, and discloses a method and system for electromagnetic transient simulation of a grid-type converter. Based on the resistance and inductance filter data and current control loop data of the grid-type converter, an admittance-based transfer matrix equation is established in the Laplace domain to construct an average value model; based on the trapezoidal integration rule, the transfer matrix equation is converted from the Laplace domain to the discrete domain to obtain a discretized admittance equation of the grid-type converter, and the discretized admittance equation is inversely discretized to obtain a time-domain discretized admittance equation of the grid-type converter; the average value model is converted into a dual-impedance form to obtain a dual-impedance equation, and based on the dual-impedance equation and the time-domain discretized admittance equation, an equivalent Thevenin impedance matrix of the grid-type converter is obtained; and based on the equivalent Thevenin impedance matrix expression, electromagnetic transient simulation of the grid-type converter is realized. The method of the present application improves the accuracy of the simulation results.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic device simulation, and in particular to an electromagnetic transient simulation method and system for a grid-following converter. Background Art

[0002] Distributed renewable energy sources are primarily connected to traditional power grids via grid-connected converters based on power electronics to achieve efficient energy conversion and stable transmission. However, power electronic devices have highly dynamic characteristics, generating complex electromagnetic transients during operation. These electromagnetic transients have a significant impact on grid stability, power quality, and the safe operation of equipment. Therefore, using electromagnetic transient simulation of grid-connected converters to design and analyze power grid systems containing distributed renewable energy sources has become a key step in ensuring reliable grid operation.

[0003] Most existing technologies use electromagnetic transient simulation methods based on state variables and node analysis. However, when modeling power electronic devices, this method uses a controlled current source with a virtual damper to inject current into the external system following the output current of the grid-type converter. Due to the existence of the virtual damper, there is a large deviation between the simulation results and the actual situation, and the accuracy is difficult to guarantee.

[0004] Therefore, how to improve the accuracy of electromagnetic transient simulation of grid-following converters has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] The present invention provides a method and system for electromagnetic transient simulation of a grid-following converter, so as to solve the technical problem of how to improve the accuracy of electromagnetic transient simulation of a grid-following converter, thereby achieving the effect of improving the accuracy of electromagnetic transient simulation of a grid-following converter.

[0006] In a first aspect, the present invention provides a method for electromagnetic transient simulation of a grid-type converter, the method comprising: establishing an admittance-based transfer matrix equation in a Laplace domain based on resistance and inductance filter data of the grid-type converter and current control loop data of the grid-type converter, and constructing an average value model based on the transfer matrix equation;

[0007] Based on the trapezoidal integration rule, the transfer matrix equation is converted from the Laplace domain to the discrete domain to obtain a discretized admittance equation of the grid-type converter, and the discretized admittance equation is inversely discretized to obtain a time-domain discretized admittance equation of the grid-type converter, wherein the time-domain discretized admittance equation is set to represent the transfer relationship between the output current of the grid-type converter and the common coupling point voltage using the synthetic conductance matrix in the average value model and the history term in the average value model;

[0008] Converting the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtaining an equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation;

[0009] According to the equivalent Thevenin impedance matrix expression, the electromagnetic transient simulation of the grid-following converter is realized.

[0010] Preferably, the admittance-based transfer matrix equation is established in the Laplace domain based on the resistance and inductance filter data of the grid-type converter and the current control loop data of the grid-type converter, including:

[0011] Based on the resistance and inductance filter data of the grid-following converter, an inductance-voltage equation of the resistance and inductance filter of the grid-following converter in the Laplace domain is constructed, and an admittance operation is performed on the inductance-voltage equation to obtain an admittance equation of the resistance and inductance filter;

[0012] Obtaining a converter system equation based on the resistance-inductance filter admittance equation and current control loop data of the grid-following converter;

[0013] According to the current control loop data and a proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, a first admittance basis transfer matrix equation is derived in a Laplace domain in the synchronous rotating coordinate system, and according to Clarke transform and modulation circuit data of a common coupling point filter, the first admittance basis transfer matrix equation is converted to a stationary coordinate system to obtain a second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system;

[0014] According to the converter system equation and the first admittance basis transfer matrix equation, a first transfer matrix equation in the Laplace domain in the synchronous rotating coordinate system is constructed; according to the converter system equation and the second admittance basis transfer matrix equation, a second transfer matrix equation in the Laplace domain in the stationary coordinate system is constructed.

[0015] Preferably, the transfer matrix equation is converted from the Laplace domain to the discrete domain based on the trapezoidal integration rule to obtain the discretized admittance equation of the grid-following converter, including:

[0016] According to the trapezoidal integration rule, the bilinear mapping relationship between the Laplace operator and the discrete operator is obtained;

[0017] Based on the bilinear mapping relationship, the Laplace operator in the transfer matrix equation is transformed to obtain a discretized admittance equation.

[0018] Preferably, performing an inverse discrete transformation on the discretized admittance equation to obtain a time-domain discretized admittance equation of the grid-following converter includes:

[0019] Performing an inverse discrete transformation on the discretized admittance equation to obtain an initial time-domain discretized admittance equation;

[0020] Constructing a dynamic impedance equation for the grid-following converter, and transforming the initial time-domain discretized admittance equation according to the dynamic impedance equation to obtain an improved time-domain discretized admittance equation;

[0021] The improved time-domain discretized admittance equation is converted into a three-phase coordinate system to obtain the time-domain discretized admittance equation of the grid-following converter.

[0022] Preferably, the average value model is converted into a dual-impedance form to obtain a dual-impedance equation, and based on the dual-impedance equation and the time-domain discretized admittance equation, an equivalent Thevenin impedance matrix expression of the grid-following converter is obtained, including:

[0023] According to the average value model, the transfer relationship is represented by an equivalent Thevenin impedance matrix and a historical voltage source of the time-domain discretized admittance equation to obtain a dual impedance equation;

[0024] The dual impedance equation is solved according to the time-domain discretized admittance equation to obtain the equivalent Thevenin impedance matrix expression of the grid-following converter.

[0025] In a second aspect, the present invention further provides a grid-type converter electromagnetic transient simulation system to implement the above-mentioned grid-type converter electromagnetic transient simulation method, the system comprising: an average value model construction module, a discretization processing module, an equivalent Thevenin impedance matrix construction module, and an electromagnetic transient simulation implementation module;

[0026] The average value model construction module is used to establish an admittance-based transfer matrix equation in a Laplace domain based on the resistance and inductance filter data of the grid-following converter and the current control loop data of the grid-following converter, and construct a average value model according to the transfer matrix equation;

[0027] The discretization processing module is configured to convert the transfer matrix equation from the Laplace domain to the discrete domain based on the trapezoidal integration rule to obtain a discretized admittance equation of the grid-type converter, and perform an inverse discretization transformation on the discretized admittance equation to obtain a time-domain discretized admittance equation of the grid-type converter, wherein the time-domain discretized admittance equation is configured to represent a transfer relationship between the output current of the grid-type converter and the voltage at the common coupling point using a synthetic conductance matrix in the average value model and a history term in the average value model;

[0028] The equivalent Thevenin impedance matrix building module is used to convert the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtain an equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation;

[0029] The electromagnetic transient simulation implementation module is used to implement the electromagnetic transient simulation of the grid-following converter according to the equivalent Thevenin impedance matrix expression.

[0030] Preferably, the average value model building module includes: a resistance and inductance filter operation unit, a converter system equation building unit, an admittance basis transfer matrix equation acquisition unit and a transfer matrix equation building unit;

[0031] The resistance and inductance filter calculation unit is used to construct an inductance-voltage equation of the resistance and inductance filter of the grid-type converter in the Laplace domain based on the resistance and inductance filter data of the grid-type converter, and perform an admittance calculation on the inductance-voltage equation to obtain an admittance equation of the resistance and inductance filter;

[0032] The converter system equation construction unit is configured to obtain a converter system equation based on the resistance-inductance filter admittance equation and the current control loop data of the grid-following converter;

[0033] The admittance basis transfer matrix equation acquisition unit is configured to derive a first admittance basis transfer matrix equation in a Laplace domain in the synchronous rotating coordinate system based on the current control loop data and a proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, and convert the first admittance basis transfer matrix equation into a stationary coordinate system based on Clarke transform and modulation circuit data of a common coupling point filter to obtain a second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system;

[0034] The transfer matrix equation construction unit is used to construct the first transfer matrix equation of the Laplace domain in the synchronous rotating coordinate system according to the converter system equation and the first admittance basis transfer matrix equation, and to construct the second transfer matrix equation of the Laplace domain in the stationary coordinate system according to the converter system equation and the second admittance basis transfer matrix equation.

[0035] Preferably, the discretization processing module includes: a mapping relationship construction unit and a conversion unit;

[0036] The mapping relationship construction unit is used to obtain a bilinear mapping relationship between the Laplace operator and the discrete operator according to the trapezoidal integration rule;

[0037] The conversion unit is used to convert the Laplace operator in the transfer matrix equation based on the bilinear mapping relationship to obtain a discretized admittance equation.

[0038] Preferably, the discretization processing module further includes: a first transformation unit, a second transformation unit and a third transformation unit;

[0039] The first transformation unit is configured to perform an inverse discrete transformation on the discretized admittance equation to obtain an initial time-domain discretized admittance equation;

[0040] The second transformation unit is configured to construct a dynamic impedance equation for the grid-following converter, and transform the initial time-domain discretized admittance equation according to the dynamic impedance equation to obtain an improved time-domain discretized admittance equation;

[0041] The third transformation unit is used to transform the improved time-domain discretized admittance equation into a three-phase coordinate system to obtain the time-domain discretized admittance equation of the grid-following converter.

[0042] Preferably, the equivalent Thevenin impedance matrix building module includes: a dual impedance equation acquisition unit and a solution unit;

[0043] The dual-impedance equation acquisition unit is configured to obtain a dual-impedance equation by expressing the transfer relationship using an equivalent Thevenin impedance matrix and a historical voltage source of the time-domain discretized admittance equation according to the average value model;

[0044] The solving unit is used to solve the dual-impedance equation according to the time-domain discretized admittance equation to obtain the equivalent Thevenin impedance matrix expression of the grid-following converter.

[0045] This application provides a method and system for electromagnetic transient simulation of a grid-connected converter. Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0046] The electromagnetic transient simulation method of the grid-following converter disclosed in the present application is based on the trapezoidal integration rule, which converts the transfer matrix equation from the Laplace domain to the discrete domain to construct the discretized admittance equation of the grid-following converter, gives full play to the advantages of the trapezoidal integration rule in terms of accuracy and good numerical stability, converts the average value model into a dual-impedance form, reduces numerical uncertainty, and improves the accuracy of the simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic diagram of the steps of a grid-type converter electromagnetic transient simulation method provided by a preferred embodiment of the present invention;

[0048] Figure 2 This is a structural diagram of an electromagnetic transient simulation system for a grid-following converter provided by a preferred embodiment of the present invention;

[0049] Reference numerals:

[0050] 1-Average value model construction module, 2-Discretization processing module, 3-Equivalent Thevenin impedance matrix construction module, 4-Electromagnetic transient simulation implementation module. DETAILED DESCRIPTION

[0051] The following is a detailed explanation of the embodiments of the present invention in conjunction with the accompanying drawings. The embodiments are provided for illustrative purposes only and cannot be understood as limitations on the present invention. The accompanying drawings are for reference and illustration purposes only and do not constitute a limitation on the scope of patent protection of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In the description of the present invention, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0052] The term "and / or" as used herein includes any and all combinations of one or more of the related listed items. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances.

[0053] In describing the present invention, it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0054] See also Figure 1 FIG. 1 is a schematic diagram of steps of a method for electromagnetic transient simulation of a grid-following converter shown in FIG. 1 . In an embodiment of the present invention, a method for electromagnetic transient simulation of a grid-following converter is provided, the method comprising:

[0055] S1. Based on the grid-type converter's resistance and inductance filter data and the grid-type converter's current control loop data, establish an admittance-based transfer matrix equation in the Laplace domain, and construct an average value model based on the transfer matrix equation. In a preferred embodiment of the present application, the grid-type converter is assumed to have a common two-stage topology and employ sinusoidal pulse width modulation, connected to an external system via a common coupling point, and controlled using a proportional-integral decoupled vector control strategy based on a synchronous rotating coordinate system or a proportional resonant control strategy based on a stationary coordinate system. The grid-type converter's resistance and inductance filter (RL filter) and circuit control loop are key to admittance transfer matrix modeling. Based on the grid-type converter's resistance and inductance filter data and the grid-type converter's current control loop data, an admittance-based transfer matrix equation is established in the Laplace domain. Specifically, based on the resistance and inductance filter data of the grid-following converter, the inductance-voltage equation of the resistance and inductance filter of the grid-following converter in the Laplace domain is constructed, and the admittance operation is performed on the inductance-voltage equation to obtain the admittance equation of the resistance and inductance filter. Based on the current control loop data of the grid-following converter and the admittance equation of the resistance and inductance filter, the converter system equation is obtained. The converter system equation is expressed as:

[0056]

[0057] in, Indicates the output current of the grid-following converter, represents the transfer matrix between the output current of the grid-following converter and the corresponding output voltage at the common coupling point, represents the output voltage at the point of common coupling, represents the transfer matrix between the output current of the grid-following converter and the reference current of the grid-following converter, Indicates the reference current of the grid-following converter.

[0058] For the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system, according to the current control loop data and the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system, the first admittance basis transfer matrix equation is derived in the Laplace domain in the synchronous rotating coordinate system. The first admittance basis transfer matrix equation in the Laplace domain in the synchronous rotating coordinate system is expressed as:

[0059]

[0060]

[0061] in, Indicates the grid-following converter Axis and The output current component of the axis and the corresponding common coupling point Axis and The transfer matrix between the shaft output voltage components, represents the voltage feed-forward coefficient, represents the filter value, Indicates the filter resistance value, Indicates the grid-following converter Axis and The output current component of the axis and the grid-following converter Axis and The transfer matrix between the reference currents of the axes, and represents the proportional-integral (PI) gain, Represents the 2×2 identity matrix.

[0062] According to the converter system equation and the first admittance basis transfer matrix equation, the first transfer matrix equation in the Laplace domain under the synchronous rotating coordinate system is constructed. The first transfer matrix equation is expressed as follows:

[0063]

[0064] in, Indicates the grid-following converter Axis and Shaft output current component, represents the Laplace operator, Indicates point of common coupling Axis and The output voltage component of the shaft, Indicates the grid-following converter Axis and Reference current component of the axis.

[0065] Furthermore, the grid-type converter is connected to the external system through a common coupling point filter, specifically an LCL filter. For the proportional resonant controller control strategy based on the stationary coordinate system, the output current component of the grid-type converter is converted from the three-phase coordinate system to the stationary coordinate system based on the Clarke transformation to obtain the first current output component of the grid-type converter in the stationary coordinate system. The first current output component of the grid-type converter in the stationary coordinate system is expressed as:

[0066]

[0067] in, represents the output current component of the grid-following converter in the stationary coordinate system, represents the three-phase coordinate transformation matrix, Represents the output current component of the grid-type converter in the three-phase coordinate system, Represents the voltage component at the common coupling point in the three-phase coordinate system.

[0068] in, Expressed as:

[0069]

[0070] For the LCL filter at the common coupling point, the voltage-current relationship equation in the Laplace domain stationary coordinate system is expressed as:

[0071]

[0072] in, represents the output current in the stationary coordinate system, represents the inductance on the converter side, represents the inductor series resistance, represents the capacitor in parallel with the resistor, represents the modulated output voltage component of the grid-type converter in the stationary coordinate system, Represents the collected output voltage components of the grid-type converter in the stationary coordinate system.

[0073] According to the voltage-current relationship equation of the LCL filter in the Laplace domain stationary coordinate system, the first current output component of the grid-following converter in the stationary coordinate system is re-expressed, and the second current output component is expressed as:

[0074]

[0075]

[0076] in, represents the output voltage component of the common coupling point in the stationary coordinate system, Indicates the filter capacitor value.

[0077] Construct the modulated output voltage component of the grid-following converter in the stationary coordinate system. The modulated output voltage component is expressed as:

[0078]

[0079]

[0080] in, represents the transfer function of the proportional resonant (PR) controller, Indicates the grid-following converter Axis and The reference current of the axis, and represents the proportional resonant (PR) controller gain, represents the cutoff frequency of the proportional resonant (PR) controller, Represents the nominal angular frequency of the proportional resonant (PR) controller.

[0081] Will Substitute the expression of the modulated output voltage component and the expression of the voltage-current relationship equation into Finally, the expression of the modulated output voltage component and the expression of the voltage-current relationship equation are substituted into the expression of the second current output component. After coefficient conversion, the second transfer matrix equation under the proportional resonance control strategy based on the stationary coordinate system is obtained. The second transfer matrix equation is expressed as:

[0082]

[0083] in, represents the first set of coefficients, Indicates the grid-following converter Axis and The output current component of the axis and the corresponding common coupling point Axis and The transfer matrix between the shaft output voltage components, Indicates the grid-following converter Axis and The output current component of the axis and the grid-following converter Axis and Transfer matrix between the reference current components of the axes.

[0084] The first set of coefficients is expressed as:

[0085]

[0086]

[0087]

[0088] in, Indicates the inductance value on the converter side, Indicates the grid side inductance value.

[0089] and is the second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system.

[0090] According to the first transfer matrix equation, a first average value model of a proportional-integral (PI) decoupled vector control strategy based on a synchronous rotating coordinate system is constructed, and according to the first transfer matrix equation, a second average value equation of a proportional resonant control strategy based on a stationary coordinate system is constructed.

[0091] S2. Based on the trapezoidal integration rule, the transfer matrix equation is converted from the Laplace domain to the discrete domain to obtain the discretized admittance equation of the grid-type converter, and the discretized admittance equation is inversely discretized to obtain the time-domain discretized admittance equation of the grid-type converter. The time-domain discretized admittance equation is set to characterize the transfer relationship between the output current of the grid-type converter and the common coupling point voltage using the synthetic conductance matrix in the average value model and the history term in the average value model; the average value model is a continuous time domain simulation, and the output current of the grid-type converter is represented by a controlled current source with a virtual damper to inject current into the external power grid system. Due to the existence of the virtual damper, there are problems such as decreased numerical accuracy, decreased stability and difficulty in selecting the time step. In a preferred embodiment of the present application, the average value model is discretized and re-expressed to construct a transfer matrix equation based on the equivalent Thevenin impedance matrix and the voltage history term, so as to achieve effective simultaneous solution of the grid-type converter and the external system and remove the influence of the virtual damper.

[0092] Specifically, for the first transfer matrix equation, the Laplace operator " " is replaced by , to discretize the first transfer matrix equation and obtain the first discretized admittance equation.

[0093] The trapezoidal integration rule is a numerical integration method used to convert continuous transfer functions into discrete ones. For the integral of a continuous function over an interval, the trapezoidal integration rule approximates the integral value by the area of ​​a trapezoid formed by the lines connecting the two endpoints of the interval. In other words, the current integral value is equal to the previous integral value plus the current trapezoidal area. The core of the trapezoidal integration rule is to relate the Laplace operator s to the discrete operator z through an integral relationship, resulting in a bilinear mapping relationship between the Laplace operator s and the discrete operator z.

[0094] The bilinear mapping relationship between the Laplace operator s and the discrete operator z is:

[0095]

[0096] in, Indicates the time step.

[0097] According to the bilinear mapping relationship, the first transfer matrix equation is converted into the first discretized admittance equation, which is expressed as:

[0098]

[0099] in, Indicates the grid-type converter in the discrete domain Axis and The output current component of the shaft, represents the second set of coefficients, Indicates the common coupling point in the discrete domain Axis and The output voltage component of the shaft, Indicates the grid-type converter in the discrete domain Axis and Reference current component of the axis.

[0100] The second set of coefficients is expressed as:

[0101]

[0102]

[0103]

[0104] Apply the inverse discretization transform (inverse z-transform) to the first discretized admittance equation, Transformed into a delay corresponding to the time step, the first initial discretized admittance equation is obtained. The first initial discretized admittance equation is expressed as:

[0105]

[0106] According to the dynamic impedance model set for the grid-following converter, a dynamic impedance equation is obtained. According to the dynamic impedance equation, the first initial discretized admittance is converted to obtain a first improved time-domain discretized admittance equation. The first improved time-domain discretized admittance equation is expressed as:

[0107]

[0108] in, It represents the first synthetic conductance matrix of the grid-following converter in the first average value model in the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system in the fixed rotating coordinate system. express Common coupling point in the stationary coordinate system at all times Axis and The voltage component of the shaft, express The first history item of the grid-following converter in the first average value model in the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system in the fixed rotating coordinate system.

[0109] The first resultant conductance matrix is ​​expressed as:

[0110]

[0111] The first history item is represented as:

[0112]

[0113] Among them, according to the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system, the grid-following converter is Axis and The reference current components of the axis are expressed as:

[0114]

[0115] in, Indicates the active power reference value, Indicates the reactive power reference value.

[0116] Since the first improved discretized admittance equation is a fixed rotating coordinate system, it is converted to a three-phase coordinate system so that it can be connected to the external system. After the conversion, the first time-domain discretized admittance equation of the grid-following converter is obtained. The first time-domain discretized admittance equation is expressed as:

[0117]

[0118] in, It represents the output current of the grid-type converter in the three-phase coordinate system. It represents the second synthetic conductance matrix of the grid-following converter in the average value model in the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system in the three-phase coordinate system. express The voltage of the common coupling point in the three-phase coordinate system at the moment, express The second history term of the grid-following converter in the average value model in the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system in the fixed rotating coordinate system.

[0119] The second composite conductance matrix is ​​expressed as:

[0120]

[0121] in, is the pseudo-inverse matrix of the Park transform.

[0122] The second history item is represented as:

[0123]

[0124] For the second transfer matrix equation, use the trapezoidal integration rule to transform the Laplace operator " " is replaced by , to discretize the second transfer matrix equation and obtain the second discretized admittance equation.

[0125] According to the bilinear mapping relationship, the second transfer matrix equation is converted into the second discretized admittance equation, which is expressed as:

[0126]

[0127] in, Indicates the grid-type converter in the discrete domain Axis and The output current component of the shaft, represents the third set of coefficients, Indicates the common coupling point in the discrete domain Axis and The output voltage component of the shaft, Indicates the grid-type converter in the discrete domain Axis and Reference current component of the axis.

[0128] The third set of coefficients is expressed as:

[0129]

[0130]

[0131]

[0132] in, 、 、 、 、 、 They represent the intermediate calculation parameters of the discretized admittance equation in the proportional resonance control strategy in the stationary coordinate system, 、 、 、 、 、 represents the intermediate calculation parameter of the denominator coefficient of the discretized admittance equation of the stationary coordinate system, 、 、 、 、 、 They represent the intermediate calculation parameters of the discretized admittance equation in the proportional resonance (PR) control strategy in the stationary coordinate system.

[0133] Apply the inverse discretization transform (inverse z-transform) to the second discretized admittance equation, Transformed into a delay corresponding to the time step, the second initial time-domain discretized admittance equation is obtained. The second initial time-domain discretized admittance equation is expressed as:

[0134]

[0135] in, Indicates the output current of the converter at the historical moment The output current value, Indicates the common coupling point at the historical moment The voltage value, Indicates the converter at a historical moment The output current value.

[0136] According to the dynamic impedance equation of the grid-following converter, the second initial time-domain discretized admittance equation is transformed to obtain the second improved time-domain discretized admittance equation. The second improved time-domain discretized admittance equation is expressed as:

[0137]

[0138] in, It represents the third synthetic conductance matrix of the grid-type converter in the average value model in the proportional resonant control strategy based on the stationary coordinate system. express The third history item of the average value model of the grid-type converter in the proportional resonant control strategy based on the stationary coordinate system at the moment of stationary coordinate system, express Common coupling point in the stationary coordinate system at all times Axis and The voltage component of the shaft.

[0139] The third composite conductance matrix is ​​expressed as:

[0140]

[0141] The third history item is represented as:

[0142]

[0143] Among them, according to the proportional resonance control strategy based on the stationary coordinate system, the grid-following converter is Axis and The reference current components of the axis are expressed as:

[0144]

[0145] Since the second improved time-domain discretized admittance equation is a stationary coordinate system, it is converted to a three-phase coordinate system so that it can be connected to the external system. After the conversion, the second time-domain discretized admittance equation of the grid-following converter is obtained. The second time-domain discretized admittance equation is expressed as:

[0146]

[0147] in, It represents the fourth synthetic conductance matrix of the grid-type converter in the average value model in the proportional resonant control strategy based on the stationary coordinate system in the three-phase coordinate system, express The fourth history item in the average value model of the grid-type converter in the proportional resonant control strategy based on the stationary coordinate system in the three-phase coordinate system at time instant.

[0148] The fourth composite conductance matrix is ​​expressed as:

[0149]

[0150] in, Represents the pseudo-inverse matrix of the Clarke transform.

[0151] The fourth history item is represented as:

[0152]

[0153] S3. Convert the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtain the equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation; in the field of electromagnetic transient simulation of power systems based on state variables, the interface of the average value model is connected to the external system by virtualizing the synthetic conductance matrix as a coupling resistor and the history term as a controlled current source. In this case, the interface requires a virtual buffer, which increases the numerical rigidity and introduces numerical uncertainty. In a preferred embodiment of the present application, in order to solve this problem, the average value model is converted into a dual-impedance form to obtain a dual-impedance equation. Under the proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, it is the first dual-impedance equation. The first dual-impedance equation is expressed as:

[0154]

[0155] in, represents the first equivalent Thevenin impedance matrix under the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system, The history voltage source representing the time-domain discretized admittance equation under the proportional-integral decoupled vector control strategy based on a synchronous rotating coordinate system.

[0156] Furthermore, according to the first time-domain discretized admittance equation, the first dual-impedance equation is solved to obtain the first equivalent Thevenin impedance matrix expression of the grid-following converter under the proportional-integral decoupling vector control strategy based on the synchronous rotating coordinate system. The first equivalent Thevenin impedance matrix expression is:

[0157]

[0158] Similarly, in the proportional resonant control strategy based on the stationary coordinate system, the second dual impedance equation is expressed as:

[0159]

[0160] in, represents the first equivalent Thevenin impedance matrix under the proportional resonant control strategy based on the stationary coordinate system, The history voltage source representing the time-domain discretized admittance equation under the proportional resonant control strategy based on the stationary coordinate system.

[0161] Furthermore, the second dual-impedance equation is solved according to the second time-domain discretized admittance equation to obtain the second equivalent Thevenin impedance matrix expression of the grid-following converter under the proportional resonant control strategy based on the stationary coordinate system. The second equivalent Thevenin impedance matrix expression is expressed as:

[0162]

[0163] S4. According to the equivalent Thevenin impedance matrix expression, the electromagnetic transient simulation of the grid-type converter is realized; in a preferred embodiment of the present application, the external system is equivalent to a voltage source vector and a Thevenin impedance matrix through the equivalent Thevenin impedance matrix expression, and according to the time-domain discretized admittance equation, the synchronous solution of the grid-type converter and the external system is realized through coupled resistance branches.

[0164] In a preferred embodiment of the present invention, based on the resistance and inductance filter data of the grid-following converter and the current control loop data of the grid-following converter, an admittance-based transfer matrix equation is established in the Laplace domain, and an average value model is constructed according to the transfer matrix equation; based on the trapezoidal integration rule, the transfer matrix equation is converted from the Laplace domain to the discrete domain to obtain a discretized admittance equation of the grid-following converter, and the discretized admittance equation is inversely discretized to obtain a time-domain discretized admittance equation of the grid-following converter, and the time-domain discretized admittance equation is set to characterize the transfer relationship between the output current and the common coupling point voltage of the grid-following converter by the synthetic conductance matrix in the average value model and the historical term in the average value model; the average value model is converted into a dual-impedance form to obtain a dual-impedance equation, and based on the dual-impedance equation and the time-domain discretized admittance equation, an equivalent Thevenin impedance matrix expression of the grid-following converter is obtained; according to the equivalent Thevenin impedance matrix expression, electromagnetic transient simulation of the grid-following converter is realized. The electromagnetic transient simulation method for a grid-following converter disclosed in this application is based on the trapezoidal integration rule, which converts the transfer matrix equation from the Laplace domain to the discrete domain to construct a discretized admittance equation for the grid-following converter. It gives full play to the advantages of the trapezoidal integration rule in terms of accuracy and good numerical stability, converts the average value model into a dual-impedance form, reduces numerical uncertainty, and improves the accuracy of the simulation results.

[0165] Accordingly, if Figure 2 The schematic diagram of the structure of the electromagnetic transient simulation system of a grid-type converter is shown. Based on a method for electromagnetic transient simulation of a grid-type converter, an embodiment of the present invention further provides an electromagnetic transient simulation system of a grid-type converter to implement the electromagnetic transient simulation method of a grid-type converter disclosed in an embodiment of the present invention. The system includes: an average value model construction module 1, a discretization processing module 2, an equivalent Thevenin impedance matrix construction module 3, and an electromagnetic transient simulation implementation module 4;

[0166] The average value model construction module 1 is used to establish an admittance-based transfer matrix equation in the Laplace domain based on the resistance and inductance filter data of the grid-type converter and the current control loop data of the grid-type converter, and construct a average value model according to the transfer matrix equation;

[0167] The discretization processing module 2 is configured to convert the transfer matrix equation from the Laplace domain to the discrete domain based on the trapezoidal integration rule to obtain a discretized admittance equation of the grid-type converter, and perform an inverse discretization transformation on the discretized admittance equation to obtain a time-domain discretized admittance equation of the grid-type converter, wherein the time-domain discretized admittance equation is configured to represent a transfer relationship between the output current of the grid-type converter and the voltage at the common coupling point using a synthetic conductance matrix in the average value model and a history term in the average value model;

[0168] The equivalent Thevenin impedance matrix construction module 3 is used to convert the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtain an equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation;

[0169] The electromagnetic transient simulation implementation module 4 is used to implement the electromagnetic transient simulation of the grid-following converter according to the equivalent Thevenin impedance matrix expression.

[0170] Furthermore, the average value model construction module 1 includes: a resistance and inductance filter operation unit, a converter system equation construction unit, an admittance basis transfer matrix equation acquisition unit and a transfer matrix equation construction unit;

[0171] The resistance and inductance filter calculation unit is used to construct an inductance-voltage equation of the resistance and inductance filter of the grid-type converter in the Laplace domain based on the resistance and inductance filter data of the grid-type converter, and perform an admittance calculation on the inductance-voltage equation to obtain an admittance equation of the resistance and inductance filter;

[0172] The converter system equation construction unit is configured to obtain a converter system equation based on the resistance-inductance filter admittance equation and the current control loop data of the grid-following converter;

[0173] The admittance basis transfer matrix equation acquisition unit is configured to derive a first admittance basis transfer matrix equation in a Laplace domain in the synchronous rotating coordinate system based on the current control loop data and a proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, and convert the first admittance basis transfer matrix equation into a stationary coordinate system based on Clarke transform and modulation circuit data of a common coupling point filter to obtain a second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system;

[0174] The transfer matrix equation construction unit is used to construct the first transfer matrix equation of the Laplace domain in the synchronous rotating coordinate system according to the converter system equation and the first admittance basis transfer matrix equation, and to construct the second transfer matrix equation of the Laplace domain in the stationary coordinate system according to the converter system equation and the second admittance basis transfer matrix equation.

[0175] Furthermore, the discretization processing module 2 includes: a mapping relationship construction unit and a conversion unit;

[0176] The mapping relationship construction unit is used to obtain a bilinear mapping relationship between the Laplace operator and the discrete operator according to the trapezoidal integration rule;

[0177] The conversion unit is used to convert the Laplace operator in the transfer matrix equation based on the bilinear mapping relationship to obtain a discretized admittance equation.

[0178] Furthermore, the discretization processing module 2 further includes: a first transformation unit, a second transformation unit and a third transformation unit;

[0179] The first transformation unit is configured to perform an inverse discrete transformation on the discretized admittance equation to obtain an initial time-domain discretized admittance equation;

[0180] The second transformation unit is configured to construct a dynamic impedance equation for the grid-following converter, and transform the initial time-domain discretized admittance equation according to the dynamic impedance equation to obtain an improved time-domain discretized admittance equation;

[0181] The third transformation unit is used to transform the improved time-domain discretized admittance equation into a three-phase coordinate system to obtain the time-domain discretized admittance equation of the grid-following converter.

[0182] Furthermore, the equivalent Thevenin impedance matrix building module 3 includes: a dual impedance equation acquisition unit and a solution unit;

[0183] The dual-impedance equation acquisition unit is configured to obtain a dual-impedance equation by expressing the transfer relationship using an equivalent Thevenin impedance matrix and a historical voltage source of the time-domain discretized admittance equation according to the average value model;

[0184] The solving unit is used to solve the dual-impedance equation according to the time-domain discretized admittance equation to obtain the equivalent Thevenin impedance matrix expression of the grid-following converter.

[0185] For the specific definition of a grid-type converter electromagnetic transient simulation system, please refer to the above-mentioned definition of a grid-type converter electromagnetic transient simulation method, which will not be repeated here. A person of ordinary skill in the art will appreciate that the various modules and steps described in conjunction with the embodiments disclosed in the present invention can be implemented in hardware, software, or a combination of both. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0186] In summary, the embodiment of the present application provides a method and system for electromagnetic transient simulation of a grid-type converter, which solves the technical problem of how to improve the accuracy of electromagnetic transient simulation of a grid-type converter. The method includes: establishing a transfer matrix equation based on admittance in the Laplace domain based on the resistance and inductance filter data of the grid-type converter and the current control loop data of the grid-type converter, and constructing an average value model based on the transfer matrix equation; based on the trapezoidal integration rule, converting the transfer matrix equation from the Laplace domain to the discrete domain to obtain the discretized admittance equation of the grid-type converter, and performing the discrete admittance analysis on the admittance model. The inverse discrete transformation of the admittance equation is performed to obtain the time-domain discretized admittance equation of the grid-type converter. The time-domain discretized admittance equation is set to represent the transfer relationship between the output current of the grid-type converter and the common coupling point voltage by the synthetic conductance matrix in the average value model and the history term in the average value model; the average value model is converted into a dual-impedance form to obtain a dual-impedance equation, and based on the dual-impedance equation and the time-domain discretized admittance equation, the equivalent Thevenin impedance matrix expression of the grid-type converter is obtained; based on the equivalent Thevenin impedance matrix expression, the electromagnetic transient simulation of the grid-type converter is realized. The electromagnetic transient simulation method of the grid-type converter disclosed in this application, based on the trapezoidal integration rule, converts the transfer matrix equation from the Laplace domain to the discrete domain to construct the discretized admittance equation of the grid-type converter, gives full play to the advantages of the trapezoidal integration rule in terms of accuracy and good numerical stability, converts the average value model into a dual-impedance form, reduces numerical uncertainty, and improves the accuracy of the simulation results.

[0187] Each embodiment in this specification is described in a progressive manner, and the same or similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. It should be noted that the various technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0188] The above-described embodiments merely represent several preferred implementations of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art could make several improvements and substitutions without departing from the technical principles of the present application, and such improvements and substitutions should also be considered within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be based on the scope of protection of the claims.

Claims

1. A method for electromagnetic transient simulation of a grid-following converter, characterized in that: The method comprises: Based on the resistance and inductance filter data of the grid-following converter and the current control loop data of the grid-following converter, establishing an admittance-based transfer matrix equation in the Laplace domain, and constructing an average value model according to the transfer matrix equation; Based on the trapezoidal integration rule, the transfer matrix equation is converted from the Laplace domain to the discrete domain to obtain a discretized admittance equation of the grid-type converter, and the discretized admittance equation is inversely discretized to obtain a time-domain discretized admittance equation of the grid-type converter, wherein the time-domain discretized admittance equation is set to represent the transfer relationship between the output current of the grid-type converter and the common coupling point voltage using the synthetic conductance matrix in the average value model and the history term in the average value model; Converting the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtaining an equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation; According to the equivalent Thevenin impedance matrix expression, electromagnetic transient simulation of the grid-following converter is realized; The average value model is converted into a dual-impedance form to obtain a dual-impedance equation, and based on the dual-impedance equation and the time-domain discretized admittance equation, an equivalent Thevenin impedance matrix expression of the grid-following converter is obtained, including: According to the average value model, the transfer relationship is represented by an equivalent Thevenin impedance matrix and a historical voltage source of the time-domain discretized admittance equation to obtain a dual impedance equation; The dual impedance equation is solved according to the time-domain discretized admittance equation to obtain the equivalent Thevenin impedance matrix expression of the grid-following converter.

2. The electromagnetic transient simulation method for a grid-connected converter according to claim 1, wherein: The admittance-based transfer matrix equation is established in the Laplace domain based on the resistance and inductance filter data of the grid-based converter and the current control loop data of the grid-based converter, including: Based on the resistance and inductance filter data of the grid-following converter, an inductance-voltage equation of the resistance and inductance filter of the grid-following converter in the Laplace domain is constructed, and an admittance operation is performed on the inductance-voltage equation to obtain an admittance equation of the resistance and inductance filter; Obtaining a converter system equation based on the resistance-inductance filter admittance equation and current control loop data of the grid-following converter; According to the current control loop data and a proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, a first admittance basis transfer matrix equation is derived in a Laplace domain in the synchronous rotating coordinate system, and according to Clarke transform and modulation circuit data of a common coupling point filter, the first admittance basis transfer matrix equation is converted to a stationary coordinate system to obtain a second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system; According to the converter system equation and the first admittance basis transfer matrix equation, a first transfer matrix equation in the Laplace domain in the synchronous rotating coordinate system is constructed; according to the converter system equation and the second admittance basis transfer matrix equation, a second transfer matrix equation in the Laplace domain in the stationary coordinate system is constructed.

3. The electromagnetic transient simulation method for a grid-connected converter according to claim 1, wherein: The method of converting the transfer matrix equation from the Laplace domain to the discrete domain based on the trapezoidal integration rule to obtain the discretized admittance equation of the grid-following converter includes: According to the trapezoidal integration rule, the bilinear mapping relationship between the Laplace operator and the discrete operator is obtained; Based on the bilinear mapping relationship, the Laplace operator in the transfer matrix equation is transformed to obtain a discretized admittance equation.

4. The electromagnetic transient simulation method for a grid-connected converter according to claim 1, wherein: The performing of an inverse discrete transformation on the discretized admittance equation to obtain a time-domain discretized admittance equation of the grid-following converter includes: Performing an inverse discrete transformation on the discretized admittance equation to obtain an initial time-domain discretized admittance equation; Constructing a dynamic impedance equation for the grid-following converter, and transforming the initial time-domain discretized admittance equation according to the dynamic impedance equation to obtain an improved time-domain discretized admittance equation; The improved time-domain discretized admittance equation is converted into a three-phase coordinate system to obtain the time-domain discretized admittance equation of the grid-following converter.

5. A grid-following converter electromagnetic transient simulation system, used to implement the grid-following converter electromagnetic transient simulation method according to any one of claims 1 to 4, characterized in that: The system includes: an average value model construction module, a discretization processing module, an equivalent Thevenin impedance matrix construction module and an electromagnetic transient simulation implementation module; The average value model construction module is used to establish an admittance-based transfer matrix equation in a Laplace domain based on the resistance and inductance filter data of the grid-following converter and the current control loop data of the grid-following converter, and construct a average value model according to the transfer matrix equation; The discretization processing module is configured to convert the transfer matrix equation from the Laplace domain to the discrete domain based on the trapezoidal integration rule to obtain a discretized admittance equation of the grid-type converter, and perform an inverse discretization transformation on the discretized admittance equation to obtain a time-domain discretized admittance equation of the grid-type converter, wherein the time-domain discretized admittance equation is configured to represent a transfer relationship between the output current of the grid-type converter and the voltage at the common coupling point using a synthetic conductance matrix in the average value model and a history term in the average value model; The equivalent Thevenin impedance matrix building module is used to convert the average value model into a dual-impedance form to obtain a dual-impedance equation, and obtain an equivalent Thevenin impedance matrix expression of the grid-following converter based on the dual-impedance equation and the time-domain discretized admittance equation; The electromagnetic transient simulation implementation module is used to implement the electromagnetic transient simulation of the grid-following converter according to the equivalent Thevenin impedance matrix expression; The equivalent Thevenin impedance matrix building module includes: a dual impedance equation acquisition unit and a solution unit; The dual-impedance equation acquisition unit is configured to obtain a dual-impedance equation by expressing the transfer relationship using an equivalent Thevenin impedance matrix and a historical voltage source of the time-domain discretized admittance equation according to the average value model; The solving unit is used to solve the dual-impedance equation according to the time-domain discretized admittance equation to obtain the equivalent Thevenin impedance matrix expression of the grid-following converter.

6. The electromagnetic transient simulation system for a grid-connected converter according to claim 5, wherein: The average value model construction module includes: a resistance and inductance filter operation unit, a converter system equation construction unit, an admittance basis transfer matrix equation acquisition unit and a transfer matrix equation construction unit; The resistance and inductance filter calculation unit is used to construct an inductance-voltage equation of the resistance and inductance filter of the grid-type converter in the Laplace domain based on the resistance and inductance filter data of the grid-type converter, and perform an admittance calculation on the inductance-voltage equation to obtain an admittance equation of the resistance and inductance filter; The converter system equation construction unit is configured to obtain a converter system equation based on the resistance-inductance filter admittance equation and the current control loop data of the grid-following converter; The admittance basis transfer matrix equation acquisition unit is configured to derive a first admittance basis transfer matrix equation in a Laplace domain in the synchronous rotating coordinate system based on the current control loop data and a proportional-integral decoupling vector control strategy based on a synchronous rotating coordinate system, and convert the first admittance basis transfer matrix equation into a stationary coordinate system based on Clarke transform and modulation circuit data of a common coupling point filter to obtain a second admittance basis transfer matrix equation in the Laplace domain in the stationary coordinate system; The transfer matrix equation construction unit is used to construct the first transfer matrix equation of the Laplace domain in the synchronous rotating coordinate system according to the converter system equation and the first admittance basis transfer matrix equation, and to construct the second transfer matrix equation of the Laplace domain in the stationary coordinate system according to the converter system equation and the second admittance basis transfer matrix equation.

7. The electromagnetic transient simulation system for a grid-connected converter according to claim 5, wherein: The discretization processing module includes: a mapping relationship construction unit and a conversion unit; The mapping relationship construction unit is used to obtain a bilinear mapping relationship between the Laplace operator and the discrete operator according to the trapezoidal integration rule; The conversion unit is used to convert the Laplace operator in the transfer matrix equation based on the bilinear mapping relationship to obtain a discretized admittance equation.

8. The electromagnetic transient simulation system for a grid-connected converter according to claim 5, wherein: The discretization processing module further includes: a first transformation unit, a second transformation unit and a third transformation unit; The first transformation unit is configured to perform an inverse discrete transformation on the discretized admittance equation to obtain an initial time-domain discretized admittance equation; The second transformation unit is configured to construct a dynamic impedance equation for the grid-following converter, and transform the initial time-domain discretized admittance equation according to the dynamic impedance equation to obtain an improved time-domain discretized admittance equation; The third transformation unit is used to transform the improved time-domain discretized admittance equation into a three-phase coordinate system to obtain the time-domain discretized admittance equation of the grid-following converter.

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