A Simulation Modeling Method for a Converter Connected to a System

Abstract

The present invention provides a simulation modeling method for a converter-connected system, including: based on the harmonic spectrum generated when the converter is connected to the power grid circuit, through Fourier transform and symmetrical component method, converting the harmonic signals from the fundamental frequency to the highest order into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase stationary coordinate system; performing DQN coordinate transformation on the positive sequence signals, negative sequence signals and zero sequence signals, and obtaining six DC components through Park transformation, combining and encapsulating the six DC components to obtain a signal matrix in the DQN coordinate system; establishing signal operation rules in the DQN coordinate system based on the signal matrix in the DQN coordinate system; constructing the transfer relationship between each module in the power grid circuit based on the signal operation rules in the DQN coordinate system, so as to establish a mathematical transfer model of the converter-connected system in the DQN coordinate system. The present invention can improve the accuracy and calculation speed of simulation calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and distribution in power systems, and particularly to a simulation modeling method for a converter-connected system. Background Art

[0002] With the gradual development of the new energy industry, the problem of new energy systems connecting to the power grid has attracted wide attention from relevant scientific research personnel. At present, impedance modeling methods are mainly adopted in the research on power system simulation modeling, and the improvement of simulation speed mainly relies on improving the model efficiency and increasing the simulation step size.

[0003] From the perspective of signal theory, high-frequency signals have a small time constant and a short oscillation change time. By down-converting high-frequency signals into low-frequency signals, the time constant can be made larger, "slowing down" the change process, and better simulating with a large simulation step size. Common down-conversion methods for signals include the dynamic vector method, the traditional phasor method, the Park transformation method, etc.

[0004] However, these existing methods still have problems such as low accuracy and slow calculation speed in simulation calculations. Summary of the Invention

[0005] In view of this, the present invention provides a simulation modeling method for a converter-connected system to improve the accuracy and calculation speed of simulation calculations.

[0006] A simulation modeling method for a converter-connected system includes:

[0007] Step S1, based on the harmonic spectrum generated when the converter is connected to the power grid circuit, through Fourier transform and symmetrical component method, convert the harmonic signals from the fundamental frequency to the highest order into positive sequence signals, negative sequence signals, and zero sequence signals in the ABC three-phase stationary coordinate system;

[0008] Step S2, perform DQN coordinate transformation on the positive sequence signal, negative sequence signal, and zero sequence signal, and through Park transformation, transform the positive sequence signal into a positive sequence DC component on the d-axis and a positive sequence DC component on the q-axis, transform the negative sequence signal into a negative sequence DC component on the d-axis and a negative sequence DC component on the q-axis, transform the zero sequence signal into a zero sequence DC component on the d-axis and a zero sequence DC component on the q-axis, and then arrange them in the order of harmonic order and positive-negative-zero sequence relationship, and combine and package the six DC components to obtain a signal matrix in the DQN coordinate system;

[0009] Step S3, based on the signal matrix in the DQN coordinate system, establish the signal operation rules in the DQN coordinate system;

[0010] Step S4, based on the signal operation rules in the DQN coordinate system, construct the transfer relationship between each module in the power grid circuit, thereby establishing a mathematical transfer model of the converter-connected system in the DQN coordinate system.

[0011] According to the converter access system simulation modeling method provided by the present invention, the modeling process of the converter access system is directly transferred from the traditional and static ABC coordinate system to multiple rotating DQN coordinate systems. The original AC signals in the ABC coordinate system with various frequency components are directly converted into DC signals in the DQN coordinate system. This not only preserves all the spectral components of the system and improves the accuracy of system simulation calculations, but also effectively slows down the change rate of instantaneous values, thereby greatly increasing the simulation step size and improving the system simulation calculation speed. Therefore, it has the advantages of fast calculation speed and high calculation accuracy. In addition, the present invention calculates all variables as DC signals, overcomes the non-linear periodic problem of the converter accessing the power system, increases the harmonic analysis frequency, and can be applied to the analysis of system unbalanced conditions, and is easy to modify and optimize according to different scenarios and requirements. Description of the Drawings

[0012] Figure 1 is a flowchart of the converter access system simulation modeling method provided by the embodiment of the present invention;

[0013] Figure 2 is a comparison diagram of the simulation modeling results of a simple power grid circuit. Detailed Embodiments

[0014] The following details the embodiments of the present invention. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the embodiments of the present invention and should not be construed as limiting the present invention.

[0015] Please refer to Figure 1 , the embodiment of the present invention provides a converter access system simulation modeling method, including steps S1 to S4:

[0016] Step S1, based on the harmonic spectrum generated when the converter accesses the power grid circuit, through Fourier transform and symmetrical component method, convert the harmonic signals from the fundamental frequency to the highest order into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase static coordinate system.

[0017] Among them, the symmetrical component method is used to decompose any set of asymmetric signals into three independent vectors of positive sequence, negative sequence and zero sequence, and the signals in the ABC three-phase static coordinate system are decomposed into positive sequence signals, negative sequence signals and zero sequence signals. The results are as follows:

[0018] ;

[0019] ;

[0020] ;

[0021] Among them, is the positive-sequence signal, is the negative-sequence signal, is the zero-sequence signal, represents time, 、 and respectively represent the amplitudes of the positive-sequence signal, the negative-sequence signal, and the zero-sequence signal, 、 and respectively represent the phases of the positive-sequence signal, the negative-sequence signal, and the zero-sequence signal, represents the signal frequency.

[0022] Positive-sequence signal 、Negative-sequence signal are both three-phase symmetrical signals, and the zero-sequence signal is three signals in the same direction and identical.

[0023] Step S2: Perform DQN coordinate transformation on the positive-sequence signal, negative-sequence signal, and zero-sequence signal, and transform the positive-sequence signal into the positive-sequence DC component on the d-axis and the positive-sequence DC component on the q-axis through Park transformation, transform the negative-sequence signal into the negative-sequence DC component on the d-axis and the negative-sequence DC component on the q-axis, transform the zero-sequence signal into the zero-sequence DC component on the d-axis and the zero-sequence DC component on the q-axis, and then arrange them according to the harmonic order and the positive-negative zero-sequence relationship, and perform combined encapsulation on the six DC components to obtain the signal matrix in the DQN coordinate system.

[0024] Among them, in step S2, when transforming the positive-sequence signal into the positive-sequence DC component on the d-axis and the positive-sequence DC component on the q-axis, and transforming the negative-sequence signal into the negative-sequence DC component on the d-axis and the negative-sequence DC component on the q-axis, the following formula is satisfied:

[0025] ;

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] Among them, represents the positive-sequence DC component on the d-axis, Represents the positive-sequence DC component on the q-axis, Represents the negative-sequence DC component on the d-axis, Represents the negative-sequence DC component on the q-axis.

[0032] For the zero-sequence components that are the same for the three phases obtained by the symmetrical component method, they cannot be directly transformed in coordinates according to the methods of positive sequence and negative sequence.

[0033] In this embodiment, in the process of transforming the zero-sequence signal into the zero-sequence DC component on the d-axis and the zero-sequence DC component on the q-axis, first use the AC zero-sequence signal as the signal of the axis system, and add a delay of the fundamental wave period to the AC zero-sequence signal to create the signal of the axis system (90-degree delay signal), then, the signal of the axis system is , the signal of the axis system is , and then use the following formula for transformation:

[0034] ;

[0035] ;

[0036] ;

[0037] Among them, represents the zero-sequence DC component on the d-axis, represents the zero-sequence DC component on the q-axis, represents the amplitude of the zero-sequence signal, represents the phase angle of the zero-sequence signal.

[0038] In step S2, the expression of the signal matrix in the DQN coordinate system is:

[0039]

[0040] Among them, represents the signal matrix in the DQN coordinate system corresponding to the signal , represents the positive-sequence DC component on the d-axis based on the decomposition of the original signal, represents the positive-sequence DC component on the q-axis based on the decomposition of the original signal, represents the negative-sequence DC component on the d-axis based on the decomposition of the original signal, represents the negative-sequence DC component on the q-axis based on the decomposition of the original signal, represents the zero-sequence DC component on the d-axis based on the decomposition of the original signal, represents the zero-sequence DC component on the q-axis based on the decomposition of the original signal, 、 , respectively represent the positive-sequence fundamental harmonic component, positive-sequence second harmonic component, and positive-sequence n harmonic component on the d-axis, , , respectively represent the positive-sequence fundamental harmonic component, positive-sequence second harmonic component, and positive-sequence n harmonic component on the q-axis, , , respectively represent the negative-sequence fundamental harmonic component, negative-sequence second harmonic component, and negative-sequence n harmonic component on the d-axis, , , respectively represent the negative-sequence fundamental harmonic component, negative-sequence second harmonic component, and negative-sequence n harmonic component on the q-axis, , , respectively represent the zero-sequence fundamental harmonic component, zero-sequence second harmonic component, and zero-sequence n harmonic component on the d-axis, , , respectively represent the zero-sequence fundamental harmonic component, zero-sequence second harmonic component, and zero-sequence n harmonic component on the q-axis.

[0041] Step S3: Based on the signal matrix in the DQN coordinate system, establish the signal operation rules in the DQN coordinate system.

[0042] Among them, the signal operation rules include signal addition calculation, signal subtraction calculation, signal multiplication calculation, signal integration calculation, and signal differentiation calculation.

[0043] In step S3, first simplify the signal corresponding signal matrix in the DQN coordinate system, and simplify the signal corresponding signal matrix in the DQN coordinate system. The simplification results are:

[0044] ;

[0045] ;

[0046] ;

[0047] ;

[0048] ;

[0049] ;

[0050] ;

[0051] ;

[0052] ;

[0053] wherein, represents the DC component of the signal , , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the q-axis, represents the DC component of the signal , , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the q-axis;

[0054] Then, the expression for signal addition calculation is:

[0055] ;

[0056] wherein, represents the result of signal addition calculation;

[0057] The expression for signal subtraction calculation is:

[0058] ;

[0059] wherein, represents the result of signal subtraction calculation;

[0060] Since , have inconsistent numbers of rows and columns and cannot be directly multiplied. In this embodiment, the expression for signal multiplication calculation is:

[0061] ;

[0062] ;

[0063] ;

[0064] ;

[0065] ;

[0066] ;

[0067] ;

[0068] ;

[0069] Among them, represents the result of signal multiplication calculation, represents signal and signal product, the DC component of , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the d-axis, represents the (n - 1)th harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the d-axis.

[0070] Regarding signal integration calculation and signal differentiation calculation, to simulate the state change of a dynamic system, the bilinear transformation method is used to convert continuous signals into types that can be processed by a digital system. The input signal and system-related parameters (such as time constant, frequency, etc.) are used to calculate the state update of the system. By setting a reasonable sampling step, the signal values at each moment are gradually operated: among them, the integration operation extracts the signal by accumulation, and the differentiation calculation captures the instantaneous change of the signal by difference. By gradually cycling and updating the state at each moment, the state of the next moment is calculated, and a feedback mechanism is set to feedback the state of the previous moment into the current input to improve the stability and accuracy of the system.

[0071] Step S4: Based on the signal operation rules in the DQN coordinate system, construct the transfer relationships among various modules in the power grid circuit, thereby establishing a mathematical transfer model of the converter-connected system in the DQN coordinate system.

[0072] Specifically, extract the transfer function or state-space model among various modules in the power grid circuit to describe the dynamic characteristics of the converter-connected system. Through coordinate transformation, convert the traditional state-space model to the DQN coordinate system, redefine the state variables, simplify the mathematical representation of the system's dynamic behavior, construct the signal transfer relationships among various modules according to the DC signal matrix, use the signal operation rules in the DQN coordinate system to express the transfer relationships among various modules, establish an analytical model in the DQN coordinate system, and realize the simulation modeling of the converter-connected system.

[0073] The method of this embodiment is simulated and tested as follows:

[0074] Figure 2 It is a comparison chart of the simulation modeling results of a simple power grid circuit. In the simple power grid circuit, the simulation modeling results in the traditional ABC coordinate system, the simulation modeling results of the present invention, and the real results are compared and analyzed. From Figure 2 It can be seen that the results of the three overlap very highly, indicating that the simulation modeling of the present invention has a relatively high accuracy.

[0075] According to the simulation modeling method of the converter-connected system in the above embodiment, the modeling process of the converter-connected system is directly transferred from the traditional and static ABC coordinate system to multiple rotating DQN coordinate systems. The original AC signals in the ABC coordinate system are directly converted into DC signals in the DQN coordinate system. This not only can retain all the spectral components of the system, improve the accuracy of system simulation calculation, but also effectively slow down the change speed of the instantaneous value, thereby greatly increasing the simulation step size and improving the system simulation calculation speed. Therefore, it has the advantages of fast calculation speed and high calculation accuracy. In addition, the present invention calculates by converting all variables into DC signals, overcomes the non-linear periodic problem of the converter connected to the power system, increases the harmonic analysis frequency and can be applied to the analysis of system unbalanced conditions, and is easy to modify and optimize according to different scenarios and requirements.

[0076] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims.

Claims

1. A simulation modeling method for a converter-connected system, characterized in that Including: Step S1: Based on the harmonic spectrum generated when the converter is connected to the power grid circuit, through Fourier transform and symmetrical component method, convert the harmonic signals from the fundamental frequency to the highest order into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase stationary coordinate system; Step S2: Perform DQN coordinate transformation on the positive sequence signal, negative sequence signal and zero sequence signal, and through Park transformation, transform the positive sequence signal into the positive sequence DC component on the d-axis and the positive sequence DC component on the q-axis, transform the negative sequence signal into the negative sequence DC component on the d-axis and the negative sequence DC component on the q-axis, transform the zero sequence signal into the zero sequence DC component on the d-axis and the zero sequence DC component on the q-axis, then arrange them in the order of harmonic order and the relationship of positive, negative and zero sequence, and combine and package the six DC components to obtain the signal matrix in the DQN coordinate system; Step S3: Based on the signal matrix in the DQN coordinate system, establish the signal operation rules in the DQN coordinate system; Step S4: Based on the signal operation rules in the DQN coordinate system, construct the transfer relationship between each module in the power grid circuit, so as to establish the mathematical transfer model of the converter access system in the DQN coordinate system.

2. The simulation modeling method for a converter access system according to claim 1, wherein Step S1 satisfies the following formula: ； ； ； Among them, is the positive-sequence signal, is the negative-sequence signal, is the zero-sequence signal, represents time, 、 and represent the amplitudes of the positive-sequence signal, negative-sequence signal and zero-sequence signal respectively, 、 and represent the phases of the positive-sequence signal, negative-sequence signal and zero-sequence signal respectively, represents the signal frequency.

3. The method for simulating and modeling the converter access system according to claim 2, wherein In Step S2, during the process of transforming the positive sequence signal into the positive sequence DC component on the d-axis and the positive sequence DC component on the q-axis, and transforming the negative sequence signal into the negative sequence DC component on the d-axis and the negative sequence DC component on the q-axis, the following formula is satisfied: ； ； ； ； ； ； Among them, represents the positive-sequence DC component on the d-axis, represents the positive-sequence DC component on the q-axis, represents the negative-sequence DC component on the d-axis, represents the negative-sequence DC component on the q-axis; In the process of transforming the zero-sequence signal into the zero-sequence DC component on the d-axis and the zero-sequence DC component on the q-axis, first use the AC zero-sequence signal as the signal in the axis system, add a delay of the fundamental wave period to the AC zero-sequence signal to create the signal in the axis system. Then, the signal in the axis system is , the signal in the axis system is , and then use the following formula for transformation: ； ； ； Among them, represents the zero-sequence DC component on the d-axis, represents the zero-sequence DC component on the q-axis, represents the amplitude of the zero-sequence signal, represents the phase angle of the zero-sequence signal.

4. The simulation modeling method for a converter access system according to claim 3, wherein In Step S2, the expression of the signal matrix in the DQN coordinate system is: Among them, represents the signal signal matrix in the DQN coordinate system corresponding to, represents the positive-sequence DC component on the d-axis based on the decomposition of the original signal, represents the positive-sequence DC component on the q-axis based on the decomposition of the original signal, represents the negative-sequence DC component on the d-axis based on the decomposition of the original signal, represents the negative-sequence DC component on the q-axis based on the decomposition of the original signal, represents the zero-sequence DC component on the d-axis based on the decomposition of the original signal, represents the zero-sequence DC component on the q-axis based on the decomposition of the original signal, , , respectively represent the positive-sequence fundamental harmonic component, positive-sequence second harmonic component, positive-sequence n th harmonic component on the d-axis, , , respectively represent the positive-sequence fundamental harmonic component, positive-sequence second harmonic component, positive-sequence n th harmonic component on the q-axis, , , respectively represent the negative-sequence fundamental harmonic component, negative-sequence second harmonic component, negative-sequence n th harmonic component on the d-axis, , , respectively represent the negative-sequence fundamental harmonic component, negative-sequence second harmonic component, negative-sequence n th harmonic component on the q-axis, , , respectively represent the zero-sequence fundamental harmonic component, zero-sequence second harmonic component, zero-sequence n th harmonic component on the d-axis, , , respectively represent the zero-sequence fundamental harmonic component, zero-sequence second harmonic component, zero-sequence n th harmonic component on the q-axis.

5. The simulation modeling method for a converter access system according to claim 4, characterized in that In Step S3, the signal operation rules at least include signal addition calculation, signal subtraction calculation, signal multiplication calculation; First, simplify the signal in the signal matrix corresponding to the DQN coordinate system and simplify the signal in the signal matrix corresponding to the DQN coordinate system The simplification results are as follows: ； ； ； ； ； ； ； ； ； Among them, represents the DC component of the signal , , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the q-axis, represents the DC component of the signal , , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of the signal on the q-axis; Then, the expression of the signal addition calculation is: ； Among them, represents the result of signal addition calculation; The expression of the signal subtraction calculation is: ； Among them, represents the result of signal subtraction calculation; The expression of the signal multiplication calculation is: ； ； ； ； ； ； ； ； Among them, represents the result of signal multiplication calculation, represents signal and signal the product of the DC component of , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of signal on the d-axis, , , respectively represent the fundamental harmonic component, second harmonic component, and nth harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the d-axis, represents the (n - 1)th harmonic component of signal on the q-axis, represents the (n - 1)th harmonic component of signal on the d-axis.

6. The simulation modeling method for a converter access system according to claim 1, wherein Step S4 specifically includes: Extract the transfer function or state space model between each module in the power grid circuit to describe the dynamic characteristics of the converter access system, transform the traditional state space model to the DQN coordinate system through coordinate transformation, redefine the state variables, simplify the mathematical representation of the system dynamic behavior, construct the signal transfer relationship between each module according to the DC signal matrix, use the signal operation rules based on the DQN coordinate system to express the transfer relationship between each module, establish the analytical model in the DQN coordinate system, and realize the simulation modeling of the converter access system.

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