Simulation modeling method for converter access system

Abstract

The invention provides a converter access system simulation modeling method, which comprises the following steps of: based on a harmonic frequency spectrum generated when a converter is accessed to a power grid circuit, converting a harmonic signal from a fundamental frequency to the highest number of times into a positive sequence signal, a negative sequence signal and a zero sequence signal under an ABC three-phase static coordinate system through Fourier transform and a symmetric component method; performing DQN coordinate transformation on the positive sequence signal, the negative sequence signal and the zero sequence signal, obtaining six direct current components through Park transformation, and performing combined packaging on the six direct current components to obtain a signal matrix under a DQN coordinate system; establishing a signal operation rule under the DQN coordinate system based on the signal matrix under the DQN coordinate system; and based on a signal operation rule under the DQN coordinate system, constructing a transfer relationship among modules in a power grid circuit, so as to establish a mathematical transfer model of the converter access system under the DQN coordinate system. The precision and the calculation speed of simulation calculation can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power transmission and distribution of electric power systems, and in particular to a method for simulating and modeling a converter access system. Background Art

[0002] With the gradual development of the new energy industry, the issue of connecting new energy systems to the power grid has attracted widespread attention from relevant researchers. At present, the research on power system simulation modeling mainly adopts the impedance modeling method, and the improvement of simulation speed mainly relies on improving model efficiency and increasing simulation step size.

[0003] From the perspective of signal theory, the time constant of high-frequency signals is small and the oscillation change time is short. By reducing the frequency of high-frequency signals to low-frequency signals, the time constant can be increased, the change process can be "slowed down", and the simulation can be better simulated with a large simulation step. Commonly used frequency reduction methods for signals include dynamic vector method, traditional phasor method, Park transformation method, etc.

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

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

[0006] A converter access system simulation modeling method, comprising: Step S1, based on the harmonic spectrum generated when the converter is connected to the grid circuit, the harmonic signals from the fundamental frequency to the highest order are converted into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase stationary coordinate system through Fourier transform and symmetrical component method; Step S2, performing DQN coordinate transformation on the positive sequence signal, the negative sequence signal and the zero sequence signal, and transforming the positive sequence signal into a positive sequence DC component on the d axis and a positive sequence DC component on the q axis through Park transformation, transforming the negative sequence signal into a negative sequence DC component on the d axis and a negative sequence DC component on the q axis, and transforming 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 arranging them according to the order of harmonic orders and the positive, negative and zero sequence relationship, combining and packaging the six DC components, and obtaining a signal matrix in the DQN coordinate system; Step S3, establishing a signal operation rule in the DQN coordinate system based on the signal matrix in the DQN coordinate system; Step S4, based on the signal operation rules in the DQN coordinate system, construct the transmission relationship between the modules in the power grid circuit, so as to establish a mathematical transmission model of the converter access system in the DQN coordinate system.

[0007] 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, static ABC coordinate system to multiple rotating DQN coordinate systems. The original frequency domain AC signals in the ABC coordinate system are directly converted into DC signals in the DQN coordinate system, which can not only retain all the spectrum components of the system and improve the accuracy of the system simulation calculation, but also effectively slow down the speed of change of the instantaneous value, thereby greatly increasing the simulation step size and improving the system simulation calculation speed, thus having the advantages of fast calculation speed and high calculation accuracy. In addition, the present invention converts all variables into DC signals for calculation, overcomes the nonlinear periodicity problem of the converter access to the power system, increases the frequency of harmonic analysis and can be applied to the analysis of the unbalanced working condition of the system, and is easy to modify and optimize according to different scenarios and needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A flowchart of a converter access system simulation modeling method provided by an embodiment of the present invention; Figure 2 This is a comparison chart of simulation modeling results of a simple power grid circuit. DETAILED DESCRIPTION

[0009] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the embodiments of the present invention, and should not be construed as limiting the present invention.

[0010] See also Figure 1 The embodiment of the present invention provides a converter access system simulation modeling method, including steps S1 to S4: Step S1, based on the harmonic spectrum generated when the converter is connected to the grid circuit, the harmonic signals from the fundamental frequency to the highest order are converted into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase stationary coordinate system through Fourier transform and symmetrical component method.

[0011] Among them, the symmetrical component method is used to decompose any set of asymmetrical signals into three independent vectors of positive sequence, negative sequence and zero sequence, and the signal in the ABC three-phase stationary coordinate system is decomposed into positive sequence signal, negative sequence signal and zero sequence signal. The results are as follows: ; ; ; in, is the positive sequence signal, is a negative sequence signal, is the zero sequence signal, Indicates time, , and Respectively represent the amplitude of the positive sequence signal, the amplitude of the negative sequence signal and the amplitude of the zero sequence signal, , and Respectively represent the phase of the positive sequence signal, the phase of the negative sequence signal and the phase of the zero sequence signal, Indicates the signal frequency.

[0012] positive sequence signal , negative sequence signal All are three-phase symmetrical signals, zero-sequence signals Three signals with the same direction.

[0013] Step S2, performing DQN coordinate transformation on the positive sequence signal, the negative sequence signal and the zero sequence signal, and transforming the positive sequence signal into a positive sequence DC component on the d axis and a positive sequence DC component on the q axis through Park transformation, transforming the negative sequence signal into a negative sequence DC component on the d axis and a negative sequence DC component on the q axis, and transforming 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 arranging them in order of harmonic order and positive, negative and zero sequence relationship, combining and packaging the six DC components, and obtaining a signal matrix in the DQN coordinate system.

[0014] Wherein, in step S2, in the process of converting 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 converting 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: ; ; ; ; ; ; in, 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.

[0015] For the zero-sequence components with the same three-phase structure obtained by the symmetrical component method, their coordinates cannot be directly transformed according to the positive sequence and negative sequence methods.

[0016] In this embodiment, in the process of converting the zero-sequence signal into the zero-sequence DC component on the d-axis and the zero-sequence DC component on the q-axis, the zero-sequence signal of the AC is first used as The shaft signal is created by adding a delay of the fundamental wave period to the AC zero sequence signal. The signal of the axis system (90 degree delayed signal), then, The axis signal is , The axis signal is , and then transform it using the following formula: ; ; ; in, 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.

[0017] In step S2, the expression of the signal matrix in the DQN coordinate system is obtained as follows:

[0018] in, Indicates signal The corresponding signal matrix in the DQN coordinate system, It represents the positive sequence DC component on the d-axis based on the decomposition of the original signal. It represents the positive sequence DC component on the q axis based on the decomposition of the original signal. It represents the negative sequence DC component on the d-axis based on the decomposition of the original signal. It represents the negative sequence DC component on the q axis based on the decomposition of the original signal. It represents the zero-sequence DC component on the d-axis based on the decomposition of the original signal. It represents the zero-sequence DC component on the q-axis based on the decomposition of the original signal. , , They represent the positive sequence first harmonic component, positive sequence second harmonic component, positive sequence n Subharmonic components, , , They represent the positive sequence first harmonic component, positive sequence second harmonic component, positive sequence n Subharmonic components, , , They represent the negative-sequence first harmonic component, negative-sequence second harmonic component, and negative-sequencen Subharmonic components, , , They represent the negative-sequence first harmonic component, negative-sequence second harmonic component, and negative-sequence n Subharmonic components, , , They represent the zero-sequence first harmonic component, zero-sequence second harmonic component, and zero-sequence n Subharmonic components, , , They represent the zero-sequence first harmonic component, zero-sequence second harmonic component, and zero-sequence n Subharmonic components.

[0019] Step S3: Based on the signal matrix in the DQN coordinate system, a signal operation rule in the DQN coordinate system is established.

[0020] The signal operation rules include signal addition calculation, signal subtraction calculation, signal multiplication calculation, signal integration calculation and signal differentiation calculation.

[0021] In step S3, the signal The corresponding signal matrix in the DQN coordinate system Simplify and The corresponding signal matrix in the DQN coordinate system Simplify it and the result is: ; ; ; ; ; ; ; ; ; in, Indicates signal The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the q axis, Indicates signal The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, the second harmonic component, and the nth harmonic component on the q axis; Then, the expression for signal addition calculation is: ; in, Represents the result of signal addition calculation; The expression for signal subtraction calculation is: ; in, Represents the result of signal subtraction calculation; because , The number of rows and columns of are inconsistent and cannot be directly multiplied. In this embodiment, the expression for signal multiplication calculation is: ; ; ; ; ; ; ; ; in, represents the result of signal multiplication calculation, Indicates signal and signal The product of The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the q axis, Indicates signal The n-1 harmonic component on the q axis, Indicates signal The n-1 harmonic component on the d-axis, Indicates signal The n-1 harmonic component on the q axis, Indicates signal The n-1th harmonic component on the d-axis.

[0022] Regarding signal integral calculation and signal differential calculation, in order to simulate the state change of the dynamic system, the bilinear change method is used to convert the continuous signal into a type that can be processed by the digital system. Input signal The system status update is calculated based on the system-related parameters (such as time constant, frequency, etc.). By setting a reasonable sampling step, the signal value at each moment is calculated step by step: the integral operation extracts the signal by accumulation, and the differential operation captures the instantaneous change of the signal by difference. The status is updated moment by moment in a step-by-step cycle, the status of the next moment is calculated, and a feedback mechanism is set to feed back the status of the previous moment to the current input to improve the stability and accuracy of the system.

[0023] Step S4, based on the signal operation rules in the DQN coordinate system, construct the transmission relationship between the modules in the power grid circuit, so as to establish a mathematical transmission model of the converter access system in the DQN coordinate system.

[0024] Specifically, the transfer function or state space model between modules in the power grid circuit is extracted to describe the dynamic characteristics of the converter access system. The traditional state space model is converted to the DQN coordinate system through coordinate transformation, the state variables are redefined, and the mathematical representation of the system dynamic behavior is simplified. The signal transmission relationship of each module is constructed according to the DC signal matrix, and the transmission relationship between each module is expressed by using the signal operation rules based on the DQN coordinate system. An analytical model under the DQN coordinate system is established to realize the simulation modeling of the converter access system.

[0025] The method of this embodiment is simulated and tested as follows: Figure 2 This is a comparison chart of simulation modeling results of a simple power grid circuit. In the simple power grid circuit, the simulation modeling results under the traditional ABC coordinate system, the simulation modeling results of the present invention and the real results are compared and analyzed. Figure 2 It can be seen that the results of the three are highly consistent, indicating that the simulation modeling of the present invention is highly accurate.

[0026] According to the converter access system simulation modeling method of the above embodiment, the converter access system modeling process is directly transferred from the traditional, static ABC coordinate system to multiple rotating DQN coordinate systems. The original frequency domain AC signals in the ABC coordinate system are directly converted into DC signals in the DQN coordinate system, which can not only retain all the spectrum components of the system and improve the accuracy of the system simulation calculation, but also effectively slow down the change rate of the instantaneous value, thereby greatly increasing the simulation step size and improving the system simulation calculation speed, thus having the advantages of fast calculation speed and high calculation accuracy. In addition, the present invention converts all variables into DC signals for calculation, overcomes the nonlinear periodicity problem of converter access to the power system, increases the frequency of harmonic analysis and can be applied to the analysis of unbalanced working conditions of the system, and is easy to modify and optimize according to different scenarios and needs.

[0027] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A converter access system simulation modeling method, characterized in that: include: Step S1, based on the harmonic spectrum generated when the converter is connected to the grid circuit, the harmonic signals from the fundamental frequency to the highest order are converted into positive sequence signals, negative sequence signals and zero sequence signals in the ABC three-phase stationary coordinate system through Fourier transform and symmetrical component method; Step S2, performing DQN coordinate transformation on the positive sequence signal, the negative sequence signal and the zero sequence signal, and transforming the positive sequence signal into a positive sequence DC component on the d axis and a positive sequence DC component on the q axis through Park transformation, transforming the negative sequence signal into a negative sequence DC component on the d axis and a negative sequence DC component on the q axis, and transforming 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 arranging them according to the order of harmonic orders and the positive, negative and zero sequence relationship, combining and packaging the six DC components, and obtaining a signal matrix in the DQN coordinate system; Step S3, establishing a signal operation rule in the DQN coordinate system based on the signal matrix in the DQN coordinate system; Step S4, based on the signal operation rules in the DQN coordinate system, construct the transmission relationship between the modules in the power grid circuit, so as to establish a mathematical transmission model of the converter access system in the DQN coordinate system.

2. The converter access system simulation modeling method according to claim 1, characterized in that: Step S1 satisfies the following formula: ； ； ； in, is the positive sequence signal, is a negative sequence signal, is the zero sequence signal, Indicates time, , and Respectively represent the amplitude of the positive sequence signal, the amplitude of the negative sequence signal and the amplitude of the zero sequence signal, , and Respectively represent the phase of the positive sequence signal, the phase of the negative sequence signal and the phase of the zero sequence signal, Indicates the signal frequency.

3. The converter access system simulation modeling method according to claim 2, characterized in that: In step S2, the positive sequence signal is transformed into a positive sequence DC component on the d axis and a positive sequence DC component on the q axis, and the negative sequence signal is transformed into a negative sequence DC component on the d axis and a negative sequence DC component on the q axis, and the following equation is satisfied: ； ； ； ； ； ； in, 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 converting the zero-sequence signal into the zero-sequence DC component on the d-axis and the zero-sequence DC component on the q-axis, the zero-sequence signal of the AC is first used as The shaft signal is created by adding a delay of the fundamental wave period to the AC zero sequence signal. The signal of the shaft system is, The axis signal is , The axis signal is , and then transform it using the following formula: ； ； ； in, 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 converter access system simulation modeling method according to claim 3, characterized in that: In step S2, the expression of the signal matrix in the DQN coordinate system is obtained as follows: in, Indicates signal The corresponding signal matrix in the DQN coordinate system, It represents the positive sequence DC component on the d-axis based on the decomposition of the original signal. It represents the positive sequence DC component on the q axis based on the decomposition of the original signal. It represents the negative sequence DC component on the d-axis based on the decomposition of the original signal. It represents the negative sequence DC component on the q axis based on the decomposition of the original signal. It represents the zero-sequence DC component on the d-axis based on the decomposition of the original signal. It represents the zero-sequence DC component on the q-axis based on the decomposition of the original signal. , , They represent the positive sequence first harmonic component, positive sequence second harmonic component, positive sequence n Subharmonic components, , , They represent the positive sequence first harmonic component, positive sequence second harmonic component, positive sequence n Subharmonic components, , , They represent the negative-sequence first harmonic component, negative-sequence second harmonic component, and negative-sequence n Subharmonic components, , , They represent the negative-sequence first harmonic component, negative-sequence second harmonic component, and negative-sequence n Subharmonic components, , , They represent the zero-sequence first harmonic component, zero-sequence second harmonic component, and zero-sequence n Subharmonic components, , , They represent the zero-sequence first harmonic component, zero-sequence second harmonic component, and zero-sequence n Subharmonic components.

5. The converter access system simulation modeling method according to claim 4, characterized in that: In step S3, the signal operation rules at least include signal addition calculation, signal subtraction calculation, and signal multiplication calculation; First, the signal The corresponding signal matrix in the DQN coordinate system Simplify and The corresponding signal matrix in the DQN coordinate system Simplify it and the result is: ； ； ； ； ； ； ； ； ； in, Indicates signal The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the q axis, Indicates signal The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, the second harmonic component, and the nth harmonic component on the q axis; Then, the expression for signal addition calculation is: ； in, Indicates the result of signal addition calculation; The expression for signal subtraction calculation is: ； in, Represents the result of signal subtraction calculation; The expression for signal multiplication calculation is: ； ； ； ； ； ； ； ； in, represents the result of signal multiplication calculation, Indicates signal and signal The product of The DC component of , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the d-axis, , , Respectively represent signals The first harmonic component, second harmonic component, and nth harmonic component on the q axis, Indicates signal The n-1 harmonic component on the q axis, Indicates signal The n-1 harmonic component on the d-axis, Indicates signal The n-1 harmonic component on the q axis, Indicates signal The n-1th harmonic component on the d-axis.

6. The converter access system simulation modeling method according to claim 1, characterized in that: Step S4 specifically includes: The transfer function or state space model between modules in the power grid circuit is extracted to describe the dynamic characteristics of the converter access system. The traditional state space model is converted to the DQN coordinate system through coordinate transformation, the state variables are redefined, and the mathematical representation of the system dynamic behavior is simplified. The signal transmission relationship of each module is constructed according to the DC signal matrix. The signal operation rules based on the DQN coordinate system are used to express the transmission relationship between the modules. An analytical model under the DQN coordinate system is established to realize the simulation modeling of the converter access system.

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