A method and system for evaluating time-varying harmonic transfer relationship of a power distribution system

Abstract

The application discloses a kind of time-varying harmonic transmission relationship evaluation method and system of power distribution system, method includes: constructing the relationship of each frequency harmonic current and voltage at the grid-connected port of power electronic equipment, and the relationship of different frequency harmonics of each node of power distribution system;When the power electronic equipment connected to the nth node in the system injects harmonic current into the system, iteratively solve the harmonic voltage variation and harmonic current variation of each node in the power distribution system caused thereby;Establish the harmonic transmission relationship of each node of power distribution system considering the time-varying characteristics of harmonic;When any node injects time-varying harmonic current into the power distribution system, according to the frequency of injected current, the time-varying law of harmonic voltage and current generated thereby at other nodes is determined, and the harmonic current deviation generated by the response of the node affected by other nodes.The application solves the analytical problem of the influence source of multi-node harmonic voltage when multi-node harmonic current is injected simultaneously.

Description

Technical Field

[0001] This invention relates to the field of harmonic analysis technology for power distribution systems, and in particular to a method and system for evaluating time-varying harmonic transmission relationships in power distribution systems. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the large-scale application of power electronic equipment in power distribution systems, harmonic disturbance sources are more widely distributed within these systems, leading to increasingly serious harmonic problems. While generating harmonics, power electronic equipment also exhibits significant dynamic interaction with the power distribution network, drastically altering the system's harmonic propagation characteristics. The harmonics generated by power electronic equipment are influenced by both their own emission characteristics and those of other equipment in the power distribution system. After propagating through the power distribution system lines, they generate new harmonic components, further exacerbating the harmonic problem. Severe harmonic distortion can lead to issues such as renewable energy disconnection from the grid and equipment burnout.

[0004] Assessing the time-varying harmonic propagation characteristics of power distribution systems is fundamental and crucial for analyzing the harmonic variation patterns at each node within the system. Compared to time-domain analysis, harmonic frequency-domain analysis methods offer faster solution speeds, lower computational complexity, and the ability to analyze harmonic propagation characteristics. However, existing harmonic frequency-domain analysis methods for power distribution systems typically only focus on changes in harmonic states. This approach ignores the variations at each node within the system under harmonic current injection conditions, making it difficult to clarify the extent of harmonic impact and the system's resilience. Consequently, it fails to guide mitigation measures and seriously threatens the safe and stable operation of the power distribution system. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a method and system for evaluating the time-varying harmonic propagation relationship in power distribution systems. This method fully considers the superimposed effects of the harmonic generation and response characteristics of power electronic devices, and evaluates the propagation relationship of harmonic voltages and currents at various frequencies at each node of the system after the power electronic devices are connected. This provides theoretical support for clarifying the propagation law of harmonics in the system and the system's harmonic tolerance capability.

[0006] In some implementations, the following technical solutions are adopted:

[0007] A method for evaluating the time-varying harmonic propagation relationship of a power distribution system includes:

[0008] The power distribution system is modeled as a multivariable input and multivariable output control system. The multivariable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multivariable output is the harmonic voltage of each node.

[0009] Based on the typical topology of power electronic equipment, the relationship between harmonic current and voltage at each frequency at the grid connection port of power electronic equipment is constructed, as well as the relationship between harmonics of different frequencies at each node of the power distribution system.

[0010] Based on the above relationship, when the power electronic equipment connected to the nth node in the system injects harmonic current into the system, the harmonic voltage change and harmonic current change of each node in the power distribution system caused by this are iteratively solved.

[0011] Based on the calculation results of harmonic voltage and harmonic current changes, the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics is established.

[0012] When any node injects a time-varying harmonic current into the power distribution system, the time-varying laws of harmonic voltages and currents of other nodes are determined based on the frequency of the injected current, as well as the harmonic current deviation of that node caused by the influence of other nodes.

[0013] As an optional approach, the relationship between harmonic currents and voltages at the grid connection ports of power electronic devices is constructed, specifically as follows:

[0014] ΔV g,n =Z n ΔI g,n ;

[0015] Among them, Z n Let ΔV be the harmonic coupling impedance matrix of the nth node in the system, used to describe the conversion relationship between harmonic currents and harmonic voltages of different frequencies; g,n This is a matrix composed of harmonic voltages of various frequencies on the grid side of power electronic equipment; ΔI g,n It is a matrix composed of harmonic currents of various frequencies on the grid side of power electronic equipment.

[0016] As an optional approach, the relationship between different frequency harmonics of each node in the power distribution system is constructed, specifically as follows:

[0017]

[0018] Among them, [I gh [U] represents the matrix formed by the h-th harmonic currents at each node; gh [Y] represents the matrix formed by the h-th harmonic voltages of each node; Bh ] represents the h-th harmonic equivalent admittance matrix between nodes, where h = 1, 3, ..., H, and H is the highest harmonic order considered.

[0019] As an optional approach, when the power electronic equipment connected to the nth node in the system injects harmonic current into the system, the resulting changes in harmonic voltage and harmonic current at each node in the power distribution system are iteratively solved. Specifically:

[0020] The relationship between harmonic currents and voltages at the grid connection ports of power electronic devices, and the relationship between harmonics of different frequencies at various nodes of the power distribution system, are combined to obtain the multi-frequency harmonic coupling relationship model Y of the power distribution system.

[0021] For the power electronic device connected to the nth node in the system, a harmonic current ΔI is injected into the system. g,n Using the multi-frequency harmonic coupling relationship model Y of the power distribution system, the harmonic voltage [U] of each node in the power distribution system is obtained. gh ] (1) Based on the harmonic voltages [U] of each node in the power distribution system gh ] (1) Using the multi-frequency harmonic coupling relationship model Y of the power distribution system, the harmonic currents [I] at each node in the power distribution system are obtained. gh ] (1) At this time, the other nodes will also affect the harmonic current of the nth node, and the resulting harmonic current deviation is denoted as δI. g,n (1) The superscript (1) indicates the first iteration.

[0022] Repeat the above process until the harmonic voltage [U] is reached in two consecutive iterations. gh ] (i) with [U gh ] (i+1) The convergence condition is met, and the harmonic power flow iteration process ends; the harmonic voltage change at each node in the power distribution system is recorded as [ΔU]. gh The change in harmonic current at each node is [ΔI]. gh ], where the harmonic current deviation of the nth node caused by the influence of other nodes is δI. g,n .

[0023] As an optional approach, a harmonic transmission relationship is established for each node of the power distribution system, taking into account the time-varying characteristics of harmonics. Specifically:

[0024] Based on the calculation results of harmonic voltage and harmonic current changes, the harmonic transmission relationship of each node in the power distribution system is constructed.

[0025] Considering the time-varying characteristics of the harmonic current injected into each node of the power distribution system, a time sequence matrix of the harmonic current injected into each node is established.

[0026] By utilizing the time-series matrix of the harmonic current injected into each node, the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics is established.

[0027] As an optional solution, the harmonic transmission relationship of each node in the power distribution system is constructed, specifically as follows:

[0028] [ΔU gh ] = M h [ΔI gh ];

[0029] Among them, M h The transmission matrix of h-th harmonic current and voltage at each node of the power distribution system; [ΔU gh ] and [ΔI gh These represent the changes in harmonic voltage and harmonic current at each node in the power distribution system at the end of the iteration.

[0030] As an optional approach, a timing matrix for the injected harmonic current at each node is established, specifically as follows:

[0031] For the power electronic equipment connected to the nth node, the time-series variation matrix ΔI of its harmonic current is... gT,n for:

[0032]

[0033] in, Indicates t i The harmonic current injected into the system by the power electronic device at node n at time t1~t n This indicates the time period being considered.

[0034] As an optional approach, a harmonic transmission relationship is established for each node of the power distribution system, taking into account the time-varying characteristics of harmonics. Specifically:

[0035] [ΔU gTh ] = M Th [ΔI gTh ];

[0036] Among them, M Th For the time-varying transfer matrix of h-th harmonic current and voltage at each node of the power distribution system, [ΔU gTh ] and [ΔI gTh [ ] are matrices composed of time-varying harmonic voltages and time-varying harmonic currents at each node in the power distribution system.

[0037] In other embodiments, the following technical solutions are adopted:

[0038] A system for evaluating the time-varying harmonic propagation relationship of a power distribution system includes:

[0039] The model building module is used to model the power distribution system as a multivariable input and multivariable output control system. The multivariable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multivariable output is the harmonic voltage of each node.

[0040] The relationship building module is used to construct the relationship between harmonic currents and voltages at the grid connection ports of power electronic devices, as well as the relationship between harmonics of different frequencies at various nodes of the power distribution system, based on the typical topology of power electronic devices.

[0041] The iterative solution module is used to iteratively solve the harmonic voltage and harmonic current changes of each node in the power distribution system caused by the harmonic current injected into the system by the power electronic equipment connected to the nth node, based on the above relationship; and to establish the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics based on the calculation results of the harmonic voltage and harmonic current changes.

[0042] The evaluation module is used to determine the time-varying laws of harmonic voltages and currents of other nodes and the harmonic current deviations of the node caused by the influence of other nodes when any node injects time-varying harmonic current into the power distribution system based on the frequency of the injected current.

[0043] In other embodiments, the following technical solutions are adopted:

[0044] A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded and executed by the processor to evaluate the time-varying harmonic propagation relationship of the power distribution system described above.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] (1) The present invention models the power distribution system as a control system with multiple inputs and multiple outputs. Thus, the mapping relationship between multi-node harmonic current and harmonic voltage can be established by accumulating the mapping relationship between a single variable and multiple variables, which simplifies the modeling process of harmonic transmission relationship in the power distribution system and solves the problem of analyzing the source of influence of multi-node harmonic voltage when multiple harmonic currents are injected at the same time.

[0047] (2) This invention constructs the coupling relationship between harmonic currents and voltages at the grid connection port of power electronic equipment, and combines the relationship between harmonics of different frequencies at each node of the power distribution system. It uses an iterative solution method to realize the synchronous calculation of multi-node multi-frequency harmonics in the power distribution system. While ensuring the accuracy of the calculation, it greatly improves the solution efficiency. It is extremely suitable for harmonic analysis of complex power distribution systems with large-scale power electronic equipment access.

[0048] (3) At the end of the iteration process, the present invention can obtain the change of harmonic voltage and the change of harmonic current of each node in the power distribution system, as well as the response component of the harmonic current of the power electronic equipment under the influence of the system harmonic voltage. Thus, the superposition effect of the harmonic generation and response generation characteristics of the power electronic equipment itself is analyzed, overcoming the problem of inaccurate evaluation of harmonic transmission relationship caused by ignoring the response component in the traditional method.

[0049] (4) This invention takes into account the time-varying characteristics of the harmonic current injected into each node of the power distribution system, making it more suitable for power distribution systems with rapidly changing operating states and continuous fluctuations in the background, thus avoiding the impact of using a unified model on the accuracy of harmonic transmission assessment of the power distribution system.

[0050] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0051] Figure 1 This is a flowchart of the method for evaluating the time-varying harmonic transmission relationship of a power distribution system in an embodiment of the present invention;

[0052] Figure 2 This is a schematic diagram of a multivariable input and multivariable output control system for a power distribution system in an embodiment of the present invention;

[0053] Figure 3 This is a schematic diagram of a typical topology of a power electronic device in an embodiment of the present invention;

[0054] Figure 4 This is a schematic diagram of a typical control method for power electronic equipment in an embodiment of the present invention;

[0055] Figure 5 This is a flowchart of the iterative solution for harmonic power flow in the power distribution system in an embodiment of the present invention. Detailed Implementation

[0056] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0057] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0058] Example 1

[0059] In one or more embodiments, a method for evaluating the time-varying harmonic propagation relationship of a power distribution system is disclosed, combined with Figure 1 Specifically, it includes the following processes:

[0060] S1: Model the power distribution system as a multivariable input and multivariable output control system, where the multivariable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multivariable output is the harmonic voltage of each node.

[0061] The control system diagram is as follows Figure 2 As shown, the system has N nodes. Without considering harmonic currents generated by power electronic devices, the Newton-Raphson algorithm is used to calculate the fundamental power flow of the distribution system, and the power and voltage of each node are used as reference values ​​for the operating power and voltage of the power electronic devices. For the nth node in the system, the fundamental operating voltage of the connected power electronic device is V. g,n The apparent power during operation is S. n .

[0062] S2: Based on the typical topology of power electronic equipment, construct the relationship between harmonic current and voltage at each frequency at the grid connection port of the power electronic equipment, as well as the relationship between harmonics of different frequencies at each node of the power distribution system.

[0063] Typical topologies of power electronic devices include: Figure 3 As shown, based on the typical topology of power electronic devices, the changes in harmonic voltage at the nodes connected to the power electronic devices are analyzed when the harmonic current generated by the power electronic devices changes.

[0064] For any power electronic device connected to any node in the system, the harmonic current it generates and the harmonic voltage at the grid connection point satisfy the following relationship:

[0065] ΔV cf -ΔV g =Z g ΔI g ;

[0066] ΔV c -ΔV cf =Z c ΔI c ;

[0067] ΔV cf =(ΔI) c -ΔI g )Z cf ;

[0068] Where, ΔV g ΔVc ΔV cf This matrix, ΔI, consists of harmonic voltages of various frequencies from the grid side, rectifier side, and AC filter capacitor of the power electronic equipment. g ΔI c Z is a matrix composed of harmonic currents of various frequencies generated on the grid side and rectifier side of power electronic equipment. g Z represents the impedance of the power electronic equipment on the grid side. c Z represents the converter-side impedance of the power electronic equipment. cf This is the equivalent impedance of the AC filter capacitor.

[0069] For this power electronic device, the matrix ΔV composed of harmonic voltages of each frequency on the DC side dc The matrix ΔI composed of harmonic currents of various frequencies dc The following relationship must be satisfied:

[0070] ΔV dc =(ΔI) s -ΔI dc )Z dc ;

[0071] Where, ΔI s Z is a matrix composed of equivalent harmonic source currents of power electronic equipment. dc This is the equivalent impedance on the DC side of the power electronic equipment.

[0072] For this power electronic device, the matrix composed of harmonic voltages of each frequency on both the AC and DC sides and the matrix composed of harmonic currents of each frequency satisfy the following relationship:

[0073]

[0074] Where S represents the conversion relationship of harmonic voltage and current at various frequencies on both the AC and DC sides of the power electronic device, which is related to the control method of the power electronic device. Typical control methods for power electronic devices are as follows: Figure 4 As shown, by taking the operating voltage, operating current and operating power of the power electronic device as input, the conversion relationship S of the harmonic voltage and current of each frequency on both the AC and DC sides of the power electronic device can be output.

[0075] Based on the above conversion relationship, the relationship between the harmonic currents and voltages at the grid connection port of the power electronic equipment connected to the nth node in the system can be obtained as follows:

[0076] ΔV g,n =Z n ΔI g,n ;

[0077] Among them, Z nZ is the harmonic coupling impedance matrix of the nth node in the system, used to describe the conversion relationship between harmonic currents and harmonic voltages of different frequencies; n The method for determining ΔV is already publicly available in existing technology, and therefore will not be described in detail. g,n This is a matrix composed of harmonic voltages of various frequencies on the grid side of power electronic equipment, with dimensions consistent with the harmonic frequency H under consideration; ΔI g,n It is a matrix composed of harmonic currents of various frequencies on the grid side of power electronic equipment, and its dimensions are consistent with the harmonic frequency H under consideration.

[0078] In this embodiment, based on the node correlation relationship and the equivalent impedance of each node in the power distribution system, the relationship of different frequency harmonics of each node in the power distribution system is constructed as follows:

[0079]

[0080] Among them, [I gh [U] represents the matrix formed by the h-th harmonic currents at each node; gh [Y] represents the matrix formed by the h-th harmonic voltages of each node; Bh ] represents the h-th harmonic equivalent admittance matrix between nodes, where h = 1, 3, ..., H, and H is the highest harmonic order considered.

[0081] S3: Based on the above relationship, when the power electronic equipment connected to the nth node in the system injects harmonic current into the system, the harmonic voltage change and harmonic current change of each node in the power distribution system caused by this are solved iteratively.

[0082] In this embodiment, considering the relationship between different frequency harmonics at each node of the power distribution system, and the relationship between harmonic currents and voltages at the grid connection ports of power electronic devices, when the power electronic device connected to the nth node injects a harmonic current ΔI into the system... g,n At that time, the resulting changes in harmonics at various frequencies in the system can be solved iteratively, such as Figure 5 As shown, the specific steps are as follows:

[0083] S301: Based on the relationship between different frequency harmonics at each node of the power distribution system and the relationship between harmonic current and voltage at the grid connection port of power electronic equipment, the multi-frequency harmonic coupling relationship model Y of the power distribution system can be obtained by combining the following:

[0084] S302: For the power electronic equipment connected to the nth node in the system, a harmonic current ΔI is injected into the system. g,n Using the multi-frequency harmonic coupling relationship model Y of the power distribution system, the harmonic voltage [U] of each node in the power distribution system can be obtained. gh ] (1) The superscript (1) indicates the first iteration.

[0085] S303: Based on the harmonic voltage of each node in the power distribution system [U] gh ] (1) Using the multi-frequency harmonic coupling relationship model Y of the power distribution system, the harmonic currents [I] at each node in the power distribution system can be obtained. gh ] (1) At this time, other nodes will also affect the harmonic current of the nth node. Assume that the initial state of the harmonic current of each node in the power distribution system is [I gh ] (0) After the first iteration, the harmonic current becomes [I gh ] (1) ,[ΔI gh ] (1) =[I gh ] (1) -[I gh ] (0) Then the variable [ΔI] gh ] (1) The element corresponding to the nth row is δI. g,n (1) .

[0086] S304: Repeat steps S302 and S303 until the harmonic voltage [U] of two adjacent iterations is reached. gh ] (i) with [U gh ] (i+1) The convergence condition max(|[U] is satisfied. gh ] (i) –[U gh ] (i+1) If |) < ε (ε represents the harmonic power flow iteration convergence error), it indicates that the harmonic power flow iteration process has ended;

[0087] S305: At the end of the iteration process, the change in harmonic voltage at each node in the power distribution system is [ΔU]. gh The change in harmonic current at each node is [ΔI]. gh ], where the harmonic current deviation of the nth node caused by the influence of other nodes is δI. g,n [ΔU] gh [ΔI] is the difference between the last harmonic voltage and the harmonic voltage at the time of the first iteration. gh [ΔI] is the difference between the last harmonic current and the harmonic current during the first iteration. gh The element corresponding to the nth row in the diagram is δI. g,n .

[0088] S4: Based on the calculation results of harmonic voltage and harmonic current changes, establish the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics.

[0089] In this embodiment, considering the case where harmonic currents are injected into N nodes of the power distribution system, based on the harmonic power flow calculation results of the power distribution system, the harmonic transmission relationship of each node in the power distribution system can be constructed as follows:

[0090] [ΔU gh ] = M h [ΔI gh ];

[0091] Among them, M h This is the transmission matrix for the h-th harmonic current and voltage at each node of the power distribution system. Because [ΔU gh ] and [ΔI gh It is known that M can be solved using data fitting methods (such as least squares method, machine learning methods, etc.). h .

[0092] For the power electronic equipment connected to the nth node, its harmonic current is ΔI. g,n +δI g,n Due to the change δI g,n Harmonic current ΔI g,n There is a nonlinear relationship, therefore the change δI g,n With harmonic current ΔI g,n The relationship can be obtained through fitting. The specific fitting method can be implemented using polynomial fitting, which is easily achievable by those skilled in the art.

[0093] Considering the time-varying characteristics of the harmonic current injected into each node of the power distribution system, a time-series matrix of the harmonic current injected into each node is established. For the power electronic equipment connected to the nth node, its harmonic current time-series variation matrix ΔI is... gT,n as follows:

[0094]

[0095] In the formula, Indicates t i The harmonic current injected into the system by the power electronic device at node n at time t1~t n This indicates the time period being considered.

[0096] Using the harmonic current time-series variation matrix of each node, the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics can be established as follows:

[0097] [ΔU gTh ] = M Th [ΔI gTh ]

[0098] Among them, M Th For the time-varying transfer matrix of h-th harmonic current and voltage at each node of the power distribution system, [ΔU gTh] and [ΔI gTh [ ] are matrices composed of time-varying harmonic voltages and time-varying harmonic currents at each node in the power distribution system.

[0099] In this embodiment, the time-varying matrix can be divided into equal time periods according to the harmonic assessment requirements. For example, for data with high time requirements, each hour can be divided into a time period; for data with low time requirements, each 4-hour period can be divided into a time period.

[0100] S5: When any node injects a time-varying harmonic current into the power distribution system, based on the frequency h of the injected current, the time-varying transfer matrix of the h-th harmonic current and voltage of each node in the power distribution system can be used to clearly determine the time-varying laws of the harmonic voltage and current of other nodes, as well as the harmonic current deviation of the node caused by the influence of other nodes.

[0101] Example 2

[0102] In one or more embodiments, a time-varying harmonic propagation relationship evaluation system for power distribution systems is disclosed, specifically including:

[0103] The model building module is used to model the power distribution system as a multivariable input and multivariable output control system. The multivariable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multivariable output is the harmonic voltage of each node.

[0104] The relationship building module is used to construct the relationship between harmonic currents and voltages at the grid connection ports of power electronic devices, as well as the relationship between harmonics of different frequencies at various nodes of the power distribution system, based on the typical topology of power electronic devices.

[0105] The iterative solution module is used to iteratively solve the harmonic voltage and harmonic current changes of each node in the power distribution system caused by the harmonic current injected into the system by the power electronic equipment connected to the nth node, based on the above relationship; and to establish the harmonic transmission relationship of each node in the power distribution system considering the time-varying characteristics of harmonics based on the calculation results of the harmonic voltage and harmonic current changes.

[0106] The evaluation module is used to determine the time-varying laws of harmonic voltages and currents of other nodes and the harmonic current deviations of the node caused by the influence of other nodes when any node injects time-varying harmonic current into the power distribution system based on the frequency of the injected current.

[0107] The specific implementation methods of the above modules are the same as those in Example 1, and will not be described in detail again.

[0108] Example 3

[0109] In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions adapted to be loaded by the processor and executed by the time-varying harmonic propagation relationship evaluation method for power distribution systems described in Embodiment 1.

[0110] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0111] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0112] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0113] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for evaluating time-varying harmonic transfer relationship of a power system with distributed generation, characterized in that, The method comprises the following steps: Modeling the power utilization system as a multivariable input and multivariable output control system, wherein the multivariable input is the harmonic current generated by the nonlinear power electronic device connected to each node, and the multivariable output is the harmonic voltage of each node; Based on the typical topology of the power electronic device, the relationship between the harmonic current and voltage at the grid-connected port of the power electronic device and the relationship between the harmonic of different frequencies at each node of the power utilization system are constructed; Based on the above relationship, when the power electronic equipment connected to the system injects harmonic current, the harmonic voltage and current changes of each node in the power system are solved iteratively. n Based on the above relationship, when the power electronic equipment connected to the system injects harmonic current, the harmonic voltage and current changes of each node in the power system are solved iteratively. Based on the calculation results of the harmonic voltage variation and the harmonic current variation, the harmonic transmission relationship of each node of the power utilization system considering the time-varying characteristics of the harmonic is established; When time-varying harmonic current is injected into the power utilization system from any node, the time-varying rules of the harmonic voltage and current of other nodes generated by the injected current frequency and the harmonic current deviation of the node affected by other nodes are determined; The relationship between the harmonic current and voltage at the grid-connected port of the power electronic device is constructed, and the relationship between the harmonic of different frequencies at each node of the power utilization system is constructed. ； wherein, Z n is the harmonic coupling impedance matrix of the i-th node in the system, used to describe the conversion relationship between the harmonic currents and the harmonic voltages of different frequencies; n is the harmonic coupling impedance matrix of the i-th node in the system, used to describe the conversion relationship between the harmonic currents and the harmonic voltages of different frequencies; is the matrix composed of the harmonic voltages of different frequencies at the grid side of the power electronic equipment; is the matrix composed of the harmonic currents of different frequencies at the grid side of the power electronic equipment; The relationship between the harmonic current and voltage at the grid-connected port of the power electronic device is constructed, and the relationship between the harmonic of different frequencies at each node of the power utilization system is constructed. ； in,[ I gh ] represents each node h The matrix formed by the subharmonic currents; U gh ] represents each node h The matrix formed by the subharmonic voltages; Y Bh ] indicates the relationship between nodes h The equivalent admittance matrix for the second harmonic is given by h = 1, 3, ..., H, where H is the highest harmonic order considered.

2. The method for evaluating the time-varying harmonic propagation relationship of a power distribution system as described in claim 1, characterized in that, When the system is the n When the power electronic equipment connected to a node injects harmonic current into the system, the resulting changes in harmonic voltage and harmonic current at each node in the power distribution system are iteratively solved. Specifically: The relationship between harmonic currents and voltages of each frequency at the grid-connected port of power electronic equipment and the relationship between harmonics of each frequency at each node of the power utilization system are solved to obtain a multi-frequency harmonic coupling relationship model of the power utilization system Y ; For the first node in the system n injects harmonic current Δ I g,n , using the multi-frequency harmonic coupling relationship model of the power utilization system Y , the harmonic voltage of each node in the power utilization system is obtained U gh ] (1) U gh ] (1) , using the multi-frequency harmonic coupling relationship model of the power utilization system Y , the harmonic current of each node in the power utilization system is obtained I gh ] (1) At this time, other nodes will also affect the harmonic current of the first node, and the harmonic current deviation generated in response is denoted as Δ n The relationship between the harmonic current and voltage at the grid-connected port of the power electronic device is constructed, and the relationship between the harmonic of different frequencies at each node of the power utilization system is constructed. g,n (1) ; the superscript (1) indicates the first iteration process;​​ The above process is repeated until the harmonic voltage of two adjacent iteration processes U gh ] (i) and U gh ] (i+1) , the convergence condition is met, the harmonic flow iteration process is ended, the harmonic voltage variation of each node in the power utilization system is recorded as [Δ U gh ], the harmonic current variation of each node is [Δ I gh ], wherein the harmonic current deviation of the first n node affected by other nodes is Based on the calculation results of the harmonic voltage variation and the harmonic current variation, the harmonic transmission relationship of each node of the power utilization system considering the time-varying characteristics of the harmonic is established. g,n .

3. The method for evaluating the time-varying harmonic propagation relationship of a power distribution system as described in claim 1, characterized in that, The time sequence matrix of the harmonic current injected into each node of the power utilization system is established considering the time-varying characteristics of the harmonic current injected into each node of the power utilization system. The time sequence matrix of the harmonic current injected into each node of the power utilization system is established considering the time-varying characteristics of the harmonic current injected into each node of the power utilization system. The time sequence matrix of the harmonic current injected into each node of the power utilization system is established considering the time-varying characteristics of the harmonic current injected into each node of the power utilization system. The method comprises the following steps:

4. The method for evaluating the time-varying harmonic propagation relationship of a power distribution system as described in claim 3, characterized in that, The model construction module is used for modeling the power utilization system as a multivariable input and multivariable output control system, wherein the multivariable input is the harmonic current generated by the nonlinear power electronic device connected to each node, and the multivariable output is the harmonic voltage of each node; ； wherein, M h for each node of the power distribution system h sub-harmonic current and voltage transfer matrix; and respectively the harmonic voltage variation and the harmonic current variation for each node of the power distribution system at the end of the iteration.

5. The method of claim 3, wherein the time-varying harmonic transfer relationship of the power system is evaluated by solving the following equation: ###0001### where, V is the voltage of the power system, I is the current of the power system, Z is the impedance of the power system, and j is the imaginary unit. The relationship construction module is used for constructing the relationship between the harmonic current and voltage at the grid-connected port of the power electronic device and the relationship between the harmonic of different frequencies at each node of the power utilization system based on the typical topology of the power electronic device; For the first n node to access power electronic devices, the timing change matrix Δ I gT,n is: ； wherein, represents t i the node at the moment n harmonic current injected by the power electronics device at the node, t 1~ t n to denote the time period under consideration.

6. The method for evaluating the time-varying harmonic propagation relationship of a power distribution system as described in claim 3, characterized in that, Based on the calculation results of the harmonic voltage variation and the harmonic current variation, the harmonic transmission relationship of each node of the power utilization system considering the time-varying characteristics of the harmonic is established; ； wherein, M Th for each node of the power distribution system h the time-varying sub-harmonic current and voltage transfer matrix, [Δ U gTh the time-varying harmonic voltage and time-varying harmonic current matrices, [Δ I gTh the time-varying harmonic voltage and time-varying harmonic current matrices, [Δ 7. A power system time-varying harmonic transfer relationship evaluation system, characterized by, The evaluation module is used for determining the time-varying rules of the harmonic voltage and current of other nodes generated by the injected current frequency and the harmonic current deviation of the node affected by other nodes when time-varying harmonic current is injected into the power utilization system from any node. The relationship between the harmonic current and voltage at the grid-connected port of the power electronic device is constructed, and the relationship between the harmonic of different frequencies at each node of the power utilization system is constructed. The relationship between the harmonic current and voltage at the grid-connected port of the power electronic device is constructed, and the relationship between the harmonic of different frequencies at each node of the power utilization system is constructed. The iterative solution module is used to solve the problem based on the above relationships, when the system's... n When the power electronic equipment connected to a node injects harmonic current into the system, the harmonic voltage and harmonic current changes of each node in the power distribution system caused by this are iteratively solved. The instructions are adapted to be loaded and executed by the processor to perform the power utilization system time-varying harmonic transmission relationship evaluation method according to any one of claims 1-6. ​ ​ ； wherein, Z n is the harmonic coupling impedance matrix of the i-th node in the system, used to describe the conversion relationship between the harmonic currents and the harmonic voltages of different frequencies; n is the harmonic coupling impedance matrix of the i-th node in the system, used to describe the conversion relationship between the harmonic currents and the harmonic voltages of different frequencies; is the matrix composed of the harmonic voltages of different frequencies at the grid side of the power electronic equipment; is the matrix composed of the harmonic currents of different frequencies at the grid side of the power electronic equipment; ​ ； where, I gh represents the matrix of the harmonic voltage at each node h formed by the sub-harmonic currents; where, U gh represents the matrix of the harmonic voltage at each node h formed by the sub-harmonic voltages; where, Y Bh represents the matrix of the harmonic admittance between each node h formed by the sub-harmonic equivalent admittance, h = 1, 3,..., H, H being the highest harmonic number considered.

8. A terminal device comprising a processor and a memory, the processor configured to implement instructions; the memory configured to store a plurality of instructions, the terminal device characterized by, ​

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