Method and system for evaluating time-varying harmonic transfer relation of power distribution and utilization system

Abstract

The invention discloses a power distribution and utilization system time-varying harmonic transfer relation evaluation method and system. The method comprises the following steps: constructing a relation between harmonic current and voltage of each frequency at a grid-connected port of power electronic equipment and a relation between harmonics of different frequencies of each node of a power distribution and utilization system; when the power electronic equipment connected to the nth node in the system injects harmonic current into the system, the harmonic voltage variation and harmonic current variation of each node in the power distribution and utilization system caused by the harmonic current are iteratively solved; establishing a harmonic transfer relation of each node of the power distribution and utilization system considering the harmonic time-varying characteristic; when any node injects time-varying harmonic current into the power distribution and utilization system, the time-varying rule of harmonic voltage and current of other nodes generated according to the frequency of the injected current and the harmonic current deviation generated when the node is influenced and responded by other nodes are determined. According to the invention, the problem of analysis of the influence source of the multi-node harmonic voltage when the multi-node harmonic current is injected at the same time is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of harmonic analysis of power distribution systems, and in particular to a method and system for evaluating time-varying harmonic transfer relations in power distribution systems. Background Art

[0002] The statements in this section merely provide 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 the power distribution system, the sources of harmonic disturbances are more widely distributed in the system, and the harmonic problem of the power distribution system is becoming increasingly serious. While generating harmonics, power electronic equipment has significant dynamic interactions with the distribution network, which has caused a huge change in the harmonic propagation characteristics of the system. The harmonics generated by power electronic equipment are affected by both the emission characteristics of the power electronic equipment itself and the harmonics generated by other equipment in the power distribution system. After propagation through the power distribution system lines, new harmonic components are generated in response, resulting in the continued aggravation of the harmonic problem in the power distribution system. Severe harmonic distortion may cause problems such as new energy disconnection from the grid and equipment burning.

[0004] Evaluating the time-varying harmonic transfer characteristics of the power distribution system is the basis and key to analyzing the harmonic change rules of each node in the system. Compared with time domain analysis, the harmonic frequency domain analysis method has a fast solution speed and low computational complexity, and can analyze the harmonic propagation characteristics. However, the existing harmonic frequency domain analysis methods of the power distribution system usually only focus on the changes in the harmonic state. This method ignores the change rules of each node in the system under the condition of harmonic current injection, making it difficult to clarify the impact of harmonics on the system and the tolerance of the system, thus failing to guide the implementation of governance measures, which seriously threatens the safe and stable operation of the power distribution system. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a method and system for evaluating the time-varying harmonic transfer relationship of a power distribution system, which fully considers the superimposed influence of the harmonic generation and response generation characteristics of the power electronic equipment itself, and evaluates the transfer relationship of the harmonic voltage and current of each frequency at each node of the system after the power electronic equipment is connected, which can provide theoretical support for clarifying the propagation law of harmonics in the system and the harmonic tolerance capability of the system.

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

[0007] A method for evaluating time-varying harmonic transfer relations in a power distribution system, comprising:

[0008] The power distribution system is modeled as a control system with multi-variable input and multi-variable output, wherein the multi-variable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multi-output variable is the harmonic voltage of each node;

[0009] Based on the typical topological structure of power electronic equipment, the relationship between the harmonic current and voltage of each frequency at the grid-connected port of power electronic equipment, as well as the relationship between the harmonics of different frequencies at each node of the power distribution system are constructed;

[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 variation and harmonic current variation, the harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics.

[0012] When any node injects time-varying harmonic current into the power distribution system, the time-varying laws of harmonic voltages and currents of other nodes generated thereby are determined according to the frequency of the injected current, as well as the harmonic current deviation caused by the response of this node to the influence of other nodes.

[0013] As an optional solution, the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment is constructed, specifically:

[0014] ΔV g,n =Z n ΔI g,n ;

[0015] Among them, Z n is the harmonic coupling impedance matrix of the nth node in the system, which is used to describe the conversion relationship between harmonic currents and harmonic voltages of different frequencies; ΔV g,n is the matrix composed of the harmonic voltages of various frequencies on the grid side of the 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 solution, the relationship between the harmonics of different frequencies at each node of the power distribution system is constructed, specifically:

[0017]

[0018] Among them, [I gh ] represents the matrix composed of the hth harmonic current of each node; [U gh ] represents the matrix composed of the hth harmonic voltage of each node; [Y Bh ] represents the hth harmonic equivalent admittance matrix between each node, h = 1, 3, ..., H, H is the highest harmonic order considered.

[0019] As an optional solution, 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, specifically:

[0020] The relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, and the relationship between the harmonics of different frequencies at each node 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 equipment connected to the nth node in the system, the 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 of each node in the power distribution system [U gh ] (1) , 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 current of each node in the power distribution system [I gh ] (1) , at this time, other nodes will also affect the harmonic current of the nth node, and the harmonic current deviation generated by this response is recorded as δI g,n (1) ; The superscript (1) indicates the first iteration process;

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

[0023] As an optional solution, the harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics, specifically:

[0024] Based on the calculation results of harmonic voltage variation and harmonic current variation, the harmonic transfer relationship of each node in the power distribution system is constructed;

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

[0026] The harmonic transfer relationship of each node in the power distribution system is established by using the timing matrix of harmonic current injected into each node, considering the time-varying characteristics of harmonics.

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

[0028] [ΔU gh ]=M h [ΔI gh ];

[0029] Among them, M h is the hth harmonic current and voltage transfer matrix of each node in the power distribution system; [ΔU gh ] and [ΔI gh ] are the harmonic voltage change and harmonic current change of each node in the power distribution system at the end of iteration.

[0030] As an optional solution, a timing matrix for injecting harmonic current into each node is established, specifically:

[0031] For the power electronic device connected to the nth node, the time series change matrix of the harmonic current ΔI gT,n for:

[0032]

[0033] in, Indicates t i The harmonic current injected into the system by the power electronic equipment at node n at time t1~t n represents the time period under consideration.

[0034] As an optional solution, the harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics, specifically:

[0035] [ΔU gTh ]=M Th [ΔI gTh ];

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

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

[0038] A time-varying harmonic transfer relationship evaluation system for a power distribution system, comprising:

[0039] A model building module is used to model the power distribution system as a control system with multi-variable input and multi-variable output, wherein the multi-variable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multi-output variable is the harmonic voltage of each node;

[0040] A relationship building module is used to build the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, and the relationship between the harmonics of different frequencies at each node of the power distribution system based on the typical topological structure of the power electronic equipment;

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

[0042] The evaluation module is used to determine the time-varying laws of harmonic voltages and currents of other nodes generated by any node injecting time-varying harmonic currents into the power distribution system according to the frequency of the injected current, as well as the harmonic current deviation generated by the node being affected by other nodes.

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

[0044] A terminal device includes a processor and a memory, wherein the processor is used to implement instructions; the memory is used to store multiple instructions, wherein the instructions are suitable for being loaded by the processor and executing the above-mentioned method for evaluating time-varying harmonic transfer relations in a power distribution system.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The present invention models the power distribution system as a control system with multi-variable input and multi-variable output. Therefore, 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 the harmonic transfer relationship of the power distribution system and solves the problem of analyzing the source of the influence of multi-node harmonic voltage when multi-node harmonic currents are injected simultaneously.

[0047] (2) The present invention constructs the coupling relationship between the harmonic currents and voltages of various frequencies at the grid-connected port of the power electronic equipment, and combines the relationship between the 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 and multi-frequency harmonics of the power distribution system. While ensuring the calculation accuracy, it greatly improves the solution efficiency. It is extremely suitable for harmonic analysis of the complex structure of the power distribution system under the access of large-scale power electronic equipment.

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

[0049] (4) The present invention takes into account the time-varying characteristics of harmonic currents injected into each node of the power distribution system, and is more suitable for power distribution systems with rapidly changing operating conditions and continuously fluctuating backgrounds, thereby avoiding the impact of the use of a unified model on the accuracy of harmonic transfer assessment of the power distribution system.

[0050] Other features and advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a flow chart of a method for evaluating the time-varying harmonic transfer relationship of a power distribution system in an embodiment of the present invention;

[0052] Figure 2 Schematic diagram of a multi-variable input and multi-variable output control system for a power distribution system according to an embodiment of the present invention;

[0053] Figure 3 Schematic diagram of a typical topological structure of a power electronic device in an embodiment of the present invention;

[0054] Figure 4 Schematic diagram of a typical control method of a power electronic device in an embodiment of the present invention;

[0055] Figure 5 The figure is a flow chart of iterative solution of harmonic power flow in the power distribution system in an embodiment of the present invention. DETAILED DESCRIPTION

[0056] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0057] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0058] Embodiment 1

[0059] In one or more embodiments, a method for evaluating the time-varying harmonic transfer relationship of a power distribution system is disclosed, combining Figure 1 , specifically including the following process:

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

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

[0062] S2: Based on the typical topological structure of power electronic equipment, the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, as well as the relationship between the harmonics of different frequencies at each node of the power distribution system are constructed.

[0063] Typical topologies of power electronic equipment are as follows: Figure 3 As shown, based on the typical topological structure of power electronic equipment, the changes in the harmonic voltage of the node to which the power electronic equipment is connected are analyzed when the harmonic current generated by the power electronic equipment changes.

[0064] For any power electronic device connected to a node in the system, the harmonic current generated by it 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 are the matrices composed of the harmonic voltages of each frequency of the power electronic equipment grid side, the rectifier side and the AC filter capacitor, ΔI g , ΔI c are matrices composed of harmonic currents of various frequencies generated by the grid side and rectifier side of the power electronic equipment, Z g is the impedance of the power electronic equipment on the grid side, Z c is the impedance of the power electronic equipment converter side, Z cf is the equivalent impedance of the AC filter capacitor.

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

[0070] ΔV dc =(ΔI s -ΔI dc )Z dc ;

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

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

[0073]

[0074] Among them, S is the conversion relationship between the harmonic voltage and current of each frequency on both sides of the AC and DC of the power electronic equipment, which is related to the control method of the power electronic equipment. The typical control method of power electronic equipment is as follows: Figure 4 As shown, by taking the operating voltage, operating current and operating power of the power electronic equipment as input, the conversion relationship S of the harmonic voltage and current of each frequency on both sides of the AC and DC of the power electronic equipment can be output.

[0075] Based on the above conversion relationship, the relationship between the harmonic current and voltage of each frequency at the grid-connected 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 nis the harmonic coupling impedance matrix of the nth node in the system, which is used to describe the conversion relationship between harmonic currents and harmonic voltages of different frequencies; Z n The method for determining ΔV is already known in the prior art and will not be described in detail. g,n is the matrix composed of the harmonic voltages of various frequencies on the grid side of the power electronic equipment, and its dimension is consistent with the harmonic frequency H considered; ΔI g,n It is a matrix composed of harmonic currents of various frequencies on the grid side of power electronic equipment, and its dimension is consistent with the harmonic frequency H considered.

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

[0079]

[0080] Among them, [I gh ] represents the matrix composed of the hth harmonic current of each node; [U gh ] represents the matrix composed of the hth harmonic voltage of each node; [Y Bh ] represents the hth harmonic equivalent admittance matrix between each node, h = 1, 3, ..., H, H is the highest harmonic order considered.

[0081] S3: Based on the above relationship, when the power electronic device 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.

[0082] In this embodiment, combined with the relationship between the harmonics of different frequencies at each node of the power distribution system and the relationship between the harmonic currents and voltages of various frequencies at the grid-connected port of the power electronic equipment, when the power electronic equipment connected to the nth node in the system injects a harmonic current ΔI into the system g,n When , the harmonic changes of each frequency in the system caused by this can be solved iteratively, such as Figure 5 As shown, the specific steps are as follows:

[0083] S301: Based on the relationship between the harmonics of different frequencies at each node of the power distribution and utilization system and the relationship between the harmonic currents and voltages of different frequencies at the grid-connected ports of the power electronic equipment, a multi-frequency harmonic coupling relationship model Y of the power distribution and utilization system can be obtained;

[0084] S302: injecting harmonic current ΔI into the system for the power electronic device connected to the nth node in the system g,n , using the multi-frequency harmonic coupling relationship model Y of the power distribution system, the harmonic voltage of each node in the power distribution system [U gh ] (1) , the superscript (1) indicates the first iteration process;

[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 current of each node in the power distribution system [I gh ] (1) , at this time, other nodes will also affect the harmonic current of the nth node. Assuming 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: Execute S302 and S303 repeatedly until the harmonic voltage [U gh ] (i) with [U gh ] (i+1) , satisfying the convergence condition max(|[U gh ] (i) –[U gh ] (i+1) |)<ε (ε represents the harmonic power flow iteration convergence error), it means that the harmonic power flow iteration process is over;

[0087] S305: When the iteration process ends, the harmonic voltage variation of each node in the power distribution system is [ΔU gh ], the harmonic current variation of each node is [ΔI gh ], where the harmonic current deviation caused by the nth node affected by other nodes is δI g,n . [ΔU gh ] is the difference between the last harmonic voltage and the first iteration harmonic voltage, [ΔI gh ] is the difference between the last harmonic current and the first iteration harmonic current, [ΔI gh ] The element corresponding to the nth row is δI g,n .

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

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

[0090] [ΔU gh ]=M h [ΔI gh ];

[0091] Among them, M h is the hth harmonic current and voltage transfer matrix of each node in the power distribution system. gh ] and [ΔI gh ] It is known that M can be solved by data fitting methods (such as least squares method, machine learning method, 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 and harmonic current ΔI g,n There is a nonlinear relationship, so the change δI g,n and harmonic current ΔI g,n The relationship can be obtained by fitting. The specific fitting method can be implemented by polynomial fitting, which is easy to implement for those skilled in the art.

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

[0094]

[0095] In the formula, Indicates t i The harmonic current injected into the system by the power electronic equipment at node n at time t1~t n represents the time period under consideration.

[0096] By using the harmonic current time series variation matrix of each node, the harmonic transfer 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 is the time-varying transfer matrix of the hth harmonic current and voltage at each node of the power distribution system, [ΔU gTh] and [ΔI gTh ] are matrices composed of the time-varying harmonic voltages and time-varying harmonic currents of 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 evaluation requirements. For example, for data with higher time requirements, it can be divided into one time period every hour; for data with lower time requirements, it can be divided into one time period every 4 hours.

[0100] S5: When any node injects time-varying harmonic current into the power distribution system, according to the injected current frequency h, using the h-order harmonic current and voltage time-varying transfer matrix of each node in the power distribution system, the time-varying laws of the harmonic voltage and current of other nodes generated thereby, as well as the harmonic current deviation caused by the node's response to the influence of other nodes can be clearly determined.

[0101] Embodiment 2

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

[0103] A model building module is used to model the power distribution system as a control system with multi-variable input and multi-variable output, wherein the multi-variable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multi-output variable is the harmonic voltage of each node;

[0104] A relationship building module is used to build the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, and the relationship between the harmonics of different frequencies at each node of the power distribution system based on the typical topological structure of the power electronic equipment;

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

[0106] The evaluation module is used to determine the time-varying laws of harmonic voltages and currents of other nodes generated by any node injecting time-varying harmonic currents into the power distribution system according to the frequency of the injected current, as well as the harmonic current deviation generated by the node being affected by other nodes.

[0107] The specific implementation of the above modules is the same as that in Example 1 and will not be described in detail.

[0108] Embodiment 3

[0109] In one or more embodiments, a terminal device is disclosed, which includes a processor and a memory, the processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded by the processor and executing the method for evaluating time-varying harmonic transfer relationships in a power distribution system described in Example 1.

[0110] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

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

[0112] In the implementation process, each step of the above method can be completed by an integrated logic circuit of hardware in a processor or an instruction in the form of software.

[0113] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it 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 on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for evaluating the time-varying harmonic transfer relationship of a power distribution system, characterized in that: include: The power distribution system is modeled as a control system with multi-variable input and multi-variable output, wherein the multi-variable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multi-output variable is the harmonic voltage of each node; Based on the typical topological structure of power electronic equipment, the relationship between the harmonic current and voltage of each frequency at the grid-connected port of power electronic equipment, as well as the relationship between the harmonics of different frequencies at each node of the power distribution system are constructed; 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; Based on the calculation results of harmonic voltage variation and harmonic current variation, the harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics. When any node injects time-varying harmonic current into the power distribution system, the time-varying laws of harmonic voltages and currents of other nodes generated thereby are determined according to the frequency of the injected current, as well as the harmonic current deviation caused by the response of this node to the influence of other nodes.

2. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 1, characterized in that: Construct the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, specifically: ΔV g,n =Z n ΔI g,n ; Among them, Z n is the harmonic coupling impedance matrix of the nth node in the system, which is used to describe the conversion relationship between harmonic currents and harmonic voltages of different frequencies; ΔV g,n is the matrix composed of the harmonic voltages of various frequencies on the grid side of the 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.

3. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 1, characterized in that: Construct the relationship between the harmonics of different frequencies at each node of the power distribution system, specifically: Among them, [I gh ] represents the matrix composed of the hth harmonic current of each node; [U gh ] represents the matrix composed of the hth harmonic voltage of each node; [Y Bh ] represents the hth harmonic equivalent admittance matrix between each node, h = 1, 3, ..., H, H is the highest harmonic order considered.

4. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 1, characterized in that: 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 as follows: The relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, and the relationship between the harmonics of different frequencies at each node of the power distribution system, are combined to obtain the multi-frequency harmonic coupling relationship model Y of the power distribution system; For the power electronic equipment connected to the nth node in the system, the 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 of each node in the power distribution system [U gh ] (1) , 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 current of each node in the power distribution system [I gh ] (1) , at this time, other nodes will also affect the harmonic current of the nth node, and the harmonic current deviation generated by this response is recorded as δI g,n (1) ; The superscript (1) indicates the first iteration process; Repeat the above process until the harmonic voltage [U gh ] (i) with [U gh ] (i+1) , the convergence condition is met, and the harmonic power flow iteration process ends; the change of harmonic voltage at each node in the power distribution system is recorded as [ΔU gh ], the harmonic current variation of each node is [ΔI gh ], where the harmonic current deviation caused by the nth node affected by other nodes is δI g,n .

5. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 1, characterized in that: The harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics, specifically: Based on the calculation results of harmonic voltage variation and harmonic current variation, the harmonic transfer relationship of each node in the power distribution system is constructed; Considering the time-varying characteristics of harmonic current injected into each node of the power distribution system, a time sequence matrix of harmonic current injected into each node is established; The harmonic transfer relationship of each node in the power distribution system is established by using the timing matrix of harmonic current injected into each node, considering the time-varying characteristics of harmonics.

6. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 5, characterized in that: Construct the harmonic transfer relationship of each node in the power distribution system, specifically: [ΔU gh ]=M h [ΔI gh ]; Among them, M h is the hth harmonic current and voltage transfer matrix of each node in the power distribution system; [ΔU gh ] and [ΔI gh ] are the harmonic voltage change and harmonic current change of each node in the power distribution system at the end of iteration.

7. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 5, characterized in that: Establish the timing matrix of harmonic current injection at each node, specifically: For the power electronic device connected to the nth node, the time series change matrix of the harmonic current ΔI gT,n for: in, Indicates t i The harmonic current injected into the system by the power electronic equipment at node n at time t1~t n represents the time period under consideration.

8. A method for evaluating time-varying harmonic transfer relations in a power distribution system as claimed in claim 5, characterized in that: The harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics, specifically: [ΔU gTh ]=M Th [ΔI gTh ]; Among them, M Th is the time-varying transfer matrix of the hth harmonic current and voltage at each node of the power distribution system, [ΔU gTh ] and [ΔI gTh ] are matrices composed of the time-varying harmonic voltages and time-varying harmonic currents of each node in the power distribution system.

9. A time-varying harmonic transfer relationship evaluation system for a power distribution system, characterized in that: include: A model building module is used to model the power distribution system as a control system with multi-variable input and multi-variable output, wherein the multi-variable input is the harmonic current generated by the nonlinear power electronic equipment connected to each node, and the multi-output variable is the harmonic voltage of each node; A relationship building module is used to build the relationship between the harmonic current and voltage of each frequency at the grid-connected port of the power electronic equipment, and the relationship between the harmonics of different frequencies at each node of the power distribution system based on the typical topological structure of the power electronic equipment; An iterative solution module is used to iteratively solve the harmonic voltage change and harmonic current change of each node in the power distribution system caused by the power electronic equipment connected to the nth node in the system injecting harmonic current into the system based on the above relationship; Based on the calculation results of harmonic voltage variation and harmonic current variation, the harmonic transfer relationship of each node in the power distribution system is established considering the time-varying characteristics of harmonics. The evaluation module is used to determine the time-varying laws of harmonic voltages and currents of other nodes generated by any node injecting time-varying harmonic currents into the power distribution system according to the frequency of the injected current, as well as the harmonic current deviation generated by the node being affected by other nodes.

10. A terminal device, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executing the method for evaluating the time-varying harmonic transfer relationship of a power distribution system as described in any one of claims 1-8.

Images