Method, system, equipment and medium for measuring and predicting background harmonics of regional power grid

Abstract

The invention relates to a method, a system, equipment and a medium for measuring and predicting background harmonics of a regional power grid, and the method comprises the steps: obtaining a topological graph of the regional power grid in the current year, and determining a simulation region of a specific voltage level in the topological graph according to an actual demand; modeling the simulation region based on the power grid circuit data of the regional power grid to obtain an initial harmonic model of the regional power grid; taking the actual measurement value of the harmonic current of the regional power grid in the current year as an initial iteration value, operating the initial harmonic model, and continuously iterating until the harmonic current and the actual measurement value output by model simulation meet a preset error requirement, so as to obtain a harmonic model of a simulation region corresponding to the specific voltage level of the regional power grid in the current year; and adjusting the harmonic model according to the power grid circuit data of the transformed or planned year regional power grid, and calculating the harmonic distribution of any point of the transformed or planned year regional power grid based on the adjusted harmonic model. The method can be widely applied to the field of high-voltage alternating-current network planning and design.

Description

Technical Field

[0001] The present invention relates to the field of power quality, and particularly to a method, system, device, and medium for measuring and predicting background harmonics in a regional power grid. Background Art

[0002] There are often harmonic flows in the power grid. These harmonics may originate from generator sets, saturated transformers, or DC converters, etc. After passing through capacitive and inductive devices in the power grid, the harmonics may be further amplified, showing voltage or current distortion, and causing equipment failures such as transformer noise, heating, and capacitor bulging.

[0003] Under the conditions of a new power system, with the large-scale access of various power electronic inverter loads, the number of harmonic sources in the system has increased sharply. Power electronic inverters will inevitably generate harmonics due to non-linearity during the commutation process, and some are high-frequency harmonics. The large-scale deployment of non-linear facilities such as new energy, energy storage, and high-speed railways has injected a large amount of harmonics into the power system, resulting in an increase in the harmonic distortion rate in the current AC power grid and a very complex harmonic spectrum.

[0004] The transmission characteristics of harmonics are different from those of fundamental waves, or rather, the harmonic characteristics of power grid equipment are different from those of fundamental waves. The analysis of harmonic conduction requires special software. General power system analysis software such as PSD and BPA can only analyze the conduction of fundamental waves. Only special software such as ETAP, HAP, and NIMSCAN can calculate the harmonic impedance characteristics in the system and analyze the harmonic transmission in the AC network.

[0005] Excessive harmonics cause heating of coil-type equipment and breakdown of capacitor-type equipment, and will also interfere with user equipment, burn circuit boards, and interfere with pump machines, etc. Therefore, accurately calculating the harmonic level of a local power grid is of great significance for designing and manufacturing equipment in this area. The equipment in this area should have the ability to withstand the highest harmonic level that may appear in the future in this area. When the AC power grid needs to be transformed or the future AC power grid is planned, an accurate, reasonable, and practical method is particularly needed to predict the background harmonic level of the transformed or developed regional AC power grid based on the current harmonic level of the power grid. Summary of the Invention

[0006] Aiming at the above problems, the purpose of the present invention is to provide a method, system, device, and medium for measuring and predicting background harmonics in a regional power grid, and to achieve the purpose of large-scale transmission of new energy power based on the measured harmonic level of the existing power grid, the system conditions of the existing power grid, and the system conditions after transformation or development.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for measuring and predicting background harmonics of a regional power grid, comprising the following steps: Obtain the topology diagram of the regional power grid in the current year, and determine a simulation area of a specific voltage level in the topology diagram according to actual requirements; Based on the grid circuit data of the regional power grid, model the simulation area to obtain an initial harmonic model of the regional power grid; Take the measured harmonic current value of the regional power grid in the current year as the initial iteration value, run the initial harmonic model, and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, so as to obtain the harmonic model of the simulation area corresponding to the specific voltage level of the regional power grid in the current year; Adjust the harmonic model according to the grid circuit data of the regional power grid after transformation or in the planned year, and calculate the harmonic distribution at any point of the regional power grid after transformation or in the planned year based on the adjusted harmonic model.

[0008] Furthermore, the step of obtaining the topology diagram of the regional power grid in the current year and determining a simulation area of a specific voltage level in the topology diagram according to actual requirements includes: Determine the specific voltage level and the area to be transformed or developed in the regional power grid in the current year as the area of concern; Regard any busbar of any substation in the area of concern as a point, and regard any line or transformer as a line, and determine the boundary points of the area of concern; Expand outward from the boundary points of the area of concern and expand to other voltage levels at the same time to obtain primary outgoing lines and primary nodes; Among them, expanding outward from the boundary points of the area of concern and expanding to other voltage levels at the same time to obtain primary outgoing lines and primary nodes includes: Expand outward from the boundary points of the area of concern, regard the points separated from the boundary points by one line as primary nodes, and regard this separated line as a primary outgoing line at the same time; Regard the busbars on the other voltage level sides of the transformers in the substations within the area of concern as primary nodes, and regard the transformers as primary outgoing lines; Regard the area of concern, primary nodes and primary outgoing lines together as the simulation area corresponding to the specific voltage level of the regional power grid in the current year.

[0009] Furthermore, the step of modeling the simulation area based on the grid circuit data of the regional power grid to obtain an initial harmonic model of the regional power grid includes: For the area of interest, use software that meets the preset requirements to model all devices within the area of interest; for each first-level node, use an equivalent power source and equivalent harmonic impedance to equivalent the fundamental wave characteristics and harmonic characteristics of each first-level node outside the area of interest, obtaining an equivalent model outside the area of interest; combine the harmonic models of all devices inside the area of interest with the equivalent model outside the area of interest to obtain the initial harmonic model of the regional power grid for the current year; or Extend one more line from each first-level node outside the simulation area to obtain second-level nodes. This line is the second-level outgoing line, and the connections between second-level nodes are also used as second-level outgoing lines, expanding the original simulation area to include second-level nodes; measure the total harmonic current flowing from the second-level nodes outside the simulation area into the simulation area as the equivalent harmonic current source of the second-level nodes, and measure the fundamental wave voltage of the second-level nodes as the fundamental wave voltage source of the second-level nodes to obtain the initial harmonic model of the regional power grid for the current year.

[0010] Furthermore, the step of using an equivalent power source and equivalent harmonic impedance to equivalent the fundamental wave characteristics and harmonic characteristics of each first-level node outside the area of interest to obtain an equivalent model outside the area of interest includes: For the first-level nodes extended from the boundary points of the area of interest, for the part of the network connected to them outside the area of interest, first calculate the equivalent fundamental wave voltage source and equivalent fundamental wave impedance of these network parts, calculate the equivalent harmonic impedance of these network parts, and use the equivalent fundamental wave voltage source in series with the equivalent harmonic impedance with impedance values set at each frequency and then in parallel with an iterable equivalent harmonic current source instead; among them, the initial iteration value of the equivalent harmonic current source is the sum of the measured harmonic currents of all parts of this first-level node outside the area of interest; For the first-level nodes extended from the busbars of other voltage levels of the transformers in the substations within the area of interest, use an equivalent fundamental wave voltage source in series with an equivalent fundamental wave impedance and then in parallel with an iterable equivalent harmonic current source instead, where the initial iteration value of the equivalent harmonic current source is the sum of the measured harmonic currents of all parts of this first-level node outside the area of interest.

[0011] Furthermore, the step of using the measured harmonic current value of the regional power grid for the current year as the initial iteration value, running the initial harmonic model, and continuously iterating until the harmonic current output by the model simulation meets the preset error requirement to obtain the harmonic model of the simulation area of a specific voltage level of the regional power grid for the current year includes: ① Use the measured harmonic current value of the regional power grid for the current year as the initial iteration value, run the initial harmonic model, and obtain the harmonic currents on all first-level outgoing lines; ② Based on the deviation between the harmonic currents on all first-level outgoing lines and the measured values, adjust the amplitude and phase angle of each harmonic of the equivalent harmonic current source corresponding to each first-level node, and then return to step ①; ③ Determine whether the harmonic current on each primary outgoing line after adjustment is similar to the measured value. If so, end the iteration; otherwise, return to step ② to continue the adjustment.

[0012] Further, the measured value includes the harmonic currents of all outgoing lines of the primary nodes expanded outward from the boundary points of the concerned area and the harmonic currents of the other voltage levels of the transformers corresponding to the primary nodes expanded from the busbars of the other voltage levels of the transformers in the substations within the concerned area. When measuring the harmonic current, the measurement methods include the following two: First: In the same time period, measure the harmonic currents of the same phase of all primary nodes within a preset duration, and the current transformers used need to ensure that they can cover the considered frequency band. Second: In the same time period of several consecutive working days, measure the harmonic currents of the same phase of each primary node in batches step by step.

[0013] Further, when adjusting the harmonic model according to the power grid circuit data of the regional power grid after transformation or in the planned year, it includes: Based on the harmonic model corresponding to the specific voltage level of the regional power grid in the current year, keeping the equivalent harmonic current source, equivalent fundamental voltage source, and equivalent fundamental and harmonic impedances of each primary node unchanged, adjust the wiring and equipment parameters within the concerned area according to the expected wiring and equipment parameters of the regional power grid after transformation; or Based on the harmonic model corresponding to the specific voltage level of the regional power grid in the current year, adjust the wiring and equipment parameters within the concerned area according to the expected wiring and equipment parameters in the planned year within the concerned area; then, for the equivalent fundamental impedance and equivalent fundamental voltage source corresponding to each primary node, recalculate according to the power grid circuit data in the planned year; for the equivalent harmonic impedance corresponding to each primary node, recalculate the equivalent harmonic impedance of the power network outside the simulation area for each primary node according to the power grid circuit data in the planned year; for the equivalent harmonic current source of each primary node, multiply the original equivalent harmonic current source by the annual average growth rate of the load and the number of years according to the local annual average growth rate of the load. If typical harmonic sources are newly connected to each primary node in the planned year, add the typical harmonic spectra after considering the capacity and network conversion of these typical harmonic sources to each equivalent harmonic current source.

[0014] In the second aspect, the present invention provides a system for measuring and predicting the background harmonics of a regional power grid, including: A simulation area determination module, configured to obtain the topology diagram of the regional power grid in the current year and determine the simulation area of a specific voltage level in the topology diagram according to actual requirements. A harmonic model establishment module, configured to model a simulation area based on power grid circuit data of a regional power grid to obtain an initial harmonic model of the regional power grid; An iterative calculation module, configured to use the measured harmonic current value of the regional power grid in the current year as an initial iterative value, run the initial harmonic model, and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, so as to obtain the harmonic model of the simulation area corresponding to a specific voltage level of the regional power grid in the current year; A harmonic prediction module, configured to adjust the harmonic model according to the power grid circuit data of the regional power grid after transformation or in the planned year, and calculate the harmonic distribution at any point in the regional power grid after transformation or in the planned year based on the adjusted harmonic model.

[0015] Thirdly, the present invention provides a computer-readable storage medium storing one or more programs, where the one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any method.

[0016] Fourthly, the present invention provides a computing device, including: one or more processors and a memory, where the memory stores one or more programs and is configured to be executed by the one or more processors, and the one or more programs include instructions for executing any method.

[0017] Due to the above technical solutions adopted by the present invention, it has the following advantages: 1. Based on basic power principles such as Thevenin's theorem, the present invention correctly and reasonably predicts and calculates the harmonic levels of the power grid after transformation and development from the principle, which conforms to the actual situation of the power grid; 2. For the feasibility of actual implementation, the present invention makes appropriate simplifications. For example, it is considered that the harmonic current of the secondary node will not be affected by the change of the system parameters in the concerned area, the harmonic current on the low-voltage side of the transformer will not change due to the grid connection of the high-voltage level, and the harmonics are the same at the same time period within a working day. This is a reasonable simplification and is more convenient for actual measurement and calculation operations; The present invention considers the most severe harmonic conditions for the development of the power grid and gives special consideration to the increased large harmonic sources, which has practical significance for the design and planning of power grid equipment. Therefore, the present invention can be widely applied to the field of power quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings: Figure 1It is a flowchart of the method for measuring and predicting background harmonics after the transformation or development of the regional power grid provided by the embodiments of the present invention; Figure 2 It is a schematic structural diagram of a certain typical power grid in the first embodiment of the present invention; Figure 3 It is a topological diagram of a certain typical power grid in the first embodiment of the present invention; Figure 4 It is the harmonic and fundamental wave equivalence of the boundary nodes in the first embodiment of the present invention; Figure 5 It is the simple equivalence of the harmonics and fundamental waves on the low-voltage side of the internal nodes in the first embodiment of the present invention; Figure 6 It is to equivalent a certain typical power grid according to the method in the first embodiment in the first embodiment of the present invention; Figure 7 It is to equivalent a certain typical power grid according to the method in the second embodiment in the second embodiment of the present invention. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0020] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless otherwise clearly specified in the context, 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, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0021] In order to accurately predict the harmonic level of the power grid after transformation or development, so as to put forward technical requirements for the equipment in the power grid, in some embodiments of the present invention, a method for measuring and predicting the background harmonics of the regional power grid is proposed. This method measures the existing power grid harmonic level and predicts the future power grid harmonic level based on it. Based on the harmonic equivalent method that conforms to the circuit principle, a reasonable range is selected on the basis of calculating the current power grid system data to build a harmonic model of the current regional network, and the correctness of the harmonic model is verified according to the on-site measured harmonic data. Thus, when the power grid parameters change, the future power grid harmonic level can be calculated by changing the model wiring and parameters. The present invention obtains the harmonics in the power grid after the power grid development through reasonable prediction of the growth of harmonic sources. On the other hand, for the sake of simplicity in practical application, a method for reducing the calculation process in model building by expanding the regional scope is proposed, believing that the harmonics outside a larger range are not affected by the changes in the internal regional network parameters, so as to quickly obtain a harmonic equivalent model at the boundary point.

[0022] Correspondingly, in some other embodiments of the present invention, a system for measuring and predicting the background harmonics of the regional power grid is provided.

[0023] Embodiment 1 As Figure 1 shown, this embodiment provides a method for measuring and predicting the background harmonics of the regional power grid, which includes the following steps: 1) Obtain the topology diagram of the regional power grid in the current year, and determine the simulation area of a specific voltage level in the topology diagram according to actual needs; 2) Measure the power grid circuit data of the regional power grid, and build a model for the simulation area based on the power grid circuit data of the regional power grid to obtain the initial harmonic model of the regional power grid in the current year; 3) Take the measured value of the harmonic current of the regional power grid in the current year as the initial iteration value, run the initial harmonic model, and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, and obtain the harmonic model of the simulation area of the regional power grid in the current year; 4) After the internal transformation or development of the regional power grid, adjust the harmonic model in step 3) according to the power grid circuit data of the regional power grid after transformation or in the planned year, and calculate the harmonic distribution at any point of the regional power grid after transformation or in the planned year based on the adjusted harmonic model.

[0024] Further, in the above step 1), the following steps are included: 1.1) Determine the specific voltage level and the area to be transformed or developed in the regional power grid in the current year as the "area of concern"; 1.2) Regard any busbar of any substation in the "area of concern" as a "point", and regard any line or transformer as a "line", and determine the boundary points of the "area of concern"; 1.3) Expand outward from the boundary points of the "area of interest" and also expand to other voltage levels to obtain "primary outgoing lines" and "primary nodes"; 1.4) Use the "area of interest", "primary nodes", and "primary outgoing lines" together as the simulation area.

[0025] As Figure 2 shown, when performing topology extraction on the current-year regional power grid based on preset rules, any busbar of any substation in the current-year regional power grid can be regarded as a "point", and any line or transformer can be regarded as a "line", and the topology diagram of this regional power grid is extracted (as Figure 3 shown). Among them, the busbars on the other voltage levels of the transformers in the substations within the "area of interest" should also be regarded as "primary nodes", and this transformer is the "primary outgoing line". Then, determine the simulation area of the specific voltage level of the regional power grid according to actual needs in the topology diagram.

[0026] In practical applications, generally, the power grid to be renovated or the developing power grid that we are concerned about will be limited within a certain range. Therefore, in the topology diagram, a minimum enclosing network that encloses the part of the power grid to be renovated or the developing power grid can be found, with "points" as the boundary.

[0027] In this embodiment, the part within this minimum enclosing network is used as the "area of interest", as Figure 2 shown by the range enclosed by the black solid line; these points on the boundary are used as "boundary points", as shown by the double-line circular marks in Figure 3 .

[0028] Find all the "points" outside the "area of interest" that are separated from the "boundary points" by one "line" as "primary nodes", and this intervening line is used as the "primary outgoing line". All the "points" and "lines" within the "area of interest", all the "primary nodes" and "primary outgoing lines", and the connecting lines between the "primary nodes" form the "simulation area" that should be simulated and modeled, as Figure 2 shown by the range enclosed by the dashed line in, and the "primary nodes" are Figure 3 shown by the single-line circular marks in.

[0029] Furthermore, in step 2) above, the following steps are included: 2.1) For the "area of interest", use software that meets the preset requirements to model all the devices within the "area of interest"; 2.2) For each "primary node", perform equivalence on the fundamental wave characteristics and harmonic characteristics respectively, that is, use an equivalent power source and harmonic impedances with impedance values set at each frequency to represent the power network outside the "area of interest" to obtain an equivalent model outside the "area of interest"; 2.3) Combine the harmonic models of all devices inside the "area of concern" with the equivalent model outside the "area of concern" to obtain the initial harmonic model of the regional power grid for the current year.

[0030] Furthermore, in step 2.1) above, in this embodiment, models of all devices inside the "simulation area" are built in software such as ETAP and HAP, mainly including devices such as transformers, AC lines, shunt capacitors, and shunt reactors.

[0031] Furthermore, in step 2.2) above, in this embodiment, an equivalent power source and a harmonic impedance with impedance values set separately at each frequency are used to represent the power network outside the "simulation area". Specifically, it mainly includes fundamental wave equivalence and harmonic equivalence.

[0032] The fundamental wave equivalence has a very mature theoretical basis and methods. Generally, the method of "fundamental wave voltage in series with fundamental wave impedance" by Thevenin is used for equivalence. Using software such as PSD (a power system software analysis tool of the System Institute of China Electric Power Research Institute) or PSASP (a software package developed by the Power System Technology Branch of China Electric Power Research Institute for power system analysis and calculation), based on the power grid circuit data of the entire regional power grid (i.e., the power grid circuit data describing line impedance, transformer impedance, transformer voltage, etc., generally used for power flow calculation), the equivalent fundamental wave voltage source V1 and equivalent fundamental wave impedance Z1 of the power network outside the corresponding simulation area at each boundary point can be calculated. Among them, the methods of using PSD and PSASP for fundamental wave equivalence and calculating the equivalent fundamental wave voltage source and equivalent fundamental wave impedance are well-known techniques to those skilled in the art, and the present invention will not elaborate on this.

[0033] The basic principle of harmonic equivalence is the same as that of fundamental wave equivalence. However, since the harmonic sources in the system are often current sources, and the accuracy of measuring harmonics by current transformers is often higher than that of voltage transformers, the method of "harmonic current source in parallel with harmonic impedance" by Norton can be used for harmonic equivalence. The harmonic impedance is an impedance that is less studied by those skilled in the art compared to the fundamental wave impedance. Software such as NIMSCAN (a harmonic impedance scanning software developed by Italian company Teshmont Consulting) can be used to calculate the equivalent harmonic impedance Zn of the power network outside the corresponding simulation area at each boundary point based on the power grid circuit data of the current regional power grid. The equivalent harmonic current source can be an equivalent harmonic current source with an initial value to be determined, and it is determined by continuously iterating later to make the harmonic current inside the simulation area similar to the measured value.

[0034] Since the characteristic of the equivalent impedance value of each harmonic of the external power grid changing with frequency is very complex, it is difficult to use a single or several device components to simulate the harmonic impedance characteristic of a local network. Therefore, in this embodiment, after obtaining the equivalent fundamental impedance using PSD, PSASP, etc. and obtaining the equivalent harmonic impedance using NIMSCAN, etc., software such as ETAP (a comprehensive analysis software system for power electrical analysis and power energy management developed and produced by the OTI Group of the United States) and HAP (a harmonic analysis software developed and produced by ABB) that can set the harmonic impedance value separately according to discrete harmonic frequencies needs to be used for modeling and simulation.

[0035] As Figure 4 shown, finally, the "primary node" outside each boundary point can be characterized by an equivalent fundamental voltage source in series with a frequency-varying impedance whose impedance values at the fundamental frequency and harmonic frequencies are set to the equivalent fundamental impedance value and the equivalent harmonic impedance value respectively, and then in parallel with an equivalent harmonic current source. Thus, the equivalent model of the entire network is formed.

[0036] Furthermore, in the above step 2.2), it should be noted that for each "point" in the "area of interest", that is, the substation where each bus is located, the buses on the other voltage levels of the corresponding transformer should also be regarded as "primary nodes", and the parts connected to them outside the "simulation area" should also be subjected to fundamental and harmonic equivalence. This transformer is the "primary outgoing line" corresponding to this primary node.

[0037] Furthermore, in the above step 3), the following steps are included: 3.1) Run the initial harmonic model of the regional power grid established in step 2) to obtain the harmonic currents on all "primary outgoing lines"; 3.2) Based on the harmonic currents on all "primary outgoing lines" and the measured values, after adjusting the amplitudes and phases of each harmonic of the equivalent harmonic current source corresponding to each "primary node" according to the preset rules, return to step 3.1); 3.3) Judge whether the harmonic currents on each "primary outgoing line" after adjustment are similar to the measured values. If so, end the iteration; otherwise, return to step 3.2) to continue the adjustment.

[0038] Furthermore, in the above step 3.2), in order to implement the above equivalent method, the harmonic currents of all outgoing lines of each "primary node" and the harmonic currents of all voltage levels of the transformer corresponding to the "primary node" should be measured on site. The initial iteration value of the equivalent harmonic current source of each primary node can be set to the sum of the currents of all parts of the primary node outside the "simulation area", that is, the current injected from the primary node into the "simulation area".

[0039] For the low-voltage or medium-voltage busbars of a transformer, it is often difficult to obtain accurate external grid circuit data. It is relatively difficult to calculate the harmonic impedance, and the influence of the harmonic impedance on the low-voltage and medium-voltage sides on the harmonic power flow distribution of the concerned voltage level is not significant due to the isolation effect of the transformer. For the convenience of engineering applications, only an equivalent harmonic current source can be used to equivalent the harmonic characteristics of the external parts of the low-voltage and medium-voltage busbars of these transformers, that is, it is considered that the external harmonic equivalent impedance is infinite. The value of this equivalent harmonic current is the sum of the currents of all parts outside the "simulation area" measured at the low-voltage and medium-voltage busbars of this transformer. However, since the fundamental wave calculation is relatively simple, the fundamental wave characteristics can still be characterized by the calculated equivalent fundamental voltage source and equivalent fundamental impedance. As Figure 5 shown.

[0040] After the above equivalence, we can get Figure 2 The equivalent circuit diagram of the area is as Figure 6 shown.

[0041] To implement the above equivalent method, the harmonic currents on the other voltage levels of the transformer, which is used as the "primary node", should be measured on-site.

[0042] To make the above modeling and equivalent methods feasible, when measuring the harmonic voltage and harmonic current on-site, the amplitude and phase should be measured simultaneously, and they should be of the same phase. Moreover, all the harmonic voltage and current data should be at the same time, so that these measured harmonics have electrical mutual relevance. Special attention should be paid to the selection of current transformers and voltage transformers during measurement. The measurement frequency band of the transformers should cover the target frequencies to be studied.

[0043] Furthermore, in step 4) above, after the internal transformation or development of the regional power grid, the harmonic model is adjusted according to the expected wiring and equipment parameters of the regional power grid after transformation or in the planned year, which is divided into the following two working conditions: When predicting the harmonics after the internal transformation of the power grid, the following should be carried out: Based on the power grid harmonic model of the current "simulation area" verified by the above method, keep the equivalent harmonic current source, equivalent fundamental voltage source, and equivalent fundamental and harmonic impedances of each primary node unchanged. According to the expected wiring and equipment parameters of the regional power grid after transformation, adjust the wiring and equipment parameters within the "concerned area". That is, since the transformation only occurs within the "concerned area" and will not affect the harmonic characteristics outside the simulation area, on the basis of fixed external harmonic characteristics, under the condition of the adjusted network parameters of the "concerned area", run the simulation model to calculate the harmonic distribution at any point after the transformation of the "concerned area".

[0044] When predicting the harmonics after the development of the regional power grid in the prediction area, the following steps should be taken: Based on the power grid harmonic model of the current "simulation area" verified by the above method, adjust the wiring and equipment parameters in the "area of concern" according to the expected wiring and equipment parameters in the planned year; Then, for the equivalent fundamental wave impedance and equivalent fundamental wave voltage source corresponding to each primary node, they should be recalculated using system simulation software such as PSD and PSASD based on the power grid circuit data in the planned year; For the equivalent harmonic impedance corresponding to each primary node, the equivalent harmonic impedance of the power network outside the simulation area corresponding to each primary node should be recalculated using software such as NIMSCAN based on the power grid circuit data in the planned year; The equivalent harmonic current source for each primary node should be adjusted and increased according to the development of the AC system. A feasible adjustment method is: According to the average annual growth rate of the load in the local power grid, multiply the equivalent harmonic current source corresponding to each primary node (including the primary nodes one level away from the area of concern by outgoing lines and the primary nodes on the medium-voltage side and low-voltage side of the transformers in the substations within the area of concern) by the average annual growth rate of the load and the number of years, assuming that the proportion of non-linear loads in the increased load is the same, to obtain the equivalent harmonic current source in the planned year.

[0045] In addition, it should be noted that if some typical large harmonic loads are planned to be connected to the simulation area in the planned year, such as new energy power plants and substations like photovoltaic and wind power, or traction loads like high-speed railways, special considerations should be given. These large harmonic loads have their own typical harmonic spectra. Their specific spectra should be calculated based on the capacity and typical harmonic spectra of these large harmonic loads, and this specific spectrum should be added to the equivalent harmonic current source at the corresponding primary node or on the medium-voltage side and low-voltage side of the corresponding substation transformer.

[0046] In particular, if these large loads are connected around the primary node, the equivalent harmonic current of this large harmonic load should be equivalent to the primary node using the power grid circuit data in the planned year and the location of the substation where the large harmonic load is specifically connected, and this equivalent value should be linearly added to the current spectrum of the original equivalent harmonic current source of this primary node.

[0047] Embodiment 2 The method for measuring and predicting the background harmonics after the transformation and development of the regional power grid in Embodiment 1 conforms to the basic circuit theory and the actual development of the power grid. However, in some cases, it is often difficult to obtain the system power grid circuit data of large regional power grids, and harmonic impedance scanning is a technology with a relatively high technical threshold and low popularity rate, and many units have not mastered it. In this case, for the consideration of engineering practical applications, the above method for predicting background harmonics can be reasonably simplified.

[0048] Specifically, the method is to extend a "line" from the primary node outside the "simulation area", and the obtained node is the "secondary node". This line is the "secondary outgoing line". In addition, the connection lines between the "secondary nodes" are also "secondary outgoing lines". Expand the original "simulation area" to include the secondary outgoing lines. Measure the sum of the currents of all parts of the secondary nodes outside the "simulation area", that is, the current injected into the "simulation area" from the secondary nodes, and use this as a constant harmonic current source to inject into the simulation area, and fix the boundary harmonic conditions of the secondary nodes. Measure the fundamental voltage of these secondary nodes and use this as a constant fundamental voltage source to fix the boundary fundamental conditions of the secondary nodes. This is actually equivalent to considering that the equivalent harmonic impedance of the secondary nodes outside the simulation area is infinite and the equivalent fundamental impedance is zero. It is also equivalent to considering that the equivalent fundamental impedance and harmonic impedance of the part of the primary outgoing line outside the simulation area are the impedances of the secondary outgoing lines, and considering that the harmonic power flow outside the secondary outgoing lines is not affected by the grid parameters in the area of concern.

[0049] After the above equivalence, we can obtain Figure 2 The equivalent circuit diagram of the area is as Figure 7 shown.

[0050] When using the above simplified method to predict background harmonics, a practical problem that may be encountered is that if there are no devices such as shunt reactors or shunt capacitors in the simulation area to make the current flow into the ground, using harmonic current sources to fix the harmonic boundary conditions at all secondary nodes in the area will lose a degree of freedom due to Kirchhoff's current law, that is, the sum of all currents injected into an area must be zero, and it cannot be established in the simulation model. Therefore, a node should be selected, which can be a secondary node, or a medium-voltage side or low-voltage side node of a substation transformer in the area of concern, as shown by the dashed boxes in Figure 6 and Figure 7 Measure its harmonic voltage as the boundary harmonic condition of this node. In the actual power grid, since the voltage monitoring of the power grid at 110 kV voltage level and above generally uses capacitive voltage transformers (CVTs), and capacitive voltage transformers (CVTs) cannot accurately measure harmonic voltages, the node selected to measure harmonic voltages to fix the boundary harmonic conditions should be at 66 kV voltage level and below, or ensure that the harmonic voltage is measured by an electromagnetic voltage transformer.

[0051] In the above simplified method for predicting background harmonics, the same steps can be used to process the wiring, equipment parameters, and equivalent harmonic sources in the "simulation area" model, and simulate and calculate the background harmonic levels after the internal transformation of the power grid and the development of the regional power grid.

[0052] In addition to the difficulty in obtaining system grid circuit data, difficulties in on-site measurement will also be encountered in actual operation. Under the limitations of limited time, manpower, and material resources, if the area of concern is large, it is often impossible to conduct harmonic measurements at all primary and secondary nodes at the same time. For the feasibility of engineering applications, it can be considered that the harmonic power flow is approximately the same at the same time on five working days per week (excluding Saturdays and Sundays). Therefore, the harmonic data of all planned measurement nodes or lines can be gradually measured at the same time period on several consecutive working days.

[0053] Embodiment 3 The above Embodiment 1 provides a method for measuring and predicting the background harmonics of a regional power grid. Correspondingly, this embodiment provides a system for measuring and predicting the background harmonics of a regional power grid. The system provided in this embodiment can implement the method for measuring and predicting the background harmonics of a regional power grid in Embodiment 1, and this system can be implemented in a software, hardware, or a combination of software and hardware manner. For example, this system can include integrated or separate functional modules or functional units to execute the corresponding steps in each method of Embodiment 1. Since the system in this embodiment is basically similar to the method embodiment, the description process in this embodiment is relatively simple, and the relevant parts can refer to the partial description of Embodiment 1. The embodiments of the system provided in this embodiment are only illustrative.

[0054] The system for measuring and predicting the background harmonics of a regional power grid provided in this embodiment includes: A simulation area determination module, configured to obtain the topology diagram of the regional power grid in the current year, and determine a simulation area of a specific voltage level in the topology diagram according to actual requirements; A harmonic model establishment module, configured to model the simulation area based on the grid circuit data of the regional power grid to obtain an initial harmonic model of the entire regional power grid; An iterative calculation module, configured to run the initial harmonic model and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, to obtain the harmonic model of the simulation area corresponding to the specific voltage level of the regional power grid in the current year; A harmonic prediction module, configured to adjust the harmonic model according to the grid circuit data of the regional power grid after transformation or in the planned year after the internal transformation or development of the regional power grid, and calculate the harmonic distribution at any point in the regional power grid after transformation or in the planned year based on the adjusted harmonic model. [[ID=!17]]

[0055] Further, the simulation area determination module includes: A concerned area determination module, configured to determine the specific voltage level and the area to be transformed or developed in the regional power grid in the current year as the "concerned area"; A topology extraction module, which is used to regard any busbar of any substation in the "area of interest" as a "point", any line or transformer as a "line", and determine the boundary points of the "area of interest". An expansion module, which is used to expand outward from the boundary points of the "area of interest" and expand to other voltage levels at the same time, so as to obtain "primary outgoing lines" and "primary nodes". A simulation area module, which is used to use the "area of interest", "primary nodes" and "primary outgoing lines" together as the simulation area corresponding to a specific voltage level of the regional power grid in the current year.

[0056] Furthermore, a harmonic model establishment module includes: A first model establishment module, which is used for the "area of interest", using software that meets preset requirements to model all devices in the area of interest; for each "primary node", using an equivalent power source and an equivalent harmonic impedance to equivalent the fundamental wave characteristics and harmonic characteristics of each "primary node" outside the "area of interest", so as to obtain an equivalent model outside the "area of interest"; combining the harmonic models of all devices inside the "area of interest" with the equivalent model outside the "area of interest", so as to obtain the initial harmonic model of the regional power grid in the current year. A second model establishment module, which is used to expand one more "line" from each "primary node" to the outside of the simulation area to obtain "secondary nodes", and this line is the "secondary outgoing line", and the connection lines between "secondary nodes" are also used as "secondary outgoing lines", and expand the original simulation area to include "secondary nodes"; measure the sum of the harmonic currents flowing from the "secondary nodes" to the inside of the simulation area outside the simulation area as the equivalent harmonic current source of the "secondary nodes", and measure the fundamental wave voltage of the secondary nodes as the fundamental wave voltage source of the "secondary nodes", that is, it is considered that the harmonic impedance of the network part of the "secondary nodes" outside the simulation area is infinite and the fundamental wave impedance is zero, so as to obtain the initial harmonic model of the regional power grid in the current year.

[0057] Furthermore, an iterative calculation module includes: A simulation module, which is used to run the initial harmonic model to obtain the harmonic currents on all "primary outgoing lines". An adjustment module, which is used to adjust the amplitudes and phases of the harmonic components of the equivalent harmonic current source corresponding to each "primary node" based on the deviation between the harmonic currents on all "primary outgoing lines" and the measured values, and then return to the simulation module. A judgment module, which is used to judge whether the harmonic currents on each "primary outgoing line" after adjustment are similar to the measured values. If so, end the iteration, otherwise return to the adjustment module to continue the adjustment.

[0058] Furthermore, a harmonic prediction module includes: The transformed prediction module is used to keep the equivalent harmonic current sources, equivalent fundamental voltage sources, and equivalent fundamental and harmonic impedances of each "primary node" unchanged based on the harmonic model corresponding to a specific high-elegance level of the regional power grid in the current year, and adjust the wiring and equipment parameters within the "area of concern" according to the expected wiring and equipment parameters of the transformed regional power grid. The developed prediction module is used to, based on the harmonic model corresponding to a specific high-elegance level of the regional power grid in the current year, adjust the wiring and equipment parameters within the "area of concern" according to the expected wiring and equipment parameters in the planned year. Then, for the equivalent fundamental impedance and equivalent fundamental voltage source corresponding to each "primary node", they should be recalculated using the PSD or PSASD system simulation software based on the power grid circuit data in the planned year. For the equivalent harmonic impedance corresponding to each "primary node", the equivalent harmonic impedance of the power network outside the simulation area of each "primary node" should be recalculated using the NIMSCAN software based on the power grid circuit data in the planned year. For the equivalent harmonic current source of each "primary node", the original equivalent harmonic current source should be multiplied by the average annual growth rate of the load and the number of years. If typical harmonic sources are newly connected to each "primary node" in the planned year, the typical harmonic spectra after considering the capacity and network conversion of these typical harmonic sources should be added to each equivalent harmonic current source.

[0059] Embodiment 4 This embodiment provides a processing device corresponding to the method for measuring and predicting background harmonics of a regional power grid provided in Embodiment 1. The processing device can be a processing device for a client, such as a mobile phone, laptop computer, tablet computer, desktop computer, etc., to execute the method of Embodiment 1.

[0060] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, the memory, and the communication interface are connected through the bus to complete communication with each other. A computer program that can run on the processor is stored in the memory. When the processor runs the computer program, it executes the method for measuring and predicting background harmonics of a regional power grid provided in Embodiment 1.

[0061] Preferably, the memory can be a high-speed random access memory (RAM: Random Access Memory), and may also include a non-volatile memory, such as at least one disk memory.

[0062] Preferably, the processor can be a general-purpose processor of various types such as a central processing unit (CPU), a digital signal processor (DSP), etc., which is not limited here.

[0063] Embodiment 5 The method for measuring and predicting background harmonics of a regional power grid in Embodiment 1 can be specifically implemented as a computer program product, which may include a computer-readable storage medium having thereon computer-readable program instructions for executing the method for measuring and predicting background harmonics of a regional power grid described in Embodiment 1.

[0064] A computer-readable storage medium can be a tangible device that retains and stores instructions for use by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the foregoing.

[0065] Those skilled in the art should understand that the embodiments of the present invention may be provided as a method, a system, or a computer program product. Therefore, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce means for realizing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks. These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including instruction means that realizes the functions specified in Figure 1 one or more of the flows Figure 1 or blocks. These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are performed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide means for realizing the functions specified in Figure 1 one or more of the flows Figure 1Steps of functions specified in one or more boxes.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific implementation manners of the present invention, and any modification or equivalent substitution that does not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A method for measuring and predicting background harmonics of a regional power grid, characterized in that, The steps include: Obtain the topology diagram of the regional power grid for the current year, and determine the simulation area of a specific voltage level in the topology diagram according to actual requirements; Based on the power grid circuit data of the regional power grid, model the simulation area to obtain the initial harmonic model of the regional power grid; Take the measured harmonic current value of the regional power grid for the current year as the initial iteration value, run the initial harmonic model, and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, so as to obtain the harmonic model of the simulation area corresponding to a specific voltage level of the regional power grid for the current year; Adjust the harmonic model according to the power grid circuit data of the regional power grid after transformation or in the planned year, and calculate the harmonic distribution at any point of the regional power grid after transformation or in the planned year based on the adjusted harmonic model.

2. The method for measuring and predicting background harmonics of a regional power grid according to claim 1, characterized in that The obtaining of the topology diagram of the regional power grid for the current year and the determination of the simulation area of a specific voltage level in the topology diagram according to actual requirements include: Determine the specific voltage level of concern and the area to be transformed or developed in the regional power grid for the current year as the area of concern; Regard any busbar of any substation in the area of concern as a point, and any line or transformer as a line, and determine the boundary points of the area of concern; Expand outward from the boundary points of the area of concern and expand to other voltage levels at the same time to obtain the primary outgoing lines and primary nodes; Among them, expanding outward from the boundary points of the area of concern and expanding to other voltage levels at the same time to obtain the primary outgoing lines and primary nodes includes: Expand outward from the boundary points of the area of concern, regard the point separated from the boundary point by one line as the primary node, and regard this separated line as the primary outgoing line at the same time; Regard the busbars on the other voltage level sides of the transformers in the substations within the area of concern as primary nodes, and the transformers as primary outgoing lines; Regard the area of concern, the primary nodes and the primary outgoing lines together as the simulation area corresponding to a specific voltage level of the regional power grid for the current year.

3. A method for measuring and predicting background harmonics of a regional power grid according to claim 2, characterized in that, The modeling of the simulation area based on the power grid circuit data of the regional power grid to obtain the initial harmonic model of the regional power grid includes: For the area of concern, use software that meets the preset requirements to model all equipment within the area of concern; for each primary node, use an equivalent power source and equivalent harmonic impedance to equivalent the fundamental wave characteristics and harmonic characteristics of each primary node outside the area of concern to obtain an equivalent model outside the area of concern; combine the harmonic models of all equipment inside the area of concern with the equivalent model outside the area of concern to obtain the initial harmonic model of the regional power grid for the current year; or Expand one more line from each primary node to the outside of the simulation area to obtain secondary nodes, this line is the secondary outgoing line, and the connection lines between the secondary nodes are also used as secondary outgoing lines, and expand the original simulation area to include the secondary nodes; measure the total harmonic current flowing from the secondary nodes to the inside of the simulation area outside the simulation area as the equivalent harmonic current source of the secondary nodes, and measure the fundamental wave voltage of the secondary nodes as the fundamental wave voltage source of the secondary nodes to obtain the initial harmonic model of the regional power grid for the current year.

4. The method for measuring and predicting background harmonics of a regional power grid according to claim 3, wherein For each primary node, the fundamental wave characteristics and harmonic characteristics of each primary node outside the concerned area are equivalent using an equivalent power source and an equivalent harmonic impedance to obtain an equivalent model outside the concerned area, including: For the primary nodes extended from the boundary points of the concerned area, for the part of the network connected to them outside the concerned area, first calculate the equivalent fundamental wave voltage source and equivalent fundamental wave impedance of these network parts, calculate the equivalent harmonic impedance of these network parts, and after connecting the equivalent fundamental wave voltage source in series with the equivalent harmonic impedance with impedance values set at each frequency, then connect them in parallel with an iterative equivalent harmonic current source to replace; among them, the initial iterative value of the equivalent harmonic current source is the sum of the measured harmonic currents of all parts of this primary node outside the concerned area; For the primary nodes extended from the busbars on the other voltage levels of the transformers in the substations within the concerned area, replace them with an equivalent fundamental wave voltage source and an equivalent fundamental wave impedance connected in series, and then connected in parallel with an iterative equivalent harmonic current source, among which, the initial iterative value of the equivalent harmonic current source is the sum of the measured harmonic currents of all parts of this primary node outside the concerned area.

5. A method for measuring and predicting background harmonics of a regional power grid according to claim 2, characterized in that, Using the measured harmonic current values of the regional power grid in the current year as the initial iterative value, running the initial harmonic model, and continuously iterating until the harmonic current output by the model simulation meets the preset error requirement to obtain the harmonic model of the simulation area of the specific voltage level of the regional power grid in the current year, including: ① Using the measured harmonic current values of the regional power grid in the current year as the initial iterative value, running the initial harmonic model to obtain the harmonic currents on all primary outgoing lines; ② Based on the deviation between the harmonic currents on all primary outgoing lines and the measured values, adjust the amplitude and phase angle of each harmonic of the equivalent harmonic current source corresponding to each primary node, and then return to step ①; ③ Judge whether the harmonic currents on each primary outgoing line after adjustment are similar to the measured values. If so, end the iteration; otherwise, return to step ② to continue the adjustment.

6. A method for measuring and predicting background harmonics after the transformation or development of a regional power grid as described in claim 5, characterized in that, The measured values include the harmonic currents of all outgoing lines of the primary nodes extended from the boundary points of the concerned area and the harmonic currents on the other voltage levels of the transformers corresponding to the primary nodes extended from the busbars on the other voltage levels of the transformers in the substations within the concerned area; When measuring the harmonic current, the measurement methods include the following two: First: In the same time period, measure the harmonic currents of the same phase of all primary nodes within a preset duration, and the current transformers used need to ensure that they can cover the considered frequency band; Second: In the same time period of several consecutive working days, gradually measure the harmonic currents of the same phase of each primary node in batches.

7. A method for measuring and predicting background harmonics of a regional power grid according to claim 2, characterized in that, When adjusting the harmonic model according to the grid circuit data of the regional power grid in the transformed or planned year, it includes: Based on the harmonic model corresponding to the specific voltage level of the regional power grid in the current year, keep the equivalent harmonic current source, equivalent fundamental wave voltage source, equivalent fundamental wave, and harmonic impedance of each "primary node" unchanged, and adjust the wiring and equipment parameters within the concerned area according to the expected wiring and equipment parameters of the transformed regional power grid; or Based on the harmonic model corresponding to a specific voltage level of the regional power grid in the current year, adjust the wiring and equipment parameters in the area of concern according to the expected wiring and equipment parameters in the planned year; then, recalculate the equivalent fundamental impedance and equivalent fundamental voltage source corresponding to each first-level node based on the power grid circuit data in the planned year; for the equivalent harmonic impedance corresponding to each first-level node, recalculate the equivalent harmonic impedance of the power network outside the simulation area for each first-level node according to the power grid circuit data in the planned year; for the equivalent harmonic current source of each first-level node, multiply the original equivalent harmonic current source by the annual average growth rate of the load and the number of years according to the local annual average growth rate of the load. If typical harmonic sources are newly connected to each first-level node in the planned year, add the typical harmonic spectra after considering the capacity and network conversion of these typical harmonic sources to each equivalent harmonic current source.

8. A system for measuring and predicting background harmonics in a regional power grid, characterized in that, Including: A simulation area determination module, configured to obtain the topology diagram of the regional power grid in the current year and determine the simulation area of a specific voltage level in the topology diagram according to actual requirements; A harmonic model establishment module, configured to model the simulation area based on the power grid circuit data of the regional power grid to obtain the initial harmonic model of the regional power grid; An iterative calculation module, configured to use the measured harmonic current value of the regional power grid in the current year as the initial iteration value, run the initial harmonic model, and continuously iterate until the harmonic current output by the model simulation meets the preset error requirement, so as to obtain the harmonic model of the simulation area corresponding to a specific voltage level of the regional power grid in the current year; A harmonic prediction module, configured to adjust the harmonic model according to the power grid circuit data of the regional power grid after transformation or in the planned year, and calculate the harmonic distribution at any point of the regional power grid after transformation or in the planned year based on the adjusted harmonic model.

9. A computer-readable storage medium storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any of the methods described in claims 1 to 7.

10. A computing device, characterized in that, Including: One or more processors and a memory, wherein the memory stores one or more programs and is configured to be executed by the one or more processors. The one or more programs include instructions for executing any of the methods described in claims 1 to 7.

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