CN116976256A - A characteristic signal frequency selection method based on identifying system impedance detection islands - Google Patents
A characteristic signal frequency selection method based on identifying system impedance detection islands Download PDFInfo
- Publication number
- CN116976256A CN116976256A CN202310815439.9A CN202310815439A CN116976256A CN 116976256 A CN116976256 A CN 116976256A CN 202310815439 A CN202310815439 A CN 202310815439A CN 116976256 A CN116976256 A CN 116976256A
- Authority
- CN
- China
- Prior art keywords
- impedance
- model
- grid
- frequency
- characteristic signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
-
- G—PHYSICS
- G06—COMPUTING OR CALCULATING; COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/30—Circuit design
- G06F30/32—Circuit design at the digital level
- G06F30/33—Design verification, e.g. functional simulation or model checking
- G06F30/3323—Design verification, e.g. functional simulation or model checking using formal methods, e.g. equivalence checking or property checking
-
- G—PHYSICS
- G06—COMPUTING OR CALCULATING; COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2113/00—Details relating to the application field
- G06F2113/04—Power grid distribution networks
-
- H02J2103/30—
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Theoretical Computer Science (AREA)
- Power Engineering (AREA)
- Evolutionary Computation (AREA)
- Geometry (AREA)
- General Engineering & Computer Science (AREA)
- Measurement Of Resistance Or Impedance (AREA)
Abstract
The invention discloses a characteristic signal frequency selection method based on an identification system impedance detection island, which comprises the following steps: establishing a power grid model; obtaining measured impedance in a grid-connected mode and in an island mode according to a power grid model; selecting a frequency of the characteristic signal according to the impedance; on the basis of analyzing the impedance-frequency characteristics of each element of the system, the impedance-frequency characteristics of the grid-connected points of the system during grid-connected and off-grid operation are obtained, a specific characteristic frequency selection basis is provided for a harmonic impedance measurement island detection method, and the sensitivity and reliability of island detection are improved.
Description
Technical Field
The invention relates to the technical field of power system detection, in particular to a characteristic signal frequency selection method for detecting islanding based on impedance of an identification system.
Background
With the access of high-proportion new energy, the protection control of the power distribution network also meets new challenges, wherein the island problem is particularly prominent, and island detection is essential for the safe operation of the power distribution network. The occurrence of islanding threatens the safety of power grid maintenance personnel and also causes damage to system equipment, for example, when reclosing, a distributed power generation device in a system may be out of synchronization with a power grid, so that a circuit breaker device is damaged, and a high impact current may be generated, thereby damaging the distributed power generation device in the islanding system and even leading to re-tripping of the power grid. The current island detection method can be divided into an active method and a passive method, but has the following problems: when the source load power is matched, a detection blind area is entered, the detection failure is caused by the dilution effect when the multi-distributed power supply is connected, the anti-islanding protection malfunction is caused by the disturbance when the system is in normal operation, the electric energy quality is influenced by the detection signal, and the like. The island detection method based on harmonic impedance measurement in the active method is representative, but the selection of the characteristic signal frequency is not based, so that the island detection accuracy is not high.
For example, an "island detection method based on harmonic impedance characteristic function pattern recognition" disclosed in chinese patent literature, its bulletin number: CN104111409B, discloses a method for collecting voltage of the distributed grid-connected power generation system at the point of common coupling in the island state and the non-island state and access current of the distributed grid-connected power generation system; (2) Establishing a harmonic impedance characteristic function phi (k) according to the voltage value and the current value acquired in the step (1) to obtain a characteristic vector space; (3) Training a learning sample through pattern recognition to obtain discrimination capability of an island state and a non-island state of the distributed grid-connected power generation system, but the scheme does not select the frequency of the characteristic signals, so that the detection sensitivity and the reliability are low.
Disclosure of Invention
In order to select the characteristic signal frequency in the prior art, the invention provides the characteristic signal frequency selection method for detecting the island based on the impedance of the identification system, which can amplify the island characteristic and improve the island detection sensitivity and reliability.
In order to achieve the above object, the present invention provides the following technical solutions:
a characteristic signal frequency selection method for detecting islanding based on impedance of an identification system comprises the following steps:
establishing a power grid model;
obtaining measured impedance in a grid-connected mode and in an island mode according to a power grid model;
the frequency of the characteristic signal is selected according to the impedance. Firstly, establishing a power grid model for simulation, and enabling the power grid model to simulate a state which is most difficult to detect in island detection by modifying parameters; then, respectively determining characteristic impedance of different parts in the power grid model, and determining impedance in different modes of the grid-connected point according to the characteristic impedance of the different parts; and finally, determining the frequency of the detection signal according to the impedance-frequency characteristics of the grid-connected point in different modes. Island characteristics can be amplified, and island detection sensitivity and reliability are improved.
Preferably, the building of the power grid model includes modeling the high-voltage power grid by using an RL series equivalent model, modeling the distribution line by using a frequency-dependent parameter model, and modeling the load by using an RLC parallel model. After modeling equivalent is carried out on the power grid, the overhead line and the load in the power grid, the island mode of the power grid is conveniently simulated, and the measured impedance under different modes is obtained.
Preferably, after the power grid model is established, the RL parameter in the high-voltage power grid model is determined through power frequency impedance, and the frequency variation parameter in the distribution line model is determined through PSCAD. The power frequency impedance is determined in advance, the distribution line is simulated through a known centralized parameter model, and the power frequency impedance is generated through PSCAD according to the line erection height and the geometric average distance. Thereby realizing an analog power grid.
Preferably, the measured impedance in the grid-connected mode is a parallel impedance of the system impedance at the upstream line end and the load impedance at the downstream line end of the distributed power access point. Can include the impedance of the downstream line when it is normally connected.
Preferably, the measured impedance in the island mode is the load-on-line impedance of the line downstream of the distributed power access point. Can include the impedance at the time of disconnection of the downstream line.
Preferably, the method comprises the steps of respectively determining curves of measured impedance along with frequency change in a grid-connected mode and an island mode, and taking the frequency with the largest impedance amplitude difference except the power frequency as the frequency of a characteristic signal. The frequency of the characteristic signal is selected according to the relation between the impedance frequency by determining the change curve between the impedance and the frequency in different modes, so that the island detection accuracy of the characteristic signal can be improved.
Preferably, after the load is modeled by adopting an RLC parallel model, the local load power and the photovoltaic output are balanced, so that the RLC load resonates at the power frequency. The most difficult-to-detect island state can be simulated.
Preferably, obtaining the measured impedance includes respectively performing topology and series-parallel operation on the impedance model of each part in the power grid model to obtain the parallel network point measured impedance when the grid connection and the off-grid operation are performed. And obtaining measured impedance through equivalent impedance or characteristic impedance of each part in the power grid, and further bringing in component parameters to obtain an impedance characteristic curve.
The invention has the following advantages:
(1) On the basis of analyzing the impedance-frequency characteristics of each element of the system, the impedance-frequency characteristics of the grid-connected points of the system during grid-connected and off-grid operation are obtained, a specific characteristic frequency selection basis is provided for a harmonic impedance measurement island detection method according to the impedance-frequency characteristics, and the sensitivity and reliability of island detection are improved; (2); (3).
Drawings
The drawings in the following description are merely exemplary and other implementations drawings may be derived from the drawings provided without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a schematic diagram of a simplified AC distribution network with multiple photovoltaic grid-connected via an inverter in an embodiment.
Fig. 2 is a schematic diagram of an equivalent impedance model of the power grid in the embodiment.
Fig. 3 is a schematic diagram of a uniform transmission line distribution parameter frequency-variant model in an embodiment.
FIG. 4 is a schematic diagram of an impedance equivalence model of a local load in an embodiment.
Fig. 5 is a schematic diagram of impedance characteristics obtained by connecting elements in series and parallel in the embodiment.
FIG. 6 is a schematic diagram of impedance-frequency characteristics of grid-connected points in a parallel-to-off-grid operation state in an embodiment.
Fig. 7 is a schematic diagram of the relationship between the probe signal frequency and the line length in the embodiment.
Detailed Description
The following description of the embodiments of the invention is intended to be illustrative of the specific embodiments of the invention in which all other embodiments of the invention, as would be apparent to one skilled in the art without undue burden, are included in the scope of the invention.
The basic principle of the proposed method is illustrated by a simplified ac distribution network comprising a plurality of photovoltaic grid-connected via inverters as shown in fig. 1. In the figure, a photovoltaic power supply is connected to a public coupling point (point of the common coupling, PCC) through a direct current boost converter, an inverter and a transformer in sequence, and then is connected to a power grid through a section of line. When the system is subjected to larger disturbance or fault to cause the breaker KPCC to be disconnected, the photovoltaic power generation system and the local load form an island.
The method comprises the following steps of establishing a power grid model; and modeling a high-voltage power network by adopting an RL series equivalent model, modeling a distribution line by adopting a frequency-dependent parameter model, and modeling a load by adopting an RLC parallel model. And determining the RL parameter in the high-voltage power grid model through the power frequency impedance, and determining the frequency variation parameter in the distribution line model through the PSCAD. Firstly, establishing a power grid model for simulation, and enabling the power grid model to simulate a state which is most difficult to detect in island detection by modifying parameters; then, respectively determining characteristic impedance of different parts in the power grid model, and determining impedance in different modes of the grid-connected point according to the characteristic impedance of the different parts; and finally, determining the frequency of the detection signal according to the impedance-frequency characteristics of the grid-connected point in different modes. And the optimal selection of island detection frequency signals in the specific power grid structure is realized.
1) System impedance model building
(1) Equivalent electric network
In this example, the power grid is equivalent by using a three-phase voltage source with internal resistance in the form of RRL (the nature is still RL model), and the equivalent impedance model is shown in fig. 2. Wherein R is 1s ＝0.4Ω，R 1p ＝1000Ω，L 1p ＝0.0175H。
(2) Overhead line
The overhead line adopts a frequency-variable distribution parameter model, as shown in fig. 3. And regarding the uniform single-phase line as a two-port network, calculating the input impedance of the line under different working conditions at the tail end by using a transmission line equation, and further analyzing the impedance characteristic of the line. Ru (f) and Lu (f) are respectively line resistance and inductance in unit length, and are respectively 0.0347 omega/km and 1.3483mH/km at power frequency; gu and Cu are the line-to-ground conductance and the distributed capacitance of unit length respectively, and the distribution capacitance of unit length is 0.0087 mu F/km because the line-to-ground conductance of the distribution network is very small and is ignored in the following analysis;the voltages at the input end and the tail end are respectively; ZL is the end load impedance.
In the end-to-load condition, it is assumed that the transmission line is terminated with a load Z L The in-end impedance is expressed as
Wherein Zc is the characteristic impedance of the transmission line, calculated by equation (2); gamma is the propagation constant of the transmission line, calculated by equation (3); l is the line length.
(3) Load of
The local load is equivalent to the RLC parallel model shown in fig. 4, and the quality factor is 2.5. In order to construct the most difficult to detect state of the island, the local load power should be balanced with the photovoltaic output, i.e. the RLC load resonates at the power frequency. The parameters are calculated according to formula (4).
Wherein P, V, f is the rated power, rated voltage and rated operating frequency of the local load respectively; qf is the load figure of merit, taken as 2.5.
2) System parallel/off-grid impedance-frequency characteristic comparison
The impedance models of the above parts are subjected to series-parallel operation according to the topology shown in fig. 1, so that the parallel network point measuring impedance during the parallel and off-network operation can be obtained, and the expressions are shown as formulas (5) and (6).
Wherein, zs, Z load1 、Z load2 Equivalent impedance converted to 10kV side for the power grid, the load1 and the load 2 respectively; z is Z ci 、l i 、y i The characteristic impedance, line length, propagation constant of the overhead line Li, i=1, 2,3, respectively.
The impedance characteristic curves shown in fig. 5 are drawn by substituting the system element parameters according to equations (5) and (6). In the figure, Z 1 The equivalent impedance of the transformer and the Load1 is connected to the end of the line L1 in fig. 1; zs is the grid side equivalent impedance; z is Z 1s Is Z 1 Equivalent impedance obtained by connecting Zs in parallel; z is Z l1s Terminating Z for line L2 1s Is a constant current source. As can be seen from the figure, zs.apprxeq.Z 1s <<Z l1s The circuit between the grid connection point and the bus of the power grid is explained to influence the equivalent impedance Z l1s Is a major factor in (a) is provided.
The relationship between the equivalent impedance and the frequency of the grid-connected point during grid-connected and off-grid operation of the power distribution network system shown in fig. 1, namely the impedance-frequency characteristic of the grid-connected point, can be further obtained from fig. 5, and is shown in fig. 6. It can be seen that when the characteristic frequency is within the range of 0-400 Hz, the characteristic frequency impedance at the grid-connected point before and after island formation has a large difference, and the characteristic frequency impedance can be used as a criterion for island detection. In order to improve the island protection sensitivity, the frequency corresponding to the maximum difference between the island protection sensitivity and the island protection sensitivity can be further obtained and used as the basis for selecting the frequency of the detection signal. In the figure, the corresponding frequency of the point with the largest difference except the power frequency is 165.96Hz and is also a parallel resonance point of grid-connected impedance, so that 165Hz can be approximately selected as the frequency of a detection signal.
In order to explore the influence of the line length between the grid-connected point and the bus of the power distribution network on the frequency selection of the detection signal, the line length variation range is set to be 0-50 km, and the relationship between the frequency of the detection signal and the line length is obtained, as shown in fig. 7. It can be seen that as the distance between the grid-tie point and the distribution network bus increases, the frequency of the selected detection signal decreases, i.e., the grid-tie impedance parallel resonance frequency decreases, and approaches 50Hz.
While the invention has been described in detail in the foregoing general description and specific examples, it will be apparent to those skilled in the art that modifications and improvements can be made thereto. Accordingly, such modifications or improvements may be made without departing from the spirit of the invention and are intended to be within the scope of the invention as claimed.
Claims (8)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310815439.9A CN116976256A (en) | 2023-07-05 | 2023-07-05 | A characteristic signal frequency selection method based on identifying system impedance detection islands |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310815439.9A CN116976256A (en) | 2023-07-05 | 2023-07-05 | A characteristic signal frequency selection method based on identifying system impedance detection islands |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116976256A true CN116976256A (en) | 2023-10-31 |
Family
ID=88475952
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310815439.9A Pending CN116976256A (en) | 2023-07-05 | 2023-07-05 | A characteristic signal frequency selection method based on identifying system impedance detection islands |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116976256A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN120280869A (en) * | 2025-06-10 | 2025-07-08 | 湖南工程学院 | Relay protection analysis method and system for distributed photovoltaic access power distribution network |
-
2023
- 2023-07-05 CN CN202310815439.9A patent/CN116976256A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN120280869A (en) * | 2025-06-10 | 2025-07-08 | 湖南工程学院 | Relay protection analysis method and system for distributed photovoltaic access power distribution network |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN104793148B (en) | Distributed generator islanding detection method based on grid entry point characteristic harmonics voltage measurement | |
| CN102253283B (en) | A kind of distributed micro-grid grid-connected island detection method based on Wavelet Packet Energy Spectrum | |
| CN106501668B (en) | A traditional distribution network single-phase disconnection fault line selection method | |
| Guha et al. | A passive islanding detection approach for inverter-based distributed generation using rate of change of frequency analysis | |
| CN106786424A (en) | Send out method for pilot protection of circuit in new energy station based on current waveform similarity | |
| WO2021213211A1 (en) | Cable insulation impedance detection method and device | |
| CN105182189B (en) | The inverter combined based on electric voltage frequency and measurement impedance disturbs formula isolated island detection method | |
| CN103983880A (en) | Anti-islanding protection capability detection device and testing method of grid-connected inverter | |
| CN104638671B (en) | Based on introducing particle cluster algorithm and the island detection method of phase perturbation | |
| CN110618314B (en) | Harmonic wave responsibility division method for resisting short-circuit fault interference of power distribution system | |
| CN110824275A (en) | Micro-grid AC/DC bus interface converter demonstration test platform | |
| CN109387713B (en) | Hybrid method for distributed grid-connected island detection | |
| Guerrero et al. | A ground fault location method for DC systems through multiple grounding connections | |
| CN108683162B (en) | The wind power system time domain full dose longitudinal protection method differentiated based on fault model | |
| CN116976256A (en) | A characteristic signal frequency selection method based on identifying system impedance detection islands | |
| CN110645888A (en) | Winding deformation judgment method based on frequency response analysis FRA | |
| Khoker et al. | A current based hybrid algorithm using discrete wavelet transform and Hilbert transform for detection and classification of power system faults in the presence of solar energy | |
| CN203929928U (en) | The anti-isolated island energy of a kind of grid-connected converter force checking device | |
| CN110161395A (en) | The state of insulation on-line monitoring method and its monitoring system of inverter AC motor | |
| CN211826314U (en) | A grid-connected test device for wind turbines | |
| CN114384319A (en) | Grid-connected inverter island detection method, system, terminal and medium | |
| CN114696301A (en) | Double-fed wind power plant output line single-phase grounding protection method and system | |
| CN112949729A (en) | Control algorithm for micro-grid current conversion | |
| Sarangi et al. | Active islanding detection and analysis of total harmonic distortion for inverter-interfaced microgrid based on high-frequency signal installation | |
| Datta et al. | Harmonic distortion, inter-harmonic group magnitude and discrete wavelet transformation based statistical parameter estimation for line to ground fault analysis in microgrid system |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |