CN-122017390-A - Island detection method and system based on Goertzel algorithm and quality factor entropy dispersion

CN122017390ACN 122017390 ACN122017390 ACN 122017390ACN-122017390-A

Abstract

A island detection method and system based on Goertzel algorithm and quality factor entropy dispersion comprises the steps of collecting three-phase voltage and current signals of distributed power generation, conducting double-domain leakage suppression processing on the signals to obtain accurate fundamental wave parameters, conducting re-fundamental wave construction and harmonic signal separation on the accurate fundamental wave parameters to obtain residual harmonic signals, conducting directional spectrum analysis on specific subharmonics in the residual harmonic signals by means of Goertzel algorithm to obtain voltage amplitude values and current amplitude values of the specific harmonics, calculating harmonic impedance amplitude values according to the voltage amplitude values and the current amplitude values of the specific harmonics, obtaining quality factor entropy dispersion corresponding to the specific harmonics based on the harmonic impedance amplitude values, conducting island detection according to the quality factor entropy dispersion corresponding to the specific harmonics, and obtaining detection results. According to the invention, the uniformity of load quality factor distribution is quantized by utilizing the information entropy theory, so that the detection blind area can be reduced, and the detection efficiency and accuracy are improved.

Inventors

TONG JUN
ZHAN ZHICHENG
LUO HUAN
ZHANG MIN
YANG HUIHUI
XIAO YUANQING
ZHOU XIONGWEI

Assignees

北京四方继保工程技术有限公司
北京四方继保自动化股份有限公司
四方继保（武汉）软件有限公司

Dates

Publication Date: 20260512
Application Date: 20251230

Claims (11)

1. Island detection method based on Goertzel algorithm and quality factor entropy dispersion is characterized by comprising the following steps: Step 1, collecting three-phase voltage and current signals at a public connection point of a distributed power generation system; step 2, performing double-domain leakage suppression processing on the three-phase voltage and current signals, wherein the double-domain leakage suppression processing comprises time domain processing and frequency domain processing, and obtaining accurate fundamental wave parameters; Step 3, carrying out fundamental wave reconstruction and harmonic signal separation on the accurate fundamental wave parameters to obtain a residual harmonic signal; Step 4, carrying out directional spectrum analysis on specific harmonic waves in the residual harmonic wave signals by adopting a Goertzel algorithm to obtain voltage amplitude values and current amplitude values of the specific harmonic waves; Step 5, calculating a harmonic impedance amplitude according to the voltage amplitude and the current amplitude of the specific harmonic, and obtaining a quality factor entropy dispersion corresponding to the specific harmonic based on the harmonic impedance amplitude; and 6, performing island detection according to the quality factor entropy dispersion corresponding to the specific harmonic wave to obtain a detection result.
2. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 1, wherein, The step 2 comprises the following steps: Step 2-1, time domain processing, namely, the collected three-phase voltage and current signals form an original signal Three-stage cascade adaptive filter is adopted for the original signal Performing time domain filtering to obtain a fundamental wave signal after the time domain filtering; and 2-2, frequency domain processing, namely precisely analyzing the fundamental wave signal subjected to time domain filtering by adopting a DFT frequency offset correction algorithm to obtain precise fundamental wave parameters.
3. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 2, wherein, The adoption of three-stage cascade self-adaptive filter to the original signal The processing method specifically comprises the following steps: The three-stage cascade adaptive filter comprises a first-order differential filter H 1 , a first-order integrating filter H 2 and a first-order integrating filter H 3 ; the first-order differential filter H 1 , the first-order integrating filter H 2 and the first-order integrating filter H 3 are respectively used for filtering direct current components and even harmonics, 3 rd order and 3 integer times of harmonics, 5 th order and 7 th order characteristic harmonics in the original signals; The fundamental wave signal after time domain filtering is S [ n ] H 1 *H 2 *H 3 .
4. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 3, wherein, The precise fundamental wave parameters include precise real part of fundamental wave component Imaginary part Amplitude value And phase of The acquisition mode is as follows: input signal at time t The method comprises the following steps: Wherein, the For the signal amplitude value, Is the fundamental wave initial phase angle, the input signal is the fundamental wave signal after time domain filtering, Is the rated frequency of the power frequency, Is the frequency offset; Discretizing the input signal, setting N point of sampling every wave, sampling frequency as Sampling interval is Sampling value at time k The method comprises the following steps: Sampling value at k time After the rectangular window is adopted for truncation and discrete Fourier transform is carried out, the initial real part of the discrete Fourier transform result And an initial imaginary part The method comprises the following steps of: zero crossing frequency measurement is carried out on fundamental wave signals, fundamental frequency is tracked in real time, and current frequency values are obtained According to the current frequency value Obtaining the rated frequency of the power frequency Frequency offset of (2) The method comprises the following steps: combining sampled values at time k Sum-frequency difference For the initial real part And an initial imaginary part Performing preliminary correction to obtain a real part after the preliminary correction And imaginary part The method comprises the following steps: Correcting amplitude The method comprises the following steps: combining the correction system to obtain the final corrected real part And imaginary part The method comprises the following steps: Wherein, the , , , , , , And Are correction coefficients.
5. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 4, wherein, The step 3 specifically includes: obtaining a reconstructed fundamental wave time domain signal according to the accurate fundamental wave parameters : = Wherein n refers to the nth data window; from the reconstructed fundamental time domain signal And the original signal of the original signal Obtaining residual harmonic signals : 。
6. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 1, wherein, The specific subharmonics in the step 4 are 5 subharmonics, 7 subharmonics and 9 subharmonics.
7. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 1, wherein, In the step 5, the quality factor entropy dispersion corresponding to the specific harmonic is calculated as follows: Calculating the harmonic impedance amplitude of PCC points at each specific harmonic order h, wherein the amplitude is Zpcc (j omega h ): |Zpcc(jω h )|=|Vh|/|Ih| Wherein Zpcc is impedance of a public connection point, j is an imaginary unit, omega h is angular frequency of h specific harmonic, and Vh and Ih are harmonic voltage and current when the specific harmonic is h respectively; obtaining impedance amplitude value (Zpcc (jomega 1 )) I under fundamental wave frequency, and calculating load quality factor square value under harmonic frequency h : Taking the square value of the load quality factor as a random variable, and calculating the probability value corresponding to each subharmonic: Wherein, the Representing a probability value corresponding to the h harmonic; Shannon entropy for calculating the probability value : Calculating normalized entropy dispersion, and carrying out normalized treatment on shannon entropy to obtain quality factor entropy dispersion corresponding to specific harmonic : Wherein, the Representing the number of specific harmonics used in the calculation.
8. The island detection method based on Goertzel algorithm and quality factor entropy dispersion according to claim 1, wherein, The step 6 specifically includes: Setting a threshold sigma and dispersing the quality factor entropy corresponding to the specific harmonic Comparing the detection result with a threshold value to obtain a detection result: If it is And judging that the system is in a grid-connected state. If it is And judging that the island state occurs, immediately sending out an off-grid instruction, and disconnecting the distributed power supply from the power grid.
9. An island detection system based on a Goertzel algorithm and a quality factor entropy dispersion, for implementing the island detection method based on the Goertzel algorithm and the quality factor entropy dispersion according to any one of claims 1 to 8, comprising: The signal acquisition module is used for acquiring three-phase voltage and current signals at a public connection point of the distributed power generation system; the leakage suppression module is used for carrying out fundamental wave frequency tracking and double-domain leakage suppression processing on the three-phase voltage and current signals to obtain accurate fundamental wave parameters; The reconstruction and separation module is used for carrying out reconstruction and harmonic signal separation on the accurate fundamental wave parameters to obtain a residual harmonic signal; The frequency analysis module is used for carrying out directional spectrum analysis on specific subharmonics in the residual harmonic signals by adopting a Goertzel algorithm to obtain voltage amplitude values and current amplitude values of the specific harmonics; The quality factor entropy dispersion calculation module is used for calculating a harmonic impedance amplitude according to the voltage amplitude and the current amplitude of the specific harmonic and obtaining the quality factor entropy dispersion corresponding to the specific harmonic based on the harmonic impedance amplitude; And the detection module is used for carrying out island detection according to the quality factor entropy dispersion corresponding to the specific harmonic wave to obtain a detection result.
10. A terminal comprises a processor and a storage medium, and is characterized in that: The storage medium is used for storing instructions; The processor being operative according to the instructions to perform the steps of the islanding detection method as claimed in any one of claims 1-8.
11. A computer readable storage medium having stored thereon a computer program, characterized in that the program when executed by a processor implements the steps of the islanding detection method as claimed in any one of claims 1-8.

Description

Island detection method and system based on Goertzel algorithm and quality factor entropy dispersion Technical Field The invention relates to the technical field of grid-connected operation safety detection, in particular to an island detection method and system based on Goertzel algorithm and quality factor entropy dispersion. Background Island effect is an important safety problem faced when a Distributed Generation (DG) system is operated in grid connection. When the power grid is disconnected due to faults or scheduled overhauls, the distributed power supply continues to supply power to the local load, so that an independent power supply island which is not controlled by the power grid is formed. The islanding may endanger equipment and personnel life safety and affect the restoration of the power supply to the grid. Therefore, standards such as IEEE Std 1547.1-2020 and GB/T33593-2017 at home and abroad all force that the grid-connected inverter must have an island detection function, and the island is effectively detected within 2 seconds and grid-connected connection is disconnected. The existing island detection method mainly comprises the following three types: 1. the method is based on the communication method, and the state of the circuit breaker at the power grid side is monitored through a power line carrier communication or wireless communication mode. The method can realize zero blind area detection theoretically, but has high cost, depends on the reliability of a communication channel, is difficult to guarantee in real-time in a complex power distribution network environment, and limits the large-scale application of the method. 2. The active detection method is to judge whether island occurs or not by injecting small-amplitude disturbance (such as active frequency shift AFD, reactive power disturbance, harmonic injection and the like) into the power grid and observing the response of the power grid. The method can effectively reduce detection dead zone (NDZ), but the injected disturbance can degrade the power quality and increase the Total Harmonic Distortion (THD) of the system. Particularly in a multiple inverter parallel system, the disturbance signals may be diluted or interfere with each other, resulting in detection failure or performance degradation. 3. Passive detection by monitoring abrupt features of local electrical quantities (e.g., voltage, frequency, phase, harmonics, etc.) of a Point of Common Connection (PCC) to detect islanding. The method is simple and feasible, does not influence the quality of electric energy, and is the most widely applied method at present. However, when the output power of the distributed power supply is close to the balance of the local load power, the traditional over/under voltage (OVP/UVP) and over/under frequency (OFP/UFP) protection methods have small voltage and frequency changes, have large detection dead zones, and cannot meet the standard requirements. In order to overcome the defects of the traditional passive method, researchers in recent years propose a passive detection method based on harmonic characteristics, which is mainly divided into two directions: 1. the harmonic impedance method is based on the principle that when grid-connected operation is performed, harmonic impedance at PCC points is formed by parallel connection of power grid impedance and load impedance, and the power grid impedance is usually far smaller than the load impedance, so that the method plays a leading role. After the island occurs, the power grid impedance disappears, and the harmonic impedance of the PCC point is suddenly changed into load impedance. Islanding can be detected by injecting specific harmonic perturbations and measuring changes in the PCC point harmonic impedance. However, in order to cope with the frequency variation characteristics of the load impedance, this method generally requires FFT full spectrum analysis, and is large in calculation amount, poor in real-time performance, and susceptible to spectrum leakage due to frequency offset, and the calculation accuracy is lowered. 2. The harmonic voltage method is to directly utilize the amplitude variation of the characteristic subharmonic voltage (such as 3 times, 5 times, 7 times and the like) of the PCC point after the island occurs to construct a criterion. The method does not need to inject disturbance, but is easily interfered by the background harmonic wave of the power grid, the dynamic response speed is influenced by a filtering link, and the adaptability is insufficient under the condition of a weak power grid. In summary, the prior art mainly has the following drawbacks: 1. the traditional passive method (voltage/frequency) has a huge detection dead zone (NDZ) in a power balance state, the threshold value is difficult to set, and the sensitivity and the reliability are difficult to be compatible. 2. The active detection method is characterized in that dead zone reduction is replaced at