CN110221147B - Power quality detection and analysis method based on multi-composite optimization algorithm - Google Patents
Power quality detection and analysis method based on multi-composite optimization algorithm Download PDFInfo
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Abstract
The invention relates to a power quality detection and analysis method of a multi-composite optimization algorithm. The invention firstly adopts EEMD method to denoise and decompose the sampled electric signal. The amplitude, frequency, attenuation factor and initial phase angle of each of the decomposed IMFs are then processed using the Prony algorithm. In order to improve the accuracy and precision of calculation, the improved dragonfly algorithm is added in the calculation process to be combined with the Prony algorithm to obtain a new intelligent algorithm (temporarily called DP algorithm in the invention) to solve the IMF. In order to obtain better effect, the invention introduces signal-to-noise ratio in DP algorithm, so as to judge the accuracy of the algorithm, and the final result is more accurate.
Description
Technical Field
The invention relates to a power quality detection and analysis method based on a multi-composite optimization algorithm, and belongs to the technical field of power quality detection and analysis of a power grid.
Background
In recent years, rapid development of social economy and continuous improvement of social productivity rapidly improve the living standard of people and rapidly increase the power load of a power supply network. Various impact loads and nonlinear loads in a power grid are rapidly increased, various high-precision equipment is widely applied to a power system, particularly, the condition of electric energy quality in the power system is more and more complicated along with the grid connection of new energy, such as wind power generation, photovoltaic power generation and the like, which has low stability and high randomness, and the electric energy quality problem has attracted more and more attention of various social circles. Therefore, the detection problem of the power quality by related departments is more and more emphasized. However, in reality, discrete data of a power system is often affected by a plurality of error causes at the same time, and the data includes attenuated dc components, inter-harmonics, noise, and the like. Accurately extracting parameters such as amplitude, frequency and the like of periodic signals in the power fault transient signals is important for state analysis, fault diagnosis, control and protection of a power system. The study of scholars at home and abroad has been extensively and intensively conducted. How to extract the characteristic information of the power quality disturbance signal is the basis of the identification and correct classification of the power quality disturbance signal.
Disclosure of Invention
The invention aims to provide a method for detecting and analyzing the quality of electric energy.
In order to achieve the above object, the technical solution of the present invention is to provide a power quality detection and analysis method of a multi-composite optimization algorithm, which is characterized by comprising the following steps:
step 1, EEMD decomposition is carried out after denoising a sampled power failure transient signal by adopting an EEMD method, each IMF component is obtained after EEMD decomposition, and the ith IMF component is recorded as cki(t), performing integration average processing on the IMF components obtained each time, and recording the ith IMF component obtained after processing as ci(t),N is the total number of the Gaussian white noise, the larger N is, the larger the corresponding IMF sum of the Gaussian white noise tends to be 0, and the more the decomposition result approaches to the true value;
step 2, setting the maximum iteration times TmaxSetting a signal-to-noise ratio threshold SNR', and setting the iteration number t to be 0;
and 3, substituting each IMF component obtained in the step 1 as an initial value of a dragonfly algorithm to calculate the separation degree, the alignment degree, the cohesion degree, the food attraction force and the natural enemy repulsion force of each dragonfly individual, wherein:
the separation degree of the ith dragonfly individual is SiThen, there are:
wherein X represents the position of the ith dragonfly individual, and X represents the position of the ith dragonfly individualjThe position of the dragonfly individuals adjacent to X is shown, and N dragonfly individuals adjacent to X are shared;
the ith dragonfly individualAlignment degree of AiThen, there are:
in the formula, VjRepresenting the speed of the dragonfly individual adjacent to X;
the cohesion degree of the ith dragonfly individual is CiThen, there are:
the food attraction of the ith dragonfly individual is FiThen, there are:
Fi=X+-X
in the formula, X+Indicating a food source location;
the repulsive force of the ith individual dragonfly is EiThen, there are:
Ei=X-+X
in the formula, X-Representing the position of the natural enemy;
step 4, setting an alignment degree weight a, a separation degree weight s, a cohesion degree weight c and an inertia factor w, and calculating to obtain an improved natural enemy factor e 'and an improved food factor f':
f'=λ·f
e'=β·e
wherein f represents a food factor before improvement, e represents a natural enemy factor before improvement,
step 5, obtaining the updated position X of the improved dragonfly according to the improved natural enemy factor e' and the food factor ft+1Then, there are:
ΔXt+1=(sSi+aAi+cCi+f'Fi+e'Ei)+wΔXt
Xt+1=Xt+ΔXt+1
in the formula,. DELTA.XtIndicates the update step size, XtThe current position of the ith dragonfly individual;
step 6, setting the new position parameter Xt+1Bringing inTo solve forBring results intoTo find an objective function, wherein:denotes the fitting estimate of x (n), akCoefficient of expression characteristic equation, bkDenotes the complex number corresponding to x (n) fitting estimate,representing the complex number corresponding to the fitting estimated value x (n), and z represents an objective function;
step 7, calculating to obtain ak、Ak、θkAnd fk,AkIs the amplitude of the k order, fkIs the k-th order frequency, θkFor the k-th phase:
Ak=|bk|
in the formula, zkRepresenting the root obtained by solving the polynomial, and delta t representing the sampling interval;
step 9, if T is more than or equal to TmaxOr SNR < SNR', ending the method, otherwise, returning to the step 3.
The invention firstly adopts EEMD method to denoise and decompose the sampled electric signal. The amplitude, frequency, attenuation factor and initial phase angle of each of the decomposed IMFs are then processed using the Prony algorithm. In order to improve the accuracy and precision of calculation, the improved dragonfly algorithm is added in the calculation process to be combined with the Prony algorithm to obtain a new intelligent algorithm (temporarily called DP algorithm in the invention) to solve the IMF. In order to obtain better effect, the invention introduces signal-to-noise ratio in DP algorithm, so as to judge the accuracy of the algorithm, and the final result is more accurate.
Drawings
Fig. 1 and 2 are flow charts of the present invention.
Detailed Description
The invention is further elucidated with reference to the drawing. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
The invention provides a power quality detection analysis method of a multi-composite optimization algorithm, which is based on the following algorithm:
first) Prony algorithm
The Prony algorithm has been widely applied in signal analysis in recent years, and the feasibility of the Prony algorithm has been proved. The Prony algorithm can directly estimate the amplitude, frequency, attenuation factor, and initial phase angle in the signal.
Let x (0), x (1).. and x (N-1) be the sampled data. Then:
wherein N is 0,1,2, …, N-1; k is 1,2, …, P
bkRepresents the complex number corresponding to the fitting estimation value of x (n),denotes the complex number, A, corresponding to the fitting estimate of x (n)kIs the amplitude of the k order, alphakIs a damping factor of the k-th order, fkIs the k-th order frequency, θkAt is the k-th order phase and Δ t is the sampling interval.
Constructing an objective function:
the solution using the difference equation is given below:
equation (1) is a homogeneous solution of the following constant coefficient linear difference equation:
Thus, x (n) can be viewed as the output of a P-th order AR model excited by noise u (n). Solving the regular equation of the AR model can obtain the parameter akSubstituting the formula and obtaining z by root finding of polynomialkWhere k is 1,2, …, P, the order P may be determined according to the AIC criterion of the AR model.
According to formula (1), then
Using least squares solution to obtain [ b1,b2…bP]T. B is formed bykIt is possible to obtain:
Ak=|bk| (4)
in the above formula: k is 1,2, …, P
The fitted signal and the original signal have certain errors, and the signal-to-noise ratio is used for representing that: the larger the better, the signal-to-noise threshold SNR' is set as a criterion for evaluation.
Second) EEMD Process
When the power system normally operates, the waveform is relatively stable. The frequency, the amplitude, the initial phase and the attenuation factor of the signal are analyzed by using a Prony algorithm, the analysis process is simple, and the accuracy of the analysis result is high. However, when the harmonic pollution of the power system is serious, the Prony algorithm is susceptible to noise interference, so that the result analysis is inaccurate. In this case, noise-aided analysis can be applied to EMD by the improved EEMD method to promote anti-aliasing decomposition, and good noise reduction can be achieved while suppressing mode aliasing. The inherent modal component of the noise signal after EEMD decomposition better reveals the physical connotation of the original signal, so that the physical essence of the noise signal is clearer. Therefore, the invention firstly carries out EEMD decomposition on the signal and then carries out Prony analysis on each decomposed IMF component, thereby rapidly and accurately identifying the oscillation mode parameters.
The problem of aliasing of the traditional mode can be solved through multiple EMD after Gaussian white noise is superimposed. When the original signal is added to a white noise background with uniform frequency, signal regions with different time scales can be automatically mapped to a proper scale related to the white noise of the background. After the overall average value after noise is added for many times is averaged by using the principle that the statistical average value of an uncorrelated random sequence is 0, the noise is eliminated, and the overall average value is considered as a signal per se so as to eliminate the modal aliasing phenomenon. The algorithm steps are as follows.
(1) Normally distributed white noise sequence nk(t) to the time series x (t);
x'k(t)=x(t)+nk(t) (9)
(2) adding the time sequence x after the normal distribution white noise sequencek(t) EMD decomposition is carried out on the whole to obtain each IMF component and the component is recorded as cki(t) and a remainder denoted as rkn(t)。
(3) Repeating the steps (1) and (2) for 100 times, and adding a new normal distribution white noise sequence each time;
(4) and performing integrated average processing on the IMF components obtained each time.
In the formula ci(t) represents the final i-th IMF component after EEMD decomposition. And N is the total number of the Gaussian white noise. The larger N is, the larger IMF sum of the corresponding white noise tends to be 0, and the more the decomposition result tends to be a true value.
Third) dragonfly algorithm
In the dragonfly algorithm, the individual dragonfly behaviors mainly include: the main functions of the actions are respectively to avoid mutual collision among individuals around the dragonfly group, ensure the speed consistency among the individuals around the group, ensure the movement of the individuals around the group to an average position, ensure the individuals in the group to be close to a food source and ensure the individuals in the group to avoid natural enemies. The specific meaning and mathematical expression method of these individual behaviors are as follows:
(1) the separation degree means avoiding collision between dragonfly and adjacent individual
(2) Registration refers to the tendency of adjacent individuals to maintain the same velocity.
(3) Cohesion means that the dragonfly tends to gather towards the centre of the adjacent individual.
(4) The food attraction refers to the attraction of food to dragonflies.
Fi=X+-X (15)
(5) The repulsive force of natural enemy means the repulsive force of dragonfly to natural enemy
Ei=X-+X (16)
Wherein, X represents the position of the current dragonfly individual; xjRepresents the position of the jth adjacent dragonfly individual; vjRepresenting the speed of the jth adjacent dragonfly individual; n represents the number of individuals adjacent to the ith dragonfly individual; x+Indicating a food source location; x-Indicating the location of the natural enemy. According to the 5 dragonfly behaviors, the step length and the position of the next generation dragonfly are calculated as follows:
in the above formula, t represents the current iteration number; i represents the ith dragonfly individual; xtRepresenting the current position of the t generation population; Δ Xt+1Representing the next generation population position updating step length; xt+1Representing the individual position of the next generation population; s represents a separation degree weight; a represents an alignment weight; c represents a cohesion weight; f represents a food factor; e represents a natural enemy factor; w represents the inertial weight.
Fourth) improved dragonfly algorithm:
the method aims to improve the rapidity and the accuracy of the dragonfly optimization algorithm. So as to better solve the target optimization problem, the following improvement strategies are proposed:
for f, a food factor; e represents the natural enemy factor to improve
The updated position of the improved dragonfly can be obtained according to the new weight factor as follows:
based on the above algorithm, the specific process of the electric energy quality detection and analysis method based on the multi-composite optimization algorithm provided by the invention is shown in the flow chart 1, and the steps are as follows:
(1) firstly, EEMD decomposition processing is carried out on the collected electric signals, specifically according to a formula x'k(t)=x(t)+nk(t) adding normally distributed white noise. Adding the time sequence x after the normal distribution white noise sequencek(t) EMD decomposition is carried out on the whole to obtain each IMF component and the component is recorded as cki(t) and a remainder denoted as rkn(t) is thatAnd performing integrated average processing on the IMF components obtained each time.In the formula ci(t) represents the final jth IMF component obtained after EEMD decomposition. N is the total number of the added Gaussian white noise, the larger N is, the IMF sum of the corresponding white noise tends to be 0, and the more the decomposition result approaches to the true value.
(2) Each c isi(t) as an initial value for the dragonfly algorithm Fi=X+-X;Ei=X-+ X. Wherein X represents the position of the current dragonfly individual; xjRepresents the position of the jth adjacent dragonfly individual; vjIs shown asThe speed of j adjacent dragonfly individuals; n represents the number of individuals adjacent to the ith dragonfly individual; x+Indicating a food source location; x-represents the location of a natural enemy.
(3) Setting an alignment degree weight a, a separation degree weight s, a cohesion degree weight c and an inertia factor w according to a formula
f'=λ·f
e'=β·e
(4) According toTo calculate the position of the next generation and to bring the new position parameters into the formulaTo solve forSubstituting the result into a formulaTo find the objective function.
(5) Let t be t +1 at the same time according to the formulaAnd calculating the signal-to-noise ratio, and judging whether the iteration times and the signal-to-noise ratio meet the conditions. Until the requirements are met, according to the formula:
Ak=|bk|
Through verification, the electric energy quality detection and analysis method based on the multi-composite optimization algorithm can better detect and analyze the electric energy quality of the power grid, and has relatively simple implementation process and good practical value.
Claims (1)
1. A power quality detection analysis method of a multi-composite optimization algorithm is characterized by comprising the following steps:
step 1, EEMD decomposition is carried out after denoising a sampled power failure transient signal by adopting an EEMD method, each IMF component is obtained after EEMD decomposition, and the ith IMF component is recorded as cki(T), performing integration average processing on the IMF components obtained each time, and recording the ith IMF component obtained after processing as ci(T),N is the total number of the Gaussian white noise, the larger N is, the larger the corresponding IMF sum of the Gaussian white noise tends to be 0, and the more the decomposition result approaches to the true value;
step 2, setting the maximum iteration times TmaxSetting a signal-to-noise ratio threshold SNR', and setting the iteration number t to be 0;
and 3, substituting each IMF component obtained in the step 1 as an initial value of a dragonfly algorithm to calculate the separation degree, the alignment degree, the cohesion degree, the food attraction force and the natural enemy repulsion force of each dragonfly individual, wherein:
the separation degree of the ith dragonfly individual is SiThen, there are:
wherein X represents the position of the ith dragonfly individual, and X represents the position of the ith dragonfly individualjThe position of the dragonfly individuals adjacent to X is shown, and N dragonfly individuals adjacent to X are shared;
the alignment degree of the ith dragonfly individual is AiThen, there are:
in the formula, VjRepresenting the speed of the dragonfly individual adjacent to X;
the cohesion degree of the ith dragonfly individual is CiThen, there are:
the food attraction of the ith dragonfly individual is FiThen, there are:
Fi=X+-X
in the formula, X+Indicating a food source location;
the repulsive force of the ith individual dragonfly is EiThen, there are:
Ei=X-+X
in the formula, X-Representing the position of the natural enemy;
step 4, setting an alignment degree weight a, a separation degree weight s, a cohesion degree weight c and an inertia factor w, and calculating to obtain an improved natural enemy factor e 'and an improved food factor f':
f'=λ·f
e'=β·e
wherein f represents a food factor before improvement, e represents a natural enemy factor before improvement,
step 5, obtaining the updated position X of the improved dragonfly according to the improved natural enemy factor e' and the food factor ft+1Then, there are:
ΔXt+1=(sSi+aAi+cCi+f'Fi+e'Ei)+wΔXt
Xt+1=Xt+ΔXt+1
in the formula,. DELTA.XtIndicates the update step size, XtThe current position of the ith dragonfly individual;
step 6, setting the new position parameter Xt+1Bringing inTo solve forBring results intoTo find an objective function, wherein:denotes the fitting estimate of x (n), akCoefficient of expression characteristic equation, bkDenotes the complex number corresponding to x (n) fitting estimate,representing the complex number corresponding to the fitting estimated value x (n), and z represents an objective function;
step 7, calculating to obtain ak、Ak、θkAnd fk,AkIs the amplitude of the k order, fkIs the k-th order frequency, θkFor the k-th phase:
Ak=|bk|
in the formula, zkRepresenting the root obtained by solving the polynomial, and delta t representing the sampling interval;
step 9, if T is more than or equal to TmaxOr SNR<SNR', the method is ended, otherwise, step 3 is returned.
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