CN110719122A

CN110719122A - Automatic impedance matching method based on improved PSO algorithm

Info

Publication number: CN110719122A
Application number: CN201810754777.5A
Authority: CN
Inventors: 不公告发明人
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-07-11
Filing date: 2018-07-11
Publication date: 2020-01-21

Abstract

The invention discloses an automatic impedance matching method based on an improved PSO algorithm, and changes of load impedance of power line carrier communication are matched by adjusting a capacitance value in a pi-type passive matching network through establishing a target function. The power line carrier communication conditions when the load impedance is capacitive, resistive and inductive are well matched, and carrier frequency points of 150kHz, 260kHz and 480kHz are selected for carrying out simulation verification on the network. The result shows that the particle swarm algorithm based on the pi-type passive matching network can better automatically match the change of the load impedance of the power line carrier communication, and obviously improve and improve the transmission efficiency of the power line carrier communication.

Description

Automatic impedance matching method based on improved PSO algorithm

Technical Field

The invention belongs to the technical field of power line communication, and relates to an automatic impedance matching method based on an improved PSO algorithm, which is used for an automatic power line impedance matching system.

Background

With the continuous and deep research of the intelligent power distribution network, the gradual application of a big data analysis technology puts forward higher and higher requirements on the power distribution communication network. The Power Line Communication (PLC) technology has a natural Communication channel and flexible convenience of application, has become an important choice for medium-voltage distribution Communication networks, and has a strong application potential in the field of medium-voltage distribution network distribution automation. In a power line carrier communication system, a power line channel has a complex environment, a large number of electric devices are connected in parallel, a complex interference effect is generated on the channel, and a power line is not specially designed for communication of high-frequency signals, so that the communication environment is very poor. The open line environment, the complex network structure and the variable load characteristics of the high-noise-attenuation-ratio high-power-consumption high-frequency-ratio high-power-consumption high-power.

Improper matching of the input impedance and the output impedance of the power line carrier communication may cause generation of standing waves to affect the coupling efficiency of signals, and even completely block the power line carrier communication. A same fixed passive circuit is added between a power line carrier signal generation module and load impedance, so that a signal is coupled into a power line channel most effectively under certain signal transmitting power, but the load impedance of the power line is a variable value, and a fixed impedance matching network cannot ensure that a carrier communication network is in an optimal impedance matching state for a long time.

In order to improve the efficiency of power line carrier communication and solve the problem of signal transmission caused by impedance mismatching, the invention provides an automatic impedance matching method based on an improved PSO algorithm, which comprises the following steps: 1) establishing a pi-type passive impedance matching network, and matching the changed resistance by adjusting the capacitance value; 2) the particle swarm algorithm is designed and improved to calculate the capacitance value in the matching network, so that the power line carrier communication can be well matched when loads with different properties and different frequency points.

Disclosure of Invention

The invention aims to provide a high-efficiency impedance matching system for medium-voltage power line carrier communication, which solves the problem that the communication effect quality is poor or even communication cannot be realized due to unmatched impedance in the conventional PLC communication.

The technical scheme adopted by the invention comprises the following steps:

step 1: establishing a passive impedance matching circuit

A pi-type matching network is selected, and the adjustable inductor has a large volume, so that the pi-type passive impedance network consists of a fixed inductor and two adjustable capacitors.

Step 2: establishing an automatic impedance matching circuit

When the load impedance changes or the frequency fluctuates and changes to change the characteristic impedance of the power line, the element parameters of the passive matching network are automatically adjusted, so that real-time matching is realized. The load impedance is changed by using the change of the load as a disturbance quantity, the load impedance is measured in real time and optimized, an optimal solution of the element is obtained through iterative calculation, and the optimal solution is fed back to a passive impedance matching circuit at the input end of the system.

And step 3: computing element values for a matching network using an improved PSO algorithm

1) Signal source for calculating equivalent circuitInput impedance Z_in：

In the formula, the load impedance Z_l＝R+jX，

Is the center frequency of the power line carrier signal.

2) Calculating the signal source output impedance Z of the equivalent circuit_eq：

In the formula C₁And C₂Two adjustable capacitance parameters.

3) Establishing an objective function:

when the input impedance of the power line carrier communication is equal to the conjugate value of the output impedance through the LC passive network, the maximum output power of the signal is obtained, the signal attenuation is minimum, and the target function f_xComprises the following steps:

in the formula, theta_inAnd theta_eqRespectively the deflection angle of the input impedance and the output impedance. When f is_xWhen the minimum value is obtained, C₁And C₂For the best solution, the power line carrier communication efficiency is high.

4) Calculating improved particle swarm algorithm parameters

V_i+1＝w*V_i+c₁*r₁*(pbest-x_i)+c₂*r₂*(gbest-x_i) (4)

X_i+1＝X_i+V_i(5)

In the formula, V_iIs the velocity phasor of particle evolution, X_iFor the location phasor of the particle evolution, pbest is the best location found by the particle itself, and gbest is the finding of all particles in the populationThe best position of (a); r is₁And r₂Is a random number between 0 and 1; c. C₁And c₂Is a learning factor, is a set of non-negative constants; w is the inertia weight factor of the algorithm, and the inertia factor is linearly reduced by using an LDW (Linear scaling weight) algorithm:

where G is the number of iterations of the current algorithm and G_maxFor maximum iterative evolution of the algorithm, w_maxIs the maximum value of the inertial weight factor, w_minIs the minimum value of the inertial weight factor.

And 4, step 4: calculating element parameters of matching circuit by algorithm

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a diagram of an optional pi-type matching network;

FIG. 2 is an automatic impedance matching system architecture;

FIG. 3 is an equivalent matching circuit diagram;

FIG. 4 is a flow chart of a particle swarm algorithm routine;

FIG. 5 is an algorithm optimization process with resistive load;

FIG. 6 is a process of load-capacitive algorithm optimization;

FIG. 7 is an algorithm optimization process with load being perceptual;

Detailed Description

The invention aims to design an automatic impedance matching method based on an improved PSO algorithm, so as to better automatically match the change of load impedance of power line carrier communication and obviously improve and improve the transmission efficiency of the power line carrier communication.

So that the manner in which the features and advantages of the invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings.

Signal source output impedance R_sTaking 50 omega, taking the carrier frequency of 150kHz, 260kHz and 480kHz commonly used for current low-voltage power line carrier communication, and taking the inductance L of 17 muH; c₁，C₂For matching two parameters in the network, the learning factor is taken as c₁＝c₂2, inertial weight factor w_maxIs 0.9 at the maximum value and w at the minimum value_minTake 0.4. The population particle number is 20, the dimension of each particle is 2 dimensions, and the iterative evolution number of the algorithm is set to be 100.

And (3) simulating the low-voltage power line carrier communication circuit with carrier frequencies of 150kHz, 260kHz and 480kHz respectively by using MATLAB under the condition that load impedance is respectively resistive, capacitive and inductive, wherein the impedance values of the load are respectively 5 omega, 5+ j5 omega and 5-j5 omega.

1. Particle position and velocity are initialized and particle fitness values are calculated. A population of particles is initialized in a feasible solution space, each particle representing an optimal solution to a fitness function.

2. And searching individual extremum and group extremum. The optimal velocity phasors and position phasors for individual and population of particles are found and updated.

3. And calculating the fitness value of the particle, and updating the individual extremum and the group extremum of the particle.

4. Judging whether the calculated particle extreme value meets the condition, and if so, obtaining the optimal value of the particle; if not, the inertia factor of the algorithm is changed linearly, and the second step of calculation is carried out again. The optimal values obtained by the PSO algorithm optimization of the example are shown in the following table:

TABLE 1 calculated element values for the PSO Algorithm

As shown in fig. 5, 6, and 7, a PSO algorithm with a reduced inertia factor is adopted, and when the iteration reaches about 20 generations in the optimization process of the objective function under three load conditions, the optimal value is obtained step by step. When the load is resistive, the optimization speed is fastest, and the curve difference under three frequency points is small; when the load is capacitive or inductive, the convergence speed is reduced, and the carrier frequency has a large influence on the optimization convergence of the objective function. Simulation results show that the PSO-based power line carrier communication impedance automatic matching algorithm can perform good automatic impedance matching on the changes of various load impedances on common narrow-band power line carrier frequency points.

When the resistive load is shown in fig. 5, the optimization speed of the objective function is fastest, and the difference of the optimization curves at three frequency points is small; as shown in fig. 6 and 7, when the load impedance is inductive or capacitive, the convergence rate of the algorithm is significantly reduced compared to that of a pure resistive load, and the carrier frequency has a larger influence on the optimal convergence of the objective function than that of the pure resistive load. The convergence speed of the PSO algorithm is substantially slowed down as the carrier frequency increases. The result shows that the PSO-based power line carrier communication impedance automatic matching algorithm can have better automatic impedance matching on the common narrowband power line carrier frequency point for the change of various load impedances.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims

1. An automatic impedance matching method based on an improved PSO algorithm is characterized in that: due to the open line environment of the power line carrier communication channel, the complex network structure and the variable load characteristics, the channel has the characteristics of high noise, high attenuation, impedance mismatching and the like, so that the reliability of the power line carrier communication needs to be improved as a hotspot of research, and at present, the main research focuses on analyzing the impedance of a power grid and the impedance matching characteristics to improve the reliability of a system. The impedance matching is a basic condition for enabling a channel to achieve maximum power transmission and reflection-free transmission, aiming at the characteristics of power line impedance, the invention designs a Pi-type passive power line impedance matching system based on PSO, and the scheme has important significance for improving the communication efficiency and reliability of a power line carrier communication system.

2. The passive impedance matching circuit of claim 1, wherein: the impedance matching circuit has simple structure and less elements, and consists of two capacitors and one inductor. The adjustable inductor has a relatively large volume, and is inconvenient to integrate and modularize, so that a variable capacitor mode is adopted. Although the structure of the L-type matching circuit is simpler, the range of matching is limited at the same time. The pi-type passive network is slightly complex, but has a wider impedance matching range, so that a fixed inductor and a capacitor with adjustable capacitance are selected to form a pi-type matching network.

3. The matching algorithm according to claim 1, characterized in that: the particle swarm optimization can place variables to be optimized into particles and seek the optimal solution among solutions without encoding the variables to be solved before solving like a genetic algorithm, and is easy to realize in programming. In the particle swarm algorithm, all particles move in a solution space at any speed, the particle can record the best positions of all the particles passing through the particle and share the best positions in a group while the particle moves, and each particle can realize evolution through sharing and learning. The invention uses an improved particle swarm algorithm based on the particle swarm algorithm as an intelligent algorithm for adjusting the element parameters in the matching network, changes the fixed inertia weight factor in the traditional particle swarm algorithm into a linear reduction mode in the iteration process, and effectively avoids the target function from falling into the local optimal solution in the iteration process.

4. The impedance matching method described in claim 1, characterized mainly by: in a practical circuit, the internal resistance of the signal source includes a non-linear element such as an amplifier, which makes the internal resistance of the signal source equal to the equivalent input impedance of the load, and the impedance of the signal source and the load presents non-linearity especially when the signal source and the load are transformers. The invention mainly analyzes the automatic matching characteristic of the particle swarm algorithm to the load impedance, thereby simplifying the circuit model and assuming that the internal resistance of a signal source is a constant value. The power line carrier signal generating device is generally designed as a pure resistor, and the power line layout at the load end is complex, and capacitive and inductive loads exist. An equivalent circuit of power line carrier communication added to the pi-type passive network is shown in fig. 2.

5. The automatic impedance matching method of claim 1, wherein: when the load changes or the signal frequency changes, the element parameters of the passive matching network are automatically adjusted, so that the dynamic load impedance and the signal source impedance are subjected to real-time conjugate matching. The adjustment parameters of the passive matching network are put into the independent variables of the objective function, so that the element parameters for solving the impedance matching system are converted into the optimal values for searching the objective function, programming realization in a digital processor is facilitated, and the optimization of the objective function can adopt an optimization algorithm. The effect of the optimization matching algorithm is as follows: the parameters of the network changes are captured, and countermeasures for matching the changes, namely the parameters of elements of the matching network, are rapidly calculated.

6. The automatic impedance matching method according to claim 1, having the advantages of: the fixed weight factor in the traditional particle swarm algorithm is changed into a linear reduction mode in the iteration process, and the target function is effectively prevented from falling into a local optimal solution in the re-iteration process. The PSO-based power line has better automatic impedance matching on the change of load impedance of various properties on a carrier frequency point of a narrow-band power line, which can be used by a carrier communication impedance automatic matching system. The results show that the objective functions all gradually obtain the optimal values after 20 iterations.