Janusz Walczak

Strategies for optimal allocation and sizing of active power filters

Some new approaches to active compensator allocation and sizing in distribution networks have been proposed in the paper. A few objective functions as well as their advantages and disadvantages have been given. Moreover, software which enables practical verification of the strategies has been described.

Comparison of classic and optimization approach to active power filters sizing and placement

Purpose – In most applications the active power filters (APFs) are used to reduce harmonic distortion of a nonlinear load which is located near the APF installation point. This classic approach allows to reduce the distortion introduced to the power system but do not guarantee that the cost of the APFs installation is optimal. The purpose of this paper is to compare the classic approach to harmonic compensation with an optimization method of sizing and placement of the APFs in an existing distributed power network. Design/methodology/approach – An exemplary real-life power system with distributed nonlinear loads was modeled using PCFLO power analysis software. Next, Matlab was used to implement the classic method and the optimization algorithm. Between Matlab and PCFLO a specially written Java middleware was used to provide a seamless workflow integration. Findings – It was shown that the presented optimization method may lead to superior results in comparison with the classic approach. Simulation results...

Analysis of Resonance Phenomena in Series RLC Circuit with Supercapacitor

The article concerns an analysis of phase and magnitude resonance conditions for a series RLC circuit with supercapacitor. Supercapacitor behavior differs from classic dielectric capacitors, therefore their mathematical models are more complicated, using, in particular, fractional calculus. Simple, fractional—order model has been taken into analysis and simulations. Results have been verified experimentally. Proper selection of the resonance circuit parameters R, L, R S and C determines either phase or magnitude resonance.

Frequency representations of one‐port networks

Purpose – Analysis of harmonics propagation in power systems requires information about models of non‐linear loads which are the main source of harmonics. The purpose of the paper is to present a method of parameter determination of non‐linear loads.Design/methodology/approach – A method of parameter determination of a model has been described in the article. This method has been developed assuming that mathematical description of a non‐linear load is known. In order to obtain a harmonic representation of this model for one‐phase loads the theory of harmonic balance method has been used.Findings – Parameters of the current or voltage controlled sources can be expressed as a function of any number of voltage or current harmonics. In the case under consideration the network input current is a function of input voltage and its derivatives. Thus, contrary non‐linear element with inertialess characteristics, the first harmonic of the current depends not only on amplitude but also on frequency of the voltage ac...

Current spectrum estimation using Prony's estimator and coherent resampling

Purpose – A highly accurate method of current spectrum estimation of a nonlinear load is presented in this paper. Using the method makes it possible to evaluate the current injection frequency domain model of a nonlinear load from previously recorded time domain voltage and current waveforms. The paper aims to discuss these issues. Design/methodology/approach – The method incorporates the idea of coherent resampling (resampling synchronously with the base frequency of the signal) followed by the discrete Fourier transform (DFT) to obtain the frequency spectrum. When DFT is applied to a synchronously resampled signal, the spectrum is free of negative DFT effects (the spectrum leakage, for example). However, to resample the signal correctly it is necessary to know its base frequency with high accuracy. To estimate the base frequency, the first-order Pronys frequency estimator was used. Findings – It has been shown that the presented method may lead to superior results in comparison with window interpolated...

Deterministic model of electric arc furnace – a closed form solution

Purpose – Electric arc furnaces are usually modelled using combined models which divide the phenomenon taking place in real objects into a deterministic and a stochastic or chaotic parts. The former is expressed by a nonlinear differential equation. The goal of this paper was to obtain a closed form of the solution to one of the most popular nonlinear differential equations used for the AC electric arc modelling.Design/methodology/approach – The solution has been obtained in the time domain by a sequence of transformations of the original nonlinear equation which lead to a linear equation, for which a closed form solution is known.Findings – The paper provides a set of parameters for which the solution to the nonlinear differential equation describing electric arc can be obtained in a closed form.Research limitations/implications – There are still some parameter values for which the solution can be found only numerically. Moreover, due to the nature of the phenomena occurring in electric arc furnaces, in ...

Analysis of deterministic model of electric arc furnace

A closed form of the solution to a differential equation used for the AC electric arc modeling has been derived in the paper. A special case of periodic excitations has been considered and the appropriate formulae have been given. Having a closed form of the solution rather than the numerical one enables better understanding of the phenomena described by the equation. Moreover, it makes easier the extension of the arc model in order to cover the time-varying character of the arc waveforms, e.g. using stochastic approach. Theoretical considerations have been illustrated by a simulation experiment.

Generalized Spectrum Analysis by Means of Neural Networks

The problem of determination of generalized signal spectrum using neural networks has been investigated. The paper contains the formalization of the problem and is focused on building of a neural network that may be used to calculate coefficients of the generalized Fourier series for various base functions. The theoretic considerations have been illustrated by an example of analysis of a signal belonging to the Hilbert space of signals with finite energy for Laguerre’s base and a wavelet base.

Impulse Responses of Generalized First Order LTV Sections

In this article, the model of the first order parametric section linear time varying (LTV) has been described. The parameter of the section under examination is non-periodically variable. These sections are the elementary blocks constituting more complex systems of parametric filters. The method aiming to determinate the impulse response of the LTV section has been presented. The results have been illustrated by an example.

Neural Approach to Time-Frequency Signal Decomposition

The problem of time-frequency decomposition of signals by means of neural networks has been investigated. The paper contains formalization of the problem as an optimization task followed by a proposition of recurrent neural network that can be used to solve it. Depending on the applied base functions, the neural network can be used for calculation of several standard time-frequency signal representations including Gabor. However, it can be especially useful in research on new signal decompositions with non-orthogonal bases as well as a part of feature extraction blocks in neural classification systems. The theoretic considerations have been illustrated by an example of analysis of a signal with time-varying parameters.