Tomasz Sikorski

Time–Frequency Analysis of Complex Space Phasor in Power Electronics

This paper considers applying nonparametric and parametric methods for the calculation of the time-frequency representation of nonstationary signals in power electronics. A space phasor is proposed as a complex representation of a three-phase signal to calculate the spectrum of positive-and negative-sequence components. The developed methods are tested with nonstationary multiple-component signals occurring during the fault operation of inverter-fed drives. First, the main differences between parametric and nonparametric methods are underlined. Then, some aspects of additional kernel functions are introduced on the basis of Wigner and Choi-Williams distributions. An additional comparison of uncertainty of measurements using the described methods, as well as a widely used Fourier technique, can be useful for practitioners. The proposed methods allow tracking instantaneous frequency as well as magnitude that can lead to applications in the diagnosis and power quality areas.

Evolutionary algorithm for detection and localization of faults in HVDC systems

The aim of this work is to analyze evolutionary algorithms in point of application for detection and localization of faults in HVDC systems. Considered faults are localized at DC side. The initial condition for the algorithm is low sampling rate up to 5-100kHz. This condition eliminates application of traditional traveling wave technique due to not sufficient time resolution. It is proposed to base criterion of the fault location on relation between distance of the fault and amplitude of aperiodic decaying component in current during transient. In order to estimate the amplitude of the aperiodic component a genetic algorithm is proposed. Using benchmarking signals a reference function of distance of the fault in relation to the amplitude of aperiodic component is created. Having this function it is possible to calculate fault location using estimated by genetic algorithm amplitude during the fault. This paper presents advantages and disadvantages of proposed technique.

Time-frequency analysis of complex space-phasor in power electronics

This paper considers applying Wigner distribution and min-norm method (subspace method) with sliding window, for calculation time-frequency representation of non-stationary signals in power electronics. Space-phasor was used as a complex representation of 3-phase signal in order to calculate spectrum of positive and negative-sequence. The proposed methods were tested with nonstationary multiple-component signals occurring during the fault operation of inverter-fed drive. Time and frequency resolution and phase dependence of the tested methods were investigated and compared with the parameters of the frequency estimation via FFT.

Wide-area system of registration and processing of power quality data in power grid with distributed generation: Part I. System description, functional tests and synchronous recordings

This paper presents the developed and built comprehensive system of registration, archiving and data processing for the wide-area monitoring of power quality in a separated part of real power grid with distributed renewable generation. Real case studies related to localization of sources of voltage disturbances are presented.

Power quality disturbances in power system with distributed generation

This work is concentrated on assessment of contribution of distributed generation, represented by small hydro power plants (SHP), in power quality disturbances at low and medium voltage in distribution networks. Investigations are based on the dispersed synchronized measurements at low voltage level including two small hydro power plants and utilization substation, connected to the same medium voltage line. Dynamic aspect of SHP work represented by starting generators, switching on capacitor banks are tracked in point of local and mutual influence.

Advanced signal processing methods for analysis of non-stationary signals in power systems

This paper aims to consider using the wavelet transform (WT), Wigner-Ville distribution (WVD) and Choi-Williams distribution (CWD) for spectrum estimation of nonstationary signals in power systems. The main goal is to emphasize the advantage and disadvantage of the mentioned methods in comparison with the short-time Fourier transform (STFT). The aspect of frequency resolution is explored on the basis of signals at the output of the simulated frequency converter, which is a major issue when diagnosis problems of drive faults are considered.

Time-Frequency Analysis of Power Distortion under Fault Conditions for Grid Connected Wind Turbine

This paper serves the idea of designing appropriate method for complex investigations of transient states in wind power plants. Proposed algorithms belong to two-dimensional time-frequency representations. Additional dimension allows to obtain simultaneous information about frequency of distortion components as well as its duration time. Two algorithms were proposed: short-time Fourier transform (STFT) and Choi-Williams Distribution (CWD). In order to explore advantages and disadvantages of the method in application for wind power plants area, several experiments were performed using model of squirrel-cage induction machine connected directly to the grid. Investigated phenomena concerned power distortion caused by different kind of faults as well as influence of wind speed on instantaneous character of the transient states.

Transformation matrices of different transformer types in voltage dips direction finder

This paper presents principles of consideration of transformer winding connections in process of transfer of voltage dips across transformer. The aim of the work is to define transformation matrices and investigate its application for different types of voltage dips. Results of the algorithm with implemented transformation matrices is presented. The transformation matrices can be used for correction of the decision about dips direction finder.

Power quality in low-voltage distribution network with distributed generation

The aim of this work is to combine electromagnetic compatibility standardization and control strategy of low-voltage distributed generations in order to define possible impact of the generation unit on power quality at the point of common coupling with low-voltage distribution network. Selected relations between power quality indices and parameters as well as regulation characteristic of the distributed generation is discussed. Verification of predicted impact of the distributed generation on power quality is performed using a field-measurement case study of power quality behaviour in real photovoltaic system connected to low-voltage distribution network..

Signal processing method for faults location in DC transmission system

The paper describes the use of advanced signal processing method for analysis of faults in DC transmission systems in order to determine the fault location. The fault location is based on estimation of amplitude and frequency of decaying oscillating component in current during transient. The investigation shows the results of parametric Prony model application.