Evaluation of two fundamental positive-sequence detectors for highly distorted and unbalanced systems

This paper presents an evaluation of the performance of two different Positive-Sequence Detectors. This evaluation is made by comparing a PLL (Phase-Locked- Loop), combined with Lagrange Multipliers Method, with an Adaptive Filter. Both algorithms aim to detect the positive sequence at the fundamental frequency on a given three-phase system voltages or currents. The purpose of this evaluation is to assess the better Positive-Sequence Detector for custom power devices, such as Active Power Filters. The comparative analysis was based on the evaluation of a series of steady state performance arameters (phase and amplitude errors, THD and unbalance) and on the response time. The tests were made to study the behavior of both approaches when working with highly distorted and unbalanced signals. This work was carried out using the computer simulation tool PSCAD/EMTDC.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/EEA-EEL/104569/2008.FEDER Funds - Operational Programme for Competitiveness Factors – COMPET

New results on cycle–slipping in pendulum–like systems

n this paper, we examine dynamics of multidimensional control systems obtained as feedback interconnections of stable linear blocks and periodic nonlinearities. The simplest of such systems is the model of mathematical pendulum (with viscous friction), so we call such systems pendulum-like. Other examples include, but are not limited to, coupled vibrating units, networks of oscillators, Josephson junction arrays and numerous synchronization circuits used in radio and telecommunication engineering. Typically, a pendulum-like system has infinite sequence of equilibria, and one of the central problems addressed in the theory of such systems is to find the conditions of "global stability", or gradient-like behavior ensuring that every solution converges to one of the equilibria points. If a system is gradient-like, another problem arises, being the main concern of this paper: can we find the terminal equilibrium, given the initial condition of the system? It is well known that solutions do not converge, in general, to the nearest equilibrium; this phenomenon is known as cycle-slipping. For a pendulum, cycle-slipping corresponds to multiple rotations of the pendulum about its suspension point. In this paper, we estimate the number of slipped cycles for general pendulum-like systems by means of periodic Lyapunov functions and the Kalman-Yakubovich-Popov lemma

Comparative analysis between different approaches for single-phase PLLs

"In press"This paper presents a comparative analysis between two distinct synchronizing circuits, which are usually applied as the core of control algorithms for single-phase power quality applications. One of these synchronizing circuits corresponds to a single-phase Phase-Locked Loop (PLL), implemented in α-β coordinates (αβ-PLL), whereas the other one corresponds to the Enhanced PLL (E-PLL). The major contribution of this paper is to present a single-phase PLL oriented to power quality applications, with a very simple structure, capable to be synchronized with the fundamental component of an input signal (voltage or current), even considering substantial disturbances, such as, frequency deviations, phase shifts, harmonic components and amplitude variations. Simulation and experimental results, involving these two synchronizing circuits submitted to three different test cases, are provided in order to compare their transient and steady-state performance. Moreover, it is also presented a comparison involving the processing speed and memory requirements of these synchronizing circuits in the DSP TMS320F28335

A new method for analysis of signal harmonic distortion byevaluation of power quality

Naučna rasprava izložena u ovoj tezi bavi se analizom kvaliteta električne energije. Visok nivo električne energije podrazumeva da su napon napajanja i struja potrošača idealne sinusoide sa tačno određenom amplitudom i učestanošću. Bilo kakva odstupanja od idealnog nazivaju se izobličenja i najčešće se karakterišu sa harmonicima. Poslednjih godina dolazi do naglog razvoja poluprovodničkih komponenata. Takve komponente su uticale na ubrzan razvoj snažnih uređaja energetske elektronike. Ti uređaji su nelinearnog karaktera, što dovodi do pojave harmonika u signalima napona i struja elektroenergetskog sistema. Prvi problem kojim se bavi ova teza je analiza talasnih oblika struja ispravljača. Metode primenjene za analizu su wavelet transformacija (VT) i modulated overlapped transformacija (MLT). MLT nadoknađuje nedostatak VT da dekomponuje signal u odgovarajuće podopsege koji mogu sadržati i više harmonika i daje tačnu informaciju o svakom harmoniku. Obe metode su pogodne za offline analizu. Za online analizu predložen je hibridni metod baziran na diskretnoj Furijeovoj transformaciji (DFT) i adaptivnom pojasnom filteru (EPLL). Hibridni metod je zadržao dinamički odziv DFT-a, dok je EPLL obezbedio sinhronizaciju sa osnovnom učestanošću sistema. Hibridni metod daje dovoljno tačnu informaciju o osnovnom i višim harmonicima samo ako su njihove učestanosti ceolobrojni umnožak učestanosti osnovnog harmonika. U slučaju pojave interharmonika, odnosno kada taj odnos više ne važi, hibridni metod ne daje tačne rezultate. Za analizu takvih signala predložen je novi metod, koji je baziran na adaptivnom diskretnom pojasnom filteru (ANF) t.j. metod koristi diskretni pojasni filter za modelovanje harmonijskih komponenata u ulaznom signalu, dok se prošireni Kalmanov filter (EKF) koristi kao adaptivni mehanizam. Novi metod je preuzeo osobinu ANF-a da može adaptivno da prati promene učestanosti i osobinu EKF-a da ima bolji dinamički odziv. Metode su implementirane na digitalnom procesoru za obradu signala i upoređene sa postojećim metodama. Metode pokazuju prednosti u odnosu na druge metode.Scientific research in this thesis discusses power quality analysis. High power quality assumes that both the voltage power supply and the load current are ideal sinusoidal signals with a precisely defined amplitude and frequency. Any deviations from this ideal vaweform are considered as distortion and are characterised by harmonics. Over the last few decades, there has been a rapid development of semiconductor components. Such components made an impact on the fast development of power electronics devices. These devices are nonlinear, introducing harmonics in both voltage and current of the power grid. The first issue researched in this thesis is the analysis of the rectifier voltage and current waveforms. Methods used for the analysis are the wavelet transform (WT) and the modulated overlapped transform (MLT). The MLT overcomes the drawback of the WT, which decomposes the signal into subbands that can contain more harmonics, and gives accurate information about every harmonic. Both methods are suitable for offline analysis. For online analysis, a hybrid method is proposed, based on the discrete Fourier transform (DFT) and the adaptive notch filter (EPLL). The hybrid method retains a good dynamic response of the DFT whereas the EPLL provides a synchronisation with the fundamental system frequency. The hybrid method provides accurate information on the fundamental and the higher harmonics only if their frequencies are integer multiples of the fundamental frequency. In the case of interharmonics, i.e. when this integer ratio is not valid, the hybrid method does not provide accurate results. In order to analyse such signals, a new method is proposed. It is based on discrete adaptive notch filter (ANF), i.e. the method uses a discrete notch filter for modeling the harmonic components in the input signal, whereas an Extended Kalman Filter (EKF) is used as an adaptation algorithm. The adaptive notch Kalman filter inherited the property of the ANF to adaptively track changes in the frequency and the property of the EKF to have a faster dynamic response. Methods have been implemented in a digital signal processor and compared with the existing ones. The methods show advantages compared to other methods

A phase locked loop for the synchronization of power quality instruments in the presence of stationary and transient disturbances

Power quality instrumentation requires accurate fundamental frequency estimation and signal synchronization, even in the presence of both stationary and transient disturbances. In this paper, the authors present a synchronization technique for power quality instruments based on a single-phase software phase-locked loop (PLL), which is able to perform the synchronization, even in the presence of such disturbances. Moreover, PLL is able to detect the occurrence of a transient disturbance. To evaluate if and how the synchronization technique is adversely affected by the application of stationary and transient disturbing influences, appropriate testing conditions have been developed, taking into account the requirements of the in-force standards and the presence of the voltage transducer

Novel method for detection of voltage dips in the grid with distributed generation

U ovoj doktorskoj disertaciji je predstavljena je nova metoda za detekciju propada napona, zasnovana na Rekurentnoj neuronskoj mreži i analizi u harmonijskom domenu. Metoda je namenjena za primenu u savremenim distributivnim mrežama koje sadrže obnovljive izvore, i u skladu sa tim je optimizovana i testirana. Pametna metoda postiže izuzetne rezultate u brzini detekcije, sa prosečnim vremenom detekcije manjim od 1 ms, uz izuzetnu pouzdanost (preko 97%). U doktorskoj disertaciji dokazana je i druga hipoteza, a to je da je moguće predvideti dubinu propada algoritmom zasnovanim na harmonijskoj analizi.In this PhD thesis, a novel method for the detection of voltage dips (sags), based on the Recurrent Neural Network and analysis in the frequency domain, is presented. The method is intended for use in the modern distribution grids that contains renewable sources, and accordingly it is optimized and tested. The smart method achieves exceptional results in detection speed, with an average detection time of less than 1 ms and with high reliability (over 97%). In the PhD thesis, another hypothesis is proved, which claims that is possible to predict the depth of dip with algorithm based on the harmonic analysis

Estimação de harmônicos e inter-harmônicos baseada na técnica de invariância rotacional aplicada a sub-bandas do espectro

The Estimation of Signal Parameters via Rotational Invariance Technique (ESPRIT), which is a high resolution parametric estimation method, has gained attention of the researchers due to its high performance for harmonic and inter-harmonic parameters’ estimation of power system signals. Nevertheless, this method presents high computational complexity and is very sensitive to colored noise. With the aim of reducing computational complexity and improving the performance for colored noise scenarios, this work presents a new harmonic and inter-harmonic parameter estimation method based on rotational invariance technique and multirate signal processing through the use of filter banks, called ESPRIT-FB. Adopting the classical multirate signal processing approach, the proposed method decimate the signal in each sub-band, which reduces the number of samples of the signal to be processed in each sub-band and, as a result, reduces the size of the data matrix built by the rotational invariance technique. Moreover, the proposed method can be used in its dynamic form, Dynamic ESPRIT-BF (D-ESPRIT-BF), where the filter bank is designed according to the signal characteristics, or the method can be used with a fixed pre-designed filter bank. It was show that the computational complexity of the proposed method, for the fixed filter bank case, can be up to L2 times smaller than the conventional ESPRIT, where L is the decimator factor used in the sub-bands. The proposed method was evaluated with synthetic and real power system signals and compared with with the conventional ESPRIT. The results showed that the proposed method improves the accuracy and the precision and reduces the computational complexity with reference to the conventional one. The proposed method was also compared to Wavelet Sliding Window ESPRIT Hybrid method, called here W-SWESPRIT, showing better performance for the studied cases. It is also worth to mention, that colored noise scenarios were simulated, and the results showed that the ESPRIT-BF highly improves the estimation performance in comparison with the conventional one. Therefore, this work is an important contribution to the area, improving the performance, reducing the computational complexity and enlarging the range of applications of the ESPRIT method.O método de estimação de parâmetros baseado na técnica de invariância rotacional ESPRIT ganhou atenção dos pesquisadores pelo seu bom desempenho para estimar harmônicos e inter-harmônicos em sinais do sistemas de potência, devido ao fato de ser um método paramétrico de alta resolução. No entanto, este método tem a desvantagem de apresentar alta complexidade computacional e alta sensibilidade em cenários com ruído colorido. Desta forma, o presente trabalho propõe um novo método de estimação de harmônicos e inter-harmônicos baseado na técnica de invariância rotacional ESPRIT e processamento de sinais multitaxa através do uso de banco de filtros, denominado neste trabalho como Método ESPRIT com Banco de Filtros (ESPRIT-BF), com o objetivo de reduzir a complexidade computacional e melhorar o desempenho das estimativas em cenários com ruído colorido. Seguindo a abordagem clássica de processamento multitaxa, o método realiza a decimação do sinal nas sub-bandas do espectro, o que reduz o número de pontos do sinal em cada sub-banda e, consequentemente, o tamanho da matriz de dados construída pela técnica de invariância rotacional. Além disso, o ESPRIT-BF pode ser utilizado de forma a se ajustar ao sinal em análise, uma vez que o banco de filtros tem projeto orientado pelo sinal ou através de sua forma fixa, onde o banco de filtros é previamente projetado. Para o caso em que o ESPRIT-BF é utilizado com um número fixo de filtros, foi demonstrado que o método apresenta uma complexidade computacional L2 vezes menor que o ESPRIT convencional, onde L é o fator de decimação utilizado nas sub-bandas. O método proposto foi utilizado para estimação de harmônicos e inter-harmônicos em sinais sintéticos e reais, e comparado com o ESPRIT convencional. Os resultados mostraram que o método proposto é mais exato, mais preciso e possui menor complexidade computacional que o ESPRIT convencional. O método também foi comparado com Wavelet Sliding Window ESPRIT Hybrid, denominado neste trabalho de W-SW-ESPRIT, tendo apresentado desempenho superior. Foram também analisados casos de sinais corrompidos por ruídos coloridos e, na totalidade deles, o método proposto apresentou desempenho bastante superior ao ESPRIT convencional, fato importante de ser destacado. Assim, o presente trabalho traz importante contribuição ao melhorar o desempenho da estimação, reduzir a complexidade computacional e ampliar os cenários (incluindo ruído colorido) de utilização do método ESPRIT

Desenvolvimento de um condicionador unificado de qualidade de energia monofásico com controlo invertido

Dissertação do mestrado em Engenharia Eletrónica Industrial e ComputadoresA Qualidade de Energia Elétrica (QEE) é um tema cada vez mais importante no ramo da engenharia, pois os problemas na rede elétrica podem levar a que os equipamentos não funcionem corretamente. Isso, faz com que muitos clientes, no sector industrial serviços tenham prejuízos económicos muito elevados. Porém, muitos desses problemas ocorrem devido às cargas utilizadas pelos clientes que “poluem” a rede elétrica com potência reativa e harmónicas. Existem equipamentos de eletrónica de potência que mitigam estes problemas de Qualidade de Energia Elétrica, entre eles o Condicionador Unificado de Qualidade de Energia (Unified Power Quality Conditioner - UPQC). Esta dissertação aborda uma nova topologia deste equipamento chamado Condicionador Unificado de Qualidade de Energia com Controlo Invertido (iUPQC) Monofásico com a adição de baterias, para permitir o modo de alimentação ininterrupta da instalação (Uninterruptible Power Supply – UPS) denominando-se assim iUPQC-UPS. Um UPQC é um equipamento constituído por um condicionador ativo série (Conversor CC-CA) e um condicionador ativo paralelo (Conversor CC-CA) que ligam a um barramento CC comum. Este barramento irá ligar às baterias a partir de um conversor CC-CC bidirecional. O objetivo do UPQC com controlo invertido é que o condicionador ativo série absorva da rede a potência ativa necessária impondo uma corrente sinusoidal do lado da rede, enquanto que o condicionador ativo paralelo fornece às cargas uma tensão sinusoidal com frequência e valor eficaz normalizado. Desta forma, todas a potência reativa e harmónicas serão fornecidos pelo condicionador ativo paralelo. Esta dissertação apresenta um estudo bibliográfico dos condicionadores ativos de potência que mitigam os problemas de QEE, das topologias dos conversores de potência e dos seus algoritmos de controlo. Com base neste estudo, foi usada a ferramenta PSIM para fazer simulações dos modos de funcionamento do iUPQC-UPS. Posteriormente, foi desenvolvido o protótipo do iUPQC-UPS, constituído pelo sistema de controlo, sistema de comando e sistema de potência. Por ultimo, o protótipo foi validado ao retirar os resultados experimentais de todos os modos de funcionamento.Electrical Power Quality is an increasingly important topic in the engineering field, as the problems created in the electrical network lead to the equipment not working properly. This causes many customers in the industrial services sector to have very high economic losses. However, many of these problems occur due to the loads used by customers that “pollute” the Electric Grid with reactive power and harmonics. There are power electronics equipment that mitigate these Power Quality problems, among them the Unified Power Quality Conditioner (UPQC). This dissertation approaches a new topology of this equipment called Unified Power Quality Conditioner with Inverted Control (iUPQC) with the addition of batteries, to allow the uninterruptible power supply of the installation (Uninterruptible Power Supply - UPS), thus called iUPQC- UPS. This equipment consists of a series active conditioner (DC-AC converter) and a parallel active conditioner (DC-AC converter) that connect to a common DC bus. This bus will connect to the batteries from a bidirectional DC-DC converter. The objective is that the series active conditioner absorbs the necessary power from the power grid while imposing a sinusoidal current on the power grid side, while the shunt active conditioner provides the loads with a sinusoidal voltage with normalized frequency and effective value. In this way, all reactive power and harmonics will be provided by the shunt active conditioner The batteries will charge or discharge as needed by the network. That is, if the power of the network is greater than the power of the loads, the batteries will use power from the network to charge. If the power of the network is less than the power of the loads, the batteries will discharge when supplying power to the loads.Este trabalho de dissertação está enquadrado no projeto IC&DT “Quality4Power – Enhancing the Power Quality for Industry 4.0 in the era of Microgrids”, financiado pela Fundação para a Ciência e Tecnologia, com a referência PTDC/EEI-EEE/28813/201