The influence of different voltage waveforms and grain sizes in electrical steels losses

Square and two-level pulse width modulation (PWM) magnetic induction waveforms are investigated and their effect on electrical steels losses as a function of the grain size is determined. The increase of hysteresis losses-as compared to that resulting from sinusoidal voltages-occurs only for two-level PWM waveforms. Total losses are lower for square waveform, and the difference between losses under square and sinusoidal waveform increase with increasing grain size, result explained with the loss separation model. (C) 2008 Elsevier B.V. All rights reserved.

Digitally-implemented naturally sampled PWM suitable for multilevel converter control

For dynamic closed loop control of a multilevel converter with a low pulse number (ratio of switching frequency to synthesized fundamental), natural sampled pulse-width modulation (PWM) is the best form of modulation. Natural sampling does not introduce distortion or a delayed response to the modulating signal. However previous natural sampled PWM implementations have generally been analog. For a modular multilevel converter, a digital implementation has advantages of accuracy and flexibility. Re-sampled uniform PWM is a novel digital modulation technique which approaches the performance of natural PWM. Both hardware and software implementations for a five level multilevel converter phase are presented, demonstrating the improvement over uniform PWM.

Power converter topologies for wind energy conversion systems: Integrated modeling, control strategy and performance simulation

This paper presents new integrated model for variable-speed wind energy conversion systems, considering a more accurate dynamic of the wind turbine, rotor, generator, power converter and filter. Pulse width modulation by space vector modulation associated with sliding mode is used for controlling the power converters. Also, power factor control is introduced at the output of the power converters. Comprehensive performance simulation studies are carried out with matrix, two-level and multilevel power converter topologies in order to adequately assert the system performance. Conclusions are duly drawn.

Comando de ondulador de tens��o trif��sico por PWM e t��cnica U/F com implementa����o por microcontrolador

Disserta����o para obten����o do grau de Mestre em Engenharia Electrot��cnica Ramo de Automa����o e Electr��nica Industrial

Simulation of offshore wind system with two-level converters: HVDC power transmission

A new integrated mathematical model for the simulation of offshore wind energy conversion system performance is presented in this paper. The mathematical model considers an offshore variable-speed turbine in deep water equipped with a permanent magnet synchronous generator using full-power two-level converter, converting the energy of a variable frequency source in injected energy into the electric network with constant frequency, through a high voltage DC transmission submarine cable. The mathematical model for the drive train is a concentrate two mass model which incorporates the dynamic for the structure and tower due to the need to emulate the effects of the moving surface. Controller strategy considered is a proportional integral one. Also, pulse width modulation using space vector modulation supplemented with sliding mode is used for trigger the transistor of the converter. Finally, a case study is presented to access the system performance. �� 2014 IEEE.

A simulation of integrated photovoltaic conversion into electric grid

This paper presents a systemic modeling for a PV system integrated into an electric grid. The modeling includes models for a DC-DC boost converter and a DC-AC two-level inverter. Classical or fuzzy PI controllers with pulse width modulation by space vector modulation associated with sliding mode control is used for controlling the PV system and power factor control is introduced at the output of the system. Comprehensive performance simulation studies are carried out with the modeling of the DC-DC boost converter followed by a two-level power inverter in order to compare the performance with the experimental results obtained during in situ operation with three commercial inverters. Also, studies are carried out to assess the quality of the energy injected into the electric grid in terms of harmonic distortion. Finally, conclusions regarding the integration of the PV system into the electric grid are presented. (C) 2014 Elsevier Ltd. All rights reserved.

Simulation of offshore wind system with two levels converters: HVDC power transmission

A new integrated mathematical model for the simulation of offshore wind energy conversion system performance is presented in this paper. The mathematical model considers an offshore variable-speed turbine in deep water equipped with a permanent magnet synchronous generator using full-power two-level converter, converting the energy of a variable frequency source in injected energy into the electric network with constant frequency, through a high voltage DC transmission submarine cable. The mathematical model for the drive train is a concentrate two mass model which incorporates the dynamic for the structure and tower due to the need to emulate the effects of the moving surface. Controller strategy considered is a proportional integral one. Also, pulse width modulation using space vector modulation supplemented with sliding mode is used for trigger the transistor of the converter. Finally, a case study is presented to access the system performance. �� 2014 IEEE.

Constru����o de um variador de frequ��ncia

A dificuldade de controlo de um motor de indu����o, bem como o armazenamento de energia CC e posterior utiliza����o como energia alternada promoveram o desenvolvimento de variadores de frequ��ncia e inversores. Assim, como projeto de tese de mestrado em Automa����o e Sistemas surge o desenvolvimento de um variador de frequ��ncia. Para elabora����o do variador de frequ��ncia efetuou-se um estudo sobre as t��cnicas de modula����o utilizadas nos inversores. A t��cnica escolhida e utilizada �� a Sinusoidal Pulse Width Modulation (SPWM). Esta t��cnica baseia-se na modela����o por largura de impulso (PWM), o qual �� formado por compara����o de um sinal de refer��ncia com um sinal de portadora de elevada frequ��ncia. Por sua vez, a topologia escolhida para o inversor corresponde a um Voltage Source Inverter (VSI) de ponte trif��sica completa a tr��s terminais. O desenvolvimento da t��cnica de modula����o SPWM levou ao desenvolvimento de um modelo de simula����o em SIMULINK, o qual permitiu retirar conclus��es sobre os resultados obtidos. Na fase de implementa����o, foram desenvolvidas placas para o funcionamento do variador de frequ��ncia. Assim, numa fase inicial foi desenvolvida a placa de controlo, a qual cont��m a unidade de processamento e que �� respons��vel pela atua����o de Insulated Gate Bipolar Transistors (IGBTs). Para al��m disso, foi desenvolvida uma placa para prote����o dos IGBTs (evitando condu����o simult��nea no mesmo terminal) e uma placa de fontes isoladas para alimenta����o dos circuitos e para atua����o dos IGBTs. Ainda, foi desenvolvida a t��cnica de SPWM em software para a unidade de controlo e finalmente foi desenvolvida uma interface gr��fica para intera����o com o utilizador. A valida����o do projeto foi conseguida atrav��s da varia����o da velocidade do motor de indu����o trif��sico. Para isso, este foi colocado a funcionar a diversas frequ��ncias de funcionamento e a diferentes amplitudes. Para al��m disso, o seu funcionamento foi tamb��m validado utilizando uma carga trif��sica equilibrada de 3 l��mpadas de forma a ser visualizada a varia����o de frequ��ncia e varia����o de amplitude.

Simulation of a-Si PV system grid connected by boost and inverter

This paper is about a PV system connected to the electric grid by power electronic converters, using classical PI controller. The modelling for the converters emulates the association of a DC-DC boost with a two-level power inverter (TwLI) or three-level power inverter (ThLI) in order to follow the performance of a testing experimental system. Pulse width modulation (PWMo) by sliding mode control (SMCo) associated with space vector modulation (SVMo) is applied to the boost and the inverter. The PV system is described by the five parameters equivalent circuit. Parameter identification and simulation studies are performed for comparison with the testing experimental system.

Controlo da velocidade e posi����o de um tapete rolante

A utiliza����o eficiente da energia �� essencial para a competitividade econ��mica de um pa��s. Sendo a intensidade energ��tica de Portugal elevada, onde a utiliza����o de motores el��tricos, absorve cerca de metade da energia el��trica consumida na ind��stria, a utiliza����o de conversores eletr��nicos de pot��ncia permite obter economias de energia. Nesta tese pretende-se controlar a velocidade e o posicionamento de um tapete rolante atrav��s da utiliza����o de um conversor eletr��nico de pot��ncia. Na fundamenta����o te��rica s��o referidos os conceitos de varia����o da tens��o e frequ��ncia, controle escalar e vetorial, modela����o por largura de pulso (PWM) assim como a retifica����o e ondula����o da tens��o de um variador de velocidades. Na parte pr��tica ser�� utilizado um servo motor, controlado por um variador eletr��nico de velocidades, para efetuar o referido projeto. �� ainda objeto desta tese o estudo dos par��metros fundamentais assim como a pesquisa dos par��metros a utilizar para o desempenho pretendido.

Implementation and comparison of different switching techniques for shunt active power filters

This paper presents a comparison between three switching techniques that can be used in three-phase four-wire Shunt Active Power Filters (SAPFs). The implemented switching techniques are: Periodic-Sampling (PS), Triangular Carrier Pulse-Width Modulation (TC-PWM) and Space Vector PWM (SVPWM). The comparison between them is made in terms of the compensated currents THD%, implementation complexity, necessary CPU time and SAPF efficiency. To perform this comparison are presented and analyzed several experimental results, obtained with a 20 kVA Shunt Active Power Filter prototype, specially developed for this purpose. The control system of the developed SAPF is based in the p-q Theory with a grid synchronization algorithm p-PLL.

Desenvolvimento de um Controlador com DSP para um Motor CA de 30 kW para o CEPIUM

Disserta����o de mestrado integrado em Engenharia Eletr��nica Industrial e Computadores

Verkkovaihtosuuntaajan vektoris����d��n toteutus FPGA-piirill��

Verkkovaihtosuuntaajalla pystyt����n muuntamaan tasaj��nnite vaihtoj��nnitteeksi ja p��invastoin. Verkkovaihtosuuntaajan toiminta perustuu tehokytkinten ohjaukseen ja sopivan modulointimenetelm��n k��ytt����n. Vektoris����d��ss�� vaihtosuuntaajanvirrat ja j��nnitteet esitet����n kompleksitasossa, jolloin virta- ja j��nnitekomponentit voidaan esitt���� vektoreina. Vektoris����d��ss�� verkkovaihtosuuntaajan ohjaustoteutetaan laskemalla kompleksitasossa vektoreille arvot, jotka tuottavat vaihtosuuntaajan l��ht����n halutun vektorin. Koska FPGA-piirit mahdollistavat nopean rinnakkaisen laskennan, soveltuvat ne hyvin vektoris����d��n toteuttamiseen. FPGA-piirien rakenteesta johtuen on s����t��j��rjestelm��n suunnittelussa huomioitava kiinte��n pilkun lukujen riitt��v�� bittileveys ja j��rjestelm��n diskretointiaika. Ty��ss�� suunnitellaan verkkovaihtosuuntaajan vektoris����t�� ja tutkitaan bittileveyden vaikutusta s����d��n toteuttamiseen FPGA-piirill��. Bittileveyden tarkasteluun esitet����n k��ytett��v��ksi tilastollisia menetelmi��. Ty��ss�� tarkastellaan kiinte��n pilkun j��rjestelm��n ja liukulukuj��rjestelm��n erosuureen tilastollisia tunnusmerkkej�� sek�� histogrammia. Tarkasteluissa huomattiin, ett�� maksimivirhe itsess����n ei tarjoa riitt��v��sti tietoa erosuureen jakautumisesta. N��in ollen maksimivirhe ei ole kaikissa tilanteissa sovelias menetelm�� riitt��v��n bittitarkkuuden m����ritt��miseen. Ty��ss�� esitet����n riitt��v��n bittitarkkuuden m����rittelemiseen k��ytett��v��ksi otossuureista otosvarianssia, keskipoikkeamaa ja vaihteluv��li��.

Analysis of the voltage source inverter with small DC-link capacitor

IIn electric drives, frequency converters are used to generatefor the electric motor the AC voltage with variable frequency and amplitude. When considering the annual sale of drives in values of money and units sold, the use of low-performance drives appears to be in predominant. These drives have tobe very cost effective to manufacture and use, while they are also expected to fulfill the harmonic distortion standards. One of the objectives has also been to extend the lifetime of the frequency converter. In a traditional frequency converter, a relatively large electrolytic DC-link capacitor is used. Electrolytic capacitors are large, heavy and rather expensive components. In many cases, the lifetime of the electrolytic capacitor is the main factor limiting the lifetime of the frequency converter. To overcome the problem, the electrolytic capacitor is replaced with a metallized polypropylene film capacitor (MPPF). The MPPF has improved properties when compared to the electrolytic capacitor. By replacing the electrolytic capacitor with a film capacitor the energy storage of the DC-linkwill be decreased. Thus, the instantaneous power supplied to the motor correlates with the instantaneous power taken from the network. This yields a continuousDC-link current fed by the diode rectifier bridge. As a consequence, the line current harmonics clearly decrease. Because of the decreased energy storage, the DC-link voltage fluctuates. This sets additional conditions to the controllers of the frequency converter to compensate the fluctuation from the supplied motor phase voltages. In this work three-phase and single-phase frequency converters with small DC-link capacitor are analyzed. The evaluation is obtained with simulations and laboratory measurements.

Hybrid LC Filter for Power Electronic Drives: Theory and Implementation

Power electronic converter drives use, for the sake of high efficiency, pulse-width modulation that results in sequences of high-voltage high-frequency steep-edged pulses. Such a signal contains a set of high harmonics not required for control purposes. Harmonics cause reflections in the cable between the motor and the inverter leading to faster winding insulation ageing. Bearing failures and problems with electromagnetic compatibility may also result. Electrical du/dt filters provide an effective solution to problems caused by pulse-width modulation, thereby increasing the performance and service life of the electrical machines. It is shown that RLC filters effectively decrease the reflection phenomena in the cable. Improved (simple, but effective) solutions are found for both differential- and common-mode signals; these solutions use a galvanic connection between the RLC filter star point and the converter DC link. Foil chokes and film capacitors are among the most widely used components in high-power applications. In actual applications they can be placed in different parts of the cabinet. This fact complicates the arrangement of the cabinet and decreases the reliability of the system. In addition, the inductances of connection wires may prevent filtration at high frequencies. This thesis introduces a new hybrid LC filter that uses a natural capacitance between the turns of the foil choke based on integration of an auxiliary layer into it. The main idea of the hybrid LC filter results from the fact that both the foil choke and the film capacitors have the same roll structure. Moreover, the capacitance between the turns (���intra capacitance���) of the foil inductors is the reason for the deterioration of their properties at high frequencies. It is shown that the proposed filter has a natural cancellation of the intra capacitance. A hybrid LC filter may contain two or more foil layers isolated from each other and coiled on a core. The core material can be iron or even air as in the filter considered in this work. One of the foils, called the main foil, can be placed between the inverter and the motor cable. Other ones, called auxiliary foils, may be connected in star to create differential-mode noise paths, and then coupled to the DC link midpoint to guarantee a traveling path, especially for the common-mode currents. This way, there is a remarkable capacitance between the main foil and the auxiliary foil. Investigations showed that such a system can be described by a simple equivalent LC filter in a wide range of frequencies. Because of its simple hybrid construction, the proposed LC filter can be a cost-effective and competitive solution for modern power drives. In the thesis, the application field of the proposed filter is considered and determined. The basics of hybrid LC filter design are developed further. High-frequency behaviour of the proposed filter is analysed by simulations. Finally, the thesis presents experimental data proving that the hybrid LC filter can be used for du/dt of PWM pulses and reduction of common-mode currents.