An high-speed parametric ADC and a co-designed mixer for CMOS RF receivers

Dissertação apresentada na faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Electrotécnica e de Computadores

Controlo de conversores de potência genéricos por FPGA

Dissertação para obtenção do grau de Mestre em Engenharia Eletrotécnica Ramo de Automação e Eletrónica Industrial

Projecto e implementação de uma fonte de alta tensão para produção de descargas eléctricas

O objetivo deste trabalho consistiu em projetar, construir e testar um protótipo em laboratório de uma fonte de alimentação de alta tensão que permita descargas elétricas {estáveis e de dimensões reduzidas}, de modo a que possa ser utilizada, dada a sua essencialidade, na fabricação de redes de período longo (LPG) em fibra ótica nos chamados turning points. Estes são pontos de elevada sensibilidade, fundamentais no desenvolvimento tecnológico de sensores em fibra ótica, em particular, de sensores refractométricos. O protótipo da fonte de alimentação é composto por um regulador do tipo BUCK, um inversor para alimentação do transformador de alta tensão, o circuito de realimentação e controlo PWM e um microcontrolador para o comando da fonte. Posteriormente procedeu-se à otimização dos parâmetros de descarga, o que conduziu a fabricação de redes de período longo com períodos inferiores a 150 micrómetros. Este é um resultado sem paralelo a nível internacional no que concerne ao uso da técnica do arco elétrico.

Modelamento e simulação de um sistema inversor trifásico para injeção de energia na rede de distribuição a partir de fontes renováveis do tipo FV

Este trabalho baseia se na necessidade de aumentar as fontes renováveis de energia, reduzindo assim a dependência de fontes não renováveis, principalmente as poluentes como as de provenientes de combustíveis fosseis. A fonte de energia renovável explorada neste trabalho é a advinda de energia solar, com a utilização de painéis solares e métodos de extração para converter esta energia em energia elétrica e assim poder utilizar esta energia de forma eficiente. A energia produzida por painéis fotovoltaicos se apresenta em forma de corrente continua, tendo assim a necessidade do uso de conversores CC-CA, ou ditos inversores de tensão, para utilização da mesma, já que a maioria do equipamentos que utilizam energia elétrica são construídos em forma a serem abastecidos com energia elétrica em corrente alternada. Como este trabalho foca na injeção da energia produzida pelos painéis FV na rede de distribuição de baixa tensão, faz se necessário o uso de um PLL para garantir que o sistema inversor esteja em sincronismo com a rede de distribuição e possa garantir a entrega de energia ativa. Por fim mas não menos importante, é utilizado neste projeto técnicas de MPPT para garantir um maior aproveitamento da energia proveniente dos painéis FV, ajudando assim a melhorar a eficácia deste tipo de energia, sendo mais fiável e viável.

Comprehensive comparison of a current-source and a voltage-source converter for three-phase EV fast battery chargers

This paper presents a comprehensive comparison of a current-source converter and a voltage-source converter for three-phase electric vehicle (EV) fast battery chargers. Taking into account that the current-source converter (CSC) is a natural buck-type converter, the output voltage can assume a wide range of values, which varies between zero and the maximum instantaneous value of the power grid phase-to-phase voltage. On the other hand, taking into account that the voltage-source converter (VSC) is a natural boost-type converter, the output voltage is always greater than the maximum instantaneous value of the power grid phase-to-phase voltage, and consequently, it is necessary to use a dc-dc buck-type converter for applications as EV fast battery chargers. Along the paper is described in detail the principle of operation of both the CSC and the VSC for EV fast chargers, as well as the main equations of the power theory and current control strategies. The comparison between both converters is mainly established in terms of the total harmonic distortion of the grid current and the estimated efficiency for a range of operation between 10 kW and 50 kW.

Three-phase three-level current-source converter for EVs fast battery charging systems

This paper presents a three-phase three-level fast battery charger for electric vehicles (EVs) based in a current-source converter (CSC). Compared with the traditional voltage-source converters used for fast battery chargers, the CSC can be seen as a natural buck-type converter, i.e., the output voltage can assume a wide range of values, which varies between zero and the maximum instantaneous value of the power grid phase-to-phase voltage. Moreover, using the CSC it is not necessary to use a dc-dc back-end converter in the battery side, and it is also possible to control the grid current in order to obtain a sinusoidal waveform, and in phase with the power grid voltage (unitary power factor). Along the paper is described in detail the proposed CSC for EVs fast battery charging systems: the circuit topology, the power control theory, the current control strategy and the grid synchronization algorithm. Several simulation results of the EV fast battery charger operating with a maximum power of 50 kW are presented.

Predictive control of a current-source inverter for solar photovoltaic grid interface

Solar photovoltaic systems are an increasing option for electricity production, since they produce electrical energy from a clean renewable energy resource, and over the years, as a result of the research, their efficiency has been increasing. For the interface between the dc photovoltaic solar array and the ac electrical grid is necessary the use of an inverter (dc-ac converter), which should be optimized to extract the maximum power from the photovoltaic solar array. In this paper is presented a solution based on a current-source inverter (CSI) using continuous control set model predictive control (CCS-MPC). All the power circuits and respective control systems are described in detail along the paper and were tested and validated performing computer simulations. The paper shows the simulation results and are drawn several conclusions.

Bidirectional battery charger with grid-to-vehicle, vehicle-to-grid and vehicle-to-home technologies

This paper presents the development of na on-board bidirectional battery charger for Electric Vehicles (EVs) targeting Grid-to-Vehicle (G2V), Vehicle-to-Grid (V2G), and Vehicle-to-Home (V2H) technologies. During the G2V operation mode the batteries are charged from the power grid with sinusoidal current and unitary power factor. During the V2G operation mode the energy stored in the batteries can be delivered back to the power grid contributing to the power system stability. In the V2H operation mode the energy stored in the batteries can be used to supply home loads during power outages, or to supply loads in places without connection to the power grid. Along the paper the hardware topology of the bidirectional battery charger is presented and the control algorithms are explained. Some considerations about the sizing of the AC side passive filter are taken into account in order to improve the performance in the three operation modes. The adopted topology and control algorithms are accessed through computer simulations and validated by experimental results achieved with a developed laboratory prototype operating in the different scenarios.

Simulation of OWES with five-Level converter linked to the grid: Harmonic assessment

This paper deals with a computing simulation for an offshore wind energy system taking into account the influence of the marine waves action throughout the floating platform. The wind energy system has a variable-speed turbine equipped with a permanent magnet synchronous generator and a full-power five level converter, injecting energy into the electric grid through a high voltage alternate current link. A reduction on the unbalance of the voltage in the DC-link capacitors of the five-level converter is proposed by a strategic selection of the output voltage vectors. The model for the drive train of the wind energy system is a two mass model, including the dynamics of the floating platform. A case study is presented and the assessment of the quality of the energy injected into the electric grid is discussed.

Optimization of magnetoelectric composites based on electroactive polymers for energy harvesting and sensor application

Tese de Doutoramento em Engenharia de Materiais.

Boost converter

In this project, we want to implement a theoretical typology of a converter, the Boost converter, which is also named “Step-up converter”. We also want to bring it to the practical area, where we could work and obtain a useful service, particularly our objective is to obtain a power supply for a notebook. We will give the possibility to work, charge etc. our device in the car and obtain another work station

Hybrid model of a double-fed induction machine and back-to-back converter

This report details the port interconnection of two subsystems: a power electronics subsystem (a back-to-back AC/AC converter (B2B), coupled to a phase of the power grid), and an electromechanical subsystem (a doubly-fed induction machine (DFIM), coupled mechanically to a flywheel and electrically to the power grid and to a local varying load). Both subsystems have been essentially described in previous reports (deliverables D 0.5 and D 4.3.1), although some previously unpublished details are presented here. The B2B is a variable structure system (VSS), due to the presence of control-actuated switches: however from a modelling and simulation, as well as a control-design, point of view, it is sensible to consider modulated transformers (MTF in the bond-graph language) instead of the pairs of complementary switches. The port-Hamiltonian models of both subsystems are presents and coupled through a power-preserving interconnection, and the Hamiltonian description of the whole system is obtained; detailed bond-graphs of all the subsystems and the complete system are provided.

Nosturin tehonsyöttö rinnankytketyillä verkkovaihtosuuntaajilla

Taajuusmuuttajaohjatuissa nosturikäytöissä taakkaa laskettaessa syntyvä energia on muutettava lämmöksi jarruvastuksissa tai syötettävä takaisin sähköverkkoon esimerkiksi verkkovaihtosuuntaajalla. Verkkovaihtosuuntaajaa on tyypillisesti käytetty suurissa satamanostureissa, joiden tehontarve on yli 1000 kW. Työssä tutkitaan useista yhteiseen välipiiriin rinnankytketyistä nimellisteholtaan 250 kW:n verkkovaihtosuuntaajista koostuvan verkkoonjarrutuslaitteiston soveltuvuutta nosturikäyttöön. Lisäksi johdetaan yhtälöt verkkoonjarrutuslaitteiston virran laskemiseksi, kun nosturin mekaaniset arvot tunnetaan. Viidestä erityyppisestä nosturista esitellään esimerkkitoteutus rinnankytketyillä verkkovaihtosuuntaajilla. Aiemmin vastusjarruttavina toteutettujen nostureiden kustannuksia verrataan verkkovaihtosuuntaajilla toteutettuihin ratkaisuihin. Esimerkkinostureista esitetään nosturin työsykliin perustuva arvio verkkoonjarrutuksen tuomasta energian säästöstä. Tehtyjen mittausten perusteella käytetty menetelmä verkkovaihtosuuntaajien rinnan kytkemiseksi osoittautui nosturikäytössä toimivaksi. Kustannuslaskelmien perusteella verkkovaihtosuuntaajalla toteutetusta nosturista tulee materiaalikustannuksiltaan vastusjarruttavaa kalliimpi, vaikka paljon tilaa vievät vastuskaapit voidaankin jättää pois.

Moottorimalliton skalaarisäätö

Työssä tutkitaan nopeusanturittoman vaihtovirtakäytön skalaarisia ohjaus- ja säätömenetelmiä. Työn alussa esitetään perusteoriat taajuusmuuttajista ja oikosulkumoottoreista. Tämän jälkeen esitellään yleisimmin kirjallisuudessa esiintyneet skalaariohjaukset ja –säädöt. Vektorisäätöä ja erityisesti moottoriparametrien vaikutusta säädön toimivuuteen esitellään lyhyesti. Työn tavoitteena on ACS800 taajuusmuuttajan skalaarisäädön tutkiminen. ACS800:n nykyinen skalaarisäätö on liian sidoksissa vektorisäätöön, joten simulointien ja kirjallisuustutkimuksen tarkoituksena on täysin vektorisäädöstä eriytetyn skalaarisäädön kehitysmahdollisuuksien tutkiminen. Kirjallisuudessa esiintyneiden säätöjen avulla muodostetaan diskreettiaikainen toteutus skalaarisäädölle vaihtovirtakäytössä, jossa on käytössä virran ja välipiirijännitteen takaisinkytkentä. Säädettävää moottoria mallinnetaan jatkuvaaikaisella L-sijaiskytkennällä. Välipiirin mallinnus toimii myös jatkuva-aikaisena lukuun ottamatta välipiirin tasavirtakomponenttia, joka muodostetaan virran takaisinkytkennän ja PWM-modulaattorin kytkinasentojen avulla. Simuloinnin tarkoituksena on mallintaa skalaarisäädön suurimpia ongelmia, kuten virta- ja välijännitesäätöä. Tuloksista voidaan päätellä, että perussäädöt toimivat moitteettomasti, mutta erityisesti virtasäätöä tulisi kehittää.

Developing of AC magnetometer and investigation of magnetic properties of LSMO

In this work AC magnetometer was developed and primary test measurements were performed for temperature range from 77 K up to 350 K in frequency range from 1 kHz up to 20 kHz. In the course of the present work dependencies of magnetization on temperature for Lao7Sr03Mni _yFeyO3 with y = 0.15, 0.20, 0.25 were obtained in DC magnetic field using SQUID magnetometer and in AC magnetic field using the developed AC magnetometer. Lai.XSrXMnO3 (LSMO) compounds belong to the class of Mn perovskites, which demonstrate very high degree of spin polarization. These materials are of great importance for nowadays applications in spintronics, where spin polarized electron transport is used. Spin glass like behavior was found as a characteristic feature of these solid solutions with the freezing temperature in the range 65 — 210 K.