Charge equalization is a major issue in the service of batteries since they are frequently connected in series to obtain higher output voltage levels for most applications. With series connection, imbalance may happen to the operating batteries during either charging or discharging periods. The imbalance among batteries concerns the operating efficiency and the battery lifetime. The main object of this dissertation is to solve the problem of charge inequality. The importance of charge equalization is first addressed. The problem is demonstrated by experiments of charging/discharging processes. Then, the techniques of battery charging and charge equalization are reviewed. To improve charge equalization, a dynamic balance charging scheme is developed on the basis of buck-boost conversion. The balance charging scheme can be realized by two configurations, that is, ¡§forward allotting¡¨ or ¡§backward allotting¡¨ configurations. The circuits are composed of several duplicated subcircuits and operated by digital control kernel, therefore, they are easy to be applied on battery sets with different numbers of batteries. By dynamically re-allocating the energy drawing from satiated batteries and allotted to hungry ones, the series-connected batteries can reach balance state more efficiently. The balance charging circuits can be employed during off-line or even discharging. However, on observing that the output voltage will vary in a big range when the battery set is discharged, the charge equalization can be integrated with voltage regulation on the output. Evolve from this idea, a balance discharging circuit¡@topology based on multi-winding transformer is proposed. The experiments in this dissertation are carried out on lead-acid batteries, therefore, the reactions and characteristics of lead-acid batteries are discussed. However, the proposed circuits are not restricted to be applied on lead-acid batteries only. Experimental results confirm the theoretical analyses and manifest the effectiveness of the designed circuits.

Although the locomotive of a train is energized, in general, other railcars are not. This prevents commercial rail companies from installing sensor equipment on the railcars. Thus, several different solutions have been proposed to provide energy for commercial railcars. One such solution is a vibration-based energy harvester which can be mounted in the suspension coils of the railcar. The harvester translates the linear motion of the suspension vibration into rotational motion to turn a 3-phase AC generator. When subjected to real-world suspension displacements, the harvester is capable of generating peak energy levels in excess of 70 W, although the average energy harvested is much lower, around 1 W. A battery pack can be used to store the useful energy harvested. However, a power conditioning circuit is required to convert the 3-phase AC energy from the harvester into DC for the battery pack. The power converter should be capable of extracting maximum power from the energy harvester as well as acting as a battery manager. Experimental results with the energy harvester conclude that maximum power can be extracted if the harvester is loaded with 2 . In order to maintain a constant input impedance, the duty cycle of the power converter must be fixed. Conversely, output regulation requires the duty cycle to change dynamically. Consequently, there is a tradeoff between extracting maximum power and prolonging the battery life cycle. The proposed converter design aims to achieve both maximum power transfer and battery protection by automatically switching between control modes. The proposed converter design uses an inverting buck-boost converter operating in discontinuous conduction mode to maintain a constant input impedance through a fixed duty cycle. This constant input impedance mode is used to extract maximum power from the harvester when the battery is not close to fully charged. When the battery is near fully charged, extracting maximum power is not as important and the duty cycle can be controlled to regulate the output. Specifically, one-cycle control is used to regulate the output by monitoring the input voltage and adjusting the duty cycle accordingly. Finally, the converter is designed to shut down once the battery has been fully charged to prevent overcharging. The result is a power converter that extracts maximum power from the energy harvester for as long as possible before battery protection techniques are implemented. Previous related studies are discussed, tradeoffs in converter design are explained in detail, and an experimental prototype is used to confirm operation of the proposed control scheme. / Master of Science

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / This work presents procedures for modeling a Buck-Boost converter based on offline parametric identification techniques, with employment of black box and gray box models. For the identification of the control-to-output-voltage transfer function, the nonlinear Hammerstein model is employed, a particularly interesting structure to identify DC-DC converters for its ability to incorporate nonlinear static characteristic aside from the dynamic behavior of the plant. The identification of the mentioned transfer function is achieved from input and output data, obtained in simulations. In order to identify transfer function parameters, a restricted least squares algorithm is used. As for the identification of the control-to-inductor-current transfer function, a linear black box first order model is considered, with its parameters being determined from systemâs frequency response. In order to show the modelâs utility, a control system is designed based on the identified expressions. The control system employed is the digital version of type 3 compensator for the voltage loop and type 2 compensator for the current loop, both operating under or logics. The identification results of the system presented excellent agreement between the obtained parametric models and the converterâs behavior, showing the reliability of the identification techniques employed in this work. Furthermore, the control system designed from the identified transfer functions presented good performance, providing stability and quick disturbance rejection, bolstering the validity of parametric identification methods applied to the Buck-Boost converter. / Este trabalho apresenta procedimentos para a modelagem de um conversor Buck-Boost com base em tÃcnicas de identificaÃÃo paramÃtricas offline com emprego de modelos matemÃticos tipo caixa preta e caixa cinza. Para a identificaÃÃo da funÃÃo de transferÃncia que relaciona a tensÃo de saÃda e a razÃo cÃclica, à empregado o modelo nÃo linear de Hammerstein, estrutura particularmente interessante para aplicaÃÃo em identificaÃÃo de conversores CC-CC por incorporar a caracterÃstica estÃtica nÃo linear da planta de forma dissociada ao seu comportamento dinÃmico. A identificaÃÃo da funÃÃo de transferÃncia citada à feita a partir de dados de entrada e saÃda do sistema, medidos em simulaÃÃo. Para determinaÃÃo dos parÃmetros da funÃÃo de transferÃncia que relaciona a tensÃo de saÃda e a razÃo cÃclica, à utilizado um algoritmo de mÃnimos quadrados nÃo recursivo com restriÃÃes. Quanto à identificaÃÃo da funÃÃo de transferÃncia que relaciona a corrente no indutor e a razÃo cÃclica, à empregado um modelo caixa preta linear de primeira ordem, sendo os parÃmetros de tal modelo determinados a partir da resposta em frequÃncia do sistema. Visando mostrar a utilidade dos modelos paramÃtricos, à realizado um projeto de controle com base nas expressÃes identificadas. O sistema de controle adotado à a versÃo digital de um compensador tipo 3 para a malha de tensÃo e de um compensador tipo 2 para a malha de corrente, que operam de forma alternada segundo a lÃgica ou. Os resultados de identificaÃÃo do sistema apresentam uma excelente concordÃncia entre os modelos paramÃtricos obtidos e o comportamento do conversor, mostrando a confiabilidade das tÃcnicas de identificaÃÃo empregadas nesse trabalho. Adicionalmente, o sistema de controle projetado a partir das funÃÃes de transferÃncia estimadas apresentou bom desempenho, garantindo estabilidade e rÃpida rejeiÃÃo a distÃrbios, reforÃando a validade dos mÃtodos de identificaÃÃo paramÃtrica aplicados ao conversor Buck-Boost.

Due to the differences in batteries of a series-connected battery bank, the restored capacity in each battery may not be the same when being charged. In order to extend battery cycle life, the charger for the battery bank must have the capability of charging equalization. This thesis proposes a non-dissipative balance charging circuit based on buck-boost topology for a series-connected battery bank. Each battery in a battery bank is associated with a buck-boost converter. This topology can efficiently alleviate the unbalance of charge among batteries by taking off the charge from the affluently charged batteries and then allotting to those insufficient ones. To accomplish this complicated and accurate control, a digital signal processor (DSP) with sensors and interface circuits is adopted. It monitors the variations of battery voltages, activates the associated buck-boost converter, and adjusts the duty ratio of the converter to regulate the energy to be released. In virtue of the adoption of digital control kernel, the control circuit can be simple and the control flexibility can be favored. A battery bank with four series connected lead-acid batteries is used for illustrating the operating behavior and describing the operation modes of the balance charging circuit. The results of experiments convincingly advocate the applicability of the proposed approach.

This thesis proposes a single-stage high-power-factor electronic ballast with series-resonant inverter for rapid-start fluorescent lamps with zero glow current during preheating period. A buck-boost converter is integrated into the ballast as the power-factor-corrector. Two auxiliary windings are wound on the same core of the buck-boost inductor for filament heating. During the preheating period, the buck-boost converter is initiated while the series-resonant inverter is disabled by controlling the corresponding active power switches. Due to zero voltage across the lamp, the glow current can be effectively eliminated. As the filaments reach appropriate emission temperature, the series-resonant inverter is activated. The lamp is then ignited and consequently operated at the rated lamp power. Circuit analyses and experimental tests of the proposed preheating control scheme are carried out on an electronic ballast for a T8-40W rapid-start fluorescent lamp.

A single-phase, buck-boost based, dual-output AC-DC converter is studied in this thesis. The converter has two DC outputs with opposite polarities, which share the same ground with the input power line. The power stage performance, including the input filter, is studied and procedure to select power components is given. The circuit model is analyzed to develop appropriate control. Zerocrossing distortion of the source input current is addressed and a solution is proposed. Experimental results are satisfactory in that a high power factor line current results for steady-state operation.

In this dissertation the ac-link universal power converters, which are a new class of power converters, are introduced and studied in detail. The inputs and outputs of these converters may be dc, ac, single phase, or multi-phase. Therefore, they can be used in a variety of applications, including photovoltaic power generation, wind power generation, and electric vehicles. In these converters the link current and voltage are both alternating and their frequency can be high, which leads to the elimination of the dc electrolytic capacitors and the bulky low-frequency transformers. Therefore, the ac-link universal power converters are expected to have higher reliability and smaller size. Moreover, these converters are soft switching, which results in negligible switching losses and minimized current and voltage stress over devices. In the first part of the dissertation, the parallel ac-link universal power converter is studied in detail. This converter is an extension of the buck-boost converter. The series ac-link universal power converter, which is dual of the parallel ac-link universal power converter, is proposed in the second part of this dissertation. This converter is an extension of the Cuk converter. A modified configuration with fewer switches, named sparse ac-link universal power converter is proposed in the third part of this dissertation. The sparse ac-link universal power converters can appear as parallel or series. The performance of all these configurations is evaluated through simulations and experiments.

No description available.

Energy-efficient radio frequency (RF) power amplifiers (PAs) are critical and paramount to achieve longer battery life in state-of-the-art portable systems because they typically determine and dominate the power consumption of such devices. In this dissertation, a high-efficiency, linear RF PA with a dynamically adaptive supply and bias current control for code division multiple access (CDMA) and wideband CDMA (WCDMA) is conceived, simulated, and experimentally demonstrated with a discrete PCB-level design and in integrated circuit (IC) form. The PA efficiency is improved by dynamically adjusting both its supply voltage and bias current, there by minimizing its quiescent power dissipation. The PA supply voltage is derived from the battery by a noninverting, synchronous buck-boost switching regulator because of its flexible functionality and high efficiency. Adjusting the PA supply voltage and bias current by tracking the output power, instead of following the complete envelope in large baseband bandwidth wireless applications, is achieved by a converter with a lower switching frequency and consequently higher light-load efficiency, which translates to prolonged battery life. A discrete PCB-level prototype of the proposed system with 915 MHz center frequency, CDMA IS-95 signal having 27-dBm peak-output power resulted in more than four times improvement in the average efficiency compared to a fixed-supply class-AB PA while meeting the required performance specifications. In the IC solution fabricated in AMIs 0.5-micron CMOS process through MOSIS, a dual-mode, buck-boost converter with pulse-width modulation (PWM) control for high power and pulse-frequency modulation (PFM) for low power is designed and implemented to improve the PA efficiency during active and standby operation, respectively. The performance of the dynamically adaptive supply and bias control IC was validated by realizing a 25-dBm, 1.96 GHz center frequency, WCDMA PA over an input supply range of 1.4 4.2 V. The PA with dual-mode power supply and bias control IC showed an average-efficiency improvement of seven times compared to a fixed-supply class-AB PA, which translates to five times improvement in battery life assuming the PA is active for 2 % of the total time and in standby mode otherwise.

Στην παρούσα διπλωματική εργασία διερευνώνται οι προδιαγραφές για την εγκατάσταση και τη διασύνδεση με το δίκτυο διανομής ενός οικιακού φωτοβολταϊκού συστήματος. Ο όρος «οικιακό» αναφέρεται σε φωτοβολταϊκά συστήματα μικρής ισχύος, έως 10 kWp, τα οποία τοποθετούνται πάνω σε κτίρια ή ενσωματώνονται σε αυτά ενώ παρέχουν ηλεκτρική ενέργεια στο δίκτυο μέσω της ίδιας παροχής του κτιρίου. Τα οικιακά φωτοβολταϊκά παρουσιάζουν πολλά πλεονεκτήματα ώστε να αποτελέσουν πόλο έλξης για τους μελλοντικούς παραγωγούς όπως θερμική μόνωση, ηχομόνωση, ηλιο-προστασία, δεν απαιτούν επιπλέον χώρο για την εγκατάσταση τους, συνεισφέρουν στην κάλυψη του φορτίου αιχμής, δε περιλαμβάνουν κινητά μέρη, προσφέρουν έναν ελκυστικό σχεδιασμό κτιρίου και αντικαθιστούν συμβατικά κατασκευαστικά υλικά. Στο πρώτο κεφάλαιο παρουσιάζεται μια θεωρητική ανασκόπηση της φύσης της ηλιακής ακτινοβολίας. Στο δεύτερο κεφάλαιο γίνεται μια περιγραφή του ηλιακού κυττάρου, των φωτοβολταϊκών πλαισίων και των αρχών λειτουργίας τους, καθώς και παρουσιάζονται τα ηλεκτρικά χαρακτηριστικά τους και οι παράγοντες που τα επηρεάζουν. Εν συνεχεία, στο τρίτο κεφάλαιο μπορούμε να δούμε τα κριτήρια με τα οποία επιλέγεται ο τόπος και ο τρόπος εγκατάστασης ενός φωτοβολταϊκού συστήματος, και παρουσιάζονται οι αρχές σχεδιασμού του συστήματος ξεκινώντας από την επιλογή του αντιστροφέα μέχρι τα μέσα προστασίας και την καλωδίωση. Στο τέταρτο κεφάλαιο παρουσιάζονται οι απαιτήσεις που πρέπει να τηρούνται ώστε να καθίσταται εφικτή η διασύνδεση με το δίκτυο ΧΤ μιας εγκατάστασης παραγωγής ενέργειας. Επιπλέον, εξετάζονται τα κριτήρια τήρησης των ανωτέρω απαιτήσεων, όπως η επάρκεια του δικτύου, η διαμόρφωση των προστασιών της διασύνδεσης, οι μεταβολές της τάσης, το φαινόμενο flicker, η έγχυση αρμονικών, η νησιδοποίηση και οι επιπτώσεις στα συστήματα Τηλεχειρισμών Ακουστικής Συχνότητας. Εν τέλει, στο πέμπτο κεφάλαιο πραγματοποιούνται προσομοιώσεις για την μελέτη των παραπάνω προδιαγραφών σε δύο διατάξεις που εξομοιώθηκαν με το πρόγραμμα PSCAD. Η μια διάταξη περιλαμβάνει μια φωτοβολταϊκή συστοιχία ισχύος 9.6 kWp, έναν μετατροπέα υποβιβασμού τάσης ο οποίος κάνει την ανίχνευση του σημείου μεγίστης ισχύος, έναν τριφασικό αντιστροφέα με παλμοδότηση SPWM, το φίλτρο LC για τη μείωση του αρμονικού περιεχομένου, έναν μετασχηματιστή απομόνωσης και ανύψωσης τάσης 150V/400V, το δίκτυο ΧΤ και το οικιακό φορτίο. Η δεύτερη διάταξη διαφοροποιείται από την πρώτη στο ότι δεν περιλαμβάνει μετατροπέα υποβιβασμού τάσης, έτσι ο αντιστροφέας αναλαμβάνει την ανίχνευση του σημείου μεγίστης ισχύος. Αρχικά παρουσιάζεται η απόκριση των συστημάτων σε κανονικές συνθήκες λειτουργίας και μέση φόρτιση, ενώ εξετάζεται και η επίδραση των τιμών των ελεγκτών στην απόκριση τους. Στη συνέχεια, γίνεται η μελέτη αρμονικών και η διερεύνηση της επίδρασης της ακτινοβολίας στους συντελεστές ολικής αρμονικής παραμόρφωσης ρεύματος και τάσης, και στο συντελεστή ισχύος. Έπειτα εξετάζεται η απόκριση των συστημάτων σε απότομες μεταβολές της ακτινοβολίας και του φορτίου. Τέλος διερευνώνται οι διακυμάνσεις της τάσης που εμφανίζονται σε οριακές καταστάσεις λειτουργίας του φωτοβολταϊκού και φόρτισης του δικτύου ενώ εξετάζονται και οι επιπτώσεις στα συστήματα Τηλεχειρισμών Ακουστικής Συχνότητας. / The aim of the present thesis is the study of the installation and grid-interconnection requirements and specifications of a domestic photovoltaic system. The term “domestic” refers to low power photovoltaic systems (up to 10 kWp), installed or integrated into buildings while providing electric power to the grid through the buildings main power connection. Domestic photovoltaic systems have a number of advantages, such as thermal / sound insulation, solar protection, they do not require extra space in order to be installed, they can contribute in the case of high power demand, they do not require any moving parts, they can prove attractive in terms of building design and even eventually substitute conventional building materials. These advantages are bound to put them in the center of electric power producers’ attention in the immediate future. In the first chapter a theoretic overview of the nature of solar radiation is presented. In the second chapter, photovoltaic cells and panels as well as their function and electrical properties are briefly analyzed. In the third chapter, the criteria of the photovoltaic system’s installation location and method – from the selection of a proper inverter to the system’s electrical protection equipment and wiring. In the fourth chapter the requirements that must be met in order to establish a connection with the power distribution grid are being presented. The relevant criteria such as: a) power grid adequacy, b) proper design and configuration of the grid connection protection equipment, c) voltage variations, d) flickering, e) voltage/current harmonics, f) islanding, and g) effects on 175Hz remote-operation systems are being studied. Finally, in the fifth chapter, PSCAD-realized simulations with two configurations are presented. The first configuration consists of a 9.6kWp photovoltaic array, a dc-to-dc buck converter which implements a maximum-power-point-tracking algorithm, a SPWM-pulsed three-phase inverter, a LC harmonic filter, an isolating 150V/400Vvoltage transformer, the low-voltage grid and a domestic electric load. The second configuration does not include a buck converter and thus, the maximum-power-point-tracking algorithm is implemented on the inverter. The systems’ response in normal operating conditions and with a medium load as well as the effect of different controller gains in the aforementioned response are initially presented. Afterwards, the system’s voltage/current harmonics and the effect of solar radiation in the Total Harmonic Distortion and Power factors are being studied. In continuation the system’s response in rapid change of solar irradiance / electrical load is presented. Finally, voltage variations which appear in boundary operating conditions of the grid and photovoltaic system, as well as the impact on 175Hz remote-operation systems are studied.