Este trabalho apresenta o estudo de um carregador de baterias monofÃsico aplicado a veÃculos elÃtricos. Este carregador à composto por dois estÃgios de processamento de energia e um circuito digital de supervisÃo para controlar a tensÃo sobre o banco de baterias e a corrente de recarga das mesmas. O primeiro estÃgio consiste de um conversor CA-CC bridgeless com caracterÃstica de alto fator de potÃncia, e o segundo estÃgio à representado por um conversor CC-CC fullbridge com isolamento em alta frequÃncia e comutaÃÃo sob tensÃo nula (Zero Voltage Switching â ZVS). Para ambos os conversores, foi realizada uma anÃlise qualitativa e quantitativa, bem como apresentados exemplos de projeto para facilitar o dimensionamento dos componentes. Finalmente, com os componentes escolhidos, foi montado um protÃtipo que permite carregar de uma atà oito baterias de 12 V conectadas em sÃrie. O sistema apresenta como especificaÃÃes: tensÃo de entrada alternada de 220 VÂ15%; tensÃo de saÃda contÃnua de 120 V; corrente de saÃda contÃnua de 20 A; e potÃncia mÃdia de saÃda de 2,4 kW. / This work presents a single-phase battery charger for electric vehicles. This converter is composed by two energy processing stages and a digital circuit to control the voltage across the batteries and their respective charging current. The first stage is a high power factor ACDC bridgeless converter, while the second one consists on a ZVS (Zero Voltage Switching) high frequency isolated DC-DC full-bridge converter. For both converters, the qualitative and quantitative analyses have been performed, as well as design examples have been presented in order to ease the components calculation. Finally, a prototype that allows charging up to eight series-connected 12 V batteries has been built. The system specifications are: AC input voltage of 220 V Â15%; DC output voltage of 120 V; DC output current of 20 A; and average output power of 2.4 kW.

This thesis proposes a high efficiency driving circuit for multiple light emitting diode (LED) lamps with dimming feature. The driving circuit consists of essentially a high-frequency half-bridge series resonant inverter with multiple output transformers, on which primary windings are connected in series, while secondary sides are loaded by LED lamps rated at different powers with different turn ratios. By controlling the frequency of the inverter, the resonant current as well as the lamp current can be regulated simultaneously. On the other hand, the LED lamps can be dimmed individually by the associated dimming switches with integral cycle control. The tactful circuit ensures a high circuit efficiency owing to less conducting losses and zero-voltage switching (ZVS) operation of the active power switches of the inverter and zero current switching (ZCS) operation of the dimming switches. Two prototype circuits designed for 60 W three RGB LED lamps and 50 W five white light LED lamps have been built and tested to verify the analytical predictions. Experimental results demonstrate that the driving circuit can operate the LED lamps at a high efficiency with a wide dimming range. The lamp power can be dimmed to 10% with frequency control, while whole dimming range can be achieved with integral cycle control. The circuit efficiency with integral cycle control is relatively higher than that with frequency control. The measured efficiencies for the two designed circuit are 93% and 90%, respectively, under the rated powers.

A high-frequency half-bridge series resonant inverter with multiple output transformers is developed for driving multiple cold-cathode fluorescent lamps (CCFLs) with dimming feature. The primary sides of the transformers are connected in series with the resonant inverter to have an identical current, while the secondary sides are loaded by CCFLs with galvanic isolation to each other. To ensure a high circuit efficiency, the active power switches of the inverter are designed to be switched on at zero voltage. The resonant current of the inverter can be regulated by controlling the switching frequency of the inverter, so that all CCFLs can be dimmed simultaneously. On the other hand, the primary sides of the output transformers are associated with parallel switches to dim the CCFLs individually. These dimming switches are operated at a low frequency by integral cycle control with zero current switching (ZCS) to reduce the switching losses. The resonant circuit is tactfully designed to alleviate the variation of the resonant current caused by the switching of dimming switches. A laboratory circuit is built for driving 5 CCFLs. The intended circuit performances are confirmed by test results. The variation of the resonant current is less than 10% when the dimming switches are switching, and the measured efficiency for the circuit is 96.15% under the rated powers.

General-purpose step-down converter is essential in electronic system for processing energy from high-voltage rail to low-voltage circuits. The applications can be found at the auxiliary supplies in automobile, industrial and communication systems. Buck converter is a common circuit topology to fulfill step-down conversion, especially in low-power application since it is well-studied and straightforward. However, it suffers from low duty cycle under high step-down condition, and typically operates in continuous conduction mode (CCM) that generates large switching loss. On the other hand, as an extension of the buck converter, tapped-inductor (TI) buck converter has larger duty cycle while maintaining the structural simplicity. Therefore, the main objective of this thesis is to explore the potential of TI buck converter as a wide conversion range, high power density and high efficiency topology for low power application. To achieve high efficiency at switching frequency of MHz-level, synchronous conduction mode (SCM) is applied for turn-on losses elimination. The operation principle and power stage design of SCM TI buck is first introduced. The design of high switching frequency coupled inductor is emphasized since its size plays a critical role in power density. Loss breakdown is also provided to perform a comprehensive topological study. Secondly, detailed zero-voltage-switching (ZVS) condition of SCM TI buck is derived so that the converter does not experience redundant circulating energy. The experimental results of 15-W SCM TI buck converter prototypes are provided with 90.7% of peak power stage efficiency. The size of coupled inductor is down to 116 mm3. To enhance light-load efficiency, a variable frequency control scheme based on derived ZVS conditions is implemented with the switching frequency ranging from 2 MHz to 2.9 MHz. / Master of Science / General-purpose step-down converter is essential in electronic system for processing energy from high-voltage rail to low-voltage circuits. The applications can be found at the auxiliary supplies in automobile, industrial and communication systems. Typically, the ultimate goals of general-purpose step-down converter are versatility, high efficiency and compact size. Recently, tapped-inductor (TI) buck converter is studied since it could overcome the drawback of commonly used buck converter under high step-down conversion. Therefore, the potential of TI buck converter as a general-purpose step-down converter candidate is explored in this thesis, including control method, hardware design, etc. The thesis verifies that TI buck converter could have compact size while remaining efficient and adaptable.

An efficient Light Emitting Diode (LED) lamp driver circuit is proposed for retrofitting the conventionally used incandescent lamps with existing TRIAC dimmer. The dimming feature in a wide range of firing angle from 30¢X to 130¢X can be accomplished by means of double pulse-width modulation (DPWM) and analog current regulation. The LED lamp driver adopts a flyback converter with an auxiliary active power MOSFET for synchronous switch and an associated inductor for zero voltage switching (ZVS), leading to lower switching loss and thus achieving a higher circuit efficiency. In the thesis, the mode operation of the driver circuit is analyzed and the design equations are derived accordingly. A laboratory circuit is designed for an 50 W LED lamp which is composed of 45 high-brightness white LEDs in series. Experiments are carried out to test the circuit performances with two dimming schemes. The experimental results indicate that the driver can achieve a circuit efficiency of 95 % at the rated output. When the LED lamp is dimmed, the circuit efficiency with DPWM is higher than that with the analog current regulation. On the other hand, the LED lamp dimmed by analog current regulation has a higher efficiency but a less color shift by DPWM.

Modern arc welding machines utilize controllable high frequency DC/DC power supply with high dynamic and steady state current regulation performance. In the design robustness, small size and low weight, low complexity, and high efficiency are the defining criteria. The most suitable approach for a 5 kW arc welding machine power supply application is the high frequency Full-Bridge Phase-Shifted Zero Voltage Switching (FB-PS-ZVS) DC/DC converter with an isolation transformer. This converter not only gives the advantage of zero voltage switching for a wide load current range, it also provides reduced Electromagnetic Interference (EMI) and reduced component stress compared to standard PWM converters. In this thesis a FB-PS-ZVS DC/DC converter with 5 kW power rating is designed for modern arc welding machine applications. IGBTs are utilized at 50 kHz switching frequency for high efficiency and control bandwidth. The output current of the DC/DC converter is controlled via a Digital Signal Processor (DSP) control platform. The performance of the designed DC/DC converter is evaluated via the computer simulations and the experimental study of the constructed prototype.

In this thesis, the conventional pulse-width modulated (PWM) and zero-voltage switching (ZVS) quasi-resonant buck converters are analyzed and a variable-frequency control technique is proposed to regulate the output voltage due to the immediate input line and load changes. The quasi-resonant technique provides favorable switching conditions for active switch to reduce switching losses and electromagnetic interference (EMI). The method is based on shaping the voltage across the active switch in quasisinusoidal fashion and the switching action occurs with nearly zero voltage across the active switch. This requires only two additional components to the conventional PWM buck converter. The proposed quasi-resonant converter is capable of operating in megahertz range with a significant improvement in performance and power density. Detailed analytic and small-signal models of the ZVS quasi-resonant buck converter are established and the switching behavior is investigated in order to provide nearly zerovoltage turn-on. The performance of the ZVS quasi-resonant technique is verified with the computer simulations. The results are compared with the experiments in the laboratory involving both the open-loop and closed-loop operations. The detailed experiment procedure is added to use this converter for educational purposes.

In this thesis a two-stage AC/DC/DC power converter is designed and implemented. The AC/DC input stage of the converter consists of the two&amp / #8211 / phase interleaved boost topology employing the average current mode control principle. The output stage consists of a zero voltage switching phase shifted full bridge (ZVS&amp / #8211 / PS&amp / #8211 / FB) DC/DC converter. For the input stage, main design goals are obtaining high input power factor, low input current distortion, and well regulated output dc voltage, and obtaining these attributes in a power converter with high power density. For the input stage, the interleaved structure has been chosen in order to obtain reduced line current ripple and EMI, reduced power component stresses, and improved power density. The control of the pre&amp / #8211 / regulator is provided by utilizing a new commercial monolithic integrated circuit, which provides interleaved continuous conduction mode power factor correction (PFC). The output stage is formed by utilizing the available prototype hardware of a ZVS&amp / #8211 / PS&amp / #8211 / FB DC/DC converter and mainly the system integration and controller design and implementation studies have been conducted. The converter small signal model is derived and utilizing its transfer function and employing voltage loop control, the output voltage regulator has been designed. The output voltage controller is implemented utilizing a digital signal processor (DSP). Integrating the AC/DC preregulator and DC/DC converter, a laboratory AC/DC/DC converter system with high overall performance has been obtained. The overall system performance has been verified via computer simulations and experimental results obtained from laboratory prototype.

The objective of the research is to develop a cost-effective high-power bi-directional dc/dc converter with low total-device ratings, reduced system parasitic effects, and a wide input/output range. Additional objectives of the research are to develop a small-signal model and control methods, and to present performance characterizations. Device stresses in the proposed topology are controlled to maintain minimal levels by varying the duty ratio and phase-shift angle between the primary and the secondary bridges, which results in a low total-device rating, when compared to conventional bi-directional dc/dc topologies. In the proposed topology, soft switching, which reduces power loss, can be realized under specific operating conditions. When the condition that causes minimal device stress is satisfied, zero-voltage switching (ZVS) can be obtained. In the research, ZVS capability is explored for a wide range of voltage conditions as well as for the minimal device-stress condition. The performance characterization includes verifying the soft-switching regions and power-loss estimation. Another part of the thesis is the controller design of the converter. Small-signal models and feedback controllers are developed, and the controllers are experimentally validated. Because in the isolated high-frequency converters, transformer saturation is an important issue, a method to prevent transformer saturation is proposed and experimentally validated.

There is an increasing demand for power converters with small size, light weight, high conversion efficiency and higher power density. Also, in many applications, there is a need for dc-to-dc converters to accept dc input voltage and provide regulated and/or isolated dc output voltage at a desired voltage level including telecommunications equipment, process control systems, and in industry applications. This thesis presents the analysis, design, simulation and experimental results of three-phase high-frequency transformer isolated resonant converters. The first converter presented is a three-phase LCC-type dc-dc resonant converter with capacitor output filter including the effect of the magnetizing inductance of the three-phase HF transformer. The equivalent ac load resistance is derived and the converter is analyzed by using approximation analysis approach. Base on this analysis, design curves have been obtained and a design example is given. Intusoft simulation results for the designed converter are given for various input voltage and for different load conditions. The experimental verification of the designed converter performance was established by building a 300 W rated power converter and the experimental results have been given. It is shown that the converter works in zero-voltage switching (ZVS) at various input voltage and different load conditions. A three-phase (LC)(L)-type dc-dc series-resonant converter with capacitive output filter has been proposed. Operation of the converter has been presented using the operating waveforms and equivalent circuit diagrams during different intervals. An approximate analysis approach is used to analyze the converter operation, and design procedure is presented with a design example. Intusoft simulation results for the designed converter are given for input voltage and load variations. Experimental results obtained in a 300 W converter are presented. Major advantages of this converter are the leakage and magnetizing inductances of the high-frequency transformer are used as part of resonant circuit and the output rectifier voltage is clamped to the output voltage. The converter operates in soft-switching for the inverter switches for the wide variations in supply voltage and load and it requires narrow switching frequency variation (compared to LCC-type) to regulate the output voltage. A three-phase high-frequency transformer isolated interleaved (LC)(L)-type dc-dc series-resonant converter with capacitive output filter using fixed frequency control is proposed. The converter operation for different modes is presented using the operating waveforms and equivalent circuit diagrams during different intervals. This converter is modeled and then analyzed using the approximate complex ac circuit analysis approach. Based on the analysis, design curves were obtained and the design procedure is presented with a design example. The designed converter is simulated using PSIM software to predict the performance of the converter for variations in supply voltage and load conditions. The converter operates in ZVS for the inverter switches with minimum input voltage and loses ZVS for two switches in each bridge for higher input voltages. / Graduate