GaN-Based High Efficiency Transmitter for Multiple-Receiver Wireless Power Transfer

Wireless power transfer (WPT) has attracted great attention from industry and academia due to high charging flexibility. However, the efficiency of WPT is lower and the cost is higher than the wired power transfer approaches. Efforts including converter optimization, power delivery architecture improvement, and coils have been made to increase system efficiency.In this thesis, new power delivery architectures in the WPT of consumer electronics have been proposed to improve the overall system efficiency and increase the power density.First, a two-stage transmitter architecture is designed for a 100 W WPT system. After comparing with other topologies, the front-end ac-dc power factor correction (PFC) rectifier employs a totem-pole rectifier. A full bridge 6.78 MHz resonant inverter is designed for the subsequent stage. An impedance matching network provides constant transmitter coil current. The experimental results verify the high efficiency, high PF, and low total harmonic distortion (THD).Then, a single-stage transmitter is derived based on the verified two-stage structure. By integration of the PFC rectifier and full bridge inverter, two GaN FETs are saved and high efficiency is maintained. The integrated DCM operated PFC rectifier provides high PF and low THD. By adopting a control scheme, the transmitter coil current and power are regulated. A simple auxiliary circuit is employed to improve the light load efficiency. The experimental results verify the achievement of high efficiency.A closed-loop control scheme is implemented in the single-stage transmitter to supply multiple receivers simultaneously. With a controlled constant transmitter current, the system provides a smooth transition during dynamically load change. ZVS detection circuit is proposed to protect the transmitter from continuous hard switching operation. The control scheme is verified in the experiments.The multiple-reciever WPT system with the single-stage transmitter is investigated. The system operating range is discussed. The method of tracking optimum system efficiency is studied. The system control scheme and control procedure, targeting at providing a wide system operating range, robust operation and capability of tracking the optimized system efficiency, are proposed. Experiment results demonstrate the WPT system operation

A new active power controller in dual active bridge DC-DC converter with a minimum-current-point-tracking technique

This article proposes a new controller for power regulation in dual active bridge (DAB) dc-dc converter based on a new scheme that tracks minimum RMS current to ensure minimum losses. The proposed controller is based on an implementation of perturb and observe (PO) tracking method that enables minimum current point tracking (MCPT) at any desired level of active power transfer and dc voltage ratio. The PO is embedded in a closed-loop control scheme which simultaneously regulates active power in DAB converter. The nonlinear I - V characteristic of DAB presents the basis for this proposed controller and the rationale of using PO algorithm. The proposed controller does not require complex nonlinear converter modeling and is not circuit parameter dependent. Design procedure of the proposed controller is presented, and extensive simulation is carried out using MATLAB/Simulink to validate the effectiveness of the proposed MCPT closed-loop controller. An experimental prototype also substantiates the results achieved

Control of wireless power transfer system for dynamic charging of electric vehicles

L'abstract è presente nell'allegato / the abstract is in the attachmen

Comunicações óticas de alto débito em espaço livre

Signal distribution through high capacity links is nowadays a requirement that is becoming more crucial than ever. Therefore, the introduction of fifth generation mobile networks lead to the need for high capacity fronthaul and backhaul. Fiber distributions are commonly available in developed countries, however there are some areas that do not sustain this type of resource, such as in areas with low residential user density. To overcome the idea that resources are allocated only in these areas, free space optics (FSO) present a suitable and lower cost solution and can be used in temporary events (e.g. when the fiber is disrupted). Free space optics is an optical type of communication that requires line of sight, where the atmosphere is the transmission medium. Due to changes in the atmospheric conditions, free space optics systems suffer from variable attenuation. In the scope of this work, the atmospheric interaction is the subject of study. To accomplish link optimization, several alternatives are studied, being based on channel prediction along side with probabilistic constellation shaping. A concave mirror together with a positioning system is also used to overcome structure sway and other sources of pointing error. In the lab, the estimation processes are used to produce 64-QAM connection with variable transmission rates between 400 Gbit/s and 500 Gbit/s and the gain from using adaptive modulation is evaluated. In the last stage, an automatic gimbal positioning system is also tested for several control algorithms.Atualmente, a distribuição de sinais por meio de canais de alta capacidade é um requisito cada vez mais crucial. Nesse sentido, a progressiva introdução de novas tecnologias de acesso móvel de quinta geração desempenha um papel fundamental, fomentando a necessidade de desenvolver novas técnicas de transmissão de alto débito para redes de fronthaul e/ou backhaul. As distribuições de fibra estão bem disseminadas entre os países desenvolvidos, no entanto, existem algumas áreas que não sustentam esse tipo de recurso, o que é comum em regiões de baixa densidade de clientes residenciais. Para combater a ideia de que os recursos são alocados apenas nas grandes áreas, a ótica de espaço livre apresenta uma solução adequada. Alternativamente, devido à facilidade e rapidez de instalação, as comunicações óticas de espaço livre podem ser utilizadas como alternativa à fibra em casos de destruição da mesma. A comunicação ótica em espaço livre é um tipo de comunicação direcional que requer linha de vista, sendo a atmosfera o meio de propagação. Devido às variações atmosféricas, as comunicações oticas de espaço livre sofrem atenuação variável. No decorrer deste trabalho, a interação atmosférica é objeto de estudo. Para realizar a otimização do canal de transmissão, várias alternativas são estudadas, baseando-se na previsão de canais em tempo real em conjunto com modulação probabilística da constelação. Um espelho côncavo equipado com sistema de posicionamento é também usado para superar as vibrações e outras fontes de erro posicional. No laboratório, os processos de estimativa são usados para adaptar uma conexão 64-QAM com taxas de transmissão entre 400 Gbit/s e 500 Gbit/s. O ganho do uso da modulação adaptativa é avaliado face a formatos de modulação fixos. No último estágio, o sistema de posicionadores é também testado, com o intuito de avaliar o seu impacto na estabilidade do canal.Mestrado em Engenharia Eletrónica e Telecomunicaçõe