Optimization of LLC resonant converters

Usualmente, na área da eletrónica de potência, tem que existir um trade off entre densidade de potencia e o rendimento, por forma a desenhar dispositivos que sejam pequenos o suficiente, para ocupar o mínimo espaço, mas ao mesmo tempo altamente eficientes, por forma a maximizar a energia consumida em trabalho resultante, especialmente em veículos elétricos, onde existem várias etapas de conversão de energia. O presente trabalho visa estudar os conversores ressonantes e as suas topologias associadas, continuando o estudo realizado pela Mestre Maria Ruxandra Luca em parceria com a Universidade de Oviedo, tendo como principal objetivo a otimização de um conversor ressonante LLC de 4.2 para carregamento de baterias. Este tipo de conversor é mais vantajoso quando comparado com os conversores tradicionais, devido à utilização do conceito de ressonância e de técnicas Soft Switching, como o Zero Current Switch (ZCS) e Zero Voltage Switch (ZVS). Estar em ressonância significa, ter um comportamento resistivo pelo facto da soma de todas as impedâncias do tanque de ressonante ser nula. Isto leva a que a corrente esteja em fase com a tensão, permitindo o mínimo de perdas, para uma situação em que o ganho do conversor é unitário. Porém, para alterar o valor da tensão da saída do conversor, este ganho tem que ser alterado (com a modulação de frequência), levando o conversor a trabalhar fora da sua zona de ressonância, com um desfasamento entre tensão e corrente, aumentando significativamente as perdas nos semicondutores comutadores. O uso de técnicas Soft Switching, como o Zero Current Switch (ZCS) e Zero Voltage Switch (ZVS), permite a minimização de perdas de comutação quando o conversor trabalha fora de ressonância, utilizando mecanismos como a equalização da corrente no transformador (entre corrente magnetizante e corrente série) e Dead-Time para fazer com que as comutações sejam feitas quando a corrente e a tensão estão a zero. Devido á menor taxa de perdas nas comutações, o uso de frequências mais elevadas é possível, obtendo assim conversores com uma maior densidade de potência, mantendo uma operação com elevada eficiência. Neste trabalho é apresentado um breve capítulo do estado da arte, em que diversos modos de conversão DC-DC são apresentados, comparando as suas vantagens e desvantagens, seguido de uma análise às arquiteturas e topologias mais utilizadas nos conversores ressonantes. Com o objetivo de aumentar a eficiência, são descritos os andares do conversor onde existem mais perdas, com as suas causas, e possíveis soluções como o uso de transístores de alta mobilidade de eletrões, (do Inglês High Electron Mobility Transitors HEMT) combinados com materiais wide band-gap, que permitem operar de forma mais eficiente quando comparados com semicondutores de silício, a utilização de air-gap distribuído, bobines entrelaçadas e o fio de Litz, para minimizar as correntes de Eddy produzidas no transformador, e ainda a utilização de retificação síncrona em substituição aos díodos retificadores. De seguida, num terceiro capítulo, é apresentada a configuração base do conversor LLC ressonante para o carregamento de baterias de iões de lítio, detalhando cada um dos blocos associados, acompanhado de uma análise teórica por forma a permitir compreender o funcionamento do conversor, quais os principais fatores mais importantes, e qual o impacto da frequência de comutação no comportamento do conversor. Neste capítulo é ainda apresentado o processo de desenho deste conversor discriminando quais os parâmetros iniciais necessários, com uma análise detalhadas das perdas associadas ao design base, finalizando com o estudo, das diferentes arquiteturas do conversor nos andares de conversão AC-DC e DC-AC, e da retificação síncrona com a utilização de HEMTs, na eficiência do conversor. Simulações serão então conduzidas posteriormente utilizando modelos reais dos componentes presentes no conversor, com o uso do software LTSpice, comparando de forma detalhada o design base, com os designs otimizados previamente obtidos, de forma a observar o impacto das alterações propostas. Inicialmente foi previsto construir o conversor apresentado em [1] e o conversor otimizado mais eficiente, testá-los experimentalmente, mas devido à situação atual da pandemia Sars-Cov (Covid 19), o mesmo não foi possível, a tempo de entregar este trabalho, sendo este, um dos trabalhos futuros. Este trabalho foi desenvolvido em parceria com a Universidad de Oviedo, com o grupo de investigação LEMUR na Escuela Politécnica de Ingeniería de Gijón, onde foram feitas as analises teóricas e simulações do conversor de ressonância LLC

Computer-aided design and optimization of high-efficiency LLC series resonant converter

High conversion efficiency is desired in switch mode power supply converters. Computer-aided design optimization is emerging as a promising way to design power converters. In this work a systematic optimization procedure is proposed to optimize LLC series resonant converter full load efficiency. A mode solver technique is proposed to handle LLC converter steady-state solutions. The mode solver utilizes numerical nonlinear programming techniques to solve LLC-state equations and determine operation mode. Loss models are provided to calculate total component losses using the current and voltage information derived from the mode solver. The calculated efficiency serves as the objective function to optimize the converter efficiency. A prototype 300-W 400-V to 12-V LLC converter is built using the optimization results. Details of design variables, boundaries, equality/inequality constraints, and loss distributions are given. An experimental full-load efficiency of 97.07 is achieved compared to a calculated 97.4 efficiency. The proposed optimization procedure is an effective way to design high-efficiency LLC converters. © 1986-2012 IEEE.published_or_final_versio

One-Quadrant Switched-Mode Power Converters

This article presents the main topics related to one-quadrant power converters. The basic topologies are analysed and a simple methodology to obtain the steady-state output-input voltage ratio is set out. A short discussion of different methods to control one-quadrant power converters is presented. Some of the reported derived topologies of one-quadrant power converters are also considered. Some topics related to one-quadrant power converters such as synchronous rectification, hard and soft commutation, and interleaved converters are discussed. Finally, a brief introduction to resonant converters is given.Comment: 25 pages, contribution to the 2014 CAS - CERN Accelerator School: Power Converters, Baden, Switzerland, 7-14 May 201

Optimization methodology for efficient LLC resonant converter with power factor correction circuit

High efficiency is required in power conversion circuits. A systematic optimization procedure is presented in this paper to optimize LLC series resonant converter efficiency where the effect of LLC input voltage variation cased by power factor correction circuit is considered. A mode solver technique is proposed to handle LLC converter steady-state solutions under different input voltage conditions. Loss models are provided to calculate total component losses using the current and voltage information derived from the mode solver. A prototype 300W 12V output LLC converter is built using the optimization results. Experimental results are presented.postprintThe 6th IET International Conference on Power Electronics, Machines and Drives (PEMD 2012), University of Bristol, UK., 27-29 March 2012. In The I E T Conference Publication Series, 2012, Conference no. CP592, p. 1-

Design Optimization Of Llc Topology And Phase Skipping Control Of Three Phase Inverter For Pv Applications

The world is heading towards an energy crisis and desperate efforts are being made to find an alternative, reliable and clean source of energy. Solar Energy is one of the most clean and reliable source of renewable energy on earth. Conventionally, extraction of solar power for electricity generation was limited to PV farms, however lately Distributed Generation form of Solar Power has emerged in the form of residential and commercial Grid Tied Micro-Inverters. Grid Tied Micro-Inverters are costly when compared to their string type counterparts because one inverter module is required for every single or every two PV panels whereas a string type micro-inverter utilizes a single inverter module over a string of PV panels. Since in micro-inverter every panel has a dedicated inverter module, more power per panel can be extracted by performing optimal maximum power tracking over single panel rather than over an entire string of panels. Power per panel extracted by string inverters may be lower than its maximum value as few of the panels in the string may or may not be shaded and thereby forming the weaker links of the system. In order to justify the higher costs of Micro-Inverters, it is of utmost importance to convert the available power with maximum possible efficiency. Typically, a microinverter consists of two important blocks; a Front End DC-DC Converter and Output DCAC Inverter. This thesis proposes efficiency optimization techniques for both the blocks of the micro-inverter. iv Efficiency Optimization of Front End DC-DC Converter This thesis aims to optimize the efficiency of the front end stage by proposing optimal design procedure for resonant parameters of LLC Topology as a Front End DC-DC Converter for PV Applications. It exploits the I-V characteristics of a solar panel to design the resonant parameters such that resonant LLC topology operates near its resonant frequency operating point which is the highest efficiency operating point of LLC Converter. Efficiency Optimization of Output DC-AC Inverter Due to continuously variable irradiance levels of solar energy, available power for extraction is constantly varying which causes the PV Inverter operates at its peak load capacity for less than 15% of the day time. Every typical power converter suffers through poor light load efficiency performance because of the load independent losses present in a power converter. In order to improve the light load efficiency performance of Three Phase Inverters, this thesis proposes Phase Skipping Control technique for Three Phase Grid Tied Micro-Inverters. The proposed technique is a generic control technique and can be applied to any inverter topology, however, in order to establish the proof of concept this control technique has been implemented on Three Phase Half Bridge PWM Inverter and its analysis is provided. Improving light load efficiency helps to improve the CEC efficiency of the inverter

Current driven synchronous rectifier with saturable current transformer and dynamic gate voltage control for LLC resonant converter

This paper proposes an improved current driven synchronous rectifier with saturable current transformer and dynamic gate voltage control feature for LLC resonant converter efficiency improvement. A model of saturable current transformer is proposed. Compared with other voltage driven and current-driven synchronous rectifier, this current driven synchronous rectifier has several outstanding characteristics. This synchronous rectifier is completely self-contained. It needs no external signal or power supply. It is also insensitive to parasitic inductance. Inherent dynamic gate voltage control reduces gate loss in the MOSFET by saturable current transformer. A 300W 400V-12V converter is built to demonstrate the advantages of the proposed current driven synchronous rectifier. High efficiency at 98% can be achieved. There is more than 4% efficiency improvement compared with schottky diode.published_or_final_versio

Single Stage PFC Flyback AC-DC Converter Design

This paper discusses a 100 W single stage Power Factor Correction (PFC) flyback converter operating in boundary mode constant ON time methodology using a synchronous MOS-FET rectifier on the secondary side to achieve higher efficiency. Unlike conventional designs which use two stage approach such as PFC plus a LLC resonant stage or a two stage PFC plus flyback, the proposed design integrates the PFC and constant voltage regulation in a single stage without compromising the efficiency of the converter. The proposed design is advantageous as it has a lower component count. A design of 100 W flyback operating from universal input AC line voltage is demonstrated in this paper. The experimental results show that the power factor (PF) is greater than 0.92 and total harmonic distortion (iTHD) is less than 20% for a load varying from 25 % to 100 %. The experimental results show the advantages of a single stage design.Comment: Published in: 2020 IEEE International Conference on Electronics, Computing and Communication Technologies (CONECCT