Design Methodology of Tightly Regulated Dual-Output LLC Resonant Converter Using PFM-APWM Hybrid Control Method

A dual-output LLC resonant converter using pulse frequency modulation (PFM) and asymmetrical pulse width modulation (APWM) can achieve tight output voltage regulation, high power density, and high cost-effectiveness. However, an improper resonant tank design cannot achieve tight cross regulation of the dual-output channels at the worst-case load conditions. In addition, proper magnetizing inductance is required to achieve zero voltage switching (ZVS) of the power MOSFETs in the LLC resonant converter. In this paper, voltage gain of modulation methods and steady state operations are analyzed to implement the hybrid control method. In addition, the operation of the hybrid control algorithm is analyzed to achieve tight cross regulation performance. From this analysis, the design methodology of the resonant tank and the magnetizing inductance are proposed to compensate the output error of both outputs and to achieve ZVS over the entire load range. The cross regulation performance is verified with simulation and experimental results using a 190 W prototype converter

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Department of Electrical EngineeringA resonant converter has been widely used in various industrial applications, since it has high power conversion efficiency. The increase of the power density is necessary to obtain high cost-effectiveness and design freedom on the electric products. A high switching frequency operation can be an effective method to obtain the high power density of power converters. In this dissertation, three topic will be discussed to obtain the high power conversion efficiency and the high power density for the resonant converter, as follows: First, the power stage and feedback loop are designed for the high switching frequency operation. The power stage is designed to obtain the high power conversion efficiency at the high switching frequency operation. In addition, the feedback loop is designed to guarantee the stability. Second, the control algorithm is proposed to obtain the tight output voltage regulation at the high switching frequency operation. The operational principle and design of control algorithm are analyzed to obtain the tight output voltage regulation. Third, the spread spectrum technique (SST) will be applied to the resonant converter to reduce the electromagnetic interference (EMI), which can improve the power density with small EMI filter size. In this research, the design constraint to implement the SST on the resonant converter is analyzed to obtain the dual functionality properly. In addition, the control algorithms are proposed to achieve tight output voltage regulation and EMI reduction, simultaneously. All the proposed design considerations and control algorithms are verified with the simulation and experimental results.clos

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

Nonisolated switching-capacitor-integrated three- port converters with seamless PWM/PFM modulation

Efficiency and power density of power converters for interfacing photovoltaic panels, energy storage components such as batteries, and loads in photovoltaic (PV) systems become more and more important. Compared with individual converter design for different terminals, power-integrated multiport converters shows obvious advantages in simplifying the system structure, reducing the component count, and improving the operation reliability. Originated from the high power-density switched capacitor topology, a nonisolated switching-capacitor-integrated three-port converter (SCI-TPC) is presented to achieve single-stage direct power conversion among three ports. In order to minimize the cross-regulation effect, pulse-width-modulation (PWM) and pulse-frequency-modulation (PFM) are adopted to realize the flexible power regulation and achieve power balance among three ports. Main operation modes, power flow distribution, and power transfer characteristic are analyzed. With the seamless PWM and PFM hybrid modulation, the current stress can be reduced and the overall conversion efficiency over a full operating range can be improved. Main experimental results are provided to validate the effectiveness of the proposed concept

Design, Control, and Implementation of High Frequency LLC Resonant Converter

Department of Electrical EngineeringA high switching frequency operation has been introduced with much interest in research and industrial areas to improve the power density of power converters. However, its implementation is difficult for an elaborate switch mode power supply which has high efficiency and stable operation. In this paper, a power stage and a feedback controller design will be considered for proper operation, stability, and high power conversion efficiency of the high frequency LLC resonant converter. The power density can be improved by adopting high switching frequency which allows small sized passive components. At the high switching frequency, the size reduction of the passive components such as transformer, and output capacitor will be estimated to obtain the high power density design. In addition, the design method of the magnetizing inductance design method will be derived to achieve the zero voltage switching (ZVS) at the high switching frequency operation. In aspect of frequency domain, the smaller output capacitor which has small capacitance and low effective series resistance (ESR) changes the small-signal behavior of the converter???s power stage. It can make the converter unstable by increasing the crossover frequency in the loop gain of the small-signal model. The effect of the smaller output capacitance should be analyzed for stability analysis using a proper small-signal model of the LLC resonant converter. Therefore, the proper design methods of the feedback compensator are derived to obtain sufficient phase margin in the bode plot of the converter???s loop gain for its stable operation. The design considerations of the power stage and the feedback loop will be verified with the performance comparison of 100 kHz and 500 kHz switching frequency LLC resonant converters. Since the switching performance of state-of-art power switches has been improved, the power converter can operate over a 1 MHz switching frequency. In this paper, GaN E-HEMTs are used to achieve the high switching frequency operation due to its small channel resistance and small output capacitance. However, the GaN E-HEMTs also have different switching operation characteristics to other conventional silicon-based MOSFETs. Therefore, the high speed switching characteristics of the GaN E-HEMT should be analyzed to obtain proper operation for a half-bridge type LLC resonant converter using a boostrap gate drive circuit. Moreover, a soft start algorithm for the high switching frequency is analyzed to suppress inrush currents at the cold start operation of the converter. All the design considerations using the GaN E-HEMT are verified with a 240 W prototype LLC resonant converter operating at 1 MHz switching frequency.ope

Optimal inductor current in boost DC/DC converters operating in burst mode under light-load conditions

This letter analyzes how the efficiency of boost dc/dc converters operating in burst mode under light-load conditions can be improved by an appropriate selection of the inductor current that transfers energy from the input to the output. A theoretical analysis evaluates the main power losses (fixed, conduction, and switching losses) involved in such converters, and how do they depend on the inductor current. This analysis shows that there is an optimal value of this current that causes minimum losses and, hence, maximum efficiency. These theoretical predictions are then compared with experimental data resulting from a commercial boost dc/dc converter (TPS61252), whose average inductor current is adjustable. Experimental results show that the use of the optimal inductor current, which was around 340 mA for an output voltage of 5 V, provides an efficiency increase of 7%.Peer ReviewedPostprint (author's final draft