Analysis and Design of a Hybrid Dickson Switched Capacitor Converter for Intermediate Bus Converter Applications

By 2020 it is predicted that 1/3 of all data will pass through the cloud. With society\u27s growing dependency on data, it is vital that data centers, the cloud\u27s physical house of content, operate with optimal energy performance to reduce operating costs.Unfortunately, today\u27s data centers are inefficient, both economically and environmentally. This has led to an increase in demand for energy-efficient servers. One opportunity for improved efficiency is in the power delivery architecture which delivers power from the grid to the motherboard. In this dissertation, the main focus is the intermediate bus converter (IBC), used for the intermediate conversion, typically 48-12V/5V, in server power supplies. The IBC requires compact design so that it can be placed as close to the load as possible to enable more space for computing power and high efficiency to reduce the need for external cooling. Most commonly used converter topologies today include expensive bulky magnetics hindering the converter\u27s power density. Furthermore, high output current of an IBC makes the efficiency very sensitive to any resistance, such as magnetic parasitic resistance or PCB trace resistance. In this work, analytical loss models are used to review the advantages and disadvantages of frequently used IBC topologies such as the phase-shifted full bridge and LLC. The Hybrid Dickson Switched Capacitor (HDSC) topology is also analyzed. The HDSC\u27s high step-down conversion ratio and low dependence on magnetics due to the reduced applied volt-seconds, provides a new opportunity for applications such as the intermediate bus converter. The HDSC designs the on-time of devices in order to achieve soft-charging between flying capacitors. Other advantages of the HDSC include low switch stress, small magnetics and adjustable duty cycle for voltage regulation. Challenges, such as minimizing parasitic inductance and resistance between flying capacitors, are addressed and recommendations for PCB layout are provided. In this paper, a 4:1 24-5V and 8:1 48-5V, 100W GaN-based HDSC is designed and tested. The influences of capacitor mismatch and limitations placed on soft-charging operation for the HDSC is also modeled. This analysis can be used as a tool for designers when selecting flying capacitors

PCB Layer Optimization of Planar Medium Frequency Transformer for On-Board EV Chargers

Planar medium frequency transformer (MFT) is a promising solution for on-board electric vehicle (EV) chargers, to achieve high power density and high efficiency. The trend towards higher power densities and higher efficiencies exposes a number of limitations on conventional litz wire transformers, especially for increasing the current density. Litz wire current density is limited by the temperature, due to poor thermal management capabilities. PCBs, however, have better thermal management capabilities, which allows for higher current densities. This paper optimizes planar MFT windings focusing on maximizing current density and the simplicity of the implementation. The losses, power density and thermal constraints are investigated and a pareto-front is created based on optimal solutions. High efficiency and power densities are achieved from 2D/3D FEM simulations. A solution within thermal constraints is selected and a prototype is built based on similar ratings. Tests with different current densities are carried out on the prototype and the temperatures are compared. The results verify that planar MFT with high current densities are feasible solutions for high efficiency and high power density MFTs

Energy-efficient and Power-dense DC-DC Converters in Data Center and Electric Vehicle Applications Using Wide Bandgap Devices

The ever increasing demands in the energy conversion market propel power converters towards high efficiency and high power density. With fast development of data processing capability in the data center, the server will include more processors, memories, chipsets and hard drives than ever, which requires more efficient and compact power converters. Meanwhile, the energy-efficient and power-dense converters for the electric vehicle also result in longer driving range as well as more passengers and cargo capacities. DC-DC converters are indispensable power stages for both applications. In order to address the efficiency and density requirements of the DC-DC converters in these applications, several related research topics are discussed in this dissertation. For the DC-DC converter in the data center application, a LLC resonant converter based on the newly emerged GaN devices is developed to improve the efficiency over the traditional Si-based converter. The relationship between the critical device parameters and converter loss is established. A new perspective of extra winding loss due to the asymmetrical primary and secondary side current in LLC resonant converter is proposed. The extra winding loss is related to the critical device parameters as well. The GaN device benefits on device loss and transformer winding loss is analyzed. An improved LLC resonant converter design method considering the device loss and transformer winding loss is proposed. For the DC-DC converter in the electric vehicle application, an integrated DC-DC converter that combines the on-board charger DC-DC converter and drivetrain DC-DC converter is developed. The integrated DC-DC converter is considered to operate in different modes. The existing dual active bridge (DAB) DC-DC converter originally designed for the charger is proposed to operate in the drivetrain mode to improve the efficiency at the light load and high voltage step-up ratio conditions of the traditional drivetrain DC-DC converter. Design method and loss model are proposed for the integrated converter in the drivetrain mode. A scaled-down integrated DC-DC converter prototype is developed to verify the design and loss model

Design of a Low-Capacitance Planar Transformer for a 4 kW/500 kHz DAB Converter

International audienceIncreasing electrification in transport sectors, from automotive to aerospace, highlights the need for low size and high power density components. The recent advent of planar technology theoretically allows to reduce considerably the size of the magnetic components. This article focuses on the design of a high frequency planar transformer intended to be used in a 4 kW 500 kHz DAB converter. In particular, the inter-winding capacitances are assessed, as they have a strong influence on the behaviour of the DAB, and in some extreme cases may impede operation entirely. Analytical and finite element models are used to evaluate the stray elements of the transformer (resistance of the conductors, inter-winding capacitance and leakage inductance), and the resulting circuit model is compared with experimental measurements. This work focuses on influences of design parameters on the transformer stray elements

A Comprehensive Review on Planar Magnetics and the Structures to Reduce the Parasitic Elements and Improve Efficiency

Due to the need for highly efficient and compact power electronic converters to operate at higher frequencies, traditional wire-wound magnetics are not suitable. This paper provides a comprehensive review of planar magnetic technologies, discussing their advantages as well as associated disadvantages. An extensive review of the research literature is presented with the aim of suggesting models for planar magnetics. Several strategies are proposed to overcome the limitations of planar magnetics, including winding conduction loss, leakage inductance, and winding capacitance. The goal of this study is to provide engineers and researchers with a clear roadmap for designing planar magnetic devices

A 1-MHz Series Resonant DC-DC Converter with a Dual-Mode Rectifier for PV Microinverters

The photovoltaic (PV) output voltage varies over a wide range depending on operating conditions. Thus, the PV-connected converters should be capable of handling a wide input voltage range while maintaining high efficiencies. This paper proposes a new series resonant dc-dc converter for PV microinverter applications. Compared with the conventional series resonant converter, a dual-mode rectifier is configured on the secondary side, which enables a twofold voltage gain range for the proposed converter with a fixed-frequency phase-shift modulation scheme. The zero-voltage switching turn-on and zero-current switching turn-off can be achieved for active switches and diodes, thereby, minimizing the switching losses. Moreover, a variable dc-link voltage control scheme is introduced to the proposed converter, leading to a further efficiency improvement and input-voltage-range extension. The operation principle and essential characteristics (e.g., voltage gain, soft-switching, and root-mean-square current) of the proposed converter are detailed in this paper, and the power loss modeling and design optimization of components are also presented. A 1-MHz 250-W converter prototype with an input voltage range of 17-43 V is built and tested to verify the feasibility of the proposed converter

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

Input Parallel Output Series Structure of Planar Medium Frequency Transformers for 200 kW Power Converter: Model and Parameters Evaluation

Nowadays, the demand for high power converters for DC applications, such as renewable sources or ultra-fast chargers for electric vehicles, is constantly growing. Galvanic isolation is mandatory in most of these applications. In this context, the Solid State Transformer (SST) converter plays a fundamental role. The adoption of the Medium Frequency Transformers (MFT) guarantees galvanic isolation in addition to high performance in reduced size. In the present paper, a multi MFT structure is proposed as a solution to improve the power density and the modularity of the system. Starting from 20 kW planar transformer model, experimentally validated, a multi- transformer structure is analyzed. After an analytical treatment of the Input Parallel Output Series (IPOS) structure, an equivalent electrical model of a 200 kW IPOS (made by 10 MFTs) is introduced. The model is validated by experimental measurements and tests

Pushing the Boundary of the 48 V Data Center Power Conversion in the AI and IoT Era

openThe increasing interest in cloud-based services, the Internet-of-Things and the take-over of artificial intelligence computing require constant improvement of the power distribution network. Electricity consumption of data centers, which drains a consistent slice of modern world energy production, is projected to increase tremendously during the next decade. Data centers are the backbone of modern economy; as a consequence, energy-aware resource allocation heuristics are constantly researched, leading the major IT services providers to develop new power conversion architectures to increase the overall webfarm distribution efficiency, together reducing the resulting carbon footprint and maximizing their investments. As higher voltage distribution yields lower conduction losses, vendors are moving from the 12 V rack bus to 48 V solutions together with research centers and especially data center developers. As mentioned, efficiency is crucial to address in this scenario and the whole conversion chain, i.e. from the 48 V bus to the CPU/GPU/ASIC voltage, must be optimized to decrease wasted energy inside the server rack. Power density for this converters family is also paramount to consider, as the overall system must occupy as less area and volume as possible. LLC resonant converters are commonly used as IBCs (intermediate bus converters), together with their GaN implementations because of their multiple advantages in efficiency and size, while multiphase-buck-derived topologies are the most common solution to step-down-to and regulate the final processor voltage as they're well-know, easy to scale and design. This dissertation proposes a family of non-isolated, innovative converters capable of increasing the power density and the efficiency of the state-of-the-art 48 V to 1.8/0.9 V conversion. In this work three solutions are proposed, which can be combined or used as stand-alone converters: an ASIC on-chip switched-capacitor resonant voltage divider, two unregulated Google-STC-derived topologies for the IBC stage (48 V to 12 V and 48 V to 4.8 V + 10.6 V dual-output) and a complete 48 V to 1.8 V ultra-dense PoL converter. Each block has been thoroughly tested and researched, therefore mathematical and experimental results are provided for each solution, together with state-of-the-art comparisons and contextualization.The increasing interest in cloud-based services, the Internet-of-Things and the take-over of artificial intelligence computing require constant improvement of the power distribution network. Electricity consumption of data centers, which drains a consistent slice of modern world energy production, is projected to increase tremendously during the next decade. Data centers are the backbone of modern economy; as a consequence, energy-aware resource allocation heuristics are constantly researched, leading the major IT services providers to develop new power conversion architectures to increase the overall webfarm distribution efficiency, together reducing the resulting carbon footprint and maximizing their investments. As higher voltage distribution yields lower conduction losses, vendors are moving from the 12 V rack bus to 48 V solutions together with research centers and especially data center developers. As mentioned, efficiency is crucial to address in this scenario and the whole conversion chain, i.e. from the 48 V bus to the CPU/GPU/ASIC voltage, must be optimized to decrease wasted energy inside the server rack. Power density for this converters family is also paramount to consider, as the overall system must occupy as less area and volume as possible. LLC resonant converters are commonly used as IBCs (intermediate bus converters), together with their GaN implementations because of their multiple advantages in efficiency and size, while multiphase-buck-derived topologies are the most common solution to step-down-to and regulate the final processor voltage as they're well-know, easy to scale and design. This dissertation proposes a family of non-isolated, innovative converters capable of increasing the power density and the efficiency of the state-of-the-art 48 V to 1.8/0.9 V conversion. In this work three solutions are proposed, which can be combined or used as stand-alone converters: an ASIC on-chip switched-capacitor resonant voltage divider, two unregulated Google-STC-derived topologies for the IBC stage (48 V to 12 V and 48 V to 4.8 V + 10.6 V dual-output) and a complete 48 V to 1.8 V ultra-dense PoL converter. Each block has been thoroughly tested and researched, therefore mathematical and experimental results are provided for each solution, together with state-of-the-art comparisons and contextualization.Dottorato di ricerca in Ingegneria industriale e dell'informazioneopenUrsino, Mari