Holistic Design Of Resonant Dc Transformer On Constant Voltage Conversion Cascaded Stability And High Efficiency

This book is devoted to the optimum design of the DCT in a hybrid AC/DC microgrid, which takes into account not only the influence of different inductors/capacitors values, but also numerous design goals (i.e., VCG, efficiency, stability and so on). This book examines the DCT's design problem in detail. It begins by reviewing existing DCTs in, the hybrid AC/DC microgrid and their design problems. Following that, this book proposes a family of DCT optimization design approaches to ensure that the designed DCT has good power transmission and voltage regulation ability in the hybrid AC/DC microgrid, even when the actual inductors/capacitors values fluctuate with practical power and temperature. Following that, this book provides a family of multi-objective optimization design methodologies for the DCT to guarantee that it concurrently achieves the requirements of VCG, efficiency, and system stability. This book also covers how to control the DCT in a hybrid AC/DC microgrid optimally and generically.

This book is devoted to resonant energy conversion in power electronics. It is a practical, systematic guide to the analysis and design of various dc-dc resonant inverters, high-frequency rectifiers, and dc-dc resonant converters that are building blocks of many of today's high-frequency energy processors. Designed to function as both a superior senior-to-graduate level textbook for electrical engineering courses and a valuable professional reference for practicing engineers, it provides students and engineers with a solid grasp of existing high-frequency technology, while acquainting them with a number of easy-to-use tools for the analysis and design of resonant power circuits. Resonant power conversion technology is now a very hot area and in the center of the renewable energy and energy harvesting technologies.

Numbers alone are enough to describe the importance of DC/DC converters in modern power engineering. There are more than 500 recognized topologies, with more added each year. In their groundbreaking book Advanced DC/DC Converters, expert researchers Luo and Ye organized these technologies into six generations and illustrated their principles and operation through examples of over 100 original topologies. In chapters carefully drawn from that work, Synchronous and Resonant DC/DC Conversion Technology, Energy Factor, and Mathematical Modeling provides a focused, concise overview of synchronous and multiple-element resonant power converters. This reference carefully examines the topologies of more than 50 synchronous and resonant converters by illustrating the design of several prototypes developed by the authors. Using more than 100 diagrams as illustration, the book supplies insight into the fundamental concepts, design, and applications of the fifth (synchronous) and sixth (multiple-element resonant) converters as well as DC power sources and control circuits. The authors also discuss EMI/EMC problems and include a new chapter that introduces the new concept of Energy Factor (EF) and its importance in mathematical modeling as well as analyzing the transient process and impulse response of DC/DC converters. Synchronous and Resonant DC/DC Conversion Technology, Energy Factor, and Mathematical Modeling supplies a quick and accessible guide for anyone in need of specialized information on synchronous and resonant DC/DC converter technologies.

The development in power conversion technology is in constant demand of high power efficiency and high power density. The DC-DC power conversion is an indispensable stage for numerous power supplies and energy related applications. Particularly, in PV micro-inverters and front-end converter of power supplies, great challenges are imposed on the power performances of the DC-DC converter stage, which not only require high efficiency and density but also the capability to regulate a wide variation range of input voltage and load conditions. The resonant DC-DC converters are good candidates to meet these challenges with the advantages of achieving soft switching and low EMI. Among various resonant converter topologies, the LLC converter is very attractive for its wide gain range and providing ZVS for switches from full load to zero load condition. The operation of the LLC converter is complicated due to its multiple resonant stage mechanism. A literature review of different analysis methods are presented, and it shows that the study on the LLC is still incomplete. Therefore, an operation mode analysis method is proposed, which divides the operation into six major modes based on the occurrence of resonant stages. The resonant currents, voltages and the DC gain characteristics for each mode is investigated. To obtain a thorough view of the converter behavior, the boundaries of every mode are studied, and mode distribution regarding the gain, load and frequency is presented and discussed. As this operation mode model is a precise model, an experimental prototype is designed and built to demonstrate its accuracy in operation waveforms and gain prediction. Since most of the LLC modes have no closed-form solutions, simplification is necessary in order to utilize this mode model in practical design. Some prior approximation methods for converter's gain characteristics are discussed. Instead of getting an entire gain-vs.-frequency curve, we focus on peak gains, which is an important design parameters indicating the LLC's operating limit of input voltage and switching frequency. A numerical peak gain approximation method is developed, which provide a direct way to calculate the peak gain and its corresponding load and frequency condition. The approximated results are compared with experiments and simulations, and are proved to be accurate. In addition, as PO mode is the most favorable operation mode of the LLC, its operation region is investigated and an approximation approach is developed to determine its boundary. The design optimization of the LLC has always been a difficult problem as there are many parameters affecting the design and it lacks clear design guidance in selecting the optimal resonant tank parameters. Based on the operation mode model, three optimization methods are proposed according to the design scenarios. These methods focus on minimize the conduction loss of resonant tank while maintaining the required voltage gain level, and the approximations of peak gains and PO mode boundary can be applied here to facilitate the design. A design example is presented using one of the proposed optimization methods. As a comparison, the L-C component values are reselected and tested for the same design specifications. The experiments show that the optimal design has better efficiency performance. Finally, a generalized approach for resonant converter analysis is developed. It can be implemented by computer programs or numerical analysis tools to derive the operation waveforms and DC characteristics of resonant converters.

Transportation electrification and distributed generation are proven effective strategies to counter climate change. Modern generation and transportation aim to bring down the carbon footprint by transforming the fossil fuel-driven society with alternate energy sources and electric propulsion, respectively. However, harnessing energy from renewable sources is not straight forward but demands a suitable power electronic interface. Similarly, electric transportation propulsion system demands for specific power conversion stages. These power electronic conversion systems include dc-dc converter and dc-ac inverter. Cost, efficiency, power density, and weight are the major requirements of these converters. To obtain these merits, high-frequency soft-switching converters are selected and designed. Resonant converters with a suitable resonance have been usually explored for voltage-fed switching converters to obtain soft-switching of the semiconductor devices at high-frequency. However, owing to the high voltage gain requirements of the solar/fuel cells/batteries, this thesis explores current-fed topologies with different resonant circuits with natural voltage gain. In traditional voltage-fed resonant converters, it is observed that the converter characteristics can be fine-tuned to design the requirements by proper selection of resonant tank. In addition, the resonant tank can integrate the transformer non-idealities and circuit/device parasitic in circuit operation thereby suppressing the consequent voltage spikes across the semiconductor devices. Since voltage-fed converters is fundamentally not suitable for high voltage gain and low voltage applications, this thesis attempts to improve current-fed dc/dc converter characteristics with resonant tanks. In this thesis, a current-fed load resonant DC/DC converter topology is proposed whose characteristics are tuneable with the adopted resonant tank. Further, this thesis proposes a simple technique to ease and improve accuracy of the Fundamental Harmonic Analysis (FHA), which would have been complex otherwise due to capacitive termination of proposed converter. Initially, the characteristics of the proposed converter topology with a parallel resonance derived LCC-T resonant tank is studied to implement zero voltage switching (ZVS) and zero current switching (ZCS) of the semiconductor devices. Three-phase topology of the same has been investigated and analysed. Following the study and a need to further improve the characteristics of resonant dc/dc converter, a series resonance based LCL resonant converter, a dual of the parallel resonance tank is studied and analysed. The load resonant converters are redeemed for integration of PV/fuel cells. Further, for high power applications, suitability of load resonant converters is verified by adopting resonant tank in three-phase topology. Proof-of-concept hardware prototypes are designed and developed in the laboratory to demonstrate the performance and the merits of the proposed soft-switching resonant converter topologies as well as to prove the proposed theory and the claims.

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.

This book covers several research items related to LLC resonant converters, which were published in a Special Issue of Energies on the subject area of "Advances in High-Efficiency LLC Resonant converter". It focuses on emerging power electronic topologies related to the LLC resonant converter, and its design methodology and control algorithms. Topics of interest include LLC resonant topologies, resonant tank design methodology for high efficiency, power loss analysis in LLC resonant converters, high-frequency magnetics for resonant converters, wide band-gap devices applied to LLC resonant converter, and advanced control algorithm for LLC resonant converter.

Piezoelectric transformers (PTs) are a promising energy storage alternative for power converter miniaturization. PTs offer galvanic isolation and voltage transformation like traditional magnetic transformers, but have more advantageous power scaling properties at low volumes. Despite these advantages, most attempts at magnetic-less PT-based dc-dc converters have limited whole-converter efficiencies. These attempts typically rely on standard resonant converter topologies not designed to effectively utilize PTs, along with off-the-shelf PTs not optimized for dc-dc power conversion. In this thesis, we propose a two-pronged approach at designing high-efficiency, high-power-density PT-based converters: (1) circuit-level design strategies and (2) component-level design strategies to optimize PT components for power conversion. At the circuit level, we select high-efficiency topologies and switching sequences that most efficiently utilize PTs as sole energy storage components in dc-dc converters. At the component-level, we present geometry conditions that can aid designers in achieving PT components with both high efficiency and high power density. The strategies and analyses presented in this thesis are validated through simulation of an example PT-based converter design.

Today's large-scale utility applications with microinverter and batteries require DC/DC converters with a wide voltage range capabilities in order to fulfil the wide voltage system requirements. It has been shown that the LLC resonant converter is a good solution for wide voltage range applications because it is typically controlled by frequency-modulation. However, to achieve a wide voltage range, the LLC converter needs to operate in a wide switching-frequency range. This leads to increased switching losses and increased circulating current. Moreover, a small inductor ratio or/and low-quality factor are required to increase the voltage gain. Therefore, the small magnetizing inductance causes a high magnetizing current with high conduction loss, making it hard to design magnetic components. Several resonant converters for wide voltage range applications have been proposed in the open literature to improve efficiency. In first part, a novel LLC converter with a reconfigurable rectifier structure is proposed to regulate the wide voltage range photovoltaic (PV) panel. The proposed converter can operate in three operation modes that leads to a narrow switching-frequency range close to the resonant-frequency resulting in increased converter performance efficiency. The benefits of this topology include improved efficiency and narrow switchingfrequency range while achieving soft-switching in all MOSFETs and diodes. In second part, a new three-port LLC converter for a PV microinverter with high-DC bus applications is proposed. Two control modulations are adopted to regulate the power flow. On the primary side, two switches are implemented to reduce the conduction losses. On the secondary side, two rectifiers are employed in one structure to make the proposed converter operate close to the resonant-frequency and to boost the voltage with a moderate transformer. The proposed converter can achieve softswitching for all MOSFETs and diodes, resulting in improved efficiency and realizing a narrow switching-frequency range.

The demand for power converters is on the rise due to their ability to achieve high power conversion efficiency, small size, light weight and reduced cost. DC-DC converters are used in many applications where, the output voltage needs to be regulated for wide variations in the input voltage and the load. They are also used in applications where electrical isolation is required. Power generation from renewable energy sources suffers from highly fluctuating output voltages. Electrical isolation of renewable energy sources from the grid is essential. Therefore, DC-DC converters are used as an integral part of the power electronic interface required for grid integration of renewable energy sources such as wave energy power conversion. In this dissertation as a first step, the power converters used in wave energy applications are classified and compared. Analysis, design, simulation and experimental results of fixed frequency controlled HF transformer isolated DC-DC resonant converters are presented.