Distributed energy is an attractive alternative to typical centralized energy sources specifically for remote locations not accessible to the electricity grid. With the continued advancement into new renewable technologies like solar, wind, fuel cell etc., off-grid standalone systems are becoming more attractive and even compeating on a cost basis for rural locations. Along with the environmental and sustainable movement, these technologies are only going to get more and more popular as time goes on. Power electronic converters are also advancing which will help the shift in electricity options. Creating innovative power electronic systems will be important when moving toward smaller, more e cient and higher power density solutions. As such, this thesis will aim to design and create an integrated power electronic system for an o -grid standalone solar application designed for remote rural locations with no access to electricity, or in locations which could bene t from such a system. It is designed for a DC input source from 24V-40V, such as a solar panel, and can operate four di erent loads; one 12V-24V 100 W DC load, charge a 48V battery, run three 5V cell phone charger outputs and run one 230V, 50Hz, 1 kW AC load. A boost converter, buck converter, phase shifted full bridge isolated DC-DC converter and a single phase inverter are implimented in the integrated system to achieve these outputs. A comparison of similar products on the market are presented and compared with the proposed design by showing the product speci cations, advantages and disadvantages of each. A discussion of each converter in the system is presented and will include operation, design and component selection. An in-depth design process for the inductor within the boost converter is presented and will cover core, winding design and an optimization algorithm using the Genetic Algorithm (GA) is used to compare di erent ferrite based C-C shaped inductors. More speci cally, the core material selected is Ferroxcube 3C97 and the inductor comparions are between di erent Litz bundled windings from New England Wire Tecnologies and a customized rectangular winding. The GA optimizes around the lowest volume by comparing the di erent inductor designs using the di erent Litz winding constructions and the custom rectangular winding constrictuion. The rectangular winding achieves the lowest volume and will be compared with a three phase interleaved boost design implimenting a CoilCraft inductor. The buck converter is the simplest converter and is designed using the traditional methods in literature. An in-depth design process for the phase shifted full bridge converter is also done wherein the zero voltage switching (ZVS) is achieved. The DC-AC inverter is the last converter designed within the integrated system and covers input capacitor sizing, and output lter design. There are speci c distributed energy standards that must be followed when connecting loads to the system and so the purpose of the lter is to lter out the voltage harmonics. The control techniques for each converter is also discussed and shown to operate in both simulation and in experimentally. The losses within the system are discussed and the required equations are de ned / Thesis / Master of Applied Science (MASc)

付記する学位プログラム名: 京都大学卓越大学院プログラム「先端光・電子デバイス創成学」 / 京都大学 / 新制・課程博士 / 博士(工学) / 甲第24620号 / 工博第5126号 / 新制||工||1980(附属図書館) / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 土居 伸二, 教授 小嶋 浩嗣, 准教授 薄 良彦, 教授 引原 隆士 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

This work explores the design, construction, and analysis of a novel DC-DC converter which incorporates combinations of switching capacitors and inductors to achieve an integer voltage divider function, without the need for a feedback loop controller to achieve the desired output voltage. The proposed Hybrid Voltage Divider additionally provides zero voltage switching (ZVS) at turn on transitions which yields improved overall efficiency of the converter. Besides a proof-of-concept via computer simulations, another primary goal of this thesis is to demonstrate the functionalities of the proposed Zero Voltage Switching Hybrid Voltage Divider (ZVS-HVD) through hardware prototyping. The proposed ZVS-HVD was designed and constructed to provide a 2:1 division with 24V input voltage at 120W maximum output power utilizing 500kHz switching frequency. Findings from simulations and hardware tests verify that the converter effectively provides the desired 12V output at varying loads with less than 5% voltage ripple. The efficiency of the converter reaches 95.02% at full load and peak efficiency of 96.33% at 55% load. Moreover, the converter consistently maintains the ZVS operations across all switches under varying loads. Overall, results verify the feasibility of the proposed ZVS HVD converter as an alternative solution in providing high efficiency DC voltage division without the need for complex feedback circuitry.

The aim of this work is to develop a two-port black-box dc-dc converter modeling methodology for system level simulation and analysis. The models do not require any information about the components, structure, or control parameters of the converter. Instead, all the information needed to build the models is collected from unterminated experimental frequency response function (FRF) measurements performed at the converter power terminals. These transfer funtions are known as audiosuceptibility, back current gain, output impedance, and input admittance. The measurements are called unterminated because they do not contain any information about the source and/or the load dynamics. This work provides insights into how the source and the load affect FRF measurements and how to decouple those effects from the measurements. The actual linear time invariant model is obtained from the experimental FRFs via system identification. Because the the two-port model obtained from a set of FRFs is linear, it will be valid in a specific operating region defined by the converter operating conditions. Therefore, to satisfy the need for models valid in a wide operating region, a model structure that combines a family of linear two-port models is proposed. One structure, known as the Wiener structure, is especially useful when the converter nonlinearities are reflected mainly in the steady state currents and voltage values. The other structure is known as a polytopic structure, and it is able to capture nonlinearities that affect the transient and steady state converter behavior. The models are used for prediction of steady state and transient behavior of voltages and currents at the converter terminals. In addition, the models are useful for subsystem interaction and small signal stability assesment of interconnected dc distribution systems comprising commericially available converters. This work presents for first time simulation and stability analysis results of a system that combines dc-dc converters from two different manufucturers. All simulation results are compared against experimental results to verify the usefulness of the approach. / Ph. D.

Electromagnetic transient and dynamic modeling and simulation studies are presented for a StatCom-SMES compensator in power systems. The transient study aims to better understand the transient process and interaction between a high power/high voltage SMES coil and its power electronics interface, dc-dc chopper. The chopper is used to attach the SMES coil to a StatCom. Following the transient study, the integration of a StatCom with SMES was explored to demonstrate the effectiveness of the combined compensator in damping power oscillations. The transient simulation package PSCAD/EMTDC has been used to perform the integrated modeling and simulation studies. A state of the art review of SMES technology was conducted. Its applications in power systems were discussed chronologically. The cost effective and feasible applications of this technology were identified. Incorporation of a SMES coil into an existing StatCom controller is one of the feasible applications, which can provide improved StatCom operation, and therefore much more flexible and controllable power system operation. The SMES coil with the following unique design characteristics of 50MW (96 MW peak), 100 MJ, 24 kV interface has been used in this study. As a consequence of the high power/ high voltage interface, special care needs to be taken with overvoltages that can stress the insulation of the coil. This requires an investigation of transient overvoltages through a detailed modeling of SMES and its power electronics interface. The electrical model for the SMES coil was developed based on geometrical dimensions of the coil. The interaction between the SMES coil and its power electronics interface (dc-dc chopper for the integration to StatCom) was modeled and simulated to identify transient overvoltages. Transient suppression schemes were developed to reduce these overvoltages. Among these are MOV implementation, surge capacitors, different configurations of the dc-dc chopper. The integration of the SMES coil to a StatCom controller was developed, and its dynamic behavior in damping oscillations following a three-phase fault was investigated through a number of simulation case studies. The results showed that the addition of energy storage to a StatCom controller can improve the StatCom-alone operation and can possibly reduce the MVA rating requirement for the StatCom operating alone. The effective location selection of a StatCom-SMES controller in a generic power system is also discussed. / Ph. D.

This dissertation presents the derivation, analysis and application issues of advanced topologies with coupled inductors. The proposed innovative solutions can achieve significant performance improvement compared to the state-of-the-art technology. New applications call for high-efficiency high step-up DC-DC converters. The basic topologies suffer from extreme duty ratios and severe rectifier reverse recovery. Utilizing coupled inductor is a simple solution to avoid extreme duty ratios, but the leakage inductance associated with the coupled inductor induces severe voltage stress and loss. An innovative solution is proposed featuring with efficient leakage energy recovery and alleviated rectifier reverse recovery. Impressive efficiency improvement is achieved with a simple topology structure. The coupled inductor switching cell is identified. Topology variations and evaluations are also addressed. The concept that utilizes coupled inductors to alleviate rectifier reverse recovery is then extended, and new topologies suitable for other applications are generated. The proposed concept is demonstrated to solve the severe rectifier reverse recovery that occurs in continuous current mode (CCM) boost converters. Significant profile reduction and power density improvement can be achieved in front-end CCM power factor correction (PFC) boost converters, which are the overwhelmingly choice for use in telecommunications and server applications. This dissertation also proposes topologies to realize the single-stage parallel PFC by utilizing coupled inductors. Compared to the state-of-the-art single-stage PFC converters, the proposed topologies introduce a new power flow pattern that minimizes the bulk-capacitor voltage stress and the switch current stress. / Ph. D.

With the fast advance in VLSI technology, smaller, more powerful digital system is available. It requires power supply with higher power density, lower profile and higher efficiency. PWM topologies have been widely used for this application. Unfortunately, hold up time requirement put huge penalties on the performance of these topologies. Also, high switching loss limited the power density achievable for these topologies. Two techniques to deal with hold up time issue are discussed in this dissertation: range winding solution and asymmetric winding solution, the efficiency at normal operation point could be improved with these methods. To reduce secondary rectifier conduction loss, QSW synchronous rectifier is developed, which also helps to achieve ZVS for symmetrical half bridge converter. Although with these methods, the efficiency of front end DC/DC converter could be improved, the excessive switching loss prohibited higher switching frequency. To achieve the targets, topologies with high switching frequency and high efficiency must be developed. Three resonant topologies: SRC, PRC and SPRC, are been investigated for this application because of their fame of low switching loss. Unfortunately, to design with hold up requirement, none of them could provide significant improvements over PWM converter. Although the negative outcome, the desired characteristic for front end application could be derived. Base on the desired characteristic, a thorough search is performed for three elements resonant tanks. LLC resonant topology is found to posses the desired characteristic. From comparison, LLC resonant converter could reduce the total loss by 40% at same switching frequency. With doubled switching frequency, efficiency of LLC resonant converter is still far better than PWM converters. To design the power stage of LLC resonant converter, DC analysis is performed with two methods: simulation and fundamental component simplification. Magnetic design is also discussed. The proposed integrated magnetic structure could achieve smaller volume, higher efficiency and easy manufacture. To make practical use of the topology, over load protection is a critical issue. Three methods to limit the stress under over load situation are discussed. With these methods, the converter could not only survive the over load condition, but also operate for long time under over load condition. Next small signal characteristic of the converter is investigated in order to design the feedback control. For resonant converter, state space average method is no longer valid. Two methods are used to investigate the small signal characteristic of LLC resonant converter: simulation and extended describing function method. Compare with test results, both methods could provide satisfactory results. To achieve both breadth and depth, two methods are both used to reveal the myth. With this information, compensator for feedback control could be designed. Test circuit of LLC resonant converter was developed for front end DC/DC application. With LLC topology, power density of 48W/in3 could be achieved compare with 13W/in3 for PWM converter. / Ph. D.

Fuel cells are a clean, high-efficiency source for power generation. This innovative technology is going to penetrate all aspects in our life, from utility distributed power, transportation applications, down to power sources for portable devices such as laptop computer and cell phones. To enable the usage of fuel cell, developing power converters dedicated for fuel cells becomes imminent. Currently, the full-bridge converter is the dominating topology in high power dc/dc applications. Although multiphase converters have been proposed, most of them are dealing with high input-voltage systems, and their device characteristic is not suitable for a low voltage source such as a fuel cell. For a high power fuel cell system, high voltage conversion ratios and high input currents are the major obstacles to achieving high-efficiency power conversions. This dissertation proposes a novel 3-phase 6-leg dc/dc power converter with transformer isolation to overcome these obstacles. Major features of the proposed converter include: (1) Increase converter power rating by paralleling phases, not by paralleling multiple devices; (2) Double the output voltage by transformer delta-wye connection, thus lowering the turns-ratio; (3) Reduce the size of output filter and input dc bus capacitor with interleaved control; (4) Achieve Zero-Voltage Zero-Current Switching (ZVZCS) over a wide load range without auxiliary circuitry. High conversion efficiency above 96% is verified with different measurement approaches in experiments. This dissertation also presents the power stage and control design for the proposed converter. Control design guideline is provided and the design result is confirmed with both simulation and hardware experiments. When using the fuel cell for stationary utility power applications, a low-frequency ripple interaction was identified among fuel cell, dc/dc converter and dc/ac inverter. This low frequency ripple tends to not only damage the fuel cell, but also reduce the source capability. This dissertation also investigates the mechanism of ripple current propagation and exploits the solutions. A linearized ac model is derived and used to explain the ripple propagation. An active ripple reduction technique by the use of the current loop control is proposed. This active current loop control does not add extra converters or expensive energy storage components. Rather, it allows a reduction in capacitance because the ripple current flowing into the capacitor is substantially reduced, and less capacitance can be used while maintaining a clean dc bus voltage. The design process and guideline for the proposed control is suggested, and the effectiveness of this active control is validated by both simulation and experimental results. / Ph. D.

The objective of the thesis is to introduce a new fuzzy logic control application, develop the associated mathematical theory and prove the concept and its advantages through comparative simulation with existing, classical, methods. A stable fuzzy logic controller for the master-slave current sharing loop of a paralleled DC-DC system is presented that exhibits a considerably improved large signal performance over the presently employed, small signal designed compensators, both in terms of system response and control effort. Because of high system complexity, the present small signal designs are unable to give a good response for large load changes and line transients. Fuzzy logic, by dealing naturally with nonlinearities, offers a superior controller type, for this type of applications. The design uses a PID expert to derive the fuzzy inference rules, and simulation results show a good parameter insensitive transient response over a wide range load-step responses, e.g., from 25% to 75% of the nominal load. Current sharing control is formulated as a tracking problem and stability is ensured through adaptation or supervisory control on a Lyapunov trajectory. The technique benefits also from the heuristic approach to the problem that overcomes the complexity in modeling such systems and, hence, offers a practical engineering tool, amenable to both analog and digital implementations. / Ph. D.

With the increasing demand for clean and renewable energy, new distribution network concepts, such as DC microgrids and distributed power generation networks, are being developed. One key component of such networks is the grid-interfacing DC-DC power converter that can transfer power bi-directionally while having a wide range of voltage step-up and step-down capabilities. Also, with the proliferated demand for electric vehicle chargers, battery energy storage systems, and solid-state transformers (SST), the bi-directional high-power DC-DC converter plays a more significant role in the renewable energy industry. To satisfy the requirements of the high-power bi-directional wide-range DC-DC converter, different topologies have been compared in this thesis, and the four-switch buck-boost (FSBB) converter topology has been selected as the candidate. This work investigates the operation principle of the FSBB converter, and a digital real-time low-loss quadrangle current mode(QCM) control implementation, which satisfies the zero-voltage-switching (ZVS) requirements, is proposed. With the QCM control method, the FSBB converter efficiency can be further increased by reducing the inductor RMS current and device switching loss compared to traditional continuous current mode(CCM) control and discontinuous current mode(DCM) control. Although the small signal model has been derived for FSBB under CCM control, the small ripple approximation that was previously used in the CCM model no longer applies in the QCM model and causing the model to be different. To aid the control system compensator design, QCM small signal model is desired. In this thesis, a small signal model for FSBB under QCM control is proposed. A 50 kW silicon carbide (SiC) based grid-interfacing converter prototype was constructed to verify the QCM control implementation and small signal model of the FSBB converter. For driving the 1.2kV SiC modules, an enhanced gate driver with fiber optic (FO) based digital communication capability was designed. Digital on-state and off-state drain-source voltage sensors and Rogowski coil-based current sensors are embedded in the gate driver to minimize the requirement for external sensors, thus increasing the power density of the converter unit. Also, Rogowski-coil-based current protection and drain-source voltage-based current protection is embedded in the gate driver to prevent SiC switching device from damage. / Master of Science / The renewable energy sector is driving the development of new distribution networks, such as DC microgrids and distributed power generation networks. One crucial component of these networks is the grid-interfacing DC-DC power converter, which can transfer power in both directions while maintaining a wide voltage range. This study evaluates various topologies and selects the four-switch buck-boost (FSBB) converter topology to meet the demands of high-power, bi-directional, and wide-range DC-DC converters. This work analyzed the operation of the FSBB converter and proposed a novel simplified quadrangle current mode (QCM) control implementation. With the QCM control method, the FSBB converter efficiency can be further improved by reducing losses compared to conventional control methods. This study also provides a small signal model, which can be used to aid the control loop compensator design where application of FSBB converter is required. A 50 kW silicon carbide (SiC) based grid-interfacing converter prototype, which was constructed to validate the proposed QCM control implementation and small signal model of the FSBB converter. As part of the converter unit,the enhanced gate driver design and implementation is presented in this thesis. This gate driver is designed with fiber optic-based digital communication, drives the wide bandgap SiC modules. The gate driver also features embedded digital on-state and off-state drain-source voltage sensors and non-intrusive current sensors to minimize external sensor requirements, thereby increasing the power density of the converter unit. The gate driver also incorporates high bandwidth current protection and drain-source voltage-based current protection to protect the SiC switching device from damage.