DC-DC and AC-DC Converters Based on Three-Phase DC-DC Topologies

Power electronics is the field of electrical engineering that uses power semiconductor devices along with passive elements such as inductors, capacitor and transistors to convert electrical power that can be generated by a source to a form that is suitable for user loads. The main focus of this thesis is on the development of new DC-DC and AC-DC topologies that are based on three-phase DC-DC converters. Three-phase DC-DC converters take an input DC voltage, convert it into a high-frequency AC voltage that is then stepped up or down, then rectify and filter this voltage to produce an output DC voltage. They are implemented with a high-frequency three-phase transformer in their topology rather than a single-phase transformer. These converters are very attractive over other topologies that have a single-phase transformer in their topologies for several reasons. First, just one three-phase DC-DC converter can be used instead of using three DC-DC converters in parallel for particular applications; this advantage is especially attractive for higher power applications. In addition, by using three-phase DC-DC converters, the ripple of the source current is significantly reduced and that means less filtering is needed. Moreover, the components of the converter will have less current stress because current is split among three-phases. In this thesis, new DC-DC and AC-DC converters that are based on three-phase DC-DC topology are proposed. The proposed converters use fewer active switches than other previously proposed converters of similar type, thus resulting in lower cost and simpler operation. For each of the proposed converters, its steady-state characteristics are determined by mathematical analysis and procedure for the design of key converter components is developed. The feasibility of each proposed converter has been confirmed with results that have been obtained from experimental prototypes. For one of the proposed converters, a comparison between the operation of one of the proposed converters operating with traditional silicon devices (Si) and that with the converter operating with new silicon-carbide devices (SiC) was made to examine its performance with both types of devices

Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

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

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics

High power modular converters for grid interface applications

Scientists at European Organization for Nuclear Research (CERN) are currently conducting feasibility studies for the Compact linear collider (CLIC); their proposed next experimental setup for gathering information on the fundamental particles of matter. This experiment will involve the simultaneous pulsing of 1300 klystron modulators to produce a 140us, 39GW pulse with a 50 Hz repetition rate. This proposal presents many demands for the connected power system as an effort is made to "hide" this pulse from the local distribution network - instead drawing only the constant average power of approximately 300MW. This challenge is considered in this work. In order to understand the optimal approach both the power system architectures and power electronics interfaces must be considered simultaneously. An approach to the optimisation of the power system architecture is described in this thesis. It is clear from this exercise that the optimum power converter topology for the interface between the electricity distribution network and the klystron modulators is the Modular Multilevel Converter (MMC). This converter is mainly used in modern HVDC transmission circuits as a result of its high efficiency and ability to produce high quality AC waveforms. Pulsing of the klystron modulators does however create further challenges for the inner control loops of an MMC. The placement of the pulse can create imbalances in the DC capacitors of the MMC submodules which may result in tripping of the converter if not corrected. This thesis proposes three arm balancing solutions to be applied together with the decoupled AC and DC side controller designed for the specified application. These proposed solutions to the aforementioned problems are successfully validated using simulation work in PLECS and using data from a laboratory scale prototype of one of the MMC interface power converters

High power modular converters for grid interface applications

Scientists at European Organization for Nuclear Research (CERN) are currently conducting feasibility studies for the Compact linear collider (CLIC); their proposed next experimental setup for gathering information on the fundamental particles of matter. This experiment will involve the simultaneous pulsing of 1300 klystron modulators to produce a 140us, 39GW pulse with a 50 Hz repetition rate. This proposal presents many demands for the connected power system as an effort is made to "hide" this pulse from the local distribution network - instead drawing only the constant average power of approximately 300MW. This challenge is considered in this work. In order to understand the optimal approach both the power system architectures and power electronics interfaces must be considered simultaneously. An approach to the optimisation of the power system architecture is described in this thesis. It is clear from this exercise that the optimum power converter topology for the interface between the electricity distribution network and the klystron modulators is the Modular Multilevel Converter (MMC). This converter is mainly used in modern HVDC transmission circuits as a result of its high efficiency and ability to produce high quality AC waveforms. Pulsing of the klystron modulators does however create further challenges for the inner control loops of an MMC. The placement of the pulse can create imbalances in the DC capacitors of the MMC submodules which may result in tripping of the converter if not corrected. This thesis proposes three arm balancing solutions to be applied together with the decoupled AC and DC side controller designed for the specified application. These proposed solutions to the aforementioned problems are successfully validated using simulation work in PLECS and using data from a laboratory scale prototype of one of the MMC interface power converters

Advanced Mobile Robotics: Volume 3

Mobile robotics is a challenging field with great potential. It covers disciplines including electrical engineering, mechanical engineering, computer science, cognitive science, and social science. It is essential to the design of automated robots, in combination with artificial intelligence, vision, and sensor technologies. Mobile robots are widely used for surveillance, guidance, transportation and entertainment tasks, as well as medical applications. This Special Issue intends to concentrate on recent developments concerning mobile robots and the research surrounding them to enhance studies on the fundamental problems observed in the robots. Various multidisciplinary approaches and integrative contributions including navigation, learning and adaptation, networked system, biologically inspired robots and cognitive methods are welcome contributions to this Special Issue, both from a research and an application perspective

NASA Tech Briefs, October 1995

A special focus in this issue is Data acquisition and analysis. Topics covered include : Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Life Sciences; Mechanics; Machinery; Fabrication Technology; and Mathematics and Information Sciences. Also included in this issue are Laser Tech Briefs and Industry Focus: Motion Control/ Positioning Equipmen