REGULATED TRANSFORMER RECTIFIER UNIT FOR MORE ELECTRIC AIRCRAFTS

The impending trends in the global demand of more-electric-aircrafts with higher efficiency, high power density, and high degree of compactness has opened up numerous opportunities in front of avionic industries to develop innovative power electronic interfaces. Traditionally, passive diode-bridge based transformer rectifier units (TRU) have been used to generate a DC voltage supply from variable frequency and variable voltage AC power out of the turbo generators. These topologies suffer from bulky and heavy low-frequency transformer size, lack of DC-link voltage regulation flexibility, high degree of harmonic contents in the input currents, and additional cooling arrangement requirements. This PhD research proposes an alternative approach to replace TRUs by actively controlled Regulated Transformer Rectifier Units (RTRUs) employing the advantages of emerging wide band gap (WBG) semiconductor technology. The proposed RTRU utilizing Silicon Carbide (SiC) power devices is composed of a three-phase active boost power factor correction (PFC) rectifier followed by an isolated phase-shifted full bridge (PSFB) DC-DC converter. Various innovative control algorithms for wide-range input frequency operation, ultra-compact EMI filter design methodology, DC link capacitor reduction approach and novel start-up schemes are proposed in order to improve power quality and transient dynamics and to enhance power density of the integrated converter system. Furthermore, a variable switching frequency control algorithm of PSFB DC-DC converter has been proposed for tracking maximum conversion efficiency at all feasible operating conditions. In addition, an innovative methodology engaging multi-objective optimization for designing electromagnetic interference (EMI) filter stage with minimized volume subjected to the reactive power constraints is analyzed and validated experimentally. For proof-of-concept verifications, three different conversion stages i.e. EMI filter, three-phase boost PFC and PSFB converter are individually developed and tested with upto 6kW (continuous) / 10kW (peak) power rating, which can interface a variable input voltage (190V-240V AC RMS) variable frequency (360Hz – 800Hz) three-phase AC excitation source, emulating the airplane turbo generator and provide an AC RMS voltage of 190V to 260V. According to the experimental measurements, total harmonic distortion (THD) as low as 4.3% and an output voltage ripple of ±1% are achieved at rated output power. The proposed SiC based RTRU prototype is ~8% more efficient and ~50% lighter than state-of-the art TRU technologies

Review of multiport power converters for distribution network applications

Multiport power converters integrate three or more energy devices into a single (potentially highly controllable and efficient) hub. These characteristics suggest that multiport power converters may be valuable for the decarbonisation of distribution networks, where the increase of converter-interfaced devices has degraded system reliability and efficiency. This review analyses the suitability of a wide range of multiport power converter solutions for four example distribution network applications (where previous studies have focussed on a limited range of topologies or applications) and the research areas that can progress their maturity. A review of grid codes and standards overviews the base capability that multiport power converters are likely to require, some of which are carried forward as requirements for a novel comparison tool. The comparison tool is developed to qualify and score reviewed topologies in terms of a range of features that are weighted for the applications. Isolated and partially-isolated topologies perform well due to their flexibility to be configured for the specifications and their operational capabilities (including modularity and voltage decoupling). Further research should focus on the complex control interactions between ports and scaling of these topologies for medium voltages. In contrast, many direct current non-isolated topologies do not qualify due to their low flexibility to be configured for the applications. This suggests that future research could focus on the development of a more flexible non-isolated multiport power converter configuration to take advantage of the high efficiency and low footprint that these topologies might otherwise offer for low voltage applications

Power Electronic Topologies with High Density Power Conversion and Galvanic Isolation for Utility Interface

The past decade has seen a significant increase in the number of applications where power electronic converters play a major role. Renewable energy systems such as wind turbines, solar photovoltaics, etc. employ power converters to interface with the utility grid. More and more power converters are being used in transportation sector such as in electric vehicles, locomotives, aircrafts, ships and submarines. Advancements in power converter topologies and devices have constantly pushed the limits and standards applicable in different markets towards better efficiency, lower cost and higher power density. Especially for large power systems such as wind turbine generators, adjustable speed drives, locomotives, etc., achieving smaller footprint at low cost and high efficiency has become a major challenge. These factors generate the major impetus towards the research undertaken in this dissertation. In applications that require integration with the utility grid, the bulkiest components are usually the transformers, inductors and DC electrolytic capacitors. Instead of using a line frequency transformer to interface any power electronic system with the utility grid directly, it is possible to use a power converter to transform the line frequency AC into a higher frequency AC that can be fed to a medium or high frequency transformer. These transformers are much smaller and lighter compared to line frequency transformers. This dissertation elucidates these concepts in detail in the first section as well as at the beginning of each subsequent section, along with a summary of such techniques already proposed in the literature. The sections in this dissertation propose and discuss several architectures (approaches) adhering to the earlier stated concepts that enable higher power density energy conversion for applications such as wind turbines, adjustable speed drives, data centers, energy storage systems, etc. Detailed operational analysis, design example, control strategy, simulation results and experimental results are shown for each concept or topology. The advantages and drawbacks are also discussed. Finally in this dissertation, the medium or high frequency transformers that can be used in the proposed approaches are analyzed in detail using ANSYS Maxwell software in terms of material, saturation, loss and size. Further, these numbers are used to estimate the relative size advantage and efficiency that can be achieved using higher frequency transformer compared to a line frequency transformer for utility interface applications. It will be shown that for many high power applications, medium frequency transformer based circuit designs can be more efficient and simpler alternatives for high frequency transformer based approaches. The specific contributions along with future research opportunities of the proposed concepts are summarized at the end

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

An Integrated Single-phase On-board Charger

With the growing demand for transportation electrification, plug-in electric vehicles (PEVs), and plug-in hybrid electric vehicles (PHEVs), cumulatively called electric vehicles (EVs) are drawing more and more attention. The on-board charger (OBC), which is the power electronics interface between the power grid and the high voltage traction battery, is an important part for charging EVs. Besides the OBC, every EV is equipped with another separate power unit called the auxiliary power module (APM) to charge the low voltage (LV) auxiliary battery, which supplies all the electronics on car including audio, air conditioner, lights and controllers. The main target of this work is a novel way to integrate both units together to achieve a charger design that is not only capable of bi-directional operation with high efficiency, but also higher gravimetric and volumetric power density, as compared with those of the existing OBCs and APMs combined. To achieve this target, following contributions are made: (i) a three-port integrated DC/DC converter, which combines OBC and APM together through an innovative integration method; (ii) an innovative zero-crossing current spike compensation for interleaved totem pole power factor correction (PFC) and (iii) a new phase-shift based control strategy to achieve a regulated power flow management with minimum circulating losses

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

Stepwise Design Methodology and Heterogeneous Integration Routine of Air-Cooled SiC Inverter for Electric Vehicle

Carrying on SiC devices, the air-cooled inverter of the electric vehicle (EV) can eliminate the traditional complicated liquid-cooling system in order to obtain a light and compact performance of the powertrain, which is considered as the trend of next-generation EV. However, the air-cooled SiC inverter lacks strategic design methodology and heterogeneous integration routine for critical components. In this article, a stepwise design methodology is proposed for the air-cooled SiC inverter in the power module, dc-link capacitor, and heat sink levels. In the power module level, an electrical-thermal-mechanical multiphysics model is proposed. The multidimension stress distribution principles in a six-in-one SiC power module are demonstrated. An improved power module is presented and confirmed by using the observed multiphysics design principles. In the dc-link capacitor level, ripple modeling of the inverter and capacitor are created. Considering the tradeoffs among ripple voltage, ripple current, and cost, optimal strategies to determine the material and minimize the capacitance of the dc-link capacitor are proposed. In the heat sink level, thermal resistance of air-cooled heat sink is modeled. Structure and material properties of the heat sink are optimally designed by using a comprehensive electro-thermal analysis. Based on the optimal design results, the prototypes of the customized SiC power module and heterogeneously integrated air-cooled inverter are fabricated. Experimental results are presented to demonstrate the feasibility of the designed and manufactured air-cooled SiC inverter.Ministry of Education (MOE)Nanyang Technological UniversityThis work was supported in part by the National Natural Science Foundation of China under Grant 51607016, in part by the National Key Research and Development Program of China under Grant 2017YFB0102303, and in part by the Singapore ACRF Tier 1 Grant RG 85/18. The work of X. Zhang was supported by the NTU Startup Grant (SCOPES)

Advanced Power Electronic Interfaces for Distributed Energy Systems Part 1: Systems and Topologies

This report summarizes power electronic interfaces for DE applications and the topologies needed for advanced power electronic interfaces. It focuses on photovoltaic, wind, microturbine, fuel cell, internal combustion engine, battery storage, and flywheel storage systems

Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering