A novel fixed switching frequency control strategy applied to an improved five-level active rectifier

A novel fixed switching frequency control strategy applied to an improved five-level active rectifier (iFLAR) is proposed. The operation with fixed switching frequency represents a powerful advantage, since the range of the produced harmonics is well identified, and it is possible to design passive filters to mitigate such harmonics. The experimental validation shows that the control strategy allows attaining an ac-side current with reduced total harmonic distortion and high power factor, which is an attractive influence for grid-connected electrical appliances. This contribution is even more relevant with the new paradigm of smart grids where higher levels of power quality are required. A theoretical analysis of the control strategy and the details of its implementation in a digital signal processor are presented. The control scheme and the developed iFLAR were experimentally confirmed using a laboratorial prototype, showing its benefits in terms of accuracy, reduced total harmonic distortion and high power factor.This work has been supported by COMPETE: POCI-010145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation – COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT – Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015 – POCI – 01–0145–FEDER–016434. Mr. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by the Portuguese FCT agency. This work is part of the FCT project 0302836 NORTE-01-0145-FEDER-030283.info:eu-repo/semantics/publishedVersio

Application of the cascaded multilevel inverter as a shunt active power filter

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A TWELVE-PULSE LOAD COMMUTATED CONVERTER DRIVE SYSTEM WITH VSI FOR STARTING UP AND ACTIVE POWER FILTERING IN AN LNG APPLICATION

Variable Frequency Drives (VFDs) are an integral component of the industry in today’s age. VFDs provide a great range of control for electrical machines, and can be integrated in a variety of applications to meet the desired objectives of operation with improved reliability and efficiency. This thesis presents the Load-Commutated Converter (LCC) drive, which belongs to the Current Source Converter (CSC) based drive system family. Such drives are widely used in high power applications, due to power handling capabilities and the maturity of the drive system. The application under study is that of a helper/starter motor for a turbine compressor in a Liquefied Natural Gas (LNG) plant. Primarily, the thesis presents real-life scenarios of drive system operation such as constant/variable speed operation at constant/varying torque. The respective controllers for the LCC drive are presented alongside their results. In addition to simulating the drive system in this LNG application, current harmonic mitigation measures are presented in this study. The typical converter topology presented in this thesis is the 12-pulse type, however comparisons with different topologies (6, 18, and 24-pulse) have also been presented. Finally, a dual-purpose external Voltage Source Inverter (VSI) is used both as a starter and an Active Power Filter (APF), therefore addressing the issues of drive/load induced harmonics and LCC starting. As a conclusion, a controlled LCC drive model is simulated in SIMULINK to emulate the drive operation in actual plant conditions. The controlled drive is further studied for the presence of harmonics and their subsequent mitigation, by using passive as well as active power filters. The results obtained present the adequacy of the control system as well as the efficacy of the filters used for harmonics mitigation. Future work revolves around improving the efficiency of the APF, and the drive control system to be more robust and reliable. The system can further be investigated for enhancements as per operational requirements

Field theoretic analysis of a class of planar microwave and opto-electronic structures

With increasing operating frequencies in CMOS RF/microwave integrated circuits, the performance of on-chip interconnects is becoming significantly affected by the lossy substrate. It is the purpose of the first part of this thesis to develop a rigorous field theoretic analysis approach for efficient characterization of single and multiple coupled interconnects on silicon substrate, which is applicable over a wide range of substrate resistivities. The frequency-dependent transmission line parameters of a microstrip on silicon are determined by a new formulation based on a quasi-electrostatic and quasi-magnetostatic spectral domain approach. It is demonstrated that this new quasi-static formulation provides the complete frequency-dependent interconnect characteristics for all three major transmission line modes of operation. In particular, it is shown that in the case of heavily doped CMOS substrates, the distributed series inductance and series resistance parameters are significantly affected by the presence of longitudinal substrate currents giving rise to the substrate skin-effect. The method is further extended to multiple coupled single and multi-level interconnect structures with ground plane and multiple coupled co-planar stripline structures without ground plane. The finite conductor thickness is taken into account in terms of a stacked conductor model. The new quasi-static approach is validated by comparison with results obtained with a full-wave spectral domain method and the commercial planar full-wave electromagnetic field solver HP/Momentum®, as well as published simulation and measurement data. In the second part of this thesis, coupled planar optical interconnect structures are investigated based on a rigorous field theoretic analysis combined with an application of the normal mode theory for coupled transmission lines. A new transfer matrix description for a general optical directional coupler is presented. Based on this transfer matrix formulation, the wavelength-dependent characteristics of multi-section optical filters consisting of cascaded asymmetric optical directional coupler sections are investigated. It is shown that by varying the asymmetry factors of the cascaded coupled waveguide sections, optical wavelength filters with different passband properties can be achieved

Power electronics technologies for renewable energy sources

Over the last decades, power grids are facing significant improvements mainly due to the integration of more and more technologies. In particular, renewable energy sources (RES) are contributing to moving from centralized energy production to a new paradigm of distributed energy production. Analyzing in more detail the requirements of the diverse technologies of RES, it is possible to identify a common and key point: power electronics. In fact, power electronics is the key technology to embrace the RES technologies towards controllability and the success of sustainability of power grids. In this context, this book chapter is focused on the analysis of diverse RES technologies from the point of view of power electronics, including the introduction and explanation of the operating principle of the most relevant RES, both in onshore and offshore scenarios. Additionally, are also presented the main topologies of power electronics converters used in the interface of RES.(undefined

Future‐proofing city power grids:FID‐based efficient interconnection strategies for major load‐centred environments

The flexible interconnection device (FID) offers significant advantages for interconnecting different distribution networks flexibly. This paper focuses on the significant advantages offered by the FID for interconnecting different distribution networks flexibly. It specifically delves into FID‐based multi‐voltage and multi‐substation distribution networks, proposing a preferable scheme applicable to major load‐centred cities. Beginning with an analysis of constructed FID‐based flexible interconnected distribution network projects, key configurations and features are summarized. Subsequently, typical configurations, electrical parameters, facilities, relevant power functionalities, and application scenarios of multi‐voltage multi‐substation distribution networks are outlined. Building upon this foundation, a suitable interconnection scheme tailored for current urban use is explored to meet the specific needs of load‐centred cities, while incorporating recent advancements in high‐power‐density IGCT technology. An EMT model of a 10 kV/10 MW IGCT‐based four‐substation distribution network is developed in PSCAD/EMTDC. Through thorough analysis under different conditions, the operational performance and benefits are evaluated, providing insights into the efficiency and resilience of the proposed FID‐based interconnection. Lastly, challenges and prospects are discussed from various perspectives to advance the development of FID‐based flexible interconnection solutions. This study aims to contribute to the advancement and implementation of robust interconnection solutions to meet the evolving needs of major load‐centred cities