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.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-02-15T13:09:47Z No. of bitstreams: 1 SILVA_Daniela_2016.pdf: 80229234 bytes, checksum: b31611b87e5042713f6fb30cf6fd48ff (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-02-15T13:10:02Z (GMT) No. of bitstreams: 1 SILVA_Daniela_2016.pdf: 80229234 bytes, checksum: b31611b87e5042713f6fb30cf6fd48ff (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-02-15T13:10:08Z (GMT) No. of bitstreams: 1 SILVA_Daniela_2016.pdf: 80229234 bytes, checksum: b31611b87e5042713f6fb30cf6fd48ff (MD5) / Made available in DSpace on 2017-02-15T13:10:14Z (GMT). No. of bitstreams: 1 SILVA_Daniela_2016.pdf: 80229234 bytes, checksum: b31611b87e5042713f6fb30cf6fd48ff (MD5) Previous issue date: 2016-05-16 / Não recebi financiamento / This research analyzes the work of the operators of a converter substation of electricity from the interior, which can be considered exhausting due to the operating modes that are intrinsic in their daily lives. The objective seeks to identify the impacts caused by organizational changes on the work of people and the system performance due to reduced staff started in 2011. The methodology used was a case study outlined by the Activity Ergonomics of Work. The results indicated that before the staff reduction procedures were performed more safely and accompanied by aspects related to learning issues and recognition of operators. It was concluded that changes in work organization impacted in accelerating the scrapping of the equipment and the precariousness of the work of operators. / Esta pesquisa analisa o trabalho dos operadores de uma subestação conversora de energia elétrica do interior paulista, que pode ser considerado desgastante devido aos modos operatórios que estão intrínsecos no seu cotidiano. Como objetivo busca identificar quais os impactos causados pelas mudanças organizacionais sobre o trabalho das pessoas e no desempenho do sistema, advindo principalmente da redução da equipe, iniciada em 2011. A metodologia aplicada foi um estudo de caso delineado pela Análise Ergonômica do Trabalho. Os resultados indicaram que antes da redução de pessoal os procedimentos eram executados de forma mais segura e acompanhados de aspectos relacionados a questões de aprendizado e reconhecimento dos operadores. Concluiu-se que as mudanças na organização do trabalho impactaram na aceleração do sucateamento dos equipamentos e na precarização do trabalho dos operadores.