This thesis investigates the design and analysis of modular medium-voltage dc/dc converter based systems. An emerging converter application is feeding offshore oil and gas production systems located in deep waters, on the sea bed, distant from the onshore terminal. The phase-controlled series-parallel resonant converter (SPRC) is selected as the dc/dc converter unit, for a 10kV dc transmission system. The converter has a high efficiency in addition to favourable soft switching characteristics offered by resonant converters which enable high frequency operation, hence designs with reduced footprints. The phase-controlled SPRC is studied in the steady-state and a new analysis is presented for the converter operational modes, voltage gain sensitivity, and analytically derived operational efficiency. The maximum efficiency criterion is used as the basis for selection of converter full load operational conditions. The detailed design of the output LC filter involves new mathematical expressions for interleaved multi-module operation. A novel large signal dynamic model is proposed for the phase-controlled SPRC with state feedback linearization. The model preserves converter large signal characteristics while providing a tool for faster simulation and simplified closed loop design and stability analysis. Using this model, a Kalman filter based estimator is proposed and applied for sensorless multi-loop output voltage control. The objective is to enhance the single-loop PI control dynamic response and closed loop stability with no additional sensors required for the inner loop state variables. Dynamic performance and robustness of the converter to operational circuit parameter variations are achieved with three new robust controllers; namely, Lyapunov, sliding mode, and predictive controllers. Finally, converter multi-module operation is studied, catering for voltage and current sharing of the subsea load-side step-down converter. To achieve a step-down voltage, the phase-controlled SPRC modules are connected in an input-series connection to share the medium level transmission voltage. Output-series and output-parallel connections are used to reach higher power levels. A new sensorless load voltage estimator is developed for converters remotely controlled. Matlab/Simulink simulations and experimental prototype results are used to substantiate all the proposed analysis techniques and control algorithms.

A modular approach for connecting dc/dc converters is a technique proposed for constructing high power level converter architectures. The main advantages of a modular approach include, increased fault tolerance introduced by redundant modules, standardization of components leading to reduced manufacturing cost and time, power systems can be easily expanded, and higher power density of the overall system, especially with interleaving. System reliability is potentially improved due to redundancy but this must be traded off against the increased number of power electronic devices. Compared with direct series/parallel connection of power devices, modularity serves better when factors such as converter reconfiguration and power level scaling, as well as interleaving to reduce filter requirements, are considered. The main objective of this work is to design, analyse, model and control modular medium-power medium-voltage dc/dc converter based systems. A typical application considered for this modular approach is feeding subsea electrically actuated oil and gas production systems, from onshore terminals, but the proposed converter can be also applied to other applications.

An invaluable academic reference for the area of high-power converters, covering all the latest developments in the field High-power multilevel converters are well known in industry and academia as one of the preferred choices for efficient power conversion. Over the past decade, several power converters have been developed and commercialized in the form of standard and customized products that power a wide range of industrial applications. Currently, the modular multilevel converter is a fast-growing technology and has received wide acceptance from both industry and academia. Providing adequate technical background for graduate- and undergraduate-level teaching, this book includes a comprehensive analysis of the conventional and advanced modular multilevel converters employed in motor drives, HVDC systems, and power quality improvement. Modular Multilevel Converters: Analysis, Control, and Applications provides an overview of high-power converters, reference frame theory, classical control methods, pulse width modulation schemes, advanced model predictive control methods, modeling of ac drives, advanced drive control schemes, modeling and control of HVDC systems, active and reactive power control, power quality problems, reactive power, harmonics and unbalance compensation, modeling and control of static synchronous compensators (STATCOM) and unified power quality compensators. Furthermore, this book: Explores technical challenges, modeling, and control of various modular multilevel converters in a wide range of applications such as transformer and transformerless motor drives, high voltage direct current transmission systems, and power quality improvement Reflects the latest developments in high-power converters in medium-voltage motor drive systems Offers design guidance with tables, charts graphs, and MATLAB simulations Modular Multilevel Converters: Analysis, Control, and Applications is a valuable reference book for academic researchers, practicing engineers, and other professionals in the field of high power converters. It also serves well as a textbook for graduate-level students.

Shows how the concepts of vectorization and design masks can be used to help the designer in comparing different designs and making the right choices. The book addresses series and parallel multicell conversion directly, and the concepts can be generalized to describe other topologies.

An all-in-one guide to high-voltage, multi-terminal converters, this book brings together the state of the art and cutting-edge techniques in the various stages of designing and constructing a high-voltage converter. The book includes 9 chapters, and can be classified into three aspects. First, all existing high-voltage converters are introduced, including the conventional two-level converter, and the multi-level converters, such as the modular multi-level converter (MMC). Second, different kinds of multi-terminal high-voltage converters are presented in detail, including the topology, operation principle, control scheme and simulation verification. Third, some common issues of the proposed multi-terminal high-voltage converters are discussed, and different industrial applications of the proposed multi-terminal high-voltage converters are provided. Systematically proposes, for the first time, the design methodology for high-voltage converters in use of MTDC grids; also applicable to constructing novel power electronics converters, and driving the development of HVDC, which is one of the most important technology areas Presents the latest research on multi-terminal high-voltage converters and its application in MTDC transmission systems and other industrially important applications Offers an overview of existing technology and future trends of the high-voltage converter, with extensive discussion and analysis of different types of high-voltage converters and relevant control techniques (including DC-AC, AC-DC, DC-DC, and AC-AC converters) Provides readers with sufficient context to delve into the more specialized topics covered in the book Featuring a series of novel multi-terminal high-voltage converters proposed and patented by the authors, Multi-terminal High Voltage Converters is written for researchers, engineers, and advanced students specializing in power electronics, power system engineering and electrical engineering.

Modular multilevel converters (MMCs) are currently widely used in medium and high voltage applications. In recent years, with the rapid development of silicon carbide (SiC) devices, growing attention has been placed on adopting SiC devices in MMCs. Thanks to the device's superior electrical and thermal characteristics, the SiC devices, especially the emerging medium voltage ones, are promising to benefit MMC based systems in numerous specifications, such as improved power density, reduced thermal stress, and higher efficiency. However, medium voltage systems can also experience challenges brought about by devices' fast switching speed, including worse electromagnetic interference (EMI), reflected wave phenomenon, and partial discharge. To better utilize the SiC devices in MMCs, this dissertation seeks to evaluate the effects of applying SiC power modules in MMCs. The analysis and discussions include the influential factors of the dv/dt seen at the load terminal, the dv/dt reduction methods, and the effect of high dv/dt on EMI noise and the system insulation design. The analysis is based on a 1 MVA MMC built with the 1.7 kV rated SiC power modules. The influential factors are discussed in three aspects: the source of high dv/dt, the propagation loop, and the control methods. The effects of the three aspects are discussed and evaluated with mathematical models, spice simulations, and hardware tests. It is straightforward that the load terminal dv/dt would change along with the device terminal dv/dt, which is the source of the high switching speed noise. Moreover, the design of passive components in a MMC system also affects the dv/dt by introducing the filtering effect. That is, the parasitic components and the arm inductors would form R-L-C networks between the power modules and the load, and the high order networks would bring down the dv/dt along the propagation loop of the switching transients. Last but not least, the control methods also affect the dv/dts at the load terminal, and the effect is realized via coordinating the switching transients of the two arm voltages. The analysis follows with the dv/dt reduction methods. Corresponding to the factors that affect the dv/dts, the voltage slew rate can be reduced by changing the power devices' switching speed, the passive components design, and different control methods. It is proved via simulation and experiments that the three methods can relieve the dv/dt stress on the load terminal with no or minor loss penalty. At the same time, the high dv/dt also introduces more concerns about the EMI noise and insulation-related issues. In this work, the insulation design concerns and the EMI performance are discussed based on the common mode model of the system. The EMI noises are evaluated with three indicators, including the leakage current that goes through the dc link middle point to the ground, the common-mode voltage of the load side neutral point, and the equivalent voltage drop on the human impedance network. The tests are carried out under different operation conditions to analyze the impact of modulation index, control methods, and the common mode impedance of the power loop.

Modeling, Operation, and Analysis of DC Grids presents a unified vision of direct current grids with their core analysis techniques, uniting power electronics, power systems, and multiple scales of applications. Part one presents high power applications such as HVDC transmission for wind energy, faults and protections in HVDC lines, stability analysis and inertia emulation. The second part addresses current applications in low voltage such as microgrids, power trains and aircraft applications. All chapters are self-contained with numerical and experimental analysis. - Provides a unified, coherent presentation of DC grid analysis based on modern research in power systems, power electronics, microgrids and MT-HVDC transmission - Covers multiple scales of applications in one location, addressing DC grids in electric vehicles, microgrids, DC distribution, multi-terminal HVDC transmission and supergrids - Supported by a unified set of MATLAB and Simulink test systems designed for application scenarios