A concise and hands-on overview of medium voltage direct current (MVDC) technology for electric power grids, written by international experts with broad experience. The book covers fundamentals, converters, transformers and control for both stationary and mobile applications.

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.

Medium Voltage Direct Current Grid is the first comprehensive reference to provide advanced methods and best practices with case studies to Medium Voltage Direct Current Grid (MVDC) for Resilience Operation, Protection and Control. It also provides technical details to tackle emerging challenges, and discuss knowledge and best practices about Modeling and Operation, Energy management of MVDC grid, MVDC Grid Protection, Power quality management of MVDC grid, Power quality analysis and control methods, AC/DC, DC/DC modular power converter, Renewable energy applications and Energy storage technologies. In addition, includes support to end users to integrate their systems to smart grid. - Covers advanced methods and global case studies for reference - Provides technical details and best practices for the individual modeling and operation of MVDC systems - Includes guidance to tackle emerging challenges and support users in integrating their systems to smart grids

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.

Much work has been done in recent years regarding the emphasis and new found importance of energy storage and energy conversion within systems that, at one time, functioned off of simple alternating current (AC) busses. With the advancement in technology has come unique and demanding electrical loads and equipment, creating a need for many different electrical topologies and requirements. The scope of the work done here is related to current efforts and interests in islanded microgrid power systems. Microgrid electrical systems are evolving and new, demanding electrical systems are being invented and introduced. For example, advancements in communication and sensor systems has brought with it increasing electrical demands, specically demands that occur in a transient manner. With these new electrical demands placed upon the islanded power system of a microgrid, new system topologies have risen up to meet these unique and transient requirements. Some of these topologies include the presence of medium voltage DC distribution busses within these systems to supply these new loads efficiently, as well as the inclusion and integration of energy storage used to augment traditional rotational generation in the event that a high power transient electrical load is placed upon the system. The inclusion of these topological changes has shown a need for modeling and evaluation of these newer, more complex systems. As these power systems become more complicated, there is an increasing number of variables that need to be considered in the integration of new systems. Energy conversion is important between the different, growing numbers of busses in place, and the evaluation of the different interactions between these busses has proven to be an expensive and difficult task to perform at the full multi-megawatt level of a typical commercial microgrid power system.The work presented here is to create a testbed of equipment and controls that are representative of this modern power system architecture, including a multitude of busses with both AC and DC voltages at different levels. These different voltage levels are to be tied together with various power electronic converters, such that energy can be transferred around the system as needed. Many different electrical loads will be implemented, in the form of traditional constant base loads and varying, transient loads of different pulse shapes and characteristics. The interactions and implications these loads have with the power system as a whole will be studied, including impacts on power quality and efficiency. These systems will operate at a power level that is more attainable than the multi-megawatt microgrid power system level, but one that is still significant enough to offer valuable insight into the operation of real, representative equipment. The power range utilized throughout this system will be between 100 and 300 kW, operating at voltages including 480 VAC 3Ø, 4160 VAC 3Ø, 1000 VDC, 6000 VDC, 12000 VDC. The specification of equipment will be presented here, along with a fundamental model of the system for analysis.

This book offers a comprehensive reference guide to the important topics of fault analysis and protection system design for DC grids, at various voltage levels and for a range of applications. It bridges a much-needed research gap to enable wide-scale implementation of energy-efficient DC grids. Following an introduction, DC grid architecture is presented, covering the devices, operation and control methods. In turn, analytical methods for DC fault analysis are presented for different types of faults, followed by separate chapters on various DC fault identification methods, using time, frequency and time-frequency domain analyses of the DC current and voltage signals. The unit and non-unit protection strategies are discussed in detail, while a dedicated chapter addresses DC fault isolation devices. Step-by-step guidelines are provided for building hardware-based experimental test setups, as well as methods for validating the various algorithms. The book also features several application-driven case studies.

A medium voltage DC (MVDC) shipboard power system (SPS) architecture is a notional candidate design for future "all-electric" ships, as it is expected to increase power density and distribution efficiency. However, the lack of experience in proven MVDC technology has inherent risks of substantial delays during the development process of controllers is larger than the risk with AC system designs. Model based system engineering methods, specifically controller hardware in the loop simulations, provide powerful means to lower the risk of a control development cycle. The ability to incrementally increase the fidelity of the model during the development and integration of a controller towards a more accurate representations of the power system network in question is expected to reduce the frequency and severity of potential problems. In the early stages of the control development, a control developer's main concern is to verify that algorithm implementation meets the functional requirements to satisfy the shipboard power system's needs. Performance of the implementation is at this stage is of less concern. There may also be limited knowledge about the specific power system that eventually will communicate with the controller. Hence, initially a reduced fidelity model may suffice. As the development process progresses, the model fidelity will evolve to ever increasing fidelity and accuracy. Eventually, the model will have to include all the relevant details and execute in real time in order to test the controller's real time performance before field deployment. A low-fidelity discrete event simulation first provides insight into the confidence of the algorithm's ability to satisfy its functions by leveraging its faster than real time nature to perform more experiments than possible in real-time. Subsequently, using a low-fidelity real-time simulation, the developer could capture the elapsed time of characteristic events performed by the controller, characterizing both the algorithm's functionality and performance with respect to wall-clock time. A first-order dynamic simulation contains a subset of the transient information in a real power system, where a developer can again test both functional and performance requirements in a more relevant environment. Finally, a high-fidelity real-time simulation is the closest model to the real world, permitting a developer to vet their implementation on the most relevant environment that is not a real power system. In order to facilitate such progressive increase in fidelity and real-time capability, an adaptable signal interface between controller and model has been developed and tested. In particular, this thesis presents design criteria and requirements for such an interface focusing on the development of a fault management approach for a breakerless (unit based) MVDC system. Each model must capture the power system characteristics such as network connectivity, power flows, generator outputs, load demands, and electrical switch states, in a monotonic fashion. That is information gradually progresses from the low-fidelity discrete event simulation to the high-fidelity real-time simulation. Each power system model can be on a different operational hardware or run with a different software, requiring an adaptable signal interface to manage the flow of information from simulation environment to the controls. Such an interface must adapt to changing communication behaviors, signal descriptions, and simulator and controller endpoints. Experimental results validate the interface design and control development process. The thesis concludes that the proposed approach is feasible while acknowledging the additional work required to continually refine the process for a more generic use in the future.