Full Selective Protection Strategy For Multi Terminal Cable Hvdc Grids Based On Hb Mmc Converters

In a near future, multi-terminal High Voltage Direct Current grids (MT-HVDC grids) appear to be a suitable solution for the integration of power electricity produced by remote offshore windfarms into the AC transmission system. Though the recourse to HVDC point-to-point links is well-known, challenges still remain for a safe operation of HVDC grids. Protection is the main technical field still under study and reliable protection strategies ensuring the best technological and economic ratio are investigated. This thesis focused on a full selective protection philosophy similar to the one applied to AC transmission systems. The consideration of cable links, Half-Bridge VSC-MMC converters and hybrid DC circuit breakers defines the frame of the study. An association of two algorithms for the identification of faults is suggested. The time available for the fault clearing process has been investigated. Simulations performed with EMTP software have been used to evaluate the reliability of the suggested strategy.

Even though today's transmission grids are predominantly based on the high voltage alternating current (HVAC) scheme, interests on high voltage direct current (HVDC) are growing rapidly during the past decade, due to the increased penetration of remote renewable energy. Voltage source converter (VSC) type is preferred over the traditional line-commutated converter (LCC) for this application, due to the advantages like smaller station footprint and no need for strong interfacing ac grid. As the state-of-the-art VSC topology, modular multilevel converter (MMC) is mostly considered. Most renewable energy sources, such as wind and solar, is usually sparsely located. Multi-terminal HVDC (MTDC) provides better use of transmission infrastructure, higher transmission flexibility and reliability, than building multiple point-to-point HVDCs. This dissertation studies the MMC-based MTDC system, including design, control and protection. Passive components design methodology in MMC is developed, with practical consideration. The developed arm inductance selection criterion considers the implementation of circulating current suppression control. And the unbalanced voltage among submodule capacitor is taken into account for submodule capacitance design. Circulating current suppression control is found to impact the MMC operating range. The maximum modulation index reduction is calculated utilizing a decoupled MMC model. A four-terminal HVDC testbed is developed, with similar control and communication architectures of the practical projects implemented. Several most typical operation scenarios and controls are demonstrated or proposed. In order to allow HVDC disconnects to online trip a line, dc line current control is proposed through station control. Utilizing the dc line current control, an automatic dc line current limiting control is proposed. Both controls have been verified in the developed testbed. A systematic dc fault protection strategy of MTDC utilizing hybrid dc circuit breaker is developed, including a new fast and selective fault detection method taking advantage of the hybrid dc circuit breaker special operation mechanism. Detailed criteria and control methods to assist system recovery are presented. A novel fault tolerant MMC topology is proposed with a hybrid submodule by adding an ultra-fast mechanical switch. The converter power loss can be almost the same as the half-bridge MMC, and 1/3 reduction compared to the similar clamp-double topology.

Design, Control and Application of Modular Multilevel Converters for HVDC Transmission Systems is a comprehensive guide to semiconductor technologies applicable for MMC design, component sizing control, modulation, and application of the MMC technology for HVDC transmission. Separated into three distinct parts, the first offers an overview of MMC technology, including information on converter component sizing, Control and Communication, Protection and Fault Management, and Generic Modelling and Simulation. The second covers the applications of MMC in offshore WPP, including planning, technical and economic requirements and optimization options, fault management, dynamic and transient stability. Finally, the third chapter explores the applications of MMC in HVDC transmission and Multi Terminal configurations, including Supergrids. Key features: Unique coverage of the offshore application and optimization of MMC-HVDC schemes for the export of offshore wind energy to the mainland. Comprehensive explanation of MMC application in HVDC and MTDC transmission technology. Detailed description of MMC components, control and modulation, different modeling approaches, converter dynamics under steady-state and fault contingencies including application and housing of MMC in HVDC schemes for onshore and offshore. Analysis of DC fault detection and protection technologies, system studies required for the integration of HVDC terminals to offshore wind power plants, and commissioning procedures for onshore and offshore HVDC terminals. A set of self-explanatory simulation models for HVDC test cases is available to download from the companion website. This book provides essential reading for graduate students and researchers, as well as field engineers and professionals who require an in-depth understanding of MMC technology.

HVDC grids and super grids have sparked so much interest these days that researchers and engineers across the globe are talking about them, studying them, supporting them, or questioning them. This book provides valuable information for researchers, industry, and policy makers. It explains why HVDC is favorable over AC technologies for power transmission; what the key technologies and challenges are for developing an HVDC grid; how an HVDC grid will be designed and operated; and how future HVDC grids will evolve. The book also devotes significant attention to nontechnical aspects such as the influence of energy policy and regulatory frameworks.This book is a result of collaboration between industry and academia. It provides theoretical insights into the design and control of MMC technology and investigates practical aspects of the project planning, design, manufacture, implementation, and commissioning of MMC-HVDC and multi-terminal HVDC transmission technologies; filling the knowledge gap between the technology specialists and VSC-HVDC project developers and key personnel involved in those projects.

This book discusses HVDC grids based on multi-terminal voltage-source converters (VSC), which is suitable for the connection of offshore wind farms and a possible solution for a continent wide overlay grid. HVDC Grids: For Offshore and Supergrid of the Future begins by introducing and analyzing the motivations and energy policy drives for developing offshore grids and the European Supergrid. HVDC transmission technology and offshore equipment are described in the second part of the book. The third part of the book discusses how HVDC grids can be developed and integrated in the existing power system. The fourth part of the book focuses on HVDC grid integration, in studies, for different time domains of electric power systems. The book concludes by discussing developments of advanced control methods and control devices for enabling DC grids. Presents the technology of the future offshore and HVDC grid Explains how offshore and HVDC grids can be integrated in the existing power system Provides the required models to analyse the different time domains of power system studies: from steady-state to electromagnetic transients This book is intended for power system engineers and academics with an interest in HVDC or power systems, and policy makers. The book also provides a solid background for researchers working with VSC-HVDC technologies, power electronic devices, offshore wind farm integration, and DC grid protection.

Presents the latest developments in switchgear and DC/DC converters for DC grids, and includes substantially expanded material on MMC HVDC This newly updated edition covers all HVDC transmission technologies including Line Commutated Converter (LCC) HVDC; Voltage Source Converter (VSC) HVDC, and the latest VSC HVDC based on Modular Multilevel Converters (MMC), as well as the principles of building DC transmission grids. Featuring new material throughout, High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition offers several new chapters/sections including one on the newest MMC converters. It also provides extended coverage of switchgear, DC grid protection and DC/DC converters following the latest developments on the market and in research projects. All three HVDC technologies are studied in a wide range of topics, including: the basic converter operating principles; calculation of losses; system modelling, including dynamic modelling; system control; HVDC protection, including AC and DC fault studies; and integration with AC systems and fundamental frequency analysis. The text includes: A chapter dedicated to hybrid and mechanical DC circuit breakers Half bridge and full bridge MMC: modelling, control, start-up and fault management A chapter dedicated to unbalanced operation and control of MMC HVDC The advancement of protection methods for DC grids Wideband and high-order modeling of DC cables Novel treatment of topics not found in similar books, including SimPowerSystems models and examples for all HVDC topologies hosted by the 1st edition companion site. High Voltage Direct Current Transmission: Converters, Systems and DC Grids, 2nd Edition serves as an ideal textbook for a graduate-level course or a professional development course.

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.

This book discusses key techniques of protection and fault ride-through in VSC-HVDC grids, including high-speed selective protection, DC fault current limitation, converter restarting, and DCCB reclosing strategies. It investigates how high-speed transient-variable-based protection can be used to improve grids’ acting sensitivity, acting reliability, and ability to withstand high transition resistance compared with traditional protection. In addition, it discusses the applicability of the pilot protections, including the current differential protection and travelign-wave based protection, in the dc grid, as well as the improved methods. Furthermore, it proposes several DC FCL topologies, which are suitable for DC grids. Lastly, in the context of overhead line application conditions, it explores converter restarting and DCCB reclosing strategies, which not only identify the fault property, but also limit the secondary damage to the system, improving the system’s operation security and reliability. As such, the book offers a comprehensive overview of original and advanced methods and techniques for the protection of VSC-HVDC grids.

In recent years, there have been considerable efforts in the design and development of technologies and techniques for more efficient harvesting of renewable energy resources to meet the ever increasing electric power demand and to limit the use of fossil fuels. In this regard, offshore wind farms have emerged as a promising solution, particularly in the North Sea, due to the vast potential of offshore wind energy. Large-scale offshore wind farms in the North Sea pose grid integration challenges such as the need for long distance submarine power transmission and managing the harvested wind energy. These challenges can be properly addressed by developing of Multi terminal dc (MTDC) systems. Future MTDC grids are expected to be built overlaying the present ac grids as well as harvesting offshore wind to build so-called "Supergrid" The work presented in this dissertation is oriented to facilitate the control and operation of future MTDC grids. The proposed approaches rely on hierarchical control architecture, inspired by the well-established automatic generation control (AGC) strategy have applied to ac grids. In the inspired hierarchical control architecture, the primary control of the MTDC grid is totally decentralized and implemented using the proposed Generalized Voltage Droop (GVD) control strategy. GVD proposes an alternative to the conventional voltage droop characteristics of voltage-regulating VSC stations, providing more generic and flexible control solution that takes into account the states of the converter stations and the ac+dc grid. The GVD control strategy can perform three different control modes, including conventional voltage droop control, fixed active power control, and fixed dc voltage control, by adjusting the GVD characteristics of the voltage-regulating converters. Such adjustment is driven by the secondary layer of the proposed hierarchical control structure. The proposed strategy improves the control and power-sharing capabilities of the conventional voltage drop, and enhances its maneuverability. This dissertation also addresses the tuning of the controllers of VSC-HVDC stations, by providing a methodology for optimized tuning of the parameters that influence their behavior. Since the VSC stations are nonlinear plants in nature, the classical approaches for tuning of the control system, which are usually based on the approximate linear model of the plants, do not lead to optimal results. Refereeing to the successful application of particle swarm optimization (PSO) algorithm in the tuning of ac grids parameters, this algorithm again is used to find optimal control parameters of VSC-HVDC stations in MTDC grids. As the last part of the proposed hierarchical control structure, the secondary control is centralized and it regulates the operating point of the grid so that optimal power flow (OPF) is achieved. In the proposed approach, an OPF algorithm is executed at the secondary control level of the MTDC grid to find the optimal reference values for the dc voltages and active power of the voltage-regulating converters. Then, at the primary control level, the GVD characteristics of the voltage-regulating converters are tuned based upon the OPF results. Via this control structure, the optimally-tuned GVD controllers lead to the optimal operation of the MTDC grid. In case of variation in load or generation of the grid, a new stable operating point is achieved based on the GVD characteristics of converter stations. Then by executing a new OPF, the GVD characteristics are re-tuned for optimal operation of the MTDC grid.

This Master Thesis presents the modelling, control and simulation of a hybrid multi-terminal High Voltage Direct Current (HVDC) grid. This network is composed by two point-to-point lines linked by a DC/DC converter. One point-to-point line is based on Line-Commutated Converters (LCC) and the other one is based on Voltage Source Converters (VSC), modeled as Modular Multilevel Converters (MMC). These two technologies are the most used ones in HVDC. The DC/DC converters chosen to analyze the multi-terminal grid are the Front-to-Front MMC and the DC-MMC. In order to achieve the final multi-terminal HVDC grid, the basics of both HVDC technologies are studied. It also includes the modelling, control and simulation of two point-to-point lines. One for LCC technology and the other one for VSC technology. The principles of DC/DC converters are also studied, including the modelling and control of a Front-to-Front MMC converter and a DC-MMC converter. Finally, simulations of the multi-terminal grid are performed with Matlab Simulink in di↵erent scenarios, including four cases for each DC/DC converter. In these di↵erent cases the DC/DC converter is placed regulating the DC voltage or controlling the power flow in the di↵erent point-to-point links.