Download or read book Modeling and Control of Modular Multilevel Converter Based on Ordinary Differential Equations and Its Applications for HVDC System written by Haihao Jiang and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "High-voltage direct current (HVDC) system is more efficient than high-voltage alternating current (HVAC) system for long-distance, bulk power transmission. Modularity, flexibility, reliability and high efficiency make the modular multilevel converter (MMC) the topology of choice in HVDC applications. Because the increasing number of installations shows that the MMC-HVDC is the HVDC of the future, this thesis is continuing research to advance the capability of the MMC-HVDC. This thesis focuses on fast simulation capability and control strategies for the MMC-HVDC. The main objectives are: (1) to develop a fast and accurate simulation model of a single MMC station and models of multi-terminal MMC-HVDC stations (MTDC-MMC); (2) to investigate the method to design proper parameters for high damping; (3) to design the MMC-HVDC with the capability of power oscillation damping (POD). Simulation is computation-intensive in MMC. The thesis develops a fast and accurate method by which an MMC station is modeled by ordinary differential equations (ODE). The proposed MMC ODE model is implemented in MATLAB SIMULINK and its correctness is validated by the MMC Detail Equivalent Model (DEM) in RT-LAB. Taking advantage of its speed and accuracy, a Four-Terminal MMC-HVDC system based on the MMC ODE model is developed. The ODE model meets the speed and accuracy requirements of power systems engineers who are concerned with planning, operation and protection studies. As the ordinary differential equations are nonlinear, small perturbation about a steady-state is applied to obtain the linearized time-periodic matrix. The steady-state takes a long time to simulate because it depends on the transients to have all damped out. The method of Aprille and Trick is applied. Simulation converges to the steady-state in one cycle of 50 Hz. The resultant linearized matrix is time-periodic. The Floquet-Lyapunov Theorem is applied to construct the state-transition matrix from the linearized time-periodic matrix. The eigenvalues of the state-transition matrix contain the coefficients of damping. Graphs of damping coefficients plotted against different sizes of circuit parameters are displayed to assist designers in realizing high damping. The thesis looks for opportunities to add value to the MMC-HVDC. The active power transmissibility of AC transmission lines is limited by the transient stability limit which is significantly below the thermal limit. Extensive research and development have been pursued to increase the transient stability limit by flexible AC transmissions system (FACTS). This thesis seeks to use the MMC-HVDC to operate as power oscillation damper to increase the power transmissibility. The thesis looks for opportunities to integrate previously proven control methods into a common universal control. The Universal Controller brings together the deadbeat control, the circulating current suppression control (CCSC), the POD and the decoupled P-Q strategy in the control of the MMC-HVDC station by the MMC ODE model. Deadbeat control enables the MMC to survive destructively large AC fault currents to improve the transient stability of AC grids"--

Download or read book Modular Multilevel Converters written by Sixing Du and published by John Wiley & Sons. This book was released on 2018-01-11 with total page 360 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Design Control and Application of Modular Multilevel Converters for HVDC Transmission Systems written by Kamran Sharifabadi and published by John Wiley & Sons. This book was released on 2016-08-22 with total page 522 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Modular Multilevel Converter Modelling and Simulation for HVDC Systems written by Davide del Giudice and published by Springer Nature. This book was released on 2022-10-21 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive review of the models and approaches that can be employed to simulate modular multilevel converters (MMCs). Each solution is described in terms of operating principle, fields of applicability, advantages, and limitations. In addition, this work proposes a novel and efficient simulation approach for MMCs based on sub-circuit isomorphism. This technique, which has its roots in the electronics fields, can be profitably exploited to simulate MMCs regardless of the model used to describe its sub-modules, including the most accurate ones. Lastly, this book considers a well-known high voltage direct current (HVDC) benchmark system consisting of two MMCs. After describing the implementation details of each benchmark component, simulation results in several scenarios (ranging from normal operating conditions to faults in the AC and DC grid) are included to validate the proposed approach and showcase its key features. Due to its educational content, this book constitutes a useful guide for PhD students and researchers interested in the topic of MMCs and their simulation. It also serves as a starting platform for junior electrical engineers who work in the field of power electronic converters for HVDC systems.

Download or read book Design Modeling and Control of Modular Multilevel Converter Based HVDC Systems written by Ghazal Falahi and published by . This book was released on 2015 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modular Multilevel Converters written by Fujin Deng and published by John Wiley & Sons. This book was released on 2023-03-29 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: Modular Multilevel Converters Expert discussions of cutting-edge methods used in MMC control, protection, and fault detection In Modular Multilevel Converters: Control, Fault Detection, and Protection, a team of distinguished researchers delivers a comprehensive discussion of fault detection, protection, and tolerant control of modular multilevel converters (MMCs) under internal and external faults. Beginning with a description of the configuration of MMCs, their operation principles, modulation schemes, mathematical models, and component design, the authors go on to explore output control, fault detection, capacitor monitoring, and other topics of central importance in the field. The book offers summaries of centralized capacitor voltage-balancing control methods and presents several capacitor monitoring methods, like the direct and sorting-based techniques. It also describes full-bridge and half-bridge submodule-based hybrid MMC protection methods and alternative fault blocking SM-based MMCs. Readers will also find: A thorough introduction to modular multilevel converters, including circuits, operation principles, modulation, mathematical models, components, and design constraints In-depth discussions of the control of modular multilevel converters, including output control, centralized capacitor voltage control, and individual capacitor voltage control Comprehensive explorations of fault detection of MMCs under IGBT faults, including short-circuit and open-circuit faults, as well as fault-tolerant control of MMCs Fulsome treatments of the control of MMCs under AC grid faults, including discussions of AC-side current control Perfect for electrical engineering researchers, Modular Multilevel Converters: Control, Fault Detection, and Protection, will also earn a place in the libraries of electrical engineers working in industry, as well as undergraduate and graduate students with an interest in MMCs.

Download or read book Modular Multilevel Converters with Interleaved Half Bridge Submodules written by Aleksandr Viatkin and published by Springer Nature. This book was released on 2023-03-29 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports on a comprehensive study on a novel high-power converter, i.e. a Modular Multilevel Converter with Interleaved Half-bridge Submodules (ISM-MMC). It describes in depth its average model, the operating principles, as well as a new control method and a hybrid modulation strategy that help to exploit the benefits of the interleaving scheme. The new power converter is particularly advantageous for high-current applications that require superb quality of input/output waveforms. Moreover, this book reports on a systematic study of the current balancing problem between parallel-connected units that commutate in non-simultaneous fashion. This is a typical issue in interleaved converters, however here it is analyzed for the first time in relation to MMC-based structures. Two control strategies are proposed to cope with this matter. By using a sensorless regulation scheme, the number of required current transducers has been minimized, reducing complexity, cost, and footprint of the hardware, while providing converter with a fast and accurate current balancing. This book also offers a comprehensive comparison between several practical designs of ISM-MMC and classical MMC for an ultra-fast electrical vehicle charger. All in all, it provides graduate students and researchers, as well as field engineers and professionals with extensive information and essential practical details on the state-of-the-art MMC and ISM-MMC design.

Download or read book Efficient Modeling of Modular Multilevel HVDC Converters MMC on Electromagnetic Transient Simulation Programs written by Udana Gnanarathna and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent introduction of a new converter topology, the modular multilevel converter (MMC) is a major step forward in voltage sourced converter (VSC) technology for high voltage, high power applications. To obtain a multilevel ac output waveform, a large number of semiconductor switches has to be used in the converter. The number of switches in the MMC for HVDC transmission is typically two orders of magnitudes larger than that in a two or three level VSC used in earlier generation. This large device count creates a computational challenge for electromagnetic transients (EMT) simulation programs, as it significantly increases the simulation time. The purpose of this research is to investigate whether the simulation can be speeded up. This research develops an efficient, time-varying Thévenin's equivalent model for the MMC converter based on partitioning the system's admittance matrix. EMT simulation results show that the proposed equivalent model can drastically reduce the computational time without loss of accuracy. The use of the proposed equivalent method is demonstrated by simulating a point to point MMC based HVDC transmission system successfully with more than 100 levels. This approach enables what was hitherto not practical; the modeling of large MMC based HVDC systems on personal computers. With the assumption of ideal switch operation and using an equivalent average capacitor value based approach, an average valued model of MMC is also proposed in this thesis. The average model can be accurately used in most of the system level studies. The control algorithms and other modeling aspects of MMC applications are also presented in this thesis. One of the advantages of multilevel converters is the low operating losses as the smaller switching frequency of each individual power electronics switch and the low voltage step change during each switching. Using a recently developed, time domain simulation approach, the operating losses of the MMC converter are estimated in this thesis. When comparing the MMC operating losses against the losses of two-level VSC, the power loss for the two-level VSC is found to be significantly higher than the power loss of the MMC.

Download or read book Dynamics and Control of Switched Electronic Systems written by Francesco Vasca and published by Springer Science & Business Media. This book was released on 2012-03-28 with total page 493 pages. Available in PDF, EPUB and Kindle. Book excerpt: The increased efficiency and quality constraints imposed on electrical energy systems have inspired a renewed research interest in the study of formal approaches to the analysis and control of power electronics converters. Switched systems represent a useful framework for modeling these converters and the peculiarities of their operating conditions and control goals justify the specific classification of “switched electronic systems”. Indeed, idealized switched models of power converters introduce problems not commonly encountered when analyzing generic switched models or non-switched electrical networks. In that sense the analysis of switched electronic systems represents a source for new ideas and benchmarks for switched and hybrid systems generally. Dynamics and Control of Switched Electronic Systems draws on the expertise of an international group of expert contributors to give an overview of recent advances in the modeling, simulation and control of switched electronic systems. The reader is provided with a well-organized source of references and a mathematically-based report of the state of the art in analysis and design techniques for switched power converters. Intuitive language, realistic illustrative examples and numerical simulations help the reader to come to grips with the rigorous presentation of many promising directions of research such as: converter topologies and modulation techniques; continuous-time, discrete-time and hybrid models; modern control strategies for power converters; and challenges in numerical simulation. The guidance and information imparted in this text will be appreciated by engineers, and applied mathematicians working on system and circuit theory, control systems development, and electronic and energy conversion systems design.

Download or read book Analytical Efficiency Evaluation of Modular Multilevel Converter MMC for High Voltage Direct Current System HVDC written by Ehtasham Mustafa and published by GRIN Verlag. This book was released on 2016-02-25 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master's Thesis from the year 2014 in the subject Electrotechnology, University of Peshawar (University of Engineering and Technology, Peshawar, Pakistan), course: High Voltage Direct Current, language: English, abstract: Modular Multilevel Converter (MMC) has become the most concerned converter topology in the High Voltage Direct Current (HVDC) transmission system, in recent times. The low switching frequency, low converter losses and flexible control made it most attractive topology. It is important to make a research on the loss calculation method of MMC and state formulae for the losses as it is a vital step during the design stage of the MMC based HVDC system. In this research work, the structure of MMC based HVDC system is discussed. Three sub module topologies’; half bridge, full bridge and clamp double sub module, are discussed. A method based on the average and root mean square (RMS) values of the current passing through the sub module is discussed. The conversion losses in the switching devices of the sub modules are calculated using the method. A cases study is taken into consideration then with certain parameters. Using these parameters a MATLAB program is developed. With the help of the program the losses and efficiency curves for each switching device by taking each sub module separately are obtained respectively. A comparison of the losses and efficiency of each sub module is also discussed. At the end those factors which effect the losses and efficiency of the sub module are discussed along with the certain aspects for the directions of future work.

Download or read book High Voltage Direct Current Transmission written by Dragan Jovcic and published by John Wiley & Sons. This book was released on 2019-08-26 with total page 565 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Multilevel Converters written by Salman Ahmad and published by John Wiley & Sons. This book was released on 2024-07-03 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Discover the deep insights into the operation, modulation, and control strategies of multilevel converters, alongside their recent applications in variable speed drives, renewable energy generation, and power systems. Multilevel converters have gained attention in recent years for medium/high voltage and high power industrial and residential applications. The main advantages of multilevel converters over two level converters include less voltage stress on power semiconductors, low dv/dt, low common voltage, reduced electromagnetic interference, and low total harmonics distortion, among others. Better output power quality is ensured by increasing the number of levels in the synthesized output voltage waveform. Several multilevel topologies have been reported in the literature, such as neutral point clamped (NPC), flying capacitor (FC), cascaded H-bridge (CHB), hybrid cascaded H-bridge, asymmetrical cascaded H-bridge, modular multilevel converters (MMC), active neutral point clamped converters (ANPC), and packed U-cell type converters and various reduced device counts and a reduced number of source-based topologies have been proposed in literature. The multilevel converter, although a proven and enabling technology, still presents numerous challenges in topologies, modulation, and control, as well as in need-based applications. Since multilevel converters offer a wide range of possibilities, research and development in the areas of multilevel converter topologies, modulation, and control in various applications are still growing. To further improve multilevel converter energy efficiency, reliability, power density, and cost, many research groups across the world are working to broaden the application areas of multilevel converters and make them more attractive and competitive compared to classic topologies. Multilevel Converters intends to provide deep insight about multilevel converter operation, modulation, and control strategies and various recent applications of multilevel converters such as in variable speed drives, renewable energy generation, and power systems.

Download or read book Topology and Control of Transformer less Modular Multilevel DC DC Converters for HVDC Grid Application written by Fei Zhang and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "A high-voltage direct current (HVDC) system is more efficient at transmitting power over long distances than a high-voltage alternating current (HVAC) system. With the increase in renewable energy integration, HVDC technology is more important for the efficient integration of distributed energy sources (DERs) into grids. The features of a modular multilevel converter (MMC) make it the topology of choice for high-power applications for HVDC systems. To interconnect DC networks with different voltage levels, a DC-DC converter is a crucial component that plays the role of the AC transformer in the AC system. This thesis focuses on the topology of a transformer-less MMC DC-DC converter for HVDC grid applications and its control strategy. The main objective of the thesis is to develop a fully switch-based MMC DC-DC topology without using a transformer or passive filters. The proposed topologies have a hybrid combination of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs). Moreover, by taking advantage of both HBSMs and FBSMs, the proposed MMC DC-DC converter has the DC fault ride-through capability, which is necessary in DC systems. A family of transformer-less hybrid MMC DC-DC converters with T-type connections is investigated. The optimal selection rules of the submodule (SM) type, based on switch utilization and DC fault blocking capability, are evaluated under different voltage conversion ratios. A modified topology is also investigated to reduce the circulating current that balances the energy between the arms, which has delta-connected FBSMs to simultaneously maintain the unity power operation of the arms with HBSMs and the DC fault ride-through capability. In addition to the topology of an MMC DC-DC converter, a control strategy based on the model predictive control (MPC) of the MMC is presented. A voltage-level based MPC is proposed to address the issue of the large computational burden of conventional MPC used in MMC applications. Instead of directly selecting the switching states, the proposed predictive control has a hierarchical structure that first selects the optimal voltage level by assuming that the capacitor voltage of all SMs is balanced and then balances the capacitor voltages by using a separate control loop. The proposed predictive control is applied to the MMC DC-DC converter to guarantee the converter's fast response during transient operation.The performance of the proposed topology and control strategy is validated using both real-time simulation and a lab-scale, experimental test bench." --

Download or read book Multi terminal High voltage Converter written by Bo Zhang and published by John Wiley & Sons. This book was released on 2018-10-19 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Modular Multilevel Converters for Electric Transportation Applications written by Deepak Ronanki and published by Wiley. This book was released on 2025-01-21 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview of the fundamentals, the technical challenges, and the control aspects of modular multilevel converters Modular multilevel converters (MMCs) have emerged in recent years as the newest breed of multilevel converters, and have received wide acceptance both in industry and academia. The benefits and desirable features of MMCs are manifold: modularity, high-quality output waveforms, absence of dc-link capacitance, and lower electromagnetic interference. MMCs rely on transformerless operation and can be a multi-motor operation, so it can be scaled to higher power and voltage levels—resulting in high efficiency—and tolerate faults to a greater degree than other systems. Modular Multilevel Converter offers a uniquely wide range of topics relating to MMCs, from electrical machines, to control theory, to electronics and power electronics. The book provides the reader with information to strengthen their understanding of basic concepts, as well as the latest technologies in propulsion systems, power supplies, and battery charging infrastructure. The scope of this resource is comprehensive with detailed discussions on different submodule design, diverse modeling approach, pulse width modulation schemes, and voltage balancing methods. It also examines charge-balancing control techniques, circulating current suppressing control schemes, and reliability enhancement features. Most significantly, the text reflects the latest technologies in electric transportation—electric railway traction, battery-charging infrastructure, and marine applications—and is aligned to current industry requirements. Modular Multilevel Converter readers will also find: Discussion of the fundamentals and important concepts with the simulations in PLECS® platform and OPAL-RT® real-time digital simulator. Coverage of the global standards such as IEC and IEEE for each application and their requirements A series of case studies that highlight aspects of MMC application A companion website that provides self-explanatory demo-simulation models of MMC with different variants of carrier-based pulse width modulation schemes Modular Multilevel Converter isa useful reference for academic researchers, design engineers, graduate courses, and other professionals in the field of electric transportation.

Download or read book Design Analysis and Operation of Hybrid Modular Multilevel Converters for HVDC Applications written by Zeng Rong and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis investigates the design, analysis, and operation of modular multilevel converters (MMC) for HVDC applications. Based on the operation principles of the MMC, the operation of MMC under asymmetrical arm impedance conditions is analysed using three equivalent sub-circuits at different freqeuncy. Detail analysis of the impact of asymmetrical conditions on the differential-mode current, the common-mode current and sub-module (SM) capacitor voltages, is performed. Based on the analysis, the corresponding control targets and an improved control strategy are designed to improve the operation performance. Considering the advantages of half-bridge based SM (HBSM) and full-bridge based SM (FBSM), a hybrid MMC (H-MMC) configuration consisting of FBSMs and HBSMs is proposed. By adopting the negative voltage state for some of the FBSMs, the output voltage range is extended to increase converter power transmission capability. By considering the relationships between the AC and DC voltages, AC, DC and arm currents, the ratio of the numbers of the FBSM to HBSM is analysed in order to maintain capacitor voltage balance and retain DC fault blocking capability. An equivalent circuit for the H-MMC is proposed, which considers each arm to be consisted of two individual voltage sources. This model is used to analyse SM capacitor voltage balancing and ripple. A two-stage selection and sorting algorithm is developed to ensure capacitor voltage balancing among the SMs. The proposed H-MMC is compared to other topologies in terms of power device utilization and power losses, and it shows that the H-MMC has higher device utilization and lower power loss than the conventional FBSM based MMC; Furthermore, The DC fault ride-through capability of the H-MMC are discussed. It is found that the H-MMC can not only isolate the DC fault, but also coniture operating at a wide DC voltage range from zero to rated value. Such two features of the H-MMC show the advantages in the hybrid configurations over the conventional FBSM and HBSM systems. Finally, two applications based on the proposed H-MMC are presented; one is a high power DC/DC converter with fault blocking capability for interconnecting large HVDC systems, and the other is a hybrid HVDC transmission system comprising a wind farm side VSC based on the H-MMC and a grid side LCC for transmitting wind power to AC grid.

Download or read book Modular Multilevel Converters with Multi frequency Power Transfer written by Yuan Li and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The MMC is the dominant voltage-sourced converter technology for HVDC systems including terrestrial power transmission and offshore wind power integration. It is also a state-of-the-art solution for emerging MVDC applications such as bipolar dc distribution and grid integration of renewable energy resources. Significant research has been recently targeting the development of new MMC-based topologies that can reap the benefits of the conventional dc-ac MMC in dc grids and hybrid ac/dc power systems. Notable examples include dc-dc converters, multi-port converters, line power flow controllers and power tapping stations. This thesis introduces the concept of multi-frequency power transfer in MMCs where the magnetics windings are multi-tasked to carry currents with multiple frequency components, namely dc and fundamental frequency. Core dc flux cancellation is imposed by appropriate orientation of the individual windings. This novel power transfer mechanism can eliminate redundant energy conversion through partial-power-processing while offering increased flexibility in converter port power flows. Based on the multi-frequency power transfer concept, new MMC-based topologies are proposed that are well suited for MVDC and HVDC grids and hybrid ac/dc systems. Firstly, a new class of single-stage modular multilevel dc-dc converter, termed the M2DC-CT, is proposed for applications requiring either high or low dc stepping ratios. By placing center-tapped transformer windings in series with the arms in each phase leg, the advantages of minimized ac arm currents and absence of dc voltage stress between windings are simultaneously obtained unlike in prior art. Modeling and analysis gives insight into the M2DC-CT multi-frequency power transfer characteristics and suitable converter controls are developed. Converter operation is validated through simulation and experiment. %The M2DC-CT is further extended into a three-port converter by addition of a grid side transformer winding. Secondly, a dual MMC structure is presented that achieves multi-frequency power transfer by tying together the three mid-points of the converter-side center-tapped transformer windings to form an additional dc port. This creates a bipolar MMC with the ability to balance the dc pole power flows in bipolar dc grids. The employed center-tapped transformer has a Volt-Ampere rating that is the same as a conventional grid interfacing transformer. Dynamic controls formulated in the $\alpha\beta$-frame provide tight regulation of the port power flows while ensuring balanced capacitor voltages. The independent pole balancing capability is confirmed through simulation of detailed MVDC-level and HVDC-level PSCAD models and rigorous experimental testing on a scaled-down laboratory prototype. Thirdly, the aforementioned multi-frequency dual MMC structure is proposed for use as a three-port MMC. It allows simultaneous dc-dc and dc-ac conversions between an ac grid and two dc systems, which is distinctly different from the earlier bipolar dc grid application. The $\alpha\beta$ controls developed earlier are easily extended for the three-port application by assigning appropriate reference signals. Steady-state and dynamic operation of the three-port dual MMC topology is validated by simulation with a HVDC-level PSCAD model and extensive experimental tests. Lastly, a detailed comparative assessment of three-port MMCs for high-power applications is conducted. The proposed three-port dual MMC structure and three-port version of the M2DC-CT are compared against two other existing three-port MMCs, on the basis of efficiency, semiconductor effort, internal energy storage and magnetics. Both MVDC and HVDC case studies are examined including several different power flow cases, with provisions for fault blocking. The results indicate the use of multi-frequency power transfer can enable significant reductions in converter operating losses and cost relative to prior art, depending on the application.