A new modular multilevel converter for HVDC applications

In the coming years, due to an increasing shift towards electric mobility and further industrialisation, a rapid growth in the demand for electricity is expected. At the same time, this energy demand must be met in a clean and sustainable manner, to reduce climate change as well as to ensure security of supply. It is predicted that the High Voltage Direct Current (HVDC) transmission technology will play a key role in the future power systems which are expected to feature higher levels of interconnection and more renewable-based generation. HVDC transmission is preferred over AC transmission in applications such as power transmission over long distances and from offshore wind sources, and interconnection of asynchronous systems. The main elements of an HVDC system are the AC/DC converters that take up the majority of the initial set up cost, and therefore, there has been a huge focus lately on improving these converters in terms of functionality, cost and efficiency. Today, the state-of-the-art converter topology for Voltage Source Converters (VSC) based HVDC transmission is the Modular Multilevel Converter (MMC), which replaced the earlier two- and three-level VSC topologies. Recently, a new breed of VSC converters, known as the `hybrid VSCs' are introduced, that combine the aspects of two- and three-level VSCs with the modular multilevel structure of the MMC. In this work, a new hybrid VSC, the Switched Mid-Point Converter (SMPC), has been proposed. While maintaining the same efficiency as the MMC, the energy storage requirement of the SMPC is shown to be less than half of that of the MMC. The operating principle and the particular voltage waveshaping of the chainlinks of the submodules is investigated. For effective operation of the SMPC, suitable control strategies are proposed. The converter concept and the developed control schemes are verified both using computer simulations and a lab-scaled experimental prototype

A new modular multilevel converter for HVDC applications

In the coming years, due to an increasing shift towards electric mobility and further industrialisation, a rapid growth in the demand for electricity is expected. At the same time, this energy demand must be met in a clean and sustainable manner, to reduce climate change as well as to ensure security of supply. It is predicted that the High Voltage Direct Current (HVDC) transmission technology will play a key role in the future power systems which are expected to feature higher levels of interconnection and more renewable-based generation. HVDC transmission is preferred over AC transmission in applications such as power transmission over long distances and from offshore wind sources, and interconnection of asynchronous systems. The main elements of an HVDC system are the AC/DC converters that take up the majority of the initial set up cost, and therefore, there has been a huge focus lately on improving these converters in terms of functionality, cost and efficiency. Today, the state-of-the-art converter topology for Voltage Source Converters (VSC) based HVDC transmission is the Modular Multilevel Converter (MMC), which replaced the earlier two- and three-level VSC topologies. Recently, a new breed of VSC converters, known as the `hybrid VSCs' are introduced, that combine the aspects of two- and three-level VSCs with the modular multilevel structure of the MMC. In this work, a new hybrid VSC, the Switched Mid-Point Converter (SMPC), has been proposed. While maintaining the same efficiency as the MMC, the energy storage requirement of the SMPC is shown to be less than half of that of the MMC. The operating principle and the particular voltage waveshaping of the chainlinks of the submodules is investigated. For effective operation of the SMPC, suitable control strategies are proposed. The converter concept and the developed control schemes are verified both using computer simulations and a lab-scaled experimental prototype

Five-Level Flying Capacitor Converter used as a Static Compensator for Current Unbalances in Three-Phase Distribution Systems

This thesis presents and evaluates a solution for unbalanced current loading in three-phase distribution systems. The proposed solution uses the flying capacitor multilevel converter as its main topology for an application known as Unbalanced Current Static Compensator. The fundamental theory, controller design and prototype construction will be presented along with the experimental results. The Unbalanced Current Static Compensator main objective is the balancing of the up-stream currents from the installation point to eliminate the negative- and zero-sequence currents originated by unbalanced single-phase loads. Three separate single-phase flying capacitor converters are controlled independently using a d-q rotating reference frame algorithm to allow easier compensation of reactive power. Simulations of the system were developed in MATLAB/SIMULINK™ in order to validate the design parameters; then, testing of the UCSC prototype was performed to confirm the control algorithm functionality. Finally, experimental result are presented and analyzed

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Operation Analysis of Thyristor Based Front-to-Front Active-Forced-Commutated Bridge DC Transformer in LCC and VSC Hybrid HVDC Networks

The active-forced-commutated (AFC) bridge employs a symmetrical thyristor-bridge with auxiliary self-commutated full-bridge chain-link (FB-CL) circuit to assist its soft transition and forced commutation. This combination can form a thyristor based voltage source converter (VSC) with significantly reduced on-state losses and dc-fault blocking capability. Due to the full topological symmetry of the AFC-bridge, either current direction or dc-link voltage polarity can be reversed for power flow reversal as for the full-bridge modular multilevel converter (FB-MMC). Thus, the AFC-bridge is compatible with both line-commutated-converter (LCC) and VSC terminals in a multi-terminal high voltage direct current (MT-HVDC) network. This paper investigates its front-to-front (F2F) dc-dc application for matching the regional dc grids in a LCC and VSC hybrid HVDC network. Simulation studies are carried out to demonstrate its potentials as a high efficiency multi-functional solution for dc-dc conversion

Modular Multilevel Converters with Integrated Split Battery Energy Storage

The electric power grid is undergoing significant changes and updates nowadays, especially on a production and transmission level. Initially, the move towards a distributed generation in contrast to the existing centralized one implies a significant integration of renewable energy sources and electricity storage systems. In addition, environmental awareness and related concerns regarding pollutant emissions have given rise to a high interest in electrical mobility. Advanced power electronics interfacing systems are expected to play a key role in the development of such modern controllable and efficient large-scale grids and associated infrastructures. During the last decade, a global research and development interest has been stimulated in the field of modular multilevel conversion, due to the well-known offered advantages over conventional solutions in the medium- and high-voltage and power range. In the context of battery energy storage systems, the Modular Multilevel Converter (MMC) family exhibits an additional attractive feature, i.e., the capability of embedding such storage elements in a split manner, given the existence of several submodules operating at significantly lower voltages. This thesis deals with several technical challenges associated with Modular Multilevel Converters as well as their enhancement with battery energy storage elements. Initially, the accurate submodule capacitor voltage ripple estimation for a DC/AC MMC is derived analytically, avoiding any strong assumptions. This is beneficial for converter dimensioning purposes as well as for the implementation improvement of several control schemes, which have been proposed in the literature. The impact of unbalanced grid conditions on the operation and design of an MMC is then investigated, drawing important conclusions regarding the choice of line current control and required capacitive storage energy during grid faults. [...

Application of the cascaded multilevel inverter as a shunt active power filter

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Emerging Converter Topologies and Control for Grid Connected Photovoltaic Systems

Continuous cost reduction of photovoltaic (PV) systems and the rise of power auctions resulted in the establishment of PV power not only as a green energy source but also as a cost-effective solution to the electricity generation market. Various commercial solutions for grid-connected PV systems are available at any power level, ranging from multi-megawatt utility-scale solar farms to sub-kilowatt residential PV installations. Compared to utility-scale systems, the feasibility of small-scale residential PV installations is still limited by existing technologies that have not yet properly address issues like operation in weak grids, opaque and partial shading, etc. New market drivers such as warranty improvement to match the PV module lifespan, operation voltage range extension for application flexibility, and embedded energy storage for load shifting have again put small-scale PV systems in the spotlight. This Special Issue collects the latest developments in the field of power electronic converter topologies, control, design, and optimization for better energy yield, power conversion efficiency, reliability, and longer lifetime of the small-scale PV systems. This Special Issue will serve as a reference and update for academics, researchers, and practicing engineers to inspire new research and developments that pave the way for next-generation PV systems for residential and small commercial applications

Contributions to Modulation and Control Algorithms for Multilevel Converters

Las actuales tendencias de la red eléctrica han lanzado a la industria a la búsqueda de sistemas de generación, distribución y consumo de energía eléctrica más eficientes. Generación distribuida, reducción de componentes pasivos, líneas DC de alta tensión son, entre otras, las posibles líneas de investigación que están actualmente siendo consideradas como el futuro de la red eléctrica. Sin embargo, nada de esto sería posible si no fuera por los avances alcanzados en el campo de la electrónica de potencia. El trabajo aquí presentado comienza con una breve introducción a la electrónica de potencia, concretamente a los convertidores de potencia conectados a red, sus estrategias de control más comunes y enfoques ante redes desbalanceadas. A continuación, las contribuciones del autor sobre el control y modulación de una topología particular de convertidores, conocidos como convertidores multinivel, se presentan como el principal contenido de este trabajo. Este tipo de convertidores mejoran la eficiencia y ciertas prestaciones, en comparación con convertidores más tradicionales, a costa de una mayor complejidad en el control al incrementar la cantidad de los componentes hardware. A pesar de que existen numerosas topologías de convertidores multinivel y algunas de ellas son brevemente expuestas en este trabajo, la mayoría de las aportaciones están enfocadas para convertidores del tipo diode-clamped converter. Adicionalmente, se incluye una aportación para convertidores del tipo multinivel modular, y otra para convertidores en cascada. Se espera que el contenido de la introducción de este trabajo, junto a las contribuciones particulares para convertidores multinivel sirva de inspiración para futuros investigadores del campo

Review of Electric Vehicle Charging Technologies, Configurations, and Architectures

Electric Vehicles (EVs) are projected to be one of the major contributors to energy transition in the global transportation due to their rapid expansion. The EVs will play a vital role in achieving a sustainable transportation system by reducing fossil fuel dependency and greenhouse gas (GHG) emissions. However, high level of EVs integration into the distribution grid has introduced many challenges for the power grid operation, safety, and network planning due to the increase in load demand, power quality impacts and power losses. An increasing fleet of electric mobility requires the advanced charging systems to enhance charging efficiency and utility grid support. Innovative EV charging technologies are obtaining much attention in recent research studies aimed at strengthening EV adoption while providing ancillary services. Therefore, analysis of the status of EV charging technologies is significant to accelerate EV adoption with advanced control strategies to discover a remedial solution for negative grid impacts, enhance desired charging efficiency and grid support. This paper presents a comprehensive review of the current deployment of EV charging systems, international standards, charging configurations, EV battery technologies, architecture of EV charging stations, and emerging technical challenges. The charging systems require a dedicated converter topology, a control strategy and international standards for charging and grid interconnection to ensure optimum operation and enhance grid support. An overview of different charging systems in terms of onboard and off-board chargers, AC-DC and DC-DC converter topologies, and AC and DC-based charging station architectures are evaluated