Functional Description and Control Design of Modular Multilevel Converters:Towards Energy Storage Applications for Traction Networks

The security of supply is becoming an important concern in the energy supply of the railway networks operated at 16.7âHz. This situation calls for the improvement of the interconnection with the 50âHz grid and creates a need for ancillary services, especially in relation to power quality. To these ends, Modular Multilevel Converters (MMC) are highly attractive as they are ideally suited for the corresponding voltage and power levels and are sufficiently versatile to adapt easily to the numerous applications affected by these needs. Besides, there attractiveness can be further increased if energy storage is embedded inside the converters, which are then able to provide a broad range of ancillary services. Practically, such a perspective is enabled by the fact that the submodules can directly integrate storage in a distributed manner, essentially limiting design concerns to control issues. By 2014, MMCs have been adopted by most major power electronics manufacturers (ABB, Siemens, Alstom, etc.) and constitute a rapidly expanding topic, drawing the attention of numerous academic research groups worldwide. This illustrates the breakthrough represented by this technology, which is notably due to the fact that their modular nature imposes operating principles that are fundamentally different from those of conventional structures, but what also allows unprecedented flexibility and scalability. Being given the numerous ongoing industrial projects in relation to railways, the relevance of MMCs in these applications is already largely proven. However, the integration of split storage in MMCs has still received only little attention. This thesis will even propose the use of hybrid split storage, which has apparently not been studied at all. In both cases, the development of energy management mechanisms has apparently not been addressed yet and the control design as a whole is also limited to few developments only. On the other hand, there are already numerous control solutions for the cases without storage, among which it is sometimes difficult to make wise choices. In this context, before adding energy storage (and its associated management mechanisms) to already complex control problems, it is important to rely on a sound basis, what is the main motivation for this thesis to develop a set of tools that can allow to take a step back on the control design in general. Firstly, this thesis proposes different representations of MMCs, providing a macroscopic view of their behavior and allowing a new interpretation of their principles of operation. As it will be seen, these results are useful to both control design and system engineering purposes. Secondly, using the principles of the Energetic Macroscopic Representation (EMR), this work presents a methodology for the systematic control design of MMCs, based on the functional inversion of a system model. Finally, the obtained results are validated on known structures before being extended to other converter systems including energy storage. In parallel to these developments, several digressions are also made to comment on the issues related to the control hardware and on the possible applications of energy storage in railways. In the end, these developments are expected to contribute to improve the modularization of the control in general, which is one of the possible ways to provide maximum flexibility, speed and effectiveness in the overall design of MMC systems for all types of applications

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. [...

Power Quality in Electrified Transportation Systems

"Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts

Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering

A review on power electronics technologies for electric mobility

Concerns about greenhouse gas emissions are a key topic addressed by modern societies worldwide. As a contribution to mitigate such effects caused by the transportation sector, the full adoption of electric mobility is increasingly being seen as the main alternative to conventional internal combustion engine (ICE) vehicles, which is supported by positive industry indicators, despite some identified hurdles. For such objective, power electronics technologies play an essential role and can be contextualized in different purposes to support the full adoption of electric mobility, including on-board and off-board battery charging systems, inductive wireless charging systems, unified traction and charging systems, new topologies with innovative operation modes for supporting the electrical power grid, and innovative solutions for electrified railways. Embracing all of these aspects, this paper presents a review on power electronics technologies for electric mobility where some of the main technologies and power electronics topologies are presented and explained. In order to address a broad scope of technologies, this paper covers road vehicles, lightweight vehicles and railway vehicles, among other electric vehicles.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UID/CEC/00319/2020. This work has been supported by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017, and by the FCT Project new ERA4GRIDs PTDC/EEI-EEE/30283/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT

High Power, Medium Frequency, and Medium Voltage Transformer Design and Implementation

Many industrial applications that require high-power and high-voltage DC-DC conversion are emerging. Space-borne and off-shore wind farms, fleet fast electric vehicle charging stations, large data centers, and smart distribution systems are among the applications. Solid State Transformer (SST) is a promising concept for addressing these emerging applications. It replaces the traditional Low Frequency Transformer (LFT) while offering many advanced features such as VAR compensation, voltage regulation, fault isolation, and DC connectivity. Many technical challenges related to high voltage stress, efficiency, reliability, protection, and insulation must be addressed before the technology is ready for commercial deployment. Among the major challenges in the construction of SSTs are the strategies for connecting to Medium Voltage (MV) level. This issue has primarily been addressed by synthesizing multicellular SST concepts based on modules rated for a fraction of the total MV side voltage and connecting these modules in series at the input side. Silicon Carbide (SiC) semiconductor development enables the fabrication of power semiconductor devices with high blocking voltage capabilities while achieving superior switching and conduction performances. When compared to modular lower voltage converters, these higher voltage semiconductors enable the construction of single-cell SSTs by avoiding the series connection of several modules, resulting in simple, reliable, lighter mass, more power dense, higher efficiency, and cost effective converter structures. This dissertation proposes a solution to this major issue. The proposed work focuses on the development of a dual active bridge with high power, medium voltage, and medium frequency control. This architecture addresses the shortcomings of existing modular systems by providing a more power dense, cost-effective, and efficient solution. For the first time, this topology is investigated on a 700kW system connected to a 13kVdc input to generate 7.2kVdc at the output. The use of 10kV SiC modules and gate drivers in an active neutral point clamped to two level dual active bridge converter is investigated. A special emphasis will be placed on a comprehensive transformer design that employs a multi-physics approach that addresses all magnetic, electrical, insulation, and thermal aspects. The transformer is designed and tested to ensure the system’s viability

Design and Control of Power Converters 2019

In this book, 20 papers focused on different fields of power electronics are gathered. Approximately half of the papers are focused on different control issues and techniques, ranging from the computer-aided design of digital compensators to more specific approaches such as fuzzy or sliding control techniques. The rest of the papers are focused on the design of novel topologies. The fields in which these controls and topologies are applied are varied: MMCs, photovoltaic systems, supercapacitors and traction systems, LEDs, wireless power transfer, etc

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics