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. [...

Ageing Mitigation and Loss Control Through Ripple Management in Dynamically Reconfigurable Batteries

Dynamically reconfigurable batteries merge battery management with output formation in ac and dc batteries, increasing the available charge, power, and life time. However, the combined ripple generated by the load and the internal reconfiguration can degrade the battery. This paper introduces that the frequency range of the ripple matters for degradation and loss. It presents a novel control method that reduces the low-frequency ripple of dynamically reconfigurable battery technology to reduce cell ageing and loss. It furthermore shifts the residual ripple to higher frequencies where the lower impedance reduces heating and the dielectric capacitance of electrodes and electrolyte shunt the current around the electrochemical reactions.Comment: 8 pages, 8 figure

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

High-performance motor drives

This article reviews the present state and trends in the development of key parts of controlled induction motor drive systems: converter topologies, modulation methods, as well as control and estimation techniques. Two- and multilevel voltage-source converters, current-source converters, and direct converters are described. The main part of all the produced electric energy is used to feed electric motors, and the conversion of electrical power into mechanical power involves motors ranges from less than 1 W up to several dozen megawatts

Controlling Techniques for STATCOM using Artificial Intelligence

The static synchronous compensator (STATCOM) is a power electronic converter designed to be shunt-connected with the grid to compensate for reactive power. Although they were originally proposed to increase the stability margin and transmission capability of electrical power systems, there are many papers where these compensators are connected to distribution networks for voltage control and power factor compensation. In these applications, they are commonly called distribution static synchronous compensator (DSTATCOM). In this paper we have focussed on STATCOM and the controlling techniques which are based on artificial intelligence