Bisection Algorithm based Indirect Finite Control Set Model Predictive Control for Modular Multilevel Converters

In this work, an idea based on the bisection algorithm is used to reduce the computational burden of indirect finite control set model predictive control (FCS-MPC) for modular multilevel converters (MMCs). The proposed method greatly reduces the search space for reaching the optimal insertion index (number of submodules to be inserted). Therefore, the strategy proposed offers similar steady-state and dynamic performance compared to full indirect FCS-MPC at a much lower computational burden. A new cost function is also proposed for indirect FCS-MPC which eliminates the need for an outer loop or additional control of differential current to regulate the summation voltages in each arm. The results of the proposed strategy are validated through simulations in MATLAB/Simulink.acceptedVersio

New configurations of power converters for grid interconnection systems

The increased penetration of renewable energy sources and other distributed energy sources has been seen nowadays. In this scenario power converters play a crucial role by providing the interconnection of these energy sources. This paper presents new configurations of power converters for grid interconnection systems. Several topologies are analyzed which are based on isolated ac-ac matrix converters

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

A New MMC Topology Which Decreases the Sub Module Voltage Fluctuations at Lower Switching Frequencies and Improves Converter Efficiency

Modular Multi-level inverters (MMCs) are becoming more common because of their suitability for applications in smart grids and multi-terminal HVDC transmission networks. The comparative study between the two classic topologies of MMC (AC side cascaded and DC side cascaded topologies) indicates some disadvantages which can affect their performance. The sub module voltage ripple and switching losses are one of the main issues and the reason for the appearance of the circulating current is sub module capacitor voltage ripple. Hence, the sub module capacitor needs to be large enough to constrain the voltage ripple when operating at lower switching frequencies. However, this is prohibitively uneconomical for the high voltage applications. There is always a trade off in MMC design between the switching frequency and sub module voltage ripple

Design and Advanced Model Predictive Control of Wide Bandgap Based Power Converters

The field of power electronics (PE) is experiencing a revolution by harnessing the superior technical characteristics of wide-band gap (WBG) materials, namely Silicone Carbide (SiC) and Gallium Nitride (GaN). Semiconductor devices devised using WBG materials enable high temperature operation at reduced footprint, offer higher blocking voltages, and operate at much higher switching frequencies compared to conventional Silicon (Si) based counterpart. These characteristics are highly desirable as they allow converter designs for challenging applications such as more-electric-aircraft (MEA), electric vehicle (EV) power train, and the like. This dissertation presents designs of a WBG based power converters for a 1 MW, 1 MHz ultra-fast offboard EV charger, and 250 kW integrated modular motor drive (IMMD) for a MEA application. The goal of these designs is to demonstrate the superior power density and efficiency that are achievable by leveraging the power of SiC and GaN semiconductors. Ultra-fast EV charging is expected to alleviate the challenge of range anxiety , which is currently hindering the mass adoption of EVs in automotive market. The power converter design presented in the dissertation utilizes SiC MOSFETs embedded in a topology that is a modification of the conventional three-level (3L) active neutral-point clamped (ANPC) converter. A novel phase-shifted modulation scheme presented alongside the design allows converter operation at switching frequency of 1 MHz, thereby miniaturizing the grid-side filter to enhance the power density. IMMDs combine the power electronic drive and the electric machine into a single unit, and thus is an efficient solution to realize the electrification of aircraft. The IMMD design presented in the dissertation uses GaN devices embedded in a stacked modular full-bridge converter topology to individually drive each of the motor coils. Various issues and solutions, pertaining to paralleling of GaN devices to meet the high current requirements are also addressed in the thesis. Experimental prototypes of the SiC ultra-fast EV charger and GaN IMMD were built, and the results confirm the efficacy of the proposed designs. Model predictive control (MPC) is a nonlinear control technique that has been widely investigated for various power electronic applications in the past decade. MPC exploits the discrete nature of power converters to make control decisions using a cost function. The controller offers various advantages over, e.g., linear PI controllers in terms of fast dynamic response, identical performance at a reduced switching frequency, and ease of applicability to MIMO applications. This dissertation also investigates MPC for key power electronic applications, such as, grid-tied VSC with an LCL filter and multilevel VSI with an LC filter. By implementing high performance MPC controllers on WBG based power converters, it is possible to formulate designs capable of fast dynamic tracking, high power operation at reduced THD, and increased power density

Novel DC Capacitor Voltage Balancing Strategy of Modular Multilevel Converter based STATCOM for Reactive Power Compensation and Voltage Improvement

In recent years, the integration of renewable energy sources and their unpredictable nature has posed significant challenges to power grid stability and voltage regulation. To address these issues, the Modular Multilevel Converter (MMC) based Static Synchronous Compensator (Statcom) has emerged as a promising solution for reactive power compensation and voltage improvement. However, one critical concern in MMC-Statcom operation is the voltage balancing of DC capacitors, which directly affects system performance and efficiency. In this research, a novel DC capacitor voltage balancing strategy is proposed for MMC-Statcom to ensure optimal operation and enhanced performance. The proposed strategy employs advanced control algorithms and innovative switching techniques to maintain balanced DC capacitor voltages under varying operating conditions. By achieving balanced capacitor voltages, the MMC-Statcom can effectively compensate reactive power and regulate the grid voltage with improved efficiency and stability. The effectiveness of the proposed DC capacitor voltage balancing strategy is extensively evaluated through simulation studies and experimental validations. Comparative analyses are performed with existing voltage balancing methods, demonstrating superior performance and robustness of the novel strategy. The results showcase its potential for practical implementation in real-world power systems. Overall, this study presents a significant advancement in MMC-Statcom technology, providing an effective solution for reactive power compensation and voltage improvement while ensuring reliable and stable grid operation. The proposed novel DC capacitor voltage balancing strategy holds the promise of contributing to the enhancement of power system stability and facilitating the integration of renewable energy sources in modern electrical grids

State Space Modelling and Control of the Modular Multilevel Converter

In der vorliegenden Arbeit wird ein neuer Ansatz zur Modellierung von Systemen basierend auf dem Modularen Multilevel Umrichter (MMC) vorgestellt. Mit Hilfe dieses Ansatzes ist es möglich, neue, effiziente Regelungsalgorithmen für das System zu entwerfen. In Zukunft wird es für netzeinspeisende Umrichter immer wichtiger, nicht nur stabil, sondern auch netzverträglich operieren zu können. Ausgehend von analytischen Differentialgleichungen wird ein Zustandsraummodell des MMC abgeleitet und eine Methode zur Entkopplung des Systems abgeleitet. Mathematische Werkzeuge erlauben eine systematische Analyse der auftretenden Steuer- und Ausgangsgrößen. Eine einfache Matrixdiagonalisierung erlaubt eine allgemeine Transformationsregel für MMC-basierte System zu formulieren. Daraus resultieren einfache Möglichkeiten, Leistungsterme zu identifizieren, die die Zweigenergien des Systems im erlaubten Betriebsbereich halten können. Zusätzlich werden Freiheitsgrade der Kreisströme und der Nullspannung formuliert. Wie für MMC-basierte Topologien erwartet, können sie zur Reduzierung der Energiepulsationen der Zweige eingesetzt werden. Mit der vorgestellten Modellbeschreibung ist es möglich, neue Optimierungsverfahren unter Einbeziehung aller Freiheitsgrade durchzuführen, die eine Reduzierung der Energiepulsationen ermöglichen

Feedforward Modulation Technique for More Accurate Operation of Modular Multilevel Converters

Modular multilevel converters have become the prominent topology for medium- and high-voltage applications. The performance of these converters highly depends on the accuracy of the used modulation approach, for which the capacitor voltage of submodules (SM) are usually assumed to be equal. This article exhibits that ignoring the capacitor voltage differences among SMs adversely affects the system performance. This becomes more obvious the larger the capacitor voltage differences are. Hence, this article proposes a more accurate feedforward modulation approach that takes into account either the instantaneous capacitor voltage value and the real output voltage in the modulation stage. As a result, in applications where larger SM voltage differences are expected, the current distortion and control performance are improved. Particularly, switching–saving approaches benefit from this method as it enables their operation with reduced switching losses without the downsides of increased distortion due to capacitor voltage differences. The proposed approach is analyzed and compared with the nearest-level modulation and with the level-shift PWM. Simulations and experimental validation are presented to confirm the effectiveness of the proposed technique.Ministerio de Ciencia, Innovación y Universidades PDI2019-105890RJ-100 y PID2019-109071RB-I00Comisión Europea H2020-821 381Junta de Andalucia P18-RT-134