The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future

A Virtual Space Vectors based Model Predictive Control for Three-Level Converters

Three-phase three-level (3-L) voltage source converters (VSC), e.g., neutral-point clamped (NPC) converters, T-type converters, etc., have been deemed to be suitable for a wide range of medium- to high-power applications in microgrids (MGs) and bulk power systems. Compared to their two-level (2-L) counterparts, adopting 3-L VSCs in the MG applications not only reduces the voltage stress across the power semiconductor devices, which allows achieving higher voltage levels, but also improves the quality of the converter output waveforms, which further leads to considerably smaller output ac passive filters. Various control strategies have been proposed and implemented for 3-L VSCs. Among all the existing control methods, finite-control-set model predictive control (FCS-MPC) has been extensively investigated and applied due to its simple and intuitive design, fast-dynamic response and robustness against parameter uncertainties. However, to implement an FCS-MPC on a 3-L VSC, a multi-objective cost function, which consists of a term dedicated specifically to control the dc-link capacitor voltages such that the neutral-point voltage (NP-V) oscillations are minimized, must be designed. Nevertheless, selecting proper weighting factors for the multiple control objectives is difficult and time consuming. Additionally, adding the dc-link capacitor voltages balancing term to the cost function distributes the controller effort among different control targets, which severely impacts the primary goal of the FCS-MPC. Furthermore, to control the dc-link capacitor voltages, additional sensing circuitries are usually necessary to measure the dc-link capacitor voltages and currents, which consequently increases the system cost, volume and wiring complexity as well as reduces overall reliability. To address all the aforementioned challenges, in this dissertation research, a novel FCS-MPC method using virtual space vectors (VSVs), which do not affect the dc-link capacitor voltages of the 3-L VSCs, was proposed, implemented and validated. The proposed FCS-MPC strategy has the capability to achieve inherent balanced dc-link capacitor voltages. Additionally, the demonstrated control technique not only simplifies the controller design by allowing the use of a simplified cost function, but also improves the quality of the 3-L VSC output waveforms. Furthermore, the execution time of the proposed control algorithm was significantly reduced compared to that of the existing one. Lastly, the proposed FCS-MPC using the VSVs reduces the hardware cost and complexity as the additional dc-link capacitor voltages and current sensors are not required, which further enhances the overall system reliability

Contrôle avancé des convertisseurs de puissance multi-niveaux pour applications sur réseaux faibles

139 p.El advenimiento progresivo de las microrredes que incorporan fuentes de energía renovable está dando lugar a un nuevo paradigma de distribución de la electricidad. Este nuevo planteamiento sirve de interfaz entre consumidores no controlados y fuentes intermitentes, implicando desafíos adicionales en materia de conversión, almacenamiento y gestión de la energía.Los convertidores de potencia se adaptan en consecuencia, en particular con el desarrollo de los convertidores multinivel, que integrando los mismos componentes que sus predecesores y un control más complejo, soportan potencias más altas y aseguran una mejor calidad de la energía.Debido al carácter híbrido de los convertidores de potencia, su control se divide comúnmente en dos partes: por un lado, el control de los objetivos continuos vinculados a la función principal de los convertidores de servir de interfaz, y, por otro, el control discreto de los interruptores de potencia, conocido con el nombre de modulación.En este contexto, las exigencias crecientes en términos de eficiencia, fiabilidad, versatilidad y rendimiento hacen necesaria una mejora de la inteligencia de la estructura de control. Para cumplir conestos requisitos, se propone tratar mediante un solo controlador ambas problemáticas, la vinculada a la función de interfaz de los convertidores y la relacionada con su naturaleza discreta. Esta decisión implica incorporar la no-linealidad de los convertidores de potencia en el controlador, lo que equivale a suprimir el bloque de modulación, que constituye la solución tradicional para linealizar el comportamiento interno de los convertidores. Se adopta un planteamiento de Control Predictivo basado en Modelos (MPC) para abordar la no-linealidad y la gran diversidad de objetivos de control que acompañan a los convertidores de potencia.El algoritmo desarrollado combina teoría de grafos ¿con algoritmos de Dijkstra, A* y otros¿ con un modelo de estado especial para sistemas conmutados al objeto de proporcionar una herramienta potente y universal, capaz de manipular simultáneamente el carácter cuantificado de los interruptores de potencia y el continuo de las entidades interconectadas por el convertidor. Se han obtenido resultados sobre la estabilidad y la controlabilidad de los modelos de estado conmutados aplicados al caso particular de los convertidores de potencia.El controlador así desarrollado y descrito se ha examinado en simulación frente a varios casos y aplicaciones: inversor aislado o conectado a la red, rectificador y convertidor bidireccional. Se ha empleado la misma estructura de control para tres topologías de convertidor multinivel: Neutral-Point Clamped, Flying Capacitor y Cascaded H-Bridge. Al objeto de adaptarse a los cambios citados, lo único que varía en el controlador es el modelo del convertidor adoptado para la predicción, así como la función de coste, que traduce los requisitos de control en un problema de optimización a solucionar por el algoritmo. Un cambio de topología resulta en una modificación del modelo interno, sin impacto sobre la función de coste, mientras que variaciones de esta función son suficientes para adaptarse a la aplicación.Los resultados muestran que el controlador logra actuar directamente sobre los interruptores de potencia en función de diversos requisitos. Los desempeños de la estructura de control propuesta son similares a los de las numerosas estructuras dedicadas a cada uno de los casos estudiados, excepto en el caso de operación en modo rectificador, en el que la versatilidad y rapidez de control obtenidos son particularmente interesantes.En definitiva, el controlador planteado puede emplearse para diferentes aplicaciones, topologías, objetivos y limitaciones. Si bien las estructuras de control lineal tradicionales han de modificarse, a menudo en profundidad, para afrontar diferentes modos de operación o requisitos de control, dichas alteraciones no tienen ningún impacto sobre la arquitectura del controlador MPC obtenido, lo que pone de manifiesto su versatilidad, así como su universalidad, también demostrada por su capacidad para adaptarse a diferentes convertidores de potencia sin modificaciones importantes. Finalmente, la solución propuesta elude por completo la complejidad de la modulación, ofreciendo simplicidad y flexibilidad al diseño del control

A Novel Control Approach to Hybrid Multilevel Inverter for High-Power Applications

This paper proposes a hybrid control scheme for a newly devised hybrid multilevel inverter (HMLI) topology. The circuit configuration of HMLI is comprised of a cascaded converter module (CCM), connected in series with an H-bridge converter. Initially, a finite set model predictive control (FS-MPC) is adopted as a control scheme, and theoretical analysis is carried out in MATLAB/Simulink. Later, in the real-time implementation of the HMLI topology, a hybrid control scheme which is a variant of the FS-MPC method has been proposed. The proposed control method is computationally efficient and therefore has been employed to the HMLI topology to mitigate the high-frequency switching limitation of the conventional MPC. Moreover, a comparative analysis is carried to illustrate the advantages of the proposed work that includes low switching losses, higher efficiency, and improved total harmonic distortion (THD) in output current. The inverter topology and stability of the proposed control method have been validated through simulation results in MATLAB/Simulink environment. Experimental results via low-voltage laboratory prototype have been added and compared to realize the study in practice.publishedVersio

An Amorphous Alloy Magnetic-Bus-Based SiC NPC Converter with Inherent Voltage Balancing for Grid-Connected Renewable Energy Systems

© 2002-2011 IEEE. This paper presents an amorphous alloy magnetic-bus-based neutral point clamped (NPC) converter for grid-connected renewable generation systems. In the proposed system, the amorphous alloy high-frequency high-power density multi-winding magnetic bus generates balanced dc supplies for the five-level (5L) NPC converter for high-quality power conversion. Compared to the traditional NPC converter topologies, the proposed magnetic-bus-based architecture does not require any control circuit for voltage balancing of the series connected capacitors. The magnetic bus inherently overcomes galvanic isolation issues and may reduce the size of the boosting inductor. In this paper, a finite control set model predictive control algorithm is derived to control the grid-connected 5L-NPC inverter for multilevel voltage synthesizing, while achieving the user-defined active and reactive power values. To verify the proposed concept, a simulation model is developed and analyzed in MATLAB/Simulink environment. To validate the technology, a scale d-down prototype test platform is developed in the laboratory with silicon carbide switching devices, which achieves high blocking voltage, low power dissipation, high switching frequency, and high-Temperature operation. Based on the simulation and the experimental results, it is expected that the proposed converter will have a great potential for widespread application in renewable generation systems including superconducting generator-based wind turbines