222 research outputs found

    Analysis and Design of Methods for Condition Monitoring of Capacitors in Multilevel Converters

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    Multi-level converters are an important class of power electronics based systems that enable seamless conversion of electrical power from one form to another. Due to its distinct merits, it finds a vast scope of application in the fields such as renewable energy, electrical power transmission, adjustable speed drives, uninterrupted power supplies and custom power devices. These merits often come at a cost of increased complexity, higher number of power semiconductor devices and higher number of energy storage elements. Multi-level converters generates staircase waveform by use of high density capacitor banks. These capacitor banks are often subject to failure due to vaporization of electrolyte forming weakest link in reliability context. This thesis addresses reliability issue by proposing an online condition monitoring method for a three-level neutral point clamped multi-level converter which can be easily integrated with existing control methods. The proposed method provides an online estimate of existing capacitance in DC-link and helps increase in reliability in terms of preventive maintenance. The validity of proposed technique is obtained by verification of the method on a 3KVA laboratory developed experimental prototype. It also addresses reliability by developing tool in terms of analytical expressions which can be used as a ready reckoner for proper design of capacitor bank employed in five-level active neutral point clamped multi-level converter. Results from this developed tool are quantitatively verified with the results obtained from converter models developed over MATLAB Simulink environment confirming their accuracy

    Four-Level Three-Phase Inverter With Reduced Component Count for Low and Medium Voltage Applications

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    Hybrid Multilevel Converters with Internal Cascaded/Paralleled Structures for MV Electric Aircraft Applications

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    Using on-board medium voltage (MV) dc distribution system has been a megatrend for next-generation electric aircraft systems due to its ability to enable a significant system mass reduction. In addition, it makes electric propulsion more feasible using MV power electronic converters. To develop high-performance high-density MV power converters, the emerging silicon carbide (SiC) devices are more attractive than their silicon (Si) counterparts, since the fast switch frequency brought by the SiC can effectively reduce the volume and weight of the filter components and thus increase the converter power density. From the converter topology perspective, with the MV dc distribution, the state-of-the-art two-level converters are no longer suitable for next-generation electric aircraft system due to the excessive dv/dt and high voltage stress across the power devices.To address these issues while still maintaining cost-effectiveness, this work demonstrates a megawatt-scale MV seven-level (7-L) Si/SiC hybrid converter prototype implemented by active-neutral-point-clamped (ANPC) converter and H-bridges which is called ANPC-H converter in this work, and a MV five-level (5-L) Si/SiC hybrid ANPC converter prototype, which are hybrid multilevel converters with internal cascaded and paralleled structures, respectively. Using multilevel circuit topology, the voltage stress across the devices and converter output voltage dv/dt are reduced. The tradeoff between the system cost and efficiency was addressed by the adoption of the Si/SiC hybrid configuration with optimized modulation strategies. Comprehensive design and evaluation of the full-scale prototypes are elaborated, including the low-inductance busbar designs, power converter architecture optimization and system integration. To control the 7-L Si/SiC hybrid ANPC-H converter prototype, a low computational burden space-vector-modulation (SVM) with common-mode voltage reduction feature is proposed to fully exploit the benefits of 7-L Si/SiC hybrid ANPC-H converter. To further reduce the converter losses and simplify control algorithm, an active hybrid modulation is proposed in this work by applying low frequency modulation in Si cells and high frequency modulation in SiC cells, thus the control framework is simplified from the 7-L SVM to a three-level SVM. To control the 5-L Si/SiC hybrid ANPC converter prototype to overall loss minimization, the low frequency modulation and high frequency modulation are also adopted for Si cells and SiC cells respectively in 5-L Si/SiC hybrid ANPC converter prototype. Compared to the SVM-based hybrid modulation in 7-L ANPC-H converter, the hybrid modulation for 5-L hybrid ANPC adopts a simpler carrier-phase-shifted pulse width modulation for its inner-paralleled high frequency SiC cells, which extensively suppresses harmonics caused by high frequency switching. With the proposed modulation strategies, extensive simulation and experimental results are provided to evaluate the performance of each power stage and the full converter assembly in both the steady-state operation and variable frequency operations of the demonstrated hybrid converters

    Hybrid Multilevel Converters with Internal Cascaded/Paralleled Structures for MV Electric Aircraft Applications

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    Using on-board medium voltage (MV) dc distribution system has been a megatrend for next-generation electric aircraft systems due to its ability to enable a significant system mass reduction. In addition, it makes electric propulsion more feasible using MV power electronic converters. To develop high-performance high-density MV power converters, the emerging silicon carbide (SiC) devices are more attractive than their silicon (Si) counterparts, since the fast switch frequency brought by the SiC can effectively reduce the volume and weight of the filter components and thus increase the converter power density. From the converter topology perspective, with the MV dc distribution, the state-of-the-art two-level converters are no longer suitable for next-generation electric aircraft system due to the excessive dv/dt and high voltage stress across the power devices.To address these issues while still maintaining cost-effectiveness, this work demonstrates a megawatt-scale MV seven-level (7-L) Si/SiC hybrid converter prototype implemented by active-neutral-point-clamped (ANPC) converter and H-bridges which is called ANPC-H converter in this work, and a MV five-level (5-L) Si/SiC hybrid ANPC converter prototype, which are hybrid multilevel converters with internal cascaded and paralleled structures, respectively. Using multilevel circuit topology, the voltage stress across the devices and converter output voltage dv/dt are reduced. The tradeoff between the system cost and efficiency was addressed by the adoption of the Si/SiC hybrid configuration with optimized modulation strategies. Comprehensive design and evaluation of the full-scale prototypes are elaborated, including the low-inductance busbar designs, power converter architecture optimization and system integration. To control the 7-L Si/SiC hybrid ANPC-H converter prototype, a low computational burden space-vector-modulation (SVM) with common-mode voltage reduction feature is proposed to fully exploit the benefits of 7-L Si/SiC hybrid ANPC-H converter. To further reduce the converter losses and simplify control algorithm, an active hybrid modulation is proposed in this work by applying low frequency modulation in Si cells and high frequency modulation in SiC cells, thus the control framework is simplified from the 7-L SVM to a three-level SVM. To control the 5-L Si/SiC hybrid ANPC converter prototype to overall loss minimization, the low frequency modulation and high frequency modulation are also adopted for Si cells and SiC cells respectively in 5-L Si/SiC hybrid ANPC converter prototype. Compared to the SVM-based hybrid modulation in 7-L ANPC-H converter, the hybrid modulation for 5-L hybrid ANPC adopts a simpler carrier-phase-shifted pulse width modulation for its inner-paralleled high frequency SiC cells, which extensively suppresses harmonics caused by high frequency switching. With the proposed modulation strategies, extensive simulation and experimental results are provided to evaluate the performance of each power stage and the full converter assembly in both the steady-state operation and variable frequency operations of the demonstrated hybrid converters

    High-power medium-voltage motor drive: converter topology, modulation, and control

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    The output power quality, device voltage sharing, power converter flying capacitor voltage ripple and motor torque ripple at low-frequency/ speed operation are the major issues in high-power medium-voltage (MV) motor drives. In this thesis, a new four-level multilevel converter (4L-MLC) is proposed for MV drive applications. The proposed converter does not require series connection of devices, thereby the voltage sharing problems will be eliminated. Also, the new MLC does not require any isolated direct current (DC) sources and eliminates the need of complex phase-shifting transformer. Furthermore, the proposed MLC is also suitable for back-to-back operation due to the presence of a common DC-link. [...

    Model Predictive Control for Power Converters and Drives: Advances and Trends

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    Model predictive control (MPC) is a very attractive solution for controlling power electronic converters. The aim of this paper is to present and discuss the latest developments in MPC for power converters and drives, describing the current state of this control strategy and analyzing the new trends and challenges it presents when applied to power electronic systems. The paper revisits the operating principle of MPC and identifies three key elements in the MPC strategies, namely the prediction model, the cost function, and the optimization algorithm. This paper summarizes the most recent research concerning these elements, providing details about the different solutions proposed by the academic and industrial communitiesMinisterio de Economia y Competitividad TEC2016-78430-RConsejeria de Innovacion, Ciencia y Empresa (Junta de Andalucia) P11-TIC-707

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

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    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
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