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In the recent years, the introduction of an alternative energy such as clean energy has become a major challenge. In this context, several sources of energy are often associated to provide the required energy to the grid. However, output of photovoltaic system and wind turbine is influenced by meteorological conditions. As a result, the power quali...
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... Moreover, high amount of switching losses occur as it requires a highfrequency pulse width modulation (PWM) scheme. Furthermore, these inverters require bulky and expensive filters due to the higher values of total harmonic distortions (THDs) in both output (i.e., before feeding into the utility grid) voltage and current of inverters [9][10][11]. Thus, multilevel inverters (MLIs) are considered as the best substitute of traditional inverters, particularly for medium voltage and high power applications as these inverters generate a high-quality staircase output voltage waveform with a lower value of the THD at low switching frequency [12]. ...
This paper presents a generalized structure of a new three-phase multilevel inverter (MLI) which ensures better performance with the minimum number of components for different applications including DC power supply-based renewable energy sources. The proposed MLI topology is developed in the form of several basic blocks which are individually made of a DC voltage source and a semiconductor switch. All the balanced DC sources required for the proposed inverter are made through a high-frequency magnetic link. The single–phase and three-phase five level (5-L) inverters with the rating of 3.5 and 100 kVA, respectively, are simulated, while a five level (5-L) single-phase inverter is implemented for demonstrating the switching strategy and different operational modes. The rigorous calculations are presented to determine switching losses and conduction losses which are minimum because only three conducting switches are responsible for generating each voltage level during every operating mode. The structure of the aforementioned inverter provides optimized value of total standing voltage (TSV = 5.5Vdc with 5-L single-phase leg) of the system. The proposed inverter offers energy conversion efficiency of 94.84% for 5-L single-phase leg which is significantly enhanced and it also minimizes the equipment ratings as well as overall costs of the entire system.
... L'idée de l'onduleur 4-niveaux hybride a été donc de remplacer des condensateurs ottants d'un onduleur FC à 4-niveaux par des super-condensateurs. L'intégration de ce dispositif de stockage interne nous permettra d'avoir un stockage d'énergie dans le convertisseur et non sur le bus DC [112,113,114]. La gure 3.12 illustre la topologie d'un seul bras i de l'onduleur hybride. ...
La généralisation des énergies renouvelables et leurs intégrations dans les réseaux de faible ou de grande puissance induit des nouveaux challenges dans la gestion et la conduite des systèmes multi-sources. Cette thèse porte sur la modélisation et la commande des convertisseurs multiniveaux hybrides. Les applications visées sont les réseaux multi-sources avec stockage de l'énergie. Les objectifs étant d'assurer deux fonctions principales : la continuité de transfert d'énergie d'une source continue renouvelable vers le réseau électrique et la compensation des fluctuations de puissance sur le bus alternatif. Les travaux de recherche dans ce mémoire ont été menés sur l'étude, la modélisation et la commande de trois structures de convertisseurs DC-AC hybrides. Dans un premier temps, nous avons utilisé des super condensateurs comme système de stockage d'énergie sur le bus DC d'un onduleur à 2-niveaux de tension. Pour répondre à nos objectifs, une commande par retour d'état avec l'intégration de l'écart en utilisant l'approche des inégalités matricielles (LMI) a été mise en place. Cette loi de commande permet d'assurer la stabilité du système avec une tension variable sur le bus continu. Ensuite, l'onduleur classique a été remplacé par un onduleur multi-niveaux à condensateurs flottants. Cette deuxième structure nous a permis de satisfaire les mêmes objectifs avec une tension de sortie de meilleur qualité et une inductance de filtrage plus petite. Grâce à une méthode d'équilibrage par la sélection de l'état redondant, les tensions intermédiaires des condensateurs flottants restent bien équilibrées dans tous les modes de fonctionnement. Enfin, nous avons intégré ce dispositif de stockage dans le convertisseur afin d'avoir un stockage d'énergie interne et non pas sur le bus continu. Pour ce faire, les condensateurs flottants ont été remplacés par des super-condensateurs et 3 nouveaux interrupteurs ont été rajoutés par bras. Un prototype de l'onduleur proposé a été réalisé sein du laboratoire LIAS. Les résultats expérimentaux, issus des trois bancs d'essais, viennent corréler et confirmer l'apport important C.
This article deals with a hybrid technique (phase conversion and phase displacement) to design a multipulse rectifier so that a medium voltage drive system annihilates an impact of harmonic components not only in a steady state but also in that state when it is not operating at rated conditions. A three-phase rectification faces power quality challenges when it is designed to supply power for a low-count dc source inverter. Hence, a set of transformers is designed with a three-phase to five-phase conversion, which makes an individual unit of rectifiers as a 10-pulse converter, and through a phase displacement, an overall converter converts into a 30-pulse converter. Moreover, a floating voltage source inverter-based four-level multilevel inverter is used to attain excellence in response at motor end. Hence, the proposed converter is capable of efficient utilization of electricity with high power quality, which is a main objective at global level. A hardware prototype of a drive system is developed for a 7.5 kW, 415 V, cage induction motor. Experimental results have demonstrated that power converters are effective in improving power quality at grid and motor. Operability and performance of the proposed power converter are experimentally validated at different loads and speeds.
This article presents a topology of an 18-pulse ac–dc and 4-level cascaded converters for a medium-voltage drive application. An isolated transformer-based 18-pulse ac–dc converter is used for enhancing the power quality at the supply end in a medium-voltage induction motor drive. Apart from this, an inverter topology, which is designed by the cascading of a two-level voltage source inverter, is designed for medium-voltage drive applications. This topology requires a smaller number of components in comparison to the hybrid four-level inverter topology, which is presented in the literature. The design of the system is carried out for an 18-pulse ac–dc converter and 4-level inverter feeding an indirect field-oriented control induction motor drive. The effect of switching and conduction losses performance of the presented inverter is analyzed and compared with the profile of the four-level inverter topology presented in the literature. A laboratory prototype of the presented 18-pulse converter and 4-level inverter is also developed to capture the performance in different operating states with a 7.5-kW (10 hp) (reduced scale) induction motor drive. The obtained results justify the practicality of this design and validate the simulated results, which are analyzed on a 298.4-kW induction motor drive. The performances of the drive system are studied based on the industry applications requirements point of view, such as power quality, losses, and dynamic stability.
Day by day, the number of electrical loads, electronic devices and communication equipment are increasing rapidly which cause a huge deficiency in electrical energy. As it is already predicted that the conventional sources of energy such as coal, fuel, natural gas etc. are coming to their limits by the year 2050, researchers have found out the sources of renewable energy including solar, wind and ocean in order to fulfill the power demand. Many technologies have been developed till now to generate the power from the renewable energy sources. The multilevel inverter (MLI) concept has obtained its place at the top of the favorite list of the researchers, as it has some outstanding features such as high modularity, low voltage stress, small common mode voltage, better harmonic profile and fault tolerant ability. But, the conventional MLI topologies require huge number of components like switch, diode, capacitor, and isolated DC source, which increases the volume, weight and cost of the system as well as reduces the reliability. In order to mitigate this limitation, three different advanced MLI topologies including half height neutral point clamped, magnetic-link based cascaded DC source, and cascaded module switched capacitor are developed in this book for low and medium power renewable energy systems that are configured with reduced number of components. As a results, the size, weight, losses, and installation costs of the system decrease significantly. However, for all of the introduced topologies, the mathematical background, operating principle, switching scheme, and loss calculation are explained in the respective chapter of this thesis. Moreover, the generation procedures of multiple balanced DC sources required for the inverters are addressed with high frequency magnetic-link. In addition, the capacitor voltage balancing problem is overcome by the topological structure. Afterward, performances of the presented MLI topologies are evaluated by simulation results carried out in MATLAB\Simulink. Finally, scaled down laboratory prototypes are developed and tested to support the simulation results as well as to confirm the feasibility of the systems. Therefore, compact, cost efficient, lightweight and highly modular MLI topologies that are compatible for low and medium power renewable energy generation
systems are achieved as outcomes of this thesis.
