A GENERAL REVIEW AND PERFORMANCE EVALUATION OF MULTI-LEVEL CONVERTERS FOR EFFICIENT POWER GENERATION AND APPLICATIONS

This paper comparatively assessed the performance status of seven different multi-level converters with respect to their output voltages, output currents and corresponding percentage total harmonic distortion under the same RL-load condition. The spectral distributions of these various multi-level converters’ waveforms obtained under normal modulation index of 0.8 are presented in this work. The significance of this paper is basically centered on the need to have an improved multi-level converter that has a better flexibility in control, which can ensure continuity in operation and can as well generate a reduced percentage harmonic distortion value under a varied modulation index. This converter will also be able to generate three level or five level output voltages depending on the point of load connection. The analysis and results obtained from this work thus showed that a five-level voltage source inverter formed by a cascade between a three-level flying capacitor and H-bridge produced a given percentage reduction in the value of harmonic distortion under the same loading condition and therefore ensures optimum performance with regard to other power converters of the same rating. http://dx.doi.org/10.4314/njt.v35i1.2

Etude des onduleurs multiplexés pour les variateurs de vitesse moyenne tension

Les systèmes entraînés par des moteurs électriques représentent la plus grande consommation totale d'électricité dans le monde, les moteurs à moyenne tension consommant environ dix pour cent de l'énergie mondiale. D'autre part, le coût de l'énergie augmente, et la consommation d'énergie devient de plus en plus importante pour des raisons économiques et environnementales. Par conséquent, les moteurs moyenne tension (MT) sont une cible évidente pour les mesures d'amélioration énergétique, non seulement pour limiter les factures d'énergie, mais aussi pour se conformer à des réglementations plus strictes. Néanmoins, seule une petite partie des moteurs MT actuellement installés sont contrôlés par des variateurs de vitesse, ce qui ouvre la porte à l'introduction de variateurs de vitesse efficaces dans un large éventail d'applications industrielles. Cette technologie aidera l'industrie du monde entier à économiser de l'énergie sans compromettre les performances ou l'efficacité de la production. Par conséquent, le marché des variateurs MT devrait connaître une croissance solide au cours de la prochaine décennie. Ce travail de thèse étudie et propose une topologie de convertisseur multiniveau triphasé basée sur le concept multiplexé qui est spécialement destinée aux applications variateurs de vitesse moyenne tension. Les principales applications potentielles sont les variateurs de vitesse quatre quadrants de 4,16 kV et 6,6 kV. Le chapitre I présente le contexte et l'état de l'art des variateurs de vitesse MT. Le contexte couvre leurs applications, leur potentiel pour réduire la consommation d'énergie dans l'industrie, les attentes du marché, et les objectifs de cette étude. L'état de l'art présente les topologies multi-niveaux classiques et avancées qui ont été implémentées en tant que produits standards pour les variateurs industriels MT, ainsi que les limites de performance et de coût des semi-conducteurs MT utilisés dans ces topologies. Le chapitre II présente la famille des convertisseurs multiplexés et propose différentes structures adaptées aux objectifs de coût et de performance de cette étude en minimisant le nombre de semi-conducteurs MT. De plus, les structures proposées sont comparées en termes de coût des semi-conducteurs avec deux solutions bien établies sur le marché. Le chapitre III présente le principe de fonctionnement de la topologie et deux schémas de modulation différents qui ont été développés pour les structures proposées précédemment. Une modulation basée sur le transport et une modulation vectorielle ont été développées pour, en association avec le principe de fonctionnement, réduire les efforts de commutation des semi-conducteurs MT. De plus, les deux schémas de modulation ont été comparés en termes de qualité de forme d'onde. Enfin, le chapitre IV présente les résultats expérimentaux qui ont validé certains aspects techniques particuliers de la structure multiplexée et certaines hypothèses formulées au cours de ce travail. Trois bancs d'essai différents (l'un étant un onduleur complet) ont été utilisés pour valider la connexion en série des IGBT de 1,7 kV et 4,5 kV, pour mesurer les énergies de commutation des semiconducteurs HT sous tension réduite et pour mesurer les inductances parasites de la structure de l'onduleur. Ces résultats ont été utilisés pour estimer l'efficacité de la structure proposée, étudier la distribution des pertes des semi-conducteurs, et comparer les performances des deux schémas de modulation développés

Operation and Efficiency Analysis of a 5-level Single-Phase Hybrid Si/SiC Active Neutral Point Clamped Converter

The ability to improve both the size and efficiency of multilevel single-phase converters is a key to uplift them as an attractive solution for industries, while the high number of switches and complex modulation techniques understandably make them unattractive. 5-level active neutral point clamped converter, due to its inherent advantages such as employing different switching frequencies and using different switch technologies, presents an ideal candidate for study. This paper performs a comprehensive analysis of the converter to highlight the advantages of it. This analysis results in a modified hybrid modulation that effectively regulates the neutral point (NP) of the dc-link. Consequently, the combination of the topology and the modified modulation make the converter ideal to utilize two different switch technologies- in this paper Silicon Carbide (SiC) and Si MOSFET. To evaluate the analysis and the effectiveness of modulation, a 2kW hybrid 5-level ANPC is built. Analyzing of the behavior of the converter current, power loss in the filter and switches are, therefore, calculated. The efficiency measurement is performed and compared with the calculated efficiency. There is a close coherency between the measurement and the calculated results and a peak efficiency of 98.4% is achieved.© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.fi=vertaisarvioitu|en=peerReviewed

Common-Mode Voltage Elimination in Multilevel Power Inverter-Based Motor Drive Applications

[EN] The industry and academia are focusing their efforts on finding more efficient and reliable electrical machines and motor drives. However, many of the motors driven by pulse-width modulated converters face the recurring problem of common-mode voltage (CMV). In fact, this voltage leads to other problems such as bearing breakdown, deterioration of the stator winding insulation and electromagnetic interferences (EMI) that can affect the lifespan and correct operation of the motors. In this sense, multilevel converters have proven to be a useful tool for solving these problems and mitigating CMV over the past few decades. Among other reasons, because they provide additional degrees of freedom when comparing with two-level converters. However, although there are several proposals in the scientific literature on this topic, no complete information has been reviewed about the CMV issues and the different multilevel alternatives that can be used to solve it. In this context, the objective of this work is to determine how multilevel power converters provide additional degrees of freedom to make the reduction of the CMV possible by using specific modulation techniques, making it easier for engineers and scientists in this field to find solutions to this problem. This document consists of a descriptive study that collects the strengths and weaknesses of most important multilevel power converters, with special emphasis on how CMV affects each of them. In addition, the differences of modulation techniques aimed to the CMV reduction are explained in terms of output voltage, operating linear range, and generated CMV. Considering this last, it is recommended to use those modulation techniques that allow the generation of CMV levels of 0 V in order to be able to completely eliminate said voltage.This work was supported in part by the Government of the Basque Country within the Fund for Research Groups of the Basque University System under Grant IT978-16; in part by the Research Program ELKARTEK under Project ENSOL2-KK-2020/00077; in part by the Secretaria d'Universitats i Recerca del Departament d'Empresa i Coneixement de la Generalitat de Catalunya; in part by the Ministerio de Ciencia, Innovacion y Universidades of Spain under Project PID2019-111420RB-I00 and Project PID2020-115126RB-I00; and in part by the FEDER Funds

Common-mode voltage elimination in multilevel power inverter-based motor drive applications

The industry and academia are focusing their efforts on finding more efficient and reliable electrical machines and motor drives. However, many of the motors driven by pulse-width modulated converters face the recurring problem of common-mode voltage (CMV). In fact, this voltage leads to other problems such as bearing breakdown, deterioration of the stator winding insulation and electromagnetic interferences (EMI) that can affect the lifespan and correct operation of the motors. In this sense, multilevel converters have proven to be a useful tool for solving these problems and mitigating CMV over the past few decades. Among other reasons, because they provide additional degrees of freedom when comparing with two-level converters. However, although there are several proposals in the scientific literature on this topic, no complete information has been reviewed about the CMV issues and the different multilevel alternatives that can be used to solve it. In this context, the objective of this work is to determine how multilevel power converters provide additional degrees of freedom to make the reduction of the CMV possible by using specific modulation techniques, making it easier for engineers and scientists in this field to find solutions to this problem. This document consists of a descriptive study that collects the strengths and weaknesses of most important multilevel power converters, with special emphasis on how CMV affects each of them. In addition, the differences of modulation techniques aimed to the CMV reduction are explained in terms of output voltage, operating linear range, and generated CMV. Considering this last, it is recommended to use those modulation techniques that allow the generation of CMV levels of 0 V in order to be able to completely eliminate said voltage.This work was supported in part by the Government of the Basque Country within the Fund for Research Groups of the Basque University System under Grant IT978-16; in part by the Research Program ELKARTEK under Project ENSOL2-KK-2020/00077; in part by the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya; in part by the Ministerio de Ciencia, Innovacion y Universidades of Spain under Project PID2019-111420RB-I00 and Project PID2020-115126RB-I00; and in part by the FEDER Funds.Peer ReviewedPostprint (author's final draft

Cross connected multilevel voltage source inverter topologies for medium voltage applications

Multilevel voltage source inverters where first introduced in the early 1980s. Since then, they have been continuously developed, offering a wide new research area in power electronics. The popularity of multilevel solutions come from the advantages that they offer: improved output quality, voltage sharing in high voltage applications, increased power density or reduction of filtering costs. Two completely new and innovative cross-connected topological families for advanced multilevel voltage source inverters are introduced in this thesis. The motivation for this work stems out from the need to generate multiple output levels while keeping the reliability as high as possible. The offered solutions are able to address the problematic, but of course they do not come without a price: A higher control complexity and more semiconductor blocking voltage capability are necessary in the design of such advanced converters. The Cross Connected Intermediate Level (CCIL) Voltage Source Inverter is the first of the two new topologies presented here. It is built as a cascade of stages using capacitors which are connected to each other by means of cross connected cell structures. The CCIL can be used in several configurations, like redundant or non-redundant switching state configurations for instance. A graphical model based on the physical properties of the inverter is proposed and an original fuzzy logic controller is designed for the balancing of the capacitor voltages and modulation of the inverter. The control algorithm is implemented and verified in simulations. The results are used to benchmark the topology against standard solutions and the conclusions are used to define what applications could benefit from such a converter structure. The Common Cross Connected Stage (CCCS) Voltage Source Inverter is the second original contribution of this work in terms of topology. It is built using the cross connected stage and its capacitor in a common configuration for the three phases of the inverter. Such a design allows to use only one stage per three phases. Because of the intrinsic three phased properties of this topology, a model based on space phasor representation is introduced. With the help of this model, a novel space phasor modulation strategy is derived and proposed. It allows to generate the three phased output voltages while using the available redundancies for balancing of the capacitor voltages. The resulting algorithm is first implemented and tested in simulation, and in a second step a test setup is built and the modulator is coded in VHDL. The simulation and experimental results obtained validate the topology and control concepts. A benchmarking of the CCCS solution is also done to understand what are the benefits and drawbacks of this solution. Analysis and comparison of the new topologies allow to evaluate in an objective way the contributions brought by this work. It is found that the newly proposed solutions cover an area of multilevel inverters where not so many solutions were available prior to this work: Generation of multiple output levels with reduced number of passive and active components (thus increasing the reliability). The drawback is a higher blocking voltage requirement. Conclusions and case study are proposed to help assess the expected performances and choose the most suitable solutions for given applications

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

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

Contributions to the design and operation of a multilevel-active-clamped Dc-Ac grid- connected power converter for wind energy conversion systems

The demand of wind energy has considerably increased during the last decades. In order to fulfil this great energy demand, wind energy conversion systems (WECS) are designed to manage higher power ratings. Currently, the most attractive power converter topology in commercial WECS is the conventional two-level back-to-back voltage-source converter (2L-B2B). However, the 2L-B2B topology could have difficulties to achieve an acceptable performance with the available switching devices for the largest WECS, even though having the cost advantage. Instead, multilevel converters increase the power without increasing neither current nor blocking voltage of the power semiconductors, enabling a cost-effective design for the largest WECS using the available switching devices. Within the multilevel converters, the 3L-NPC topology offers high penetration in the market of large WECS. However, one of its major drawbacks is that the power loss is unevenly distributed among the switching devices. Therefore, the 3L-NPC output power capability is limited by the thermal performance of the most stressed switching device, which depends on the operating point. The 3L-ANPC topology was proposed in order to improve the power loss distribution among the power semiconductors. The 3L-ANPC provides a controllable path for the neutral current. Hence, the 3L-ANPC is able to offer certain freedom to distribute the power loss among the power semiconductors. As a consequence, and compared to the 3L-NPC, the thermal performance is more uniform and the output power capability increases. However, there is still room for improvement. In light of the previous discussion, the proposed thesis defines enhanced design guidelines for the dc-ac grid-connected 3L-ANPC power converter, focused on improving its reliability and electrical performance, and following the trend of the current state of the art to define a feasible solution for the next generation of WECS. The thesis contributions are based on defining an enhanced power device configuration and a novel commutation sequence, avoiding concentrating both significant conduction and switching losses on a single power semiconductor device. This allows then selecting the most appropriate device for each converter position, which leads to a better converter efficiency and to a more uniform power loss distribution and thermal performance. This also leads to a higher converter power rating, and it is expected to improve the converter reliability.La demanda de energía eólica ha incrementado considerablemente durante las últimas décadas. Con el objetivo de satisfacer esta gran demanda, los sistemas de conversión de energía eólica (WECS) son diseñados para operar con mayores niveles de potencia. Actualmente, la topología de convertidor de potencia más atractiva en los WECS comerciales es el convertidor de dos niveles operando en fuente de tensión y configuración back to back (2L-B2B). Sin embargo, esta topología podría tener dificultades para ofrecer un comportamiento aceptable en los WECS de mayor potencia con los dispositivos actuales, incluso aunque su coste sea reducido. En cambio, los convertidores multinivel pueden incrementar la potencia sin necesidad de incrementar la corriente ni el voltaje de bloqueo de los dispositivos, permitiendo conseguir un diseño adecuado para los WECS de mayor potencia usando los dispositivos actuales. Dentro de los convertidores multinivel, la topología 3L-NPC tiene una gran aceptación en el mercado eólico, siendo una solución común en los WECS de mayor potencia. Sin embargo, su gran inconveniente es que la potencia pérdida es distribuida de una manera desequilibrada entre los dispositivos. De este modo, la potencia de salida se ve limitada por el comportamiento térmico del dispositivo más estresado a nivel térmico, el cual depende del punto de operación. De esta manera, la topología 3L-ANPC fue propuesta con el objetivo de mejorar la distribución de las pérdidas del convertidor entre los dispositivos. El convertidor 3L-ANPC proporciona un camino totalmente controlable para la conexión del punto neutro. Por lo tanto, el convertidor 3LANPC es capaz de ofrecer cierto grado de libertad para distribuir la potencia pérdida entre los dispositivos. Como consecuencia, y comparado con el convertidor 3L-NPC, el comportamiento térmico es mucho más equilibrado y la potencia de salida puede ser incrementada. Sin embargo, todavía hay margen de mejora para alcanzar mejores prestaciones en el comportamiento del convertidor 3L-ANPC. A raíz de la argumentación anterior, la tesis propuesta define nuevas guías de diseño para el convertidor 3L-ANPC cc-ca conectado a la red. Las guías de diseño están focalizadas en mejorar la fiabilidad y el comportamiento eléctrico del convertidor, respetando la tendencia del estado del arte actual para definir una solución factible para la próxima generación de WECS. Las contribuciones de la tesis están basadas en definir una configuración de dispositivos mejorada y una secuencia de conmutación novedosa, evitando concentrar grandes pérdidas de conducción y de conmutación en un mismo dispositivo. Las contribuciones permiten seleccionar el dispositivo más adecuado para cada posición del convertidor, consiguiendo una mejor eficiencia y una distribución de pérdidas y comportamiento térmico más equilibrado. Además, también permiten operar con potencias más elevadas, y mejorar la fiabilidad del convertidor.Postprint (published version

High power conversion chain for hybrid aircraft propulsion

Recently, the use of air transport systems has increased considerably. Therefore, the current environmental considerations are pushing to reduce their ecological impact. Projects such as Clean Sky 2 provide an answer to this problem, by proposing a reduction in CO2 emissions and noise pollution. The development of a hybrid-electric aircraft would reduce these emissions by reducing the size and weight of the systems and using more efficient electrical systems. This would reduce fuel consumption and therefore pollutant emissions. This work takes part into HASTECS Clean Sky 2 European project which aims to optimize the complete electrical chain of the hybrid aircraft integrating all aeronautical constraints such as partial discharges for electrical equipment placed in the non-pressurized zone. HASTECS project has set itself the challenge of doubling the specific power of electric machines including their cooling from 5 kW/kg to 10 kW/kg, while the power electronics, with their cooling system, would evolve from 15 kW/kg in 2025 to 25 kW/kg in 2035. To increase the specific power, the cooling system mass should be decreased either by optimizing its components which is done by the 4th work package (WP4) or by reducing power losses. Inverter losses reduction could be achieved by using small voltage rating components, by playing on modulation strategies or by using more performant semiconductors. The first option could be done by using multilevel architectures to avoid the direct series association. Unlike direct series association, the parallel one is easier to manage in terms of switches command so it was allowed in our studies. Several inverter topologies (2-, 3- and 5-level topologies) and modulation strategies (PWM, third harmonic injection, discontinuous PWM and full-wave) were compared using several semiconductors generations to choose the most performant solution in terms of efficiency and specific power. For the considered mission profile, the inverter could be sized for the maximum power point (takeoff) or the most extended flight phase (cruise). A comparative study of modulation strategies was carried out to highlight the structure and modulation presenting the best performance to minimize the losses for the chosen sizing points using most interesting topologies for the studied mission profile using two electrical motor windings configurations proposed by WP