Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

Single-phase transformerless inverter topologies at different levels for a photovoltaic system, with proportional resonant controller

In this paper, we have studied the topologies of single-phase transformerless inverters with different levels using a proportional-integral-resonant (PIR) AC controller, and the multi-level cascade inverter topology with sinusoidal pulse with modulation (SPWM) control in an open and closed loop. To ensure that these photovoltaic inverters can inject a defined amount of reactive power into the grid according to international regulations. Therefore, precise monitoring of the mains voltage vector by a phase-locked loop (PLL) system is applied to ensure the proper functioning of this system. For inverter topologies with less than three levels, the simulation results show that the highly efficient and reliable inverter concept (HERIC) topology performance is better than that of H5 and H6. On the other hand, the performance of the topology H6 ameliorate is superior to those of H4, H5, and HERIC in currents of leakage. On the other hand, for the control of cascaded multi-level closed-loop inverters, we notice that there is an improvement in the spectra and the elimination of all frequency harmonics, close to that of the fundamental, and a reduction in the rate of harmonic current distortion

Recently Developed Reduced Switch Multilevel Inverter for Renewable Energy Integration and Drives Application: Topologies, Comprehensive Analysis and Comparative Evaluation

Recently, multilevel inverters (MLIs) have gained lots of interest in industry and academia, as they are changing into a viable technology for numerous applications, such as renewable power conversion system and drives. For these high power and high/medium voltage applications, MLIs are widely used as one of the advanced power converter topologies. To produce high-quality output without the need for a large number of switches, development of reduced switch MLI (RS MLI) topologies has been a major focus of current research. Therefore, this review paper focuses on a number of recently developed MLIs used in various applications. To assist with advanced current research in this field and in the selection of suitable inverter for various applications, significant understanding on these topologies is clearly summarized based on the three categories, i.e., symmetrical, asymmetrical, and modified topologies. This review paper also includes a comparison based on important performance parameters, detailed technical challenges, current focus, and future development trends. By a suitable combination of switches, the MLI produces a staircase output with low harmonic distortion. For a better understanding of the working principle, a single-phase RS MLI topology is experimentally illustrated for different level generation using both fundamental and high switching frequency techniques which will help the readers to gain the utmost knowledge for advance research

The Steady-state Analysis of DC Distribution Network Embedded Droop Control and Power Flow Controller

Aiming at the DC distribution network based on the droop control, this paper proposes that the intersection of the internal characteristics of the node converter droop control and the external characteristics derived from the parameters of the DC distribution network is the actual node operation point. The quantitative relationship between the droop control characteristic parameters and the converter functions is discussed, and the comprehensive droop control characteristics of the multi-converter node is analyzed. The automatic adjustment method of droop control, containing the secondary adjustment and the third adjustment, is presented, and the power flow algorithm of DC distribution network, which considers the impact of power flow controller, droop control and automatic adjustment method, is derived. Finally, three cases about power flow controller, the secondary adjustment and the third adjustment are used to verify that droop control and its related regulation methods can optimize the operation conditions of DC distribution network.</p

A multilevel converter structure for grid-connected PV plants

A new conversion structure for three-phase grid-connected photovoltaic (PV) generation plants is presented and discussed in this Thesis. The conversion scheme is based on two insulated PV arrays, each one feeding the dc bus of a standard 2-level three-phase voltage source inverter (VSI). Inverters are connected to the grid by a traditional three-phase transformer having open-end windings at inverters side and either star or delta connection at the grid side. The resulting conversion structure is able to perform as a multilevel VSI, equivalent to a 3-level inverter, doubling the power capability of a single VSI with given voltage and current ratings. Different modulation schemes able to generate proper multilevel voltage waveforms have been discussed and compared. They include known algorithms, some their developments, and new original approaches. The goal was to share the grid power with a given ratio between the two VSI within each cycle period of the PWM, being the PWM pattern suitable for the implementation in industrial DSPs. It has been shown that an extension of the modulation methods for standard two-level inverter can provide a elegant solution for dual two-level inverter. An original control method has been introduced to regulate the dc-link voltages of each VSI, according to the voltage reference given by a single MPPT controller. A particular MPPT algorithm has been successfully tested, based on the comparison of the operating points of the two PV arrays. The small deliberately introduced difference between two operating dc voltages leads towards the MPP in a fast and accurate manner. Either simulation or experimental tests, or even both, always accompanied theoretical developments. For the simulation, the Simulink tool of Matlab has been adopted, whereas the experiments have been carried out by a full-scale low-voltage prototype of the whole PV generation system. All the research work was done at the Lab of the Department of Electrical Engineering, University of Bologna

Étude, conception et réalisation d'un convertisseur statique hybride multiniveaux tolérant aux défauts

Vu l’importance que revêt la sûreté de fonctionnement des convertisseurs statiques dans plusieurs domaines (traction électrique, génération de l’énergie électrique à partir de l’énergie éolienne, etc,... ), il est nécessaire d'examiner la continuité de service de ces systèmes même dans le cas d’un dysfonctionnement d’un des modules IGBT, d’un bras de l’onduleur ou d'une phase de machine. Ainsi, il est indispensable de concevoir de nouvelles architectures matérielles et commandes logicielles capables de fonctionner à puissance significative même en présence de défaillance touchant le système et plus particulièrement les modules IGBT de l’onduleur. Le sujet proposé s’intéresse à une nouvelle structure hybride multiniveaux tolérante aux défauts. Elle consiste à ajouter à un convertisseur triphasé 3-niveaux type NPC (Neutral Point Clamped), un quatrième bras 3-niveaux types FC (Flying Cap). Des nouvelles techniques des différentes parties de la tolérance des pannes, à savoir la détection, l’isolation, la reconfiguration matérielle et la commande en mode dégradé, sont proposées, analysées et validées sur un prototype expérimental de 15kW de puissance

Bibliography of Lewis Research Center technical publications announced in 1986

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1986. All the publications were announced in the 1986 issues of Scientific and Technical Aerospace Reports (STAR) and/or International Aerospace Abstracts (IAA). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Improving Power Quality in Cascade Multilevel Converters Based on Single-Phase Nonregenerative Power Cells

Univ Talca, Dept Ind Technol, Curico, Chile.Baier, CR (Baier, Carlos R.); Rivera, M (Rivera, Marco); Munoz, JA (Munoz, Javier A.)Interharmonics exist in the ac supply currents in ac/dc/ac drives mainly due to the poor decoupled behavior of the dc-link stage. This issue is particularly evident when different input/output operating frequencies are used, causing harmful effects on power transformers and reducing the system efficiency and power quality. Consequently, large interharmonics can be found in converters with single-phase stages, as they require large electrolytic capacitors to filter out the dc-link second harmonic of voltage and current, which is usually not fully accomplished. This is the case of the cascade multilevel converter based on single-phase power cells, where each module has a single-phase rectifier and a single-phase inverter stage that cannot be effectively decoupled with standard size capacitors. This paper shows that it is possible to improve the quality of the power cell input currents when the input/output frequencies are different in the cascade multilevel converter. This is achieved by means of magnetic couplings among the dc-links of the power cells that feed different output phases, while keeping the high power quality on the load side

Space station systems: A bibliography with indexes (supplement 10)

This bibliography lists 1,422 reports, articles, and other documents introduced into the NASA scientific and technical information system between July 1, 1989 and December 31, 1989. Its purpose is to provide helpful information to researchers, designers and managers engaged in Space Station technology development and mission design. Coverage includes documents that define major systems and subsystems related to structures and dynamic control, electronics and power supplies, propulsion, and payload integration. In addition, orbital construction methods, servicing and support requirements, procedures and operations, and missions for the current and future Space Station are included