1,720,962 research outputs found
Enhanced Level-Shifted Modulation for a Three-Phase Five-level Modified Modular Multilevel Converter (MMC)
No full textThe rapid growth of the penetration level of renewable energy sources (RESs) in low-voltage (LV) networks increases the research interest in more efficient, compact, reliable, and easily expandable energy conversion systems. The long commutation loops of the existing low-voltage multilevel converters, such as active neutral point clamped (ANPC) converters lead to high voltage overshoots induced during switching due to the significant parasitic inductance. Modular Multilevel Converters (MMC) are gaining an increased interest due to their modularity, flexibility, and short commutation loops also for some LV applications. However, several issues related to the number of components, dc capacitor requirements, and the added complexity need to be considered. This paper aims to reduce the five-level modified MMC capacitance requirements where the upper and lower submodules are connected in parallel. This reduction has been achieved using an improved modulation technique by minimizing the insertion time of the submodules that require higher capacitance. The proposed modulation is effective in reducing the inner SMs’ capacitor voltage ripple at lower modulation indices. Instead, the circulating current injection of the second harmonics effectively reduces the voltage ripple at higher modulation indices. Thus, maximum reduction of the total capacitance requirement for the entire operating range of modulation index can be achieved by a proper combination of the two solutions. Simulation and experimental results on a lab-scaled prototype verify the validity of the proposed solution
Three-Phase Modular Multilevel Converter (MMC) for Low-voltage Applications: Improved Modulation Technique Toward Less Capacitance Requirement
No full textModular Multilevel Converter (MMC) has become one of the promising topologies in medium and high power applications. Modularity, scalability, and reliability are the main features that give the MMC some advantages over other multilevel topologies when considering high number of levels. This paper presents an alternative modulation technique for a modified modular multilevel converter (M-MMC) topology for low-voltage applications. By using level-shifted carrier (LSC) modulation and the proposed sorting algorithm, the capacitance requirement for this topology can be reduced. Finally, the proposed modulation scheme and the reduction of capacitance are verified by simulation results using PLECS
Circulating Current Control for a Three-Phase Modified Modular Multilevel Converter with a Reduced Number of Current Sensors
No full textThe high capacitance requirement becomes a significant problem when modular multilevel converters (MMCs) are applied to medium or low-voltage systems. This paper proposes a capacitor voltage control scheme for a three-phase modular multilevel converter (MMC) with optimized capacitor sizing. Unlike the existing circulating current control, the proposed controller uses the middle capacitor voltage to control the second-order harmonic component of the circulating current. Therefore, it is unnecessary to measure the two arm currents; only one voltage sensor is required, which reduces the number of current sensors. The proposed controller can effectively control the circulating current to be constant or inject second-order harmonics to reduce the capacitor sizing. The detailed analysis, controller design, and performance of the proposed scheme are presented in this paper. The effectiveness of this study is confirmed by simulation and experimental results
Three-Phase Modular Multilevel Converter with Optimized Capacitor Sizing for Low-Voltage Applications
No full textHigh capacitance requirement is a major concern of modular multilevel converters (MMCs) when applied to medium- or low-voltage systems. This article presents the design procedure and development of a modified MMC topology for low-voltage applications. With respect to the conventional MMC topologies, the proposed structure is designed and optimized to have a relatively low capacitance requirement. The switching states, modulation, control, and design procedure of the different parameters, including submodule capacitor and arm inductor, are investigated in this article. Moreover, the control scheme is presented to achieve regulation of the output voltage and the circulating current. The outcomes of this study are verified by simulation and experimental results
A Single-Sensor-Based Circulating Current Controller for a Modified Three-level Modular Multilevel Converter
No full textA voltage controller for the middle capacitor of a modified modular multilevel converter (MMC) is proposed in this paper. This controller is utilized as an alternative solution to the existing circulating current controller. Unlike the circulating current controller, the second-order harmonic component of the circulating current is regulated indirectly by controlling the second-order component of the middle capacitor voltage. Using this approach, only one voltage sensor per phase is needed instead of two current sensors. The validity of the proposed control is proved by simulation and experimental results
Ripple Reduction of Active Split DC-Link 4-Wire Inverters by Phase-Shifted Multi-Carrier Modulation
Full text linkThis paper considers a multi-carrier modulation in which the phase-shifts between the carriers are adjusted to reduce the rms current flowing into the active split dc-link capacitors of four-wire three-phase inverters when the neutral node is modulated with the third harmonic. Capacitors current reduction is beneficial in terms of volume, losses, and components stresses. Considering the current ripple combination of the phases and neutral currents, the proposed approach reduces the rms current through the split dc-link capacitors compared to a standard single-carrier pulse-width modulation. It is shown that the amount of reduction depends on the modulation index and the ratio between the neutral and the output inductors. Besides, it is not significantly influenced by the unbalancing current, in the considered topology, in which the split dc-link capacitors are aimed to regulate the neutral-point voltage. Guidelines for selecting suitable phase-shifts in practical cases based on the inverter operating point are discussed. The results are demonstrated on an experimental prototype
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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