1,721,007 research outputs found
Optimization of MMC level number for battery integration in MV grid
No full textThe integration of battery energy storage systems in electrical grids is one of the most interesting challenges of the recent years. In this regard, one potential solution is based on a modular multilevel converter (MMC) with batteries directly embedded at each submodule level. This solution allows to reach medium voltage level using low voltage devices avoiding the necessity of complex battery management system to balance the high voltage battery modules. Several studies have been performed on MMC topologies to integrate storages. Nevertheless, there are not dedicated studies to analyse the effect of the number of levels on efficiency and cost of the final solution. This paper focuses on the efficiency evaluation and on the cost analysis of the MMC combined with energy storage systems. After evaluating the total power losses of the converter, the efficiency for different number of submodules is analysed. In addition, cost comparison between different solutions, taking into account several factors such as component price, converter power losses cost and operational & maintenance cost, is discussed
Comprehensive assessment of voltage and current source PV-based modular multilevel converters
Full text linkRecently, modular multilevel converters (MMCs) gained popularity for the grid integration of photovoltaic (PV), due to their many advantages, including low total harmonic distortion, high control flexibility, and distributed maximum power point (MPP) tracking capability. Two distinguished families of MMCs exist: voltage source and current source. Voltage source MMCs are mostly studied, but current source MMCs offer advantages under certain operating conditions. This article compares voltage and current source MMCs, for PV integration. To this aim, several key indicators are identified: number of components, energy stored in passive elements, semiconductor power rating, and the number of MPP trackers. The results of the analysis, performed in MATLAB©, show that for a fixed number of output voltage levels, power rating, and switching frequency, voltage source MMCs have simpler control and higher number of MPP trackers. In contrast, current source MMCs minimize the semiconductor power rating, the number of components and the energy stored in passive elements. Regarding efficiency, in the analyzed case study, voltage source MMCs perform better under both homogeneous and non-homogenous irradiance conditions. This article provides a tool to select the optimal solution based on the required target (e.g. efficiency, energy storage etc.), given the specific characteristics of the application
Neuronal responses to tilt within the rat cerebellar vermis
No full textCats corticocerebellar units within the anterior vermis are affected by the vestibular input and show directionally tuned responses. The aim of the study was investigating whether a similar representation of labyrinth signals was present in the rat cerebellar vermis by recording units activity during tilt and wobble rotations. The analysis of the neuronal discharge during both clockwise (CW) and counterclockwise (CCW) wobble allowed to determine the spatial (preferred direction) and temporal (response phase) response properties of the recorded neurons. Many units were affected by labyrinthine stimulation. "Bi-directional" units responded to both CW and CCW stimuli, being characterized by a direction of maximal sensitivity (theta(max)), the distribution of which covered all the sectors of the horizontal plane, with contralaterally pointing vectors more represented within the caudal part of the explored region. Differences in the amplitude of the CW and CCW responses indicated that neurons received a convergence of vestibular signals endowed with different spatial and temporal properties, a process that is expected to link their response phase with the tilt direction. Population vector analysis showed that recorded neurons coded both the amplitude and direction of head tilt during different types of rotational stimuli. In conclusion, the present results show that the processing of vestibular signals with complex spatiotemporal properties represents a general function of the mammalian cerebellar vermis, allowing accurate monitoring of head rotational movements (of the head) in vertical planes. Finally, in rats, different cerebellar regions seem to receive specific vestibular inputs
An MMC-based Fully Modular Ultra-Fast Charging Station Integrating a Battery Energy Storage System
No full textThe wide diffusion of electric vehicles is possible only if charging infrastructures are adequately developed. In this context, this paper proposes a novel fast-charging structure based on a modular multilevel converter (MMC) with the battery energy storage system (BESS) integrated at the submodule level along with the charging spot. In this way, bulky output filters can be avoided, and the modularity of the converter can be exploited. Moreover, the possibility to split the BESS increases the converter reliability. Lastly, considering the possible different vehicle charging powers, an optimal size of the BESS capacity to install is provided, analyzing the power flows of the regular converter operation. The presented simulation results show the advantages and drawbacks of the analyzed MMC-BESS topology
Sizing and Energy Management Strategy of a Hybrid Energy Storage System for EVs
No full textNowadays, hybrid and full-electric vehicles are promising solutions to reduce carbon emissions related to mobility. In this scenario, hybrid energy storage systems are under analysis, and continuous efforts are being made to cope with sizing and managing different sources to improve efficiency and increase sources lifetime. In the context of the IEEE VTS Challenge 2022, this paper proposes the storage system sizing and the energy management strategy for a vehicle powered by batteries and supercapacitors
MMC-Based PV Single-Phase System with Distributed MPPT
Full text linkThe presence and evolution of static power converters in electric grids are growing on a daily basis. Starting from the most used voltage source converter (VSC), passing through the use of multilevel converters, the most recent configuration is the so-called modular multilevel converter (MMC). Because of its intrinsic advantages, it is used not only in high-voltage systems but also in low- and medium-voltage ones to interface renewable energy sources such as photovoltaic (PV) panels. Several configurations and maximum power point tracker (MPPT) algorithms have been proposed and analyzed for MMC-PV-based systems. However, when using distributed MPPTs, partial shading conditions cause a problem. The PV panel can be directly connected to the MMC using its dc link or submodule. Based on this configuration, this paper proposes a novel control strategy that tracks both the ac grid current and ac circulating current for a single-phase low-voltage system to obtain the maximum power under any irradiance condition. The effectiveness of the proposed control strategy is demonstrated through time-domain simulation results
MMC-Based PV Three-Phase System with Distributed MPPT
Full text linkThe use of distributed maximum power point tracking (DMPPT) algorithms is spreading because of their higher efficiency in the case of partial shading. The possibility of integrating photovoltaic (PV) modules in a modular multilevel converter (MMC) connected to the grid has been proposed in recent literature with the advantage of integrating DMPPT algorithms. In the case of partial shading, circulating currents control is necessary to extract the maximum available power and inject symmetric currents in the grid. Novel control strategies for both the ac and dc circulating current components of a three-phase MMC-based PV were proposed and analyzed in this work. Thanks to the presence of a capacitor connected to the dc-side of the MMC, the ac circulating currents could freely be controlled to extract the maximum power from all the PV modules in any irradiance condition while maintaining low power losses. Moreover, in contrast to previous works, instead of measuring the active power of legs and compensating for their imbalance using open-loop control, the power leg mismatches are compensated exploiting the dc loop currents generated through closed loop controls. The effectiveness of the proposed control strategy was proved by simulations performed using MATLAB Simulink
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
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