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Electronics, Volume 4, Issue 2 (June 2015) , Pages 221-379

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Open AccessArticle
HMC-MAC Protocol for High Data Rate Wireless Sensor Networks
Electronics 2015, 4(2), 359-379; https://doi.org/10.3390/electronics4020359
Received: 23 April 2015 / Accepted: 9 June 2015 / Published: 15 June 2015
Cited by 4 | Viewed by 2251 | PDF Full-text (268 KB) | HTML Full-text | XML Full-text
Abstract
Using multiple channels in wireless sensor networks helps increase the overall throughput and avoid interferences. In addition, introducing multi-interface nodes further helps in increasing the packet delivery rate for those specific nodes. In this paper, we evaluate a channel allocation method based on [...] Read more.
Using multiple channels in wireless sensor networks helps increase the overall throughput and avoid interferences. In addition, introducing multi-interface nodes further helps in increasing the packet delivery rate for those specific nodes. In this paper, we evaluate a channel allocation method based on neighborhood discovery up to 3 hops and a hybrid MAC protocol designed for high data rate wireless sensor networks. We propose a network segmentation that takes into consideration the existence of multi-interface sink in order to further increase to packet delivery ratio. Our protocol, called HMC-MAC, uses Time Devision Multiple Access (TDMA) for sequencing nodes activity, and Carrier Sense Multiple Access (CSMA)/CA with Frequency Devision Multiple Access (FDMA) for simultaneous data exchange. We evaluated our method using NS2 simulator and results show that HMC-MAC protocol improves the overall network performance compared to other protocols especially with high data rate and burst traffic. Full article
(This article belongs to the Special Issue Wireless Sensor and Actuator Networks)
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Open AccessArticle
Use of Three-Level Power Converters in Wind-Driven Permanent-Magnet Synchronous Generators with Unbalanced Loads
Electronics 2015, 4(2), 339-358; https://doi.org/10.3390/electronics4020339
Received: 25 April 2015 / Accepted: 9 June 2015 / Published: 15 June 2015
Cited by 4 | Viewed by 2328 | PDF Full-text (3070 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the design and implementation of three-level power converters for wind-driven permanent-magnet synchronous generators with unbalanced loads. To increase voltage stress and reduce current harmonics in the electrical power generated by a wind generator, a three-phase, three-level rectifier is used. Because [...] Read more.
This paper describes the design and implementation of three-level power converters for wind-driven permanent-magnet synchronous generators with unbalanced loads. To increase voltage stress and reduce current harmonics in the electrical power generated by a wind generator, a three-phase, three-level rectifier is used. Because a synchronous rotating frame is used on the AC-input side, the use of a neutral-point-clamped controller is proposed to increase the power factor to unity and reduce current harmonics. Furthermore, a novel six-leg inverter is proposed for transferring energy from the DC voltage to a three-phase, four-wire AC source with a constant voltage and a constant frequency. The power converters also contain output transformers and filters for power buffering and filtering, respectively. All three output phase voltages are fed back to control the inverter output during load variations. A digital signal processor is used as the core control device for implementing a 1.5 kV, 75 kW drive system. Experimental data show that the power factor is successfully increased to unity and the total current harmonic distortion is 3.2% on the AC-input side. The entire system can attain an efficiency of 91%, and the voltage error between the upper and lower capacitors is approximately zero. Experimental results that confirm the high performance of the proposed system are presented. Full article
(This article belongs to the Special Issue Multi-Level Converters)
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Open AccessArticle
Unified Multi-Layer among Software Defined Multi-Domain Optical Networks (Invited)
Electronics 2015, 4(2), 329-338; https://doi.org/10.3390/electronics4020329
Received: 12 May 2015 / Revised: 1 June 2015 / Accepted: 9 June 2015 / Published: 11 June 2015
Cited by 2 | Viewed by 2218 | PDF Full-text (671 KB) | HTML Full-text | XML Full-text
Abstract
The software defined networking (SDN) enabled by OpenFlow protocol has gained popularity which can enable the network to be programmable and accommodate both fixed and flexible bandwidth services. In this paper, we present a unified multi-layer (UML) architecture with multiple controllers and a [...] Read more.
The software defined networking (SDN) enabled by OpenFlow protocol has gained popularity which can enable the network to be programmable and accommodate both fixed and flexible bandwidth services. In this paper, we present a unified multi-layer (UML) architecture with multiple controllers and a dynamic orchestra plane (DOP) for software defined multi-domain optical networks. The proposed architecture can shield the differences among various optical devices from multi-vendors and the details of connecting heterogeneous networks. The cross-domain services with on-demand bandwidth can be deployed via unified interfaces provided by the dynamic orchestra plane. Additionally, the globalization strategy and practical capture of signal processing are presented based on the architecture. The overall feasibility and efficiency of the proposed architecture is experimentally verified on the control plane of our OpenFlow-based testbed. The performance of globalization strategy under heavy traffic load scenario is also quantitatively evaluated based on UML architecture compared with other strategies in terms of blocking probability, average hops, and average resource consumption. Full article
(This article belongs to the Special Issue Software-Defined Optical Networks)
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Open AccessArticle
An Improved Asymmetric Cascaded Multilevel D–STATCOM with Enhanced Hybrid Modulation
Electronics 2015, 4(2), 311-328; https://doi.org/10.3390/electronics4020311
Received: 30 December 2014 / Revised: 15 May 2015 / Accepted: 27 May 2015 / Published: 3 June 2015
Cited by 3 | Viewed by 2329 | PDF Full-text (1305 KB) | HTML Full-text | XML Full-text
Abstract
Problems related to power quality, which in the last years were responsible only for small losses in low-voltage distribution systems, are now causing damage to power apparatuses and financial losses also in medium-voltage systems. The necessity of a better quality of power supply [...] Read more.
Problems related to power quality, which in the last years were responsible only for small losses in low-voltage distribution systems, are now causing damage to power apparatuses and financial losses also in medium-voltage systems. The necessity of a better quality of power supply encourages the development of new specific custom power devices directly connected in medium-voltage distribution systems. It is well know that the multilevel converters are capable of being installed directly in the medium voltage, and presents several advantages when compared with conventional two-level converters. Some topologies, like the asymmetric cascaded multilevel converter, presents difficulties in regulating the voltages of all isolated dc-link capacitors. In this context, this article presents an asymmetric nineteen-level D–STATCOM (Distribution Static Synchronous Compensator) with a reactive power and dc-link regulation control loops for generic cascaded multilevel converters in order to improve the power quality in medium-voltage distribution systems. The performance of the proposed control method for a multilevel D–STATCOM is presented and evaluated in a downscaled prototype. Full article
(This article belongs to the Special Issue Multi-Level Converters)
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Open AccessArticle
A Theoretical Study on the Operation Principle of Hybrid Solar Cells
Electronics 2015, 4(2), 303-310; https://doi.org/10.3390/electronics4020303
Received: 13 February 2015 / Revised: 15 May 2015 / Accepted: 25 May 2015 / Published: 29 May 2015
Cited by 2 | Viewed by 1885 | PDF Full-text (227 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the operation mechanism of hybrid solar cells is studied explicitly. The excitation, diffusion and dissociation of singlet and triplet excitons and charge transport of free charge carriers are studied and their corresponding rates are calculated for a flexible P3HT:SiNW hybrid [...] Read more.
In this work, the operation mechanism of hybrid solar cells is studied explicitly. The excitation, diffusion and dissociation of singlet and triplet excitons and charge transport of free charge carriers are studied and their corresponding rates are calculated for a flexible P3HT:SiNW hybrid solar cell. The rates are found to be faster for singlet than triplet excitons. Possible loss mechanisms in hybrid solar cells have also been highlighted. Full article
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Open AccessArticle
A Flexible Power Electronics Configuration for Coupling Renewable Energy Sources
Electronics 2015, 4(2), 283-302; https://doi.org/10.3390/electronics4020283
Received: 23 March 2015 / Revised: 2 May 2015 / Accepted: 4 May 2015 / Published: 11 May 2015
Cited by 5 | Viewed by 2388 | PDF Full-text (1828 KB) | HTML Full-text | XML Full-text
Abstract
A combination of series, parallel and multilevel power electronics has been investigated as a potential interface for two different types of renewable energy sources and in order to reach higher power levels. Renewable energy sources are typically dispersed in a territory, and sources, [...] Read more.
A combination of series, parallel and multilevel power electronics has been investigated as a potential interface for two different types of renewable energy sources and in order to reach higher power levels. Renewable energy sources are typically dispersed in a territory, and sources, like wind and solar, allow small to medium-scale generation of electricity. The configuration investigated in this article aims at adapting the coupling solution to the specific generation characteristics of the renewable energy source to make it fit the electrical network. The configuration consists of a combination of three-phase multilevel converters and single-phase inverters, which are designed to provide flexibility, high power quality and high efficiency. A detailed analysis and simulation is performed to identify the properties in conjunction with the electrical grid requirements and the potential challenges encountered during operation. An optimized operation example of wind generation combined with solar PV generation is presented to exemplify the flexibility and benefits of the proposed configuration. Full article
(This article belongs to the Special Issue Multi-Level Converters)
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Open AccessArticle
A 0.8–8 GHz Multi-Section Coupled Line Balun
Electronics 2015, 4(2), 274-282; https://doi.org/10.3390/electronics4020274
Received: 19 March 2015 / Revised: 18 April 2015 / Accepted: 24 April 2015 / Published: 30 April 2015
Cited by 2 | Viewed by 2412 | PDF Full-text (1414 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we propose a wideband multi-section transforming coupled-line balun using near equal length transmission line elements. The resulting design is realized by cascading several coupled-lines with minimal discontinuities. The multi-section Chebyshev matching optimizes bandwidth at the expense of passband ripple. The [...] Read more.
In this work, we propose a wideband multi-section transforming coupled-line balun using near equal length transmission line elements. The resulting design is realized by cascading several coupled-lines with minimal discontinuities. The multi-section Chebyshev matching optimizes bandwidth at the expense of passband ripple. The proposed design delivers good impedance matching and consistent 180° phase shift over 0.8–8 GHz frequency spectrum. Furthermore, the need for vias in conventional balun designs is relaxed by replacing the short-circuited (SC) terminal by its equivalent dual open-circuited (OC) element. The proposed design is simulated, fabricated, and measured. Both simulated and measured results are in a good agreement, and show an input port matching of below −9.7 dB over the design bandwidth, with a maximum phase and amplitude imbalance of 2.1° and 0.9 dB, respectively. Full article
(This article belongs to the Special Issue Microwave/ Millimeter-Wave Devices and MMICs)
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Open AccessArticle
Heterojunction Diodes and Solar Cells Fabricated by Sputtering of GaAs on Single Crystalline Si
Electronics 2015, 4(2), 261-273; https://doi.org/10.3390/electronics4020261
Received: 2 February 2015 / Revised: 7 April 2015 / Accepted: 16 April 2015 / Published: 23 April 2015
Cited by 1 | Viewed by 2412 | PDF Full-text (1579 KB) | HTML Full-text | XML Full-text
Abstract
This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF) etching treatment of the Si substrate prior [...] Read more.
This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF) etching treatment of the Si substrate prior to the GaAs sputter deposition and a subsequent annealing treatment of the complete layered system. A transmission electron microscopy (TEM) exploration of the interface reveals the formation of a few nanometer thick SiO2 interface layer and some crystallinity degree of the GaAs layer close to the interface. It was shown that an additional HF etching treatment of the Si substrate improves the short circuit current and degrades the open circuit voltage of the solar cells. Furthermore, an additional thermal annealing step was performed on some selected samples before and after the deposition of an indium tin oxide (ITO) film on top of the a-GaAs layer. It was found that the occurrence of surface related defects is reduced in case of a heat treatment performed after the deposition of the ITO layer, which also results in a reduction of the dark saturation current density and resistive losses. Full article
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Open AccessArticle
Analysis of a Multilevel Dual Active Bridge (ML-DAB) DC-DC Converter Using Symmetric Modulation
Electronics 2015, 4(2), 239-260; https://doi.org/10.3390/electronics4020239
Received: 30 January 2015 / Accepted: 2 April 2015 / Published: 20 April 2015
Cited by 17 | Viewed by 4872 | PDF Full-text (1200 KB) | HTML Full-text | XML Full-text
Abstract
Dual active bridge (DAB) converters have been popular in high voltage, low and medium power DC-DC applications, as well as an intermediate high frequency link in solid state transformers. In this paper, a multilevel DAB (ML-DAB) has been proposed in which two active [...] Read more.
Dual active bridge (DAB) converters have been popular in high voltage, low and medium power DC-DC applications, as well as an intermediate high frequency link in solid state transformers. In this paper, a multilevel DAB (ML-DAB) has been proposed in which two active bridges produce two-level (2L)-5L, 5L-2L and 3L-5L voltage waveforms across the high frequency transformer. The proposed ML-DAB has the advantage of being used in high step-up/down converters, which deal with higher voltages, as compared to conventional two-level DABs. A three-level neutral point diode clamped (NPC) topology has been used in the high voltage bridge, which enables the semiconductor switches to be operated within a higher voltage range without the need for cascaded bridges or multiple two-level DAB converters. A symmetric modulation scheme, based on the least number of angular parameters rather than the duty-ratio, has been proposed for a different combination of bridge voltages. This ML-DAB is also suitable for maximum power point tracking (MPPT) control in photovoltaic applications. Steady-state analysis of the converter with symmetric phase-shift modulation is presented and verified using simulation and hardware experiments. Full article
(This article belongs to the Special Issue Multi-Level Converters)
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Open AccessArticle
Data-Throughput Enhancement Using Data Mining-Informed Cognitive Radio
Electronics 2015, 4(2), 221-238; https://doi.org/10.3390/electronics4020221
Received: 23 November 2014 / Revised: 14 March 2015 / Accepted: 16 March 2015 / Published: 26 March 2015
Cited by 12 | Viewed by 3253 | PDF Full-text (2003 KB) | HTML Full-text | XML Full-text
Abstract
We propose the data mining-informed cognitive radio, which uses non-traditional data sources and data-mining techniques for decision making and improving the performance of a wireless network. To date, the application of information other than wireless channel data in cognitive radios has not been [...] Read more.
We propose the data mining-informed cognitive radio, which uses non-traditional data sources and data-mining techniques for decision making and improving the performance of a wireless network. To date, the application of information other than wireless channel data in cognitive radios has not been significantly studied. We use a novel dataset (Twitter traffic) as an indicator of network load in a wireless channel. Using this dataset, we present and test a series of predictive algorithms that show an improvement in wireless channel utilization over traditional collision-detection algorithms. Our results demonstrate the viability of using these novel datasets to inform and create more efficient cognitive radio networks. Full article
(This article belongs to the Special Issue Cognitive Radio: Use the Spectrum in a More Efficient Way)
Electronics EISSN 2079-9292 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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