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 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.
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 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.
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 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.
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 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.
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 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.
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, 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.