The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.
This paper proposes a hybrid energy system consisting of wind, photovoltaic and fuel cell designed to supply continuous power to the load. A simple and economic control with dc-dc converter is used for maximum power point tracking and hence maximum power extraction from the wind turbine and photovoltaic array. Due to the intermittent nature of both the wind and photovoltaic energy sources, a fuel cell is added to the system for the purpose of ensuring continuous power flow. The fuel cell is thus controlled to provide the deficit power when the combined wind and photovoltaic sources cannot meet the net power demand. In worst environmental conditions, when there is no output power from the wind or photovoltaic sources, the fuel cell will operate at its rated power of 10 kW. Hence this system under any operating condition will ensure a minimum power flow of 10 kW to the load. This hybrid system allows maximum utilization of freely available renewable energy sources like wind and photovoltaic and demand-based utilization of hydrogen-based fuel cell. The proposed system is attractive owing to its simplicity, ease of control and low cost. Also it can be easily adjusted to accommodate different and any number of energy sources. A complete description of this system is presented along with its simulation results which ascertain its feasibility.Index Terms -step-up dc-dc converter, maximum power point tracking, hybrid energy system, variable speed wind turbine, photovoltaic array, fuel cell, PWM voltage source inverter, PI controller.
A novel approach is developed in this paper for sensorless control of permanent magnet (PM) machines down to zero speed without signal injection or special pulsewidth modulation (PWM) techniques. Taking advantage of the low inductance in a PM machine, the phase current ripples under a conventional PWM excitation are measured to derive the rotor position and speed. The new approach can also be used to estimate the rotor position at standstill if a minor rotor saliency exists. Neither prior knowledge of machine parameters, nor any special signal injection, is needed for the rotor position detection. Sensorless control of a PM machine based on the proposed scheme has been investigated by comprehensive computer simulations. Experimental results are presented to verify the effectiveness of the approach.Index Terms-Current ripple, digital signal processor (DSP), permanent magnet (PM) machines, pulsewidth modulation (PWM), sensorless.
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