A novel current controller scheme for doubly fed induction generators

This paper presents a novel current control methodology for grid connected doubly-fed induction generator (DFIG) based wind energy conversion systems. Controller is based on a proportional controller with additional first order low pass filter disturbance observer which estimates the parameter dependent nonlinear feed-forward terms. The results in simulations and experimental test bed obviously demonstrate that decoupled control of active and reactive power is achieved without the necessity of additional machine parameter

The last reconnection of the Marmara Sea (Turkey) to the World Ocean : A paleoceanographic and paleoclimatic perspective

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Geology 255 (2008): 64-82, doi:10.1016/j.margeo.2008.07.005.During the late glacial, marine isotope Stage 2, the Marmara Sea transformed into a brackish lake as global sea level fell below the sill in the Dardanelles Strait. A record of the basin’s reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region. The goal of this study is to develop a high-resolution record of the lacustrine to marine transition of Marmara Sea in order to reconstruct regional and global climatic events at 24 a millennial scale. For this purpose, we mapped the paleoshorelines of Marmara Sea along the northern, eastern, and southern shelves at Çekmece, Prince Islands, and Imrali, using data from multibeam bathymetry, high-resolution subbottom profiling (chirp) and ten sediment cores. Detailed sedimentologic, biostratigraphic (foraminifers, mollusk, diatoms), X-ray fluorescence geochemical scanning, and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and dry conditions prior to 15 ka BP, warm conditions of the Bolling-Allerod from ~15 to 13 ka BP, a rapid marine incursion at 12 ka BP, still stand of Marmara Sea and sediment reworking of the paleoshorelines during the Younger Dryas at ~11.5 to 10.5 ka BP, and development of strong stratification and influx of nutrients as Black Sea waters spilled into Marmara Sea at 9.2 ka BP. Stable environmental conditions developed in Marmara Sea after 6.0 ka BP as sea-level reached its present shoreline and the basin floors filled with sediments achieving their present configuration.Support for the analyses was from NSF-OCE-0222139; OCE-9807266 and PSC-CUNY 69138-00 38

Sea-level changes during the late Pleistocene-Holocene on the southern shelves of the Black Sea

Seismic profiles and gravity cores collected from shelf areas off the Sakarya Delta and Thrace Peninsula, together with available previous studies, were evaluated in this research. A masjhoerl f-crossing erosional unconformity was observed, lying as deep as-120 m along the southern margin of the Black Sea. This erosional surface indicates a lowstand of the Black Sea's lake. The present shelf edge was therefore a former paleoshore environment of the preexisting Neoeuxinian basin. Unit 1 overlies the erosional surface and includes a widespread, thin mud drape, the Sakarya Delta, and various irregular depositional features off the Thrace Peninsula. Unit 2 was deposited at the shelf edge and consists of a lowstand sedimentary wedge (off the Sakarya Delta) and seaward prograding clinoforms (off the Thrace Peninsula), all indicative of deposition during the lowstand. Radiometric dates from sedimentary cores collected above the erosional unconformity vary between 11.8 and 8.6 ky BP. Further studies will be required to obtain a better understanding of the timing and intensity of these sea-level changes. © 2007 Springer

Experimental evaluation of sliding mode and EKF observers for network delay compensation in bilateral control

Network delays in the feedback and control loop can give rise to loss of transparency and instability in teleoperation and bilateral control systems, especially with the use of the internet as the medium of communication. This is a current problem of bilateral control, with numerous approaches taken to improve the performance in the face of network delay. This study is based on the more recent approach of taking communication delay effects into account as disturbance, and addressing the problem via the design of a disturbance observer. To this aim, a novel sliding-mode observer (SMO) and an EKF observer are developed and tested for improved performance in bilateral position control systems. The SMO runs on the master side and estimates the slave position using delayed measurement feedback from the slave side. The estimated feedback is used in a PD controller, also running on the master side, the output of which is sent to the slave through the internet as control input for trajectory tracking dynamics. As another contribution to bilateral control, in this study, an extended Kalman Filter (EKF) is also developed to estimate the variable load changes on the slave side, which are further compensated by a “plus” term added on the slave side to the PD control input sent by the master. The designed SM and EKF based bilateral control approach is tested with experiments conducted on a slave system comprising a single link arm under gravitational load. For added challenge, the system is tested for bi-directional load and reference trajectory variations and for both constant and random measurement and control input delays of 1-2 seconds in all cases. The experiment results demonstrate that the designed SM and EKF based observers perform very well under no control input delay, and well- known slave parameters and initial conditions. The developed system performs reasonably well with bi-directional load and reference variations under parameter uncertainties, and definitely maintains stability even under simultaneous random measurement and control delays of 1-2 seconds, which is considerably more than the considered delays in current literature

Pleistocene water intrusions from the Mediterranean and Caspian Seas into the Black Sea

The hydrological balance of the Black Sea is governed by riverine input and by the exchange with the Mediterranean Sea. A speleothem record from a cave in northern Turkey that tracks the isotopic signature of Black Sea surface water suggests an open connection to the Mediterranean Sea in at least twelve periods in the past 670,000 years