Browsing by Author "Zahidul Islam, Md."

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Adaptive clarke transformation based three-phase PLL under amplitude and phase unbalances in presence of harmonics
(Department of Electrical and Electronic Engineering (EEE), BUET, 2021-01-05) Zahidul Islam, Md.; Reza, Dr. Md. Shamim
Precise and fast estimation of the phase information of grid voltages is crucial for grid synchronization of various power electronic devices, which is a research trend in modern smart grid technology. However, the task of instantaneous phase estimation has become difficult as the grid voltages may contain harmonics, DC offset, frequency variations, and voltage unbalances due to an increase in renewable energy penetration to grid, and domestic and industrial non-linear loads. In this dissertation, a fast and accurate instantaneous phase estimation technique is developed to overcome the present limitations in this field. This dissertation proposes a three-phase phase locked loop (PLL) algorithm relying on adaptive Clarke transformation (ACT) for tracking the phase angle of unbalanced grid voltages associated with harmonics and DC offset. A meticulously tuned band pass filter (BPF) is inserted in each phase to remove harmonics and DC offset. Two separate algorithms are proposed to estimate the amplitudes and the phase-angle deviations of three-phase voltages. Using the estimated amplitudes and phase angle deviations, a set of analytical expressions is derived for the coefficients of Clarke transformation (CT) matrix to make them adaptive under both amplitude and phase unbalances, which is named as adaptive CT (ACT). The ACT is capable of generating orthogonal signals from unbalanced three-phase voltages, whereas the conventional CT based on constant matrix fails to do so. After getting the orthogonal voltages, a conventional SRF-PLL is used to track the phase-angles of all three-phases. A phase-correction technique is also developed to make the PLL frequency adaptive without using any frequency feedback loop.
Seismic assessment of RC frame building designed using gross and cracked sections
(Department of Civil Engineering (CE), BUET, 2020-09-22) Zahidul Islam, Md.; Siddique, Dr. Mohammad Al Amin
Bangladesh is situated in a seismically active region with a moderate seismic risk. The country has been divided into four seismic zones following the concept of Maximum Considered Earthquake (MCE) with a return period of 2475 years. A number of infrastructures have already been built in order to fulfill the increasing demand of urban population. Bangladesh National Building Code (BNBC) has been updated to a draft BNBC 2017 to consider the realistic design guidelines. The code considers the cracked section properties for designing a structure at a factored load level. A comprehensive study is conducted in the current thesis to assess the seismic performance of buildings considering cracked section properties of the structural members. For comparative seismic assessment, a regular plan of 6-, 10-, and 15-storey RC frame buildings designed with gross section and cracked section (BNBC-2017 draft) properties of RC members using conventional force-based design approach. All the considered buildings are analyzed using nonlinear static pushover analysis. The obtained results show that the inter-storey drift at design load of RC frames designed using gross section property is well within the prescribed limit of maximum permissible inter-storey drift while that of cracked section properties is beyond the maximum permissible inter-storey drift limit. The higher column reinforcement demand is shown for buildings with cracked sections that those of gross sections and this value is higher for exterior and corner columns (27.4% increase for 6-storied) than those of the interior columns. Response reduction factors of the buildings with gross section properties result higher values than those of the cracked section buildings. R values always fall below the design R for the cracked section buildings and it is obtained 3.23 instead of R value of 5 for the considered 6-storied building.