Sharif Digital Repository

Nowadays, the use of distributed generation (DG) units and microgrid systems is mainly limited to their operation in the grid-connected mode. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC). In this case, the main grid provides fixed voltage and frequency for the microgird and each DG unit regulates its power components based on the conventional dq-current control strategy. Autonomous (islanded) operation of a microgrid, however, is not as straightforward as its operation in the grid-connected mode, i.e., control and power management of an islanded microgrid is very difficult due to the stochastic... 

Zipper frames were proposed to provide a solution of prevention of forming soft Story due to the existence of unbalanced vertical load in Chevron frames. In this study, at first, by performing a nonlinear pushover analysis on the 2D zipper frames with 3, 7 and 12 story and 3 span that the middle one are braced, a Response modification factor for zipper frames is proposed. Then, The seismic behavior of zipper frames is evaluated under far and near-fault earthquakes by nonlinear time history analysis and at the end of the research, the cyclic behavior and energy absorption capacity of these frames are compared with the 2-story-X chevron frames with 3 and 7 story. It is concluded that the... 

Electrical systems are prone to voltage or current unbalance due to unbalance loads or asymmetries in network elements such as untransposed lines. Voltage and current unbalance can cause malfunction or reduction in lifetime of different elements. Voltage unbalance has been studied in a variety of publications, due to its high importance and significant effects. However, current unbalance has not gained much attention despite its undeniable influence on transformers’ and line’s lifetime. Observing high values of current unbalance in LV systems is predictable and inevitable. On the other hand, HV systems must be much more balance due to their different structure and absence of large unbalance... 

A microgrid system consists of some distributed generators (DGs) and local loads which can operate in both grid-connected and islanded modes of operation. An islanded mode of operation is required when the grid voltage deteriorates and its power quality drops. This islanding operation can be attained by opening grid-side switches or by using back-to-back (b-to-b) converters. Due to the increase of highly sensitive loads and to have better power control and higher power quality, the use of back-to-back converters has recently attracted interests among researchers. However, the major drawback of this solution is the cost of a b-to-b converter. Therefore the aim of this project is to gain some...