CONTROL & SEAMLESS TRANSFER BETWEEN GRID CONNECTED & ISLANDED MODE

Abstract

Unlike centralized power plants, the DG units are directly connected to the distribution system; most often at the customer end. The existing distribution networks are designed and operated in radial configuration with unidirectional power flow from centralized generating station to customers. The increase in interconnection of DG to utility networks can be lead to reverse power flow violating fundamental assumption in their design. This creates complexity in operation and control of existing distribution networks and offers many technical challenges for successful introduction of DG. One of the main technical -issues is the transition between islanding and grid connected operation of DG. Islanding occurs when a portion of the distribution system becomes electrically isolated from the remaining part of the power system, yet continues to be energized by the distribution generators connected to the isolated subsystem. In this work droop control characteristics is used for sharing the proper load of inverters and main grid according to their capacities in islanded and grid connected mode. Also the main issue, smooth transfer between these two modes can be covered through the control techniques used in this work. In this work both type of load, passive and inertial load has been consider and their effect is shown through the same controller implication. In this thesis power electronics based converter DG system has been used due to seamless switching of the DG operation between grid connected and islanding modes without down time, during the outages of the utility.