The Study Of DC Offset Mitigation Of Renewable Energy Sources

There is increasing interest in the use of transformer-less systems for grid connected photovoltaic applications.The transformerless grid connected inverter have number of advantages over the transformer coupled inverter such as they are cost effective,compact and more efficient so they are more attractive in the power system.But all along with many advantages it owns such a big risk which needs to be addressed properly and that is injection of DC in the distribution network because there is no isolation between the grid and PV inverters the DC current can easily flow to the distribution network from the output of inverter.Considering a fact the offset current,nonlinear behavior of current sensors and signal condition circuitry the complete removal of this DC component is almost impossible but the efforts have been made to improve the inverters and to keep the offset DC value in such limits which are not lethal to the network.This undesired DC current addition in our AC system will be the source of many problems such as saturation of transformers which result in more losses and will harm the performance and shorten the life of transformer.All along with it,it can cause the error in measurements of measuring instrument like relays operation and other protection devices.This disturbed output waveform hinders the operation and stability of electronic elements which are attached to it.Power quality measurement from the inverter is of vital importance.Here in the thesis active DC determination is checked on the bases of a DC link current sensing technique.Using a model of solar farm which is adding to the already existing grid which supplies electrical energy from other sources as well.Efforts is made to minimize the offset and improve the power quality.The end of each research is the start of next one.This research can be further improved and thus can be implemented practically with some modifications.