This paper presents a review on grid Integration and power quality issues associated with the integration of renewable energy systems in to grid and Role of power electronic devices and Flexible AC Transmission Systems related to these Issues. In this paper, recent trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented. Classification of various Power Quality Issues used by different researchers has been done and put for reference. Application of various techniques as applied to mitigate the different Power Quality problems is also presented for consideration. Power Electronics interface not only plays a very important role in efficient integration of Wind and Solar energy system but also to its effects on the power-system operation especially where the renewable energy source constitutes a significant part of the total system capacity.However there are various issues related to grid integration of RES keeping in the view of aforesaid trends it becomes necessary to investigate the possible solutions for these issues. 
                                
                                
                                    
                                    Renewable Energy System, Doubly Fed Induction Generator (DFIG), Multilevel Converter Topologies, Power Quality (PQ), Grid Connected PV, Grid Connected Wind, FACTS Devices
                                
                                
                                
                                
                                    
                                        
                                        
                                        
                                        
                                            
                                                
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