The document provides a technological review of Flexible AC Transmission System (FACTS) controllers and their applications for enhancing power quality in grid networks integrated with both conventional and renewable energy sources. It discusses the challenges posed by the intermittent nature of renewable energy, outlines various types of FACTS controllers, and explains their roles in mitigating power quality issues like voltage variations and frequency instability. The paper also highlights the benefits of FACTS technology, including improved reliability, better voltage control, and enhanced power flow management.