This document provides guidelines for applying unified power flow controllers (UPFC) in power systems. It includes letter symbols, terms and definitions, principles and configurations, design rules, performance requirements for key equipment, control and protection, insulation co-ordination, system performance and tests. This technical report applies to the UPFC based on modular multi-level converter (MMC) technology, as well as UPFC based on three-level converter technology.Cross References:IEC 60076-2IEC 62823IEC 60071-1IEC 62501IEC TR 62543IEC 60076-4IEC 61954IEC 62751-2IEC 60700-1IEC 60076-3IEC 60071-5:2014IEC 62751-1IEC 60071-2IEC 62927IEC 60633:2019IEC 62747:2014IEC TR 60146-1-2:2011IEC 60255-1:2009IEC TR 61000-2-14:2006All current amendments available at time of purchase are included with the purchase of this document.