This report collates analysis since the end of 2016 by a group of experts from across the power industry called Technical Group High Penetration (TG HP) including WindEurope. The analysis focuses on the power electronic converters that are being used as an interface towards the Alternating Current (AC) power system in a wide range of applications covering power generation, transmission and consumption/demand. These have the effect of changing the dynamic properties of the AC power system. The analysis assesses one of the potential solutions for the extreme case of Power Electronic Interfaced Power Sources (PEIPS) contributing between 60 and 100% of the total instantaneous power supply that is Grid Forming Converters (GFC). The TG HP has been reporting the developments via ENTSO-E to the Grid Connection European Stakeholder Committee (GC ESC), reflecting its initiation.