Investigation on parallel operation of two MMC-HVDC links in grid forming connected to an existing network

Abstract

The share of power electronics installations into existing ac power systems is significantly increasing due to the massive penetration of wind power plants and HVDC links. VSC-HVDC link can operate in VF -control (or grid-forming mode) when connected to a weak or islanded network to overcome the PQ-control (or grid-feeding mode) limitation. Up to now, the VF -control represents a challenge due to static and dynamic limits when several HVDC links are in parallel operation. This paper provides a dynamic performance of two HVDC links in grid forming mode connected to an islanded grid. To provide a realistic test case, the islanded grid is based on the Northern France network. AC fault and control instabilities between 2 HVDC links in VF control are analyzed in this work. These set of EMT studies provide an insight on dynamic network behavior when HVDC is operating in VF control.