Small-Signal Analysis of a Bipolar Grid-Forming MMC-HVDC Link for Offshore Wind Integration

With the advent of HVDC grids for renewable electricity transmission and long-distance interconnections, de-risking studies for control interactions among multiple converters are needed to ensure small-signal stability. This paper presents both electromagnetic transient (EMT) time-domain and frequency-domain stability analyses of an HVDC link with parallel grid-forming (GFM) converters fed by an offshore wind farm. An oscillatory instability is identified when the GFM converters are connected to the same busbar, and the impact of the AC and DC network configuration is quantified. Furthermore, two control mitigation measures are demonstrated both in the frequency domain and via EMT simulations.