Improved Stability of a Grid-Following Converter Controller Supplying Virtual Inertia and Damping

Abstract

The share of converter-interfaced generator (cig) units fuelled by renewables and scattered in distribution networks is increasing and causing the progressive phase out of synchronous generators and passive loads, which are the main source of vital parameters in ensuring frequency stability: inertia and load damping. To compensate the decreasing trend in these parameters, the control scheme of cig units, typically of grid-following (gfl) kind, may include controls blocks that emulate the electro-mechanical behaviour of synchronous generators by letting them provide virtual inertia and load damping. However, a negative trait of gfl cigs is that, contrary to grid-forming (gfm) cigs (which are affected by other drawbacks), they rely on phase locked loops (plls). This dependency may trigger instability based on the strength of the grid and cig operating conditions. In this paper, we propose a novel gfl cig control scheme that emulates the electromechanical behaviour of synchronous generators better than conventional implementations. Eigenvalue and transient stability analyses of different power systems prove that, although the pll model used is the same, the proposed gfl cig control has a higher stability margin than its conventional counterpart, and provides a frequency support comparable with a synchronous generator of same inertia and load damping.