Comparisons of Dynamic Characteristics between Grid-Forming and Grid-Following Converters

Compared to conventional grid-following (GFL) converters, grid-forming (GFM) converters are considered to provide better voltage and frequency support. Still, rigorous comparisons should be performed to reveal their different behaviors. However, most of the existing research works on comparisons between these two types of converters are focused on stability issues, whereas the pros/cons of both techniques in respect to dynamic characteristics are less studied. In this paper, this topic is fully investigated. Two aspects are considered in this paper, i.e., the transient response to an active/reactive power command from upper-level controller (e.g. an AGC/AVC), and the transient voltage and frequency support effect. The former is evaluated in a single-converter infinite-bus system, whereas the latter is studied in a synthetic down-scale grid system. Small-signal state-space models are deduced to obtain analytical transient responses, which are subsequently verified by simulation results in Matlab/Simulink. The analyses indicate that GFL converters have a fast response to power command, whereas GFM converters provide better transient voltage and frequency support.