Frequency Support Analysis in Heterogeneous Multi-machine System and Enhancement Frequency Control of The Grid-Forming Converter

With regard to the frequency response modelling of the heterogeneous multi-machine system which contains both a grid-forming converter and synchronous generator, a decoupled system frequency response (DSFR) model is derived in this paper, which is based on the distinction of time scaling of two intrinsic components, namely the averaging frequency and the differential frequency. It is found that the general motion of the frequency in each generation source can be well characterized by the dynamics of averaging frequency component, therefore the reduced-order frequency response model is further developed. By utilizing this reduced-order model, the parametric influence of GFM sources to the frequency response is revealed, including the contribution of inertia constant, droop coefficient and percentage of GFM sources, where it is found the system frequency response performance can be greatly improved by increasing the droop coefficient. Moreover, a dynamic frequency droop control (DFDC) is proposed, which features only increasing the droop coefficient of GFM converter at the initial stage of frequency response and vanishing eventually. The control performance and parameter robustness are verified by MATLAB/Simulink simulation.