Assessment of Dynamic Instabilities in Weak Grids with High Penetration of Power Electronic Loads

High penetration of remote active power electronic loads (PELs) with voltage-source converter (VSC) interface into weak grids (WGs) can induce instabilities. This is attributed to interactions between the VSCs and the high-impedance characteristic of the WG. In this work, small-signal analysis is conducted to derive the full-order linearized model of the VSC-WG interconnection. Further, participation factor analysis is utilized to identify the influence of control parameters on the system stability. Unlike previous works, two different pairs of eigenvalues are identified in the WG connection that are very sensitive to the changes in the VSC control parameters and can induce instability if the control gains are more than certain values. Several time-domain simulations are conducted on a 5 MW VSC-WG system to verify the validity of the small-signal analysis. Furthermore, a comparison of the dynamic performance of WG system is presented for the case where the VSC is connected to a stiff grid (SG).