Multi-frequency Oscillation Analysis of Cable-integrated and Grid-connected VSC in Parallel

Electromagnetic oscillation from subsynchronous range to high frequency of over 1kHz is an emerging stability issue in the power system with increasing penetration of renewables and power electronics. This paper studies the multi-frequency oscillation risks in a scenario when more than one power electronic subsystem are closely connected to the grid in parallel. One voltage source converter (VSC) is directly to the grid and another VSC is integrated through a long transmission cable. Internal and external stability of the study system are identified and analyzed based on small-signal sequence impedance models. Analysis results show how the power ratio, length of cable and different voltage level would affect the oscillatory stability of such a multi-device system. The frequency domain analysis results are demonstrated by time domain simulations on PSCAD.