Voltage Deviation and Wideband Oscillation Constrained Stability and Weakness Analysis of Hybrid GFM/GFL Multi-Converter Systems

The oscillation risk assessment and oscillation source identification pose significant challenges for heterogeneous multi-converter systems such as hybrid grid forming and grid-following renewable energy station (GFM/GFL-RES). Furthermore, the theoretical impact of GFM converter capacity and placement on the voltage support strength and resonant modes of each bus remains unexplored. To fill this gap, this paper proposes a stability assessment and weakness location method for hybrid GFM/GFL multi-converter systems. Firstly, a power flow method incorporating the reactive power support capability of the GFM converter and the multiple renewable short-circuit ratio is used to evaluate the voltage support strength at each bus. Then, a s-domain modal analysis method incorporating frequency-coupling is proposed. This method accurately extracts system resonant modes by combining modal impedance curves and a center-difference Newton Raphson iterative algorithm. Finally, the steady-state stability region is established by integrating steady-state voltage stability and small-signal stability. The method in this paper is validated through a 16-converter 34-bus GFM/GFL-RES, and the influence of GFM capacity and placement on the steady-state stability region of the system is quantified. The accuracy of the proposed stability analysis method is verified by time-domain simulation.